# VLSI Questions and Answers – Characteristics of npn Bipolar Transistors

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This set of VLSI Multiple Choice Questions & Answers (MCQs) focuses on “Characteristics of npn Bipolar Transistors”.

1. The transconductance of a bipolar is given by ______________
a) (kT/q)/Ic
b) Ic/(kT/q)
c) (q/KT)/Ic
d) Ic/(q/KT)

Explanation: Transconductance gm of a bipolar transistor is given by gm = Ic/(kT/q). Transconductance is the electrical characteristic relating the current through the output of a device to the voltage across the input of a device.

2. Transconductance depends on the process.
a) true
b) false

Explanation: Transconductance gm is independent of process.

3. gm is ______ on input voltage Vbe.
a) inversely proportional
b) proportional
c) exponentially dependent
d) is not dependent

Explanation: Transconductance gm is exponentially dependent on input voltage Vbe (base to emitter voltage).

4. gm is _______ to Ic.
a) directly proportional
b) inversely proportional
c) not dependent
d) exponentially proportional

Explanation: Transconductance gm is directly proportional to Ic, collector current.

5. Transconductance is a __________
a) weak function
b) strong function
c) weak and strong function
d) none of the mentioned

Explanation: Transconductance gm is a weak function of transistor size.

6. gm of bipolar is less than gm of MOS.
a) true
b) false

Explanation: Transconductance gm of bipolar is greater than gm of MOS if inputs are controlled by equal amounts of charge.

7. Which of the following is true when inputs are controlled by equal amounts of charge?
a) Cg(MOS) = Cbase(bipolar)
b) Cg(MOS) greater than Cbase(bipolar)
c) Cg(MOS) lesser than Cbase(bipolar)
d) Cs(MOS) lesser than Cbase(bipolar)

Explanation: Cg(MOS) = Cbase(bipolar) when inputs are controlled by equal amounts of charge, and then gm(bipolar) >> gm(MOS).

8. Which has better I/A?
a) CMOS
b) bipolar
c) nMOS
d) pMOS

Explanation: Current/Area (I/A) of bipolar is five times better than CMOS and this can be calculated using base resistance and base transit time.

9. Bipolar transistor exhibits _______ delay.
a) turn on
b) turn off
c) storage
d) all of the mentioned

Explanation: Bipolar transistors exhibits turn-on, turn-off, storage delays.

10. In bipolar transistor, which is heavily doped?
a) base region
b) emitter region
c) collector region
d) base and emitter

Explanation: In bipolar transistor, emitter region is heavily doped and the base region is lightly doped.

11. Bipolar transistor is a symmetrical device.
a) true
b) false

Explanation: Bipolar transistor is not symmetrical like other transistors.

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