1.6 Op-Amp Basics
 Basic Op-Amp
Op-amp equivalent circuit
1
Practical (Ri = high , Ro = small)
Ideal (Ri =∞ , Ro = 0)
1.6 Op-Amp Basics
 Basic Operation of Op-Amp

input voltage at minus (-)
 input voltage at plus (+)
output voltage opposite in phase
output voltage in phase
 Basic Op-Amp - Constant-gain multiplier
 Input signal is applied
through resistor Ri to the
minus input
 Output is connected to
the same minus input
through resistor Rf
Inverting constant gain multiplier
 Resulting output:
opposite in phase to input
2
signal
1.6 Op-Amp Basics
 Basic Op-Amp - Constant-gain multiplier
Op-amp ac equivalent circuit
3
1.6 Op-Amp Basics
 Basic Op-Amp - Constant-gain multiplier
Ideal Op-amp equivalent circuit
Redrawn equivalent circuit
(for circuit analysis)
4
1.6 Op-Amp Basics
 Basic Op-Amp - Constant-gain multiplier
Using Superposition
theorem
i) V1 only (set –AvVi =0)
Vi1 
Rf
R1  R f
V1
ii) –AvVi only (set V1 =0)
R1
 AvVi 
Vi 2 
R1  R f
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1.6 Op-Amp Basics
 Basic Op-Amp - Constant-gain multiplier
Vi  Vi1  Vi 2 
Vi 
Vi 
Rf
R1  R f
V1 
Rf
R f  (1  Av ) R1
Rf
Av R1
R1
 AvVi 
R1  R f
V1
V1
R f V1
Vo  AvVi  Av R f V1



Vi
Vi
Vi Av R1
R1 Vi
Rf
Vo

V1
R1
It is shown that the ratio i/o depends only on the value of Rf and R1
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1.6 Op-Amp Basics
 Basic Op-Amp - Unity Gain
If Rf = R1
Rf
Vo

 1
V1
R1
 Basic Op-Amp - Constant Gain
If Rf = 10R1
Rf
Vo

 10
V1
R1
Gain with negative sign
shows that the output
voltage has undergone
180º phase inversion
from input signal
 If we select precise values for Rf and Ri, we can obtain a wide
range of gains
 Gain accuracy depends on resistors used
 Gain is slightly affected by temperature & other circuit factors
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1.7 Practical Op Amp Circuits
 Inverting Amplifier
Inverting constant gain multiplier
Rf
V0

V1
R1
 Non-inverting Amplifier
Non-inverting constant gain multiplier
Rf
V0
 1
V1
R1
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1.7 Practical Op Amp Circuits
 Non-inverting Amplifier
Non-inverting constant-gain multiplier
Since Vi = 0, using voltage divider rule,
R1
V1 
V0
R1  R f
Equivalent circuit
Which results in;
Rf
V0 R1  R f

 1
V1
R1
R1
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1.8 Data Sheet
LM741
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1.8 Data Sheet
LM741
ABSOLUTE MAXIMUM
RATINGS
 Supply voltage = +22V
 Internal power
dissipation = 500mW
 Differential input
voltage = + 30V
 Input voltage = + 15V
ELECTRICAL
CHARACTERISTICS
Input offset voltage
Input offset current
Input bias current
Input resistance
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1.8 Data Sheet
LM741
ELECTRICAL
CHARACTERISTICS
Large signal voltage
gain
Output voltage swing
Output short circuit
current
Supply voltage
rejection ratio
Bandwidth
Slew rate
Supply current
Power consumption
12
1.8 Data Sheet
LM741
13
1.8 Data Sheet
LM741
14
1.8 Data Sheet
LM741
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