The GATE Grind

GATE 2019 EE – Question 27

Analog and Digital Electronics · Operational amplifiers: characteristics and applications · 1 mark · Multiple choice

A current controlled current source (CCCS) has an input impedance of $10\ \Omega$ and output impedance of $100\ \text{k}\Omega$. When this CCCS is used in a negative feedback closed loop with a loop gain of 9, the closed loop output impedance is

  1. $10\ \Omega$
  2. $100\ \Omega$
  3. $100\ \text{k}\Omega$
  4. $1000\ \text{k}\Omega$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (D) $1000\ \text{k}\Omega$

Explanation

Current-series/shunt feedback of this type raises the output impedance by the factor $(1+\text{loop gain})$: $100\text{ k}\Omega\times(1+9)=1000\ \text{k}\Omega$.