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1. (30 points) Consider the following feedback amplifier, the
transistors parameters are: h fe  50 , VA   .
10V
Using he feedback analysis method to find
(a) the feedback topology
v
40k
10V

2k
RL  1k
s
and the feedback network 
Rs  10k
parameters. (4 points)
(b) the amplifier gain A, the input and
output resistance Ri and Ro . Sketch the
open-loop small signal circuit. (15 points)
io
0.2mA
 10V

1k

10k
(c) the closed loop gain A f , the input /output resistance Rif and Rof (6
points)
(d) the input /output resistance Rin and Rout that exclude Rs and RL .
Sketch the overall equivalent circuit. (5 points)
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vo
2. (30 points) Consider the following MOSFET feedback amplifier, the
transistors parameters are: g m1  g m2  0.5mA / V , VA   , ,Using the
16V
16V
feedback method to find
(a) the feedback topology and the feedback
2k
2k
network  parameters. (4 points)
(b) the amplifier gain A, the input
vs

C1
Rs  0.1k
and output resistance Ri and Ro .
Sketch the open-loop small signal circuit. (15
points)
10k
RL  1k

1mA
(c) the closed loop gain A f , the input /output
100k
10k
resistance Rif and Rof (6 points)
(d) the input /output resistance Rin and Rout that exclude Rs and RL .
Sketch the overall equivalent circuit. (5 points)
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vo
2. 3. (10 points) Consider the following negative feedback amplifier. The
bode diagram shows the open loop amplifier frequency response.
(a) Find the closed loop gain A f (2
(b) Find the closed loop frequency
points)
vo
vi
A
response  Lf and  Hf . (4 points)
(c) Why we need to construct a
feedback amplifier? (4 points)
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
L
H
 10V
4. (22 points) Consider the differential amplifier
shown in the following figure. The transistor
kn' W
parameters are :
 0.1mA / V 2 . (for Q1 to Q4)
2L
 10V
Q3
Q4
vo
k n' W
 0.4mA / V 2 . (for Q5 and Q6), ,and for all
2L
v1
transistors VA  100 , Vt  1V .
Q1
v2
Q2
 10V
a. Determine the resistance R=? if the biasing
R
current of Q1 and Q2 are I Q  2mA .(3 points)
b. Determine the maximum voltage of the
common-mode input voltage. (3 points)
c. Determine the minimum voltage of the
common-mode input voltage. (3 points)
Q5
Q6
 10V
d. Find the differential gain Ad .(5 points)
e. Find the input and output resistance of the differential mode. (3
points)
f. Find the common mode gain Aicm .(5 points)
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5. (18 points) Give a logic reason to explain why the following statements
are false or true.
(i) The right side figure present a
Series-Shunt feedback amplifier,
the feedback network has to
represent in hybrid h-parameters.
(ii) The input offset current of the
MOSFET differential pair contributes by mismatching the load
resistances, mismatching in W/L, and mismatching in the threshold
voltage Vt.
(iii) It is not necessary to use the input coupling capacitor in the BJT’s
differential amplifier, since the differential pair input can reject the
differential mode input.
(iv) The right side figure present a
Series-Shunt feedback amplifier, the
feedback network has to represent
in inverse hybrid g-parameters.
(v) The sensitivity and bandwidth reduction is one of the most attractive
features of negative feedback.
(vi) A emitter resistance RE for a BJT’s differential pair can reduce the
linear operation range but increase the differential gain Aid .
(vii) For a MOSFET differential amplifier, a too small common mode input
voltage vicm will drive the differential pair transistors working in the ohm’s
mode.
(viii)For a BJT differential amplifier, the common mode input voltage can
not be too high; this voltage may result in the current mirror source
shutdown.
(ix)In the case of the input noise are much bigger than input signal, we
can use a feedback voltage amplifier to reduce the noise effect.
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