Topic :
SMALL SIGNAL TRANSISTOR CIRCUIT
Assignment 1
1.
Fig. P.1 shows a transistor amplifier circuit. Find the voltage gain, AV = Vo / Vi ; input
resistance, Ri; output resistance, Ro of the amplifier. If a large capacitor is used to
shunt across RE , what will be its effect on the voltage gain, input resistance and output
resistance?
VCC
R1
RC
5K
C
VO
C
Vi
Q1
Ro
Ri
R2
  100
RE
100
r  1 k
VA  
2.
Fig. P.1
For the two-stage cascaded amplifier circuit shown in Fig. P.2,
(a) identify the transistor configuration for the first and the second stage,
(b) draw the approximate small-signal equivalent circuit for the cascaded amplifier,
(assuming at VA =  )
(c) assuming that  = 100, r = 2k for both transistors, calculate:
the overall voltage gain, AV = Vo / Vi
i.
the overall current gain, AI = Io / Ii
ii.
the input resistance, Ri
iii.
iv. the output resistance, Ro
VCC
R3
90K
R1
100K
Io
RC
2K
C3
Ii
VO
Q1
RS
Vi
Q2
C1
C2
Ro
R2
120K
VS
Ri
RE1
5K
R4
10K
RE2
500
CE
Fig. P.2
3.
For the amplifier in Fig. P.3, given that the
transistors are identical and having  = 200,
VA = 120V. Each transistor is biased at
I C  I E  1 mA .
+12 V
3 k
vo
Find the hybrid- model for the transistors.
Draw the small-signal equivalent circuit for
the amplifier circuit.
Q1

Q2
vi

2 mA
12 V
4.
For the NMOS amplifier in Fig. P.4, replace
the transistors with hybrid- model with gm
and ro. Derive the expressions for the
v
v
voltage gains s and d .
vi
vi
vd
vs
Fig. P.4
5.
Fig. P.5 shows an IC MOS amplifier formed
by cascading two common-source stages.
Assuming the biasing current sources have
very high output resistance, find an
expression for the overall voltage gain in
I
Q2
vi
terms of gm and ro of Q1 and Q2.
vo
Q1
I
Fig. P.5
***END***