Common-mode signal: Difference between revisions

Revision as of 19:04, 15 September 2021

Revision as of 09:47, 18 September 2021

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'''Common-mode signal''' is the voltage common to both input terminals of an electrical device. In the perspective of ac power, common-mode noise is the disturbance signal between the neutral and ground conductors. In [[telecommunication]], the common-mode signal on a [[transmission line]] is also known as '''longitudinal voltage'''.

In most [[electrical circuit]]s the signal is transferred by a differential voltage between two conductors. If the voltages on these conductors are U₁ and U₂, the common-mode signal is the half-sum of the voltages:

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:<math>U_\text{cm} = \frac{U_1 + U_2}{2}</math>

In a power distribution system, ground loops are one contributor of common-mode noise between phases, neutral, and ground. The difference in potential between two physically distant grounds is the most main cause of common-mode noise. When referenced to the local common or ground, a common-mode signal appears on both lines of a two-wire cable, in phase and with equal amplitudes. Common-mode noise also can be generated from ungrounded source, it occurs if a separate power supply is utilized to power the remote device and the remote power supply is left ungrounded. Technically, a common-mode voltage is one-half the vector sum of the voltages from each conductor of a balanced circuit to local ground or common. Such signals can arise from one or more of the following sources:

* Radiated signals coupled equally to both lines,

* An offset from signal common created in the driver circuit, or