CMRR Calculator

| Added in Physics

What is CMRR?

The Common Mode Rejection Ratio (CMRR) is a key specification for differential amplifiers and operational amplifiers. It measures the amplifier's ability to reject signals that appear simultaneously and in-phase on both inputs while amplifying the difference between the inputs.

Formula

The CMRR is calculated using the following formula:

$$\text{CMRR} = \frac{\text{Differential Gain}}{\text{Common Mode Gain}}$$

Where:

  • Differential Gain is the amplification applied to the difference between the two input signals
  • Common Mode Gain is the amplification (or attenuation) applied to signals common to both inputs

Example Calculation

Calculate the CMRR when:

  • Differential Gain = 9.3
  • Common Mode Gain = 4.5

$$\text{CMRR} = \frac{9.3}{4.5} = 2.07$$

The CMRR is 2.07, indicating the amplifier's differential gain is about twice its common mode gain.

Applications

CMRR is important in:

  • Operational amplifiers - Higher CMRR means better noise rejection
  • Instrumentation amplifiers - Critical for measuring small differential signals in noisy environments
  • Audio equipment - Helps eliminate noise and interference
  • Medical equipment - Essential for accurate biological signal measurements

Frequently Asked Questions

CMRR (Common Mode Rejection Ratio) is a measure of how well an amplifier rejects common-mode signals while amplifying differential signals. It is the ratio of differential gain to common mode gain.

CMRR is calculated by dividing the differential gain by the common mode gain. A higher CMRR value indicates better performance in rejecting unwanted common-mode signals.