Hi Mike, In your posting, you said: "I designed a special PCB in support of a worldwide seminar tour for = Hewlett-Packard that clearly demonstrated unacceptable (i.e., >FCC Class = B) radiation from single, terminated, 50-Ohm traces on a 10-inch PCB." Just to be clear - are you saying that if I connected 2 properly = designed chips (driver and receiver) together with many properly = designed single-ended transmission lines, they would likely fail FCC = standards? Sorry to force you to restate something that you were so clear about, = but the statement is a bit surprising to me. My impression has been = that FCC failures were inevitably due to an error in the design - = impedance mismatches, crossing a split plane, changing reference planes, = etc. =20 I would expect differential routing to radiate significantly less EMI in = the presence of these errors, but I wouldn't expect a properly designed = board with many single-ended signals to fail EMI. Jeff Loyer -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of MikonCons@xxxxxxx Sent: Monday, October 13, 2003 12:20 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Traces don't cause EMI - really? In a message dated 10/13/2003 7:17:10 AM Pacific Standard Time,=20 leeritchey@xxxxxxxxxxxxx writes: 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. =20 In all my measurements, the lead frames of the ICs are the big = radiators.=20 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 ************** WOW! I just got a chance to review the latest SI list inputs and I'm=20 astounded at such comments. Lee, the "evidence" has been around for = decades. The IEEE=20 Proceedings published a special edition circa 1989 describing over 40=20 different surface structures on PCBs that are efficient antennas, many = of which are=20 unintentionally formed by poor trace layouts. I designed a special PCB = in=20 support of a worldwide seminar tour for Hewlett-Packard that clearly = demonstrated=20 unacceptable (i.e., >FCC Class B) radiation from single, terminated, = 50-Ohm=20 traces on a 10-inch PCB. The same board was used to demonstrate both = radiation and=20 crosstalk reductions of 6 to 14 dB by the use of guard traces between = signal=20 traces (which you recently declared as totally unnecessary). I expanded, = updated, and presented both analyses and confirming measurements at = multiple client=20 companies (including IBM, Motorola, AMD, and Johns-Hopkins), and = presented a=20 paper at SuperDesignCon 95 illustrating these same effects. IBM = published an=20 excellent paper circa 1998 at a Southern California conference (don't = recall=20 which) that compared the radiation from traces as a function of their = distance=20 from the PCB edges. The bottom line is that ANY trace with current = flowing on=20 it generates EM fields and WILL radiate at some levelof efficiency. = That's why=20 one should always look to burying high-speed traces unless they are very = short=20 relative to the rise time of the signals they conduct. Surface routed differential signal traces offer opposing polarities of = fields=20 which tend to cancel, leaving only the effect of a small loop antenna to = radiate (but they still do radiate). That's why I also favor tightly = coupled=20 (i.e., closely spaced) pairs for such applications (which, if I recall = correctly,=20 you also seem to dislike). Differential pairs are definitely different = from=20 individual traces. I have very little time for technical activities (what with the trout = season=20 coming to an end soon), but I could not let this thread slip by. Respectfully to all, Mike Michael L. Conn Owner/Principal Consultant Mikon Consulting *** Serving Your Needs with Technical = Excellence *** ------------------------------------------------------------------ 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: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages=20 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ 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