1
Dalhousie University, Department of Electrical and computer Engineering
ECED3201:
Introduction to Electronics
Fall 2007 Midterm Exam
Dr. Kamal ElSankary
Guidelines
•
Only doublesided one letter size formula sheet is allowed
.
•
Show all your work and reasoning on the exam in order to receive full or partial credit.
• Exam Time:
150 minutes
Problem 1  [3 points]:
Consider V
DD
=2.5,
v
(t)=0.01sin
t (V), and R=2k
in the circuit shown in Fig. 1 Assume
that the diode has a 0.7V drop across when the ac signal v(t) is reduced to 0.
R
V
DD
v
(
t
)
v
D
(
t
)
i
D
(
t
)
+

+

+

Fig.1
a. [0.75 pt] Find the dc current,
I
D
, in the diode.
b. [0.75 pt] Find the smallsignal resistance (ac resistance) of the diode (consider n=2).
Assume the diode is at room temperature (V
T
25mV).
c. [1.5 pt] Write mathematical expressions for the total instantaneous current
i
D
(t) and
total instantaneous voltage
v
D
(t).
Problem 2  [5 points]:
Consider the circuit shown in Fig.2.
R
1
= 10k
V
1
= 2V
v
I
+

+

V
2
= 4V
R
2
=
10k
+
+
_
_
v
O
D
1
D
2
Fig.2
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