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Unit 3: Field Effect Transistor (FET) - Practice Quiz

ECE226 — Analog Electronic Devices And Circuits 60 Questions
0 Correct 0 Wrong 60 Left
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1 FET is a _____ controlled device.

Structure and working of JFET Easy
A. Voltage
B. Current
C. Resistance
D. Power

2 The three terminals of a JFET are:

Structure and working of JFET Easy
A. Source, Gate, Drain
B. Source, Base, Drain
C. Emitter, Base, Collector
D. Anode, Cathode, Gate

3 In an n-channel JFET, the channel is made of:

Structure and working of JFET Easy
A. metal
B. p-type semiconductor
C. intrinsic semiconductor
D. n-type semiconductor

4 In a JFET, the current flows due to:

Structure and working of JFET Easy
A. Minority carriers only
B. Majority carriers only
C. Photons
D. Both majority and minority carriers

5 For an n-channel JFET, the gate-source voltage is normally:

Structure and working of JFET Easy
A. Positive
B. Negative
C. Zero always
D. Equal to

6 MOSFET stands for:

Structure and working of MOSFET Easy
A. Metal Oxide Semiconductor Field Effect Transistor
B. Metal Oxide Silicon Fast Electron Transistor
C. Multiple Oxide Semiconductor Field Effect Transistor
D. Metal Only Semiconductor Field Effect Transistor

7 In a MOSFET, the gate is electrically insulated from the channel by a layer of:

Structure and working of MOSFET Easy
A. Aluminium
B. Doped silicon
C. Copper
D. Silicon dioxide ()

8 MOSFET is also known as:

Structure and working of MOSFET Easy
A. IGFET
B. SCR
C. BJT
D. UJT

9 The two main types of MOSFET are:

Structure and working of MOSFET Easy
A. Enhancement and Depletion
B. Positive and Negative
C. Forward and Reverse
D. Active and Passive

10 In an enhancement type MOSFET, a channel is:

Structure and working of MOSFET Easy
A. Never formed
B. Physically present at manufacture
C. Induced by applying gate voltage
D. Made of metal

11 The transfer characteristic of a JFET is a plot between:

Output and transfer characteristics Easy
A. and
B. and
C. and
D. and

12 The output (drain) characteristic of a JFET is a plot of versus:

Output and transfer characteristics Easy
A.
B.
C.
D.

13 The gate-source voltage at which the drain current becomes almost zero is called:

Output and transfer characteristics Easy
A. Breakdown voltage
B. Saturation voltage
C. Pinch-off / cut-off voltage
D. Threshold voltage

14 The transfer characteristic of a JFET is approximately described by:

Output and transfer characteristics Easy
A. Faraday's law
B. Ohm's law
C. Shockley's equation
D. Kirchhoff's law

15 The transconductance of a FET is defined as:

FET parameters Easy
A. at constant
B. at constant
C. at constant
D. at constant

16 The unit of transconductance is:

FET parameters Easy
A. Siemens (mho)
B. Volt
C. Ohm
D. Farad

17 The drain resistance of a FET is given by:

FET parameters Easy
A. at constant
B. at constant
C. at constant
D. at constant

18 The amplification factor of a FET is related to and by:

FET parameters Easy
A.
B.
C.
D.

19 A FET can be used as a voltage variable resistor when it operates in the:

Application of FET as voltage variable resistor Easy
A. Ohmic (linear) region
B. Breakdown region
C. Saturation region
D. Cut-off region

20 When a FET is used as a voltage variable resistor, its channel resistance is controlled by:

Application of FET as voltage variable resistor Easy
A. Temperature only
B.
C.
D. Drain current

21 In an N-channel JFET operating in the ohmic region, the gate-to-source voltage is made more negative. What happens to the channel resistance?

Structure and working of JFET Medium
A. It becomes zero as the channel fully conducts
B. It remains constant since only controls pinch-off
C. It increases because the depletion region widens and narrows the channel
D. It decreases because more carriers are injected into the channel

22 For an N-channel JFET, the gate junction must be reverse biased for proper operation. This is achieved by making :

Structure and working of JFET Medium
A. Positive only
B. Greater than the pinch-off voltage
C. Negative or zero
D. Equal to

23 A JFET has mA and V. Using Shockley's equation, what is the drain current at V?

Output and transfer characteristics Medium
A. mA
B. mA
C. mA
D. mA

24 The transconductance of an FET is defined as the ratio of change in:

FET parameters Medium
A. Drain current to gate-source voltage at constant
B. Drain current to drain-source voltage at constant
C. Gate current to gate voltage at constant
D. Drain-source voltage to drain current at constant

25 For a JFET, the maximum transconductance (at ) relates to and as . If mA and V, find .

FET parameters Medium
A. mS
B. mS
C. mS
D. mS

26 The amplification factor of an FET is related to transconductance and drain resistance by:

FET parameters Medium
A.
B.
C.
D.

