Introduction
Common Mode Rejection Ratio (CMRR) is a critical parameter in amplifier design, indicating the device’s ability to reject common-mode signals while amplifying differential signals. This guide will help you understand CMRR, its significance, and how to calculate it.
How to Use
To calculate CMRR, you need to know the differential gain (Adiff) and the common mode gain (Acom). The formula for CMRR is:
CMRR = Adiff / Acom
The CMRR is typically expressed in decibels (dB), so you may need to take the logarithm of this ratio.
Formula
The formula for calculating the Common Mode Rejection Ratio (CMRR) is:
CMRR = Adiff / Acom
Where:
- CMRR: Common Mode Rejection Ratio
- Adiff: Differential Gain
- Acom: Common Mode Gain
Example
Let’s illustrate the calculation with an example. Suppose you have an amplifier with a differential gain (Adiff) of 1000 and a common mode gain (Acom) of 10. To find the CMRR:
CMRR = Adiff / Acom = 1000 / 10 = 100
So, the CMRR for this amplifier is 100 dB.
FAQs
Q1: Why is CMRR important in amplifier design?
A1: CMRR is crucial because it quantifies an amplifier’s ability to reject common-mode signals, reducing noise and interference in the output.
Q2: Can CMRR be negative?
A2: No, CMRR is always a positive value, as it’s a ratio of two gains.
Q3: How do I measure Adiff and Acom in practice?
A3: Measure the output voltage for a differential input and a common-mode input, respectively, and use these values in the CMRR formula.
Conclusion
Understanding CMRR is essential for designing high-quality amplifiers. A higher CMRR value indicates better noise rejection. By utilizing the CMRR formula and considering the example, you can evaluate and improve your amplifier designs.