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=== | ||
''Common mode signalling'' points at a situation where you have | |||
* a reference conductor, which both ends of this communication have in common | * a reference conductor, which both ends of this communication have in common | ||
:: often called "signal common". | :: often called "signal common". | ||
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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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Differential subtracts the voltages on two lines, for one resulting signal. | Differential subtracts the voltages on two lines, for one resulting signal. | ||
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There are a few areas where it would've been nice if it were standard - like consumer audio systems. | There are a few areas where it would've been nice if it were standard - like consumer audio systems. | ||
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===Perhaps-necessary clarification=== | |||
====Common mode, differential mode, single ended==== | |||
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Differential mode is a voltage difference | |||
: without tying either to a known level, without a shared reference | |||
: also meaning these wires are dedicated to one signal | |||
Common mode is a voltage difference | |||
: tying one to a known level | |||
: probably a reference reused for multiple signals | |||
Single ended means a signal is present on one wire and not another | |||
: which seems to describe common-mode reality (and the two are used as near-synonyms) | |||
: because yes, common mode basically implies single ended, | |||
: '''but''' single ended can be used on both common mode and differential mode | |||
:: e.g. 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 all the signal on one wire and nothing on the other (which you'd easily call single-ended), because after differential interpretation this implies the same signal, and the differential-based noise reduction is not affected at all. | |||
::: In fact, doing this inside a balanced output driver seems moderately common{{verify}} because it is a little simpler component-wise. <!--{{comment|(It may (or may not) be approximately 3dB {{verify}} quieter, but this is rarely an issue)}} and depending on what you stick after it, there may be no practical difference.{{verify}} | |||
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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|differential mode]] | |||
====Differential in more depth==== | |||
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There are some related yet distinct concepts here: | There are some related yet distinct concepts here: | ||
* '''differential signalling''' | * '''differential signalling''' | ||
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===Derived and related terms=== | ====Derived and related terms==== | ||
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Latest revision as of 00:28, 21 April 2024
✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.
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
✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.
Perhaps-necessary clarification
Common mode, differential mode, single ended
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
Differential in more depth
Practical side
Balanced audio / pro audio
See Music_-_studio_and_stage_notes#Notes_on_balanced_audio
Comparisons
See also