1.

A feedback amplifier is also called as

a) Open loop amplifier
b) Closed loop amplifier
c) Feedback network amplifier
d) Looped network amplifier
View Answer
Answer: b
Explanation: A feedback amplifier is sometimes referred as a closed loop amplifier because the feedback forms a closed
loop between input and the output.

2. How many types of configuration are available for feedback amplifier?

a) Six
b) Four
c) Two
d) Eight
View Answer
Answer: b
Explanation: There are four type of configuration are available. They are voltage series feedback, voltage shunt feedback,
Current series feedback and Current shunt feedback.

3. Which of the following is not a feedback configuration?

a) Current-series feedback
b) Voltage-shunt feedback
c) Current-Voltage feedback
d) Current-Shunt feedback
View Answer
Answer: c
Explanation: In a feedback amplifier, either current or voltage can be fed back to the input, but both current and voltage
cannot be feedback simultaneously.

4. When load current flows into the feedback circuit, the configuration is said to be
a) Current-shunt feedback
b) Voltage-shunt feedback
c) Voltage-series feedback
d) All of the mentioned
View Answer
Answer: b
Explanation: In current-series and current-shunt feedback circuit, the load current flows into the feedback circuit.

5. Find the voltage-series feedback amplifier from the given diagram?

a)
b)

c)

d)

Answer: a
Explanation: The mentioned diagram is the voltage-series feedback amplifier because the voltage across load resistor is the
input voltage to the feedback circuit.

6. On what criteria does the feedback amplifier are classified?

a) Signal fed back to input
b) Signal applied to input
c) Signal fed back to output
d) None of the mentioned

Answer: d
Explanation: The feedback amplifiers are classified according to whether the voltage or current is fed back to the input in
series or in parallel.

7. The closed loop voltage gain is reciprocal of

a) Voltage gain of op-amp
b) Gain of the feedback circuit
c) Open loop voltage gain
d) None of the mentioned

Answer: b
Explanation: Comparing the equation of closed loop voltage gain (A F) and the gain of the feedback circuit (B). AF is reciprocal
of B
=> AF = 1+( RF/ R1) ; B= R1/( R1+ RF)
=> B = 1+( R1/ RF)
Therefore, AF = 1/B.

8. Select the specifications that implies the inverting amplifier?

a) V1 = -3v, V2 = -4v
b) V1 = -2v, V2 = 3v
c) V1 = 5v, V 2 = 15v
d) V1 = 0v, V2 = 5v

Answer: d
Explanation: In inverting amplifier, the input is applied to the inverting terminal and the non-inverting terminal is grounded.
So,the input applied to inverting amplifier can be V 1 = 0v, V2 = 5v.

1. Specify the voltage gain of non-inverting amplifier with feedback amplifier with and without feedback?
a) A= Vo/Vid, AF = Vf/Vo
b) A= Vf/Vid, AF= Vo/Vf
c) A= Vo/Vid, AF= Vo / Vin
d) A= Vf/Vid, AF = Vf/Vin

Answer: c
Explanation: The voltage gain of op-amp with feedback is the open loop voltage gain, A=V o /Vid. The voltage gain of op-amp
without feedback is the closed loop voltage gain, AF = Vo /Vin .

2. If the feedback voltage and the output voltage are given as 10v and 4v. Find the gain of the feedback circuit in voltage-
series feedback amplifier?
a) 2.5v
b) 40v
c) 3v
d) 6.2v

Answer: a
Explanation: Gain of feedback, B = Vf /Vo = 10v/4v = 2.5v.

3. How is the difference voltage calculated in closed loop non-inverting amplifier?

a) Vid= Vo – Vf
b) Vid= Vin – Vf
c) Vid= Vo – Vin
d) Vid= Vf – Vin

Answer: b
Explanation: Although, the input is given to the non-inverting terminal of op-amp, the difference voltage is equal to the input
voltage minus feedback voltage is Vid= Vin – Vf.

