### Operational Amplifier Fundamentals And Effect Of Feedback In Amplifier Multiple Choice Questions And Answers

# Operational Amplifier Fundamentals

And Effect Of Feedback In Amplifier Multiple Choice Questions And Answers

1. Negative feedback in an amplifier

a) Reduces gain

b) Increase frequency &phase distortion

c) Reduces bandwidth

d) Increases noise

a) 2

b) 1

c) 1/2

d) 0

a) ∞

b)120k

c)110k

d)10k

a) 795mV

b) 395mV

c) 795 mV

d) 39.5mV

5. An ideal OP-AMP is an ideal

a) Current controlled Current source

b) Current controlled voltage source

c) Voltage controlled voltage source

d) voltage controlled current source

a) 10 volts

b) 5 volts

c) 1 volts

d) 5/2 volts

a) affects the difference mode gain Ad

b) affects the common mode gain Ac

c)affects both Ad and Ac

d) does not effect either Ad and Ac

a) CMRR

b) bandwidth

c) slew rate

d) open-loop gain

a) input voltage dependent linear transfer characteristic

b) high voltage gain

c) high input resistance

d) high CMRR

a) Ri=∞ ,A=∞ ,R0=0

b) Ri=0 ,A=∞ ,R0=0

c) Ri=∞ ,A=∞ ,R0=∞

d) Ri=0 ,A=∞ ,R0=∞

a) Reduces gain

b) Increase frequency &phase distortion

c) Reduces bandwidth

d) Increases noise

**Answer: Reduces gain**

2. A differential amplifier has a differential gain of 20,000 . CMRR=80 dB. The common mode gain is given bya) 2

b) 1

c) 1/2

d) 0

**Answer: 2**

3. The approximate input impedance of the OPAMP circuit which has Ri=10k, Rf=100k, RL=10ka) ∞

b)120k

c)110k

d)10k

**Answer: 10k**

4. An amplifier using an opamp with slew rate SR=1v/Î¼sec has a gain of 40db.if this amplifier has to faithfully amplify sinusoidal signals from dc to 20 KHz without introducing any slew-rate induced distortion, then the input signal level must not exceeda) 795mV

b) 395mV

c) 795 mV

d) 39.5mV

**Answer: 795 mV**5. An ideal OP-AMP is an ideal

a) Current controlled Current source

b) Current controlled voltage source

c) Voltage controlled voltage source

d) voltage controlled current source

**Answer: Current controlled voltage source**

6. An OPAMP has a slew rate of 5 V/Î¼ S .The largest sine wave O/P voltage possible at a frequency of 1MHZ isa) 10 volts

b) 5 volts

c) 1 volts

d) 5/2 volts

**Answer: 5/2 volts**

7. A change in the value of the emitter resistance Re in a differential amplifiera) affects the difference mode gain Ad

b) affects the common mode gain Ac

c)affects both Ad and Ac

d) does not effect either Ad and Ac

**Answer: affects the common mode gain Ac**

8. A differential amplifier is invariably used in the i/p stage of all OP-AMPs.This is done basically to provide the OP-AMPs with a very higha) CMRR

b) bandwidth

c) slew rate

d) open-loop gain

**Answer: CMRR**

9. Most of the linear ICs are based on the two-transistor differential amplifier because of itsa) input voltage dependent linear transfer characteristic

b) high voltage gain

c) high input resistance

d) high CMRR

**Answer: high CMRR**

10. The ideal OP-AMP has the following characteristics.a) Ri=∞ ,A=∞ ,R0=0

b) Ri=0 ,A=∞ ,R0=0

c) Ri=∞ ,A=∞ ,R0=∞

d) Ri=0 ,A=∞ ,R0=∞

**Answer: Ri=∞ ,A=∞ ,R0=0****11. A 741-type OP-AMP has a gain-bandwidth product of 1MHz.A non-inverting amplifier using this opamp & having a voltage gain of 20db will exhibit -3db bandwidth of**

