#### Tutorials

## Determination of Common-mode Rejection ratio, Bandwidth and Off-set null of OPAMPs

##### Krishanu Mitra

###### 20 Apr 2017

###### Read Time : 10 Minutes

In an ideal differential amplifier, differential voltage gain (A_{d}) is infinite while common mode voltage gain (A_{C}) must be zero. However, in a practical differential amplifier; A_{d} is very large and A_{C} is very small. ie., the differential amplifier provides very large amplification for difference signals and very small amplification for common mode signals. Many disturbance signals/noise signals appear as a common input signal to both the input terminals of the differential amplifier. Such a common signal should be rejected by the differential amplifier. “The ability of a differential amplifier to reject a common-mode signal is expressed by a ration called Common Mode Rejection Ratio, denoted as CMRR”. CMRR is defined as the ratio of the differential voltage gain A_{d} to common mode voltage gain A_{C}.

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