Deck 12: The Operational Amplifier

Question 1

The input offset current, IOS, is the

A)largest of two bias currents
B)sum of two bias currents
C)average of two bias currents
D)difference of two bias currents

Answer 1

D

Question 2

Figure 4 Both op- amps are compensated and have A_OL = 100 dB and f_T = 2 MHz.
Refer to Figure 4(a). The open- loop critical frequency, fc(ol), is

A)20 Hz
B)2.0 Hz
C)100 Hz
D)10 Hz

Answer 2

A

Question 3

Figure 2
Refer to Figure 2(a). The closed- loop gain, ACL, is

A)+7.8
B)+6.8
C)-6.8
D)-7.8

Answer 3

C

Question 4

Figure 3
Refer to Figure 3. As the closed- loop gain, ACL, increases, the

A)bandwidth decreases
B)input impedance increases
C)CMRR decreases
D)all of the above

Question 5

The input resistance of a BIFET is

A)low
B)dependent on the load
C)controlled by the bias current
D)none of the above

Question 6

Figure 2
Refer to Figure 2(b). The feedback fraction, B, is

A)+1
B)0
C)-1
D)none of the above

Question 7

Figure 2
Refer to Figure 2(c). The closed- loop gain, ACL, is

A)-9.2
B)+9.2
C)+8.2
D)-8.2

Question 8

A typical op- amp

A)uses dc coupling
B)has two supply voltages
C)has very high open- loop gain
D)all of the above

Question 9

Figure 5 The RC components shown represent internal R and C of a compensated op- amp.
Refer to Figure 5. Assume the input frequency is much less that fc. In this case, the overall AOL is

A)dependent on the feedback
B)equal to 1
C)halved
D)nearly unaffected

Question 10

Common- mode rejection ratio (CMRR)depends on the

A)input voltage
B)frequency
C)bias current
D)all of the above

Question 11

Figure 2
Refer to Figure 2. The circuit or circuits with a virtual ground is

A)(a)
B)(b)
C)(c)and (d)
D)all of these

Question 12

When the closed loop gain, ACL, is equal to 0 dB, the bandwidth is

A)the same as at fc
B)minimum
C)maximum
D)none of the above

Question 13

Figure 4 Both op- amps are compensated and have A_OL = 100 dB and f_T = 2 MHz.
Refer to Figure 4(a). The closed loop bandwidth, fc(cl), is

A)293 kHz
B)344 kHz
C)244 kHz
D)218 kHz

Question 14

The common- mode gain, ACM, of an op- amp with AOL = 200,000 and a CMRR of 80 dB is

A)10
B)40
C)80
D)20

Question 15

Figure 4 Both op- amps are compensated and have A_OL = 100 dB and f_T = 2 MHz.
Refer to Figure 4(a). Assume the output is a 1.0 kHz square wave that goes between +Vmax and -V_max. This fault is likely due to an

A)open Rf
B)internal open in the op- amp
C)open R_i
D)shorted R_i

Question 16

A CMRR of 110,000 is expressed in dB as

A)50.4 dB
B)106 dB
C)101 dB
D)110 dB

Question 17

Figure 4 Both op- amps are compensated and have A_OL = 100 dB and f_T = 2 MHz.
Refer to Figure 4(b). If the feedback resistor is open, the BW will equal

A)fT
B)0
C)f_c(ol)
D)none of the above

Question 18

Figure 1
Refer to Figure 1. The signal represents the output of a fast op- amp to a step input voltage. The slew rate for this op- amp is

A)90 V/ µs
B)18 V/ns
C)200 ns
D)45 V/ µs

Question 19

Figure 3
Refer to Figure 3. With a constant input, the output ranges from

A)+300 mV to +550 mV
B)-300 mV to -550 mV
C)+250 mV to +500 mV
D)-250 mV to -500 mV

Question 20

The input offset voltage is defined as a differential input dc voltage that

A)is required to balance the positive and negative supply voltages
B)forces the output to 0 V
C)is the difference in two bias voltages
D)is required to balance the two bias currents

Question 21

Differential input impedance is measured from one input to ground.

Question 22

The need for bias current compensation is reduced by

A)using a smaller input signal
B)using a BIFET op- amp
C)using a larger load
D)all of the above

Question 23

The open- loop gain is determined by the feedback circuit.

Question 24

The input stage of an op- amp is a differential amplifier.

Question 25

A common- mode input is when two equal amplitude but opposite polarity signals are applied to the inputs of a differential amplifier.

Question 26

Assume an op- amp has three different internal critical frequencies that are above the fT. The overall roll- off rate is

A)a constant -60 dB/decade
B)a composite of the three critical frequencies
C)the average of the three critical frequencies
D)a constant -20 dB/decade

Question 27

The gain- bandwidth product for a compensated op- amp is a constant.

Question 28

Figure 4 Both op- amps are compensated and have A_OL = 100 dB and f_T = 2 MHz.
Refer to Figure 4(b). The closed loop bandwidth, fc(cl), is

A)293 kHz
B)218 kHz
C)244 kHz
D)256 kHz

Question 29

The open- loop and closed- loop gains for a voltage follower equal 1.

Question 30

The output impedance of an inverting amplifier is very small.

Question 31

CMRR is the ratio of

A)differential open- loop gain to differential closed loop gain
B)inverting open- loop gain to inverting closed- loop gain
C)differential open- loop gain to common mode gain
D)inverting closed- loop gain to common mode gain

Question 32

Figure 2
Refer to Figure 2. The circuit with the highest absolute gain, |ACL|, is

A)(a)
B)(b)
C)(c)
D)(d)

Question 33

Figure 5 The RC components shown represent internal R and C of a compensated op- amp.
Refer to Figure 5. Assume the input frequency is equal to the critical frequency. The phase shift is

A)-30°
B)-90°
C)0°
D)-45°

Question 34

At low frequencies, voltage noise density goes up.

Question 35

Assume an op- amp has bias currents of 10.0 µA and 10.2 µA. The input offset current is

A)20.2 µA
B)0.2 µA
C)10.1 µA
D)none of the above

Question 36

Figure 2
Refer to Figure 2. The circuit with the lowest input impedance is

A)(a)
B)(b)
C)(c)
D)(d)