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 DC/DC Buck's Phase Margin analysis using spectre ? (Read 17693 times)
 Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley Re: DC/DC Buck's Phase Margin analysis using spect Reply #15 - Jan 04th, 2005, 5:25pm   One should never cut the feedback loop, whether you are using PSS or not. It leads to both simulation problems and lousy results. It is much better to either use the stability analysis in Spectre or the techniques outlined in my book (Designer's Guide to Spice & Spectre, section 3.4.1 on characterizing feedback amplifiers).-Ken Back to top IP Logged
 Frank Wiedmann Community Fellow Offline Posts: 677 Munich, Germany Re: DC/DC Buck's Phase Margin analysis using spect Reply #16 - Jan 4th, 2005, 11:43pm   You also might want to take another look at my reply #3 to this topic. That method does not cut the loop, so if your original circuit converges, the circuit with the PAC sources inserted should do so as well.You can find an implementation of this method for AC analysis in LTspice (free, see http://www.linear.com/company/software.jsp) at http://groups.yahoo.com/group/LTspice/files/Examples/Educational/LoopGain_Probe/... (free registration required). Back to top IP Logged
 Richard Guest Re: DC/DC Buck's Phase Margin analysis using spect Reply #17 - Jan 6th, 2005, 12:16am   Thanks Frank and Ken for your prompt reply.Frank : I downloaded the LT files. Pardon my knowledge, I find that to determine the voltage loop gain and phase response, you just need a AC=1, DC=0 voltage source inserted in the loop. (e.g. at the output and input gate of unity feedback amplifier). Why do we need to determine the current gain and subsequently : (Gv*Gi-1)/(Gv+Gi+2) function ?  I am running the DC/DC with just the voltage source (pac=1) inserted with PSS and PAC analysis, hopefully I have some good results soon. Back to top IP Logged
 Frank Wiedmann Community Fellow Offline Posts: 677 Munich, Germany Re: DC/DC Buck's Phase Margin analysis using spect Reply #18 - Jan 6th, 2005, 11:31pm   You need to determine both voltage and current gain in order to properly account for loading effects. See http://www.stanford.edu/class/ee214/handouts/h21_lecture15.pdf (and http://www.stanford.edu/class/ee214/handouts/h20_lecture14.pdf as background information) or the articles mentioned in the LTspice example. Back to top IP Logged