250+ TOP MCQs on Parameters of MOS Transistors and Answers

VLSI Multiple Choice Questions on “Parameters of MOS Transistors”.

1. The work function difference is negative for ____________
A. silicon substrate
B. polysilicon gate
C. silicon substrate & polysilicon gate
D. none of the mentioned
Answer: C
Clarification: The work function difference between gate and Si (Φms) is negative for silicon substrate and polysilicon gate.

2. Substrate bias voltage is positive for nMOS.
A. true
B. false
Answer: B
Clarification: Substrate bias voltage Vsb is positive for pMOS and negative for nMOS.

3. According to body effect, substrate is biased with respect to ___________
A. source
B. drain
C. gate
D. Vss
Answer: A
Clarification: According to body effect, the substrate is biased with respect to the source. Body effect can be seen as a change in the threshold voltage.

4. Increasing Vsb _______ the threshold voltage.
A. does not effect
B. decreases
C. increases
D. exponentially increases
Answer: C
Clarification: Increasing the substrate bias voltage Vsb, increases the threshold voltage because it depletes the channel of charge carriers.

5. Transconductance gives the relationship between ___________
A. input current and output voltage
B. output current and input voltage
C. input current and input voltage
D. output current and output voltage
Answer: B
Clarification: Transconductance expresses the relationship between output current Ids and input voltage Vgs.

6. Transconductance can be increased by ___________
A. decreasing the width
B. increasing the width
C. increasing the length
D. decreasing the length
Answer: B
Clarification: Transconductance gm of a MOS device can be increased by increasing its width and it does not depend on length.

7. Increasing the transconductance ___________
A. increases input capacitance
B. decreasing area occupied
C. decreasing input capacitance
D. decrease in output capacitance
Answer: A
Clarification: Increasing the transconductance gm results in an increase in input capacitance and area occupied as it is directly proportional.

8. Ids is _______ to length L of the channel.
A. directly proportional
B. inversely proportional
C. not related
D. logarithmically related
Answer: B
Clarification: Ids is inversely proportional to the length L of the channel and using this relationship strong dependence of output conductance on channel length can be demonstrated.

9. Switching speed of a MOS device depends on ___________
A. gate voltage above a threshold
B. carrier mobility
C. length channel
D. all of the mentioned
Answer: D
Clarification: Switching speed of a MOS device depends on gate voltage above a threshold and on carrier mobility and inversely as the square of channel length.

10. A fast circuit requires ___________
A. high gm
B. low gm
C. does not depend on gm
D. low cost
Answer: A
Clarification: A fast circuit requires gm as high as possible as the switching speed depends on gate voltage above threshold and on carrier mobility and inversely to square of channel length.

11. Surface mobility depends on ___________
A. effective drain voltage
B. effective gate voltage
C. channel length
D. effective source voltage
Answer: B
Clarification: Surface mobility is dependent on the effective gate voltage (Vgs-Vt). Electron mobility on oriented n-type inversion layer surface is larger than that on an oriented surface.

12. What is a MOS transistor?
A. minority carrier device
B. majority carrier device
C. majority & minority carrier device
D. none of the mentioned
Answer: B
Clarification: MOS transistor is a majority carrier device, in which current in a conducting channel between the source and drain is modulated by a voltage.

13. The MOS transistor is non conducting when?
A. zero source bias
B. zero threshold voltage
C. zero gate bias
D. zero drain bias
Answer: C
Clarification: The MOS transistor normally is at cut-off or becomes non-conducting with zero gate bias (gate voltage-source voltage).