EE 461G Review Problems for the Final Exam
Print your name. You must show your work to receive partial credit. You may bring a piece of
paper with formula, a calculator, a ruler, a pencil, and an eraser.
Problem 1 Draw the small-signal models for BJT and FET including both DC and AC
components. Label components, current, and voltage.
1
Problem 2 Approximately draw transfer characteristics of circuits (a) and (b) separately and
their output voltage in the space below. Point out which one is a rectifier and which one is a
clipping circuit? (Vf=0.7V)
R=2 k
D1
+
+
vIN
+
vout
D1
+
vIN
vout
R=10 k
–
–
–
–
(a)
(b)
Vout (V)
Vout
2
VIN
1
vIN
1
2
3
4
5
6
-1
-2
Transfer characteristics for (a)
Vout for (a)
Vout (V)
Vout
2
VIN
1
1
vIN
2
3
4
5
6
-1
-2
Transfer characteristics for (b)
Vout for (b)
2
Problem 3 A bipolar junction transistor amplifier with a incremental signal gain o of 100 is
shown below. (a) What type of the DC bias does this circuit have? (b) Find the DC voltage VB
from the base B to the ground; (c) The ac signal voltage vb from the base B to the ground; (d) the
output ac signal vout.
VCC =9V
RC =2k 
R1 =2k 
C
VB+vb
vs=2sint
+
iB
Vout
B
R2 =1k 
iC
-
E
iE
RE =1k 
3
Problem 4 An n-channel enhancement-mode MOSFET is connected to the circuit as shown
below. The I-V characteristic of the transistor is also shown below. (VTR=1V)
(a) Write the equation for the load line and draw the load line on the I-V curves to find the
operating point A. What is the operating region?
(b) If RL=0.4 k is connected to the output (or D and S), write the equation for the load line and
draw the load line on the I-V curves to find the operating point B. What is the operating
region?
VDD =4V
iD(mA)
RD =0.4k 
D
vs
+
–
G
V1=2.5V
iD
S
10
+
8
Vout
6
VGS=3V
2.5V
-
4
2V
2
0
0
1
2
3
4
1.5V
VDS(V)
4
Problem 5 An n-channel enhancement-mode MOSFET is connected to the circuit as shown
below. (VTR=1V) The I-V curves are shown below.
(a) Using the MOSFET model and the I-V curves below to calculate K approximately.
(b) Using the results in Problem 4 (a) to find the transconductance gm.
(c) Using the small-signal model to find output signal vout when vs= Sin(t) V.
VDD =4V
iD(mA)
RD =0.4k 
D
vs
+
–
G
V1=2.5V
iD
S
10
+
8
Vout
6
VGS=3V
2.5V
-
4
2V
2
0
0
1
2
3
4
1.5V
VDS(V)
5