Question:
An ideal op-amp has CMRR:
An ideal op-amp has CMRR:
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\textbf{Ideal op-amps} have \textbf{infinite CMRR}, \textbf{infinite input impedance}, and \textbf{zero output impedance}. Always remember these traits for theoretical analysis.
Updated On: Jun 24, 2025
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The Correct Option is C
Solution and Explanation
CMRR stands for Common Mode Rejection Ratio, which measures an op-amp's ability to reject common-mode signals—those that appear simultaneously and in-phase on both inputs.
Mathematically, it is defined as:
\[ \text{CMRR} = \dfrac{A_{d}}{A_{cm}} \] where $A_d$ is the differential gain and $A_{cm}$ is the common-mode gain.
In an ideal operational amplifier, the common-mode gain is zero (it does not amplify common-mode signals at all), and the differential gain is theoretically infinite.
Thus, the CMRR becomes:
\[ \text{CMRR} = \dfrac{\infty}{0} = \infty \] This means that an ideal op-amp has an infinite CMRR, perfectly amplifying only differential inputs while completely rejecting common-mode signals.
Mathematically, it is defined as:
\[ \text{CMRR} = \dfrac{A_{d}}{A_{cm}} \] where $A_d$ is the differential gain and $A_{cm}$ is the common-mode gain.
In an ideal operational amplifier, the common-mode gain is zero (it does not amplify common-mode signals at all), and the differential gain is theoretically infinite.
Thus, the CMRR becomes:
\[ \text{CMRR} = \dfrac{\infty}{0} = \infty \] This means that an ideal op-amp has an infinite CMRR, perfectly amplifying only differential inputs while completely rejecting common-mode signals.
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