Common mode, differential mode: Difference between revisions
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Common mode versus differential mode is about communicating a signal electrically, usually as a voltage signal. | |||
==Theoretical side== | ==Theoretical side== | ||
===Common mode=== | ===Common mode=== | ||
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That signal common is often part of the interconnect. | Such a difference is easy to consume because components tend to be references | ||
That signal common is often part of the interconnect. | |||
Because it ''needs'' to be for the other side to use it. | |||
This raises some issues, though. | |||
The resistance of the wire could potentially change the amplitide, | |||
the capacitance could alter the signal somewhat. | |||
But the larger issue often comes from that that reference ''tends'' to be tied to ground at some point. | |||
This is easy, but comes with a ''bucket'' of footnotes that just gets worse the larger the effective circuit is. | |||
to the point it's often something you may specifically want to avoid if you can, because it maykes resistive, capacitive, and inductive coupling something you need to think about reducing, and is harder to fix if you didn't think of that in the design. {{comment|(also note this is the less-precise use of the word [[ground]]. Which is sometimes irrelevant pedantry, but this is one example where ''not'' making that distinction is part of what gets you into noisy trouble and makes it harder to discuss and fix)}} | |||
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Revision as of 13:21, 14 July 2023
Common mode versus differential mode is about communicating a signal electrically, usually as a voltage signal.
Theoretical side
Common mode
Common mode signalling points at a situation where you have
- a reference conductor, which both ends of this communication have in common
- often called "signal common".
- a conductor for a signal
And the signal is the voltage difference between the two.
Differential mode / differential signalling
Single ended
Single-ended signalling basically means all the signal is on one wire, none on any other.(verify)
A lot of the time, single-ended is used as a near-synonym for common mode.
And fair enough, common mode basically implies single ended, in that there is typically a signal common, used as a reference for one or more signals, which is usually tied to some fixed level (like ground).
Yet single-ended does not necessarily imply common-mode reference.
While introductions to XLR make a big kerfuffle over sending signal/2 and -signal/2 on the two wires, it is entirely valid to send the signal on one wire and nothing on the other (which you'd easily call signle-ended), because after differential interpretation this implies the same signal at the other end and the same amount of noise reduction.
In fact, doing this is moderately common(verify) because it is a little simpler component-wise.
If a distinction is made between single ended and common mode, single-ended often refers more to the concept, common mode more to electrical reality of conductors.
Both single-ended and common mode are mainly contrasted with differential mode
Practical side
Balanced audio / pro audio
See Music_-_studio_and_stage_notes#Notes_on_balanced_audio
Comparisons
See also