Deck 9: Fet Amplifiers and Switching Circuits

Question 1

In a self- biased common- source amplifier, what purpose does resistor RG serve?

A)Keeps the gate at approximately zero volts
B)Develops the gate- source bias current
C)Prevents loading of the ac signal source
D)Both A and C above.

Answer 1

D

Question 2

Refer to the figure above. If ID = 6 mA, the value of VGS is

A)- 19.8 V.
B)- 10.2 V.
C)9 V.
D)- 9 V.

Answer 2

D

Question 3

A CS amplifier has a voltage gain of

Answer 3

A

Question 4

The ac equivalent circuit of a FET amplifier assumes that the capacitors

A)have an XC of 600 ▲ at the signal frequency.
B)are treated like opens.
C)have an XC of 1 M▲ at the signal frequency.
D)are treated like shorts.

Question 5

Refer to the figure above. If R3 opened, Vout would

A)increase.
B)decrease.
C)remain the same.
D)distort.

Question 6

Refer to the figure above. If C5 opened, the signal voltage across R7 would

A)increase.
B)be zero.
C)remain the same.
D)distort.

Question 7

Refer to the figure above. If R7 were to increase in value, Vout would

A)increase.
B)decrease.
C)remain the same.
D)distort.

Question 8

Two FET amplifiers operated in cascade have gains of 6 dB and 8 dB. The total overall gain in dB is

A)64 dB.
B)14 dB.
C)2 dB.
D)48 dB.

Question 9

Which of the following is not a FET amplifier?

A)Emitter- follower
B)Common- drain
C)Source- follower
D)Common- gate

Question 10

If the interstage coupling capacitor opens in a two stage FET amplifier, the output signal will

A)double in amplitude.
B)be slightly increased.
C)be slightly decreased.
D)be zero.

Question 11

Refer to the figure above. If R1 opened, Vout would

A)increase.
B)decrease.
C)remain the same.
D)distort.

Question 12

The capacitor connected to the source of a common source amplifier

A)is used for input coupling.
B)makes the source an ac ground point.
C)is needed for extra power supply filtering.
D)is used for output coupling.

Question 13

The main reason that the input resistance of FET amplifiers is so high is that the

A)gate junction is reverse- biased.
B)power supplies used are high voltage/low current.
C)biasing resistors are extremely small.
D)FET junctions are forward- biased and made of germanium.

Question 14

Which of the following is not an application of an analog MOSFET switch?

A)Switched capacitor circuit
B)Sample- and- hold circuit
C)Inverter
D)Analog multiplexer

Question 15

Refer to the figure above. Assuming midpoint biasing, if VGS = - 4 V, the value of RS that will provide this value is

A)1.2 k▲.
B)800 ▲.
C)80 ▲.
D)600 ▲.

Question 16

Which of the following is not a characteristic of a JFET- based cascode amplifier?

A)High input resistance
B)High frequency response
C)High gain
D)High input capacitance

Question 17

When the input signal is large, a source follower has

A)a small distortion.
B)a voltage gain of less than one.
C)a high input resistance.
D)All of the above.

Question 18

Refer to the figure above. If ID = 4 mA, IDSS = 16 mA, and VGSoff)= - 8 V, VDS would be

A)10.8 V.
B)19.2 V.
C)30 V.
D)- 6 V.

Question 19

Changing can control the voltage gain of a common- source amplifier.

A)VDD
B)gm
C)RS
D)the input voltage

Question 20

Which of the following is not part of a class D amplifier?

A)Switching amplifier
B)Low- pass filter
C)Oscillator
D)Pulse- width modulator

Question 21

Refer to the figure above. If C2 opened, Vout would

A)increase.
B)decrease.
C)remain the same.
D)distort.

Question 22

Refer to the figure above. If C2 opened, the output signal would

A)decrease and then increase.
B)increase in value.
C)not change.
D)decrease in value.

Question 23

If RS is not bypassed,

A)the dc power supply will have excessive ripple.
B)the gain will be extremely high.
C)no signal will be coupled to the output.
D)the gain will be reduced.

Question 24

Refer to the figure above. If C3 opened, Vout would

A)increase.
B)decrease.
C)remain the same.
D)distort.

Question 25

Two FET amplifiers are operated in cascade. If the gain of the amplifiers is equal and the total overall gain is 25, the gain of each amplifier is

A)12.5.
B)5.
C)2.
D)7.25.

Question 26

Refer to the figure above. If the measured value of Vout were below normal, the problem might be that

A)C2 is shorted.
B)RD is open.
C)Vin has increased.
D)C2 is open.

Question 27

Refer to the figure above. If AV1 = 18 and AVt = 288, the value of AV2 would be

A)16.
B)18.
C)49.18.
D)5184.

Question 28

A common- source amplifier has a phase shift between the input and the output.

A)360°
B)180°
C)45°
D)90°

Question 29

Refer to the figure above. If gm = 4000 µS and a signal of 75 mV rms is applied to the gate, the p- p output voltage is

A)1.13 Vp- p.
B)990 Vp- p.
C)2.8 Vp- p.
D)990 mV.

Question 30

Where is the input signal applied in a common- gate amplifier?

A)Gate
B)Drain
C)Source
D)Base

Question 31

Refer to the figure above. If Vin = 50 mVp- p, the output voltage is

A)4.4 Vp- p.
B)50 mVp- p.
C)0.044 Vp- p.
D)440 mVp- p.

Question 32

Refer to the figure above. If C4 opened, the signal voltage at the drain of Q1 would

A)increase.
B)decrease.
C)remain the same.
D)distort.

Question 33

Refer to the figure above. If the source- drain of Q2 shorted, the output signal from Q1 would

A)increase.
B)decrease.
C)remain the same.
D)distort.

Question 34

When troubleshooting a multiple stage CS amplifier, signal tracing reveals a significant amount of signal voltage at the source of the first stage. The most likely problem is

A)an open coupling capacitor from signal source.
B)too much dc supply voltage.
C)a shorted load in third stage.
D)an open source bypass capacitor.

Question 35

Two common- source amplifiers are cascaded. The overall phase shift from the input of the first amplifier to the output of the second amplifier is

A)45°.
B)90°.
C)0°.
D)180°.

Question 36

What is the role of the low- pass filter in a class D amplifier?

A)Remove hum
B)Prevent oscillation
C)Remove the modulating frequency and harmonics
D)Limit amplifier frequency response

Question 37

What component of an FET amplifier needs to be at least ten times greater than RD to ensure maximum voltage gain?

A)gm
B)r'ds
C)Rs
D)RS

Question 38

Refer to the figure above. If gm = 6500 µS and an input signal of 125 mVp- p is applied to the gate, the output voltage Vout is

A)2.68 Vp- p.
B)1.625 Vp- p.
C)0.8125 Vp- p.
D)6.25 Vp- p.

Question 39

Refer to the figure above. If R5 opened, Vout would

A)increase.
B)decrease.
C)remain the same.
D)distort.

Question 40

Refer to the figure above. If Vin = 1 Vp- p, the output voltage Vout would be

A)0 V.
B)undistorted.
C)clipped on the positive peaks.
D)clipped on the negative peaks.