Deck 12: The Operational Amplifier

Question 1

The input offset current equals the

A)difference between two base currents.
B)difference between two base- emitter voltages.
C)collector current divided by current gain.
D)average of two base currents.

Answer 1

A

Question 2

With both inputs grounded, the only offset that produces an error is the

A)input offset current.
B)input offset voltage.
C)input short circuit current.
D)input bias current.

Answer 2

B

Question 3

The two basic ways of specifying input impedance of an op- amp are

A)differential and extremely high.
B)differential and common- mode.
C)differential and common- loop.
D)closed- loop and common- mode.

Answer 3

B

Question 4

There can be no current to ground through

A)a virtual ground.
B)an ordinary ground.
C)a mechanical ground.
D)an ac ground.

Question 5

The common- mode signal is applied to

A)the inverting input.
B)the noninverting input.
C)both inputs.
D)None of the above.

Question 6

The typical input stage of an op- amp has an)

A)push- pull circuit.
B)emitter follower.
C)single- ended input and differential output.
D)two- input differential amplifier.

Question 7

It takes an op- amp 22 µs to change its output from - 15 V to +15 V. The slew rate for this amplifier is

A)0.73 V/µs.
B)1.36 V/µs.
C)0.68 V/µs.
D)660 V/µs.

Question 8

An inverting amplifier with a gain of - 8 means that

A)the stage reduces the signal by a factor of 8 from input to output.
B)the signal is attenuated by a factor of 8.
C)ac and dc signals are increased by a factor of 8 with no phase shift.
D)the signal amplitude is increased by a factor of 8 with a 180° phase shift.

Question 9

Refer to the figure above. Which circuit has a voltage gain of 1?

A)a)
B)b)
C)c)
D)None of the above.

Question 10

Refer to the figure above. Which circuit has a voltage gain of 20?

A)a)
B)b)
C)c)
D)None of the above.

Question 11

Refer to the figure above. Which components are used for offset voltage compensation?

A)R3
B)R4
C)R1 and R2
D)R2

Question 12

The closed- loop input impedance in a noninverting amplifier is

A)ideally zero.
B)sometimes less than the open- loop input impedance.
C)equal to the open- loop input impedance.
D)much greater than the open- loop input impedance.

Question 13

Refer to the figure above. If these three circuits were connected as a multiple- stage amplifier, the total voltage gain would be

A)10.
B)21.
C)210.
D)1.

Question 14

The op- amp can amplify

A)dc signals only.
B)ac signals only.
C)both ac and dc signals.
D)neither ac nor dc signals.

Question 15

In an op- amp, the CMRR is limited mostly by the

A)gain- bandwidth product.
B)the common- mode gain of the op- amp.
C)tolerance of the resistors.
D)supply voltages.

Question 16

Refer to the figure above. This op- amp has a slew rate of 1.33 V/µs. How long would it take the output voltage to change from - 12 V to +12 V?

A)36 µs
B)18 µs
C)48 µs
D)16 µs

Question 17

The feedback fraction "B"

A)may not equal 1.
B)is usually greater than 1.
C)may equal 1.
D)is always less than 1.

Question 18

Refer to c)in the figure above. If an amplifier with an input impedance of 12 k▲ and the same voltage gain is needed, the new value of R1 would be and the new value of Rf would be .

A)12 k▲, 108 k▲
B)12 k▲, 120 k▲
C)13.3 k▲, 120 k▲
D)10 k▲, 100 k▲

Question 19

What is the value of compensating resistor needed for a noninverting op- amp circuit using 10 k▲ resistors for both RI and RF?

A)100 k▲
B)5 k▲
C)20 k▲
D)10 k▲

Question 20

Refer to the figure above. Which circuit is a voltage follower?

A)a)
B)b)
C)c)
D)None of the above.

Question 21

For a given op- amp, which of these is constant?

A)AOL fcOL)
B)Feedback voltage
C)AOL
D)fCCL)

Question 22

If the unit- gain frequency is 10 MHz and the mid- band open- loop voltage gain is 200,000, the cutoff frequency is

A)25 MHz.
B)5 kHz.
C)50 Hz.
D)5 Hz.

