Deck 6: Bjt Amplifiers

Question 1

If a CE stage is direct coupled to an emitter- follower, how many coupling capacitors are there between the two stages?

A)0
B)1
C)2
D)3

Answer 1

A

Question 2

Output resistance in a common- collector amplifier circuit is stepped down by a factor of

A)Beta fi.
B)r'e + re.
C)alpha a.
D)RE "RL.

Answer 2

A

Question 3

A three- stage amplifier has a gain of 20 for each stage. The overall decibel voltage gain is

A)78 dB.
B)60 dB.
C)400 dB.
D)8,000 dB.

Answer 3

A

Question 4

The best choice for a very high power amplifier is an)

A)common- base.
B)common- emitter.
C)common- collector.
D)emitter- follower.

Question 5

Refer to the figure above. If VE = 0, the trouble might be that

A)RC is open.
B)RE is open.
C)R1 is open.
D)R2 is open.

Question 6

The voltage gain of a common- emitter amplifier, AV, can be defined as

A)AV = IeRC .
B)AV = Vb .
C)AV = IC × RC.
D)AV = RC .

Question 7

A differential amplifier should exhibit a differential gain and a common mode gain.

A)low, high
B)high, high
C)high, low
D)low, low

Question 8

The input resistance, Rinbase), of a common- emitter amplifier, consists of

A)RG " rc " fir'e.
B)re " fir'e.
C)fiac r'e.
D)rb " fire.

Question 9

Refer to the figure above. The output signal at the collector of Q1 is higher than normal. This could be caused by an)

A)open C1.
B)open base- emitter of Q1.
C)open C3.
D)open C2.

Question 10

Refer to the figure above. If the collector opened internally, the voltage on the collector would

A)remain the same.
B)decrease.
C)increase.
D)be undetermined.

Question 11

Assume that a certain differential amplifier has a differential gain of 5,000 and a common mode gain of 0.3. What is the CMRR in dB?

A)1,500 dB
B)84.44 dB
C)0.3 dB
D)62.12 dB

Question 12

Refer to the figure above. If R2 opened, the value of IC would be

A)8 mA.
B)6 mA.
C)6.67 mA.
D)10 mA.

Question 13

A differential amplifier provides an output that is the _ _ of the two input quantities.

A)sine
B)difference
C)square
D)multiplication

Question 14

To reduce the distortion of an amplified signal, you can increase the

A)load resistance.
B)emitter feedback resistance.
C)generator resistance.
D)collector resistance.

Question 15

Assume that a certain differential amplifier has a differential gain of 3,000 and a common mode gain of 0.25. What is the CMRR?

A)12,000
B)66.89
C)750
D)3,025

Question 16

The capacitor that produces an ac ground at a point in a circuit is called an)

A)ac open.
B)dc short.
C)coupling capacitor.
D)bypass capacitor.

Question 17

The input resistance of the base of an emitter follower is usually

A)low.
B)shorted to ground.
C)high.
D)open.

Question 18

Refer to the figure above. If R2 opened, VCE would be

A)4.8 V.
B)0 V.
C)20 V.
D)10 V.

Question 19

Refer to the figure above. If an emitter- bypass capacitor were installed, AV would be

A)4.96.
B)398.
C)125.
D)560.

Question 20

Which of the following is not a characteristic of the emitter- follower?

A)Low output impedance
B)Low input impedance
C)High current gain
D)Voltage gain of 1

Question 21

Removing the emitter bypass capacitor from a common- emitter amplifier

A)increases the distortion.
B)does not affect Rin.
C)decreases Rin and increases voltage gain.
D)increases Rin and decreases voltage gain.

Question 22

For a bypass capacitor to work properly, the

A)XC should be ten times greater than RE at the minimum operating frequency.
B)XC should be ten times smaller than RE at the minimum operating frequency.
C)XC should equal RE.
D)XC should be twice the value of the RE.

Question 23

Removing a bypass capacitor from a fully bypassed, common- emitter amplifier circuit will voltage gain and ac input resistance.

A)decrease, decrease
B)increase, decrease
C)decrease, increase
D)increase, increase

Question 24

The voltage gain of an amplifier is defined as the

A)ac collector current divided by the ac emitter current.
B)ac input voltage divided by the ac output voltage.
C)ac collector current divided by the ac base current.
D)ac output voltage divided by the ac input voltage.

Question 25

The value of output resistance in a common- emitter amplifier, Rout, consists of

A)RL + RC.
B)fi " RC.
C)RC.
D)RL " RC.

