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

*From*: "Peterson, James F (FL51)" <james.f.peterson@xxxxxxxxxxxxx>*To*: si-list@xxxxxxxxxxxxx*Date*: Mon, 4 Aug 2003 12:18:44 -0700

Doug, In regards to : <snip> 1. The reason we wrote the calculator in the first place was because we couldn't figure out how to make the frequency response calculation for an arbitrary number of capacitors with arbitrary values, inductance and ESR any other way. Then we figured others might have the same problem and would like access to the same tool. <snip> We've been having excellent results doing this very thing using PSPICE. We get complete control over ESR and ESL values, qty of caps, and their values. We plot the results as ohms and freq (log) - which requires a little config... regards, Jim Peterson -----Original Message----- From: Doug Brooks [mailto:doug@xxxxxxxxxx] Sent: Monday, August 04, 2003 1:42 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator As the author of this calculator, I guess I'd like to throw in my 2 cents worth! 1. The reason we wrote the calculator in the first place was because we couldn't figure out how to make the frequency response calculation for an arbitrary number of capacitors with arbitrary values, inductance and ESR any other way. Then we figured others might have the same problem and would like access to the same tool. 2. The calculator helps demonstrate (as does our article) that one thing that is REALLY desired for a smooth impedance response is a continuum of capacitor self resonant frequencies (not necessarily simply capacitor VALUES). A large number of caps with the same self resonant frequency gives you a single deep zero. Many self resonant frequencies spread over a range give you multiple zeros, spreading out the response much more effectively. MORE IMPORTANTLY, these zeros (and don't forget the poles in between) REACT with each other to provide a smoother response. The calculator helps you demonstrate and prove that. 3. Along the way, the results from the calculator provided the evidence (unexpected at the time) that moderate ESR is better than low ESR. The reason is that while low ESRs give you very deep zeros, they also lead to very high peaks. Moderate ESR gives you an OVERALL better frequency response. 4. Finally, the calculator does not address the issue of placement. My input on that question is this: Placement doesn't much matter EXCEPT for (a) the electrons must be able to get where they are needed in time (traveling at 6"/ns) and (b) loop areas (including those around and through caps) must be minimized for EMI reasons. Most people are aware of these issues, and if they are taken care of, THEN placement is no longer an issue. Hope this helps Doug Brooks > Doug Brooks' new book, "Signal Integrity Issues and Printed Circuit Board Design" has just been released by Prentice Hall. See details and ordering info at www.ultracad.com ____________________________________________________________________________ __ ------------------------------------------------------------------ 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 ------------------------------------------------------------------ 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 Calculator***From:*Doug Brooks

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