# Difference Amplifiers MCQ’s

This set of Electronic Devices & Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Difference Amplifiers”.

1. If for an amplifier the common mode input signal is vc, the differential signal id vd and Ac and Ad represent common mode gain and differential gain respectively, then the output voltage v0 is given by
a) v0 = Ad vd – Ac vc
b) v0 = – Ad vd + Ac vc
c) v0 = Ad vd + Ac vc
d) v0 = – Ad vd – Ac vc

2. If for an amplifier v1 and v2 are the input signals, vc and vd represent the common mode and differential signals respectively, then the expression for CMRR (Common Mode Rejection Ratio) is
a) 20 log (|Ad| / |Ac|)
b) -10 log (|Ac| / |Ad|)2
c) 20 log (v2 – v1 / 0.5(v2 + v1))
d) All of the mentioned

3. For the difference amplifier which of the following is true?
a) It responds to the difference between the two signals and rejects the signal that are common to both the signal
b) It responds to the signal that are common to the two inputs only
c) It has a low value of input resistance
d) The efficacy of the amplifier is measured by the degree of its differential signal to the preference of the common mode signal

4. The problem with the single operational difference amplifier is its
a) High input resistance
b) Low input resistance
c) Low output resistance
d) None of the mentioned

5. For the circuit given below determine the input common mode resistance.

a) (R1 + R3) || (R2) || + (R4)
b) (R1 + R4) || (R2 + R3)
c) (R1 + R2) || (R3 + R4)
d) (R1 + R3) || (R2 + R4)

6. For the difference amplifier shown below, let all the resistors be 10kΩ ± x%. The expression for the worst-case common-mode gain is

a) x / 50
b) x / 100
c) 2x / (100 – x)
d) 2x / (100 + x)

7. For the difference amplifier as shown in the figure show that if each resistor has a tolerance of ±100 ε % (i.e., for, say, a 5% resistor, ε = 0.05) then the worst-case CMRR is given approximately by (given K = R2/R1 = R4/R3)

a) 20 log [K+1/4ε].
b) 20 log [K+1/2ε].
c) 20 log [K+1/ε].
d) 20 log [2K+2/ε].

8. For the circuit shown below express v0 as a function of v1 and v2.

a) v0 = v1 + v2
b) v0 = v2 – v1
c) v0 = v1 – v2
d) v0 = -v1 – v2

9. Determine Ad and Ac for the given circuit.

a) Ac = 0 and Ad = 1
b) Ac ≠ 0 and Ad = 1
c) Ac = 0 and Ad ≠ 1
d) Ac ≠ 0 and Ad ≠ 1

10. Determine the voltage gain for the given circuit known that R1 = R3 = 10kΩ abd R2 = R4 = 100kΩ.

a) 1
b) 10
c) 100
d) 1000