Steve/Ron - Just to calibrate myself ... Now you DO mean a trace crossing a split orthogonally right? If so I fail to see how changing the width of the split makes things better except maybe in one condition. i.e. where a diff pair cross a split. The return current for one trace will be carried by its pair and the split will be almost invisible. The effect of crossing a split on a diff pair can be seen in a presentation by Ansoft Corp available for download from the RMCEMC website. Go to http://www.ieee.org/rmcemc the link is on the front page. You'll need to go in about 12 pages or so... Best Regards Charles Grasso Senior Compliance Engineer Echostar Communications Corp. Tel: 303-706-5467 Fax: 303-799-6222 Cell: 303-204-2974 Pager/Short Message: 3032042974@xxxxxxxx Email: charles.grasso@xxxxxxxxxxxx; Email Alternate: chasgrasso@xxxxxxxx -----Original Message----- From: steve weir [mailto:weirsp@xxxxxxxxxx] Sent: Saturday, January 22, 2005 4:19 PM To: ron@xxxxxxxxxxx; Chris.Cheng@xxxxxxxxxxxx Cc: Si-List Subject: [SI-LIST] Re: risetime effects of plane breaks Ron, Do you really mean to imply that the cross-talk falls substantially if the slot gap is increased to 2H or more? That is a new and very counterintuitive notion to me. I would be very interested in seeing any A/B model that could demonstrate such a phenomena. Regards, Steve. At 10:13 PM 1/21/2005 -0800, ron@xxxxxxxxxxx wrote: >A few years ago Intel discovered that when a trace crosses a split it >can excite a transmission line mode into the slot between the panes >called "slot line" strangely enough. If the gap is small >it works quite well and all the traces crossing it become cross-talk for >one another. > >To avoid it make the gap at least 2 or 3 times the thickness of the >dielectric. > >ADS (Agilent) has a model for slot lines with the other transmission >lines. > >Ron > >Chris Cheng wrote: > > >Scott, > >Excellent summary. That was my concern on striplines crossing with a > >bus rather than individual signals. In a way, it is like wire bond > >signal leads without the ground leads mixed among them. The signals > >start referencing each other instead. Or you can see it as a > >trade-off between adding shielding layers or spreading the bus > >spacing (decreasing routing channels) in a high density/performance > >design. My own rule of thumb is space them at least equal or larger > >than the gap itself when crossing. That's is at least a 3x decrease > >in routing channels so it is quite costly and has to be weight > >against adding shielding layers. Sometimes its worth it, sometimes > >its not. As for EMI, if you dig back some discussion I had with > >Steve, I always prefer solid ground planes referencing microstrips on > >top and bottom of PCB and then stitch the edges with ground vias. > >Hopefully any of those excited noise on the cut power planes will be > >trapped inside. > > > >-----Original Message----- > >From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx] > >Sent: Thursday, January 20, 2005 2:39 PM > >Cc: Si-List > >Subject: [SI-LIST] Re: risetime effects of plane breaks > > > > > >When this thread started I was on vacation. However, I found this > >interesting enough to resurrect some previous simulations I'd > >performed in CST Microwave Studio. After much playing, twiddling and > >generally having fun I can say several things: > >1) It's pretty easy to confirm Doug's results using 3D fullwave > >simulation. In fact, in about 30 minutes I can replicate his case and > >create a design that can be easily modified for many other > >possibilites. The microstrip split plane crossing is a no-brainer. > >Just don't do it and expect anything approaching an EMI "clean" > >system. > > > >2) Chris and Steve ... and eventually myself, wanted to know more > >about the various different stripline plane crossing configurations, > >so I setup a simulation with a VDD island not unlike what might be > >found in a memory system, and performed multiple simulations with > >dual asymmeteric stripline crossing the plane twice on it's way to > >the memory module. Not surprisingly the following is true: > > > > It is best not to cross a split plane ... even with stripline. > > If you do, it is better to cross a split that is adjacent to a > > ground plane > > It is even better if you cross a split adjacent to a ground plane on > > the stripline layer furthest away from the split plane (i.e. next to > > a ground plane) > > It is worst to cross a split plane that has no adjacent ground. > > The width of the gap in the plane makes very little difference until > > it becomes really small or really big. > > Crosstalk scales almost linearly with the number of aggressors > > crossing the split. (i.e. - it can get really bad!) > > Bypass of the split power island helps for frequencies below 500 > > MHz, provides no help for frequencies higher than 500 MHz, and as > > such has no benefit to most of the noise and crosstalk created by > > high speed signals crossing onto and off of the island. > > > >The energy released into the power/ground plane cavities by high > >speed signal split plane crossings is huge and essentially cannot be > >suppressed with bypass capacitors. Any attempt at supprerssion with > >capacitors exhibits what I call a "Whack-A-Mole" property. You can > >never get rid of those pesky little moles. All you can do is to move > >them around by thumping them. Given that all this energy is rattling > >around the PCB power planes from split plane crossings, it will > >eventually go somewhere. Since it's really easy to develop all sorts > >of resonant power island cavities that have primary resonant > >frequencies in the 500 MHz to several GHz range, it is not at all > >unlikely that any split plane crossing has an extremely strong > >potential to excite a resonance in a frequency range that will cause > >most systems to fail EMC compliance testing About all you can do is > >to shield the cavity patches using ground layers. This should reduce > >the radiated energy significantly, but will not totally eliminate it, > >since eventually it will find it's way to all those pesky device and > >package leads. > > > > > >best regards, > > > >Scott > > > > > > > > >-- >Ronald Miller >Ghz Data, Signal Integrity Consulting >7721 Sunset Ave. >Newark CA 94560 >tel 510-793-4744 >cell 510-377-9380 >fax 510-742-6686 >www.ghzdata.com > >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >List technical documents are available at: > http://www.si-list.org > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu