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tempora123

Junior Member

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two questions
Sep 15^th, 2008, 4:44am

Hello,

I have two issues and hope somebody can help me solve them.
1. After pss analysis, I choose in ADE: Results -> Direct Plot -> Main Form -> thd -> select a node in the schematic and get a plot of thd on that node. How can it be automated (I need an appropriate formula in corner analysis). When I run all corner simulations and do the same as above I get an error in ciw:
"*Error* awvfPlotDoubleWave: not a waveform - nil
*WARNING* geEcEventCB: An error occurred while applying 'geEcEventCB' to
apply('geEcEventCB '("directPlotForm" "newSelSet" (ptrnum@0xb5ca808) (133 t ((db:226645792 nil)))))"
I can't possibly run 1 corner at a time and repeat the clicks...

2. I have a Butterworth filter, Salen-Key topology with a cap inside the feedback loop.
I would like to simulate ac analysis for phase margin but I get wrong results in comparison with large signal (tran analysis) step response. I get PM of ~70deg in ac but in transient the overshoot looks like PM is 40-45deg at most. I cut the loop during ac just in front of the opamp (after the cap) so the miller multiplication doesn't apply in this case. I think that is why my results are wrong and my PM is bigger than in reality. Question is how to simulate ac then? What test bench to use to get a PM result corresponding to step response I see in tran?

Thank you for your help.
Regards,
L.S.

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Dipankar Community Member Offline Posts: 59	Re: two questions Reply #1 - Sep 15^th, 2008, 7:32am Hi Tempora, about 2. You can use stability analysis in ADE for more accurate PM measurement. need not cut the loop. With regs., Dipankar.
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Tlaloc

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Posts: 81
Dallas, TX

Re: two questions
Reply #2 - Sep 15^th, 2008, 8:28am

Regarding #1, at the bottom of the Direct Plot form, there is a button called "Add To Outputs". This adds a new output in ADE, and you can see the code to get the waveform there. It should be a getData function. I personally have not used the PSS thd, but my guess to the code would be getData("nameOfNet" ?result "thd"). This returns the waveform object which the can then manipulate through Ocean.

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tempora123

Junior Member

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Posts: 25

Re: two questions
Reply #3 - Sep 16^th, 2008, 3:59am

Hello,

Thanks for your replies.
- About stb analysis, I've tried it and I get the same results as in my ac analysis with opening/closing the loop. I can live with tran analysis results I guess because I don't think now it is possible to simulate this circuit properly with any small signal analysis.
- About thd formula in pss, the aproach mentioned works ok, I get a formula:
_drplPssThd(v("/out" ?result "pss_fd") 10000) but it works (prints results) fine only if used in one corner simulation. If I run many corners and try to plot the results I get:
*Error* awvfPlotDoubleWave: not a waveform - nil
*Error* drfGetWaveformXVec: not a waveform - nil
If trying to print:
*Error* no value at 1 , please check your entry at 'Print At' form
(in one corner simulation it shows thd vs index from 1 to 10)
However, when using printvs it shows:
*Error* X axis not numbers, can't print a portion of it
but prints the results.
I guess I can live with that for the moment. But I would like to know how to properly format this formula so that it works with no errors. Any ideas are welcome. Thanks.

Regards,
L.S.

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