ECE3050 — Assignment 13
1. The
f
gure shows a current mirror. The transistors are identical.
(a) If the base currents and the Early e
f
ect can be neglected, use the equations
I
1
=
I
S
e
V
BE
1
/V
T
I
2
=
I
S
e
V
BE
2
/V
T
V
BE
1
+
I
1
R
1
=
V
BE
2
+
I
2
R
2
to show that
I
1
exp
μ
I
1
R
1
V
T
¶
=
I
2
exp
μ
I
2
R
2
V
T
¶
(b)If
I
1
=1mA
,
R
1
=1
.
2k
Ω
,and
V
T
=25mV
,so
lv
efo
r
R
2
for
I
2
=20
µ
A
.A
n
s
w
e
r
:
R
2
=64
.
89 k
Ω
.
2. The
f
gure shows a current mirror.
(a) If the transistors are identical and the Early e
f
ect can be neglected, label all currents in
the unlabeled branches in terms of
I
O
.
(b) Write a KCL equation at the collector of
Q
1
and use it to solve for
I
O
.
(c) What is the minimum
β
for
I
O
≥
0
.
99
I
REF
?An
sw
e
r
:
β
≥
198
.
(d) What is the smallsignal output resistance
r
out
?An
sw
e
r
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 Summer '08
 HOLLIS
 Integrated Circuit, Transistor, Io, Early effect, smallsignal output resistance, IABC

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