[SI-LIST] Referencing multiple voltages in a stackup
- From: "Chris McGrath" <chris.mcgrath@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 21 Oct 2004 14:09:59 -0700
I'm putting together a stackup with roughly 20 layers that requires
distribution of five different voltages and I'm wondering what effect
running 3.3V logic (133MHz) adjacent to a lower voltage reference plane
(such as 1.5V) would have on the lower voltage reference plane. =20
I understand the concept of the power plane operating as a reference
plane, but with 4 mil cores throughout the board, I am worried about
coupling switching noise from 3.3V signals into lower voltage reference
planes adjacent to the 3.3V signals. =20
As I see it, the conservative approach would be to only route 3.3V
signals next to the 3.3V plane or next to a ground plane. However,
given the rise times involved (~ 1ns), I tend to believe that sufficient
decoupling and stitching together of ground planes in the area would
suppress any noise that could potentially couple into the lower voltage
planes. My understanding is that for the higher speed signals (over 1
GHz), it is not wise to route adjacent to any reference other than
ground and the voltage reference for the GHZ signals. My question
mainly revolves around signals running at less than 1 GHz.
I am interested in hearing any opinions you may have on the topic. We
often talk about stackups but I could not find anything in the archives
that addressed the issue of stackups with a number of different
voltages.
Thanks,
Chris
------------------------------------------
Chris McGrath
Sr. Hardware Engineer
ADIC
ph: (607) 241-4858
eM: chris.mcgrath@xxxxxxxx
------------------------------------------
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