EC2314 DIGITAL SIGNAL PROCESSING UNIT – I - INTRODUCTION
1
EC2314 DIGITAL SIGNAL PROCESSING
UNIT – I - INTRODUCTION
1. What is meant by signal and signal Processing?
A signal is defined as any physical quantity that varies with time, space, or any other
independent variable.
Signal processing is any operation that changes the characteristics of a signal. These
characteristics include the amplitude, shape, phase and frequency content of a signal.
2. What are the classifications of signals?
There are five methods of classification of signals based on different features:
a) Based on independent variable.
(i) Continuous time signal
(ii) Discrete time signal
b) Depending upon the number of independent variable
(i) One dimensional signal
(ii) Two dimensional signal
(iii)Multi-dimensional signal
c) Depending upon the certainty by which the signal can be uniquely described as.
(i) Deterministic signal
(ii) Random signal
d) Based on repetition nature
(i) Periodic signal
(ii) Non-Periodic signal
e) Based on reflection
(i) Even signal
(ii) Odd signal
3. Define – Discrete System
Discrete time system is defined as a device or algorithm that operates on a discrete time input
signal x(n) , according to some well-defined rule, to produce another discrete – time signal y(n)
called the output signal.
4. What are the classifications of discrete time systems?
The classifications of discrete time systems are:
1. Static and Dynamic system
2. Time-variant and time-invariant system
3. Linear and non-linear system
4. Stable and Unstable system
5. Causal and noncausal system
2
5. Differentiate Continuous time from Discrete time signal.
Continuous time signal: It is also referred as analog signal i.e., the signal is represented
continuously in time.
Discrete time signal : Signals are represented as sequence at discrete time intervals
6. Define – Digital Signal
A discrete time signal or digital is defined as which discrete valued represented by a finite
number of digits is referred to as a digital signal.
7. What is deterministic signal? Give example.
A signal that can be uniquely determined by a well-defined process such as a mathematical
expression or rule, or look-up table is called deterministic signal.
Example: A sinusoidal signal v(t ) Vm sin t
8. What is random signal?
A signal that is generated in a random fashion and cannot be predicted ahead of time is called
a random signal.
Example : Speech signal , ECG signal and EEG signal.
9. Define – Periodic Signal and Non-periodic Signal
Periodic signal: A periodic signal is defined as the signal x(n) is periodic with period N if and
only if x(n+N) = x(n) for all n.
Non-periodic signal: A non-periodic signal is defined as if there is no value of N that satisfies
the equation x(n+N) x(n).
10. What are the symmetric and antisymmetric signals?
Symmetric signal: A real valued signal x(n) is called symmetric if x(-n) = x(n).
Antisymmetric signal: A signal x(n) is called antisymmetric if x(-n) = -x(n).
11. What are energy and power signals?
Energy signal:
The energy of a discrete time signal x(n) is defined as E n x(n)
2
A signal x(n) is called an energy signal if and only if the energy obeys the relation
0 E . For an energy signal P = 0.
Power signal :
The average power of a discrete time signal x(n) is defined as
3
N
1
P lim
x(n)
N 2 N 1
n N
2
A signal x(n) is called power signal if and only if the average power P satisfies the condition
0 P .
12. What are the different types of signal representation?
The different types of signal representation are:
1. Graphical representation
2. Functional representation
3. Tabular representation
4. Sequence representation
13. What are the different types of operations performed on discrete-time signals?
The different types of operations performed on discrete-time signals are:
1. Delay of a signal
2. Advance of a signal
3. Folding or Reflection of a signal
4. Time scaling
5. Amplitude scaling
6. Addition of signals
7. Multiplication of signals
14. Represent the following duration sequence x(n)={1, 3, –1, –4} as a sum of weighted impulse
sequences.
Given:
x(n)={1, 3, -1, -4}
We can write
x(n) 1 x(k ) (n k )
2
1 (n 1) 3 (n) 1 (n 1) 4 (n 2)
15. What is a static and dynamic system?
A discrete time system is called static or “memory less” if its output at any instants „n‟
depends on the input samples at the same time , but not an past or future samples of the input.
Example: y(n) = ax(n)
Y(n) = ax2(n)
In any other case, the system is said to be dynamic or to have memory.
Example: y(n) = ax(n-1) + x(n-2)
y(n) = x(n) + x(n-1)
4
16. What is a time-invariant system?
A system is called time-invariant if its input-output characteristics do not change with time.
Ex.: y(n) = x(n) + x(n-1)
17. What is a causal system?
A system is said to be causal, if the output of the system at any time depends only on present
and past inputs, but does not depend on future inputs.
This can be expressed mathematically as,
y(n) = F[x(n), x(n-1), x(n-2)………]
18. Define – Stable System
Any relaxed system is said to be Bounded Input Bounded Output (BIBO) stable if and only if
every bounded input yields a bounded output. Mathematically, their exist some finite numbers,
Mx and My such that,
x(n) Mx
and
y(n) My
19. What is a linear system?
A system that satisfies the superposition principle is said to be a linear system. Superposition
principle states that , the response of the system to a weighted sum of signals be equal to the
corresponding weighted sum of the outputs of the system to each of the individuals input signals.
20. Define – Unit Sample Response (Impulse Response) of a system
The unit sample response is defined as the output signal designated as h(n), obtained from a
discrete time system when the input signal is a unit sample sequence (unit impulse).
The output y(n) of an LTI system for an input signal x(n) can be obtained by convolving the
impulse response h(n) and the input signal x(n).
y(n) x(n) h(n)
k x(k )h(n k )
21. What is the causality condition for an LTI system?
The necessary and sufficient condition for causality of an LTI system is, its unit sample
response h(n) = 0 for negative values of n i.e.,
h(n) = 0 for n<0
22. What is the necessary and sufficient condition on the impulse response for stability?
The necessary and sufficient condition guaranteeing the stability of a linear time-invariant
system is that its impulse response is absolutely summable.
h(k )
23. What is meant by discrete or linear convolution?
The convolution of discrete – time signal is known as discrete convolution. Let x(n) be the
input to an LTI system and y(n) be the output of the system. Let h(n) be the response of the
5
system to an impulse. The output y(n) can be obtained by convolving the impulse response h(n)
and the input signal x(n).
y ( n)
x ( k ) h( n k )
k
(OR)
y ( n)
h( k ) x ( n k )
k
24. What are the steps involved in the convolution process?
The steps involved in the convolution process are
1. Express both sequences in terms of the index k.
2. Folding: Fold the h(k) about the origin and obtain h(-k).
3. Time shifting: Shift the h(k) by n units to right if n is positive or left if n is negative to
obtain h(n-k).
4. Multiplication: Multiply x(k) by h(n-k) to obtain w(k)=x(k)h(n-k)
5. Summation: Sum all the values of the product w(k) to obtain the value of output y(n).
6. Increment the index n, shift the sequence h(n-k) to right by one sample and do step4.
25. What is meant by sampling process?
Sampling is the conversion of a continuous time signal(or analog signal) into a discrete –
time signal obtained by taking samples of the continuous time signal ( or analog signal ) at
discrete time instants.
26. State sampling theorem.
A sampling theorem states that the band limited continuous time signal with highest
frequency(band width) fm hertz , can be uniquely recovered from its samples provided that the
sampling rate fs is greater than or equal to 2fm samples per second.
27. Define – Nyquist Rate
The Nyquist rate is defined as the frequency 2fm, which under sampling theorem, must be
exceeded by the sampling frequency.
28. What is meant by quantization process?
The process of converting a discrete time continuous valued signal into discrete time discrete
valued signal is called quantization.
29. What is meant by aliasing effect?
The superimposition of high frequency component on the low frequency is known as
“frequency aliasing” or “aliasing effect”.
30. How can aliasing be avoided?
To avoid aliasing the sampling frequency must be greater than twice the highest frequency
present in the signal.
6
31. What is an anti-aliasing filter?
A filter used to reject frequency signals before it is sampled to reduce the aliasing is called an
anti-aliasing filter.
32. What is meant by critical sampling?
If the sampling frequency is exactly equal to the Nyquist rate is known as critical sampling.
33. What are the steps involved in the A/D conversion?
The steps involved in the A/D conversion are:
1. Sampling
2. Quantization
3. Coding
34. What is meant by quantization error?
It is the difference between the quantized value and actual sample value.
eq(n) = xq(n) - x(n)
35. What is meant by quantization level?
The value that allows in a digital signal is called the quantization level.
36. Define – Resolution or Quantization Step Size
The resolution is defined as the distance between two successive level.
37. What is meant by SQNR?
The quality of the output of the A/D converter is usually measured by the Signal to
Quantization Noise Ratio (SQNR), which is ratio of the signal power to noise power.
P
SQNR av
Pq
38. What is the use of a sample and hold circuit?
The sample and hold circuit is used to hold the sample the analog signal and hold the sampled
value constant as long as the A/D converter takes time for accurate conversion.
39. Define – Conversion Time
Conversion time may be defined as the time taken by an ADC for converting a given
amplitude, expressed in decimal value, of a quantized analog signal applied across its input
terminals into corresponding binary – equivalent value.
40. Define – Voltage Resolution
The voltage resolution is defined as
Votageresolution
VFS
2n 1
Where, VFS - full scale voltage and n - number of bits.
7
42. Define – Percentage Resolution
Percentage resolution is defined as
1
%resolution n 100
2
41. What are the advantages and disadvantages of counter-ramp type ADCs?
The advantages of counter-ramp type ADCs are:
1. The principle is simple and straightforward.
2. It is very easy to construct this ADC.
3. This basic principle is employed in many advanced ADCs.
The disadvantages counter-ramp type ADCs are:
1. Only increasing voltages can be measured.
2. The system is very slow.
3. This may be mainly used to read DC voltages.
42. What are the advantages and disadvantages of SAADC?
The advantages of SAADC are:
1. It is more accurate than the stair case (counter ramp ) ADC.
2. It maintains a high resolution.
3. It is much faster.
4. Its conversion time is much less.
The disadvantages of SAADC are:
1. It requires a complex register called the successive approximation register.
2. It is costly, as it contains more components.
43. Write the formula for conversion time of SAADC?
n
Conversiontime
f
where,
n – number of bits and
f – clock frequency
44. What are the advantages and disadvantages of flash converter?
The advantages of flash converter are:
1. The fastest conversion process (governed only by propagation delay of the gates.
2. Highest accuracy
3. Highest resolution possible by increasing the number of comparators.
The disadvantages of flash converter are:
1. Very complicated circuitry
2. Cost is proportional to the number of comparators, which in turn depends on the
resolution required.
8
45. What are the different types of analog to digital converters?
The different types of analog to digital converters are:
1. Flash A/D converter
2. Successive approximation converter
3. Counting type A/D converter
4. Over sampling Sigma – Delta converter
46. What are the different types of digital to analog converter?
The different types of digital to analog converters are
1. Weighted – resistor D/A converter
2. Resistor – ladder D/A converter
3. Over sampling D/A converter
47. Define – Z-transform.
The Z-transform of a discrete time signal or sequence is defined as the power series.
X ( z)
x ( n) z
n
n
48. What is meant by region of convergence?
The region of convergence (ROC) of X(z) is the set of all values of z for which X(z) attains a
finite value.
49. What are the properties of region of convergence?
The properties of region of convergence are:
1. The ROC is a ring or disk in the Z – plane centered at the origin.
2. The ROC cannot contain any poles.
3. The ROC of an LTI stable system contains the unit circle.
4. The ROC must be a connected region.
50. What are the properties of z-transform ?
1. Linearity: z a1 x1 (n) a2 x2 (n) a1 X 1 ( z ) a2 X 2 ( z )
m1
2. Shifting: (a) zx(n m) z m X ( z ) x(i) z mi
i 0
m
3. (b) zx(n m) z X ( z )
m
d
4. Multiplication: z n x(n) z X ( z )
dz
m
n
1
5. Scaling in z- domain: z a x(n) X a z
1
6. Time reversal : zx( n) X ( z )
7. Conjugation: z x (n) X ( z )
9
n
8. Convolution: z h(n m)r (m) H ( z ) R( z )
m 0
9. Initial value: zx(0) Lt X ( z )
z
10. Final value: zx( ) Lt (1 z 1 ) X ( z )
z 1
51. State Parseval‟s relation in z-transform.
Parseval‟s relation in z-transform state that
If x1(n) and x2(n) are complex valued sequences, then
1
1
x1 (n) x2 (n)
X 1 (v) X 2 v 1dv
2j c
v
n
52. What is the relationship between z-transform and DTFT?
The z-transform of x(n) is given by X ( z )
x ( n) z
n
…….(1)
n
where, z re j
Substituting z value in eqn (1) we get,
X (re j ) x(n)r n e jn …………… …..(2)
The Fourier transform of x(n) is given by
X ( e j )
x ( n )e
j n
…………………… .(3)
n
Eqn(2) and Eqn(3) are identical , when r=1. In the z-plane this corresponds to the locus of
points on the unit circle z 1. Hence X (e j ) is equal to X(z) evaluated along unit circle , or
X (e j ) X ( z) | z e j
For X (e j ) to exist, the ROC of X(z) must include the unit circle.
53. What are the different methods of evaluating inverse z-transform?
The different methods of evaluating inverse z-transform are:
1. Long division method
2. Partial fraction method
3. Residue method
4. Convolution method
10
54. Find the convolution of the following using z-transform.
x(n) 1,1,1 ; h(n) 1, 2,1
Solution:
Z x(n) h(n) X ( z ) H ( z )
X ( z )(1 z 1 z 2 )
H ( z ) (1 2 z 1 z 2 )
X ( z ) H ( z ) (1 3z 1 4 z 2 3z 3 z 4 )
x(n) h(n) 1,3,4,3,1
55. Define – System Function
Let x(n) and y(n) be the input and output sequences of an LTI system with impulse response
h(n). Then the system function of the LTI system is defined as the ratio of Y(z) and X(z), i.e.,
Y ( z)
H ( z)
X ( z)
where,
Y(z) is the z – transform of the output signal y(n)
X(z) is the z – transform of the input signal x(n)
UNIT – II
FAST FOURIER TRANSFORM
1. Define – Fourier Transform of a discrete time signal.
The Fourier transform of a discrete time signal x(n) is defined as
F x(n) X ( )
x ( n )e
jn
n
2. Why is the FT of a discrete time signal called signal spectrum?
By taking Fourier transform of a discrete time signal x(n) , it is decomposed into its
frequency components. Hence the Fourier transform is called signal spectrum.
3. List out the difference between Fourier transform of discrete time signal and analog signal.
1. The FT of analog signal consists of a spectrum with a frequency range to . But the
FT of discrete time signal is unique in the range to ( or 0 to 2 ) , and also it is
periodic with periodicity of 2 .
2. The FT of analog signals involves integration but FT of discrete time signals involves
summation.
11
4. Define – Inverse Fourier Transform
The inverse Fourier transform of X() is defined as
F 1 X ( ) x(n)
1
2
X ()e
jn
d
5. List out some applications of Fourier transform.
The applications of Fourier transform are
1. The frequency response of LTI system is given by the Fourier transform of the impulse
response of the system.
2. The ratio of the Fourier transform of output to Fourier transform of input is the transfer
function of the system in frequency domain.
3. The response of an LTI system can be easily computed using convolution property of
Fourier transform.
6. What is the frequency response of LTI system?
The Fourier transform of the impulse response h(n) of the system is called frequency
response of the system. It is denoted by H().
7. Write the properties of frequency response of LTI system.
The properties of frequency response of LTI system are
1. The frequency response is periodic function with a period of 2 .
2. If h(n) is real then H () is symmetric and H ( ) is antisymmetric.
3. If h(n) is complex then the real part of H ( ) is antisymmteric over the interval
0 2 .
4. The frequency response is a continuous function of .
8. Write short notes on the frequency response of first order system.
A first order system is characterized by the difference equation
y(n) x(n) ay(n 1)
The frequency response of first order system depends on the co efficient “a” in the difference
equation governing the LTI system. When the value of “a|” is in the range of 0<a<1, the first
order system behaves as a low pass filter. When the value of “a” is in the range –1<a<0, the first
order system behaves as a high pass filter.
9. Write short notes on the frequency response of second order system.
A second order system is characterized by the difference equation
y (n) 2r cos 0 y (n 1) r 2 y (n 2) x(n) r cos 0 x(n 1)
The frequency response of second order system depends on the parameters “r” and “ 0 ” in
the difference equation of the LTI system. When the value of r is in the range of 0<r<1, the
second order system behave as a resonant filter with center frequency 0 . When the value of r is
varied from 0 to 1, the sharpness of resonant peak will increase.
12
10. Define – Discrete Fourier Series
Consider a sequence xp(n) with a period of N samples so that xp(n)=xp(n/N); Then the
discrete Fourier series of the sequence xp(n) is defined as
N 1
X p (k ) x p (n)e j 2kn / N
n 0
11. What are the two basic differences between the Fourier transform of a discrete time
signal with the Fourier transform of a continuous time signal?
1. For a continuous signal, the frequency range extends from to . On the other hand,
the frequency range of a discrete – time signal extends from to ( or 0 to 2 ) .
2. The Fourier transform of a continuous signal involves integration, whereas, the Fourier
transform of a discrete – time signal involves summation process.
12. Find the Fourier transform of a sequence x(n) = 1 for 2 n 2
= 0 otherwise.
Solution:
X ( )
x(n)e jn
n
2
e
j n
n 2
e j 2 e j 1 e j e j 2
1 2 cos 2 cos 2
13. Define – Discrete Fourier Transformation of a given sequence x(n)
The N- point DFT of a sequence x(n) is
N 1
X (k ) x(n)e j 2kn / N
k= 0, 1, 2……..N-1.
n 0
14. Write the formula for N- point IDFT of a sequence X(k).
The N-point IDFT of a sequence X(k) is
1 N 1
x(n) X (k )e j 2k / N
n= 0, 1 , 2 …..N-1 .
N K 0
15. List out any four properties of DFT.
1. Periodicity
If X(k) is N- point DFT of a finite duration sequence x(n), then
x(n N ) x(n) for all n
X (k N ) X (k ) for all k .
2. Linearity
If X1(k)=DFT[x1(n)] and
X2(k)=DFT[x2(n)],
then
DFT[a1x1(n)+a2x2(n)]=a1X1(k)+a2x2(k)
13
3. Time reversal of a sequence
If DFT {x(n)}=X(k),
then
DFT{x((-n))N}=DFT{x(N-n)}=X((-k))N=X(N-k)
4. Circular time shifting of a sequence
If DFT {x(n)}=X(k),
then
DFT{x((n-l))N}=X(k) e j 2kl / N
16. IF N-point sequence x(n) has N- point DFT X(k) then what is the DFT of the following?
(i ) x (n)
(ii) x ( N n)
(iii) x(( n l )) N (iv) x(n)e j 2 ln/ N
Solution:
(i ) DFT{x (n)} X ( N k )
(ii) DFT{x ( N n)} X (k )
(iii) DFT{x((n l )) N } X (k )e j 2kl / N
(iv) DFT{x(n)e j 2 ln/ N } X ((k l )) N
1
17. Calculate the DFT of the sequence x(n) =
4
n
forN 16
N 1
Solution:
X (k ) x(n)e j 2kn / N
K=0, 1 , 2…..N-1
n0
n
15
1
e j 2kn / 16
n 0 4
1
e j k / 8
n 0 4
15
n
16
1
1 e j 2k
4
1
1 e j k / 8
4
18. State the time shifting property of DFT.
The time shifting properties of DFT states that
j 2kn / N
X (k )
If DFT[x(n)] = X(k), then DFT[x((n-m))N] = e
14
19. Find the DFT of the sequence x(n)={ 1,1,0,0 }
Solution:
N 1
X (k ) x(n)e j 2kn / N
k=0,1,2,…..N-1
n 0
3
x ( n)e j 2 kn / 4
k 0,1, 2 , 3.
n 0
3
X (0) x ( n) {1 1 0 0} 2
n 0
3
X (1) x ( n)e j n / 2 {1 j 0 0 } 1 j
n 0
3
X (2) x ( n)e j n {1 1 0 0 } 0
n 0
3
X (3) x ( n)e j 3 n / 2 {1 j 0 0 } 1 j
n 0
X ( k ) {2,1 j , 0,1 j }
20. When is the DFT X(k) of a sequence x(n) imaginary?
If the sequence x(n) is real and odd (or) imaginary and even, then X(k) is purely imaginary.
