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EE 330
Exam 2
Spring 2015
Name_ _ _ _ _ _ _ _ _ _ _ _ _ _
Instructions: This is a 50-minute exam. Students may bring 2 pages of notes (front and
back) to this exam. The points allocated to each question and each problem are as
indicated. Please solve problems in the space provided on this exam and attach extra
sheets only if you run out of space in solving a specific problem.
If references to semiconductor processes are needed beyond what is given in a
specific problem or question, assume a CMOS process is available with the following key
process parameters; µnCOX=100µA/v2 ,µpCOX=µnCOX/3 ,VTNO=1V,VTPO= - 1V,
γ =0.4V-1/2, , ϕ=0.6V, COX=2fF/µ2 , and λ = 0. If reference to a bipolar process is
made, assume this process has key process parameters JS=10-15A/µ2, β=100 and VAF = ∞.
The ratio of Boltzmann’s constant to the charge of an electron is k/q= 8.61E-5 V/K. If
any other process parameters are needed, use the process parameters associated with the
process described on the attachments to this exam. Specify clearly what process
parameters you are using in any solution requiring process parameters. Also attached to
this exam is a table that has information about large and small signal models of devices.
1. (2pts)
We developed the small-signal model of a 3-terminal device in terms of
the small-signal parameters y11,y12,y21, and y22 but then used parameters such as gm and
go in the small-signal models of the MOSFET and BJT. Why did we use these
parameters rather than the y parameters?
2. (2pts)
Why is the power dissipation in a Triac relatively small even when it is
used to switch very large currents?
3. (2pts)
Give the two major reasons the β of the lateral pnp transistor in a standard
bipolar process is much less than that of the vertical npn.
4. (2 pts)
What is the major processing step in a bipolar process that makes the size
of the bipolar transistor so big?
5. (2pts)
What is the major difference between an SCR and a Triac?
Page 1 of 10
6. (2pts)
load line?
Why is the Q-point of an amplifier often placed near the middle of the
7. (2pts)
Three different regions of operation were identified for the bipolar
transistor. Why did we focus on developing the small-signal model of the BJT in the
forward active region rather than in one of the other two regions of operation?
8. (2pts)
When designing an amplifier with either MOS transistors or BJTs, some
circuitry is usually added to establish the Q-point at the desired location. There is a name
for this extra circuitry that is used for establishing the Q-point. What is this extra
circuitry called?
9 (2pts)
Why is it necessary to calculate the Q-point when determining the
numerical value of the small signal voltage gain for transistor amplifiers even if it is
known that all MOS transistors are operating in the saturation region and all BJTs are
operating in the forward active region?
10 (2pts)
What region of operation in the MOS process corresponds to the
saturation region of operation in a Bipolar process?
Page 2 of 10
Problem 1
(16 pt) Consider the following circuit
a) Determine RB so that VOUTQ=3V
b) Determine the voltage gain with VOUTQ=3V
c) If RB is changed so that VOUTQ=11V, determine the voltage gain and compare
with that obtained in part b)
12V
5K
RB
VOUT
C1
Q1
VIN
Page 3 of 10
Problem 2 (16 pts) Though Triacs are often used to switch loads, MOS transistors also
make good switches. In the following circuit, a 25W, 12V lamp is to be switched with a
MOS device. The MOS transistor gate is driven with a 2-transistor CMOS inverter
biased with a 3.5V dc voltage relative to ground and the Boolean input, VCONT ,is used to
turn the lamp on and off. Assume the lamp can be modeled as a resistor characterized by
the 25W, 12V specification.
a) If the voltage across the lamp is to be 11.5V when it is turned on, determine the
width of the MOS switch transistor required if L=2um.
b) What is the power dissipation in the MOS switch when the lamp is ON and when
it is OFF?
12Vdc
25W
Lamp
VCONT
Page 4 of 10
Problem 3 (16 pts) Consider the following circuit where the capacitor C is very large.
a) Determine the W so that the quiescent drain voltage, VD, is 0V
b) Draw the small-signal equivalent circuit
c) Determine the small-signal voltage gain
2V
10K
VD
VIN(t)
L=2µ
W=?
C
VOUT
10K
-2V
Page 5 of 10
Problem 4 (16 pts)
The nonlinear 3-terminal device is characterized by the equations
I1 = 5V13
(
I2 = V1 • 1 + 2V22
)
I2
I1
V1
Threeterminal
Device
V2
a) Determine the small-signal model if the quiescent voltages are V1Q=2V,
V2Q=1V
b) Determine the quiescent currents I1Q and I2Q if the quiescent voltages are as
specified in part a)
c) If the circuit is biased so that the small signal input voltage is applied directly
to the input terminal and if the small signal load is a 5Ω resistor, determine the
small signal voltage gain. Assume the same quiescent voltages as specified in
part a)
Page 6 of 10
Problem 5 (16 pts) Draw the small-signal equivalent circuit for the following amplifier
structure. Assume all capacitors are large. Do not solve.
8V
500K
C1
5K
2K
M1
C2
AE=100µ
Q1
VIN
30uA
2
Q2
VD
10K
200K
VOUT
10K
Page 7 of 10
TRANSISTOR PARAMETERS
MINIMUM
Vth
3.0/0.6
SHORT
Idss
Vth
Vpt
20.0/0.6
WIDE
Ids0
20.0/0.6
LARGE
Vth
Vjbkd
Ijlk
Gamma
50/50
W/L
N-CHANNEL P-CHANNEL UNITS
-0.93
volts
439
0.69
10.0
-238
-0.90
-10.0
uA/um
volts
volts
< 2.5
< 2.5
pA/um
0.70
11.4
<50.0
0.50
-0.95
-11.7
<50.0
0.58
volts
volts
pA
V^0.5
56.9
474.57
-18.4
153.46
uA/V^2
cm^2/V*s
N+ACTIVE
>15.0
P+ACTIVE
<-15.0
K' (Uo*Cox/2)
Low-field Mobility
0.78
COMMENTS: XL_AMI_C5F
FOX TRANSISTORS
Vth
GATE
Poly
PROCESS PARAMETERS
N+ACTV P+ACTV POLY
Sheet Resistance
82.7 103.2 21.7
Contact Resistance
56.2 118.4 14.6
Gate Oxide Thickness 144
PROCESS PARAMETERS
Sheet Resistance
Contact Resistance
MTL3
0.05
0.78
PLY2_HR
984
N\PLY
824
UNITS
volts
POLY2
39.7
24.0
N_WELL
815
MTL1
0.09
MTL2 UNITS
0.09 ohms/sq
0.78 ohms
angstrom
UNITS
ohms/sq
ohms
COMMENTS: N\POLY is N-well under polysilicon.
CAPACITANCE PARAMETERS N+ACTV P+ACTV
Area (substrate)
429
721
Area (N+active)
Area (P+active)
Area (poly)
Area (poly2)
Area (metal1)
Area (metal2)
Fringe (substrate)
311
256
Fringe (poly)
Fringe (metal1)
Fringe (metal2)
Overlap (N+active)
Overlap (P+active)
POLY
82
2401
2308
POLY2
M1
32
36
M2
17
16
M3
10
12
864
61
53
17
9
34
13
32
39
28
32
48
74
53
206
278
Page 8 of 10
58
40
55
N_WELL
40
UNITS
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um^2
aF/um
aF/um
aF/um
aF/um
aF/um
aF/um
Page 9 of 10
Page 10 of 10