27 In an N-channel enhancement MOSFET, drain current begins to flow only when exceeds the threshold voltage . Below this voltage the device is:

Structure and working of MOSFET Medium
A. OFF, since no conducting channel is induced
B. ON, operating in saturation
C. Acting as a fixed resistor
D. In the ohmic region conducting fully

28 The key structural difference between a depletion-type MOSFET and an enhancement-type MOSFET is that the depletion type:

Structure and working of MOSFET Medium
A. Has no insulating oxide layer under the gate
B. Has a physically diffused channel between drain and source
C. Cannot conduct at
D. Uses a reverse-biased PN gate junction

29 Why does a MOSFET have an extremely high input resistance (of the order of or more)?

Structure and working of MOSFET Medium
A. The channel is made of intrinsic semiconductor
B. The drain and source are shorted internally
C. The gate junction is heavily forward biased
D. The gate is separated from the channel by an insulating oxide layer

30 On the output (drain) characteristics of a JFET, the region beyond pinch-off where is nearly constant with increasing is called the:

Output and transfer characteristics Medium
A. Cut-off region
B. Breakdown region
C. Ohmic region
D. Saturation (pinch-off) region

31 In the ohmic (linear) region of a JFET's output characteristics, the device behaves approximately as a:

Output and transfer characteristics Medium
A. Reverse-biased diode
B. Constant current source
C. Voltage-controlled resistor
D. Fixed voltage source

32 When a JFET is used as a voltage variable resistor (VVR), it must be operated in which region and with what constraint on ?

Application of FET as voltage variable resistor Medium
A. Ohmic region, with small
B. Saturation region, with large
C. Cut-off region, with beyond pinch-off
D. Breakdown region, with high

33 For a JFET used as a voltage variable resistor, how does the drain-to-source resistance change as moves toward the pinch-off voltage?

Application of FET as voltage variable resistor Medium
A. stays constant
B. decreases
C. increases
D. becomes negative

34 When an N-channel enhancement MOSFET is used as a switch in the ON state, it operates in the ohmic region because:

MOSFET as a switch Medium
A. the device is biased at pinch-off for constant current
B. the drain junction is reverse biased into breakdown
C. is well above and is very small, giving low
D. is below so no channel forms

35 In the OFF state of a MOSFET switch, the ideal condition is:

MOSFET as a switch Medium
A. with maximum current
B. , so no channel forms and
C. gate current equals drain current
D. , so full current flows

36 A power MOSFET switch has and carries a drain current of A when ON. What is the power dissipated in the device?

MOSFET as a switch Medium
A. W
B. W
C. W
D. W

37 Which of the following is a genuine advantage of a FET over a bipolar junction transistor (BJT)?

Advantages of FET over transistor Medium
A. Higher gain-bandwidth product in all cases
B. Larger transconductance for the same bias
C. Lower manufacturing area on an IC
D. Very high input impedance due to negligible gate current

38 A FET is often preferred over a BJT in low-noise input stages primarily because it is a:

Advantages of FET over transistor Medium
A. Unipolar device with no minority carrier (recombination) noise
B. Bipolar device with higher current gain
C. Device requiring two power supplies
D. Device with a forward-biased control junction

39 One reason FETs are said to be more thermally stable than BJTs is that in a FET:

Advantages of FET over transistor Medium
A. The device requires external heat sinks always
B. The channel resistance drops rapidly, increasing current
C. The gate current increases sharply with temperature
D. Drain current has a negative temperature coefficient, preventing thermal runaway

40 A JFET with mA and V is biased at V. Its drain current is:

Output and transfer characteristics Medium
A. mA
B. mA
C. mA
D. mA

41 An n-channel JFET has mA and V. If it operates in the saturation (pinch-off) region with V, what is the drain current ?

Output and transfer characteristics Hard
A. mA
B. mA
C. mA
D. mA

42 For a JFET with mA and V, calculate the transconductance at V.

FET parameters Hard
A. mS
B. mS
C. mS
D. mS

43 A JFET used as a voltage variable resistor operates in the ohmic region. When is made more negative (toward pinch-off), the channel resistance behaves how?

