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Notes on frequency dependent components pz analysis.

已有 790 次阅读| 2021-4-22 21:31 |系统分类:芯片设计

摘自narkive。

Riad KACED

2008-09-30 20:48:17 UTC

Dear Jorge,I Honestly never ever seen this error before. This does sound very oddfor me though. I recall having used PZ analysis on BSIM3V3 deviceswithout any worries. My best Advice is to get in touch with yourCadence AE. Don't forget to mention you Spectre version/subversion.To be honest with you, I don't really like the Spectre PZ analysis,just because it does give you the poles/zeros information only. It'ssometimes a bit hard to interpret as well. This is a pure personal ofview. When I do stability analysis, I'm always after the Gain/Phasemargins, that's why I was always doing an AC analysis by breaking theDC loop. You can also determine the Poles and Zeros with the ACAnalysis. Spectre does provide a stability analysis 'stb' as well.Please look at the Spectre doc for more information. I would recommendthis K. Kundert's Paper for a better understanding :http://www.kenkundert.com/docs/cd2001-01.pdf.BTW, give it a look at the designer's guide forum. There are loads ofthreads discussing the stability analysis over there. Reallyinteresting.I recall having asked one of my great friends at my former company 7years ago about the Stability analysis of my LDO regulator (I wasbeginning by that time). He advised me to print out the Transientwaveform of my output and see if it does oscillate or not. It was hisfriendly way to get rid of me when busy ;-)Hope this help !Kind Regards,Riad.

Riad KACED

2008-10-01 11:11:22 UTC

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Ohh Dear, there is a little misspelling mistake in my previous post.It's definitely not the DC loop to break ! but rather the AC loop. Infact, one need a DC operating point to run small signal analysis. I doapologize for this :-[Riad.

Andrew Beckett

2008-10-02 04:49:19 UTC

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Post by Riad KACEDOhh Dear, there is a little misspelling mistake in my previous post.It's definitely not the DC loop to break ! but rather the AC loop. Infact, one need a DC operating point to run small signal analysis. I doapologize for this :-[Riad.

And if you are running "stb" analysis, there's no need for any loop to getbroken during the AC analysis; the method is a direct one which means that theloop remains closed all the time, which has _lots_ of advantages.Back to the original message. This comes about if the components contain any(say) frequency-dependent capacitance. Often you see this with distributedcomponents like transmission lines - whilst the impedance will naturally varywith frequency, if the capacitance varies with frequency, then it has toapproximate it at a certain frequency. You can tell pz which frequency to use(it's on the ADE analysis form). See this snipped from "spectre -h pz" :In case there are frequency dependent components, poles and zeros are computedby approximating those components as equivalent conductances and capacitancesevaluated at 1Hz.(Note: A frequency dependent component means the capacitance or conductanceequivalent representation of the component is frequency varying. Examples aretransmission lines or bjts with excess phases. A linear capacitor is not afrequency dependent component.)17 freq (Hz) Frequency at which components will be evaluated insetting up the linearized network.Regards,Andrew.