GATE 2022 EC – Question 42
A circuit with an ideal OPAMP is shown. The Bode plot for the magnitude (in dB) of the gain transfer function ($A_V(j\omega)=V_{out}(j\omega)/V_{in}(j\omega)$) of the circuit is also provided (here, $\omega$ is the angular frequency in rad/s). The values of $R$ and $C$ are ________.
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Correct answer: (A) $R=3\ \text{k}\Omega,\ C=1\ \mu\text{F}$
Explanation
The circuit is a non-inverting amplifier with gain $1+\frac{R}{1\text{k}}$ preceded by an RC low-pass filter ($1\ \text{k}\Omega$ and $C$). The low-frequency gain in the plot is 12 dB $=4$, so $R=3\ \text{k}\Omega$. The gain falls by 3 dB (to 9 dB) at the corner frequency $\omega_c=\frac{1}{1\text{k}\cdot C}$, and the plot shows a corner close to $10^3$ rad/s, so $C=1\ \mu$F.