The GATE Grind

GATE 2024 EC – Question 18

Analog Circuits · BJT and MOSFET Amplifiers · 1 mark · Multiple choice

For the closed loop amplifier circuit shown below, the magnitude of open loop low frequency small signal voltage gain is 40. All the transistors are biased in saturation. The current source $I_{SS}$ is ideal. Neglect body effect, channel length modulation and intrinsic device capacitances. The closed loop low frequency small signal voltage gain $\dfrac{v_{out}}{v_{in}}$ (rounded off to three decimal places) is ____.

Diagram for GATE 2024 EC question 18
  1. 0.976
  2. 1.000
  3. 1.025
  4. 0.488

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) 0.976

Explanation

The output is fed back directly to the inverting input of the differential pair, so the feedback factor is $\beta=1$ (unity-gain buffer). The closed-loop gain is $\dfrac{A}{1+A\beta}=\dfrac{40}{41}=0.976$.