[SI-LIST] Re: risetime effects of plane breaks
- From: Chris Cheng <Chris.Cheng@xxxxxxxxxxxx>
- To: "'SI-List '" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 10 Jan 2005 22:53:56 -0800
Steve,
BTBT for a single line, but it gets really interesting when you cross the
entire bus. At what point the return current is going to start overlapping
each other to the extend that the wave start to be additive (call it
crosstalk or call it SSO) whatever suits your term.
-----Original Message-----
From: steve weir
To: Chris.Cheng@xxxxxxxxxxxx; SI-List
Sent: 1/10/2005 7:53 PM
Subject: Re: [SI-LIST] Re: risetime effects of plane breaks
Chris, well that is what 3D modeling software is for. For the case of
an
offset stripline, we can compare the impedance of a buried microstrip to
the stripline to get the outer impedance limits. I think you will find
that the impedance shift is in the low percents for practical
geometries. So intuitively, I agree that with an offset stripline where
it
is the far plane that gets chopped, the effects s/b quite minor. From
the
standpoint of how wide a gap is needed to show a demonstrable effect, I
think we have to get to at least X * 6 * sqrt( Er )/C >= tr. That seems
to
indicate we have to get all the way down to about a 10ps rise time
before
anything serious happens.
For the case where the cut is in the adjacent plane, the problem is a
lot
trickier. I think the critical tr falls by at least a decade if not
more.
Best Regards,
Steve.
At 07:05 PM 1/10/2005 -0800, Chris Cheng wrote:
>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=3
D=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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