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

I see, but I will be more interested in real life application where there is
a stripline crossing a cut power plane with a solid ground on the other
side. They exit in really world and I for one would like to know at what
point it will degrade the performance to an unacceptable level. 300ps edge ?
100ps edge ? 20 mil gap ? 100 mil gap ? etc. My experience suggest they can
work up to a reasonable speed (at least to the point where you start
thinking maybe differential signal makes more sense due to other design
considerations).

-----Original Message-----
From: steve weir [mailto:weirsp@xxxxxxxxxx]
Sent: Monday, January 10, 2005 6:56 PM
To: Chris.Cheng@xxxxxxxxxxxx; SI-List
Subject: Re: [SI-LIST] Re: risetime effects of plane breaks


Chris, because Zontar is listening.

Doug set-up a nice physics experiment that nicely demonstrates the bad 
things that happen when crossing a split with no other solid plane in the 
vicinity.  For my money, it aptly demonstrates several important effects 
and precisely why it would be a bad idea to put into practice.

Various people from Lee to Dan, Arpad, and yourself have pointed-out that 
under appropriate circumstances crossing a cut is not automatically the end 
of the world.  I don't think anyone proposes that crossing cuts like Doug 
has set-up comes without substantial consequences.

Best Regards,


Steve.

At 06:30 PM 1/10/2005 -0800, Chris Cheng wrote:
>Sorry but I have to ask, why would anyone will run a single edge signal at
>300ps as microstrip across a cut ground reference plane ? I can understand
>if it is a stripline with a solid ground on one reference and cut power
>planes on the other (which I have do a lot, not by choice though). What
>application will call for such routing ?
>
>-----Original Message-----
>From: steve weir [mailto:weirsp@xxxxxxxxxx]
>Sent: Monday, January 10, 2005 12:28 PM
>To: arpad.muranyi@xxxxxxxxx; SI-List
>Subject: [SI-LIST] Re: risetime effects of plane breaks
>
>
>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...
> >
> >Arpad
>
>=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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