This set of VLSI Multiple Choice Questions & Answers (MCQs) focuses on “Parameters of MOS Transistors”.
1. The work function difference is neagative for
a) silicon substrate
b) polysilicon gate
c) both of the mentioned
d) none of the mentioned
Explanation: 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.
Explanation: Substrate bias voltage Vsb is positive for pMOS and negative for nMOS.
3. According to body effect, substrate is biased with respect to
Explanation: According to body effect, 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
d) exponentially increases
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: Increasing the transconductance gm results in 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
Explanation: 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 threshold
b) carrier mobility
c) length channel
d) all of the mentioned
Explanation: Switching speed of a MOS device depends on gate voltage above 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
Explanation: 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
Explanation: 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 a oriented surface.
12. MOS transistor is a
a) minority carrier device
b) majority carrier device
c) majority & minority carrier device
d) none of the mentioned
Explanation: 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
Explanation: The MOS transistor normally is at cut-off or becomes non-conducting with zero gate bias (gate voltage-source voltage).
Sanfoundry Global Education & Learning Series – VLSI.
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