Midterm 2, ECE 448- Spring 2022, UIC Name:
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Midterm 2, ECE 448 Transistors – Spring 2022
University of Illinois at Chicago
09:30 am to 10:45 am on March 14, 2022
Name: UIN:
1. [40 points] PROBLEM # 1
A pn junction has the doping profile sketched below. Throughout the problem assume the
carrier concentrations may be neglected (n=0, p=0) in the 0 ≤ x ≤ xi region of the diode.
a. What is the built-in voltage across the junction? Justify your answer
b. Invoking the depletion approximation, make a sketch of the charge density inside
the diode versus x.
c. Obtain an analytical solution for the electric field, E(x) at all points inside the
depletion regions (-xp ≤ x ≤ xn). Show all steps and also make a sketch of E(x).
Midterm 2, ECE 448- Spring 2022, UIC Name:
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d. Draw the energy band diagram for the diode under equilibrium conditions. Clearly
indicate x = 0 and x= xi points on your diagram.
2. [10 points] PROBLEM # 2
Establish a small-signal equivalent model for the common base configuration.
Provide a summary of all the device parameters.
Midterm 2, ECE 448- Spring 2022, UIC Name:
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3. [30 points] PROBLEM # 3
Given a npn BJT where IEn = 100 μA, IEp = 1 μA, ICn = 99 μA, and ICp = 0.1 μA, calculate:
a. αT
b. γ
c. IE, IC, IB
d. αdc
e. βdc
f. ICB0 and ICE0
Midterm 2, ECE 448- Spring 2022, UIC Name:
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4. [20 points] PROBLEM # 4
a. What is base-width modulation in a bipolar junction device? How can we reduce
the effects of base width modulation?
b. What is meant by graded base in a bipolar junction device? State any advantages
or disadvantages it reflects?
