Deck 10: Amplifier Frequency Response

Question 1

The capacitor that determines the dominant lower cutoff frequency is

A)whichever capacitor has the highest fcl
B)the input coupling capacitor
C)the bypass capacitor
D)the internal transistor capacitance

Answer 1

A

Question 2

Figure 2 I_GSS (max)= 100 pA. V_GS = -2.4 V
Refer to Figure 2. Assume RS is the only resistance "seen" by C2. The value of C2 that has a lower cutoff frequency of approximately 20 Hz is

A)5.0 µF
B)50 µF
C)22 µF
D)1.0 µF

Answer 2

A

Question 3

When each amplifier stage in a two- stage amplifier has equal dominant upper critical frequencies, the overall dominant frequency is equal to

A)less than the dominant frequency of one stage
B)the dominant frequency of one stage
C)twice the dominant frequency of one stage
D)none of the above

Answer 3

A

Question 4

Figure 2 I_GSS (max)= 100 pA. V_GS = -2.4 V
Refer to Figure 2. The value of C1 that has a lower cutoff frequency of approximately 20 Hz is

A)0.10 µF
B)10 nF
C)1 nF
D)1.0 µF

Question 5

Figure 3
Refer to Figure 3. The value of C2 that will result in a lower cutoff frequency of 40 Hz is

A)0.4 µF
B)0.2 µF
C)0.8 µF
D)2.0 µF

Question 6

The parasitic base- collector capacitance of a CE or CS amplifier affects

A)only the low- frequency response
B)only the high- frequency response
C)both A and B
D)none of the above

Question 7

The high- frequency response of a circuit can be measured by

A)raising the frequency until the midrange amplitude drops to 70.7%
B)measuring the rise time of a fast pulse
C)both A and B
D)none of the above

Question 8

The midrange output of a CS amplifier with a sine wave input is phase shifted by

A)90°
B)180°
C)0°
D)none of the above

Question 9

If a voltage gain of an amplifier is halved it represents a drop of

A)-3 dB
B)-6 dB
C)0 dB
D)-10 dB

Question 10

Assume the output of an amplifier is measured in midrange as 1.5 Vpp. The output at cutoff is

A)0.75 Vpp
B)1.06 Vpp
C)0.5 V_pp D)none of the above

Question 11

The input coupling capacitor is generally smaller on a CS amplifier than its equivalent BJT counterpart because

A)Rin is higher, compensating for the smaller C
B)the FET is a voltage- controlled device, so the extra charge is not needed
C)the input signal voltage is generally smaller
D)the frequency response is more important in BJTs than FETs

Question 12

Figure 1 Assume r_e' = 15 ▲.
Refer to Figure 1. The cutoff frequency due to C1 is

A)23 Hz
B)13 Hz
C)40 Hz
D)7.2 Hz

Question 13

Assume an amplifier has a midrange voltage gain of 22. Expressed in dB, this is

A)40.3
B)26.8 dB
C)13.4 dB
D)none of the above

Question 14

Figure 5. The sec/div control is set to 0.05 µS/div.
Refer to Figure 5. From the information given, the fcu is approximately

A)7.0 MHz
B)4.7 MHz
C)13.4 MHz
D)20 MHz

Question 15

Figure 4 Response of an amplifier
Refer to Figure 4. The Bode plotter is a computer tool that

A)shows amplitude as a function of frequency
B)shows amplitude as a function of time
C)both A and B
D)none of the above

Question 16

If an amplifier has a single break frequency at the high- end of the response curve, the gain- bandwidth product for any gain c1 is equal to

A)20
B)fcu
C)1
D)fT

Question 17

Figure 1 Assume r_e' = 15 ▲.
Refer to Figure 1. Rin is approximately

A)10 k▲
B)5.7 k▲
C)3.2 k▲
D)1.8 k▲

Question 18

Figure 1 Assume r_e' = 15 ▲.
Refer to Figure 1. If the RE1 is changed to a 33 ▲ resistor, the upper cutoff frequency

A)increases
B)decreases
C)is unaffected

Question 19

The critical frequency of an amplifier is specified at a power gain of

A)-10 dB
B)0 dB
C)-3 dB
D)-6 dB

Question 20

If an amplifier has a single break frequency at the low- end of the response curve, the roll- off rate is

A)-40 dB/decade
B)-10 dB/decade
C)-20 dB/decade
D)-60 dB/decade

Question 21

Figure 4 Response of an amplifier
Refer to Figure 4. The amplifier's frequency response indicates the midrange gain is 33.6 dB. Expressed as regular gain, this is approximately

A)31
B)70
C)24
D)48

Question 22

The Miller effect lowers the high- frequency response of inverting amplifiers.

Question 23

A voltage gain of 20 dB represents a voltage gain of 10.

Question 24

At the midrange frequency of an inverting amplifier, the phase shift is 180°.

Question 25

The input coupling capacitor affects the low- frequency response.

Question 26

Figure 1 Assume r_e' = 15 ▲.
Refer to Figure 1. Assume that Cbc = 6 pF and RL= 27 k▲. The Miller input capacitance due to Cbc is

A)168 pF
B)7.0 pF
C)216 pF
D)49 pF

Question 27

Figure 3
Refer to Figure 3. Assume the unloaded gain of the amplifier is 10. The ac equivalent Thevenin circuit looking back to the drain from C2 is

A)Vth = 50 mV; Rth =5.0 k▲
B)Vth = 100 mV; Rth =5.0 k▲
C)V_th = 100 mV; R_th =10 k▲
D)V_th = 50 mV; R_th =10 k▲

Question 28

Figure 1 Assume r_e' = 15 ▲.
Refer to Figure 1. What value of RL will produce a cutoff frequency due to C3 of 25 Hz?

A)19 k▲
B)8.8 k▲
C)24 k▲
D)14 k▲

Question 29

If Vout at the lower cutoff frequency is 1.0 V, the midrange output is 0.707 V.

Question 30

A Bode plot is a graph of decibel voltage gain as a function of phase angle.

Question 31

A step- response measurement can be used to test either the high- or the low- frequency response of an amplifier.

Question 32

The phase shift at the upper cutoff frequency of an amplifier is 90°.

Question 33

The bandwidth of an amplifier is determined by the

A)the roll- off rates of the upper and lower responses
B)dominant upper and lower cutoff frequencies
C)both A and B
D)the number of physical capacitors in the circuit