Naren, I would like to clarify a few things for you, as the two responses you have received so far are not grounded in theory. Your question about serpentine traces (your term was banding) used for length matching really comes down to coupling (crosstalk), whether the aggressor in another signal, or, in your situation, the same signal (you obviously realized this as the subject line indicates). A cross-section of your serpentine traces would look something like this: |<--- w --->|<---- s ---->|<--- w --->| ____XXXXXXXXXXXXX XXXXXXXXXXXXX ^ h v____________________________________________ nearest ref. plane When you draw the electric and magnetic fields surrounding each conductor, you quickly come to the conclusion that reducing crosstalk is highly dependent upon increasing two ratios: s/w and s/h, but primarily s/h (unless h is very large with respect to s and w). This is especially the case with balanced stripline, as the presence of the second reference plane reduces coupling from trace to trace. So the rule of thumb that has developed over the years is that s should be greater than 3h. The ratio w/h is determined by the impedance of the trace. Now it just so happens that in a 50 Ohm system using FR4 for a dielectric, the w/h ratio is approximately equal to 1. This has led a number of people to substitute w for h in the rule, which may work fine in many cases but could lead you astray in general. Having an inadequate spacing can, in the worst-case, lead to severe signal distortion. Keep in mind that even with s equal to 3h, while the coupling may be small, it is not zero and will result in slightly less delay than is predicted by the actual length of copper. For high accuracy, you will need to use a field solver. I would also recommend that you pick up a copy of Dr. Howard Johnson's latest book "High-Speed Signal Propagation" and take a look at pp. 610-616. This section discusses serpentine delays and also outlines many other factors that can influence delay matching. I hope this has helped. Best regards, -Bill /************************************ / billw@xxxxxxxxxxx / / / / Advanced Electronic Concepts, LLC / / www.aec-lab.com / ************************************ ====================================================== Qazi Arif Iqbal wrote: > Naren, > Clearances are usually measured from track width basis. > Also try to avoid sharp edges. > > Qazi > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Naren > Sent: Friday, April 29, 2005 4:09 AM > To: si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] About Self coupling > > > Hello > Recently we are designing PCB @ 700 MHz (Digital) signals. > In that we are using banding (As shown in attached picture)for length > matching. As per thumb rule it should be more than 3X . > > But I am confused that X means track width or Track(PCB Copper) height? > > Anybody can clarify it? > ------------------------------------------------------------------ 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