[SI-LIST] Re: diff pair questions
- From: signal hoss <simails@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 24 Jul 2001 17:34:37 -0700 (PDT)
Chris,
I think you made the assumption on the drivers that
return current has to be on the planes.
What about designing a driver to return current on
opposite trace on pcb, so we don't need to care about
reference to planes. A similar example is eithernet
Cat-5 cable, which has no ground refernce.
The reason I asked is the scenario:
diff pair with planes refernce on pcb --> coaxial
cable --> other pcb
From pcb diff pair to cable diff pair, there seems
to have mismatch even though both have same
impendence-
one has reference to planes while the other don't.
This really puzzled me. Please advise.
Signal Hoss
--- Chris Rokusek <crokusek@xxxxxxxxxxxx> wrote:
>
> Signal,
>
> Try thinking about it as two single ended traces.
> Then in terms of return
> current, a large proportion of the return current
> for each diff trace
> actually returns on the planes rather than the
> opposite trace. So what you
> really have in terms of currents is a separate
> signal/return loop for each
> diff half. These two loops are equal and opposite
> but spaced very near each
> other (in fact on the planes they overlap at all but
> the highest frequencies
> causing cancellation, less noise, good stuff).
> Another way to visualize
> this is that the E/H field lines are "contained" by
> the planes. Thus
> impedance will vary as the plane separation is
> varied.
>
> Chris Rokusek
> Innoveda
>
__________________________________________________
Do You Yahoo!?
Make international calls for as low as $.04/minute with Yahoo! Messenger
http://phonecard.yahoo.com/
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
