Common-mode signal: Difference between revisions

Revision as of 09:47, 18 September 2021

Revision as of 15:31, 8 February 2022

Line 8:

* 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 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.

Line 15:

* [[Differential amplifier]]s or receivers that respond only to voltage differences, ''e.g.,'' those between the wires that constitute a pair. This method is particularly suited for instrumentation where signals are transmitted through DC bias.

* An inductor where a pair of signalling wires follow the same path through the inductor. E.g. in a [[bifilar winding]] configuration such as used in Ethernet magnetics.<ref>http://pulseeng.com/products/datasheets/H325.pdf {{Dead link|date=February 2022}}</ref> Useful for AC and DC signals, but will filter only higher frequency common-mode signals.

* A transformer, which is useful for AC signals only, and will filter any form of common-mode noise, but may be used in combination with a bifilar wound coil to eliminate capacitive coupling of higher frequency common-mode signals across the transformer. Used in twisted pair Ethernet.<ref>http://pulseeng.com/products/datasheets/H325.pdf {{Dead link|date=February 2022}}</ref>

Common-mode filtering may also be used to prevent egress of noise for electromagnetic compatibility purposes.