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##### Page 4
4
8)
What is the proper expression for the Thevenin equivalent resistance seen by the 10 pF load
capacitor in Fig. 1?
(a)
R
Th
=
8
K
(b)
R
Th
=
8
K
+
8
K
(c)
R
Th
=
8
K
||8
K
(d)
R
Th
=
8
K
|| 8
K
+
1
g
m
(e)
R
Th
=
8
K
|| 8
K
||1
g
m
Problems 9) and 10) concern the RC circuit shown below.
V
s
1K
1K
1
μ
F
1 pF
V
out
+
-
Figure 2
---------------------------------------------------------------------------------------------------------------------
9)
The low-frequency corner frequency for this circuit is about:
(a)
(b)
(c)
5 x 10
8
(d)
10
9
(e)
2 x 10
9
---------------------------------------------------------------------------------------------------------------------
10)
The high-frequency corner frequency for this circuit is about:
(a)
(b)
(c)
5 x 10
8
(d)
10
9
(e)
2 x 10
9

##### Page 5
5
Problems 11) - 15) concern the amplifier shown below.
Assume that g
m1
= g
m2
and that r
π1
= r
π2
.
V
CC
= +15 V
R
E
R
C
Q
2
Q
1
R
1
R
2
R
L
υ
s
R
3
C
1
C
E
C
2
C
3
Z
OUT
Figure 3
---------------------------------------------------------------------------------------------------------------------
11)
Identify the amplifier shown in Fig. 3:
(a)
CE-CE
(b)
CE-CB
(c)
CB-CE
(d)
CC-CE
(e)
CE-CC
---------------------------------------------------------------------------------------------------------------------
12)
The input impedance of the Fig. 3 amplifier is:
(a)
R
E
(b)
R
E
||(1/g
m
)
(c)
R
3
||(R
2
+ R
1
)
(d)
R
3
|| R
2
|| R
1
|| r
π
(e)
R
3
|| R
2
|| r
π

##### Page 6
6
13)
The output impedance of the Fig. 3 amplifier is:
(a)
R
3
|| R
2
(b)
R
3
|| R
2
|| R
1
(c)
R
L
(d)
R
L
|| R
C
(e)
R
C
---------------------------------------------------------------------------------------------------------------------
14)
The mid-frequency gain for the Fig. 3 amplifier is:
(a)
-g
m
R
C
|| R
L
(b)
+g
m
R
C
|| R
L
(c)
-g
m
[r
π
/(
β
+1)] x g
m
(R
C
|| R
L
)
(d)
-1
(e)
-g
m
r
π
x g
m
(R
C
|| R
L
)
---------------------------------------------------------------------------------------------------------------------
15)
The time constant associated with capacitor C
π
2
in Fig. 3 is:
(a)
[R
1
|| R
2
] C
π
2
(b)
[r
π
2
] C
π
2
(c)
[r
π
2
/ (
β
+1)] C
π
2
(d)
[R
1
+ R
2
] C
π
2
(e)
[R
1
] C
π
2

##### Page 7
7
Problems 16) -
25)
concern the two stage amplifier below (Fig. 4).
Both
transistors operate at 2 mA (I
D
= I
C
= 2 mA).
For the MOSFET:
I
D
=
2
V
gs
+
2
(
29
2
, C
gs
= 5 pF, C
gd
= 1 pF, and C
ds
= 2 pF
For the bipolar:
β
= 200, V
BE
(on) = 0.7V, C
μ
= 1 pF, C
π
= 10 pF
The low frequency corner for C
1
is 10 Hz and for C
2
is 50 Hz.
The low
frequency corner for
the gain V
OUT
/V
IN
is 100 Hz.
Fig. 4
Two Stage Amplifier
16)
The value of R
A
is (note that one end of R
A
is connected to a -10V power supply)
(a)
5.7 K
(b)
30 K
(c)
43 K
(d)
67 K
(e)
100 K
-----------------------------------------------------------------------------------------------------------
17)
The value of V
ds
is
(a)
9.8 V
(b)
10.2 V
(c)
15.6 V
(d)
19.8 V
(e)
30 V
-----------------------------------------------------------------------------------------------------------
18)
The value of R
B
is
(a) 5.1 K
(b)
9.7 K
(c)
56 K
(d)
100 K

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