# [SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator

*From*: Paul Levin <levinpa@xxxxxxxxxxxxx>*To*: si-list@xxxxxxxxxxxxx*Date*: Thu, 31 Jul 2003 13:27:36 -0700

Perhaps there are lots of people who would like to see the response. I hope that they will be directed to the entire list. Regards, Paul __________________ Abe Riazi wrote: > Dear Lee, > Please recall that when I was attending your course, we had a brief > discussion regarding the UltraCAD's ESR and Bypass Capacitor Calculator. > > I have purchased a license of the program (it costs $75.00). > > The program can help to determine the optimum > number (and values) of bypass capacitors required for a high-speed design > board. > > Douglas Brooks has written a paper, "ESR and Bypass Capacitor Self Resonant > Behavior How to Select Bypass Caps" which describes how to apply > the calculator. One point emphasized by his paper is that to achieve > optimum decoupling one needs to use a range of values of decoupling > caps (example, some 1uF caps, some 0.1uF caps, some 0.01uF caps > with low ESL) rather than just a single value of capacitor. The objective > being to produce a flat low PDS impendace over a specified broad frequency > bandwidth. > > On the other hand, I have noted that many engineers have a different > view in that they believe a SINGLE value of capacitor > (such as 0.1uF 0603 (or 0805) package with X7R dielectric ceramic chips) > should be used for ALL high frequency decoupling capacitors on the PCB. > > The UltraCAD calculator does not provide any information related > to the best required location for the decoupling caps. > > The calculator also does not account for the distributed nature > and frequency dependent loss of power planes (which can be > important at frequencies exceeding 100 MHz.) > > Subsequently, it seems to me that UltraCAD ESR and Bypass > Capacitor Calculator can be a useful tool for learning and > experimenting with various decoupling strategies, but > probably lacks the accuracy that the Cadence PDS tools > can offer (of course, the Cadence PDS tools are also significantly > more expensive). > > I also have two questions: > > 1. In your opinion, in order to achieve optimum high frequency > decoupling, is it necessary to use several different > values of ceramic caps (e.g. some 1.0 uF, some 0.1uF > some 0.01uF ceramic chips) or is it preferable to use just a > single value (such as 0.1uF) for ALL the decoupling caps on the PCB ? > > 2. Is it sufficiently accurate to determine the optimum location of > decoupling caps by applying > rules of thumb or is it necessary to simulate? > > Thank you in advance for your reply. > > Abe > > > > > > > > > -- Binary/unsupported file stripped by Ecartis -- > -- Type: application/ms-tnef > > > ------------------------------------------------------------------ > 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: > http://www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > http://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 > > > -- Paul Levin Senior Principal Engineer Xyratex Storage Systems ------------------------------------------------------------------ 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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://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

**Follow-Ups**:**[SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator***From:*john lipsius

**References**:**[SI-LIST] UltraCAD ESR and Bypass Capacitor Caculator***From:*Abe Riazi

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