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I am on Vacation until Wed the 4th.
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>From [log in to unmask], on 8/28/96 3:12 PM:
I am on Vacation until Wed the 4th.
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>From [log in to unmask], on 8/28/96 2:31 PM:
Doug,
> See Printed Circuit Design Magazine, August 96
> "The Effects of Vias on PCB Traces" where this
> effect was explicitly looked for and NOT found.
> In general, there is no practical difference in where
> you reference to, assuming reasonable ac filtering on
> the various power planes. This is especially true
> if your trace is between a power and a ground plane.
> But in the study referenced in the article, there
> were no ill effects even when a trace moved several
> layers and referenced to a completely different plane!
>
> Nevertheless, it is good practice to try to keep the
> trace confined between a single pair of planes.
>
> Doug Brooks
Oh boy, I knew this was going to be a can of worms!
It is very specific case oriented especially as you noted
with high frequency. But, someone comes on the net and
has a general problem, it's difficult to get a good handle
on it to say blanketly yes or no.
I would beg to differ with the article (believe me I'm not
trying to start a fight). Having a controlled impedence
line from one reference plane drop vertically down several layers
to another refernce plane for controlled impedence MAY be asking
for trouble. The impedence of the line vertically is uncontrolled
thus causing an impedence "bump" with the trace.
I don't disagree with what anyone has said. Just fears of my own.
Doug
*******************************************************
Doug McKean
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The comments and opinions stated herein are mine alone,
and do not reflect those of my employer.
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