21. When is the DFT X(k) of a sequence x(n) is real?
If the sequence x(n) is real and even (or) imaginary and odd , then X(k) is purely real.
22. State the circular frequency shifting property of DFT.
The circular frequency shifting property of DFT states that
If DFT[x(n)]=X(k), then DFT[x(n) e j 2 ln/ N ] X (( k l )) N
23. What is meant by zero padding? What are its uses?
The process of lengthening the sequence by adding zero – valued samples is called appending
with zeros or zero – padding.
Uses:
1. We can get “better display” of the frequency spectrum.
2. With zero padding, the DFT can be used in linear filtering.
15
24. What is meant by understand by periodic convolution?
Let x1 p (n) and x 2 p (n) be two periodic sequences each with period N with
DFS x
( n) X
DFS x1 p (n) X 1 p (k )
2p
2p
and
(k )
……………………………(1)
If X 3 p (k ) X 1 p (k ) X 2 p (k )
then the periodic sequence x3 p (n) with Fourier series coefficients X 3 p ( k ) can be obtained
by periodic convolution, defined as
N 1
x3 p (n) x1 p (m) x 2 p (n m) ………………………………(2)
n 0
The convolution in the form of eqn(2) is known as periodic convolution, as the sequences in
eqn(2) are all periodic with period N, and the summation is over one period.
25. Define – Circular Convolution
The convolution property of DFT is defined as the multiplication of the DFTs of the two
sequence equivalent to the DFT of the circular convolution of the two sequences.
X 1 (k ) X 2 (k ) DFT{x1 (n) x2 (n)}
N 1
x3 (n) x1 (m) x2 ((n m)) N
m 0
26. How is the circular convolution obtained by using graphical method?
Given two sequences x1 (n) and x 2 (n) , the circular convolution of these two sequences
x3 (n) x1 (n) Nx 2 (n) can be obtained by using the following steps.
1. Graph N samples of x1 (n) , as equally spaced points around an outer circle in counter
clockwise direction.
2. Start at the same point as x1 (n) graph N samples of x 2 (n) as equally spaced points
around an inner circle in clock wise direction.
3. Multiply corresponding samples on the two circles and sum the products to produce
output.
4. Rotate the inner circle one sample at a time in clock wise direction and go to step 3 to
obtain the next value of output.
5. Repeat step 4 until the inner circle first sample lines up with the first sample of the
exterior circle once again.
27. Distinguish between linear and circular convolution of two sequences.
Sl. No.
Linear Convolution
Circular convolution
If x(n) is a sequence of L number of If x(n) is a sequence of L number of
samples and h(n) with M number of samples and h(n) with M number of
1
samples , after convolution y(n) will samples , after convolution y(n) will
contain N=L+M-1
contain N=Max(L,M) samples.
16
2
3
Linear convolution can be used to find Circular convolution cannot be used
the response of a linear filter.
to find the response of a filter.
Zero padding is not necessary to find Zero padding is necessary to find the
the response of a linear filter.
response of a filter.
28. What are the steps involved in circular convolution?
The circular convolution involves basically four steps as the ordinary linear convolution.
They are:
1. Folding the sequence
2. Circular time shifting the folded sequence
3. Multiplying the two sequences to obtain the product sequence
4. Summing the values of product sequence
29. What are the different methods performing circular convolution?
The different methods of performing circular convolution are:
1. Graphical method
2. Stockhman‟s method
3. Tabular array method
4. Matrix method
30. Obtain the circular convolution of the following sequences
x(n)={1, 2, 1 }; h(n)={ 1, -2, 2 }
Solution:
The circular convolution of the above sequences can be obtained by using matrix method.
h(0) h(2) h(1) x(0) y (0)
h(1) h(0) h(2) x(1) y (1)
h(2) h(1) h(0) x(2) y (2)
1 2 2 1 3
2 1 2 2 2
2 2 1 1 1
y (n) 3, 2, 1
31. How is obtain linear convolution obtained from circular convolution?
Consider two finite duration sequences x9n) and h(n0 of duration L samples and N samples
respectively. The linear convolution of these two sequences produces an output sequence of
duration L+M-1 samples, whereas, the circular convolution of x(n) and h(n) give N samples
where N=Max(L,M) . In order to obtain the number of samples in circular convolution equal to
L+M-1, both x(n) and h(n) must be appended with appropriate number of zero valued samples. In
other words, by increasing the length of the sequences x(n) and h(n) to L+M-1 points and then
circularly convolving the resulting sequences we obtain the same result as that of linear
convolution.
17
32. What is meant by sectioned convolution?
If the data sequence x(n) is of long duration , it is very difficult to obtain the output sequence
y(n) due to limited memory of a digital computer. Therefore, the data sequence is divided up into
smaller sections. These sections are processed separately one at a time and combined later to get
the output.
33. What are the different methods used for the sectioned convolution?
The two methods used for the sectioned convolution are:
1. the overlap-add method
2. the overlap-save method.
34. Differentiate overlap-add method from overlap – save method.
Sl. No.
1.
2.
3.
4.
Overlap – add method
In this method the size of the input
data block is N=L+M-1
Each data block consists of the last
M-1 data points of the previous data
followed by the L new data points.
In each output block, M-1 points are
corrupted due to aliasing, as circular
convolution is employed.
To form the output sequence the first
M-1 data points are discarded in each
output block and the remaining data is
fitted together.
Overlap – save method
In this method the size of the input
data block is L.
Each data block has L points and we
M-1 zeros are appeared to compute
N-point DFT.
In this no corruption due to aliasing
as linear convolution is performed
using circular convolution.
To form the output sequence, the last
M-1 points from each output block is
added to the first (M-1) points of the
succeeding block.
35. Distinguish between DFT and DTFT.
Sl. No.
1.
2.
DFT
DTFT
Obtained by performing sampling
Sampling is performed only in time
operation in both the time and
domain.
frequency domains.
Discrete frequency spectrum
Continuous function of
36. What is meant by FFT?
The term Fast Fourier Transform (FFT) usually refers to a class of algorithms for efficiently
computing the DFT. It makes use of the symmetry and periodicity properties of twiddle factor
W NK to effectively reduce the DFT computation time.
It is based on the fundamental principle of decomposing the computation of DFT of a
sequence of length N into successively smaller discrete Fourier transforms. The FFT algorithm
18
provides speed increase factors, when compared with direct computation of the DFT, of
approximately 64 and 205 for 256 points and 1024 – point transforms respectively.
37. How many multiplications and additions are required to compute N-point DFT using
radix-2 FFT?
The number of multiplications and additions required to compute N-point DFT using radix-2
N
FFT are N log 2 N and
log 2 N respectively.
2
38. How many multiplications and additions are required to compute N-point DFT directly?
The number of multiplications and additions required to compute N-point DFT are
N ( N 1) and
N 2 respectively.
39. What is the speed improvement factor in calculating 64-point DFT of a sequence using
direct computation and FFT algorithms?
(OR)
Calculate the number of multiplications needed in the calculation of DFT and FFT with 64point sequence.
The number of complex multiplications required using direct computation is
N 2 64 2 4096
The number of complex multiplications required using FFT is
N
64
log 2 N
log 2 64 192
2
2
4096
Speed improvement factor=
21.33
192
40. What is meant by radix-2 FFT?
The FFT algorithm is most efficient in calculating N-point DFT. If the number of output
points N can be expressed as a power of 2, that is N 2 m , where m is an integer, then this
algorithm is known as radix-2 FFT algorithm.
41. What is a decimation-in-time algorithm?
The computation of 8-point DFT using radix-2 FFT, involves three stages of computations.
Here N = 8 = 23, therefore r= 2 and m = 3.
The given 8-point sequence is decimated to 2-point sequences. For each 2-point sequence, the
2-point DFT is computed. From the result of 2-point DFT the 4-point DFT can be computed.
From the result of 4-point DFT, the 8-point DFT can be computed.
42. What is decimation in frequency algorithm?
It is the popular form of the FFT algorithm. In this the output sequence X(k) is divided into
smaller and smaller subsequences.
19
43. What are the differences and similarities between DIT and DIF algorithms?
The difference between DIT and DIF are:
1. In DIT, the input is bit-reversed while the output is in natural order. For DIF, the reverse
is true, i.e., input is normal order, while the output bit is reversed. However, both DIT and
DIF can go from normal to shuffled data or vice versa.
2. Considering the butterfly diagram in DIF, the complex multiplication takes place after the
add-subtract operation.
The similarities between DIT and DIF are:
1. Both algorithms require the same number of operations to compute DFT.
2. Both algorithms require bit-reversal at some place during computation.
44. What are the applications of FFT algorithms?
The applications of FFT algorithms are:
1. Linear filtering
2. Correlation
3. Spectrum analysis
UNIT – III
DESIGN OF IIR FILTERS
1. What are the different types of structures for realization of IIR systems?
The different types of structures for realization of IIR system are:
1. Direct form I structure
2. Direct form II structure
3. Cascade form structure
4. Parallel form structure
5. Lattice – ladder form structure
2. Distinguish between recursive realization and non-recursive realization.
For recursive realization the current output y(n) is a function of past outputs, past and present
inputs. This form corresponds to an Infinite – Impulse response (IIR) digital filter.
For non-recursive realizations current output sample y(n) is a function of only past and
present inputs. This form corresponds to an Finite Impulse response (FIR) digital filter.
3. How many numbers of additions, multiplications and memory locations are
required
to realize a system H(z) having M zeros and N poles in (a) Direct form – I realization (b)
Direct form – II realization.
1. The Direct form – I realization requires M+N+1 multiplications, M+N additions
and
M+N+1 memory locations.
2. The Direct form – II realization requires M+N+1 multiplications, M+N
additions
and the maximum of (M,N) memory locations.
20
4. What is the main advantage of Direct form- II realizations when compared to Direct form –
I realization?
In Direct form – II realization, the number of memory locations required is less than that of
Direct form – I realization.
5. Define – Signal Flow Graph
A signal flow graph is defined as a graphical representation of the relationship between the
variables of a set of linear difference equations.
6. What is transposed theorem?
The transpose of a structure is defined by the following operations.
1. Reverse the directions of all branches in the signal flow graph
2. Interchange the input and outputs
3. Reverse the roles of all nodes in the flow graph
4. Summing points become branching points
5. Branching points become summing points
According to transposition theorem if we reverse the directions of all branch transmittance
and interchange the input and output in the flow graph, the system function remains unchanged.
7. What is canonic form structure?
The direct form –II realization requires minimum number of delays for the realization of the
system. Hence it is called as “Canonic form” structure.
8. What is the main disadvantage of direct form realization?
The direct form realization is extremely sensitive to parameter quantization. When the order
of the system N is large, a small change in a filter coefficient due to parameter quantization,
results in a large change in the location of the poles and zeros of the system.
9. What is the advantage of cascade realization?
Quantization errors can be minimized if we realize an LTI system in cascade form.
10. What are the different types of filters based on impulse response?
Based on impulse response, the filters are of two types. They are:
1. IIR filter
2. FIR filter
The IIR filters are of recursive type, whereby the present output sample depends on the
present input, past inputs samples and output samples.
The FIR filters are of non-recursive type whereby the present output sample depends on the
present input sample and previous input samples.
21
11. What is the general form of IIR filter?
The most general form of IIR filter can be written as
M
H ( z)
b z
k 0
k
k
N
1 ak
k 1
12. Write the magnitude of Butterworth filter. What is the effect of varying order of N on
magnitude and phase response?
The magnitude function of the Butterworth filter is given by
1
H ( j)
N 1, 2 , 3..............
1
2N 2
1
c
where, N is the order of the filter and c is the cut off frequency. The magnitude response of
the Butterworth filter closely approximates the ideal response as the order N increases. The phase
response becomes more non-linear as N increases.
13. List out the properties of Butterworth lowpass filters.
1. The magnitude response of the Butterworth filter decreases monotonically as the
frequency increases from 0 to α.
2. The magnitude response of the Butterworth filter closely approximates the ideal response
as the order N increases.
3. The Butterworth filters are all pole designs.
4. The poles of the Butterworth filter lies on a circle.
1
5. At the cut off frequency c , the magnitude of normalized Butterworth filter is
.
2
14. What is Butterworth approximation?
In Butterworth approximation, the error function is selected in such a way that the magnitude
is maximally flat in the origin (i.e., at =0) and monotonically decreasing with increasing .
15. How are the poles of Butterworth transfer function located in s- plane?
The poles of the normalized Butterworth transfer function symmetrically lies on an unit circle
in s-plane with angular spacing of
.
N
16. What is Chebyshev approximation?
In Chebyshev approximation, the approximation function is selected in such a way that the
error is minimized over a prescribed band of frequencies.
22
17. What is Type –1 Chebyshev approximation?
In type –1 Chebyshev approximation, the error function is selected in such a way that, the
magnitude response is equi-ripple in the pass band and monotonic in the stop band.
18. What is Type-2 Chebyshev approximation?
In type-2 Chebyshev approximation, the error function is selected in such a way that, the
magnitude response is monotonic in pass band and equi-ripple in the stop band. The Type -2
magnitude response is called inverse Chebyshev response.
19. Write the magnitude function of Chebyshev low pass filter.
The magnitude response of Type -1 low pass Chebyshev filter is given by
1
H a
1 2 C N2
c
where, is attenuation constant and
is the Chebyshev polynomial of the first kind of degree N.
C N
c
20. How does the order of the filter affect the frequency response of Chebyshev filter?
From the magnitude response of Type -1 Chebyshev filter it can be observed that the
magnitude response approaches the ideal response as the order of the filter is increased.
21. How is the order N of Chebyshev filter determined?
The order N of the Chebyshev filter is given by
cosh 1
N
cosh 1 s
p
0.1 p
where, 10
1 and 100.1 s 1
22. What are the properties of Chebyshev filter?
1. The magnitude response of the Chebyshev filter exhibits in ripple either in pass band or
in the stop band according to the type.
2. The magnitude response approaches the ideal response as the value of N increases.
3. The Chebyshev type–1 filters are all pole designs.
4. The poles of Chebyshev filter lies on an ellipse.
1
5. The normalized magnitude function has a value of
at the cutoff frequency c .
1 2
23
23. Compare Butterworth filter with Chebyshev Type -1 filter.
Sl. No.
Butterworth filter
Chebyshev filter
1
All pole design
All pole design
The poles lie on a circle in s2
The poles lie on a ellipse in s-plane
plane
The magnitude response is
The magnitude response is equi-ripple in
maximally flat at the origin and
3
pass band and monotonically decreasing
monotonically decreasing
in the stop band.
function of .
The normalized magnitude response has a
The normalized magnitude
1
1
value of
at the cut off frequency
response has a value of
at
4
2
1 2
the cut off frequency c .
c .
5.
Only few parameters has to be
calculated to determine the
transfer function.
A large number of parameter has to be
calculated to determine the transfer
function.
24. What are the different types of filters based on the frequency response?
The filters can be classified based on frequency response. They are (i) low pass filter (ii)high
pass filter (iii)Band pass filter (iv)Band reject filter.
25. Distinguish between FIR filter and IIR filter.
Sl. No.
1.
2.
3.
4.
FIR filter
These filters can be easily
designed to have perfectly linear
phase.
FIR filters can be realized
recursively and non –
recursively.
Greater flexibility to control the
shape of their magnitude
response.
Errors due to round-off noise are
less severe in FIR filters, mainly
because feedback is not used.
IIR filter
These filters do not have linear phase.
IIR filters are easily realized recursively.
Less flexibility, usually limited to specific
kind of filters.
The round-off noise in IIR filters is more.
26. What are the design techniques of designing FIR filters?
There are three well-known methods for designing FIR filters with linear phase. They are:
1. Windows method
24
2. Frequency sampling method
3. Optimal or minimax design.
27. What is meant understand by linear phase response?
For a linear phase filter ( ) , the linear phase filter did not alter the shape of the original
signal. If the phase response of the filter is non-linear, the output signal may be a distorted one.
In many cases a linear phase characteristic is required throughout the pass band of the filter to
preserve the shape of a given signal within the pass band. IIR filter cannot produce a linear
phase. The FIR filter can give linear phase, when the impulse response of the filter is symmetric
about its mid-point.
28. For what kind of application, can the anti-symmetrical impulse response be used?
The anti-symmetrical impulse response can be used to design Hilbert transformers and
differentiators.
29. For what kind of application, can the symmetrical impulse response be used?
The impulse response, which is symmetric and having odd number of samples can be used to
design all types of filters, i.e., low pass, high pass, band pass and band reject.
The symmetric impulse response having even number of samples can be used to design low
pass and band pass filter.
30. How are digital filters designed from the analog filters?
1. Map the desired digital filter specifications into those for an equivalent analog filter.
2. Derive the analog transfer function for the analog prototype.
3. Transform the transfer function of the analog prototype into an equivalent digital filter
transfer function.
31. Write any two procedures for digitizing the transfer function of an analog filter.
The two important procedures for digitizing the transfer function of an analog filter are:
1. Impulse invariance method.
2. Bilinear transformation method.
32. What are the requirements for a digital filter to be stable and causal?
1. The digital transfer function H(z) should be a rational function of z and the
efficients of z should be real.
2. The poles should lie inside the unit circle in z-plane.
3. The number of zeros should be less than or equal to number of poles.
co-
33. What are the requirements for an analog filter to be stable and causal?
1. The digital transfer function Ha(s) should be a rational function of s and the co-efficient
of s should be real.
2. The poles should lie on the left half of s-plane.
3. The number of zeros should be less than or equal to the number of poles.
25
34. What are the advantages and disadvantages of digital filters?
The advantages of digital filters are:
1. High thermal stability due to absence of resistors, inductors and capacitors.
2. The performance characteristics like accuracy, dynamic range, stability and tolerance can
be enhanced by increasing the length of the registers.
3. The digital filters are programmable.
4. Multiplexing and adaptive filtering are possible.
The disadvantages of digital filters are:
1. The bandwidth of the discrete signal is limited by the sampling frequency.
2. The performance of the digital filter depends on the hardware used to implement the
filter.
35. What is impulse invariant transformation?
The transformation of analog filter to digital filter without modifying the impulse response of
the filter is called impulse invariant transformation (i.e., in this transformation the impulse
response of the digital filter will be sampled version of the impulse response of the analog filter.)
36. What is the main objective of impulse invariant transformation?
The objective of this method is to develop an IIR filter transfer function whose impulse is the
sampled version of the impulse response of the analog filter. Therefore the frequency response
characteristics of the analog filter are preserved.
37. Write the impulse invariant transformation used to transform real poles with and without
multiplicity.
The impulse invariant transformation used to transform real poles (at s = - pi) without
multiplicity is
1
1
is transformed to
piT
s pi
1 e
z 1
The impulse invariant transformation used to transform multiple real pole
1
s pi
m
is transformed to
m 1
(at s = - pi) is
m 1
(1)
d
1
m 1
piT 1
(m 1) dpi 1 e z
38. What is the relation between digital and analog frequency in impulse invariant
transformation?
