[SI-LIST] Re: risetime effects of plane breaks
- From: steve weir <weirsp@xxxxxxxxxx>
- To: Chris.Cheng@xxxxxxxxxxxx
- Date: Fri, 14 Jan 2005 16:03:27 -0800
Chris, wire, insulator, plane w/split, dielectric, solid plane.
Best Regards,
Steve.
At 03:35 PM 1/14/2005 -0800, Chris Cheng wrote:
>Doug,
>Just try to understand your new stack up,
>is it :
>signal-splitplane-solid plane
>or
>splitplane-signal-solid plane ?
>
>-----Original Message-----
>From: Doug Smith [mailto:doug@xxxxxxxxxx]
>Sent: Friday, January 14, 2005 3:17 PM
>To: weirsp@xxxxxxxxxx
>Cc: emcesd2000@xxxxxxxxx; SI-List
>Subject: [SI-LIST] Re: risetime effects of plane breaks
>
>
>Wow! I didn't realize my little article would stimulate so many
>postings. Having a good discussion like this is good for us all.
>
>While teaching a seminar in San Diego yesterday I did a slight
>modification of the split plane board I used for my article this
>month. I covered the bottom plane split (opposite signal wire with
>copper tape and measured the ESD immunity via radiation from an ESD
>event. This was the first time for this setup and live for the class.
>I scoured the tape many times to make sure connection was made through
>the "conductive" adhesive.
>
>The immunity was significantly worst (0.5 Volts induced in path) than
>the path over solid plane (0.1 Volt) and better than the path where
>both planes were cut (1.5 Volts induced EMI).
>
>Doug
>
>For the 30 or so mil plane spacing of the board
>
>steve weir wrote:
> > 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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>--
>------------------------------------------------------------
> ___ _ 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
> \ _ / ] \ _ / Web: http://www.dsmith.org
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