# Linear Integrated Circuit Questions and Answers – Differential Amplifiers with Multiple Op-Amp – 1

This set of Linear Integrated Circuit Multiple Choice Questions & Answers (MCQs) focuses on “Differential Amplifiers with Multiple Op-Amp – 1”.

1. Why differential amplifiers are preferred for instrumentation and industrial applications?
a) Input resistance is low
b) Produce amplified output
c) Amplify individual input voltage
d) Reject common mode voltage

Explanation: Differential amplifiers are preferred in these applications because they are better able to reject common-mode voltage than single input circuits and present balanced input impedance.

2. Which of the following is a combination of inverting and non-inverting amplifier?
a) Differential amplifier with one op-amp
b) Differential amplifier with two op-amps
c) Differential amplifier with three op-amps
d) Differential amplifier with four op-amps

Explanation: In differential amplifier with one op-amp both the inputs are connected to separate voltage source. So, if any one of the source is reduced to zero, differential amplifier acts as an inverting or non-inverting amplifier.

3. What will be the output voltage when Vx =0v?
(Where Vx –> inverting input terminal of differential amplifier with one op-amp)
a) Vo = -(1+R F/R1)*V1
b) Vo = -(1- R F/ R1)*V1
c) Vo = (1+ R F/ R1)*V1
d) Vo = (R F/ R1)*V1

Explanation: When Vx =0v, the configuration is a non-inverting amplifier.

4. Compute the output voltage from the following circuit diagram?

a) -17v
b) -27v
c) -39v
d) -15v

Explanation: Since VB=0, the configuration becomes as an inverting amplifier. Hence, the output due to VA is
Vo = -(RF/R1)*VA = -(15kΩ/1.5kΩ)*2.7v = -10*2.7 = -27v.

5. Compute the output voltage if the input voltage is reduced to zero in differential amplifier with one op-amp?
a) Inverted Voltage
b) Same as the input voltage
c) Amplified inverted voltage
d) Cannot be determined

Explanation: It is not mentioned clearly whether inverting input or non-inverting input is reduced to zero. Therefore, the output cannot be determined.
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6. The difference between the input and output voltage are -1v and 17v. Calculate the closed loop voltage gain of differential amplifier with one op-amp?
a) -51
b) 34
c) -17
d) 14

Explanation: Voltage gain of differential amplifier with one op-amp, AD=Output voltage / Difference of input voltage
=> AD = 17v/-1v = -17v.

7. For the differential amplifier given below, determine the Vx and RF value. Assume that the circuit is initially nulled.

a) Vx = -8v, RF = 9.9kΩ
b) Vx = 8v, RF = 9.9kΩ
c) Vx = -8v, RF = -9.9kΩ
d) Vx = 8v, RF = -9.9kΩ

Explanation: The closed loop voltage gain, AD = -(RF/R1)
=> RF = -3*3.3kΩ = -9.9kΩ
The net output is given is VO=-(RF /R1)*(Vx-Vy)
=> Vx= Vy– Vo (-R1 /RF)
=> Vx = 6+6(3.3kΩ/9.9kΩ) = 6+2 = 8v.

8. The gain of differential amplifier with one op-amp is same as that of
a) The inverting amplifier
b) The non-inverting amplifier
c) Both inverting and non-inverting amplifier
d) None of the mentioned

Explanation: The gain of differential amplifier is given as AD= -(RF /R1), which is equivalent to the output voltage obtained from the inverting amplifier.

9. Find the value of input resistance for differential amplifier with one op-amp. If R1 = R2=100Ω and RF = R3 =5kΩ.
a) RIFx = 110Ω; RIFy = 6.7kΩ
b) RIFx = 100Ω; RIFy = 5.1kΩ
c) RIFx = 150Ω; RIFy = 7.2kΩ
d) RIFx = 190Ω; RIFy = 9.0kΩ

Explanation: The input resistance of inverting amplifier is RIFx = (R1) and the input resistance of non-inverting amplifier is RIFy = (R2+ R3)
=> ∴ RIFx = 100Ω and
=> RIFy =100+5kΩ =5.1kΩ.

10. What is the net output voltage for differential amplifier with one op-amp
a) Vo = -(RF /R1)*Vx
b) Vo = -(RF /R1)*(Vx -Vy)
c) Vo = (1+RF /R1)*(Vx -Vy)
d) None of the mentioned

Explanation: The net output voltage for differential amplifier with one op-amp is given as Vo= -(RF /R1)*(Vx-Vy).

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