I'm with Ray on this one. In all my power distribution analysis and correlated with measurements, die and package is a 2 1/2 D job while PCB decoupling is at least a 1D model (i.e. radial distance from the center of the die). The frequency involved on PCB is low enough to only needing 1D but there is definitely a dependency on distance from the die. I am not talking about couple hundred mils will make or break your system but you will see the differences between a few inches. This is particular true for external terminators such as SSTL-2 type for DDR or GTL I/O. -----Original Message----- From: Ray Anderson [mailto:raymond.anderson@xxxxxxx] Sent: Monday, August 11, 2003 9:36 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator Lee Ritchey wrote: > If the location of decoupling capacitors matters, perhaps some technical > demonstration would prove that. Short of such a demonstration, this is > speculation and not the sort of thing that should be used to make design > choices. > > It's time to do some good engineering on this subject and do away with > opinion. The UMR paper is good engineering. Anyone who chooses to > disagree with it has the burden of showing where it is wrong by using some > good science. > > Lee > > Lee Ritchey > leeritchey@xxxxxxxxxxxxx > Why Wait? Move to EarthLink. Or conversely, show that it doesn't matter. Take a large system board (say about 24" square) put a bunch of high current processors and ASICS on the left side of the board. Put all your decaps on the right side of the board (since you maintain position doesn't matter). In this hypothetical case I can just about guarantee the board won't function properly or pass EMI. Admittedly, it is a contrived case, but I think it illustrates the point. As far as the technical demonstration goes, we have indeed demonstrated to ourselves that position does matter. I'm not attempting to further an argument, but I do feel those who have responded with viewpoints other than yours shouldn't be chastised and accused of spreading unfounded opinion. Don't discount the chance that an opinion that differs from yours just might be correct. -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 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