Common mode signal

A signal is referred to as a common-mode signal that is sent to all inputs of a module that are relevant to the function, e.g. B. at the inputs of an operational amplifier , is applied simultaneously with the same phase.

Voltage signals in common mode are called common mode voltages. When it comes to currents, one speaks of common-mode current. Noise signals are often common mode signals. Common-mode currents can be limited with so-called common - mode chokes . In contrast to symmetrical signal transmissions , asymmetrical signal transmissions are sensitive to common-mode interference signals.

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

With two inputs (U _e1 and U _e2 ) of an operational amplifier, the common mode voltage is :

${\displaystyle U_{CM}=\left|{\frac {U_{e1}+U_{e2}}{2}}\right|}$

example

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

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  The current arrows indicate a common mode signal that is transmitted to the consumer Z via z. B. a parasitic impedance Z _e closes over the reference potential

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  The current arrows indicate a push-pull signal that flows in the same size on the forward and return conductors

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  The superposition of the common mode signal and the push-pull signal results in the real power distribution on the line

literature

• Steffen Paul, Reinhold Paul: Fundamentals of electrical engineering and electronics 1 . DC networks and their applications, Springer-Verlag, Berlin / Heidelberg 2014, ISBN 978-3-642-53948-0 .
• Joachim Franz: EMC. Fail-safe construction of electronic circuits, Teubner Verlag, Stuttgart Leipzig Wiesbaden 2002, ISBN 3-519-00397-X .

See also

• Common mode rejection
• Common mode interference
• Differential amplifier