Download 952 EE Quiz 01 ID#: Name:

1. For the following single stage CS amplifier with
 n C oxW
2L
 2 mAV 2 and
Vtn  1,V A  100 , evaluate the following：(30%)
(a) The g m parameter. (5%)
(b) The input and output resistances Ri
(c) The voltage gain Av  vo v
i
Am 
vo
vs
R s  1k
RL 
Rs  0
and Ro
RL  
.(5%)
and the midband voltage gain
.(5%)
R L  2k
(d) If the high frequency equivalent model of MOSFET is given as
following, find the upper corner frequency  H . (5%)
(e) The corner frequency C1 , C 2 and CS . with C1  10F , C2  20F and
C S  10F
(7%)
(f) Sketch the Bode diagram
C gd  1 pf
G

12V
D
g m v gs
v gs

C gs  10 pf
vo
.(3%)
vi
vs
120k
Rs
CC1
S
1
68k
CS
3k
vo
CC 2
RL
2. (20 %) For the following single stage MOSFET amplifier with
 n Cox  200A / V 2 , L  1m , W  1m and VTP  0.8, VA  100
(a) Determine the DC drain currents I D , g m and ro of MOSFET. (5 %)
(b) Find the small signal voltage gain Avo 
vo
. (5 %)
vi
(c) Find the small signal current gain Ais 
io
. (5 %)
ii
(d) Find the input and output resistance Ro and Ri . (5 %)
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3. (20 %) Consider the following system, sketch the Bode diagram.
Vo (s)
 1000s(s  50)

Vi (s) (s  1)( s  20)( s  1000)
0.1
0.1
1
1
10
10
102
102
3
104
105
104
105
4-1. Consider the following ideal operational amplifier circuit.
(a) Find the output function Vo  f (V1 ,V2 ) .(5%)
(b)What is the strategy can change the circuit to be a differential Amp.
(i.e. Vo  f (V1  V2 ) ) .(5%)

V1
V2
Vo

R1

R2

R3
R4
4-2 Consider the following Op-Amp difference amplifier.
(a) Find the differential input resistance. (3%)
(b) Find vo  f (v1 , v2 , v3 ) (7%)
R2
R1
v1

10k

v2
R1
1k

v3
R2

90k
4
vo
5. True and False (20 %)
(a) The transfer function H ( s) 
s
b
(in the case of b>>a)
sa sb
represents a high-pass circuit.
(b) In the Bode diagram the transition frequency signifies the voltage
gain falls to 0dB, therefore we also call it the half power frequency.
(c) The output signal of a differential amplifier is
vo (t )  Ad (v1  v2 )  Acm vicm , in which the vicm represent the
common mode input. The voltage gain
Ad
and
Acm
should be as
big as possible.
(d) The right side MOSFET circuit is a bad biasing
scheme, since the Drain current will varying
depend on the device and environment.
(e) Coupling and bypass capacitors affect the high frequency
characteristics of an amplifier. In general, capacitance values in the
F range typically result the lower cut-off frequency in the tens of
MHz range.
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(f) The transition frequency imply the highest speed characteristic of
a MOSFET . This phenomena can be modeled by two internal
capacitors C gs and C gd and f T 
1
.
2 (C gs  C gd )
90k
10k
(g) Consider the ideal OPA amplifier
circuit, the voltage gain is
vi

vo
90k
 (1 
).
vi
10k
vo

10k
(h) Virtual short or ground is a concept based on the open-loop gain
of an OPA tends to infinite.
(i) According to the
Miller’s theorem,
z1  z(1  k ) and
z 2  z /(1  k ) in which
k
v1
V1
Z
i2
i1
i2
i1
V2
V1
Z1 Z 2
V2
v2 .
(j) Use an op-amp IC (e.g. uA741) to design a voltage amplifier is much
easy than others transistor amplifier, since we don’t need to trade
the DC biasing problem.
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