a) 50 KHz

b) 100KHz

c) 1000/17 KHz

d) 1000/7.07 KHz

**Answer: 100KHz**

12. In the differential voltage gain & the common mode voltage gain of a differential amplifier are 48db &2db respectively, then its common mode rejection ratio is

a)23dB

b)25dB

c) 46dB

d) 50dB

**Answer: 46dB**

13. An amplifier without feedback has a voltage gain of 50,input resistance as 1 KÎ© & Output resistance of 2.5KÎ©.The input resistance of the voltage-shunt negative feedback amplifier using the above amplifier with a feedbacik factor of 0.2 is

a) 1/11KÎ©

b) 1/5KÎ©

c) 5KÎ©

d) 11KÎ©

**Answer: 1/11KÎ©**

14. Three identical amplifiers with each one having a voltage gain of 50,input resistance of 1KÎ© & output resistance of 250 ,are cascaded.The open circuit voltage gain of combined amplifier is

a) 49dB

b) 51dB

c) 98dB

d) 102dB

**Answer: 102dB**

15. Voltage Series feedback (also called series-shunt feedback) results in

a) Increase in both input & output impedances

b) Decreases in both input & output impedances

c) Increase in input impedance & decreases in output impedance

d) Decrease in input impedance & increase in output impedance

**Answer: Increase in input impedance & decreases in output impedance**

16. An ideal operational amplifier has

a) infinite output impedance

b) zero input impedance

c) infinite bandwidth

d)All of the above

**Answer: infinite bandwidth**

17. Another name for a unity gain amplifier is:

a) difference amplifier

b) Comparator

c) single ended

d) voltage follower

**Answer: voltage follower**

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

a) external voltage gain the device is capable of

b) internal voltage gain the device is capable of

c) most controlled parameter

d) same as Acl

**Answer: internal voltage gain the device is capable of**

19. A noninverting closed-loop op-amp circuit generally has a gain factor:

a) less than one

b) greater than one

c) of zero

d) equal to one

**Answer: greater than one**

20. In order for an output to swing above and l below a zero reference, the op-amp circuit requires:

a) a resistive feedback network

b) zero offset

c) a wide bandwidth

d) a negative and positive supply

**Answer: a negative and positive supply**

21. If ground is applied to the (+) terminal of an inverting op-amp, the (–) terminal will:

a) not need an input resistor

b) be virtual ground

c) have high reverse current

d) not invert the signal

**Answer: be virtual ground**

22. With negative feedback, the returning signal:

a) aids the input signal

b) is proportional to output current

c) opposes the input signal

d) is proportional to differential voltage gain

**Answer: opposes the input signal**

23. A portion of the output that provides circuit stabilization is considered to be:

a) negative feedback

b) Distortion

c) open-loop

d) positive feedback

**Answer: negative feedback**

24. How many leads does the TO-5 metal can package of an operational amplifier have?

a) 8, 10, or 12

b) 6, 8, or 10

c) 8 or 14

d) 8 or 16

**Answer: 8, 10, or 12**

25. If a noninverting amplifier has an RIN of 1000 ohms and an RFB of 2.5 kilohms, what is the RIN voltage when 1.42 mV is applied to the correct input?

a) 3.5 mV

b) Ground

c) 1.42 mV

d) 0.56 mV

**Answer: 1.42 mV**

26. Input impedance [Zin(I)] of an inverting amplifier is approximately equal to:

a) Ri

b) Rf + Ri

c) ∞

d) Rf – Ri

**Answer: Ri**

27. The closed-loop voltage gain of an inverting amplifier equals:

a) the ratio of the input resistance to the feedback resistance

b) the open-loop voltage gain

c) the feedback resistance divided by the input resistance

d) the input resistance

**Answer: the feedback resistance divided by the input resistance**

28. All of the following are basic op-amp input modes of operation EXCEPT

a) inverting mode

b) common-mode

c) double-ended

d) single-ended

**Answer: inverting mode**

29. A circuit whose output is proportional to the difference between the input signals is considered to be which type of amplifier?

