# 2021 review question Analog Electronics

```Review question 2021.06
1、
（10 points）
For the circuits shown in Figure 1(a)，vs＝10sinwt（V）. For the diode Vγ= 0.7V,
Sketch the waveform of vL。
vS
10V
π
O
2π
4π
3π
ωt
vL
＋
D4 D1
vS
＋
D3 D2
－
RL
O
vL
π
2π
4π ωt
3π
－
（a）
（b）
Figure 1
2.．
（22 points）
For the circuit in Figure 2, let β=100, VBE(on)=0.7V ,VA=100V, all the capacitors are
assumed to act as short circuits at the signal frequency.
① Calculate the Q-point (IB, IC, VCE);
② Sketch the small-signal equivalent circuit;
③ Determine the input resistance Ri=vI/is;
④ Determine the small-signal voltage gain Av=vO/vI and Avs=vO/vs;
⑤ Determine the output resistance Ro.
VCC
Rb1
27k
C1
Rs
10k
＋
vs
－
is
20uF
vI
Rb2
15k

C2
+
20uF
2.2k
+
+
9V
Rc
T
RL
2k
Re
1.2k
Figure 2

+
io
+ Ce
100uF
vO

3．
（22 points）
For the circuit in Figure 3, for transistor T2, β is known, VA=∞, for transistor T1, gm is
known, and λ=∞, all the capacitors are assumed to act as short circuits at the signal
frequency.
① Sketch the small-signal equivalent circuit;
② Determine the expression of the input resistance Ri=vI/ii;
③ Determine the expression of the small-signal voltage gain Av=vO/vI ;
④ Determine the output resistance Ro.
Figure 3
4.
Score

5.（2 problems, a total of 16 points）
1) For the circuit in Figure 3-1, assume all the op-amps are ideal, Determine the output
voltage VO.
Figure 3-1
2) For the circuit in Figure 3-2, assume all the op-amps are ideal, VBE = 0.7V when BJT is
in turn-on.
（1）Determine the voltages at node c, b and e ;
（2）When two BJT are connected in the circuit one after another, the voltmeter readings
is 200mV . Determine the β of the BJT.
R3
c
R1
+10V
5k
+
+5V
A1
20k
b
T
A2
e
vO
+
R2 5k
R
V
Figure 3-2
Score
4.（10 points）
The Zener diode voltage in Figure 4 is VZ = 6V and minimum current is Izmin=5mA, VI
=12V, R=100Ω.
（1）Determine the maximum value of IL;
（2）What is maximum power dissipation of DZ at least ?

Figure 4
Score
5.（18 points）
For the circuit in Figure 5, let β=40, VBE = 0.7V, all the capacitors are assumed to act as
short circuits within the passband.
(1) Determine Q-pint (IBQ, ICQ, VCEQ);
(2) Sketch the small-signal equivalent circuit of the amplifier;
(3) Within the passband, determine the voltage gain Av=vo/vi 、input resistance Ri and
source voltage gain Avs = vo / vs .

+
vi
Figure 5

Score
6.（3 problems, a total of 21 points）
1）For the circuit in Figure 6-1, assume MOSFET is biased in the saturation region and
gm= 2 mS, all the capacitors are assumed to act as short circuits within the passband..
（1）The small-signal voltage gain |Av| =___________；
+10V
A. 10
B. 20
C. 100
Rd
（2）The output resistance Ro =___________ k。
10k
C1
+
A. 5
B. 10
C. 20
+
R L vo
T
10k +
vi
+
Cs
Rs
VGG
Figure 6-1
3）For the circuit in Figure 6-3, | VCES | is the saturation voltage drop of T1 and T2, the
maximum possible power that can be delivered to RL is Pom =____B_______。
A.
V CC2
RL
V CC2
C.
8R L
B.
(V CC  | V CES | )2
2R L
V CC
(
D.
2
+VCC
vi
 | V CES | )
T1
C
2
T2
2R L
－VCC
Figure 6-3

RL

vo
Score
7.（1 problems, a total of 10 points）
For the circuit in Figure 7-1, let the differential-mode voltage gain is 100 in one-sided
output and the CMRR is 40dB. If vs =20mV, then:
（1）the differential-mode input voltage vid =_C_, the common-mode input voltage vic
=__B;
A. 5mV
B. 10mV
C. 20mV
D. 40mV
（2）the output voltage vo =_D__ that caused by vs.
A. 2V
B. 2.1V
C. 2.01V
D. 1.99V
+VCC
Rc
Rc
vO
T1
T2
+
vs
IO
ro
-VEE
Figure 7-1

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