Question 26

In a two- stage amplifier, the voltage gain of the first stage is 80 and the voltage gain of the second stage is 50. How much is the overall voltage gain?

A)400
B)130
C)4,000
D)72

Question 27

Refer to the figure above. Which of the following faults would account for the output voltage being lower than normal, but not a complete loss of output voltage?

A)An open C4
B)An open C1
C)An open C5
D)An open C3

Question 28

For transistors

A)the dc and ac current gains are the same.
B)amplification of signal voltage is not possible.
C)the dc and ac current gains are usually different.
D)the dc current gain is zero.

Question 29

Leaving some of the emitter resistance unbypassed in a common- emitter amplifier will

A)reduce distortion.
B)increase the input impedance.
C)stabilize the voltage gain.
D)All of the above.

Question 30

The best selection for a high input impedance amplifier is a

A)high gain common- emitter.
B)common- base.
C)low gain common- emitter.
D)common- collector.

Question 31

In a swamped amplifier, the effects of r'e become

A)significant to the analysis.
B)insignificant.
C)important to voltage gain.
D)critical to input impedance.

Question 32

If two transistors are connected as a Darlington pair and each transistor has a Beta of 175, the overall current gain of the pair equals

A)5,000.
B)3,625.
C)10,000.
D)30,625.

Question 33

Where is the output coupling capacitor connected on a common- collector amplifier?

A)Emitter
B)Collector
C)dc power supply
D)Base

Question 34

A certain transistor has a dc emitter current of 25 mA. The value of r'e is

A)1 ▲.
B)2.5 ▲.
C)1.2 ▲.
D)25 ▲.

Question 35

A bypass capacitor is placed across the emitter resistor in a voltage- divider biased common- emitter amplifier circuit. This will

A)place the emitter at ac ground.
B)reduce the emitter's dc voltage to zero.
C)shift the Q- point on the dc load line.
D)All of the above.

Question 36

The quantity r'e

A)is a dc value.
B)is temperature dependent.
C)is external to the transistor.
D)has no effect on gain in transistors.

Question 37

In general, coupling capacitors can be considered

A)open for signal voltage and a short for dc.
B)lossy.
C)short for signal voltage and an open for dc.
D)short for signal voltage and a short for dc.

Question 38

Reducing all dc sources to zero is done to help obtain the

A)complete amplifier circuit.
B)dc equivalent circuit.
C)voltage- divider biased circuit.
D)ac equivalent circuit.

Question 39

An emitter follower has a voltage gain that is

A)much less than one.
B)zero.
C)approximately equal to one.
D)greater than one.

Question 40

The primary reason an ac load line differs from a dc load line is

A)changes in current are nonlinear for small- signal amplifier operation.
B)the ac load line is not as steep as the dc load line.
C)the effective ac collector resistance is greater than the dc collector resistance.
D)the effective ac collector resistance is less than the dc collector resistance.

Question 41

Refer to the figure above. If AV1 = 75 and AV2 = 95, AVT would be

A)7125.
B)95.
C)75.
D)1275.

Question 42

The three factors that must be taken into account when determining the actual signal voltage at the base of a small signal bipolar amplifier are

A)source resistance, bias resistance, and input resistance.
B)source resistance, collector resistance, internal resistance.
C)source resistance, emitter resistance, and input resistance.
D)source resistance, bias resistance, and load resistance.

Question 43

The h- parameter, hfe, is the same as of the transistor.

A)ac Beta
B)minimum hold current
C)maximum collector current
D)dc Beta

Question 44

Increasing the resistance of the load resistor in an RC coupled common- emitter amplifier will have what effect on voltage gain?

A)Increases the voltage gain
B)Decreases the voltage gain
C)Does not affect the voltage gain

Question 45

Often a common- collector will be the last stage before the load; the main functions)of this stage is to

A)provide a high frequency path to improve the frequency response.
B)provide a large voltage gain.
C)buffer the voltage amplifiers from the low resistance load and provide impedance matching for maximum power transfer.
D)provide phase inversion.

Question 46

Which of the following is not a characteristic of the common- base amplifier?

A)High voltage gain
B)High input impedance
C)Current gain of 1
D)High output impedance

Question 47

The ac resistance r'e approximately equals

A)25 mV .
B)25 mV .
C)25 mV .
D)25 mV × IC. IB IC IE

Question 48

In a two- stage amplifier, the input resistance of the second stage

A)does not affect the voltage gain of the first stage.
B)affects the voltage gain of the first stage.
C)is in parallel with the collector resistor of the first stage.
D)Both B and C above.