Question 23

Refer to the figure above. Which components are used to set input impedance and voltage gain?

A)R4
B)R3
C)R3 and R4
D)R1 and R2

Question 24

The loop gain AOLB

A)may not equal 1.
B)is usually much smaller than 1.
C)is between 0 and 1.
D)is usually much greater than 1.

Question 25

Op- amp noise is highest at low frequencies due to

A)1/f noise.
B)white noise.
C)inductive noise.
D)?noise density
D)resistive noise.

Question 26

When the initial slope of a sine wave is greater than the slew rate,

A)the op- amp works best.
B)voltage gain is maximum.
C)the output looks exactly like the input.
D)distortion occurs.

Question 27

Refer to c)in the figure above. Vin = - 60 mV. The value of Vout is

A)about 16 V.
B)- 600 mV.
C)600 mV.
D)660 mV.

Question 28

Refer to c)in the figure above. If Rf is changed to 1 M▲, the new Acl would be

A)- 21.
B)21.
C)- 20.
D)20.

Question 29

Refer to the figure above. Which circuit has a voltage gain of 10?

A)a)
B)b)
C)c)
D)None of the above.

Question 30

If an op- amp were perfect, the CMRR would

A)be zero.
B)be very small.
C)approach infinity.
D)be less than one.

Question 31

The closed- loop voltage gain of an inverting amplifier equals

A)the input resistance.
B)the ratio of the input resistance to the feedback resistance.
C)the open- loop voltage gain.
D)the feedback resistance divided by the input resistance.

Question 32

Which op- amp parameter is dependent upon the high frequency response of the amplifier stages inside the op- amp?

A)Slew rate
B)Input offset voltage
C)Input bias current
D)Short- circuit output current

Question 33

The open- loop voltage gain Aol)of an op- amp is the

A)external voltage gain the device is capable of.
B)most controlled parameter.
C)internal voltage gain the device is capable of.
D)same as Acm.

Question 34

Refer to the figure above. Which circuit is the inverting amplifier?

A)a)
B)b)
C)c)
D)None of the above.

Question 35

The input offset current is

A)the difference between the input bias currents.
B)unimportant when a base resistor is used.
C)not related to the input bias currents.
D)less than the input offset voltage.

Question 36

With negative feedback, the returning signal

A)is proportional to differential voltage gain.
B)opposes the input signal.
C)is proportional to output current.
D)aids the input signal.

Question 37

Refer to the figure above. Which components are used for bias current compensation?

A)R2
B)R3
C)R4
D)R1 and R2

Question 38

Refer to a)in the figure above. If this circuit has a Vin = 12 Vp- p, the value of Vout would be

A)- 20 V.
B)8.48 Vp- p.
C)20 V.
D)12 Vp- p.

Question 39

The voltage gain of an op- amp is unity at the

A)unity- gain frequency.
B)cutoff frequency.
C)generator frequency.
D)power bandwidth.

Question 40

A voltage follower amplifier comes to you for service. With a sine wave input of 1 V, the output is squared off at approximately 30 V peak- to- peak. The most likely problem is

A)the input is shorted to ground.
B)open feedback loop.
C)the output is shorted to ground.
D)no dc supply voltage.

Question 41

The ideal op- amp has

A)infinite input impedance and zero output impedance.
B)infinite output impedance and zero input impedance.
C)infinite voltage gain and infinite bandwidth.
D)Both A and C.

Question 42

The voltage follower has a

A)large closed- loop output impedance.
B)closed- loop bandwidth of zero.
C)closed- loop voltage gain of unity.
D)small open- loop voltage gain.

Question 43

Refer to b)in the figure above. If this circuit has a Vin = 0.7, Vout would be

A)0 V.
B)14.7 V.
C)- 14.7 V.
D)14 V.

Question 44

What type of input is provided to an op- amp for slew- rate measurement?

A)Triangle waveform
B)Sinusoidal voltage
C)Step input voltage
D)Constant dc voltage