# VLSI Questions and Answers – FET

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

1. Field effect transistor uses ________ to control the shape.
a) electric field
b) magnetic field
c) current distribution
d) voltage distribution

Explanation: Field effect transistor uses electric field to control the shape and hence the electrical conductivity of the channel.

2. Field effect transistors are known as
a) unipolar device
b) bipolar device
c) tripolar device
d) multipolar device

Explanation: Field effect transistors are unipolar transistors as they involve single-carrier-type operation.

3. The FET has __________ input impedance.
a) low
b) high
c) all of the mentioned
d) none of the mentioned

Explanation: Field effect transistors have high input impedance. The conductivity of non-FET transistors are regulated by the input current thus it has low input impedance.

4. Field effect transistor’s conductivity is regulated by
a) input current
b) output current
c) terminal voltage
d) supply voltage

Explanation: Field effect transistor’s conductivity is regulated by the voltage applied to a terminal (the gate) which is insulated from the device.

5. In FET, the current enters the channel through
a) source
b) drain
c) gate
d) nodes

Explanation: In field effect transistor, the current enters the channel through source and the current leaves the junction through drain.
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6. Which terminal bias the transistor to operation?
a) source
b) drain
c) gate
d) base

Explanation: Other than the three terminals, source drain and gate, there is a fourth terminal called as body or base. This is used to bias the transistor to operation.

7. In FET, the width is greater than the length of the gate.
a) true
b) false

Explanation: In FET, the width is greater than the length of the gate. Length gives the distance between source and drain. Width is the extension of the transistor, in the direction perpendicular to cross section.

8. Which terminal controls the electron flow passage?
a) source
b) drain
c) gate
d) base

Explanation: Gate permits the electron to flow through or block their passage by creating or eliminating the channel between source and drain.

9. The expansion of depletion region in n-channel device makes the channel
a) narrow
b) wide
c) does not affect the channel
d) cannot be determined

Explanation: In n-channel depletion mode device, as the depletion region width expands, it encroaches the channel from the sides and the channel becomes narrow.

10. Which voltage increases the channel size?
a) negative Vgs
b) positive Vgs
c) negative Vds
d) positive Vds

Explanation: A positive gate to source voltage increases the channel size and allows the electrons to flow easily.

11. Which relation is correct?
a) Vgs greater than Vds
b) Vds greater than Vgs
c) Vds equal to Vgs
d) Vgs lesser than Vds

Explanation: In FET, for either depletion or enhancement mode device the drain to source voltage is much less than the gate to source voltage.

12. Which mode of operation of FET is used, when amplification is needed?
a) active
b) saturation
c) non saturation
d) linear

Explanation: Saturation mode, which is in between the ohmic and saturation region is used when amplification is needed.

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