[SI-LIST] Re: risetime effects of plane breaks
- From: steve weir <weirsp@xxxxxxxxxx>
- To: emcesd2000@xxxxxxxxx, SI-List <si-list@xxxxxxxxxxxxx>
- Date: Mon, 10 Jan 2005 11:21:26 -0800
Oscar, yes, it is quite a dramatic effect isn't it? I suspect that when
Lee says "it depends on how you do it" he has another contiguous plane, ie
ground underneath the split as opposed to a split on all planes as in
Doug's experiment. Assuming lots of decoupling between each of the islands
and the common ground plane the jump in coupling between lines would be
greatly suppressed.
Regards,
Steve.
At 11:00 AM 1/10/2005 -0800, Ahmad Fallah wrote:
>Hi Steve,
>
>I have repeated Doug's experiment with a modified fixture where an
>additional trace (victim) was added near (~1 cm) the "signal" line for
>X-talk measurements. I have measured a 10-fold increase in x-talk
>amplitude in going from Case 1 to Case 2.
>
>Case 1: the offending and victim lines are both drawn over a solid return
>plane.
>Case 2: the offending and victim lines are both drawn over the cut in the
>return plane
>
>Regards,
>
>Oscar
>
>
>
>steve weir <weirsp@xxxxxxxxxx> wrote:
>
>Lee, the 5cm is the length of the break. The break is only about 20-50mils
>wide. Hit the link and scroll to Figure 3. In Doug's test set-up, both of
>the two planes have been broken. Now, If one cares to do a crosstalk test,
>it looks like Doug could modify his fixture rather easily to do that. In
>the vicinity of the break, the multiple line coupling, including between
>members of a diff pair jumps.
>
>
>
>
>
>If you want to perform an entertaining experiment, take a diff pair, or
>just one active driver and a quiet line and route them over a narrow, and
>short break, say 0.25" by 0.02" and take four port S parameter
>measurements. Take another pair and do likewise, but keep extending the
>length of the slot, ie perpendicular to the traces by a factor of 2 with
>each test. Even though the width of the gap is short, by the time that
>slot becomes an inch or two long the band of frequencies where coupling is
>fairly strong will be pretty wide.
>
>http://emcesd.com/tt2005/tt010105.htm
>
>Regards,
>
>Steve
>
>
>At 04:30 PM 1/9/2005 -0800, Lee Ritchey wrote:
> >Just noticed that you call a 5 cm break relatively small. Does that mean
> >5 cm in width?
> >
> >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
> > > To: SI-List
> > > 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
> > > --
> > > -------------------------------------------------------
> > > ___ _ Doug Smith
> > > \ / ) P.O. Box 1457
> > > ========= Los Gatos, CA 95031-1457
> > > _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
> > > / /\ \ ] / /\ \ Mobile: 408-858-4528
> > > | q-----( ) | o | Email: doug@xxxxxxxxxx
> > > \ _ / ] \ _ / Website: http://www.dsmith.org
> > > -------------------------------------------------------
> > >
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