a) common-mode

b) darlington

c) differential

d) operational

**Answer: differential**

30. With negative feedback, the returning signal

a) is proportional to the output current

b) is proportional to the differential voltage gain

c) opposes the input signal

d) aids the input signal

**Answer: opposes the input signal**

31. The voltage follower has a:

a) closed-loop voltage gain of unity

b) small open-loop voltage gain

c) closed-loop bandwidth of zero

d) large closed-loop output impedance

**Answer: closed-loop voltage gain of unity**

32. The ratio between differential gain and common-mode gain is called:

a) amplitude

b) differential-mode rejection

c) common-mode rejection

d) phase

**Answer: common-mode rejection**

33. If the gain of a closed-loop inverting amplifier is 3.9, with an input resistor value of 1.6 kilohms, what value of feedback resistor is necessary?

a) 6240 ohms

b) 2.4 kilohms

c) 410 ohms

d) 0.62 kilohms

**Answer: 6240 ohms**

34. In an open-loop op-amp circuit, whenever the inverting input (–) is negative relative to the noninverting input (+), the output will:

a) swing negative

b) close the loop

c) be balanced

d) swing positive

**Answer: swing positive**

35. With a differential gain of 50,000 and a common-mode gain of 2, what is the common-mode rejection ratio?

a) –87.9 dB

b) –43.9 dB

c) 43.9 Db

d) 87.9 dB

**Answer: 87.9 dB**

36. If the input to a comparator is a sine wave, the output is a:

a) ramp voltage

b) sine wave

c) rectangular wave

d) sawtooth wave

**Answer: rectangular wave**

37. The major difference between ground and virtual ground is that virtual ground is only a:

a) voltage reference

b) current reference

c) power reference

d) difference reference

**Answer: voltage reference**

38. If an op-amp has one input grounded and the other input has a signal feed to it, then it is operating as what?

a) Common-mode

b) Single-ended

c) Double-ended

d) Noninverting mode

**Answer: Single-ended**

39. If the feedback/input resistor ratio of a feedback amplifier is 4.6 with 1.7 V applied to the noninverting input, what is the output voltage value?

a) 7.82 V

b) saturation

c) cutoff

d) 9.52 V

**Answer: 9.52 V**

40. The common-mode voltage gain is

a) smaller than differential voltage gain

b) equal to voltage gain

c) greater than differential voltage gain

d) None of the above

**Answer: smaller than differential voltage gain**

41. An ideal amplifier should have:

a) high input current

b) zero offset

c) high output impedance

d) moderate gain

**Answer: zero offset**

42. A differential amplifier has a common-mode gain of 0.2 and a common-mode rejection ratio of 3250. What would the output voltage be if the single-ended input voltage was 7 mV rms?

