# [SI-LIST] Re: risetime effects of plane breaks

• From: steve weir <weirsp@xxxxxxxxxx>
• Date: Mon, 10 Jan 2005 12:27:34 -0800

```Arpad, a jump from 10-14% coupling up to 30% or so is still very
significant.  Phase match and other common mode issues should not be
dismissed when attempting to cross a split.  The first choice should be
don't do it.  But if one must, then do so with care.

Regards,

Steve.
At 11:41 AM 1/10/2005 -0800, Muranyi, Arpad wrote:
>Even though I was just speed reading this
>thread, I didn't see this mentioned yet:
>
>You can also get by with plane breaks if the
>traces going over it are closely coupled
>differential pairs...
>
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=20
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
>On Behalf Of steve weir
>Sent: Monday, January 10, 2005 11:21 AM
>To: emcesd2000@xxxxxxxxx; SI-List
>Subject: [SI-LIST] Re: risetime effects of plane breaks
>
>Oscar, yes, it is quite a dramatic effect isn't it?  I suspect that  =
>when=20
>Lee says "it depends on how you do it" he has another contiguous plane, =
>ie=20
>ground underneath the split as opposed to a split on all planes as in=20
>Doug's experiment.  Assuming lots of decoupling between each of the =
>islands=20
>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=20
> >additional trace (victim) was added near (~1 cm) the "signal" line for=20
> >X-talk measurements.  I have measured a 10-fold increase in x-talk=20
> >amplitude in going from Case 1 to Case 2.
> >
> >Case 1: the offending and victim lines are both drawn over a solid =
>return=20
> >plane.
> >Case 2: the offending and victim lines are both drawn over the cut in =
>the=20
> >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
> > > > =3D=3D=3D=3D=3D=3D=3D=3D=3D 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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