# Electronic Devices and Circuits Questions and Answers – The Insulated-Gate FET(MOSFET) – 2

This set of Electronic Devices and Circuits Objective Questions & Answers focuses on “The Insulated-Gate FET(MOSFET) – 2”.

1. The threshold voltage of an n-channel MOSFET can be controlled by which of the following parameter?
a) Increasing the channel dopant concentration
b) Reducing the channel dopant concentration
c) Reducing the gate-oxide thickness
d) Reducing the channel

Explanation: The threshold voltage of n-channel MOSFET can be increased by reducing the channel dopant concentration or by increasing the oxide thickness.

2. MOSFET can be used as ________
a) Voltage controlled capacitor
b) Current controlled capacitor
c) Voltage controlled inductor
d) Current controlled inductor

Explanation: By using proper techniques, MOSFET can be used as Voltage controlled capacitor.

3. The effective channel length of a MOSFET in saturation decreases with increase in which of the following parameter?
a) Gate voltage
b) Drain voltage
c) Source voltage
d) Body voltage

Explanation: The channel length of a MOSFET in saturation decreases with increase in drain voltage of the MOSFET.

4. In a MOSFET operating in a saturation region, the channel length modulation effect causes
a) An increase in gate-source capacitance
b) Decrease in Trans conductance
c) Decrease in the unity gain cut off
d) Decrease in the output impedance

Explanation: Under channel length modulation, 1/rds=dIds/dVds=dIDsat=1/ro
Hence it decreases from ∞ to 1/ro.

5. Which of the following effects can be caused by decrease in temperature?
a) Increase in MOSFET current
b) Increase in BJT current
c) Decrease in MOSFET current
d) Decrease in BJT current

Explanation: MOSFET has positive temperature coefficient and drain resistance increase with decrease in temperature .Hence current decreases with decrease in temperature.
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6. At room temperature, what is the possible value for the mobility of electrons in the inversion layer of a silicon n-channel MOSFET?
a) 450 cm2/v-s
b) 1350 cm2/v-s
c) 1800 cm2/v-s
d) 3600cm2/v-s

Explanation: The mobility of electron in s-type Si semiconductor is 1350 cm2/v-s.
In Inversion layer mobility of electron is 1350 cm2/v-s.

7. The drain current of a MOSFET in saturation is given by ID=K(VGS-VP) (VGS-VP)
where k is a constant. Determine the magnitude of gm.
a) K(VGS-VT) (VGS-VT)/ VDS
b) 2K(VGS-VT)
c) ID/VGS VdS
d) K(VGS-VT) (VGS-VT)/ VGS

Explanation: gm=∂ID/∂VGS|VDS=constant
=>gm = 2K(VGS-VT).

8. The depletion type MOSFET is equivalent to normally closed switch.
a) True
b) False

Explanation: The depletion type has its gate short circuited with source terminal and hence always in On condition .Therefore we can say it as closed switch.

9. Which of the following statement is true about enhancement MOSFET?
a) It acts as closed switch
b) It acts as open switch
c) It acts as resistor with small resistance
d) Capacitor

Explanation: Because of an absence of channel in enhancement MOSFET, no current flows and hence acts as open switch.

10. For a transistor in its circuit symbol, the line between drain and source was broken, what does this indicate?
a) BJT
b) JFET
c) Depletion type MOSFET
d) Enhancement type MOSFET

Explanation: While representing a Transistor, if the solid line is broken then it represents an open switch which is Enhancement type MOSFET.

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