Common-mode signal: Difference between revisions

Revision as of 19:36, 17 January 2014

Revision as of 10:45, 30 March 2014

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'''Common-mode signal''' is the component of an [[analog signal]] which is present with one sign on all considered [[electrical conductor|conductor]]s. In [[telecommunication]], common-mode signal on a [[transmission line]] is known as '''longitudinal voltage'''.

In [[electronics]] where the signal is transferred withby differential voltage use, the common-mode signal is called a half-sum of voltages

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

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* 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</ref>

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

High frequency common mode signals, for example, [[Radio frequency|RF]] noise from a computing circuit, may be blocked using a ferrite bead clamped to the outside of a cable. These are often observable on laptop computer power supplies near the jack socket, and good quality mouse or printer USB cables and HDMI cables.<ref>http://www.elmac.co.uk/pdfs/ferrite.pdf</ref>