Rejection Capability
Logarithmic figure of merit suppresses signals appearing simultaneously on both input terminals of an amplifier. High common mode rejection ratio ensures that noise from power lines or electromagnetic interference does not corrupt the desired differential signal. The value is expressed in decibels and represents the ratio of differential gain to common mode gain.
Differential Gain
Amplification of the difference between the two inputs remains the primary function of the circuit. While the differential signal is boosted, the common mode signal is attenuated to prevent it from reaching the output stage. Precise matching of internal resistors determines the effectiveness of this separation.
Interference Suppression
Electronic environments often contain 50Hz or 60Hz hum that affects both signal leads equally. When the common mode rejection ratio is high, the amplifier ignores this shared noise and only processes the small voltage variations from the sensor itself. This capability is essential for low level signals in industrial settings.
Frequency Dependency
Rejection effectiveness typically decreases as the frequency of the common mode signal increases due to parasitic capacitances. Designers must consult the data sheet to verify that the common mode rejection ratio remains sufficient at the switching frequency of the system power supply. External shielding often supplements the amplifier performance when high frequency noise exceeds the internal limits of the component.
