# Find the value of input resistance for differential amplifier with one op-amp. If R1 = R2=100Ω and RF = R3 =5kΩ.

+1 vote
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

I have been asked this question in an interview for internship.

The above asked question is from Differential Amplifiers with Multiple Op-Amp in division Operational Amplifier Characteristics of Linear Integrated Circuits

## 1 Answer

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The correct choice is (b) RIFx = 100Ω; RIFy = 5.1kΩ

Unravel the mysteries with: 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.

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