CMVR vs CMRR: Understanding Op-Amp Differences

This article clarifies the basic differences between CMVR (Common Mode Voltage Range) and CMRR (Common Mode Rejection Ratio) as they relate to Operational Amplifiers (Op-Amps).

Operational Amplifier Basics

An Operational Amplifier, often called an Op-Amp, is a fundamental building block in analog electronics. It’s a versatile device used in a wide range of applications, from simple amplification to complex signal processing.

CMVR: Common Mode Voltage Range

The term CMVR stands for Common Mode Voltage Range. It’s a crucial parameter for differential input devices like operational amplifiers.

Essentially, the CMVR defines the range of common-mode input voltages within which the amplifier operates linearly. Outside this range, the Op-Amp’s performance degrades, and it may no longer function as intended.

The common-mode voltage (VCM) is calculated as follows:

VCM or CMVR = (V1 + V2) / 2

Where:

• V1 = Voltage at the negative (-) input
• V2 = Voltage at the positive (+) input

Think of it as the average voltage applied to both inputs simultaneously. The CMVR specifies the limits on this average voltage for proper operation.

CMRR: Common Mode Rejection Ratio

The term CMRR stands for Common Mode Rejection Ratio.

It’s a measure of the operational amplifier’s ability to reject signals that are common to both the positive (+) and negative (-) input terminals. Ideally, an Op-Amp should only amplify the difference between the two inputs and ignore any signals present on both inputs simultaneously. CMRR quantifies how well it achieves this.

CMRR is typically expressed in decibels (dB) and can be calculated using the following equation:

CMRR = Differential Mode Gain / Common Mode Gain

A higher CMRR value indicates better performance. It means the Op-Amp is more effective at rejecting common-mode signals, leading to a cleaner amplified signal.

Key Differences Summarized