a) 1.4 mV rms

b) 650 mV rms

c) 4.55 V rms

d) 0.455 V rms

**Answer: 4.55 V rms**

43. The magnitude of closed-loop voltage gain (Acl) of an inverting amplifier equals:

a) the ratio of the input resistance to the feedback resistance

b) the open-loop voltage gain Aol

c) the feedback resistance divided by the input resistance

d) the input resistance

**Answer: the feedback resistance divided by the input resistance**

44. What is the difference between common-mode and differential-mode input signals?

a) phase relationship

b) voltage

c) current

d) apparent power

**Answer: phase relationship**

46.The input offset current equals the

a) average of two base currents

b) collector current divided by the current gain

c) difference between two base-emitter voltages

d) difference between two base currents

**Answer: difference between two base currents**

47. Common-mode signals have _____.

a) the same amplitude

b) the same phase

c) the same frequency

d) All of the above

**Answer: All of the above**

48. The voltage required to force the differential output to zero is called _______

a) input-offset current

b) input-offset voltage

c) input bias current

d) slew rate voltage

**Answer: input-offset voltage**

49. The common-mode rejection ratio (CMMR) is the ratio of _____ to ______.

a) the differential voltage gain, the common-mode voltage gain

b) the differential power gain, the common-mode power gain

c) the ideal voltage gain, the actual voltage gain

d) signal voltage, noise voltage

**Answer: the differential voltage gain, the common-mode voltage gain**

50. A virtual ground is a(n) ______ ground because this point is at zero volts.

a) ordinary

b) voltage

c) chassis

d) earth

**Answer: voltage**

51. The resistors Rf and Ri in an op-amp circuit control ______ .

a) positive feedback and current gain

b) negative feedback and power gain

c) negative feedback and voltage gain

d) open and closed loop gain

**Answer: negative feedback and voltage gain**

52. ______ is NOT a characteristic of an ideal op-amp.

a) Infinite voltage gain

b) Minimum bandwidth

c) Infinite input impedance

d) Zero output impedance

**Answer: Minimum bandwidth**

53. Current cannot flow to ground through a(n) ________.

a) mechanical ground

b) ac ground

c) virtual ground

d) virtual short

**Answer: virtual ground**

54. The output of a Schmitt trigger is a

a) pulse waveform.

b) sawtooth waveform.

c) sinusoidal waveform.

d) triangle waveform.

**Answer: pulse waveform.**

56. If an op-amp comparator has a gain of 100,000, an input difference of 0.2 mV above reference, and a supply of 12 V, the output will be

a) 20 V.

b) 12 V.

c) 10 V.

d) 15 V.

**Answer: 12 V**

57. A constant-current source delivers a load current that

a) remains constant when the load resistance changes.

b) varies with load resistance.

c) varies inversely with load resistance.

d) varies inversely with input voltage.

**Answer: remains constant when the load resistance changes.**

58. The operational transconductance amplifier (OTA) is primarily a ________ -to- ________ amplifier.

a) current, voltage

b) voltage, current

c) current, resistance

d) resistance, current

**Answer: voltage, current**

58. Transconductance is the ratio of the output

a) current to the input voltage.

b) current to the input current.

c) voltage to the input voltage.

d) voltage to the input current.

**Answer: current to the input voltage.**

59. The OTA has a ________ input impedance and a ________ CMRR.

a) high, low

b) low, high

c) high, high

d) low, low

**Answer: high, high**

60. An OTA has

a) a bias-current input terminal.

b) high output impedance.

c) no fixed open-loop voltage gain.

d) all of the above

**Answer: all of the above**

61. In which of the following are operational amplifiers (op-amps) used?

a) Oscillators

b) Filters

c) Instrumentation circuits

d) All of the above

**Answer: All of the above**

62. A voltage-follower amplifier comes to you for service. You find the voltage gain to be 5.5 and the input impedance 22 k . The probable fault in this amplifier, if any, is

a) the gain is too low for this type of amplifier.

b) the input impedance is too high for this amplifier.

c) nothing is wrong. The trouble must be somewhere else.

d) none of these.

**Answer: none of these.**

63. For an op-amp having a slew rate SR = 5 V/ms, what is the maximum closed-loop voltage gain that can be used when the input signal varies by 0.2 V in 10 ms?

a) 150

b) 200

c) 250

d) 300

**Answer: 250**

64. An op-amp has an open-loop gain of 100,000 and a cutoff frequency of 40 Hz. Find the open-loop gain at a frequency of 30 Hz.

a) 800

b) 8,000

c) 80,000

d) 100,000

**Answer: 100,000**

65. What is the level of the voltage between the input terminals of an op-amp?

a) Virtually zero

b) 5 V

c) 18 V

d) 22 V

**Answer: Virtually zero**

66. An op-amp has an open-loop gain of 75,000 and a cutoff frequency of 100 Hz. At 1 kHz the open-loop gain is down by

a) 10 dB.

b) 6 dB.

C) 20 dB.

d) 3 dB.

