Jeff: There is differential mode and common mode radiation. In = differential mode, even=20 though you might have a perfect termination bus but if the loop area is = large, then you still have a chance to radiate a lot and fail FCC ( i.e. you route your = traces on outer layer ( microstrip ) and the traces are far away from power/reference = plane ).=20 Just my 2cents. Regards, MC -----Original Message----- From: Loyer, Jeff [mailto:jeff.loyer@xxxxxxxxx] Sent: Thursday, October 16, 2003 12:13 PM To: MikonCons@xxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Traces don't cause EMI - really? Hi Mike, In your posting, you said: "I designed a special PCB in support of a worldwide seminar tour for =3D Hewlett-Packard that clearly demonstrated unacceptable (i.e., >FCC Class = =3D 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 =3D designed chips (driver and receiver) together with many properly =3D designed single-ended transmission lines, they would likely fail FCC =3D standards? Sorry to force you to restate something that you were so clear about, = =3D but the statement is a bit surprising to me. My impression has been =3D that FCC failures were inevitably due to an error in the design - =3D impedance mismatches, crossing a split plane, changing reference planes, = =3D etc. =3D20 I would expect differential routing to radiate significantly less EMI in = =3D the presence of these errors, but I wouldn't expect a properly designed = =3D 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,=3D20 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 =3D plane one uses to create signal paths for logic circuits, the topic of concern = =3D in this thread, with no luck. I welcome measurements from others that supports the statement that =3D traces over planes are significant sources of EMI. So far, no one has =3D presented such evidence. Lacking such evidence, how can anyone make such claims? True, this thread concerns differential signals, but how are they =3D different from single ended signals? True, Doug Brooks' paper didn't set out to measure emissions from traces = =3D on outer layers, but it did state that measured emissions were 30+ db below what a mono pole would emit. =3D20 In all my measurements, the lead frames of the ICs are the big =3D radiators.=3D20 They make nice antennas. They stick up above the PCB and they have significant transient currents flowing through them, especially the =3D power leads. Check out a PLCC with a near field probe sometime. Time for some measurements from those who want this discussion to =3D 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=3D20 astounded at such comments. Lee, the "evidence" has been around for =3D decades. The IEEE=3D20 Proceedings published a special edition circa 1989 describing over = 40=3D20 different surface structures on PCBs that are efficient antennas, many = =3D of which are=3D20 unintentionally formed by poor trace layouts. I designed a special PCB = =3D in=3D20 support of a worldwide seminar tour for Hewlett-Packard that clearly =3D demonstrated=3D20 unacceptable (i.e., >FCC Class B) radiation from single, terminated, =3D 50-Ohm=3D20 traces on a 10-inch PCB. The same board was used to demonstrate both =3D radiation and=3D20 crosstalk reductions of 6 to 14 dB by the use of guard traces between = =3D signal=3D20 traces (which you recently declared as totally unnecessary). I expanded, = =3D updated, and presented both analyses and confirming measurements at =3D multiple client=3D20 companies (including IBM, Motorola, AMD, and Johns-Hopkins), and =3D presented a=3D20 paper at SuperDesignCon 95 illustrating these same effects. IBM =3D published an=3D20 excellent paper circa 1998 at a Southern California conference (don't = =3D recall=3D20 which) that compared the radiation from traces as a function of their = =3D distance=3D20 from the PCB edges. The bottom line is that ANY trace with current =3D flowing on=3D20 it generates EM fields and WILL radiate at some levelof efficiency. =3D That's why=3D20 one should always look to burying high-speed traces unless they are very = =3D short=3D20 relative to the rise time of the signals they conduct. Surface routed differential signal traces offer opposing polarities of = =3D fields=3D20 which tend to cancel, leaving only the effect of a small loop antenna to = =3D radiate (but they still do radiate). That's why I also favor tightly =3D coupled=3D20 (i.e., closely spaced) pairs for such applications (which, if I recall = =3D correctly,=3D20 you also seem to dislike). Differential pairs are definitely different = =3D from=3D20 individual traces. I have very little time for technical activities (what with the trout = =3D season=3D20 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 =3D 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: =3D20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages=3D20 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =3D20 ------------------------------------------------------------------ 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