VLSI Design Questions and Answers - Characteristics of npn Bipolar Transistors

1.What is the input resistance of CMOS inverter?
a) high
b) low
c) very low
d) none of the mentioned

Answer: a
Explanation: Input resistance of CMOS inverter is extremely high as it is a perfect insulator and draws no dc input source.

2. Increasing fan-out ____________ the propagation delay.
a) increases
b) decreases
c) does not affect
d) exponentially decreases

Answer: a
Explanation:In CMOS inverter, increasing the fan-out also increases the propagation delay. Fan-out is a term that defines the maximum number of digital inputs that the output of a single logic gate can feed

3.Fast gate can be built by keeping ________
a) low output capacitance
b) high on resistance
c) high output capacitance
d) input capacitance does not affect speed of the gate

Answer: a
Explanation: Fast gate can be built by keeping the output capacitance small and by decreasing the on resistance of the transistor.

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

Answer: b
Explanation: Transconductance gm is independent of process.

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

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

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

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

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

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

8. 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)

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

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

Answer: b
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

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

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