4. Why the feedback circuit is said to be negative for voltage series feedback amplifier?
a) Feedback voltage is 180o out of phase with respect to input voltage
b) Input voltage is 180o out of phase with respect to feedback voltage
c) Feedback voltage is in same phase with respect to input voltage
d) Input voltage is in same phase with respect to feedback voltage

Answer: a
Explanation: Voltage series feedback amplifier have the difference voltage, Vid = Vin -Vf. Therefore, the feedback voltage
always opposes the input voltage and is out of phase by 180o with respect to input voltage. Hence, the feedback is said to be
negative.
5. Determine the closed loop voltage gain from the given circuit. (Where gain of op-amp= 105).

a) 1090.9
b) 9821.43
c) 9166.66
d) 10000

Answer: b
Explanation: The closed loop voltage gain , AF = {[A*(R4+R5)]/[(RF+R1+(A*R1)]} = [105*(10kΩ+1kΩ)]/[1kΩ+10kΩ+(105*1kΩ)]
=11×108/112000
=> AF = 9821.43.

6. Express closed loop voltage gain (AF) in terms of open loop gain (A) and feedback circuit gain (B)?
a) AF = A/AB
b) AF = 1+ (A/AB)
c) AF = A/(1+AB)
d) AF = AB/(1+A)

Answer: c
Explanation: The closed loop voltage gain in terms of open loop gain and feedback circuit gain is expressed as AF =
A/(1+AB).

7. Which factor determines the gain of the voltage series feedback amplifier?
a) Open loop voltage gain
b) Feedback voltage
c) Ratio of two resistors
d) Gain of feedback circuit

Answer: c
Explanation: In setting the gain of the voltage series feedback amplifier, the ratio of two resistors is important and not the
absolute value of these resistors. For example: If a gain of 11 is desired, we choose R 1=1kΩ and R1=10kΩ or R1=100Ω and
RF= 1kΩ.

8. For the feedback circuit of voltage series feedback amplifier, find the feedback voltage for the specifications: R 1=1kΩ, RF =
10kΩ and Vo= 25v.
a) 12.5v
b) 22v
c) 0.9v
d) 2.3v

Answer: d
Explanation:
The feedback voltage, Vf = (R1*Vo)/(R1+RF) = (1kΩ*25v)/(1kΩ+10kΩ) = 2.272v ≅ 2.3v.

9. What must be the value of external components used in voltage series feedback amplifier?
a) Less than 1MΩ
b) Less than 10MΩ
c) Less than 100MΩ
d) Less than 0.1MΩ

Answer: a
Explanation: All external components value should be less than 1MΩ. So, that they do not adversely affect the internal
circuitry of the op-amp.

10. Find the block diagram representation of non-inverting amplifier with feedback?

a)

b)

c)

d)

Answer: a
Explanation: The mentioned block diagram is the standard form for representing a system with feedback.
11. Define the input resistance with feedback for voltage series feedback amplifier?
a) RIF = (1-AB)
b) RIF = (AB-1)
c) RIF = (1+AB)
d) None of the mentioned

Answer: c
Explanation: In feedback amplifier, the input resistance of the op-amp with feedback is (1+AB) times that of without
feedback.

12. When the non-inverting input terminal of an op-amp is equal to that of the inverting input terminal (ideally)
a) a–>∞
b) Vid ≅ 0
c) AF = 1+( RF / R1)
d) All of the mentioned

Answer: d
Explanation: When the input at both the terminal are equal, the difference input voltage, V id=Vin1– Vin2.
=> Vid≅0 (∵Vin1= Vin2)
The open loop voltage gain, A= Vo/ Vid = Vo/0 = ∞ and
the closed loop voltage gain, AF= Vo/ Vin = 1+ (RF/ R1).

1. Find the input and output resistance for the circuit shown.
Specification for 741 op-amp : A=400000 ; Ri = 33MΩ; Ro = 60Ω;
RF = 11kΩ; R1 = 2kΩ; Supply voltage = ± 15v; Maximum output voltage swing = ± 13v.

a) RIF = 66MΩ, ROF = 30Ω

b) RIF = 30MΩ, ROF = 6kΩ
c) RIF = 15kΩ, ROF = 50MΩ
d) None of the mentioned

Answer: a
Explanation: AF = 1+(RF/R1) = 1+(11kΩ/2kΩ) = 6.5;
B= 1/ AF = 1/6.5 = 0.154;
Input resistance of RIF = R1(1+AB) = 33MΩ[1+(6.5*0.154) ]= 66MΩ;
Output resistance of ROF = Ro/(1+AB) = 60/[1+(6.5*0.154) ]= 29.98 ≅30Ω.

