ECE3050
Homework Set 8
1. The
fi
gure shows the ac signal circuit of a cascade commonemitter ampli
fi
er. For each BJT,
it is given that
I
E
= 1
.
5 mA
,
α
= 0
.
99
,
β
= 99
,
r
x
= 20
Ω
,
r
0
=
∞
, and
V
T
= 0
.
025 V
. The
circuit element values are
R
S
= 1 k
Ω
,
R
E
1
=
R
E
2
= 47
Ω
,
R
C
1
=
R
C
2
= 10 k
Ω
.
(a) Looking out of the base of
Q
2
, use the Norton collector circuit of
Q
1
to show that
v
tb
2
=
−
i
c
1
R
c
1
=
−
134
.
03
v
s
R
tb
2
=
R
C
1
= 10 k
Ω
(b) Use the Norton collector circuit for
Q
2
to show that
v
o
= 8097
v
s
r
out
=
R
C
2
= 10 k
Ω
(c) Show that
r
in
=
r
ib
1
= 6
.
387 k
Ω
(d) If a resistor
R
L
= 1 k
Ω
is connected from output to ground, show that the new gain is
reduced by a factor
R
L
/
(
r
out
+
R
L
)
to the value
v
o
/v
s
= 736
.
1
and that the dB decrease
in gain is
20
.
83 dB
.
2. The ac signal circuit of a commonbase ampli
fi
er driving a commoncollector ampli
fi
er is
shown. For each BJT, it is given that
I
E
= 1
.
5 mA
,
α
= 0
.
99
,
β
= 99
,
r
x
= 20
Ω
,
r
0
=
∞
,
and
V
T
= 0
.
025 V
. The circuit element values are
R
S
= 50
Ω
,
R
C
= 10 k
Ω
,
R
E
= 1 k
Ω
.
??
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 Summer '08
 HOLLIS
 The Circuit, RC circuit, Electrical network, Circuit Element Values, Norton collector circuit

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