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Analog Electronics - Engineering

Q1:

An amplifier has input impedance of 4 kΩ and output impedance of 80 kΩ. It is used in negative feedback circuit with 10% feedback. If open loop gain is 90, the closed loop input and output impedances are

A 40 kΩ and 8 kΩ respectively

B 4 kΩ and 80 kΩ respectively

C 0.4 kΩ and 800 kΩ respectively

D 8 kΩ and 160 kΩ respectively

ANS:A - 40 kΩ and 8 kΩ respectively

Closed loop input impedance = 4 (1 + 0.1 x 90) = 40 kΩ, Closed loop Output impedance = = 8 kΩ.