2. The output resistance of the op-amp with feedback is

a) Same as that of the output resistance without feedback
b) Greater than that of the output resistance without feedback
c) Smaller than that of the output resistance without feedback
d) None of the mentioned

Answer: c
Explanation: In voltage series feedback amplifier, the output resistance is (1/(1+AB)) times the output resistance of the op-
amp. Therefore, the output resistance of the op-amp with feedback is much smaller than the output resistance without
feedback.
3. Find the output current in the voltage series feedback amplifier.
a) io ={ [Vo+(A*Vid)]/Ro}
b) io ={ [Vo-(A*Vid)]/Ro}
c) io =(Vo/Ro)*A
d) io =[A*(Vo-Vid)]/Ro

Answer: b
Explanation: The output current in voltage series feedback amplifier is given as i o ={[Vo-(A*Vid)]/Ro}.

4. Find the unity gain bandwidth for voltage series feedback amplifier?
a) UBG = Afo
b) UBG = AfF
c) UBG = Afo fF
d) UBG = AFfo

Answer: a
Explanation: The unity gain bandwidth is given as product of open loop voltage gain and break frequency of an op-amp.

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

a) fo(AB)
b) fo(AB-1)
c) fo(1+AB)
d) fo(1-AB)

Answer: c
Explanation: The bandwidth of the non-inverting amplifier with feedback is equal to its bandwidth without feedback times
(1+AB). i.e. fF=fo(1+AB).

6. How are the saturation voltage specified on the manufacture’s datasheet?

a) Negative voltage
b) Output voltage swing
c) Supply voltage
d) None of the mentioned

Answer: b
Explanation: 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.

7. What is the formula for total output offset voltage with feedback?
a) VooT = ± Vo/(1+AB)
b) VooT = ± Vsat*(1+AB)
c) VooT = ± Vsat/(1+AB)
d) VooT = ± Vo*(1+AB)

Answer: c
Explanation: The total output offset voltage with feedback = (Total output offset voltage witput feedback) / (1+AB). i.e. VooT =
± Vsat/(1+AB).

8. Which of the following has the same characteristic as that of non-inverting amplifier with feedback?
a) Perfect feedback amplifier
b) Voltage follower
c) Perfect voltage amplifier
d) All of the mentioned

Answer: c
Explanation: 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 non-inverting amplifier with feedback, it is clear that it exhibits the characteristics of
a perfect voltage amplifier.

9. What is the gain of voltage follower?

a) Gain > ∞
b) Gain –>1
c) Gain <1
d) Gain –>∞
Answer: b
Explanation: Voltage follower is non-inverting amplifier configured for unity gain. Such that the output voltage is equal to and
in phase with the input.

10. 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
Explanation: In the voltage follower the output follow the input due to unity gain. Therefore, it is attained to get higher input
resistance and output amplitude equal to input.

11. Find the input and output voltage in voltage follower circuit?
a) Vin =2v and Vout = 3v
b) Vin =10v and Vout = 11v
c) Vin =9v and Vout = 9v
d) Vin =4v and Vout = 7v

Answer: c
Explanation: Voltage follower has input voltage equal to 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 = Vout/Vin = 2v/2v = 1.

12. Voltage follower is also called as

a) None of the mentioned
b) Non-inverting amplifier
c) Inverting amplifier
d) Normal buffer

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

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

a) fF = 1000hz, VooT = ± 7.5µv.

b) fF = 100khz, VooT = ± 7.5µv.
c) fF = 10khz, VooT = ±7.5µv.
d) fF = 1000khz, VooT = ± 7.5µv.

Answer: d
Explanation: Bandwidth fF =A* fF = 200000*5= 1Mhz.
Total output offset voltage, VooT= ±Vsat/A= ±15/200000 =± 7.5µv.

1. 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
Explanation: A voltage shunt feedback amplifier forms a 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.

2. The value of feedback resistor and resistor connected in series with the input signal source are 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
Explanation: Closed loop voltage gain, AF = -RF/R1 = -10kΩ/3.3kΩ = -3.33.