**Answer: 20 dB.**

67. What is the difference output voltage of any signals applied to the input terminals?

a) The differential gain times the difference input voltage.

b) The common-mode gain times the common input voltage.

c) The sum of the differential gain times the difference input voltage and the common-mode gain times the common input voltage.

d) The difference of the differential gain times the difference input voltage and the common-mode gain times the common input voltage.

**Answer: The sum of the differential gain times the difference input voltage and the common-mode gain times the common input voltage.**

68. A three-stage op-amp can have a maximum phase lag of ________°.

a) –180

b) –90

c) –270

d) none of the above

**Answer: –270**

69. What is the open-loop gain of an op-amp at the gain-bandwidth product of the op-amp?

a) 200,000

b) 50,000

c) 200

d) 1

**Answer: 1**

70. An RC network has R = 47 k and C = 0.22 F. What is the cutoff frequency?

a) 154 Hz

b) 1540 Hz

c) 1.54 Hz

d) 15.4 Hz

**Answer: 15.4 Hz**

71. A certain op-amp has an open-loop voltage gain of 150,000. What is this gain expressed in dB?

a) 51.7 dB

b) 103.5 dB

c) 150,000 dB

d) 5.18 dB

**Answer: 103.5 dB**

72. An IC unit made using both ________ and ________ transistors is called a ________ circuit

a) bipolar, MOSFET, BiFET

b) bipolar, MOSFET, BiMOS

c) TTL, MOSFET, TailFET

d) MOSFET, TailFET, BiFET

**Answer: bipolar, MOSFET, BiMOS**

73. What is the slew rate of an op-amp if the output voltages change from 2 V to 3 V in 0.2 ms?

a) 5 V/ms

b) 3 V/ms

c) 2 V/ms

d) 1 V/ms

**Answer: 5 V/ms**

74. The maximum rate of change of the output voltage in response to a step input voltage is the ________ of an op-amp.

a) time constant

b) maximum frequency

c) slew rate

d) static discharge

**Answer: slew rate**

75. At what input voltage level does the output voltage level become numerically equal to the value of the differential gain of the amplifier?

a) Vi1 = –Vi2 = 0.25 V

b) V i1 = –V i2 = 0.50 V

c) V i1 = –V i2 = 0.75 V

d) V i1 = –Vi2 = 1.00 V

**Answer: V i1 = –V i2 = 0.50 V**

76. A practical op-amp has very ________ input impedance, very ________ output impedance, very ________ open-loop voltage gain, and a ________ bandwidth.

a) high, low, high, wide

b) high, high, low, narrow

c) low, high, high, wide

d) low, low, low, wide

**Answer: high, low, high, wide**

78. What is the level of the roll-off in most op-amps?

a) –6 dB / decade

b) –20 dB / octave

c) –6 dB / decade or –20 dB / octave

d) –20 dB / decade or –6 dB / octave

**Answer: –20 dB / decade or –6 dB / octave**

79. Calculate the output impedance of an inverting op-amp using the 741 op-amp (ro = 75 , AOL = 200 V/mV) if R1 = 100 and Rf = 1 k

a) 0.011

b) 0.00375

c) 0.0375

d) 0.375

**Answer: 0.00375**

80. The input offset voltage drift is a parameter directly related to VOS and ________.

a) ID

b) power dissipation

c) temperature

d) phase shift

**Answer: temperature**

81. What is the difference voltage if the inputs are an ideal opposite signal?

a) The differential gain times twice the input signal.

b) The differential gain times the input signal.

c) The common-mode gain times twice the input signal.

d) The common-mode gain times the input signal.

