Re: [SI-LIST] : What is effect of adjacent signal layer on PCB

Steve Weir (weirsp@a.crl.com)
Tue, 15 Jun 1999 10:58:00 -0700

This is referred to as an offset stripline. The precise modelling is a
little bit complex, but you can get fairly close with the models in Dr.
Johnson's book "High Speed Digital Design". MathCAD formula's are at the
end of the book.

Regards
At 08:18 AM 6/15/99 -0700, you wrote:
>When you have a PCB stackup that has a signal plane sandwiched between two
>ground planes, you have stripline. Zo at this point is fairly easy to
>characterize.
>
>Now, if you add a second signal layer in between the two ground planes, one
>in the X direction and the other in the Y, you still have stripline
>(asymetric), but now you have a bunch of traces crossing the path above (or
>below) your signal layer. I understand this introduces crosstalk, but what
>does it do to the characteristic impedance of your traces? Is the impedance
>still controlled? Does it vary widely, or not have much effect at all?
>
>I see a lot of stackups with this arrangement, and I wonder how Zo is
>maintained.
>
>Thanks,
>
>Chris
>
>
>
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