Common-Mode Rejection Ratio (CMRR) Analysis A Common-Mode Rejection Ratio (CMRR) analysis is a crucial technique in CMOS analog IC design that assesses the...
Common-Mode Rejection Ratio (CMRR) Analysis
A Common-Mode Rejection Ratio (CMRR) analysis is a crucial technique in CMOS analog IC design that assesses the ability of an amplifier to reject common-mode disturbances. These disturbances couple onto the amplifier's output and can significantly affect its performance.
Key concept:
Common-mode noise: Noise that is present in both input and output signals.
Differential amplifier: An amplifier with two differential inputs and two differential outputs.
CMRR Analysis:
The CMRR is calculated as the ratio of the differential gain of the amplifier to the common-mode gain.
If the CMRR is greater than 1, the amplifier has a high common-mode rejection capability.
If the CMRR is less than 1, the amplifier has poor common-mode rejection.
Impact on Amplifier Performance:
A high CMRR ensures that the output signal is relatively immune to common-mode noise.
This allows the amplifier to maintain its accuracy and performance under varying conditions.
Poor CMRR can cause distorted output signals, reduced gain, and poor stability.
Example:
Consider a single-stage differential amplifier with two inputs and one output. The differential gain of this amplifier is 1, meaning the output voltage changes in phase with the input voltage.
Using a CMRR analysis, we can determine that the CMRR is greater than 1. This indicates that the amplifier has a high common-mode rejection capability and is able to reject common-mode disturbances effectively.
Conclusion:
CMRR analysis is an essential tool for optimizing the common-mode rejection performance of CMOS analog ICs. By understanding the concept and calculating the CMRR, designers can select amplifiers that provide the desired level of common-mode rejection for specific applications