**Answer: The differential gain times twice the input signal**

82. Which of the following circuit conditions affect(s) the output offset voltage of an op-amp?

a) An input offset voltage, VIO

b) An input offset current, IIO

c) Both an input offset voltage, VIO and an input offset current, IIO

d) None of the above

**Answer: Both an input offset voltage, VIO and an input offset current, IIO**

83. A(n) ________ amplifier configuration has a higher input impedance and a lower output impedance than the op-amp itself.

a) non-inverting

b) inverting

c) voltage-follower

d) None of the above

**Answer: non-inverting**

84. The ________ amplifier configuration has the highest input impedance and the lowest output impedance of the three basic op-amp configurations.

a) non-inverting

b) inverting

c) voltage-follower

d) None of the above

**Answer: voltage-follower**

85. In which of the following operations is the resulting output signal of the differential amplifier near zero?

a) Single-ended

b) Double-ended

c) Common-mode

d) None of the above

**Answer: Common-mode**

86. What is the voltage gain of the unity follower?

a) 0

b) 1

c) –1

d) Infinity

**Answer: 1**

87. Negative feedback added to an op-amp ________ the bandwidth and ________ the gain.

a) increases, increases

b) increases, decreases

c) decreases, decreases

d) decreases, increases

**Answer: increases, decreases**

88. It takes an op-amp 22 s to change its output from –15 V to +15 V. Determine the slew rate.

a) 1.36 V/ s

b) 0.68 V/ s

c) –0.68 V/ s

d) cannot determine

**Answer: 1.36 V/ s**

89. An RC network has R = 500 k and C = 10 pF. Find the value of fc.

a) 31831 Hz

b) 31.831 kHz

c) 0.031831 MHz

d) all of the above

**Answer: all of the above**

90. What is the scale multiplier (factor) of a basic integrator?

a) R / C

b) C / R

c) –RC

d) –1 / RC

**Answer: –1 / RC**

91. Which of the following circuits is referred to as a BiMOS circuit?

a) Bipolar and FET

b) Bipolar and MOSFET

c) Opposite-type MOSFET

d) None of the above

**Answer: Bipolar and MOSFET**

92. In the differential amplifier circuit, which of the following terminals are connected together?

a) Bases

b) Collectors

c) One base to another collector

d) Emitters

**Answer: Emitters**

93. What is the cutoff frequency of an op-amp if the unity-gain frequency is 1.5 MHz and the open-loop gain is 100,000?

a) 5 Hz

b) 10 Hz

c) 15 Hz

d) 20 Hz

**Answer: 15 Hz**

94. The ________ is the voltage gain of an op-amp with external feedback.

a) Aol

b) Acl

c) Av

**Answer: Acl**

95. A(n) ________ amplifier configuration has an input impedance approximately equal to the input resistor Ri and an output impedance approximately equal to the output impedance of the op-amp itself.

a) non-inverting

b) inverting

c) voltage-follower

**Answer: inverting**

96. What is the difference voltage if the inputs are an ideal in-phase signal?

a) The differential gain times twice the input signal.

b) The differential gain times the input signal.

c) The common-mode gain times twice the input signal.

d) The common-mode gain times the input signal.

**Answer: The common-mode gain times the input signal.**

97. What is the level of the current through the amplifier input(s) to ground in an op-amp?

a) Virtually zero

b) 1.7 mA

c) 2.8 mA

d) 3.3 mA

**Answer: Virtually zero**

98. Open-loop voltage gain of an op-amp can range up to ________.

a) 10,000

b) 50,000

c) 100,000

d) 200,000

**Answer: 200,000**

99. At what input voltage level does the output voltage level become numerically equal to the value of the common-mode gain of the amplifier?

a) Vi1 = –Vi2 = 0.25 V

b) Vi1 = –Vi22 = 0.50 V

c) Vi1 = –Vi2 = 0.75 V

d) Vi1 = –Vi2 = 1.00 V

**Answer: Vi1 = –Vi22 = 0.50 V**

100. Which of the following is (are) the result of gain reduction by a feedback?

a).The amplifier voltage gain is a more stable and precise value.

b) The input impedance of the circuit is increased over that of the op-amp alone.

c) The output impedance is reduced over that of the op-amp alone.

d) All of the above

**Answer: All of the above**

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