Characteristics of Operational Amplifier MCQ - Objective Question Answer for Operational Amplifier Characteristics Quiz

81. Find the output current in the voltage series feedback amplifier.

A. i_o = { [V_o+(A*V_id)]/R_o}
B. i_o = { [V_o-(A*V_id)]/R_o}
C. i_o = (V_o/R_o)*A
D. i_o = [A*(V_o-V_id)]/R_o

Answer: B

The output current in the voltage series feedback amplifier is given as

i_o = {[V_o-(A*V_id)]/R_o}.

82. Find the unity-gain bandwidth for the voltage series feedback amplifier?

A. UBG = Af_o
B. UBG = Af_F
C. UBG = Af_o f_F
D. UBG = A_Ff_o

Answer: A

The unity-gain bandwidth is given as the product of open-loop voltage gain and breaks the frequency of an op-amp.

UBG = Af_o

83. The bandwidth of a non-inverting amplifier with feedback is equal to

A. f_o(AB)
B. f_o(AB-1)
C. f_o(1+AB)
D. f_o(1-AB)

Answer: C

The bandwidth of the non-inverting amplifier with feedback is equal to its bandwidth without feedback times (1+AB) i.e.

f_F = f_o(1+AB).

84. How are the saturation voltage specified on the manufacturer’s datasheet?

A. Negative voltage
B. Output voltage swing
C. Supply voltage
D. None of the mentioned

Answer: B

In an open-loop op-amp, the total output offset voltage (i.e. output voltage swing) is equal to either the positive or negative saturation voltage.

85. What is the formula for total output offset voltage with feedback?

A. V_oot = ± V_o/(1+AB)
B. V_oot = ± V_sat*(1+AB)
C. V_ooT = ± V_sat/(1+AB)
D. Voot = ± V_o*(1+AB)

Answer: C

The total output offset voltage with feedback = (Total output offset voltage witput feedback) / (1+AB) i.e.

V_ooT = ± V_sat/(1+AB).

86. Which of the following has the same characteristic as that of the non-inverting amplifier with feedback?

A. Perfect feedback amplifier
B. Voltage follower
C. Perfect voltage amplifier
D. All of the mentioned

Answer: C

A perfect voltage amplifier has very high input resistance, very low output resistance, stable voltage gain, large bandwidth, and very little output offset voltage.

From the analysis of the characteristic of the non-inverting amplifier with feedback, it is clear that it exhibits the characteristics of a perfect voltage amplifier.

87. What is the gain of voltage follower?

A. Gain > ∞
B. Gain –>1
C. Gain <1
D. Gain –>∞

Answer: B

A voltage follower is a non-inverting amplifier configured for unity gain. Such that the output voltage is equal to and in phase with the input.

Gain –>1

88. Which is preferred to attain higher input resistance and the output amplitude equal to input?

A. Voltage follower
B. Voltage series feedback amplifier
C. Voltage shunt feedback amplifier
D. Inverter

Answer: A

In the voltage follower, the output follows the input due to unity gain. Therefore, it is attained to get higher input resistance and output amplitude equal to the input.

89. Find the input and output voltage in voltage follower circuit?

A. V_in = 2v and V_out = 3v
B. V_in = 10v and V_out = 11v
C. V_in = 9v and V_out = 9v
D. V_in = 4v and V_out = 7v

Answer: C

The voltage follower has an input voltage equal to an output voltage. The closed-loop voltage gain is equal to one. For example, take the input and output voltage to be 2v, then

A_F = V_out/V_in = 2v/2v = 1.

90. Voltage follower is also called as

A. None of the mentioned
B. Non-inverting amplifier
C. Inverting amplifier
D. Normal buffer

Answer: B

The voltage follower is also called a non-inverting buffer because, when placed between two networks, it removes the loading on the first network.

91. Find the bandwidth and total output offset voltage of a voltage follower? The following are the specifications for the op-amp 741: A = 200000, f_o = 5hz, and supply voltage = ±15v.

A. f_F = 1000hz, V_ooT = ± 7.5µv.
B. f_F = 100khz, V_ooT = ± 7.5µv.
C. f_F = 10khz, V_ooT = ±7.5µv.
D. f_F = 1000khz, V_ooT = ± 7.5µv.

Answer: D

Bandwidth f_F = A* f_F

= 200000*5 = 1Mhz.

Total output offset voltage

V_ooT = ±V_sat/A = ±15/200000 = ± 7.5µv.

91. Voltage shunt feedback amplifier forms

A. A negative feedback
B. A positive feedback
C. Both positive and negative
D. None of the mentioned

Answer: A

A voltage shunt feedback amplifier forms negative feedback because any increase in the output signal results in a feedback signal into the inverting input causing a decrease in the output signal.

