Hi Lee, et al: Looking forward to reading your new book ... Just a couple of quick thoughts on this. > I welcome measurements from others that supports the > statement that traces > over planes are significant sources of EMI. So far, no one > has presented > such evidence. Lacking such evidence, how can anyone make > such claims? I'd like to see measurement results here too, but don't think that the lack of a specific example would allow us to say that the problem can't exist. In your measurements, were you looking at well-terminated traces? If you were looking at nice, series terminated traces rather than a fast-driven 5 inch microstrip with no termination, or using a pull-up, I could see why radiation would be minimal. I've seen a number of *simulated* results (in HyperLynx, for single traces) that radiated significantly, and were later correlated to lab results. I won't necessarily say this "proves" the point, but -- at the same time -- lacking a specific, smoking-gun example doesn't prove nonexistence ... just an inability to win in court. > True, this thread concerns differential signals, but how are > they different > from single ended signals? Flux-field cancellation for sufficiently close differential signals (right-hand rule; a key benefit for differential signaling). I don't have a specific lab example to throw into my e-mail here, but this is easy to simulate with HyperLynx ... Not a "proof," but a reasonable datapoint. Bill Hargin Mentor Graphics Corp. Systems Design Division High-Speed Tools 425-497-5079 - Direct 425-301-4425 - Mobile > -----Original Message----- > From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx] > Sent: Monday, October 13, 2003 7:07 AM > To: bdewitt@xxxxxxxxxxxxx; Charles Grasso; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Traces don't cause EMI - really? > > > Brent, > > I've tried several times to measure significant emissions > from a single > transmission line travelling over a plane at the distances > above the plane > one uses to create signal paths for logic circuits, the topic > of concern in > this thread, with no luck. > > I welcome measurements from others that supports the > statement that traces > over planes are significant sources of EMI. So far, no one > has presented > such evidence. Lacking such evidence, how can anyone make > such claims? > > True, this thread concerns differential signals, but how are > they different > from single ended signals? > > True, Doug Brooks' paper didn't set out to measure emissions > from traces on > outer layers, but it did state that measured emissions were > 30+ db below > what a mono pole would emit. > > In all my measurements, the lead frames of the ICs are the > big radiators. > They make nice antennas. They stick up above the PCB and they have > significant transient currents flowing through them, > especially the power > leads. Check out a PLCC with a near field probe sometime. > > Time for some measurements from those who want this > discussion to seriously > come to any conclusion. Anyone have any? > > Lee > > > > [Original Message] > > From: Brent DeWitt <bdewitt@xxxxxxxxxxxxx> > > To: <leeritchey@xxxxxxxxxxxxx>; Grasso, Charles > <Charles.Grasso@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> > > Date: 10/12/2003 6:44:22 PM > > Subject: RE: [SI-LIST] Re: Traces don't cause EMI - really? > > > > Hello Lee, > > > > I suspect much of the difference of opinion lies (as often > is the case) in > > subtleties of the English language. If, in your statement, > the words > > "matched transmission lines" had been exchanged for > "traces", I doubt > anyone > > would disagree. In the extreme devil's advocate case, the > trace could be > a > > resonant patch antenna over a ground plane. Clearly not what you > intended, > > but a pretty good radiator. As an intermediate case, I > expect you would > not > > disagree with the concept that mis-matched transmission > lines, even over a > > continuous ground plane, may radiate significantly. > > > > I have read and agree with Doug Brooks' well developed > paper, but I'm not > > sure it fully covers what Charles is concerned with. > > > > With respect, > > > > Brent G DeWitt > > GE Medical Systems > > > > -----Original Message----- > > From: si-list-bounce@xxxxxxxxxxxxx > > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Lee Ritchey > > Sent: Sunday, October 12, 2003 7:00 PM > > To: Grasso, Charles; si-list@xxxxxxxxxxxxx > > Subject: [SI-LIST] Re: Traces don't cause EMI - really? > > > > > > Charles, > > > > One of the papers I refer to is on my web site as well as > That of Doug > > Brooks. It is titled "90 Degree Corners, The Final Turn". > > > > The measurements were made in the lab at UMR. > > > > If there is data out there that contradicts this, it would > be good to > share > > it. > > > > It's not hard to take a near field probe and run it along > traces that are > > on outer layers of a PCB with solid planes and get similar answers. > > > > Lee > > > > > > > [Original Message] > > > From: Grasso, Charles <Charles.Grasso@xxxxxxxxxxxx> > > > To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>; si-list@xxxxxxxxxxxxx > > <si-list@xxxxxxxxxxxxx> > > > Date: 10/10/2003 9:20:28 AM > > > Subject: [SI-LIST] Traces don't cause EMI - really? > > > > > > Lee, > > > > > > I was thumbing through some of the diff pair thread and ran across > > > this comment that you had made: > > > > > > "Second, traces that run over continuous planes don't cause EMI, > > > differenrtial or otherwise. Again, there are many papers that > demonstrate > > > this as well." > > > I am sure you didn't mean this. There a many papers, > notably by Bob > > Dockey, > > > that clearly > > > show the diople-like profile of a trace over a continuous > ground plane. > > The > > > paper > > > also showed that, depending on the size of the board, the > emissions can > > > exceed the > > > FCC Class B limits - thats one trace over a continuous ground. > > > > > > Can you please expand on your comment ? > > > > > > > > > Best Regards > > > Charles Grasso > > > Senior Compliance Engineer > > > Echostar Communications Corp. > > > Tel: 303-706-5467 > > > Fax: 303-799-6222 > > > Cell: 303-204-2974 > > > Email: charles.grasso@xxxxxxxxxxxx; > <mailto:charles.grasso@xxxxxxxxxxxx; > > > > > > > Email Alternate: chasgrasso@xxxxxxxx <mailto:chasgrasso@xxxxxxxx> > > > > > > > > > > > > > > > ------------------------------------------------------------------ > > > 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 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 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 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 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