Common mode amplifiers are often used in instrumentation applications where it is necessary to amplify weak signals that are riding on a large common mode voltage. For example, a common mode amplifier could be used to amplify the signal from a strain gauge or a thermocouple.
Common mode amplifiers are typically designed using differential amplifiers. A differential amplifier is an electronic circuit that amplifies the difference between two input signals. By connecting the inputs of a differential amplifier to the two input signals, and the output of the differential amplifier to the input of a common mode amplifier, it is possible to amplify the common mode signal of the two input signals.
Common mode amplifiers can also be used to reject common mode noise. Common mode noise is noise that is present on both input signals of a differential amplifier. By amplifying the common mode signal and then subtracting it from the differential mode signal, it is possible to remove the common mode noise from the output signal.
Common mode amplifiers are an important tool for amplifying weak signals that are riding on a large common mode voltage. They are also used to reject common mode noise.