92. The value of the feedback resistor and resistor connected in series with the input signal source is equal to 10kΩ and 3.3kΩ. Calculate the closed-loop voltage gain?

A. -6.7
B. -33
C. -13.3
D. -3.33

Answer: D

Closed loop voltage gain,

A_F = -R_F/R₁

= -10kΩ/3.3kΩ = -3.33.

93. Write the formula for closed-loop voltage gain of inverting amplifier with feedback using open-loop voltage gain and gain of the feedback circuit.

A. A_F = A/(1+AB)
B. A_F = -A/(1+AB)
C. A_F = -B/(1+AB)
D. None of the mentioned

Answer: C

The closed-loop voltage gain of the amplifier is A_F = -Ak/(1+AB)

where k is a voltage attenuation factor.

In addition to phase inversion, A_F is k times the closed-loop gain of the non-inverting amplifier where k<1.

94. Voltage shunt feedback amplifiers are also called as

A. Non-inverting amplifier with feedback
B. Non-inverting amplifier without feedback
C. Inverting amplifier with feedback
D. Inverting amplifier without feedback

Answer: C

The input and output signal in the voltage series feedback amplifier is 180^o out of phase (or of opposite polarities). Due to this phase inversion, the configuration is also called an inverting amplifier with feedback.

95. The inverting input inverting of the voltage shunt feedback resistor is a commonly named as

A. Terminal ground
B. Virtual ground
C. Virtual input
D. Resistive input

Answer: B

Ideally, the difference between input voltages is zero. Therefore, the voltage at the inverting terminal is approximately equal to that of the non-inverting terminal. In other words, the inverting terminal voltage is approximately at ground potential and it is said to be virtual ground.

96. Compute R_IF for an inverting amplifier with feedback, where the value of input resistance of op-amp is 4.7kΩ.

A. 4.7kΩ
B. 9.4kΩ
C. 2.35kΩ
D. Data given is insufficient

Answer: A

In a voltage shunt feedback amplifier, the input resistance with feedback is given as R_IF = R₁ (ideally). i.e 4.7kΩ.

97. Specification of op-amp 741c is given below:
A = 200000; R_i = 2MΩ; R_o = 75Ω; Supply voltages = ±15v; output voltage swing = ±13v; f_o = 5hz.
Compute the value of output resistance, bandwidth, and closed-loop voltage gain for the circuit shown.

A. R_OF = 8.6mΩ , f_F = 53005hz and A_F = -9.36
B. R_OF = 4.12mΩ , f_F = 53005hz and A_F = -11.78
C. R_OF = 7.1mΩ , f_F = 53005hz and A_F = -16.95
D. R_OF = 1.9mΩ , f_F = 53005hz and A_F = -10

Answer: C

The output resistance of the amplifier

R_OF = R_o/(1+AB. = , where B = R₁+R_F = 330Ω/330Ω+6.2kΩ = 0.053.

= > R_OF = ±75/(1+200000*0.053) = 53005hz.

Closed loop voltage gain

A_F = -(A*K)/(1+AB

Where k = R_F/(R₁+_F)

= 6.2kΩ/(330Ω+6.2kΩ) = 0.949

= > A_F = -(200000*0.949)/[1+(200000*0.0535)] = -16.95.

98. What is the break frequency of the op-amp?

A. f_o = Unity Gain Bandwidth /closed-loop voltage gain
B. f_o = Unity Gain Bandwidth / open-loop voltage gain
C. f_o = Unity Gain Bandwidth /Gain of a feedback circuit
D. All of the mentioned

Answer: C

The break frequency of the op-amp is

f_o = Unity Gain Bandwidth /Gain of a feedback circuit

The mentioned formula is the general break frequency of any operational amplifier.

99. The total voltage offset voltage with feedback (V_ooT) equation for inverting amplifier is

A. Same as that of the non-inverting amplifier
B. k times the non-inverting amplifier, k-> voltage attenuation factor
C. Twice the equation of non-inverting amplifier
D. All of the mentioned

Answer: A

V_oot equation for inverting amplifier is the same as that of the non-inverting amplifier because, when the input signal is reduced to zero, both inverting and non-inverting amplifier results in the same circuit.

100. Which among the following is not a special case of voltage shut feedback amplifier?

A. Voltage follower
B. Current to voltage connector
C. Inverter
D. None of the mentioned

Answer: A

A voltage follower is a special case of the non-inverting amplifier ( or voltage series feedback amplifier) and it has a gain of unity.

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