The relation between analog and digital frequency in impulse invariant transformation is
given by
Digital frequency, T
where,
- Analog frequency and
T - Sampling time period
26
39. What is Bilinear transformation?
The Bilinear transformation is a conformal mapping that transforms the s-plane to z-plane. In
this mapping the imaginary axis of s-plane is mapped into the unit circle in z-plane, the left half
of s-plane is mapped into interior of unit circle in z-plane and the right half of s-plane is mapped
into exterior of unit circle in z-plane . The Bilinear mapping is a one – to-one mapping and it is
accomplished when
s
2 1 z 1
T 1 z1
40. What is the relation between digital and analog frequency in Bilinear transformation?
In Bilinear transformation, the digital frequency and analog frequency are related by the
equation,
T
Digital frequency, 2 tan 1
or
2
2
Analog frequency tan
T
2
where,
- Analog frequency
T - Sampling time period
41. What is frequency warping?
In bilinear transformation the relation between analog and digital frequencies is nonlinear.
When the s-plane is mapped into z-plane using bilinear transformation, this nonlinear
relationship introduces distortion in frequency axis, which is called frequency warping.
42. What is prewarping? Why is it employed?
In IIR filter design using bilinear transformation, the conversion of the specified digital
frequencies to analog frequencies is called prewarping.
Prewarping is necessary to eliminate the effect of warping on amplitude response.
43. Explain the technique of prewarping.
In IIR filter design using bilinear transformation the specified digital frequencies are
converted to analog equivalent frequencies, which are called prewarp frequencies. Using the
prewarp frequencies, the analog filter transfer function is designed and then it is transformed to
digital filter transfer function.
44. Compare the impulse invariant transformation with bilinear transformation.
Sl. No.
Impulse Invariant transformation
Bilinear transformation
1.
2.
3.
It is many-to-one mapping
It is one-to-one mapping.
The relation between analog and
digital frequency is linear.
To prevent the problem of aliasing the
analog filters should be band limited.
The relation between analog and digital
frequency is nonlinear.
There is no problem of aliasing and so the
analog filter need not be band limited.
27
4.
The magnitude and phase response of
analog filter can be preserved by
choosing low sampling time or high
sampling frequency.
Due to the effect of warping, the phase
response of analog filter cannot be
preserved. But the magnitude response can
be preserved by prewarping.
UNIT – IV
FIR FILTER DESGIN
1. What is the condition for the impulse response of FIR filter to satisfy constant group and
phase delay and only constant group delay?
For linear phase FIR filter to have both constant group delay and constant phase delay.
( )
For satisfying the above condition
h(n) h( N 1 n)
that is, the impulse response must be symmetrical about n
N 1
2
If one constant group delay is desired, then
( )
For satisfying the above condition
h(n) h( N 1 n)
that is, the impulse response must be antisymmetrical about n
N 1
2
2. What are the properties of an FIR filter?
1. FIR filter is always stable because all its poles are at the origin.
2. A realizable filter can always be obtained.
3. FIR filter has a linear phase response.
3. What are the steps involved in the FIR filter design?
1. Choose the desired (ideal) frequency response H d ( )
2. Take inverse Fourier transform of H d ( ) to get hd (n)
3. Convert the infinite duration hd (n) to a finite duration sequence h(n)
4. Take Z – transform of h(n) to get the transfer function H (z ) of the FIR filter
4. What is the necessary and sufficient condition for the linear phase characteristic of an FIR
filter?
The necessary and sufficient condition for the linear phase characteristic of a FIR filter is that
the phase function should be a linear function of , which in turn requires constant phase delay
or constant group delay.
28
5. How is the constant group delay and phase delay achieved in linear phase FIR filters?
Frequency response of FIR filters with constant group and phase delay
H ( ) H ( ) e j ( )
The following conditions have to be satisfied to achieve constant group and phase delay:
N 1
Phase delay,
( i.e., phase delay is constant )
2
Group delay, ( i.e., group delay is constant)
2
Impulse response, h(n) = - h( N -1 – n ) (i.e., impulse response is anti symmetric )
6. What are the possible types of impulse response for linear phase FIR filters?
There are four types of impulse response for linear phase FIR filters. They are:
1. Symmetric impulse response when N is odd.
2. Symmetric impulse response when N is even.
3. Antisymmetric impulse response when N is odd.
4. Antisymmetric impulse response when N is even.
7. List out the well-known design techniques for linear phase FIR filter.
There are three well known methods of design techniques for linear phase FIR filters. They are,
1. Fourier series method and window method.
2. Frequency sampling method.
3. Optimal filter design method.
8. Write the two concepts that lead to the Fourier series or Window method of designing FIR
filters.
The following concepts lead to the design of FIR filters by Fourier series method.
1. The frequency response of a digital filter is periodic with period equal to sampling
frequency
2. Any periodic function can be expressed as a linear combination of complex exponentials
9. Write the procedure for designing FIR filter by Fourier series method.
1. Choose the desired (ideal) frequency response H d ( ) of the filter.
2. Evaluate the Fourier series co-efficient of H d ( ) which gives the desired impulse
response hd (n) .
1
hd (n)
2
H
d
( )e jn d
3. Truncate the infinite sequence hd (n) to a finite duration sequence h(n) .
4. Take Z – transform of h(n) to get a noncausal filter transfer function H (z ) of the FIR
filter.
29
N 1
2
5. Multiply H (z ) by z
to convert noncausal transfer function to a realizable causal
FIR filter transfer function.
H (z ) z
N 1
2
N 1
2
h(0) h(n) z n z n
n 1
10. What are the disadvantages of Fourier series method?
In designing FIR filter using Fourier series method the infinite duration impulse response is
N 1
truncated at n=
. Direct truncation of the series will lead to fixed percentage overshoots
2
and undershoots before and after an approximated discontinuity in the frequency response.
11. What is Gibbs phenomenon?
One possible way of finding an FIR filter that approximates H (e j ) would be to truncate
N 1
the infinite Fourier series at n=
.The abrupt truncation of the series will lead to
2
oscillation both in pass band and in stop band. This phenomenon is known as Gibbs
phenomenon.
12. Write the procedure for designing FIR filter using windows.
1. Choose the desired (ideal) frequency response H d ( ) of the filter
2. Evaluate the Fourier series co-efficient of H d ( ) which gives the desired impulse
response hd (n)
1
hd (n)
2
H
d
( )e jn d
3. Choose a window sequence w(n) and multiply the infinite sequence hd (n) by w(n)to
convert the infinite duration impulse response to finite duration impulse response h(n)
h(n) hd (n) w(n)
4. Find the transfer function of the realizable FIR filter
H (z ) z
N 1
2
N 1
2
h(0) h(n) z n z n
n 1
30
13. What are the desirable characteristics of the window?
The desirable characteristics of the window are:
1. The central lobe of the frequency response of the window should contain most of the energy
and should be narrow.
2. The highest side lobe level of the frequency response should be small.
3. The side lobe of the frequency response should decrease in energy rapidly as tends to .
14. What is window? Why is it necessary?
One possible way of finding an FIR filter that approximates H (e j ) would be to truncate the
N 1
infinite Fourier series at n=
. The abrupt truncation of the series will lead to oscillation
2
both in passband and in stopband. These oscillations can be reduced through the use of less
abrupt truncation of the Fourier series. This can be achieved by multiplying the infinite impulse
response with a finite weighing w(n) , called a window.
15. List out the characteristics of FIR filter designed using windows.
1. The width of the transition band depends on the type of window.
2. The width of the transition band can be made narrow by increasing the value of N where
N is the length of the window sequence.
3. The attenuation in the stop band is fixed for a given window, except in case of Kaiser
Window where it is variable.
16. Write the procedure for FIR filter design by frequency sampling method.
1. Choose the desired frequency response H d ( )
~
2. Take N samples of H d ( ) to generate the sequence H ( k ).
~
3. Take inverse DFT of H ( k ). to get the impulse response h(n)
4. The transfer function H(z) of the filter is obtained by taking Z-transform of impulse
response.
17. What is meant by Optimum equiripple design criterion? Why is it followed?
In FIR filter design by Chebyshev approximation technique, the weighted approximation
error between the desired frequency and the actual frequency response is spread evenly across the
pass band and stop band. The resulting filter will have ripples in both the pass band and stop
band. This concept of design is called optimum equi-ripple design criterion.
The optimum equiripple criterion is used to design FIR filter in order to satisfy the
specifications of pass band and stop band.
18. Write the expression for frequency response of rectangular window.
The frequency response of rectangular window is given by
WR ( )
sin
N
sin
2
2
31
19. Write the characteristic features of Rectangular window.
4
1. The mainlobe width is equal to
.
N
2. The maximum sidelobe magnitude is -13dB.
3. The sidelobe magnitude does not decreases significantly with increasing.
20. List out the features of FIR filter designed using rectangular window.
1. The width of the transition region is related to the width of the mainlobe of window
spectrum.
2. Gibb‟s oscillations are noticed in the passband and stopband.
3. The attenuation in the stopband is constant and cannot be varied.
21. Write the equation specifying Hanning windows.
The equation for Hanning window is given by
2n
( N 1)
( N 1)
for
wH n (n) 0.5 0.5 cos
n
N 1
2
2
=0
Otherwise.
22. Write the equation specifying Hamming windows.
The equation for Hamming window is given by
2n
( N 1)
( N 1)
for
wH (n) 0.54 0.46 cos
n
N 1
2
2
=0
Otherwise.
23. Write the equation specifying Blackman windows.
The equation for Blackman window is given by
2n
4n
( N 1)
( N 1)
for
wB (n) 0.42 0.5 cos
0.08 cos
n
N 1
N 1
2
2
=0
Otherwise.
24. Write the equation specifying Bartlett windows.
The equation for Bartlett window is given by
2n
( N 1)
( N 1)
wT (n) 1
for
n
N 1
2
2
=0
Otherwise.
32
25. Write the equation specifying Kaiser windows.
The equation for Bartlett window is given by
2n
1
N 1
wk (n) I 0
I 0 ( )
for n
( N 1)
2
=0
Otherwise.
where, is an independent parameter.
I 0 (x) is the zeroth order Bessel function of the first kind
1 x k
I 0 ( x) 1
k 1
k! 2
2
26. Write the characteristics features of Triangular window.
The characteristics features of Triangular window are:
8
1. The mainlobe width is equal to
.
N
2. The maximum sidelobe magnitude is -25dB.
3. The sidelobe magnitude slightly decreases with increasing .
27. Why is the triangular window not good a good choice for designing FIR filters?
In FIR filters designed using triangular window the transition from passband to stopband is
not sharp and the attenuation in stopband is less when compared to filters designed with
rectangular window. For the above two reasons the triangular window is not a good choice.
28. List out the features of hanning window spectrum.
8
1. The mainlobe width is equal to
.
N
2. The maximum sidelobe magnitude is -31dB.
3. The sidelobe magnitude slightly decreases with increasing .
29. List out the features of hamming window spectrum.
8
1. The mainlobe width is equal to
.
N
2. The maximum sidelobe magnitude is -41dB.
3. The sidelobe magnitude remains constant for increasing .
33
30. Compare Rectangular window with Hanning window.
Sl. No.
Rectangular window
Hanning window
The width of mainlobe in window
The width of mainlobe in window
4
8
1
spectrum is
spectrum is
N
N
The maximum sidelobe magnitude
The maximum sidelobe magnitude in
2
in window spectrum is -13dB.
window spectrum is -31dB.
In window spectrum the sidelobe
In window spectrum the sidelobe
magnitude slightly decreases with
3
magnitude decreases with increasing
increasing
In FIR filter designed using
In FIR filter designed using Hanning
4
rectangular window the minimum
window the minimum stop band
stop band attenuation is 22dB.
attenuation is 44dB.
31. Compare Rectangular window with Hamming window.
Sl. No.
1
2
3
4
Rectangular window
The width of mainlobe in window
4
spectrum is
N
The maximum sidelobe magnitude
in window spectrum is -13dB.
In window spectrum the sidelobe
magnitude slightly decreases with
increasing
In FIR filter designed using
rectangular window the minimum
stopband attenuation is 22dB.
Hamming window
The width of mainlobe in window
8
spectrum is
N
The maximum sidelobe magnitude in
window spectrum is -41dB.
In window spectrum the sidelobe
magnitude remains constant.
In FIR filter designed using Hamming
window the minimum stopband attenuation
is 51dB.
32. Compare Hanning window with Hamming window.
Sl. No.
Hanning window
Hamming window
The width of mainlobe in window
The width of mainlobe in window spectrum is
8
8
1
spectrum is
N
N
The maximum sidelobe magnitude
The maximum sidelobe magnitude in window
2
in window spectrum is -31dB.
spectrum is -41dB.
In window spectrum the sidelobe magnitude
In window spectrum the sidelobe
remains constant. Here the increased sidelobe
magnitude decreases with
3
attenuation is achieved at the expense of
increasing
constant attenuation at high frequencies.
34
In FIR filter designed using
Hanning window the minimum stop
band attenuation is 44dB.
4
In FIR filter designed using Hamming
window the minimum stop band attenuation
is 51dB.
33. Compare Hamming window with Blackman window.
Sl. No.
1
2
3
4
5
Hamming window
The width of mainlobe in window
8
spectrum is
N
The maximum sidelobe magnitude
in window spectrum is -41dB.
In window spectrum the sidelobe
magnitude remains constant with
increasing
In FIR filter designed using
Hamming window the minimum
stop band attenuation is 51dB.
The higher value of sidelobe
attenuation is achieved at the
expense of constant attenuation at
high frequencies.
Blackman window
The width of mainlobe in window
12
spectrum is
N
The maximum sidelobe magnitude in
window spectrum is -58dB.
In window spectrum the sidelobe
magnitude decreases rapidly with
increasing
In FIR filter designed using Blackman
window the minimum stopband
attenuation is 78dB.
The higher value of sidelobe attenuation is
achieved at the expense of increased
mainlobe width.
34. List out the features of Blackman window spectrum.
The features of Blackman window spectrum are:
12
1. The mainlobe width is equal to
.
N
2. The maximum side lobe magnitude is -58dB.
3. The sidelobe magnitude slightly decreases with increasing .
4. The higher value of sidelobe attenuation is achieved at the expense of increased mainlobe
width.
35. List out the features of Kaiser window spectrum.
1. The width of mainlobe and the peak sidelobe are variable.
2. The parameter in the Kaiser window function, is an independent variable that can be
varied to control the sidelobe levels with respect to mainlobe peak.
3. The width of the mainlobe in the window spectrum (and so the transition region in the
filter) can be varied by varying the length N of the window sequence.
35
36. Compare Hamming window with Kaiser window.
Sl. No.
Hamming window
Kaiser window
The width of mainlobe in window
The width of mainlobe in window
1
8
spectrum depends on the values of and
spectrum is
N.
N
The maximum sidelobe magnitude with
The maximum sidelobe magnitude
respect to peak of mainlobe is variable
2
in window spectrum is -41dB.
using the parameter .
In window spectrum the sidelobe
In window spectrum the sidelobe
magnitude remains constant with
3
magnitude decreases with increasing
increasing
In FIR filter designed using Kaiser
In FIR filter designed using
window the minimum stopband
4
Hamming window the minimum
attenuation is variable and depends on the
stopband attenuation is 51dB.
value of .
UNIT –V
PROGRAMMABLE DSP CHIPS AND QUANTIZATION EFFECTS
1. What are the classification digital signal processors?
The digital signal processors are classified as
1. General purpose digital signal processors.
2. Special purpose digital signal processors.
2. Write some examples for fixed point DSPs.
Some examples for fixed point DSPs are:
1. TMS320C50
2. TM 320C54
3. TM 320C55
4. ADSP-219x
5. ADSP-219xx
3. Write some examples for floating point DSPs.
Some examples for floating point DSPs are:
1. TMS320C3x
2. TMS320C67x
3. ADSP-21xxx
4. What are the factors that influence selection of DSPs?
1. Architectural features
2. Execution speed
3. Type of arithmetic
4. Word length
36
5. What are the applications of PDSPs?
The applications of PDSPs are:
1. Digital cell phones
2. Automated inspection
3. Voicemail
4. Motor control
5. Video conferencing
6. Noise cancellation
7. Medical imaging
8. Speech synthesis
9. Satellite communication, etc.
6. What are the advantages and disadvantages of VLIW architecture?
The advantages of VLIW architecture are:
1. Increased performance
2. Better compiler targets
3. Potentially scalable
4. Potentially easier to program
5. Can add more execution units, allow more instruction to be packed into the VLIW
instruction.
The disadvantages of VLIW architecture are:
1. New kind of programmer/compiler complexity
2. Program must keep track of instruction scheduling
3. Increased memory use
4. High power consumption
5. Misleading MIPS ratings
7. What is meant by pipelining?
Pipelining a processor means breaking down its instruction into a series of discrete pipeline
stages which can be completed in sequence by specialized hardware.
8. What is pipeline depth?
The number of pipeline stages is referred to as the pipeline depth.
9. What is the pipeline depth of TMS320C50, TM 320C54x?
TMS320C50 – 4
TM 320C54x – 6
10. What are the different stages in pipelining?
The different stages in pipelining are:
1. the Fetch phase
2. the Decode phase
3. Memory read phase
4. the Execute phase
37
11. Write the different buses of TM 320C5x and their functions.
The „C5x architecture has four buses. They are:
1. Program bus (PB)
2. Program address bus (PAB)
3. Data read bus (DB)
4. Data read address bus (DAB)
The program bus carriers the instruction code and immediate operands from program
memory to the CPU.
The program address bus provides address to program memory space for both read and write.
The data read bus interconnects various elements of the CPU to data memory spaces.
The data read address bus provides the address to access the data memory spaces.
12. List out the various registers used with ARAU.
1. Eight auxiliary registers (AR0-AR7)
2. Auxiliary register pointer (ARP)
13. What are the elements that the control processing unit of „C5X consist of?
1. Central arithmetic logic unit (CALU)
2. Parallel logic unit (PLU)
3. Auxiliary register arithmetic unit (ARAU)
4. Memory mapped registers
5. Program controller
14. What is the function of parallel logic unit?
The function of the parallel logic unit is to execute logic operations on data without affecting
the contents of accumulator.
15. List out the on chip peripherals in „C5x.
The on-chip peripherals interfaces connected to the „C5x CPU include
1. Clock generator
2. Hardware timer
3. Software programmable wait state generators
4. General purpose I/O pins
5. Parallel I/O ports
6. Serial port interface
7. Buffered serial port
8. Time-divisions multiplexed (TDM) serial port
9. Host port interface
10. User unmaskable interrupts
38
16. What are the arithmetic instructions of „C5x?
The arithmetic instructions of „C5x are:
1. ADD
2. ADDB
3. ADDC
4. SUB
5. SUBB
6. MPY
7. MPYU
17. What are the logical instructions of „C5x?
The logical instructions of „C5x are:
1.
2.
3.
4.
5.
6.
AND
ANDB
OR
ORB
XOR
XORB
18. What are the shift instructions?
The shift instructions are:
1. ROR
2. ROL
3. ROLB
4. RORB
5. BSAR
19. What are load/store instructions?
The load/store instructions are:
1. LACB
2. LACC
3. LACL
4. LAMM
5. LAR
6. SACB
7. SACH
8. SACL
9. SAR
39
20. What are the different types of arithmetic in digital systems?
There are three types of arithmetic used in digital systems. They are:
1. Fixed point arithmetic
2. Floating point arithmetic
3. Block Floating arithmetic
21. What is meant by a fixed-point number?
In fixed-point arithmetic the positions of the binary point is fixed. The bits to the right
represent the fractional part of the number and those to the left represent the integer part. For
example, the binary number 01.1100 has the value 1.75 in decimal.
22. What is meant by block floating point representation? What are its advantages?
In block floating point arithmetic the set of signals to be handled is divided into blocks. Each
block has the same value for the exponent. The arithmetic operations within the block uses fixed
point arithmetic and only one exponent per block is stored, thus saving memory. This
representation of numbers is most suitable in certain FFT flow graphs and in digital audio
applications.
