EE 541
University of Southern California Viterbi School of Engineering
Choma
Solutions, Homework #01
5
Fall Semester, 2011
U
U
U
niversity of
S
S
S
outhern
C
C
C
alifornia
USC Viterbi School of Engineering
Ming Hsieh Department of Electrical Engineering
EE 541:
Solutions, Homework #01
Fall, 2011
Due: 08/31/2011
Choma
Solutions
−
Problem #01:
The model shown within the symbolic network “box” in Figure (P1) is a small signal, and
therefore linear, equivalent circuit of an emitter-degenerated, common emitter amplifier.
The
amplifier is driven by a voltage source whose Thévenin resistance is
R
s
, and its load termination
consists of a resistance,
R
l
in shunt with a capacitance,
C
l
.
In this problem,
R
s
= 50
, R
l
= 1.2
K
, R
e
= 120
, and
C
l
= 300 fF
.
The transistor model parameters are
r
b
= 120
, r
= 3.3 K
,
r
o
= 18 K
, and
= 220 amps/amp
.
I
V
s
R
s
R
e
r
b
r
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.
In the network box delineated in Figure (P1), the input port current,
I
1
, is identical to the branch
current,
I
, whence the controlled current satisfies
I
≡
I
1
.
The hybrid h-parameters,
h
11
and
h
21
,
are each evaluated under the condition of a short circuited output port; that is, under the condition
of
V
2
= 0
.
With
V
2
= 0
,
o
2
1
e
1
2
0
r
I
β
I
R
I
I
,
(P1-1)
which leads immediately to
2
o
e
2
21
1
o
e
V =0
β
r
R
I
h
218.54 amps/amp .
I
r
R
(P1-2)
Note that
h
21
is very close to parameter
because
r
o
>> R
e
.
Continuing with
V
2
= 0
,
1
b
π
1
e
1
2
V
r
r
I
R
I
I
,
(P1-3)
and using (P1-2) to eliminate current
I
2
in this KVL relationship,

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