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. 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