23. What are the advantages of floating point arithmetic?
The advantages of floating point arithmetic are:
1. Larger dynamic range
2. Overflow in floating point representation is unlikely
24. Compare fixed point arithmetic with floating point arithmetic.
Fixed Point Arithmetic
Fast Operation
Relatively economical
Small dynamic range
Round off error occur only for additions
Overflow occur in addition
Used in small computers
Floating Point Arithmetic
Slow Operation
More expensive because of costlier
hardware
Increased dynamic range
Round off errors can occur with both
additions and multiplication
Overflow does not arise
Used in larger, general purpose computers
25. What are the three quantization errors due to finite word length registers in digital filters?
The three quantization errors due to finite word length registers in digital filters are:
1. Input quantization error
2. Coefficient quantization error
3. Product quantization error
40
26. How are the multiplication and addition carried out in floating point arithmetic?
In floating point arithmetic, multiplications are carried out as follows:
Let f1=M1 x 2c1 and f2 = M2 x 2c2, then f3=f1x f2 = (M1xM2)2(c1+c2)
That is, mantissas are multiplied using fixed point arithmetic and the exponents are added.
The sum of two floating point numbers is carried out by shifting the bits of the mantissa of
the smaller number to the right until the exponents of the two numbers are equal and then by
adding the mantissas.
27. Write short notes on coefficient inaccuracy.
(OR)
What is coefficient quantization error? What is it‟s effect?
The filter coefficients are computed to infinite precision in theory. But, in digital computation
the filter coefficients are represented in binary and are stored in registers.
If a b bit register is used, the filter coefficients must be rounded or truncated to b bits, which
produces an error.
Due to quantization of coefficients, the frequency response of the filter may differ
appreciably from the desired response and some times the filter may actually fail to meet the
desired response and the desired specifications. If the poles of desired filter are close to the unit
circle, then those of the filter with quantized coefficients may lie just outside the unit circle,
leading to unstability
28. What is product quantization error?
Product quantization errors arise at the output of a multiplier. Multiplication of a b bit
data with a b bit coefficient results in a product having 2b bits. Since a b bit register is used, the
multiplier output must be rounded or truncated to b bits, which produces an error. This error is
known as product quantization error.
29. What is meant by input quantization error?
In DSP, the continuous time input signals are converted into digital using a b bit ADC. The
representation of continuous signal amplitude by a fixed digit produces an error is known as
input quantization error.
30. What is meant by truncation?
Truncation is process of reducing the size of binary number by discarding all bits less
significant than the least significant bit that is retained. (In the truncation of a binary number to b
bits all the less significant bits beyond bth bit are discarded)
31. What is meant by rounding?
Round is the process of reducing the size of a binary number to finite word size of b bits such
that the rounded b-bit number is closest to the original un-quantized number.
41
32. What is Quantization step size?
In digital systems, the numbers are represented in binary. With b-bit binary we can generate
b
2 different binary codes. Any range of analog value to be represented in binary should be
divided into 2b levels with equal increment. The 2b levels are called
Quantization levels and
the increment in each level is called Quantization step size. If R is the range of analog signal
then,
Quantization step size, q = R/2b.
33. What is called limit cycle?
In recursive systems when the input is zero or some nonzero constant value, the nonlinearities
due to finite precision arithmetic operations may cause periodic oscillations in the output. These
oscillations are called limit cycle.
34. What is zero input limit cycle?
In recursive system, the product Quantization may create periodic oscillations in the output.
These oscillations are called limit cycles. If the system output enters a limit cycle, it will continue
to remain in limit cycle even when the input is made zero. Hence these limit cycles are also
called zero input limit cycles.
35. What is meant by dead band?
In a limit cycle the amplitudes of the output are confined to a range of values, which is called
dead band of the filter.
36. How can the system output be brought out of limit cycle?
The system output can be brought out of limit cycle by applying an input of large magnitude,
which is sufficient to drive the system out of limit cycle.
37. What is meant by overflow limit cycle?
In fixed point addition the overflow occurs when the sum exceeds the finite word length of
the register used to store the sum. The overflow in addition may lead to oscillations in the output
which is called overflow limit cycle.
38. How can overflow limit cycle be eliminated?
The overflow limit cycles can be eliminated either by using saturation arithmetic or by
scaling the input signal to the adder.
39. What is saturation arithmetic?
In saturation arithmetic when the result of an arithmetic operations exceeds the dynamic range of
number system, then the result is set to maximum or minimum possible value. If the upper limit
is exceeded then the result is set to maximum possible value. If the lower limit is exceeded then
the result is set to minimum possible value.
42
CS2211 OBJECT ORIENTED PROGRAMMING
UNIT I
1. List out the four Object Oriented Programming concepts.
(D-09)
The Object Oriented Programming concept includes:
1. Objects
2. Classes
3. Data abstraction and encapsulation
4. Inheritance
2. What is abstract class?
(D-09)
An abstract class is one that is not used to create objects. An abstract class is designed only to
act as a base class(to be inherited by other class). It is a design concept in program development
and provides a base upon which other classes may be built.
3. Differentiate a class from a structure.
Class
1. In class, the data members are
private by default.
2. Scope resolution operator (::)
is used for defining member
functions.
3. New and delete operators are
used for allocation and
release of memory.
4. What is meant by data hiding?
(M-10)
Structure
1. In structure, the data
members are public by
default.
2. No such operators are used.
3. Malloc and Free are used
for allocation and release of
memory.
(D-10)
The insulation of the data from direct access by the program is called data hiding or
information hiding. The data is not accessible to the outside world, and only those functions
which are wrapped in the class can access it.
5. Define − Abstraction and Encapsulation
(M-11)
Data abstraction:
Data abstraction refers to the act of representing essential features without including the
background details or explanations.
Data encapsulation:
The wrapping up of data and functions into a single unit (called class) is known as
encapsulation. The data is not accessible to the outside world.
43
6. What is polymorphism?
Polymorphism is another OOP concept. Polymorphism, Greek term, means the ability to take
more than one form. An operation may exhibit different behaviors in different instances. The
behavior depends upon the types of data used in the operation.
7. Differentiate local variable from a data member.
Local variable
1. Local variable is a variable that belongs to
the current scope.
2. The variables declared inside the function
are called local variables.
3. Accessibility is not public. It can be
accessed only inside the function.
(D-11)
Data member
1. A member variable is a variable that
belongs to an object.
2. The member belonging to the class are
member variables.
3. Variables outside the class, cannot be
accessed.
8. What is static data member?
The data member declared with the keyword “static” is called static data member.
Static variables are normally used to maintain values common to the entire class.
It has the following features:
1. It is initialized to zero when the first object is created. No other initialization is
permitted.
2. Only one copy of that member is created for the entire class and is shared by all the
objects.
3. It is visible only within the class.
9. What is static member function?
The member function declared with the keyword static is called static member function.
A static member function is the one which has the following properties:
1. A static member function can access only other static members declared in the same
class.
2. It can be called using the class name instead of objects as follows,
3. class_name :: function_name;
10. Define − Pointers to Member
The address of a member of a class is taken and assigned to a pointer. This is called as
pointers to member. The address of a member can be obtained by applying the operator and to a
“fully qualified” class member name. A class member pointer can be declared using the operator ::*
with the class name.
11. What is the copy constructor?
(D-09)
The copy constructor takes a reference to an object of the same class as itself as an
argument. A copy constructor is used to declare and initialize an object from another object.
integer (integer & i) ;
integer I 2 ( I 1 ) ; or integer I 2 = I 1 ;
The process of initializing through a copy constructor is known as copy initialization.
44
12. Let out any four special properties of constructor.
(D-10)
The special properties of constructor are:
i.A constructor is a special member function whose task is to initialize the objects of its class.
ii.It is special because its name is same as the class name.
iii.The constructor is invoked whenever an object of its associated class is created.
iv.It is called constructor because it constructs the values of data members of the class.
13. What is an explicit constructor?
In explicit constructor, constructor is defined explicitly by using the keyword “explicit” is
known as an explicit constructor. The explicit constructor will be executed when we call the
constructor explicitly.
Eg:
explicit brother (string name)
{
Body of the explicit constructor
}
brother is a class name.
14. Define − Default Constructor
The constructor with no arguments is called default constructor .
Eg:
Class integer
{
int m,n;
Public:
Integer( );
…….
};
integer::integer( )//default constructor
{
m=0;n=0;
}
the statement integer a; invokes the default constructor.
15. What is an inline function?
An inline function is a function that is expanded in line when it is invoked. That compiler
replaces the function call with the corresponding function code. The inline functions are defined as
Inline function-header
{
function body
}
45
UNIT II
1. What are the operators that cannot be overloaded?
The operators that cannot be overloaded are:
1. Class member access operator (. , .*)
2. Scope resolution operator (::)
3. Size operator ( sizeof )
4. Conditional operator (?:)
(D-09)
2. What is the need for overloading the assignment operator?
(M-11)
The assignment operator is used to assign a value on the right hand side to a
variable on
the left side & if it is of a different data type then we have to perform data conversion or
type Conversion.
3. What are the different types of type conversions?
The Different types of type conversion are,
1. Conversion from basic type to class type.(data type to object)
2. Conversion from class type to basic type.(object type to data type)
3. Conversion from one class type to another class type.
4. Conversion from one data type to another data type.
4. What is operator overloading?
C++ has the ability to provide the operators with a special meaning for a data type.
This mechanism of giving such special meanings to an operator is known as Operator
overloading. Operator overloading provides a flexible option for the creation of new
definitions for C++ operators.
5. What is function prototype?
Function prototyping is not necessary in java, but what function prototyping means
is simply establishing the "signature" of the "function" (functions are referred to as 'methods'
in Java) before the method is defined. The signature includes the visibility of the function
(public, private, protected), the return type, the method name, the list of arguments the
method takes, and any throws, extends, or implements clauses.
6. What is function overloading? Write an example.
#include <iostream>
using namespace std;
/* Function arguments are of different data type */
long add(long, long);
float add(float, float);
46
int main()
{
long a, b, x;
float c, d, y;
cout << "Enter two integers\n";
cin >> a >> b;
x = add(a, b);
cout << "Sum of integers: " << x << endl;
cout << "Enter two floating point numbers\n";
cin >> c >> d;
y = add(c, d);
cout << "Sum of floats: " << y << endl;
return 0;
}
long add(long x, long y)
{
long sum;
sum = x + y;
return sum;
}
float add(float x, float y)
{
float sum;
sum = x + y;
return sum;
}
7. What is meant by dynamic casting?
(M-11)
Dynamic casts are only available in C++ and only make sense when applied to members
of a class hierarchy ("polymorphic types"). Dynamic casts can be used to safely cast a super
class pointer (or reference) into a pointer (or reference) to a subclass in a class hierarchy. If
the cast is invalid because the the real type of the object pointed to is not the type of the
desired subclass, the dynamic will fail gracefully.
8. What are templates?
(D-10)
Template is one of the features added to c++ recently.it is a new concept which enables
us defined generic class and functions and thus provides support for generic programming a
template can be used to create a family of classes or functions.
A template can be considered as a kind of macro. when an object of specific type is
defined for actual use, the template definition for that class is substituted with the required
data type.
47
9. What is a function template?
(M-11)
Function templates are special functions that can operate with generic types. This allows
us to create a function template whose functionality can be adapted to more than one type or
class without repeating the entire code for each type.
`The format for declaring function templates with type parameters
template <class identifier> function_declaration;
template <typename identifier> function_declaration;
10. What are the visibility modes in inheritance?
There are three visibilities of class members. They are
1. Public visibility
(D-09)
2. Private visibility
3. Protected visibility
Public : The class members are visible to the base class, derived classes and outside the
class through the objects.
Private : The class members are visible only to the base class itself but not to the derived
class.
Protected: The class members are visible to the base and derived classes.
11. What are access specifiers?
There are 3 access specifiers for a class/struct/Union in C++. These access specifiers
define how the members of the class can be accessed. Of course, any member of a class is
accessible within that class(Inside any member function of that same class). Moving ahead to
type of access specifiers, they are:
1. Public - The members declared as Public are accessible from outside the Class
through an object of the class.
2. Protected - The members declared as Protected are accessible from outside the class
BUT only in a class derived from it.
3. Private - These members are only accessible from within the class. No outside
Access is allowed.
12. What is meant by inheritance?
Inheritance is the process by which objects of one class acquire the properties
of another class. It supports the concept of hierarchical classification. It provides the idea of
reusability. Additional features can be added to an existing class without modifying it by
deriving a new class from it.
The syntax of deriving a new class from an already existing class is given by,
class derived-class : visibility-mode base-class
{
body of derived class
}
48
13. Write the rules for virtual function.
(M-10)
The rules for virtual function are:
1. Virtual functions must be member of some class.
2. They cannot be static members and they are accessed by using object pointers
Virtual f unction in a base class must be defined.
3. Prototypes of base class version of a virtual function and all the derived class
versions must be identical.
4. If a virtual function is defined in the base class, it need not be redefined in the
derived class.
14. What is a pure virtual function? Write the syntax.
(M-11)
1. A pure virtual function is a virtual function whose declaration ends in =0:
2. A pure virtual function makes the class it is defined for abstract. Abstract classes cannot
be instantiated. Derived classes need to override/implement all inherited pure virtual
functions. If they do not, they too will become abstract.
UNIT III
1. What happens when a raised exception is not caught by catch block?
(M-10)
When a raised exception not caught by catch block, if the match is not found, the catch
block calls a built in function terminate(), which terminate the program execution by calling a
built in function abort().
2. What is an exception?
(M-11)
Exceptions are the one which occur during the program execution, due to some fault in
the input data.
Exceptions are classified into:
i) Synchronous exception
ii) Asynchronous exception
3.
Differentiate realloc() from free().
Realloc()
1.
Realloc() is used to reallocate the
memory for variable.
2.
It is used to resize the memory held by
the pointer to the number of bytes specificed.
If the new size is larger than current size, new
memory is allocated. If it is less, the remaining
(additional) bytes are released to general
OS/application consumption.
3.
realloc(ptest,sizeof(test)*2);
(M-10)
Free()
1.
Free() is used to free the
allocated memory of a variable.
2.
It releases the memory of the
pointer passed as parameter, to the
OS/application consumption. Using the
pointer after free() will result in
undefinded results.
3.
free(p);
49
4. What are the different mechanisms of traditional error handling? What is the problem
with them?
Traditional error handling is done in 3 different ways. They are:
1. Returning error number: When a function is written, arguments are accepted and
processing start. If something in the argument is wrong or something goes wrong
while processing, The function returns an error code.
2. Global flag manipulation: There is an error variable which is globally available to all
c library functions. They can set the value of errno to indicate error. After calling the
library function ,we can check the value of errno can be checked to find out actual
error.
3. Abnormal termination of program: Whenever something goes out of bound exit() or
abort() is called.
5.
What is unexpected() function? Write an example to explain the need of it.
When a function with an exception specification throws an exception that is not listed in
its exception specification, the C++ run time does the following:
1. The unexpected() function is called.
2. The unexpected() function calls the function pointed to by un expected-handler. By
default, unexpected-handler points to the function terminate().
The default value of unexpected-handler can be replaced with the function setunexpected().
6.
List out the features included in C++ for formatting the output.
(D-10)
C Formatted I/O you have learned the formatted I/O in C by calling various standard
functions. Module will discuss how this formatted I/O implemented in C++ by using
member functions and stream manipulators.
If you have completed this C++ Data Encapsulation until C++ Polymorphism, you should
be familiar with class object. In C++ we will deal a lot with classes. It is readily available
for us to use.
Discuss the formatted I/O here, for file I/O and some of the member functions mentioned
in this Module, will be presented in another module. The discussion here will be straight to
the point because some of the terms used in this Module have been discussed extensively in C
Formatted I/O.
The header files used for formatted I/O in C++ are:
1. <iostream>
2. <iomanip>
3. <fstream>
4. <strstream>
5. <stdiostrem>
50
7. Write a short note on the meaning of the flag ios::out.
ios::out - Open for output operations
For ifstream and ofstream classes, ios::in and ios::out are automatically and respectively
assumed, even if a mode that does not include them is passed as second argument to the open
member function (the flags are combined).
For fstream, the default value is only applied, if the function is called without specifying
any value for the mode parameter. If the function is called with any value in that parameter,
the default mode is overridden and not combined.
File streams opened in binary mode perform input and output operations independently of
any format considerations. Non-binary files are known as text files, and some translations
may occur due to formatting of some special characters (like newline and carriage return
characters).
Since, the first task that is performed on a file stream is generally to open a file, these
three classes include a constructor that automatically calls the open member function and has
the exact same parameters as this member. Therefore, the previous myfile object is declared
and is conducted.
(eg): ofstream myfile ("example.bin", ios::out | ios::app | ios::binary);
8.
What is a C++ manipulator?
(M-10)
1. Manipulators are functions specifically designed to be used in conjunction with
the
insertion (<<) and extraction (>>) operators on stream objects, for example:
cout << boolalpha;
2. They are still regular functions and can also be called as any other function using a stream
object as argument, for example: boolalpha (cout);
3. Manipulators are used to change formatting parameters on streams and to insert or extract
certain special characters.
9.
What are streams? How are they useful?
The stream is the central concept of the iostream classes. You can think of
a stream object as a smart file that acts as a source and destination for bytes.
While useful for files, can also be used with cin, where the user types a key combination
representing the "end-of-file" character
1. On Unix and Mac systems, type ctrl-d to enter the end-of-file character
2. On Windows, type ctrl-z to enter the end-of-file character
count.cpp -- An example that reads in a file consisting of any number of integers, using
eof() to decide when to stop, then computes sum and average.
10. What is manipulator? Distinguish between manipulator and ios function?
Manipulators are the most common way to control output formating. #include <iomanip>
I/O manipulators that take parameters are in the <iomanip> include file. Default Floatingpoint Format.
51
11.
What is file mode?
(D-10)
File Mode - Reading and Writing Files:
File must be specified is to be opened. This means whether to create it from new,
overwrite it and whether it's text or binary, read or write and if you want to append to it. This
is done using one or more file mode specifiers which are single letters "r", "b", "w", "a" and +
(in combination with the other letters). "r" - Opens the file for reading. This fails, if the file
does not exist or cannot be found. "w" - Opens the file as an empty file for writing. If the file
exists, its contents are destroyed. "a" - Opens the file for writing at the end of the file
(appending) without removing the EOF marker before writing new data to the file; this
creates the file first, if it doesn't exist.
12.
What is namespace?
(M-11)
A namespace is designed to overcome and is used as additional information to
differentiate similar functions, classes, variables, etc., with the same name available in
different libraries. Using namespace, the context is defined where in which names are
defined. In essence, a namespace defines a scope.
Defining a Namespace:
A namespace definition begins with the keyword namespace followed by the namespace
name that follows:
namespace namespace_name {
// code declarations
}
To call the namespace-enabled version of either function or variable, prepend the
namespace name as follows:
name::code; // code could be variable or function.
13.
What is name conflict problem? How can it be solved using namespaces?
Namespaces are a relatively new C++ feature are starting to appear in C++ compilers.
Some aspects of namespaces in subsequent newsletters.
What problem do namespaces solve? Well, suppose that you buy two different generalpurpose class libraries from two different vendors, and each library has some features that
you'd like to use. You include the headers for each class library:
#include "vendor1.h"
#include "vendor2.h"
and then it turns out that the headers have this in them:
// vendor1.h
... various stuff ...
class String {
...
};
// vendor2.h
... various stuff ...
52
class String {
};
14.
What are the three standard template library adapters?
(D-11)
The STL adapters are stack, queue and priority_queue. Adapters are not first-class
containers; They do not provide the actual data-structure implementation in which elements
can be stored, because adapters do not support iterators.
