The GATE Grind

GATE 2022 EC – Question 26

Analog Circuits · Op-amp Circuits · 1 mark · Multiple select

An ideal OPAMP circuit with a sinusoidal input is shown in the figure. The 3 dB frequency is the frequency at which the magnitude of the voltage gain decreases by 3 dB from the maximum value. Which of the options is/are correct?

Diagram for GATE 2022 EC question 26
  1. The circuit is a low pass filter.
  2. The circuit is a high pass filter.
  3. The 3 dB frequency is 1000 rad/s.
  4. The 3 dB frequency is $\frac{1000}{3}$ rad/s.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) The circuit is a high pass filter.; (C) The 3 dB frequency is 1000 rad/s.

Explanation

This is an inverting amplifier with input impedance $R+\frac{1}{j\omega C}$ and feedback $2\ \text{k}\Omega$, so $\frac{V_o}{V_{in}}=-\frac{2\text{k}}{1\text{k}+1/(j\omega C)}$. The gain is small at low frequency and tends to $-2$ at high frequency, so it is a high-pass filter. The corner frequency is $\omega=\frac{1}{RC}=\frac{1}{1\text{k}\times1\ \mu\text{F}}=1000$ rad/s.