[SI-LIST] Re: risetime effects of plane breaks
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Doug Smith" <doug@xxxxxxxxxx>, "SI-List" <si-list@xxxxxxxxxxxxx>
- Date: Sun, 9 Jan 2005 16:29:06 -0800
Doug,
Whether or not it is okay to route signals over a plane split depends on
how you do it. A good reason (and the only one in my view) to split a
plane is to allow more than one voltage to be distributed in the same
plane. When proper decoupling has been done to so that both voltages have
a low impedance, the plane cut is not visible. I've done this on many PCBs
with no ill effects and, yes, I've got lots of measurements to prove it.
I'd be curious what the conditions are that cause you problems.
Lee W. Ritchey
Speeding Edge
P. O. Box 2194
Glen Ellen, CA 95442
Phone- 707-568-3983
FAX- 707-568-3504
I just used the energy it took to be angry to write some blues.
Count Basie
> [Original Message]
> From: Doug Smith <doug@xxxxxxxxxx>
> To: SI-List <si-list@xxxxxxxxxxxxx>
> Date: 1/8/2005 5:23:26 PM
> Subject: [SI-LIST] risetime effects of plane breaks
>
> I think most of us know not to route signals over plane breaks on PWBs
> as all kinds of bad things can happen when this occurs in a layout.
> But, how do you convince co-workers or your boss that a new design
> needs to avoid doing this even if added expense or project delay is
> required? Experimental data can be the key and this month my Technical
> Tidbit shows what happens to signal risetime if the signal crosses a
> plane break.
>
> Crossing Ground Plane Breaks - Part 4
> Risetime Effects on Signals
>
> Abstract: Signals that cross ground plane breaks on printed wiring
> boards (PWBs) experience degradation as well as cause EMI problems.
> Significant degradation of signal risetime is shown to occur, even
> with a relatively small ground break of five cm at risetimes on the
> order of 300 ps.
>
> The link to the article is the picture of the experimental test setup
> at the bottom of the home page at http://emcesd.com .
>
> Doug
> --
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> ___ _ Doug Smith
> \ / ) P.O. Box 1457
> ========= Los Gatos, CA 95031-1457
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