# VLSI Questions and Answers – Ids versus Vds Relationships

This set of VLSI Multiple Choice Questions & Answers (MCQs) focuses on “Ids versus Vds Relationships”.

1. Ids depends on ___________
a) Vg
b) Vds
c) Vdd
d) Vss

Explanation: Ids depends on both Vgs and Vds. The charge induced is dependent on the gate to source voltage Vgs also charge can be moved from source to drain under influence of electric field created by Vds.

2. Ids can be given by __________
a) Qc x Ʈ
b) Qc / Ʈ
c) Ʈ / Qc
d) Qc / 2Ʈ

Explanation: Ids can be given as charge induced in the channel(Qc) divided by transit time (Ʈ). Ids is equivalent to (-Isd).

3. Transit time can be given by __________
a) L / v
b) v / L
c) v x L
d) v x d

Explanation: Transit time (Ʈ) can be given by lenght of channel(L) by velocity(v). Transit time is the time required for an electron to travel between two electrodes.

4. Velocity can be given as __________
a) µ / Vds
b) µ / Eds
c) µ x Eds
d) Eds / µ

Explanation: Velocity can be given as the product of electron or hole mobility(µ) and electric field(Eds). It gives the flow velocity which an electron attains due to electric field.

5. Eds is given by __________
a) Vds / L
b) L / Vds
c) Vds x L
d) Vdd / L

Explanation: Electric field(Eds) can be given as the ratio of Vds and L. Eds is the electric field created from drain to source due to volta Vds.
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6. What is the mobility of proton or hole at room temperature?
a) 650 cm2/V sec
b) 260 cm2/V sec
c) 240 cm2/V sec
d) 500 cm2/V sec

Explanation: The value of mobility of proton or hole at room temperature is 240 cm2/V sec. This gives the measure of how fast an electron can move.

7. In resistive region __________
a) Vds greater than (Vgs – Vt)
b) Vds lesser than (Vgs – Vt)
c) Vgs greater than (Vds – Vt)
d) Vgs lesser than (Vds – Vt)

Explanation: In non saturated or resistive region, Vds lesser than Vgs – Vt where Vds is the voltage between drain and source, Vgs is the gate-source voltage and Vt is the threshold voltage.

8. What is the condition for saturation?
a) Vgs = Vds
b) Vds = Vgs – Vt
c) Vgs = Vds – Vt
d) Vds > Vgs – Vt

Explanation: The condition for saturation is Vds = Vgs – Vt since at this point IR drop in the channel equals the effective gate to channel voltage at the drain.

9. Threshold voltage is negative for __________
a) nMOS depletion
b) nMOS enhancement
c) pMOS depletion
d) pMOS enhancement

Explanation: The threshold voltage for nMOS depletion denoted as Vtd is negative.

10. The current Ids _______ as Vds increases.
a) increases
b) decreases
c) remains fairly constant
d) exponentially increases

Explanation: The current Ids remains fairly constant as Vds increases in the saturation region.

11. In linear region ______ channel exists.
a) uniform
b) non-uniform
c) wide
d) uniform and wide

Explanation: In linear region of MOSFET, the channel is uniform and narrow. This is the concentration distribution.

12. When the channel pinches off?
a) Vgs > Vds
b) Vds > Vgs
c) Vds > (Vgs-Vth)
d) Vgs > (Vds-Vth)

Explanation: In MOSFET, in saturation region, when Vds > (Vgs – Vth), the channel pinches off that is the channel current at the drain spreads out.

13. When the threshold voltage is more, leakage current will be?
a) more
b) less
c) all of the mentioned
d) none of the mentioned

Explanation: Increasing the threshold voltage, leads to small leakage current when turned off and reduces current flow when turned on.

14. MOSFET is used as ___________
a) current source
b) voltage source
c) buffer
d) divider

Explanation: MOSFET is used as current source. Bipolar junction transistor also acts as good current source.

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