15.
What are the file stream classes supported by standard template library.
The file stream classes supported to STL are:
1. ostream, istream, iostream base classes
2. The istringstream and ostringstream string streams
3. Stream iterators
UNIT-IV
1. What are the features of java?
The features of Java are:
1. Simple, Small and familiar
2. Object oriented
3. Distributed
4. Robust
5. Secure
6. Platform independent
7. Portable
8. Compiled and Interpreted
9. High performance
10. Multithreading and interactive
11. Dynamic and extensible
(J-07)
2. What is the interpreter for byte code?
(J-07)
Byte-code compiled system, source code is translated to an intermediate representation
known as bytecode. Bytecode is not the machine code for any particular computer, and may be
portable among computer architectures. The bytecode may then be interpreted by, or run on, a
virtual machine. The JIT compiler reads the bytecodes in many sections (or in full rarely) and
compiles them interactively into machine language. So,the program can run faster.
3. Define – Bytecode
(J- 10)
Bytecode is the intermediate representation of Java source code which is produced by the
Java compiler by compiling that source code. This byte code is an machine independent code. It
is not an completely a compiled code but it is an intermediate code somewhere in the middle
which is later interpreted and executed by JVM. Bytecode is a machine code for JVM. But, the
53
machine code is platform specific, whereas bytecode is platform independent that is the main
difference between them.
4. Define – JVM
(D-09)
A Java Virtual Machine (JVM), an implementation of the Java Virtual Machine specification,
interprets compiled Java binary code (called bytecode) for a computer's processor (or "hardware
platform"), so that it can perform a Java program's instructions. Java was designed to allow
application programs to be built that could be run on any platform without having to be rewritten
or recompiled by the programmer for each separate platform. A Java virtual machine makes this
possible because it is aware of the specific instruction lengths and other particularities of the
platform.
5. “Java is platform independent language”. Why?
(J-11)
One of the major features of java includes that why java is called platform independent
language.
Javac – compiler that converts source code to byte code.
JVM- interpreter that converts byte code to machine language code.
6. Write a simple java program.
Example 1: Display message on computer screen.
class First {
public static void main(String[] arguments) {
System.out.println("Let's do something using Java technology.");
}
}
7. Write the syntax to declare strings in java.
Declaring a string
Syntax:
String nameOfString = "stringValue";
String nameOfString = new String("stringValue");
Example:
String aString = "This is a string";
String aString = new String("This is a string");
(D-07)
54
8. What are the types of comments in java doc?
There are two kinds of Javadoc comments: class-level comments, and member-level
comments. Class-level comments provide the description of the classes, and member-level
comments describe the purposes of the members. Both types of comments start with /** and end
with */. For example, this is a Javadoc comment:
/** This is a Javadoc comment */
9. List out the some of the java doc tags.
To add a class hyperlink, we have to add a tag in the comment. The format of class hyperlink
tag is:
{@link <FullClassName> [Display Text]}
To add a hyper link to a method of the same class, we use the @link tag like this:
{@link #<MethodSignature> [Display Text]}
To add a hyper link to a method in a different class, we use the @link tag like this:
{@link <ClassName>#<MethodSignature> [Dsplay Option]}
10. Write the syntax of an array in java.
Declaring Array Variables:
dataType[] arrayRefVar; // preferred way.
or
dataType arrayRefVar[]; // works but not preferred way.
Note: The style dataType[] arrayRefVar is preferred. The style dataType arrayRefVar[]
comes from the C/C++ language and is adopted in Java to accommodate C/C++ programmers.
Example:
double[] myList;
// preferred way.
or
double myList[];
// works but not preferred way.
11. What is a documentation comment?
Documenting the code is crucial to help others understand it, and even to remind oneself how
your own older programs work. Unfortunately, it is easy for most external documentation to
become out of date as a program changes. For this reason, it is useful to write documentation as
comments in the code itself, where they can be easily updated with other changes.
12. Justify whether java is case sensitive or not.
Java is multi-platform-> Platform Independent language, so it is used widely in very big
softwares or games where multiple variables are needed. To differentiate among that huge no of
variables, Java is case sensitive.
If these tips are followed while coding in Java, one should avoid the most common case
sensitive errors:
* Java keywords are always written in lowercase. One can find the full list of keywords in the
reserved words list.
55
13. What is a pointer? Does java support pointers?
Pointer is a user defined data type which creates special types of variables which can hold the
address of primitive data type like char, int, float, double or user defined data type like function,
pointer etc. or derived data type like array, structure, union, enum.
1. Java do not use pointers because using pointer the memory area can be directly accessed,
which is a security issue. In this way, Java has fixed a much debated issue with C/C++
programming.
2. The JVM memory management is much more efficient and hence, it make sense that let
JVM manage the memory related things.
14. What are local variables?
1. Local variables are declared in methods, constructors, or blocks.
2. Local variables are created when the method, constructor or block is entered and the variable
will be destroyed once it exits the method, constructor or block.
3. Access modifiers cannot be used for local variables.
UNIT-V
1. Write a simple program for interface.
Declaring Interfaces:
/* File name : NameOfInterface.java */
import java.lang.*;
//Any number of import statements
public interface NameOfInterface
{
//Any number of final, static fields
//Any number of abstract method declarations\
(J-07)
2. What is the use of runnable interface?
(D-11)
The runnable interface should be implemented by any class whose instances are intended to
be executed by a thread. The class must define a method of no arguments called run.
3. Define – Interface
An interface in Java is similar to a class, but the body of an interface can include only
abstract methods and final fields (constants). A class implements an interface by providing code
for each method declared by the interface.
56
4. List out some of the java I/O classes.
(J-12)
5. Define – Thread
(J-07)
A thread is a single sequential flow of control within a program. A thread is similar to a real
process in that a thread and a running program are both a single sequential flow of control.
However, a thread is considered lightweight because it runs within the context of a full-blown
program; It takes advantage of the resources allocated for that program and the program's
environment.
6. Define – Inner Classes
Local classes are classes that are defined in a block, which is a group of zero or more
statements between balanced braces. Local classes are typically found and defined in the body of
a method.
Program of inner class:
class OuterClass
{
class InnerClass { }
}
7. Define – Local Inner Classes and Anonymous Inner Class
A class that is created inside a method is known as local inner class. If one has to invoke the
methods of local inner class, one must instantiate this class inside the method.
Anonymous Classes:
Anonymous classes enable us to make our code more concise. They enable you to declare
and instantiate a class at the same time. They are like local classes except that they do not have a
name. Use them if you need to use a local class only once.
57
8. Write a program for try and catch exception.
try {
// statements that might cause exceptions
// possibly including function calls
} catch ( exception-1 id-1 ) {
// statements to handle this exception
} catch ( exception-2 id-2 ) {
// statements to handle this exception
. . .
} finally {
// statements to execute every time this try block executes
}
(J-08)
9. What is an uncaught exception?
(J-09)
Uncaught Exception Handler can be defined at three levels. From highest to lowest they are:
1. Thread. Set Default Uncaught Exception Handler
2. Thread Group. Uncaught Exception
3. Thread. Set Uncaught Exception Handler
10. What are the different states of a thread's lifecycle?
A thread can be in one of the five states in the thread. According to sun, there is only 4 states
new, runnable, non-runnable and terminated. There is no running state. But for better
understanding the threads, we are explaining it in the 5 states. The life cycle of the thread is
controlled by JVM. The thread states are as follows:
1. New
2. Runnable
3. Running
4. Non-Runnable (Blocked)
5. Terminated
11. What is the use of synchronized keyword?
Synchronized keyword is an essential tool in concurrent programming in Java. Its overall
purpose is to only allow one thread at a time into a particular section of code, thus allowing us to
protect, For example, variables or data from being corrupted by simultaneous modifications from
different threads. Synchronized in Java to produce correctly functioning multithreaded programs.
12. What are the constructors present in the thread class?
Several constructors are available for creating new thread instances.
1. Thread()
2. Thread(String)
3. Thread(Runnable)
58
EE2301 POWER ELECTRONICS
UNIT I
POWER SEMICONDUCTOR DEVICES
Power Diode
1. What is fast recovery diode?
(N/D 04)
The fast recovery diode has low recovery time, normally less than 5 microsec. They
are used in choppers, SMPS, induction heating
2. What is reverse recovery time?
(A/M 06)
The reverse recovery time is defined as the time between the instant, forward diode
current becomes zero and 25 % of the maximum reverse current.
Power BJT
3. What are the advantages of GTO over BJT?
1.
2.
3.
4.
(N/D 04)
Higher voltage blocking capability
It is majority carrier Devices
High ratio of peak surge current to average current
Operates as a switch always
4. What are the advantages of MOSFET over BJT?
MOSFET
Power MOSFET has lower switching
losses
(A/M 08)
BJT
BJT has higher switching losses
It has low conduction losses
It has more conduction losses
It is current controlled device
It is a voltage controlled device
It is a bipolar device
It is a unipolar device
5. Why is a BJT called a current controlled device?
Power BJT is a current controlled device, because the output (collector) current can be
controlled by base current.
59
6. Draw the V–I characteristics of SCR and mark the holding current and the latching
current on the characteristics.
(N/D 04)
7. Define – Holding Current and Latching Current of SCR
(A/M 08)
The holding current is defined as the minimum value of anode current below which it
must fall to for turning off the thyristor.
The latching current is defined as the minimum value of anode current which it must
attain during turn on process to maintain conduction when gate signal is removed.
8. Write any two advantages of GTO over SCR.
1. GTO has faster switching speed
2. It has more di/dt rating at turn on
9. What are the factors that influence the turn-off time of a thyristor?
Some factors that influence the turn off time of a SCR are,
1. Recovery process
2. Recombination process
(A/M 04)
(N/D 06)
10. What is meant by the turn off time of a converter grade SCR? Mention its value.
SCR with slow turn off time is called converter grade SCR. The turn off time for
converter grade SCR is 50-100 ms.
11. What is meant by the turn off time of an inverter grade SCR?
SCR with fast turn off time is called inverter grade SCR. The turn off time for inverter
grade SCR is 3-50 ms.
12. What are the different methods of turning on of a thyristor?
The following methods are used to turn on the thyristor:
1. Forward voltage triggering
2. Gate triggering
3. dv/dt triggering
4. Temperature triggering
5. Light triggering
60
Power MOSFET
13. Why are MOSFETs not preferred for low frequency applications?
(M/J 06)
MOSFETs have high switching losses so it can‟t use low frequency application.
14. Define – Pinch Off Voltage of MOSFET
(N/D 07)
If the gate source voltage VGS is made negative enough, the channel will be
completely depleted, offering a high value of RDS and there will be no current flow from the
drain to source, IDS=0. The value of VGS is called pinch off voltage.
Power IGBT
15. Why are IGBTs becoming popular in their applications in controlled converters?
IGBT is very popular nowadays because it has,
1. Lower gate requirements
2. Lower switching losses
3. Smaller snubber circuit requirements
TRIAC
16. What are the advantages of TRIAC?
The advantages of TRIACs are,
1. TRIACs can be triggered with positive or negative polarity voltage.
2. A TRIAC needs a single fuse for protection, which also simplifies the construction
3. A TRIAC needs a single heat sink of slightly larger size, whereas anti-parallel
thyristor pair needs two heat sinks.
4. In some DC applications, SCR is required to be connected to be connected with a
parallel diode to protect against reverse voltage, where a TRIAC used may work
without diode as safe breakdown in either direction is possible.
UNIT II
PHASE CONTROLLED CONVERTERS
Two pulse converter
1. What is a two pulse converter?
(N/D 11)
Two pulse converter is defined as two triggering pulses or two sets of triggering
pulses are to be generated during every cycle of the supply to trigger the various SCRs.
2. What is meant by full converter?
(N/D 04)
A fully controlled converter or full converter uses thyristor only and there is a winder
control over the level of DC output voltage. It is also known as two quadrant converter.
3. Define – Firing Angle α
(A/M 04)
The firing angle is defined as the angle between the zero crossing of the input voltage
and the instant the thyristor is fired.
61
4. List out the merits of phase control of SCR.
Merits of phase controlled SCR are
1. Controlled output voltage
2. Less harmonics
(A/M 04)
5. Why is the power factor of a semiconverter better than that of a full converter?
(A/M 08)
When supply is given to load, the semiconverter receives less reactive power due to
freewheeling action when compared with full converter. Therefore, the power factor is better
in semiconverter.
6. What are the conditions under which a single phase fully controlled converter
operates as an inverter.
(N/D 07)
In line commutated converter, when the firing angle is 90 º to 180 º it acts as a
inverter.
7. List out the applications of phase controlled converters.
(N/D 06)
The applications of controlled rectifiers are,
1. Steel rolling mills, printing press, textile mills and paper mills employing DC motor
drives.
2. DC traction
3. Electro chemical and electro-metallurgical process
4. Portable hand tool drives
5. Magnet power supplies
6. HVDC transmission system
8. What is a half controlled rectifier?
A half controlled rectifier or semiconverter uses a mixture of diodes and thyristors
and there is a limited control over the level of DC output voltage. It is also known as onequadrant converter. Here, the output current and output voltage is always positive.
9. What is the function of a free-wheeling diode in controlled rectifier circuits?
(N/D 06)
1. It serves two processes.
2. It prevents the output voltage from becoming negative.
3. The load current is transferred from the main thyristors to the freewheeling diode,
thereby allowing all of its thyristors to regain their blocking states.
10. What is meant by commutation?
It is the process of changing the direction of current flow in a particular path of the
circuit. This process is used in thyristors for turning it off.
11. What is meant by forced commutation?
In this commutation, the current flowing through the thyristor is forced to become
zero by external circuitry.
12. What is meant by natural commutation?
Here the current flowing through the thyristor goes through a natural zero
the thyristor to turn off.
and enable
62
13. What are the different types of commutations?
The different types of commutations are
1. Natural commutation
2. Forced commutation
14. What is inversion mode in a single phase fully controlled converter?
In a single phase full converter, α>90, the voltage at the DC terminals is negative.
Therefore, power flows from load to source and the converter operates as a line commutated
inverter as source voltage VS is negative and source current is positive. This is known as
inversion mode or synchronous inversion.
15. Define – Commutation Angle or Overlap Angle
The commutation period when outgoing and incoming thyristors are conducting is
known as overlap period. The angular period, when both devices share conduction is known as
the commutation angle or overlap angle.
Performance characteristics
16. Define – Displacement Factor and Total Harmonic Distortion
(M/J 07)
The input displacement factor is defined as the cosine of the input displacement angle.
The harmonic factor of the input current is defined as the ratio of the total harmonic current
to the fundamental component.
IH = ( I2rms – I21) / I1
Effect of source inductance
17. What are the effects of source impedance in a controlled rectifier?
The effects of source impedance in the controlled rectifiers are,
1. The average output voltage is reduced
2. Reduced displacement factor
3. Output current waveform is changed
(N/D 06)
UNIT- III
DC TO DC CONVERTERS
Chopper
1. Define – Duty Cycle of DC Chopper
(N/D 06, 07)
Duty cycle means the ratio of the on time of the chopper to the total time period of the
chopper. It is denoted by α.
2. What is a DC Chopper?
(N/D 07)
A DC chopper is a high speed static switch used to obtain variable DC voltage from a
constant DC voltage.
3. What are the applications of DC Choppers?
The applications of DC choppers are,
1. Battery operated vehicles
2. Traction motor control in electric traction
63
3.
4.
5.
6.
Trolley cars
Marine hoists
Mine haulers
Electric braking
Time ratio and current limit control
4. What are the control strategies used in DC choppers?
The types of control strategies in DC choppers are,
1. Time Ratio Control (TRC)
2. Current Limit Control method (CLC)
(N/D 03)
5. What are the disadvantages of FM scheme used in Chopper?
1. Filter design is very difficult
2. FM scheme produces interference
(N/D 04)
6. What are the methods of controlling the output voltage of a chopper?
The methods of controlling the output voltage of a chopper are
1. Time Ratio Control (TRC)
2. Current Limit Control method (CLC)
(A/M 05)
7. Differentiate constant frequency control strategy from variable frequency control
strategy of varying the duty cycle of DC choppers.
Constant frequency control
Chopping frequency is constant
It has fast response
Variable frequency control
Chopping frequency is varied
It has slow response
8. What is meant by time ratio control of DC–DC converter?
In time ratio control (TRC), the value of Ton / T is varied in order to change the
average output voltage.
9. What is meant by pulse width modulation control in a DC chopper?
(M/J 07)
The PWM control method in DC chopper means, the on time T on is varied but
chopping frequency „f‟ is kept constant. The width of the pulse is varied and this type of
control is known as Pulse Width Modulation (PWM).
Buck regulator
10. What are the different types of switching regulators used in DC Choppers?
The different switched mode regulators available are,
1. Buck converter
2. Boost converter
3. Buck – Boost converter
4. Cuk converter
64
11. What is meant by buck regulator?
(M/J 07)
The buck converter is defined as, a converter used to step down an unregulated DC
input voltage to regulated variable DC output voltage.
Chopper classification
12. What are the classifications of DC to DC converter depending upon the directions of
current and voltage?
(M/J 06)
Depending on the direction of current and voltage, choppers can be classified into the
following types,
1. Type A chopper or first quadrant chopper
2. Type B chopper or second quadrant chopper
3. Type C chopper or two quadrant type A chopper
4. Type D chopper or second quadrant type B chopper
5. Type E chopper or four quadrant chopper
13. What is two-quadrant DC chopper?
(A/M 08)
A DC chopper can be operated in the I and II quadrant as well as I and IV quadrant.
Here the output voltage is always positive but output current is either positive or negative.
SMPS
14. What are the applications of SMPS?
The applications of SMPS are,
1. Computer
2. Television receiver
3. Battery charger
UNIT IV
INVERTERS
Single phase inverter
1. List out the industrial applications of inverters.
The applications of inverters are,
1. Adjustable speed drives
2. Induction heating
3. Stand-by aircraft power supplies
4. UPS
5. HVDC transmission
(A/M 04)
2. What is the purpose of connecting diode in antiparallel with thyristors, in inverter?
(A/M 04)
For RL loads, load current will not be in phase with load voltage and the diodes
connected in antiparallel will allow the current to flow when the main thyristors are turned
off. These diodes are called feedback diodes.
65
3. What is meant by inverter?
An inverter means a device that converts DC power into AC power at desired output
voltage and frequency.
PWM technique
4. What is PWM?
(A/M 05)
PWM control means, a fixed DC input voltage is given to the inverter and a controlled
AC output voltage is obtained by adjusting the on and off periods of the inverter components.
This is the most popular method of controlling the output voltage and this method is termed
as PWM control.
5. Define – Modulation Index of PWM.
(N/D 05)
The amplitude modulation index defined as the ratio of reference voltage ER to the
control voltage EC and it is denoted by M.
M = ER / Ec
where,
M - Modulation index
ER - reference voltage
Ec - control voltage
6. What are the modulation techniques used in an inverter?
1. Single pulse width modulation
2. Multi pulse with modulation
3. Sinusoidal pulse width modulation
(M/J 06)
7. What are the advantages of PWM control?
The advantages of PWM control are,
1. The output voltage can be obtained without any additional components
2. Lower order harmonics can be eliminated or minimized along with its output voltage
control. As the higher order harmonics can be filtered easily, the filtering
requirements are minimized.
Current source inverter
8. List out the applications of CSI.
The applications of a CSI are,
1. Induction heating
2. Lagging VAR compensation
3. Speed control of AC motors
4. Synchronous motor starting
9. Differentiate VSI from CSI.
Sl. No.
