Lee Ritchey wrote: > UMR did a paper in 1995 that determined location is not important as long > as you don't cut up the power planes. Others have repeated those same > tests, as have I, and come up with the same answers. > > The proponents of location matters need to do some testing to show that > their position is valid. > > Lee > > Lee W. Ritchey > Speeding Edge > P. O. Box 2194 > Glen Ellen, CA 95442 > Phone- 707-568-3983 > FAX- 707-568-3504 > OK, how about a thought experiment. Scenario one: -------------- You've got a rather large PCB (say 24" x 24") with no cuts in the power planes. The board has a fast, current hungry chip (say 400 MHz clock rate, 80psec rise time, 50 amps of transient current) in one corner clocking away. Some number of appropriate decaps are located within an inch of the chip. Everything works OK (whatever that means...). Scenario two: ------------- You've got a rather large PCB (say 24" x 24") with no cuts in the power planes. The board has the same fast, current hungry chip in one corner clocking away. The same decaps as were used in scenario one are now located at the opposite corner of the board (about 34 inches away). Does everything still work OK? Without actually doing the experiment, I'll go out on a limb and venture to say no. Granted, this is an extreme contrived example, but I really don't think you can make a blanket statement and say that the location of the decoupling capacitors on a PCB is a "don't care" decision. -Ray Anderson Sun Microsystems Inc. ------------------------------------------------------------------ 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