What does the term "Common Mode Rejection" refer to in relation to differential amplifiers?

The term "Common Mode Rejection" specifically refers to the ability of a differential amplifier to reject signals that are present simultaneously and equally on both input lines, meaning it effectively ignores unwanted noise or interference that is common to both inputs. This feature is vital in applications where it is necessary to amplify the difference between two signals while minimizing the impact of any noise that is present on both lines, such as when measuring small physiological signals in polysomnography.

The emphasis on rejecting identical inputs allows for a cleaner and more accurate representation of the desired differential signal. This capacity is quantified by the Common Mode Rejection Ratio (CMRR), which defines the effectiveness of the differential amplifier in differentiating between the desired signal and the common noise. This is particularly important in clinical settings where the integrity of the data is critical for diagnosis and treatment.