Application of FET as voltage variable resistor Hard
A. Increases because the depletion region widens, narrowing the conducting channel until it approaches pinch-off where resistance becomes very large
B. Decreases because more carriers are attracted
C. Remains constant since it is set only by
D. Becomes negative

44 An n-channel enhancement MOSFET with V is used as a switch. For it to operate as a closed switch (deep triode/ohmic region), which condition on and must hold?

MOSFET as a switch Hard
A. exactly
B. and
C. and
D. and

45 In a depletion-type n-channel MOSFET, applying a negative has what effect on the pre-existing channel?

Structure and working of MOSFET Hard
A. It enhances the channel, increasing above
B. It forward biases the gate oxide
C. It depletes the channel of electrons, reducing below
D. It has no effect since the channel is physically built in

46 A JFET is biased so that . What is the corresponding in terms of pinch-off voltage ?

Output and transfer characteristics Hard
A.
B.
C.
D.

47 A JFET has an amplification factor and a drain resistance k. What is its transconductance ?

FET parameters Hard
A. mS
B. mS
C. mS
D. mS

48 Which statement best explains why FETs generate less noise than BJTs?

Advantages of FET over transistor Hard
A. FET conduction involves majority carriers only, avoiding carrier recombination noise associated with minority-carrier injection across junctions in a BJT
B. FETs use two junctions instead of one
C. FETs have a lower input impedance which shorts out noise
D. FETs operate at higher currents that swamp noise

49 In an n-channel JFET, the drain current saturates (pinch-off begins) when the channel is depleted near the drain end. The pinch-off condition at the drain is best expressed as:

Structure and working of JFET Hard
A. regardless of
B.
C.
D.

50 A power MOSFET switch conducting A has m. What is the conduction power loss?

MOSFET as a switch Hard
A. W
B. W
C. W
D. W

51 Two n-channel JFETs are identical except that Device A has V and Device B has V, both with the same . At V, which device carries more drain current?

Output and transfer characteristics Hard
A. Neither conducts at V
B. Device A, because smaller means higher gain
C. Device B, because a larger makes the fractional turn-off smaller for the same
D. Both carry equal current

52 The drain resistance of a FET in the saturation region is defined as which of the following partial derivatives?

FET parameters Hard
A.
B.
C.
D.

53 For a JFET operating as a VVR, the small-signal drain resistance near is approximately . If , V, and V, find .

Application of FET as voltage variable resistor Hard
A.
B.
C.
D.

54 Why does an enhancement-type MOSFET show zero drain current when (with applied)?

Structure and working of MOSFET Hard
A. The source and drain are shorted internally
B. No conducting channel exists until exceeds to invert the surface and form the channel
C. The built-in channel is fully depleted by drain voltage
D. The oxide layer breaks down instantly

55 An n-channel enhancement MOSFET ( V, mA/V) has V. In the ohmic region with small , estimate using .

MOSFET as a switch Hard
A.
B.
C.
D.

56 A designer replaces a BJT input stage with a JFET to improve input impedance. The main reason FETs offer much higher input impedance is:

Advantages of FET over transistor Hard
A. The FET operates only at low frequencies
B. The FET has a higher transconductance than the BJT
C. The FET drain current is independent of temperature
D. The gate-channel junction is reverse biased (or oxide isolated), so gate current is negligible

57 A JFET operating in saturation has V producing mA, and V producing mA. Estimate at this operating point.

Output and transfer characteristics Hard
A. mS
B. mS
C. mS
D. mS

58 In an n-channel JFET, why must the gate-source junction always be operated under reverse bias?

Structure and working of JFET Hard
A. Reverse bias increases the drain current linearly
B. Forward bias would reduce the pinch-off voltage to zero
C. Reverse bias converts the JFET into a MOSFET
D. Forward biasing the gate junction would inject gate current and destroy the high-input-impedance, voltage-controlled behavior

59 A JFET has mS and is used in a common-source amplifier with drain resistance k (assume ). What is the approximate voltage gain magnitude?

FET parameters Hard
A.
B.
C.
D.

60 A key structural reason a MOSFET gate has extremely high input resistance (higher than a JFET) is that:

Structure and working of MOSFET Hard
A. The gate uses a reverse-biased pn junction
B. The channel is made of insulating material
C. The gate is separated from the channel by a thin insulating oxide (SiO) layer, blocking DC gate current entirely
D. The source and gate are the same terminal
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