Common Mode Rejection Ratio
Common Mode Rejection Ratio - Related Videos
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FAQs
CMRR is governed by the ratio between differential gain and common-mode gain. Differential gain describes how strongly the system responds to the voltage difference between inputs, while common-mode gain describes its response to signals shared by both inputs. A large ratio indicates that the circuit emphasizes the desired difference while contributing relatively little output from shared signals.
The decibel form, calculated as 20 log10 of the gain ratio, provides a compact way to represent the relationship between differential and common-mode responses. Because the ratio can vary substantially, logarithmic notation makes comparisons easier. A higher CMRR value in decibels signifies stronger rejection of signals appearing identically at both inputs.
Common-mode gain indicates how much of a shared input signal can still influence the output. Ideally, that response remains small compared with the response to the input difference, but any remaining common-mode gain reduces rejection performance. Examining this quantity helps engineers understand why interference may appear in measurements even when it reaches both inputs with the same polarity.
CMRR is especially important in instrumentation amplifiers, sensor interfaces, and data-acquisition systems that handle low-level measurements. In these systems, electromagnetic noise, ground fluctuations, or signals coupled through cables can affect both inputs. Strong rejection helps preserve the measured difference, improving signal integrity and supporting more accurate acquisition of sensor or instrumentation signals.
Engineers first determine the circuit's differential gain and common-mode gain, then form their ratio. They can express the result directly as a gain ratio or convert it to decibels using 20 log10 of that ratio. Comparing the resulting value across circuits or measurement systems shows which design provides more effective suppression of shared interference.
In sensor interfaces and data-acquisition systems, unwanted signals may accompany the desired measurement through electromagnetic coupling, ground fluctuations, or cables. The system's CMRR indicates how effectively those shared contributions are suppressed relative to the input difference. A higher value generally supports cleaner signal recovery and better measurement accuracy when low-level signals coexist with common interference.