1
VSI
Input voltage is maintained
constantly
The output voltage does not
(N/D 04)
(N/D 03, 06, 07)
CSI
Input current is constant but
adjustable
The output current does not depend
66
2
3
4
depend on the load
The magnitude of the output
current and its waveform
depends on the nature of the
load impedance
It requires feedback diodes
Commutation circuit is
complicated i.e. it contains
capacitors and inductors.
on the load
The magnitude of the output voltage
and its waveform depends on the
nature of the load impedance
It does not require feedback diodes
Commutation circuit is simple i.e. it
contains only capacitors.
10. What are the advantages of current source inverter?
The two advantages of CSI are,
1. CSI does not require any feedback diodes.
2. Commutation circuit is simple as it involves only thyristors.
(M/J 07)
UNIT V
AC TO AC CONVERTERS
AC voltage controller
1. What is an AC voltage controller?
(M/J 10)
An AC voltage controller means it converts fixed alternating voltage into a variable
voltage without change in frequency.
2. What are the applications of AC voltage controllers?
The applications of AC voltage controllers are,
1. Domestic and industrial heating
2. Lighting control
3. Speed control of single phase and three phase ac motors
4. Transformer tap changing
3. What are the types AC voltage controllers?
1. Single phase AC voltage controller
2. Three phase AC voltage controller
(M/J 13)
4. What is meant by unidirectional or half-wave AC voltage controller?
(N/D 11)
In a unidirectional or half-wave AC voltage controller, the power flow is controlled
only during the positive half-cycle of the input voltage.
5. What is meant by bidirectional or half-wave AC voltage controller?
(N/D 10)
In a bidirectional or half-wave AC voltage controller, the power flow is controlled
during both cycles of the input voltage.
67
Cycloconverter
6. What is meant by cycloconverter?
(N/D 12)
A cycloconverter converts input power at one frequency to output power at another
frequency with one-stage conversion. Cycloconverter is also known as frequency changer.
7. What are the two types of cycloconverters?
The two types of cyclo-converters are,
1. Step-up cyclo-converters
2. Step-down cyclo-converters
8. What are the applications of cycloconverters?
The applications of cyclo-converters are,
1. Induction heating
2. Speed control of high power ac drives
3. Static VAR generation
9. What is meant by negative converter group in a cycloconverter?
The negative converter group in a cycloconverter is the part of the cycloconverter
circuit that permits the flow of current during the negative half cycle of output current is
called negative converter group.
10. What is a positive converter group in a cycloconverter?
The positive converter group in a cycloconverter is the part of the cycloconverter
circuit that permits the flow of current during the positive half cycle of output current is
called positive converter group.
68
EE2302 ELECTRICAL MACHINES – II
UNIT I
SYNCHRONOUS GENERATOR
1. Why are almost all large size synchronous machines constructed with rotating field
system type?
The following are the principal advantages of the rotating field system type
construction of synchronous machines:
1. The relatively small amount of power, about 2%, required for field system via sliprings and brushes.
2. For the same air gap dimensions, which are normally decided by the kVA rating,
more space is available in the stator part of the machine for providing more
insulation to the system of conductors, especially for machines rated for 11kV or
above.
3. Insulation to stationary system of conductors is not subjected to mechanical stresses
due to centrifugal action.
4. Stationary system of conductors can easily be braced to prevent deformation.
5. It is easy to provide cooling arrangement for a stationary system of conductors.
6. Firm stationary connection between external circuit and system of conductors enable
the machine to handle large amount of volt-ampere as high as 500MVA.
2. Write the equation for frequency of emf induced in an altenator.
Frequency of emf induced in an alternator, f , expressed in cycles per second or Hz,
is given by the following equation F = (PN)/120 Hz, Where P- Number of poles N-Speed in
rpm
3. How are alternators classified?
According to type of field system
1. Stationary field system type
2. Rotating field system type
3. According to shape of field system
4. Salient pole type
5. Smooth cylindrical type
4. Name the types of alternators based on their rotor construction.
Alternators can be classified into the following two types according to its rotor construction.
They are
1. mooth cylindrical type alternator
2. Salient pole alternator
5. Why do cylindrical Alternators operate with steam turbines?
Steam turbines are found to operate at fairly good efficiency only at high speeds.
The high speed operation of rotors tends to increase mechanical losses and so the rotors
should have a smooth external surface. Hence, smooth cylindrical type rotors with less
69
diameter and large axial length are used for synchronous generators driven by steam
turbines with either 2 or 4 poles.
6. Which type of synchronous generators is used in Hydro-electric plants?
As the speed of operation is low for hydro turbines used in Hydro-electric plants,
salient pole type synchronous generators are used. These allow better ventilation and also
have other advantages over smooth cylindrical type rotor.
7. What are the advantages of salient pole type construction used i n s ynchronous
machines?
The advantages of salient-pole type construction are as follows:
1. They allow better ventilation
2.
pole faces are so shaped that the radial air gap length increases from the pole
centre to the pole tips so that the flux distribution in the air-gap is sinusoidal
in shape which will help the machine to generate sinusoidal emf
3.
to variable reluctance the machine develops additional reluctance power which
is independent of excitation
8. Why is the stator core of Alternator laminated?
The stator core of Alternator is laminated to reduce eddy current loss.
9. How does electrical degree differ from mechanical degree?
Mechanical degree is the unit for accounting the angle between two points based on
their mechanical or physical placement. Electrical degree is used to account the angle
between two points in rotating electrical machines. Since all electrical machines operate
with the help of magnetic fields, the electrical degree is accounted with reference to the
magnetic field. 180 electrical degree is accounted as the angle between adjacent North and
South poles.
10. What is distributed winding?
When coil-sides belonging to each phase are housed or distributed in more than one
slot under each pole region, then the winding is called distributed winding. A full pitch coil
has width of coil otherwise called coil-span as 180º - angle between adjacent slots in
electrical degree and x= 1,2,3…
11. Why is short-pitch winding preferred over full-pitch winding?
Short-pitch winding is preferred over full-pitch winding because,
1. Waveform of the emf can be approximately made to a sine wave and distorting
harmonics can be reduced or totally eliminated.
2. Conductor material copper, is saved in the back and front end connections due to
less coil-span.
3. Fractional slot winding with fractional number of slots/phase can be used which in
turn reduces the tooth ripples.
4. Mechanical strength of the coil is increased
70
12. Define – Winding Factor
The winding factor Kd is defined as the ratio of phasor addition of emf induced in all
the coils belonging to each phase winding to their arithmetic addition.
13. Why are alternators rated in kVA and not in kW?
The continuous power rating of any machine is generally defined as the power the
machine or apparatus can deliver for a continuous period so that the losses incurred in the
machine gives rise to a steady temperature rise not exceeding the limit prescribed by the
insulation class. Apart from the constant loss incurred in Alternators is the copper loss,
occurring in the 3 –phase winding which depends on I2R, the square of the current
delivered by the generator. As the current is directly related to the apparent – power
delivered by the generator, the Alternators have only their apparent power in VA/kVA/MVA
as their power rating.
14. What are the causes of changes in voltage in alternators when loaded?
Variations in terminal voltage in Alternators on load condition are due to the
following causes:
1. Voltage variation due to the resistance of the winding, R
2.
tage variation due to the leakage reactance of the winding, Xt
15. What is meant by armature reaction in Alternators?
The interaction between flux set up by the current carrying armature and the main is
defined as the armature reaction.
16. What is meant by synchronous impedance of an Alternator?
The complex addition of resistance, R and synchronous reactance, jXs can be
represented together by a single complex impedance Zs called synchronous impedance.In
complex form Zs = (R + jXs ).
17. What is meant by load angle of an Alternator?
The phase angle introduced between the induced emf phasor, E, and terminal voltage
phasor, U, during the load condition of an Alternator is called load angle.
UNIT II SYNCHRONOUS MOTOR
1. Write the various methods for predetermining the voltage regulation of 3-phase
alternator.
The following are the three methods which are used to predetermine the voltage
regulation of smooth cylindrical type Alternators:
1. Synchronous impedance / EMF method
2. Ampere-turn / MMF method
3. Potier / ZPF method
71
2. How is synchronous impedance calculated from OCC and SCC?
Synchronous impedance is calculated from OCC and SCC as |Zs| = E0/Isc(for
same If) A compromised value of Zs is normally estimated by taking the ratio of (E0/Isc) at
normal field current Ifn. A normal field current Ifn is one which gives rated voltage Ur on
open circuit. |Zs| = Ur/Iscn
3. What are the advantages and disadvantages of estimating the voltage regulation of an
Alternator by EMF method?
Advantages:
1. Simple no load tests (for obtaining OCC and SCC) are to b
2. Calculation procedure is much simpler
Disadvantage:
The value of voltage regulation obtained by this method is always higher than
the actual value
4. Why i s t h e syn ch ron ou s i mp ed an c e meth od of es ti m ati n g v ol tag e
r egu l at i on considered as a pessimistic method?
Compared to other methods, the value of voltage regulation obtained by the
synchronous impedance method is always higher than the actual value and therefore
this method is called the pessimistic method.
5. In what way does the ampere-turn method differ from synchronous impedance
method?
The ampere-turn /MMF method is the converse of the EMF method in the sense that
instead of having the phasor addition of various voltage drops/EMFs, here the phasor
addition of MMF required for the voltage drops are carried out. Further the effect of
saturation is also taken care of.
6. What are the test data required for predetermining the voltage regulation of an
alternator by MMF method?
Data required for MMF method are:
1. Effective resistance per phase of the 3-phase winding R
2. Open circuit characteristic (OCC) at rated speed/frequency
3. Short circuit characteristic (SCC) at rated speed/frequency
7. Why is the MMF method of estimating the voltage regulation considered an
optimistic method?
Compared to the EMF method, MMF method, involves more number of complex
calculation steps. Further the OCC is referred twice and SCC is referred once while
predetermining the voltage regulation for each load condition. Reference of OCC takes care
of saturation effect. As this method requires more effort, the final result is very close to the
actual value. Hence this method is called optimistic method.
72
8. Write the conditions to be satisfied before connecting two alternators in parallel.
The following are the three conditions to be satisfied by synchronizing the additional
alternator with the existing one or the common bus-bars.
1. The terminal voltage magnitude of the incoming alternator must be made equal to the
existing alternator or the bus-bar voltage magnitude.
2. The phase sequence of the incoming alternator voltage must be similar to the bus- bar
voltage.
3. The frequency of the incoming alternator voltage must be the same as the bus-bar
voltage.
9. How do the synchronizing lamps indicate the correctness of phase sequence
between existing and incoming Alternators?
The correctness of the phase sequence can be checked by looking at the three sets of
lamps connected across the 3-pole of the synchronizing switch. If the lamps grow bright
and dark in unison it is an indication of the correctness of the phase sequence. If on the
other hand, they become bright and dark one after the other, connections to any two
machine terminals have to be interchanged after shutting down the machine.
10. What are the advantages and disadvantages of three dark lamps method of
synchronizing?
Advantages:
1. The synchronous switch using lamps is inexpensive
2. Checking for correctness of the phase sequence can be obtained in a simple
manner which is essential especially when the Alternator is connected for the first
time or for fresh operation after disconnection.
Disadvantage:
The rate of flickering of the lamps only indicates the frequency
difference between the bus-bar and the incoming Alternator. The frequency of the
incoming alternator in relation to the bus-bar frequency is not available.
11. How is synchronoscope used for synchronizing alternators?
Synchronoscope can be used for permanently connected alternators where the
correctness of phase sequence is already checked by other means. Synchronoscope is
capable of rotating in both directions. The rate of rotation of the pointer indicates the
amount of frequency difference between the alternators. The direction of rotation indicates
whether incoming alternator frequency is higher or lower than the existing alternator. The
TPST switch is closed to synchronize the incoming alternator when the pointer faces the
top thick line marking.
73
12. Why a r e synchronous generators constructed with more synchronous reactance
and negligible resistance?
The presence of more resistance in the synchronous generators will resist or oppose
their synchronous operation. More reactance in the generators can cause good reaction
between the two and help the generators to remain in synchronism in spite of any
disturbance occurring in any one of the generators.
13. List out the factors that affect the load sharing in parallel operating generators.
The total active and reactive power delivered to the load connected across the
common bus-bars, are shared among synchronous generators operating in parallel, based on
the following three factors
1. Prime-mover characteristic/input
2. Excitation level
3. Percentage synchronous impedance and its R/X ratio
14. How does the change in prime mover input affect the load sharing?
An increase in prime-mover input to a particular generator causes the active power
shared by it to increase and a corresponding decrease in active-power shared by other
generators. The change in reactive power sharing is less appreciable. The frequency of the
bus-bar voltage will also subject to slight increase in value.
15. How does change in excitation affect the load sharing?
The decrease in excitation in one generator causes the reactive power shared by it to
decrease and a corresponding increase in reactive-power shared by other generators. The
change in active-power sharing is less appreciable. There will be a slight decrease in
terminal voltage magnitude also.
16. What steps are to be taken before disconnecting one alternator from parallel
operation?
The following steps are to be taken before disconnecting one alternator from parallel
operation:
1. The prime-mover input of the outgoing generator has to be decreased and that of
other generators has to be increased and by this the entire active-power delivered
2. The excitation of the outgoing generator has to be decreased and that of other
generators has to be increased and by this the entire reactive-power delivered by
the outgoing generator is transferred to other generators
3. After ensuring that the current delivered by the outgoing generator is zero, it has to
be disconnected from parallel operation.
74
17. What is meant by infinite bus-bars?
The source or supply lines with non-variable voltage and frequency are called infinite
bus-bars. The source lines are said to have zero source impedance and infinite rotational
inertia.
18. How does increase in excitation of the Alternator connected to infinite bus- bars
affect this operation?
Increase in excitation level of the synchronous generator will effectively increase the
reactive component of the current supplied by the generator and hence the active power
delivered.
19. An a lternator is found to have its terminal voltage on load condition more than
that on no load. What is the nature of the load connected?
The nature of the load is of leading power factor, load consisting of resistance and
capacitive reactance.
UNIT III – THREE PHASE INDUCTION MOTOR
1. State the principle of 3 phase induction motor.
While starting, rotor conductors are stationary and they cut the revolving magnetic
field and so an emf is induced in them by electromagnetic induction. This induced emf
produces a current if the circuit is closed. This current opposes the cause by Lenz‟s law and
hence the rotor starts revolving in the same direction as that of the magnetic field.
2. Why is an induction motor called a rotating transformer?
The rotor receives electric power in exactly the same way as the secondary of
a two-winding transformer receiving its power from the primary. Therefore, an induction
motor can be called as a rotating transformer i.e. one in which primary winding is stationary
but the secondary is tree to rotate.
3. List out the advantages of skewing.
The advantages of skewing are,
1. It reduces humming effect.
2. It reduces magnetic locking of the stator and rotor.
4. What are the effects of increasing rotor resistance on starting current and starting
torque?
The effects of increasing rotor resistance on starting current and starting torque are:
1. The additional external resistance reduces the rotor current and hence the current
drawn from the supply.
2. It improves the starting torque developed by improving the power factor in high
proportion to the decrease in rotor current.
75
5. What is slip of an induction motor?
The slip speed is defined as the percentage difference of relative speed to
synchronous speed. It is expressed as,
S = (Ns - N)/Ns*100
6. What are the advantages of slip-ring induction motor?
The advantages of slip-ring induction motor are:
1. Rotor circuit is accessible for external connection.
2. By adding external resistance to the rotor circuit the starting current is reduced with
the added advantage of improving starting torque.
3. Additional speed control methods can be employed with the accessibility in the rotor
circuit.
7. What are the various losses that occur in an induction motor?
The various losses that occur in an induction motor are:
1. Magnetic losses Wi,
2. Electrical losses Wcu
3. Mechanical losses Wm
8. What are the tests to be conducted for predetermining the performance of a 3 phase
induction Motor?
The tests to be conducted for predetermining the performance of a 3 phase induction motor
are:
1. No load test
2. Blocked rotor test
9. What is meant by circle diagram of an induction motor?
This circle diagram is used to predict the performance of the machine at different
loading conditions as well as mode of operation. When an I M operates on constant voltage
and constant frequency source, the loci of stator current phasor is found to fall on a circle.
10. What are the advantages of direct load test for a 3 phase induction motor?
The advantages of direct load test for a 3 phase induction motor are,
1. Direct measurement of input and output parameters yield accurate results
2. Aside from the usual performance other performances like mechanical vibration,
noise etc can be studied.
3. By operating the motor at full load for a continuous period, the final steady
temperature can be measured.
76
11. What is cogging of an induction motor?
When the number of teeth in stator and rotor are equal, the stator and rotor teeth have
a tendency to align themselves exactly to minimum reluctance position. In such case the
rotor may refuse to accelerate. This phenomenon is called magnetic locking or cogging.
UNIT IV – STARTING AND SPEED CONTROL OF
THREE PHASE INDUCTION MOTOR
1. Write the different types of starters used for induction motor.
The different types of starters used for induction motor are,
1. Primary resistor
2. Autotransformer starter
3. Star-delta starter
4. Rotor rheostat
2. What are the advantages of a primary resistance starter of induction motor?
The advantages of a primary resistance starter of induction motor are,
1. Starting torque to full load torque is x2 of that obtained with direct switching or
across the line starting.
2. This method is useful for smooth starting of small machines only.
3. What are the advantages of an autotransformer starter?
The advantages of an autotransformer starter are,
1. Reduced voltage is applied across the motor terminal.
2. There is a provision for no-voltage and over-load protection.
4. Write the relationship between starting current and full load current of an
autotransformer starter.
The relationship between starting current and full load current of an autotransformer
starter is given by, I2 = K. Isc
where,
K = Transformation ratio
I2 = Full load current
Isc = Starting current
5. Write the relationship between starting torque of an induction motor with an
autotransformer starter and star delta starter
Star delta starter is equivalent to an autotransformer starter in the ratio of 58% in
approximation.
77
6. How is the starting current reduced using rotor resistance starter?
The controlling resistance is in the form of a rheostat, connected in star. The
resistance being gradually cut-out of the rotor circuit as the motor gathers speed. Increasing
the rotor resistance, not only in the rotor current reduced at starting, but at the same time
starting torque is also increased due to improvement in power factor.
7. Write the methods of speed control on stator side of an induction motor.
The methods of speed control on stator side of an induction motor are,
1. By changing the applied voltage
2. By changing the applied frequency
3. By changing the number of stator poles.
8. Write the methods of speed control from rotor side of an induction motor.
The methods of speed control from rotor side of an induction motor are,
1. Rotor rheostat control
2. By operating two motors in concatenation or cascade
3. By injecting an emf in the rotor circuit
9. What are the applications of speed control of an induction motor by pole changing
method?
The applications of speed control of an induction motor by pole changing method are,
1. Elevator motors
2. Traction motors
3. Small motors driving machine tools
10. How is the speed control achieved by changing the number of poles?
Synchronous speed of induction motor can also be changed by changing the number
of stator poles. This change of number of poles is achieved by having two or more entirely
independent stator windings in the same slots.
11. What are the limitations of rotor rheostat speed control of an induction motor
The limitations of rotor rheostat speed control of an induction motor are,
1. With increase in rotor resistance, I2R losses also increase which decrease the
operating efficiency of the motor. In fact, the loss is directly proportional to the
reduction in the speed.
2. Double dependence of speed, not only on R2 but also on load as well.
12. Write the three possible methods of speed control of cascaded connection of an
induction motor.
The three possible methods of speed control of cascaded connection of an induction motor
are,
1. Main motor may be run separately from the supply
78
2. Auxiliary motor may be run separately from the mains.
3. The combination may be connected in cumulative cascade.
13. How is the tandem operation of induction motor started?
When the cascaded set is started, the voltage at frequency, f is applied to the stator
winding of main motor. An induced emf of the same frequency is produced in main motor
(rotor) which is supplied to the auxiliary motor. Both the motors develop a forward torque.
