# Diffusion Capacitance MCQ’s

This set of Analog Electronic Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Diffusion Capacitance”.

1. If the diffusion capacitance is directly proportional only to the lifetime of holes in N side then ________
a) The diode is a p+n junction diode
b) The diode is a pn+ junction diode
c) The diode is a p+n+ diode
d) The diode can have any type of pn junction

2. Diffusion capacitance is larger than transition capacitance.
a) True
b) False
c) Both are same
d) Depends on doping concentrations

3. On which of these does the diffusion capacitance of a diode not depend upon?
a) Forward current
b) Dynamic conductance
c) Doping concentration
d) Reverse resistance

4. In a diode, the change in voltage being applied across it is 2V. The change in minority carriers outside the depletion region is 1.2×10-8. Find diffusion capacitance.
a) 6 pF
b) 6 μF
c) 1.2 nF
d) 6nF

5. Consider two almost similar diodes, whose diffusion capacitances are C1 and C2, and doping concentrations of 1020 /cubic centimeter and 1016/cubic centimeter. Find C1C2.
a) 100
b) 0.01
c) 10000
d) 0.0001

6. Consider a step graded diode, which has built in voltage 0.7V, and depletion width 2μm. Depletion width is W2 when a reverse bias voltage of 11.3 V is applied. Find W2?
a) 8.28μm
b) 8μm
c) 4.14 μm
d) 9.88 μm

7. The minority charge concentration can be represented as Q = V2 – 33V. If the voltage being applied is now 5V, find the diffusion capacitance.
a) 1μF
b) 0.1μF
c) 10μF
d) 0.9μF

8. If the relative permittivity of a diode remains constant, its area is doubled and its doping concentration is quadrupled. What is its new diffusion capacitance, of originally it was CD?
a) 4CD
b) 2CD
c) 3CD
d) CD