[SI-LIST] Re: Help...
- From: "Jones, James R" <James_R_Jones@xxxxxxxx>
- To: 'Hinet' <wftinghi@xxxxxxxxxxxxxx>, manjusha@xxxxxxxxxxx,si-list@xxxxxxxxxxxxx
- Date: Mon, 10 Feb 2003 09:25:55 -0600
Steve,
I have not personally done studies on this topic, but I can share my
understanding, and hope that someone on the list may be able to further
elaborate....
Imagine that you have a 1/2 oz copper differential trace that is 5 mils wide
with some spacing, say X. For large X, the majority of the E field exists
between each trace of the diff pair and the reference plane. At high
frequency, the current in the trace will be confined to one skin depth times
5 mils wide of trace. Now imagine that X is small (tightly coupled). Now
most of the E field exists between the two traces. The current is confined
to one skin depth time .7 mils thick of trace.... a much smaller
cross-section, hence lossier.
I have seen rather lengthy threads on this list regarding tightly coupled
vs. loosely coupled pairs, and I thought this to be an interesting argument.
I have not personally done a lot of work to verify this, so if someone has,
and would like to share, I would love to see it.
JR
-----Original Message-----
From: Hinet [mailto:wftinghi@xxxxxxxxxxxxxx]
Sent: Friday, February 07, 2003 9:27 PM
To: Jones, James R; manjusha@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: Help...
> Also, tightly coupled traces will crosstalk even
> less, but be wary of losses due to fringing effects.
>
Could you explain why the losses would be increased by tight coupling in
more details?
Thanks!
Steve
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