Deck 6: BJT Amplifiers

Question 1

Figure 4
Refer to Figure 4. The arrangement of transistors is called a

A)Sziklai pair
B)differential pair
C)Darlington pair
D)complementary follower

Answer 1

C

Question 2

The ac emitter resistance, re', is

A)is directly proportional to IE
B)generally measured with an ohmmeter
C)both A and B
D)none of the above

Answer 2

D

Question 3

Figure 7
Refer to Figure 7. Describe the expected signals at Vout1 and Vout2 with respect to the input

A)Vout1 is inverted; Vout2 is not- inverted
B)Vout1 is not- inverted; Vout2 is inverted
C)both are inverted
D)neither signal is inverted

Answer 3

A

Question 4

Figure 2
Refer to Figure 2. The input resistance at the base, Rin(base), is approximately

A)12 k▲
B)8.5 k▲
C)17 k▲
D)5.8 k▲

Question 5

Figure 3
Refer to Figure 3. Rin is approximately

A)1.0 k▲
B)1.8 k▲
C)4.5 k▲
D)2.7 k▲

Question 6

Figure 6 Assume there is no loading effect of Q₂/Q₃ on Q₁ and R_L is the load.
Refer to Figure 6. The total voltage gain is approximately

A)75
B)100
C)25
D)50

Question 7

Figure 5
Refer to Figure 5. Express the overall voltage gain as a standard voltage gain

A)100,000
B)1000
C)316
D)562

Question 8

Figure 4
Refer to Figure 4. Assume each transistor has a fiac of 100. The overall fiac is

A)200
B)1,000
C)100
D)10,000

Question 9

The measurement unit for fiac is

A)the ohm
B)the volt
C)the ampere
D)there are no units as it is a ratio

Question 10

Figure 7
Refer to Figure 7. Assume an identical signal is applied to input- 1 and input- 2 and further assume that RC1 = RC2. For this case, the ideal output is

A)zero
B)RC1/RE
C)RC1/2RE
D)twice the input

Question 11

In a common- base (CB)amplifier

A)open
B)connected through a large resistor to ground
C)the base lead is at dc ground
D)the base lead is at ac ground

Question 12

The hybrid parameter that is the same as fiac is

A)hrb
B)hfe
C)hrc
D)hoc

Question 13

Figure 4
Refer to Figure 4. The input signal is an 8 Vpp sine wave driving a load that is a 16 ▲ speaker. The power delivered to the speaker is approximately

A)250 mW
B)0.75 W
C)1 W
D)0.5 W

Question 14

Figure 6 Assume there is no loading effect of Q₂/Q₃ on Q₁ and R_L is the load.
Refer to Figure 6. Assume R2 is open. This would cause

A)no ac output
B)the dc voltage on Q1 base to decrease
C)an increase in I_E1
D)all of the above

Question 15

Figure 1
Refer to Figure 1. To calculate the input resistance looking in at Vin, you do not need to consider the value of

A)fiac
B)RC
C)R_E
D)the bias resistors

Question 16

A CB amplifier has an advantage when you need

A)high input impedance
B)high frequency response with impedance matching
C)high current gain
D)all of the above

Question 17

Figure 1
Refer to Figure 1. Looking in at Vin, the input resistance is approximately

A)5.6 k▲
B)14 k▲
C)39 k▲
D)1.8 k▲

Question 18

Figure 6 Assume there is no loading effect of Q₂/Q₃ on Q₁ and R_L is the load.
Refer to Figure 6. The dc voltage across RL should be approximately

A)6.3 V
B)5.2 V
C)7.5 V
D)4.0 V

Question 19

Figure 2
Refer to Figure 2. This circuit is an example of a

A)common- emitter amplifier
B)common- collector amplifier
C)common- base amplifier
D)none of the above

Question 20

Figure 1
Refer to Figure 1. If a large capacitor is placed in parallel with RE, the input resistance will

A)increase
B)decrease
C)remain the same

Question 21

A typical common- base (CB)amplifier has

A)high current gain
B)high input resistance
C)high voltage gain
D)all of the above

Question 22

Figure 3
Refer to Figure 3. VE is approximately

A)1.0 V
B)5.0 V
C)2.5 V
D)7.5 V

Question 23

To calculate the end points for an ac load line, it is assumed that

A)the load resistor is removed
B)RC is in parallel with RE
C)ac and dc resistances are the same
D)capacitors are shorted

Question 24

Figure 5
Refer to Figure 5. Explain the purpose of R1 and R2

A)R1 is the input resistance of Q2; R2 is the output resistance of Q1
B)R1 and R2 are the collector and emitter resistors of Q1
C)R1 is the output resistance of Q1; R2 is the input resistance of Q2
D)R1 and R2 are the bias resistors of Q2

Question 25

Power gain can be found by multiplying current gain by the input resistance.

Question 26

Figure 1
Refer to Figure 1. To calculate the input resistance looking in at Vin, dc sources are replaced with

A)the bias resistors
B)a ground
C)an open
D)the ac emitter resistance

Question 27

Figure 3
Refer to Figure 3. The power delivered to RL is approximately

A)160 mW
B)360 mW
C)240 mW
D)80 mW

Question 28

In a CC amplifier, the power gain is approximately equal to the

A)voltage gain
B)current gain squared times RL
C)voltage gain squared divided by R_L
D)current gain

Question 29

Figure 2
Refer to Figure 2. If RE1 and RE2 were switched, the

A)both the input resistance and the gain would increase
B)the input resistance would decrease and the gain would be unchanged
C)the input resistance would increase and the gain would decrease
D)IC would increase

Question 30

An amplifier can invert the phase of a signal and still be a linear amplifier.

Question 31

Figure 6 Assume there is no loading effect of Q₂/Q₃ on Q₁ and R_L is the load.
Refer to Figure 6. The input resistance is approximately

A)3.6 k▲
B)4.5 k▲
C)2.4 k▲
D)3.0 k▲

Question 32

A bypass capacitor normally should have high reactance.

Question 33

Figure 2
Refer to Figure 2. The voltage gain is approximately

A)28
B)47
C)39
D)19

Question 34

Figure 7
Refer to Figure 7. Assume output is taken between Vout1 and Vout2. This condition is a

A)double ended input with a differential output
B)differential input with a differential output
C)single ended input with a differential output
D)single ended input with a single ended output

Question 35

Figure 3
Refer to Figure 3. The power gain is approximately

A)5
B)20
C)40
D)10

Question 36

Figure 5
Refer to Figure 5. The overall voltage gain of the amplifier in dB is

A)55 dB
B)50 dB
C)60 dB
D)none of the above

Question 37

If a load resistor is connected to a CE amplifier, the gain will decrease.

Question 38

The Sziklai pair uses two types of transistors, an npn and a pnp.

Question 39

Figure 1
Refer to Figure 1. The ac emitter resistance, re', is approximately

A)680 ▲
B)8 ▲
C)13 ▲
D)25 ▲

Question 40

Figure 4
Compare Figure 4 to Figure 3. The two- transistor circuit in Figure 4 has

A)increased power gain
B)much more voltage gain
C)much higher input resistance
D)all of the above

Question 41

A differential amplifier should have a high common- mode rejection ratio.

Question 42

The power gain of a CC amplifier is approximately 1.

Question 43

The internal emitter resistance of a transistor is a dc resistance.