As the shaft speed rises, the rotor frequency of main motor falls and so does the synchronous
speed of auxiliary motor. The set settles down to a stable sped when the shaft speed become
equal to the speed of rotating field of Auxiliary motor
14. Write the method of speed control by injecting emf in the rotor circuit.
The speed of an induction motor is controlled by injecting a voltage in the rotor
circuit. It is necessary for the injected voltage to have the same frequency as the slips
frequency
15. What are the advantages and disadvantages of slip power scheme?
The advantages of slip power scheme are,
1. Easier power control
2. Higher efficiency
The disadvantages of slip power scheme are,
1. Reactive power consumption.
2. Low power factor at reduced speed.
16. Write the types of slip power recovery schemes.
The types of slip power recovery schemes are,
1. Scherbius system
2. Kramer drive
UNIT V
SINGLE PHASE INDUCTION MOTORS AND SPECIAL MACHINES
1. Write the two windings of a single-phase induction motor.
The two windings of a single-phase induction motor are,
1. Running winding (main winding)
2. Starting winding (auxiliary winding)
2. What are the various methods available for making a single-phase motor self-starting?
The various methods available for making a single-phase motor self-starting are,
1. By splitting the single phase
2. By providing shading coil in the poles
3. Repulsion start method.
79
3. What is the main difference between the principle of operation of a 3 phase and single
phase induction motors?
When three-phase supply is given to 3-phase induction motor, a rotating magnetic
field is produced and the rotor-starts rotating. But when single-phase supply is given to
single-phase motor only a pulsating flux is produced. So motor is not self-starting. Therefore
to make it self-starting split-phase arrangement is made by providing an auxiliary winding.
4. Write the main difference in construction of an AC series motor and a DC series
motor.
The main difference in construction of an AC series motor and a DC series motor are,
1. The entire iron structure of the field cores and yoke are laminated to reduce the eddy
current loss
2. Number of turns in the field winding is reduced to have large reactance and higher
power factor.
3. AC series motors are provided with commutating poles
5. Write the advantages of a capacitor run type motor.
The advantages of a capacitor run type motor are,
1. It has high starting and running torques
2. Current drawn is less because of higher power factor
3. It can be started with some load.
6. How can the rotation of a universal motor be reversed?
1. The direction of rotation of the concentrated-pole (or salient-pole) type universal
motor may be reversed by reversing the flow of current through either the armature
or field windings.
2. The direction of rotation of the distributed field compensating type universal motor
may be reversed by interchanging either the armature or field leads and shifting the
brushes against the direction in which the motor win rotate.
7. Why is a single-phase induction motor not self-starting?
When the motor is fed from a single-phase supply, its stator winding produces an
alternating or pulsating flux, which develops no torque. Therefore, a single-phase motor is
not self-starting.
8. List out the applications of a universal motor.
The applications of a universal motor are,
1. Used for sewing machines
2. Table fans
3. Vacuum cleaners
4. Hair driers
5. Blowers
80
9. Write the advantages of capacitor run induction motor.
The advantages of capacitor run induction motor are,
1. Running torque is more.
2. Power factor during running is more, thereby line current is reduced.
10. What is a universal motor?
A universal motor is defined as a motor, which may be operated either on direct
current or single phase A.C supply, at approximately, the same speed and output.
11. What is the use of shading ring in a shaded pole motor?
The shading coil causes the flux in the shaded portion to lag behind the flux in
unshaded portion of pole. This gives in effect a rotation of flux across the pole face and
under the influence of this moving flux a starting torque is developed.
12. Write the advantages of a capacitor start motor.
The advantages of a capacitor start motor are,
1. The starting current of capacitor start motor is less than resistance split phase motor
2. Starting torque of the capacitor motor is twice that of resistance start motor.
13. What are the different types of single phase induction motor?
The different types of single phase induction motor are,
1. Split-phase motor
2. Shaded pole motor
3. Single phase series motor
4. Repulsion motor
5. Reluctance motor
14. Write the two different theories with which principle of 1 phase induction motors are
explained.
The two different theories employed for explaining the principle of single phase induction
motors are
1. Double revolving field theory
2. Cross field theory
81
EE2303
TRANSMISSION AND DISTRIBUTION
UNIT I
INTRODUCTION
1. Why are all transmission and distribution systems 3 phase systems?
A 3 phase AC circuit using the same size conductors as the single phase circuit can
c a r r y three times the powers which can be carried by a1 phase circuitand uses 3conductors
for the 2 phasesand one conductorfor the neutral. Thus a 3phase circuit is more economical than
a 1 phase circuit interms of initial cost as well as the losses. Therefore all transmission and
distribution systems are 3 phase systems.
2. Why are the transmission systems mostly overhead systems?
Because of the cost consideration,the transmission systems are mostly overhead
systems.
3. Why do all overhead lines use ACSR conductors?
ACSR conductors comprise of hard drawn aluminium wire stranded around a core of
single or multiple strand galvanized steel wire. They provide the necessary conductivity
while the steel provides the necessary mechanical strength. It has less corona loss. The
breaking load is high and has less weight.
4. Why are transmission lines 3 phase 3 wire circuits while distributionlines are 3 phase 4
wire circuits?
A balanced 3 phase circuit does not require the neutral conductor, as the
instantaneous sum of the 3 line currents are zero. Therefore the transmission lines and feeders
are 3 phase 3 wire circuits. The distributors are 3 phase 4 wire circuits because a neutral wire
is necessary to supply the 1 phase loads of domestic and commercial consumers.
5. Why is overhead line conductors invariably stranded?
They are stranded to make them flexible during erection and while in service.
6. Write the advantages of interconnected systems.
Any area fed from one generating station during overload hours can be fed from another
power station. Thus reserved capacity required is reduced, reliability of supply increased and
efficiency increased.
7. What is a ring distributor?
A ring distributor is a distributor which is arranged to form a closed circuit and is fed at
one or more than one point.
8. State any two advantages of ring main system.
1. Less voltage fluctuations at consumer‟s terminals
2. Less copper is required as each part of the ring carries less current than in radial
system.
82
9. What are the disadvantages of a 3wire system?
1. In 3 wire system a third wire is required
2. The safety is partially reduced
3. A balancer is required and therefore cost is increased.
10. What are the advantages of a 3 wire DC distribution system over a 2 wire DC
distribution system?
If a 3 wire system is used to transmit the same amount of power over the same distance
with same efficiency with same consumer voltage we require 0.3125 times of copper as
required in a 2 wire system.
11. State Kelvin‟s law.
The annual expenditure on the variable part of the transmission system should be equal
to the annual cost of energy wasted in the conductor used in that system.
12. State any two limitations of Kelvin‟s law.
It is difficult to estimate accurately the annual charge on the capital outlay. It does not
give the exact economical size of the conductor.
13. Define – Resistance of the transmission line
Resistance of the transmission line is defined as the loop resistance per unit length of
the line in a single phase system. In a 3 phase system it is defined as the resistance per phase.
14. What are the advantages of high voltage AC transmission?
1. The power can be generated at high voltages.
2. The maintenance of ac substation is easy and cheaper.
15. What are the disadvantages of high voltage AC transmission?
1. An AC line requires more copper than a DC line.
2. The construction of an AC line is more complicate than the construction of a DC
transmission line.
3. Due to skin effect in the AC system the effective resistance of the line is increased
UNIT II
TRANSMISSION LINE PARAMETERS
1. Define – Inductance of a line
Inductance of a line is defined as the loop inductance per unit length of the line. Its
unit is henry per meter.
2. Define – Capacitance of a line
Capacitance of a line is defined as shunt capacitance between the two wires per unit
line length. Its unit is farad per meter.
3. What is meant by skin effect?
The steady current when flowing through the conductor does not distribute uniformly,
rather it has the tendency to concentrate near the surface of the conductor. This phenomenon
is called skineffect.
83
4. Why is skin effect absent in DC system?
The steady current when flowing through a conductor distributes itself uniformly over
the whole cross section of the conductor .That is why skin effect is absent in DC system.
5. What is the effect of skin effect on the resistance of the line?
Due to skin effect the effective area of cross-section of the conductor through which
current flow is reduced. Hence the resistance of the line is increased when AC current is
flowing.
6. On what factors does the skin effect depend?
The skin effect depends on nature of the material, diameter of the wire and frequency
and shape of the wire.
7. What is called symmetrical spacing?
In 3 phase system when the line conductors are equidistant from each other then it is
called symmetrical spacing.
8. What is the necessity for a double circuit line?
To reduce the inductance per phase and to increase the efficiency
9. Write the factors governing the inductance of a line.
The factors governing inductance of a line are:
1. Radius of the conductor
2. Spacing between the conductors.
10. Define –Neutral Plane
It is defined as a plane where electric field intensity and potential is zero.
11. Define – Proximity Effect
The alternating magnetic flux in a conductor caused by the current flowing in a
neighbouring conductor gives rise to a circulating current which causes an apparent increase
in the resistance of the conductor. This phenomenon is called proximity effect.
12. What is the effect of proximity effect?
It results in the non-uniform distribution of current in the cross-section, and the
increase of resistance.
13. What is called a composite conductor?
A conductor which operates at high voltages and is composed of 2 or more subconductors and run electrically in parallel is called composite conductors.
14. What is meant by bundle conductor?
It is a conductor made up of 2 or more sub conductors and is used as one phase
conductors.
15. What are the advantages of using bundled conductors?
The advantages of using bundled conductors are as follows:
1. Reduced reactance
2. Reduced voltage gradient
84
3. Reduced corona loss
4. Reduced Interference
16. What is meant by transposition of line conductors?
Transposition is meant by changing in the positions of the three phases on the line
supports twice over the total length of the line. The line conductors in practice are so
transposed that each of the three possible arrangements of conductors exist for one-third of
the total length of the line.
UNIT III
MODELLING AND PERFORMANCE OF TRANSMISSION LINES
1. What is meant by corona?
The phenomenon of violet glow, hissing noise and production of ozone gas in an over
headline is called corona.
2. What are the factors that affect corona?
The factors that affect corona are,
1. Atmosphere
2. Conductor size
3. Spacing between conductors
4. Line voltage
3. Define – Critical Disruptive Voltage
It is defined as the minimum phase voltage at which corona occurs.
4. Define – Visual Critical Voltage
It is defined as the minimum phase voltage at which corona appears all along the line
conductors.
5. Write any two merits of corona.
The merits of corona are,
1. Reduces the effects of transients produced by surges
2. System performance is improved.
6. Write the two demerits of corona.
The two demerits of corona are,
1. The transmission efficiency is affected.
2. Corrosion occurs.
7. Write the methods of reducing the corona effect.
By increasing the conductor size and conductor spacing.
8. Why are ACSR conductors used in lines?
If the size of the conductor is larger, corona effect is reduced and reduces the
proximity effect. Hence they are used in lines.
85
9. Define – Medium Lines
Lines having length between 60 and 150 km and line voltages between 20 and 100 kV
are called medium lines.
10. Define – Short Lines
Lines having lengths below 60 km and voltages below 20 kV are called short lines.
11. Write the limitations of end condenser method.
This over estimates the effects of line capacitance. It is assumed to be lumped or
concentrated.
12. What is meant by voltage stability?
The ability of the system to maintain the voltage level within its acceptable limits is
called voltage stability.
13. What is meant by shunt compensation?
Shunt compensation is the use of shunt capacitors and shunt reactors is the line to
avoid voltage instability.
UNIT IV
INSULATORSAND CABLES
1. Why are cables not used for long distance transmission?
Cables are not used for long distance transmissions due to their large charging
currents.
2. List out the main parts of the cable?
The main parts of the cable are,
1. Conductor
2. Dielectric
3. Sheath
3. What is the function of a conductor?
A conductor provides the conducting path for the current.
4. What is the purpose of insulation in a cable?
The insulation or dielectric withstands the service voltage and isolates the conductor
with other objects.
5. What is the function of sheath in a cable?
The sheath does not allow the moisture to enter and protects the cable from all
external influences like chemical or electrochemical attack fire, etc..
6. Write the conductor materials in cables.
The conducting materials in cables are,
1. Copper
2. Aluminium
86
7. What is the purpose of stranding of conductors?
The purpose of stranding of conductors are:
1. Stranding increases the resistance of the cable
2. It has flexibility
8. Define – Segmental Conductors
The stranded wires which are compacted by the rollers to minimize the air spaces
between the individual wires are called segmented conductors. Here the conductor size is
reduced for a given conductance.
9. Write the properties of insulating materials.
It should have high insulation resistance, high dielectric strength, good mechanical
properties, non-hygroscopic, capable of being operated at high temperatures, low thermal
resistance and low power factor.
10. Write the commonly used power cables.
Impregnated paper, Polyvinylchloride and Polyethene
11. Write the advantages of PVC over paper insulated cables.
The advantages of PVC over paper insulated cables are,
1. Reduced cost and weight
2. Insulation is resistant to water
3. Simplified jointing
4. Increased flexibility
5. No plumbing required
12. Write the merits of paper insulated cables.
The merits of paper insulated cables are,
1. High current carrying capacity,
2. Long life
3. Greater reliability
13. Write the advantages of polythene insulators.
The advantages of polythene insulators are,
1. They are non-hygroscopic
2. Light in weight
3. Low dielectric constant
4. Low loss factor
5. Low thermal resistance
14. By what materials are cable sheaths made?
1. Lead sheaths
2. Aluminium sheaths
15. In what ways are Al sheaths superior to lead sheaths?
Al sheaths are smaller in weight, have high mechanical strength, greater conductivity,
cheap, easy to manufacture and install and withstand the required gas pressure without
reinforcement.
87
16. Where is CSA sheath used in cables ?
Corrugated seamless aluminium sheath is used in high voltage oil filled cables and
telephone lines.
UNIT V
SUBSTATION, GROUNDING SYSTEM AND DISTRIBUTION SYSTEM
1. Define – Sag of a line
Sag of a line is defined as the difference in level between the points of supports and
the lowest point of the conductor.
2. Write the factors that affect sag in the transmission line.
The factors that affect sag in the transmission line are,
1. Weight of the conductor
2. Length of the span
3. Working tensile strength
4. Temperature
3. What is the reason for the sag in the transmission line?
While erecting the line, if the conductors are stretched too much between supports
then there prevails an excessive tension on the line which may break the conductor. In order
to have safe tension in the conductor, a sag in the line is allowed.
4. How is the capacitance effect taken into account in a long line?
They have sufficient length and operate at voltage higher than 100 kV. The effects of
capacitance cannot be neglected. Therefore, in order to obtain reasonable accuracy in long
lines, the capacitance effects are taken.
5. Write the limitations of nominal T and pi methods in the line problems.
Generally the capacitance is uniformly distributed over the entire length of the line.
But for easy calculations the capacitance is concentrated at one or two points .Due to these
effects there are errors in the calculations.
6. What are the limitations of end condenser method?
There is considerable error in calculations because the distributed capacitance has
been assumed to be lumped or concentrated. This method over estimates the effects of the
line capacitance.
7. What is meant by end condenser method?
It is a method used for obtaining the performance calculations of medium lines. Here
the capacitance of the line is lumped or concentrated at the receiving end.
8. What is meant by power circle diagram?
It is a diagram drawn for the transmission lines network involving the generalized
circuit constants and the sending end and receiving end voltage.
88
9. What are the voltage regulating equipments that used in transmission system?
The voltage regulating equipments that used in transmission system are,
1. Synchronous motors
2. Tap changing transformers
3. Series and shunt capacitors
4. Booster transformers
5. Compound generators
6. Induction regulator
10. Write the methods used for voltage control of lines.
The methods used for voltage control of lines are,
1. Tap changing auto-transformer
2. Booster transformer
3. Excitation control
4. Induction regulator
11. What is meant by sending end power circle diagram?
The circle drawn with sending end true and reactive power as the horizontal and
vertical co-ordinates are called sending end power circle diagram.
12. What is meant by receiving end power circle diagram?
The circle drawn with receiving end values are called receiving end power circle
diagram.
13. What is meant by neutral grounding?
Connecting the neutral or star point of any electrical equipment (generator,
transformer, etc..) to earth is called neutral earthing.
14. What is meant by substation?
The assembly of apparatus used to change some characteristic ( e.g. : voltage, AC to
DC frequency power factor, etc.) of electric supply is called a substation.
89
EC2311 COMMUNICATION EHGINEERING
UNIT I
MODULATION SYSTEMS
1. Define – Amplitude modulation
Amplitude Modulation defined as the process of changing the amplitude of a high
frequency carrier signal in proportion with the instantaneous value of the modulating signal.
2. Define – Modulation index and percent modulation for an AM wave
Modulation index is defined as an amount of amplitude change present in an AM
waveform .It is also called as coefficient of modulation. Mathematically modulation index is
where m = Modulation coefficient
Em = Peak change in the amplitude of the output waveform voltage
Ec = Peak amplitude of the un modulated carrier voltage
Percent modulation gives the percentage change in the amplitude of the
output wave when the carrier is acted on by a modulating signal.
3. Define – Low level Modulation
Low level modulation is defined as the modulation that takes place prior to the output element of
the final stage of the transmitter. For low level AM modulator class A amplifier is used.
4. Define – High level Modulation
High level modulation is defined as the modulation that takes place in the final element of the
final stage where the carrier signal is at its maximum amplitude. For high level modulator class C
amplifier is used.
5. What is the advantage of low level modulation?
The advantage of low level modulation is:
Less modulating signal power is required to achieve a high percentage of modulation
6. Distinguish between low level and high level modulation.
S.NO Low level modulation
High level modulation
1
In
low level
modulation,
modulation takes place prior
to the output element of the
final stage of the transmitter.
In high level modulation, the modulation
takes place in the final element of the
final stage where the carrier signal is at
its maximum amplitude.
2
It requires less power to It requires a much higher amplitude
achieve a high percentage of modulating signal to achieve a
modulation.
reasonable percent modulation.
90
7. Define – Image frequency
Image frequency is defined as any frequency other than the selected radio frequency
carrier that, if allowed to enter a receiver and mix with the local oscillator, will produce a cross
product frequency that is equal to the intermediate frequency.
8. Define – Local oscillator tracking
Local oscillator tracking is defined as the ability of the local oscillator in a receiver to oscillate
either above or below the selected radio frequency carrier by an amount equal to the intermediate
frequency throughout the entire radio frequency band.
9. Define – High side injection tracking
High side injection tracking is defined as the local oscillator should track above the incoming RF
carrier by a fixed frequency equal to
10. Define – Low side injection tracking
Low side injection tracking is defined as the local oscillator should track below the RF
carrier by a fixed frequency equal to
.
11. Define – Tracking error. How is it reduced?
Tracking error is defined as the difference between the actual local oscillator frequency
and the desired frequency. It is reduced by a technique called three point tracking.
12. Define – Image frequency rejection ratio
Image frequency rejection ratio is defined as the measure of the ability of pre selector to
reject the image frequency.
Mathematically, IFRR is
where
13. Define – Heterodyning
Heterodyning is defined as the process of mixing two frequencies together in a nonlinear
device or to translate one frequency to another using nonlinear mixing.
14. What are the disadvantages of conventional (or) Double Side Band Full Carrier
system?
The disadvantages of DSBFC system are :
(i). Carrier power constitutes two thirds or more of the total transmitted power. This is a major
drawback because the carrier contains no information. The sidebands contain the information
(ii). Conventional AM systems utilize twice as much bandwidth as needed with single sideband
systems
91
14. Define – Single sideband suppressed carrier AM.
Single sideband suppressed carrier is defined as a form of amplitude modulation in which the carrier
is totally suppressed and one of the sidebands removed.
15. Define – AM vestigial sideband
AM vestigial sideband is defined as a form of amplitude modulation in which the carrier and
one complete sideband are transmitted and a portion of the second sideband is transmitted.
