Common-mode signal

As a common mode signal, a signal is referred to, the same time is applied to all the relevant inputs to the function of a block, for example, to the inputs of an operational amplifier with the same phase.

Voltage signals in synchrony called common mode voltages. At currents one speaks of the common mode current. Interfering signals are often common-mode signals. Common mode currents can be limited by so-called common-mode chokes. Unbalanced signal transmissions, as opposed to balanced signal transmission, sensitive to Gleichtaktstörsignalen.

Real signals are usually a superposition of the common mode and differential-mode signal.

With two inputs ( Vi1 and Vi2 ) of an operational amplifier, the common mode voltage ( engl. common mode voltage):

Example

The following figures show a common mode signal, a push-pull signal and the superposition of the two signals to the real current distribution.

The current arrows indicate a push-pull signal flowing in the same size on return conductor

The superposition of the common mode signal and push-pull signal provides a real current distribution on the line