[SI-LIST] Re: slots in planes (once again)
- From: wolfgang.maichen@xxxxxxxxxxxx
- To: Gene Glick <gglick@xxxxxxxxxxxx>
- Date: Thu, 22 Jul 2010 11:04:21 -0700
Hello Gene,
for a single ended line, as long as the slot is at least 3-6 line widths
away from the trace it will have negligible impact on impedance and signal
integrity. This is because there is hardly any portion of the return
current flowing further away than that - and if there is no current to be
impacted by a detour, there is no effect.
Second, closely spaced differential pairs are quite insensitive to breaks
in the reference plane (with "closely spaced I mean the two lines of the
pairs are close together). In a very naive picture you can imagine the
return currents of true and complement canceling each other when they
arrive at the slot, and build up again at the other side of the slot.
There is some additional path (loop area) associated with that since the
current has to go from true to complement trace, but as long as the
distance between the two traces is small the parasitic inductance
associated with it is small as well.
Wolfgang
Gene Glick <gglick@xxxxxxxxxxxx>
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07/22/2010 10:55 AM
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Subject
[SI-LIST] slots in planes (once again)
Realizing that slots in a plane (ground, for example) are a bad idea, is
it ever acceptable?
Here's something some info from Henry Ott:
http://www.hottconsultants.com/techtips/tips-slots.html
He says "don't", but then says well, if you do so, don't allow any lines
to cross them. OK, I'm good by that. But, don't slotted planes give
rise to eddy currents around the aperture (even if nothing ever crosses
the slots)?
gene
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