VLSI Questions and Answers – CMOS Inverter

This set of VLSI Multiple Choice Questions & Answers (MCQs) focuses on “CMOS Inverter”.

1. CMOS inverter has ______ regions of operation.
a) three
b) four
c) two
d) five

Explanation: CMOS inverter has five distinct regions of operation which can be determined by plotting CMOS inverter current versus Vin.

2. If n-transistor conducts and has large voltage between source and drain, then it is said to be in _____ region.
a) linear
b) saturation
c) non saturation
d) cut-off

Explanation: If n-transistor conducts and has large voltage between source and drain, then it is in saturation.

3. If p-transistor is conducting and has small voltage between source and drain, then it is said to work in ________
a) linear region
b) saturation region
c) non saturation resistive region
d) cut-off region

Explanation: If p-transistor is conducting and has small voltage between source and drain, then it is said to be in unsaturated resistive region.

4. In the region where inverter exhibits gain, the two transistors are in _______ region.
a) linear
b) cut-off
c) non saturation
d) saturation

Explanation: In the region where the inverter exhibits gain, the two transistors n and p operates in saturation region.

5. If both the transistors are in saturation, then they act as ________
a) current source
b) voltage source
c) divider
d) buffer

Explanation: When both the transistors are in saturation, then act as current sources so that the equivalent circuit is two current sources between Vdd and Vss.

6. If βn = βp, then Vin is equal to ________
a) Vdd
b) Vss
c) 2Vdd
d) 0.5Vdd

Explanation: If βn = βp, then Vin = 0.5Vdd which implies that the changeover between logic levels is symmetrically disposed about the point.

7. Mobility depends on ________
a) Transverse electric field
b) Vg
c) Vdd
d) Channel length

Explanation: Mobility is affected by the transverse electric field and thus also depends on Vgs and the mobility of p-device and n-device are inherently unequal.

8. In CMOS inverter, transistor is a switch having ________
a) infinite on resistance
b) finite off resistance
c) buffer
d) infinite off resistance

Explanation: In CMOS inverter, transistor is a switch having finite on resistance and infinite off resistance.

9. CMOS inverter has ______ output impedance.
a) low
b) high
c) very high
d) none of the mentioned

Explanation: CMOS inverter has low output impedance and this makes it less prone to noise and disturbance.

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

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

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

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.

12. 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

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

Sanfoundry Global Education & Learning Series – VLSI.

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