U
niversity of
S
outhern
C
alifornia
USC Viterbi School of Engineering
Ming Hsieh Department of Electrical Engineering
EE 541:
Homework Assignment #01-02
Fall, 2010
Due: 09/09/2010
Choma
Problem #01:
The model shown within the symbolic network “box” in Figure (P1) is a
linearized equivalent circuit of an emitter-degenerated, common emitter amplifier.
The ampli-
fier is driven by a voltage source whose Thévenin resistance is
R
s
, and its load termination con-
sists of a resistance,
R
l
in shunt with a capacitance,
C
l
.
In this problem,
R
s
= 50
Ω
, R
l
= 1.2 K
,
R
e
= 120
, and
C
l
= 300 fF
.
The transistor model parameters are
r
b
= 90
, r
π
= 2.8 K
, r
o
=
25 K
, and
β
= 120 amps/amp
.
β
I
+
−
V
s
R
s
R
e
r
b
r
π
C
l
R
l
I
r
o
I
2
V
2
I
1
V
1
R
out
R
in
Figure (P1)
(a).
Derive analytical expressions for each of the four h-parameters of the degenerated common
emitter amplifier.
(b).
Using the h-parameter expressions deduced in Part (a), derive analytical expressions for
the low frequency, open loop values of voltage gain,
V
2
/V
s
, input resistance,
R
in
, and output
resistance,
R
out
.
(c).
Using the h-parameter expressions deduced in Part (a), derive an analytical expression for
the low frequency loop gain of the amplifier.
Discuss the influence that the emitter degen-
eration resistance,
R
e
, has on this loop gain.
(d).
Using appropriate preceding results, compute numerical, low frequency values for:
i.
the open loop input resistance;
ii.
the driving point input resistance;
iii.
the open loop output resistance;
iv.
the driving point output resistance;
v.
the loop gain;
vi.
the open loop voltage gain;
vii.
the closed loop voltage gain.
(e).
Can the analytical expressions for the closed loop voltage gain deduced in Part (b) and the
loop gain deduced in Part (c) be adequately approximated by relatively simple algebraic