Common-mode signal: Difference between revisions

Revision as of 17:27, 7 June 2023

Revision as of 16:23, 11 November 2023

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'''Common-mode{{short signal''' is the voltagedescription|Voltage common to both input terminals of an electrical device. In [[telecommunication]], the common-mode signal on a [[transmission line]] is also known as '''longitudinal voltage'''.}}

In most [[electrical circuitengineering]]s, the'''common-mode signal''' is transferred by a differentialthe [[voltage]] betweencommon twoto conductors.both Ifinput the[[Terminal voltages(electronics)|terminal]]s onof thesean conductorselectrical aredevice. U₁In and U₂[[telecommunication]], the common-mode signal ison thea [[Arithmetictransmission mean|averageline]] ofis thealso voltages:known as '''longitudinal voltage'''.

In most [[electrical circuit]]s the signal is transferred by a differential voltage between two [[Electrical conductor|conductors]]. If the voltages on these conductors are {{math|''U''₁}} and {{math|''U''₂}}, the common-mode signal is the [[Arithmetic mean|average]] of the voltages:

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

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

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. 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:

When referenced to the local common or [[Ground (electricity)|ground]], a common-mode signal appears on both lines of a two-wire cable, [[in phase]] and with equal amplitudes. 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

* A ground differential between the transmitting and receiving locations.

[[Noise (electronics)|Noise]] induced into a cable, or transmitted from a cable, usually occurs in the common mode, as the same signal tends to be picked up by both conductors in a two-wire cable. Likewise, RF noise transmitted from a cable tends to emanate from both conductors. Elimination of common-mode signals on cables entering or leaving electronic equipment is important to ensure [[electromagnetic compatibility]]. Unless the intention is to transmit or receive radio signals, an electronic designer generally designs electronic circuits to minimise or eliminate common-mode effects.

==Methods of eliminating common-mode signals==