Deck 9: Common-Emitter Amplifiers

Question 1

The disadvantage of swamping a CE amplifier is that it

A) increases voltage gain.
B) decreases voltage gain.
C) increases input impedance.
D) decreases input impedance.

Answer 1

decreases voltage gain.

Question 2

A BJT has measured values of IB = 1 mA and IC = 80mA. When IB is varied by ±100 μA, IC changes by ±10 mA. What is the value of ac beta for the device?

A) 80
B) 10
C) 100
D) 800

Answer 2

100

Question 3

A common-emitter amplifier may be swamped to

A) decrease the input impedance of an amplifier.
B) reduce variations in voltage gain.
C) increase the value of Av for an amplifier.
D) cause all of the above to occur.

Answer 3

reduce variations in voltage gain.

Question 4

The common-emitter amplifier provides

A) voltage gain, current gain, and power gain.
B) voltage gain and power gain, but no current gain.
C) current gain and power gain, but no voltage gain.
D) current gain and voltage gain, but no power gain.

Question 5

If a bypass capacitor opens, the value of rʹe

A) increases.
B) decreases.
C) does not change.

Question 6

By design, the reactance of a bypass capacitor is extremely at the amplifierʹs lowest operating frequency.

A) low
B) high

Question 7

What is the value of Av for the amplifier?

A) 400
B) 150
C) 200
D) 33.33

Question 8

A BJT has measured values of IB = 1 mA and IC = 80mA. When IB is varied by ±100 μA, IC changes by ±10 mA. What is the value of dc beta for the device?

A) 80
B) 10
C) 100
D) 800

Question 9

A BJT has values of hFE = 200 and hfe = 120. The ac current gain for the device is

A) 200.
B) 120.
C) 24,000.
D) 320.

Question 10

By design, the reactance of a coupling capacitor is extremely at the amplifierʹs lowest operating frequency.

A) low
B) high

Question 11

The input and output signal voltages for a common-emitter amplifier are

A) always 180° out of phase.
B) 180° out of phase in all but one amplifier configuration.
C) in phase in all but one amplifier configuration.
D) always in phase.

Question 12

The amplifier has a value of VE = 1.1 V. What is the approximate value of Av for the circuit?

A) 11
B) 110
C) 485
D) Cannot be determined with the information given

Question 13

Why is dc isolation between amplifier stages important?

A) It allows an ac signal to be coupled from a source stage to a load stage.
B) It prevents the dc biasing of the source stage from affecting the dc biasing of the load stage.
C) It allows a dc signal to be coupled from a source stage to a load stage.

Question 14

Which of the following would indicate that the load in Figure has opened?

A) An increase in the value of VE
B) An increase in the value of VC
C) An increase in the value of Av

Question 15

The input and output signal currents for a common-emitter amplifier are

A) always 180° out of phase.
B) 180° out of phase in all but one amplifier configuration.
C) in phase in all but one amplifier configuration.
D) always in phase.

Question 16

The amplifier in Figure has values of RC = 10 kΩ, rʹe = 25 Ω, and Ai = 15. What is the value of Ap for the circuit?

A) 375
B) 6,000
C) 400
D) Cannot be determined with the information given.

Question 17

A CE amplifier has values of VB = 5 V and RE = 2 kΩ. What is the value of rʹe for the transistor?

A) 10 Ω
B) 5 Ω
C) 11.7 Ω
D) Cannot be determined with the information given.

Question 18

Which of the following conditions would indicate that an emitter bypass capacitor is open?

A) The presence of a dc voltage at the emitter terminal of the BJT
B) The presence of an ac voltage at the emitter terminal of the BJT
C) The loss of the ac signal at the base terminal of the BJT
D) None of the above.

Question 19

When using an oscilloscope to verify the operation of a CE amplifier, you must remember to

A) adjust the TIME/DIV setting on the oscilloscope when going from the amplifier input to the amplifier output.
B) adjust the VOLTS/DIV setting on the oscilloscope when going from the amplifier input to the amplifier output.
C) connect the external trigger of the oscilloscope to the circuit under test.
D) take all of the steps listed above.

Question 20

What is the value of Zbase for the circuit in Figure ?

A) 3.75 kΩ
B) 300 kΩ
C) 5 kΩ
D) 400 kΩ

Question 21

A CE amplifier is constructed using RC = 3.3 kΩ and RL = 12 kΩ. The transistor has the ~
Following specifications: hfe = 120, hie = 5 kΩ, hre = 4 × 10=4, and hoe = 2500 μS. What is the
Value for Av for this amplifier?

A) Approximately 62.2
B) Approximately 79.1
C) Approximately 287.8
D) None of the above.

Question 22

What is the value of r`e?

A) 25 Ω
B) 26 Ω
C) 28 Ω
D) 30 Ω

Question 23

A swamped amplifier has values of hie = 3 kΩ, hfe = 150, hFE = 200, rE = 300 Ω, and RE = 1.2 kΩ.
What is the value of Zbase for the circuit?

A) 3 kΩ
B) 183 kΩ
C) 48 kΩ
D) None of these are correct.

Question 24

A transistor has the following values: hfe = 120, hFE = 200, hie = 5 kΩ, hre = 4 × 10-4, and hoe = 2500 μS. What is the value of rʹe for the device?

A) 4 × 10-4 Ω
B) 41.7 Ω
C) 400 Ω
D) 25 Ω

Question 25

The base input impedance of a BJT is listed on its spec sheet as

A) hfe.
B) hre.
C) hie.
D) hoe.

Question 26

If a 10 kΩ load resistance is connected to the circuit, the voltage gain

A) Increases.
B) Decreases.
C) Does not change significantly.

Question 27

For circuit analysis purposes, the most commonly used h-parameters are

A) hie and hoe.
B) hre and hfe.
C) hie and hre.
D) hfe and hie.

Question 28

What is the approximate value of Zbase?

A) 2.77 kΩ
B) 4.62 kΩ
C) 27.6 kΩ
D) 45.8 kΩ

Question 29

What is the approximate value of Zin?

A) 867
B) 992 Ω
C) 1.21 kΩ
D) None of the above.

Question 30

If the 8.2 kΩ and 1.5 kΩ biasing resistors are changed to 16 kΩ and 3 k Ω respectively, the circuit voltage gain

A) Increases.
B) Decreases.
C) Does not change significantly.

Question 31

What is the approximate value of Av?

A) 22.2
B) 170
C) 5
D) None of the above are correct.