1. What is CMRR?

Common-mode rejection ratio (CMRR) is a measure of a differential amplifier's ability to reject common-mode signals (signals that appear simultaneously and in-phase on both inputs). It's defined as the ratio of differential gain to common-mode gain.

2. How Does the Calculator Work?

The calculator uses the CMRR equation:

Where:

• \( A_d \) — Differential gain (V/V)
• \( A_c \) — Common-mode gain (V/V)

Explanation: The higher the CMRR, the better the amplifier is at rejecting common-mode signals. CMRR is often expressed in decibels (dB) as \( 20 \log_{10}(CMRR) \).

3. Importance of CMRR

Details: CMRR is crucial in applications where small differential signals must be amplified in the presence of large common-mode signals, such as in instrumentation amplifiers, medical equipment, and communication systems.

4. Using the Calculator

Tips: Enter the differential gain (Ad) and common-mode gain (Ac) in volts per volt (V/V). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a good CMRR value?
A: Good instrumentation amplifiers typically have CMRR values of 100 dB or more. Values above 80 dB are generally considered good.

Q2: Why is CMRR important in amplifiers?
A: High CMRR allows amplifiers to reject noise and interference that appears equally on both input lines, amplifying only the desired differential signal.

Q3: How does frequency affect CMRR?
A: CMRR typically decreases with increasing frequency due to mismatches in amplifier components at higher frequencies.

Q4: What factors affect CMRR?
A: Component matching, resistor tolerances, and amplifier design all affect CMRR. Better matched components yield higher CMRR.

Q5: How can I improve CMRR in my circuit?
A: Use precision-matched resistors, high-quality operational amplifiers, and proper PCB layout techniques to maximize CMRR.