EMG-amplifiers act as differential amplifiers and their main purpose is the ability to reject or eliminate artifacts.
The differential amplification detects the potential differences between the electrodes and cancels external
interferences out. Typically external noise signals reach both electrodes with no phase shift. These
“common mode” signals are signals equal in phase and amplitude. The term "common mode gain" refers to
the input-output relationship of common mode signals. The "Common Mode Rejection Ratio" (CMRR)
represents the relationship between differential and common mode gain and is therefore a criteria for the
quality of the chosen amplification technique. The CMRR should be as high as possible because the elimination
of interfering signals plays a major role in quality. A value >95dB is regarded as acceptable (11,
SENIAM, ISEK).