[SI-LIST] Re: About common-mode
- From: "Ingraham, Andrew" <a.ingraham@xxxxxxxx>
- To: <Fu.Gerg@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 4 Nov 2003 11:03:26 -0500
> I see a document to explain the common-mode as follows:
> common-mode refers to signals that occur on both traces of a
> differential signal pair or on both the single-ended trace and ground.
> I have a question, where is the return path? Confused...
Probably on what we call "ground".
If we're talking about differential traces on a circuit board, the return
path is mostly the "ground" and power planes that surround the traces.
For common-mode currents on something like a coax cable, the return path
might be a chassis, or any other conductors that go between the source and
the load.
"Ground" is never ground; or stated another way, no two grounds are the
same. You can have several "ground" paths in a circuit between point A and
point B, and they are not all carrying the same currents. You can have
currents that go out one "ground" path and back (in the opposite direction)
on another "ground" path.
Regards,
Andy
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