16. What are the advantages of Single Side Band transmission?
The advantages of SSBSC are
(i). Power conservation: In SSB only one sideband is transmitted and the carrier is suppressed.
So less power is required to produce essentially the same quality signal.
(ii). Bandwidth conservation: Single Side Band transmission requires half as much bandwidth
as conventional AM double side band transmission.
(iii). Noise reduction: The thermal noise power is reduced to half that of a double side band
system.
17. What are the disadvantages of single side band transmission?
The disadvantages of single side band transmission are :
(i). Complex receivers: Single side band systems require more complex and expensive receivers
than conventional AM transmission.
(ii). Tuning Difficulties: Single side band receivers require more complex and precise tuning
than conventional AM receivers.
18. Define – Direct frequency modulation
Direct frequency modulation is defined as the frequency of constant amplitude carrier signal
which is directly proportional to the amplitude of the modulating signal at a rate equal to the
frequency of the modulating signal.
19. Define – Indirect frequency Modulation
Indirect frequency modulation is defined as the phase of a constant amplitude carrier directly
proportional to the amplitude of the modulating signal at a rate equal to the frequency of the
modulating signal.
20. Define – Instantaneous frequency deviation
The instantaneous frequency deviation is the instantaneous change in the frequency of the
carrier and is defined as the first derivative of the instantaneous phase deviation.
21. Define – Frequency deviation
Frequency deviation is defined as the change in frequency that occurs in the carrier when it is
acted on by a modulating signal frequency. The Frequency deviation is typically given as a peak
frequency shift in Hertz (∆f).The peak to peak frequency deviation (2∆f) is sometimes called carrier
swing.
92
22. State Carson rule.
Carson rule states that the bandwidth required to transmit an angle modulated wave is twice
the sum of the peak frequency deviation and the highest modulating signal frequency.
23. Define – Deviation ratio.
Deviation ratio is defined as the maximum peak frequency deviation divided by the
maximum modulating signal frequency. Mathematically, the deviation ratio is
24. What is direct FM?
Direct FM is a type of angle modulation, where the frequency of the carrier is varied
directly by the modulating signal. This means an instantaneous frequency deviation is directly
proportional to amplitude of the modulating signal.
25. What is indirect FM?
Indirect FM is a type of angle modulation, where FM is obtained by phase modulation
of the carrier. This means, an instantaneous phase of the carrier directly proportional to amplitude
of the modulating signal.
UNIT II
DIGITAL COMMUNICATION
1. What are the advantages of digital transmission?
The advantages of digital transmission are:
(i). Digital signals are better suited to processing and multiplexing than analog signals.
(ii). Digital transmission systems are more noise resistant than the analog transmission
systems.
(iii). Digital systems are better suited to evaluate error performance.
2. What are the disadvantages of digital transmission?
The disadvantages of digital transmission are:
(i). The transmission of digitally encoded analog signals requires more bandwidth.
(ii). It requires additional encoding and decoding circuitry.
3. Define – Pulse code modulation
Pulse code modulation is defined as the process in which the analog signal is sampled and
converted to fixed length serial binary number. The binary number varies according to the
amplitude of the analog signal.
93
4. What is the purpose of sample and hold circuit?
The purpose of sample and hold circuit is to periodically sample the analog input signal
and converts those samples to a multilevel PAM (Pulse Amplitude Modulation) signal.
5.
State Nyquist sampling rate.
Nyquist sampling rate states that, the minimum sampling rate is equal to twice the highest
audio input frequency.
6. State the causes of fold over distortion.
Fold over distortion states that the minimum sampling rate (f s) is equal to twice the highest
audio input frequency (fa).If fs is less than two times fa, distortion will result.
The side frequencies from one harmonic fold over the sideband of another harmonic. The
frequency that folds over is an alias of the input signal hence, the name “aliasing” or “fold over
distortion”.
7. Define – Overload distortion
Overload distortion is defined as the magnitude of sample which exceeds the highest
quantization interval.
8. Define – Quantization
Quantization is defined as the process of changing the actual values to the standard values.
9. Define – Dynamic range
Dynamic range is defined as the ratio of the largest possible magnitude to the
smallest possible magnitude. Mathematically, dynamic range is
10. Define – Coding efficiency
Coding efficiency is defined as the ratio of the minimum number of bits required
to achieve a certain dynamic range to the actual number of PCM bits used. Mathematically,
11. Define – Companding
Companding is defined as the process in which the higher amplitude analog signals are
compressed prior to transmission, then expanded at the receiver.
12. Define – Slope overload. How is it reduced?
Slope overload is defined as the value of analog signal which is greater than the delta
modulated value.
Slope overload is reduced by increasing the clock frequency and by increasing
the
magnitude of the minimum step size.
94
13. Define – Granular noise. How is it reduced?
Granular noise is defined as the original input signal has relatively constant
amplitude, the reconstructed signal has variations that were not present in the original signal.
Granular noise can be reduced by decreasing the step size.
14. What is adaptive delta modulation?
Adaptive delta modulation is similar to delta Modulation (DM) with the ability to adjust the
slope of the tracking signal. In feedback adaptation, the adaptation is made based on the history of
the quantizer‟s output.
15. Define – Peak frequency deviation for FSK
Peak frequency deviation (f) is defined as the difference between the carrier rest
frequency and either the mark or space frequency.
16. Define - Modulation index for FSK
The modulation index in FSK is defined as
where, h = FM modulation index called the h factor in FSK.
= fundamental frequency of the binary modulating signal.
f = Peak frequency deviation.
17. Define – Bit rate
Bit rate is defined as the number of bits that are conveyed or processed per unit of time.
18. Define – Baud rate
Baud rate is defined as the number of bits transmitted per second.
19. Define – QAM
Quadrature Amplitude Modulation is defined as a form of digital modulation
where digital information is contained in both the amplitude and phase of the transmitted carrier.
20. Write the relationship between the minimum bandwidth required for an FSK
system and the bit rate.
The relationship between the minimum bandwidth required for an FSK system and the bit rate is
given below
where, B = minimum bandwidth (Hertz)
f = minimum peak frequency deviation (Hertz) and
= bit rate
95
21. Define – MSK .
MSK is defined as a special type of continuous phase – frequency shift keying (CPFSK)
where the peak frequency deviation is equal to ¼ of the bit rate and the modulation index.
22. Compare binary PSK with QPSK.
SI. No. BPSK
QPSK
1.
One bit forms a symbol.
Two bits form a symbol.
2.
Two possible symbols.
Four possible symbols.
3
Minimum bandwidth is twice of fb. Minimum bandwidth is equal to fb.
4.
Symbol duration = Tb.
Symbol duration = 2Tb.
23. What happens to the probability of error in M-ary FSK as the value of M increases?
The Euclidean distance between the symbols reduces, as the value of „M‟ increases,.
Hence, the symbols come closer to each other. This increase the probability of error in M-ary
systems.
UNIT III
SOURCE CODES, LINE CODES AND ERROR CONTROL
1. Define – Shannon Entropy
Shannon entropy, which quantifies the expected value of the information contained in a
message. Entropy is typically measured in bits, or bans. Shannon entropy is the average
unpredictability in a random variable, which is equivalent to its information content.
2. Define –Shannon source coding theorem
Shannon's source coding theorem (or noiseless coding theorem) establishes the limits to
possible data compression, and the operational meaning of the Shannon entropy.
Define – Shannon limit
The Shannon limit or Shannon capacity of a communication channel is the theoretical
maximum information transfer rate of the channel, for a particular noise level.
3.
4. Define – Huffman coding
Huffman coding is an entropy encoding algorithm used for lossless data compression. The
term refers to the use of a variable-length code table for encoding a source symbol (such as a
character in a file) where the variable-length code table has been derived in a particular way based on
the estimated probability of occurrence for each possible value of the source symbol.
96
5.
What are the uses of Modified Huffman coding?
Modified Huffman coding is used in fax machines to encode black on white images
(bitmaps). It combines the variable length codes of Huffman coding with the coding of repetitive data
in run-length encoding.
6. Define – Signal to Noise Ratio
Signal to Noise Ratio is defined as the ratio of the strength of an electrical or other signal
carrying information to that of unwanted interference. It is expressed in decibels.
Define – NRZ
Non-return-to-zero (NRZ) line code is a binary code in which 1s are represented by one
significant condition (usually a positive voltage) and 0s are represented by some other
significant condition (usually a negative voltage), with no other neutral or rest condition.
7.
Define – RZ
Return-to-zero (RZ) describes a line code used in telecommunication signals in which the
signal drops (returns) to zero between each pulse. This takes place even if a number of consecutive 0's
or 1's occur in the signal. The signal is self-clocking.
8.
9.
Define Error control coding
Error control coding is a developing methods for coding to check the correctness of the bit
stream transmitted. The bit stream representation of a symbol is called the codeword of that symbol.
10. Mention the types of error control.
The types of error control codes are
i)
Linear Block Codes
ii)
Repetition Codes
iii)
Convolution Codes
11. Define – Linear Block Codes
A code is linear if two codes are added using modulo-2 arithmetic produces a third codeword
in the code. Consider a (n, k) linear block code. Here,
1. n represents the codeword length
2. k is the number of message bit
3. (n - k )bits are error control bits or parity check bits generated from message using an appropriate
rule.
12. Define – Repetition Codes
This is the simplest of linear block codes. Here, a single message bit is encoded into a block
of n identical bits, producing an (n, 1) block code. This code allows variable amount of redundancy. It
has only two codewords – (i) all-zero codeword (ii) all-one codeword.
97
13. Define – convolution Codes
A convolution code is a type of error-correcting code in which Each m-bit information
symbol (each m-bit string) to be encoded is transformed into an n-bit symbol, where m/n is the
code rate and
the transformation is a function of the last k information symbols, where k is the constraint length of
the code.
14. Define – Block Codes
Block codes comprise the large and important family of error-correcting codes that encode
data in blocks. The Block Codes are conceptually useful because they allow coding theorists,
mathematicians, and computer scientists to study the limitations of all block codes in a unified way.
Such limitations often take the form of bounds that relate different parameters of the block code to
each other, such as its rate and its ability to detect and correct errors.
15. Define – Modified AMI Codes.
Modified AMI codes are Alternate Mark Inversion (AMI) line codes in which bipolar
violations may be deliberately inserted to maintain system synchronization. There are several types of
modified AMI codes, used in various T-carrier and E-carrier systems.
16. Define – Shannon Fano coding.
In Shannon Fano coding, the symbols are arranged in order from most probable to least probable, and
then divided into two sets whose total probabilities are as close as possible to being equal. All
symbols then have the first digits of their codes assigned symbols in the first set receive "0" and
symbols in the second set receive "1".
UNIT – IV
MULTIPLE ACCESS TECHNIQUES
1. What is Multiplexing?
Multiplexing is a process of combining several message signals for their
simultaneous transmission over the same channel.
2. Define – Spread Spectrum Modulation
In telecommunication and radio communication, spread-spectrum techniques
are methods by which a signal (e.g. an electrical, electromagnetic, or acoustic signal)
generated with a particular bandwidth is deliberately spread in the frequency domain,
resulting in a signal with a wider bandwidth.
98
3. How are spread spectrum methods classified?
The different types of spread-spectrum methods are BPSK / DSSS QPSK /
DSSS, MSK / DSSS, coherent slow frequency-hop spread spectrum (FHSS), non-coherent
slow-frequency-hop spread spectrum, non-coherent fast frequency-hop spread spectrum, and
hybrid DSSS/FHSS.
4. List the applications of spread spectrum.
Spread spectrum and CDMA are cutting-edge technologies widely used in operational
radar, navigation and telecommunication systems and play a pivotal role in the development
of the forthcoming generations of systems and networks.
5. What are the advantages of SDMA?
[A/M - 12]
SDMA Space Division Multiple Access is a channel access method used in radio
telecommunication systems such as mobile cellular networks. SDMA is based on the creation
of parallel data streams travelling from multiple antennas (also known as spatial
(multiplexing).
6. Mention the applications of multiple access techniques used in wired communication.
Time division multiple access (TDMA) is a channel access method for shared
medium networks. It allows several users to share the same frequency channel by
dividing the signal into different time slots. The users transmit in rapid succession, one
after the other, each using its own time slot. This allows multiple stations to share the
same transmission medium (e.g. radio frequency channel) while using only a part of its
channel capacity.
7. Mention the advantages of CDMA system.
The advantages of CDMA system are:
[N/D - 10]
1. CDMA employs spread-spectrum technology and a special coding scheme (where
each transmitter is assigned a code)
2. CDMA is used as the access method in many mobile phone standards such as
cdmaOne, CDMA2000 (the 3G evolution of CDMAOne), and WCDMA (the 3G
standard used by GSM carriers), which are often referred to as simply CDMA
8.
What is FDMA?
Frequency Division Multiple Access or FDMA is a channel access method used
in multiple-access protocols as a channelization protocol. FDMA gives users an
individual allocation of one or several frequency bands, or channels. It is particularly
common place in satellite communication. FDMA, like other Multiple Access systems,
coordinates access between multiple users.
99
9. Define – Time Division Multiplexing
Time-division multiplexing (TDM) is a method of transmitting and receiving
independent signals over a common signal path by means of synchronized switches at
each end of the transmission line so that each signal appears on the line only a fraction of
time in an alternating pattern.
10. Distinguish between TDMA and FDMA
TDMA :
Time division multiple access (TDMA) is a channel access method for shared
medium (usually radio) networks. It allows several users to share the same frequency
channel by dividing the signal into different time slots
FDMA:
Frequency Division Multiple Access or FDMA is a channel access method used
in multiple-access protocols as a channelization protocol. FDMA gives users an
individual allocation of one or several frequency bands, allowing them to utilize
the allocated radio spectrum without interfering.
11. What are the advantages and the disadvantages of FDMA?
The advantages and the disadvantages of FDMA are :
FDMA or Frequency Division Multiple Access, allows users to access a single channel,
through a shared frequency; this system is advantageous as it is run through a satellite and
offers users the chance to share a channel easily without time delays.
The disadvantage of FDMA is the expense of running the system, which requires
costly, custom filters and other technical equipment.
12. What is CDMA?
Code division multiple access (CDMA) is a channel access method used by various
radio communication technologies
CDMA is an example of multiple access, which is where several transmitters can send
information simultaneously over a single communication channel. This allows several
users to share a band of frequencies.
13. What are the disadvantages of CDMA?
The disadvantages of CDMA are:
1. As the number of users increases, the overall quality of service decreases
2. Self-jamming
3. Near- Far problem arises
100
14. What is space division multiple access (SDMA)?
Space Division Multiple Access (SDMA) is a channel access method based on
creating parallel spatial pipes next to higher capacity pipes through spatial multiplexing and
diversity, by which it is able to offer superior performance in radio multiple access
communication systems
15. What are the differences between FDMA, TDMA and CDMA?
CDMA :
1. Same frequency is used by every user and simultaneous transmission occurs.
2. Every narrowband signal is multiplied by wideband spreading signal, usually known as
codeword Every user has a separate pseudo-codeword, i.e., orthogonal to others only the
desired codeword is detected by the receivers and others appear as noise. It is mandatory
for the receivers to know about the transmitter‟s codeword.
FDMA :
1. Bandwidth of Channel is relatively narrow (30 KHz), known as narrowband system Little
or no equalization is needed for spreading symbol time.
2. Framing or synchronization bits are not needed for continuous transmission.
TDMA :
1. All slots are assigned cyclically.
2. Overhead tradeoffs are size of data payload and latency.
UNIT-V
SATELLITE, OPTICAL FIBER-POWERLINE, SCADA
1. Define Geo synchronous satellite?
Geo synchronous or geo stationary satellites are those that orbit in a circular pattern with
an angular velocity equal to that of Earth. Geosynchronous satellites have an orbital time of
approximately 24 hours, same as the earth thus geosynchronous satellites appear to be stationary
as they remain in a fixed position in respect to a given point on earth.
2.
State Snell‟s law.
The angle of refraction can be larger smaller than the angle of incidence, depending on the
refractive indexes of the two materials. Snell‟s law stated mathematically is
N1 sinФ1 = N2 sinФ2
where
N1- refractive index of material1
N2-refractive index of material2
Ф1- Angle of incidence
Ф2 - Angle of refraction
101
3. Write about the uplink and downlink frequencies used in satellite communication system.
Transmissions from base station to mobile units are called forward links, whereas
transmissions from mobile units to base station are called reverse links. Forward links are called
uplinks.
4. Define
Angle of inclination of satellite orbit
The angle of inclination is the angle between the earth equatorial plane and the orbital
plane of a satellite measured counterclockwise at the point in the orbit where it crosses the
equatorial plane traveling from south to north
5.
What is Geosynchronous satellite?
Geosynchronous satellite provides a ‟Big picture‟, view, enabling coverage of
weather events. This is especially useful for monitoring severe local storms and tropical
cyclones.
6. What is meant by Apogee and Perigee?
The distance of the satellite from the earth varies according to its position. Typically
two points of greatest interest are the highest point above the earth – the Apogee and the
lowest point –the Perigee
7. Define – Look angles of a satellite
The coordinates to which the earth station antennas must be pointed to communicate
with the satellite is called look angles.
8. List any two advantages and disadvantages of Geosynchronous satellite.
The Advantages of Geosynchronous satellite:
Satellites have revolutionized global communications, television broadcasting and weather
forecasting and have a number of defence applications.
The Disadvantages of Geosynchronous satellite:
1. High altitude.
2. Incomplete Geographical coverage.
9. Define –Numerical Aperture
The Numerical Aperture of an optical system is a dimensionless number that characterizes
the range of angles over which the system can accept or emit light.
10. Expand and define EIRP.
In communication systems, Equivalent Isotropically Radiated Power (EIRP) is the amount of
power that a theoretical isotropic antenna would emit to produce the peak power density
observed in the direction of maximum gain.
102
11. State the advantages of fiber optic system.
The advantages of fiber optic system are :
1. Less expensive
2. Less signal degradation
3. Higher carrying capacity
4. Low power
5. Light weight
12. Define – Critical angle in optical fibers
The Critical angle (minimum angle for total internal reflection) is determined by the
difference in index of reflection between the core and cladding materials.
13. Define- Single mode fiber
A single mode optical fiber is an optical fiber designed to carry the light only directly
down the fiber .
14. What is SCADA?
SCADA (Supervisory Control And Data Acquisition) is a system operating with
coded signals over communication channels to provide control of remote equipment.
15. What are the advantages of optical fiber communication?
The advantages of optical fiber communication are:
1. Greater information capacity
2. Immunity to crosstalk
3. Immunity to static
4. Interference Environmental
5. Immunity Safety
6. Security
16. Define – Critical angle
Critical angle is defined as the minimum angle of incidence at which a light ray may strike
the interface of two media and result in an angle of refraction of 0°or greater.
17. Define – Single Mode and Multimode propagation
Single mode propagation is defined as the only one path through which the light propagates
down the cable.
Multimode propagation is defined as the light propagates down the cable through one or more
path.
103
18. What are the disadvantages of injection laser diode?
The disadvantages of injection laser diode are :
ILDs are typically on the order of 10 times more expensive than LEDs because ILDs
operate at higher powers, they typically have a much shorterlife time than LEDs. ILDs are
more temperature dependent than LEDs.
19. Define – Modal Dispersion
Modal dispersion or pulse spreading is caused by the difference in the propagation times of
light rays that take different paths down a fiber. Modal dispersion can occur only in multimode
fibers. It can be reduced by using single mode step index fibers and graded index fibers.
20. Define – Angle of elevation
Angle of elevation is the vertical angle formed between the direction of travel of an
electromagnetic wave radiated from an earth station antenna pointing directly toward a satellite
and the horizontal plane.
21. Define – Azimuth angle
Azimuth is the horizontal angular distance from a reference direction, either the southern or
northern most point of the horizon.
© Copyright 2024