[SI-LIST] Re: risetime effects of plane breaks
- From: John Lin (林朝煌) <John@xxxxxxxxxxxx>
- To: <Chris.Cheng@xxxxxxxxxxxx>, "SI-List" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 11 Jan 2005 12:57:57 +0800
Hi all,
How about differential pair signals. Differential pair actually doesn't =
need a ground reference (or virtual ground).=20
If not considering the mismatch, which cause common mode noise, then not =
having solid ground shall be adoptable. Right?
Thanks,
John=20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Chris Cheng
Sent: Tuesday, January 11, 2005 11:05 AM
To: SI-List
Subject: [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=20
>understand if it is a stripline with a solid ground on one reference=20
>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=20
>significant. Phase match and other common mode issues should not be=20
>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=20
> >mentioned yet:
> >
> >You can also get by with plane breaks if the traces going over it are =
> >closely coupled differential pairs...
> >
> >Arpad
>
>=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3
>D=3D3D
>=3D
> =
>=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D20
> >
> >-----Original Message-----
> >From: si-list-bounce@xxxxxxxxxxxxx=20
> >[mailto:si-list-bounce@xxxxxxxxxxxxx]
=3D
> >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 =20
> >=3D when=3D20 Lee says "it depends on how you do it" he has another=20
> >contiguous plane, =3D ie=3D20 ground underneath the split as opposed =
to a=20
> >split on all planes as in=3D20 Doug's experiment. Assuming lots of=20
> >decoupling between each of the =3D islands=3D20 and the common ground =
> >plane the jump in coupling between lines would be
=3D
> >
> >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=20
> > >an=3D20 additional trace (victim) was added near (~1 cm) the =
"signal"=20
> > >line
for=3D20
> > >X-talk measurements. I have measured a 10-fold increase in=20
> > >x-talk=3D20 amplitude in going from Case 1 to Case 2.
> > >
> > >Case 1: the offending and victim lines are both drawn over a solid=20
> > >=3D
> >return=3D20
> > >plane.
> > >Case 2: the offending and victim lines are both drawn over the cut=20
> > >in =3D
> >the=3D20
> > >return plane
> > >
> > >Regards,
> > >
> > >Oscar
> > >
> > >
> > >
> > >steve weir <weirsp@xxxxxxxxxx> wrote:
> > >
> > >Lee, the 5cm is the length of the break. The break is only about =
=3D
> >20-50mils
> > >wide. Hit the link and scroll to Figure 3. In Doug's test set-up,=20
> > >both
=3D
> >of
> > >the two planes have been broken. Now, If one cares to do a=20
> > >crosstalk =3D
> >test,
> > >it looks like Doug could modify his fixture rather easily to do=20
> > >that. =3D
> >In
> > >the vicinity of the break, the multiple line coupling, including =
=3D
> >between
> > >members of a diff pair jumps.
> > >
> > >
> > >
> > >
> > >
> > >If you want to perform an entertaining experiment, take a diff=20
> > >pair, or just one active driver and a quiet line and route them=20
> > >over a narrow, =3D
> >and
> > >short break, say 0.25" by 0.02" and take four port S parameter=20
> > >measurements. Take another pair and do likewise, but keep extending =
> > >the length of the slot, ie perpendicular to the traces by a factor=20
> > >of 2 =3D
> >with
> > >each test. Even though the width of the gap is short, by the time=20
> > >that slot becomes an inch or two long the band of frequencies where =
> > >coupling
=3D
> >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=20
> > > >that =3D
> >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
=3D
> >PWBs
> > > > > as all kinds of bad things can happen when this occurs in a =
=3D
> >layout.
> > > > > But, how do you convince co-workers or your boss that a new=20
> > > > > design needs to avoid doing this even if added expense or=20
> > > > > project delay =3D
> >is
> > > > > required? Experimental data can be the key and this month my =
=3D
> >Technical
> > > > > Tidbit shows what happens to signal risetime if the signal=20
> > > > > crosses
=3D
> >a
> > > > > plane break.
> > > > >
> > > > > Crossing Ground Plane Breaks - Part 4 Risetime Effects on=20
> > > > > Signals
> > > > >
> > > > > Abstract: Signals that cross ground plane breaks on printed=20
> > > > > wiring boards (PWBs) experience degradation as well as cause=20
> > > > > EMI =3D
> >problems.
> > > > > Significant degradation of signal risetime is shown to occur,=20
> > > > > even with a relatively small ground break of five cm at=20
> > > > > risetimes on =3D
> >the
> > > > > order of 300 ps.
> > > > >
> > > > > The link to the article is the picture of the experimental=20
> > > > > test =3D
> >setup
> > > > > at the bottom of the home page at http://emcesd.com .
> > > > >
> > > > > Doug
> > > > > --
> > > > > -------------------------------------------------------
> > > > > ___ _ Doug Smith
> > > > > \ / ) P.O. Box 1457
> > > > > =3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D Los Gatos, CA =
95031-1457 _ / \ / \=20
> > > > > _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile:=20
> > > > > 408-858-4528
> > > > > | q-----( ) | o | Email: doug@xxxxxxxxxx
> > > > > \ _ / ] \ _ / Website: http://www.dsmith.org
> > > > > -------------------------------------------------------
> > > > >
> > > > > --------------------------------------------------------------
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