RE: [SI-LIST] : Regarding plane splits

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From: Chan, Michael (Michael.Chan@compaq.com)
Date: Wed Nov 22 2000 - 10:35:46 PST


What happen if the split is for two different voltage planes?

MChan

-----Original Message-----
From: Ritchey Lee [mailto:leeritchey@earthlink.net]
Sent: Wednesday, November 22, 2000 11:39 AM
To: Zabinski, Patrick J.
Cc: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : Regarding plane splits

All of these discussions fail to take into account the fact that the
ground plane and the two power planes msut be well decoupled in order to
create a low impedance source for the switching currents that are involved
in those same swithcing edges. If this had been done well, the power
planes will, of necessity, be shorted to the ground plane and that will be
the path around the split.

In my experience, people who see the effects of a split have failed to do
a good job of power plane decoupling. Learn how to do this well and
splits won't bother you.

Lee

Zabinski, Patrick J. wrote:

> Aloke,
>
> As I mentioned in a recent posting, there are conditions in which
> routing stripline in a configuration you describe sees no effects
> from the split. More specifically, if your trace layer is "closer"
> to the solid ground plane than the split power planes, then the
> solid plane has "more" of an influence on the trace. As such, you
> will "less" of a discontinuity from the split. I've tested this
> in the lab under several conditions, and I believe this to be true.
>
> However, the reason I used "'s in the above statements is that I
> haven't taken my experiments far along enough to be able to provide
> any guidance as to how "close" is "close enough" to reduce the
> discontinuity effects to the point where your system can tolerate
> them.
>
> In what I call a 50/50 case where the stripline layer is centered
> vertically in the stackup such that the distance to the solid ground
> plane is the same as the distance to the split plane, you will notice
> the discontinuities.
>
> Pat
>
> >
> > Hello all,
> > I had a doubt regarding plane splits:
> >
> > In the stackup, if there is a power plane on one side of the signal
> > layer and a ground plane on the other side of the signal
> > layer(symmetric
> > stripline config), and if the ground plane is a solid ground plane
> > having no discontinuities, then can I have splits in the
> > power plane and
> > run traces over the splits? Is the ground plane alone not
> > sufficient to
> > provide paths for return currents?
> >
> > With regards,
> > Aloke
> >
> >
> >
> >
>
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