3. Write the formula for closed loop voltage gain of inverting amplifier with feedback using open loop voltage gain and gain of
feedback circuit.
a) AF= A/(1+AB)
b) AF= -A/(1+AB)
c) AF= -B/(1+AB)
d) None of the mentioned

Answer: c
Explanation: 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, AF is k times the closed loop gain of the non-inverting amplifier where k<1.

4. 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
Explanation: The input and output signal in voltage series feedback amplifier are 180 o out of phase (or of opposite polarities).
Due to this phase inversion, the configuration is also called as inverting amplifier with feedback.
5. Find the block diagram representation for inverting amplifier with feedback
a)

b)

c)

d)
Answer: b
Explanation: The block diagram of non-inverting amplifier is identical to that of inverting amplifier except for the voltage
attenuation factor or block. However, the major difference is that a voltage summing junction is being used as a model for
what is actually a current summing.

6. 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
Explanation: Ideally, the difference between input voltages is zero. Therefore, the voltage at the inverting terminal is
approximately equal to that of non-inverting terminal. In other words, the inverting terminal voltage is approximately at
ground potential and it is said to be virtual ground.

7. Compute RIF 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
Explanation: In voltage shunt feedback amplifier, the input resistance with feedback is given as R IF = R1 (ideally).

8. Specification of op-amp 741c is given below:

A=200000; Ri=2MΩ; Ro=75Ω; Supply voltages= ±15v; output voltage swing =±13v; fo=5hz.

Compute the value of output resistance, bandwidth and closed loop voltage gain for the circuit shown.
a) ROF=8.6mΩ , fF= 53005hz and AF=-9.36
b) ROF=4.12mΩ , fF= 53005hz and AF=-11.78
c) ROF=7.1mΩ , fF = 53005hz and AF=-16.95
d) ROF=1.9mΩ , fF= 53005hz and AF=-10

Answer: c
Explanation: Output resistance of the amplifier, R OF= Ro/(1+AB) =, where B= R1+RF = 330Ω/330Ω+6.2kΩ = 0.053.
=> ROF= ±75/(1+200000*0.053) = 53005hz.
Closed loop voltage gain, AF= -(A*K)/(1+AB), Where k= RF/(R1+F) = 6.2kΩ/(330Ω+6.2kΩ) = 0.949
=> AF = -(200000*0.949)/[1+(200000*0.0535)] = -16.95.
9. What is the break frequency of the op-amp?
a) fo = Unity Gain Bandwidth /closed loop voltage gain
b) fo = Unity Gain Bandwidth / open loop voltage gain
c) fo = Unity Gain Bandwidth /Gain of feedback circuit
d) All of the mentioned

Answer: c
Explanation: The mentioned formula is the general break frequency of any operational amplifier.

10. The total voltage offset voltage with feedback (VooT) equation for inverting amplifier is
a) Same as that of 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
Explanation: Voot 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.

11. 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
Explanation: A voltage follower is a special case of non-inverting amplifier ( or voltage series feedback amplifier) and it has a
gain of unity.

12. Compute the output voltage for the given circuit

a) -2.6v
b) -27.8v
c) -26.7v
d) -0.267v

Answer: c
Explanation: The given circuit is a current to voltage converter. Since V1 =0v and V1= V2.
=> iin = Vin /R1 = 4/ 1.5kΩ =2.67mA.
The output voltage Vo = -iin *RF = -2.67mA*10kΩ = -26.7v.

13. At what condition an inverting amplifier works as an inverter

a) R1 = RF+ RL
b) RF =( R1*Vin )/RL
c) R1 = RF
d) R1 = Vo/(Vin *RL)

Answer: c
Explanation: If R1 = RF, the inverting amplifier will work as an inverter.

14. Determine the output waveform for the given input signal

a)

b)

c)

d)
Answer: a
Explanation: Given, Vin = 3Vpp sinewave at 1khz (Therefore F=1/T=1/ms =1khz)
=> iin = Vin /R1 = 3/ 470=6.4mA
=> Vo=- iin *RF=6.4mA*4.7kΩ = 30 Vpp sinewave at 1khz.