ECE3050
Homework Set 2
1. A diode has the parameters
I
S
= 10 fA
,
n
= 2
, and
V
T
= 25 mV
.
(a) Calculate
r
d
for
V
D
= 0
.
6 V
.
r
d
=
nV
T
I
D
+
I
S
=
nV
T
e
−
V
D
/nV
T
I
S
= 30
.
72 M
Ω
(b) Calculate
r
d
for
V
D
= 0 V
.
r
d
=
nV
T
I
S
= 5
×
10
12
Ω
(c) At what voltage does
r
d
exceed
10
15
Ω
?
V
D
=
nV
T
ln
μ
nV
T
I
S
r
d
¶
=
−
0
.
265 V
2. A diode currentcontrolled attenuator circuit is shown. It is given that
R
= 20 k
Ω
. The diode
parameters are
n
= 2
and
V
T
= 0
.
025 V
.
(a) Calculate the bias current which will provide a smallsignal attenuation of
20 dB
, i.e.
v
o
/v
s
= 0
.
1
.
I
=
2
nV
T
R
"
μ
v
o
v
s
¶
−
1
−
1
#
= 45
µ
A
(b) If the current is halved, what is the new attenuation? (
−
14
.
8 dB
). (c) If the current is
doubled, what is the new attenuation? (
−
25
.
6 dB
)
3. A diode has the current
I
D
1
= 1 mA
for
V
D
1
= 0
.
55 V
and
I
D
2
= 2 mA
for
V
D
2
= 0
.
58 V
. If
I
S
¿
I
D
1
, determine the ideality factor or emission coe
ﬃ
cient
n
and the saturation current
I
S
.
n
=
V
D
2
−
V
D
1
V
T
ln (
I
D
2
/I
D
1
)
= 1
.
73
I
S
=
I
D
1
exp (
V
D
1
/nV
T
)
=
I
D
2
exp (
V
D
2
/nV
T
)
= 3
.
03 nA
4. The diagram shows a zener diode regulator. It is given that
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 Summer '08
 HOLLIS
 Volt, Calculate

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