Fall 2005
1.
For the following bridge circuit, find out the current on the branch of
R
5
.
Please notice the
current direction and give the current in the right magnitude AND sign. (15 pts)
2.
For a similar circuit with
R
5
replaced by a capacitor of 1pF, what is the dominant time
constant as observed from the driving point A? (15 pts)
3.
For the following circuits, what is the input impedance as defined by
R
in
=v
x
/i
x
?
Your
expression should only contain the circuit elements, not any node voltage or currents. (15 pts)
Find the nodal voltage on R
2
from superposition of ix and
β
ix, we can write down by inspection:
(
29
2
1
1
R
R
i
v
R
x
x
in
+
+
=
=
β
R
1
=1k
Ω
R
2
=1k
Ω
R
3
=3k
Ω
R
4
=6k
Ω
R
5
=2k
Ω
V
S
=3V
I
R5
+

+

Thevenin equivalents from the two
branches:
0.5k
Ω
2k
Ω
2k
Ω
1.5V
2V
I
R5
I
R5
=

0.11mA (magnitude: 10
pts; sign: 5 pts)
R
1
=1k
Ω
R
2
=1k
Ω
R
3
=3k
Ω
R
4
=6k
Ω
C
1
=1pF
A
From the previous Thevenin
circuit,
RC
=2.5k
Ω
*1pF=2.5ns.
1
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 Fall '07
 SPENCER
 Microelectronics, pts, RC circuit, Pn junction, RC time constant

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