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DC/DC Buck's Phase Margin analysis using spectre ? (Read 85191 times)
Ken Kundert
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Re: DC/DC Buck's Phase Margin analysis using spect
Reply #60 - Oct 18th, 2006, 7:25pm
 
You might want to try using a piecewise linear approximation rather than tanh(), and use cross functions at the corners so that you know the simulator spends some time within the linear region.

-Ken
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Jason UCB
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Re: DC/DC Buck's Phase Margin analysis using spect
Reply #61 - Oct 20th, 2006, 8:30pm
 
thanks for the advice.
I did try a piecewise linear model, with (virtually) identical results.  I will try adding the cross functions & see what happens.
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fet
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Re: DC/DC Buck's Phase Margin analysis using spectre ?
Reply #62 - Aug 6th, 2009, 4:07am
 
Hope this article on EDN helps.

Periodic steady-state and small-signal analyses of switching regulators
http://www.edn.com/article/CA6579651.html

It compares the results between averaged model and PSTB simulation.

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Frank Wiedmann
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Re: DC/DC Buck's Phase Margin analysis using spectre ?
Reply #63 - Aug 20th, 2014, 2:24am
 
fet wrote on Aug 6th, 2009, 4:07am:
Hope this article on EDN helps.

Periodic steady-state and small-signal analyses of switching regulators

It compares the results between averaged model and PSTB simulation.


This article is now at http://edn.com/design/analog/4327245/Periodic-steady-state-and-small-signal-anal....
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AMSA
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Re: DC/DC Buck's Phase Margin analysis using spectre ?
Reply #64 - Sep 2nd, 2014, 5:51am
 
Hi, I know that this thread is old but right now I am trying to do the same thing that Richard did and Jason too.

I am trying to get the frequency response of my dc-dc converter with the loop closed. I have inserted a VSIN with the PAC field at 1V and I have connected the positive terminal do the VSIN to the output of the converter and the negative to the input of the error amplifier.

After running the PSS + PAC analysis, I ask for the amplitude in dB20 on the left side of the VSIN and what I get is this:

http://postimg.org/image/b7d4v1mt3/

This result is strange because the response starts at 0dB and that shouldn't be right?

After that I tried to use the PSS + PSTB analysis replacing the VSIN source by the iprobe and the result that i got, asking for the loop gain option in the PSTB separator was this:

http://postimg.org/image/4lsqcxpr5/

If we go back to the PSS + PAC analysis, instead of selecting the left side of the VSIN source, selecting the right side I get almost the same shape and values of the PSS + PSTB analysis but inverted.

From what I have read all over the place I think that I am placing the PAC and/or iprobe in the correct place, I think I am configuring in the right way the analysis and I get this different results.

Can anyone help me out here? I am out of ideas and I don't have a clue on how to solve this.

Thanks in advance.

Kind regards.

EDIT: I forgot to tell that my converter is operating at very high frequency > 300MHz.
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sheldon
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Re: DC/DC Buck's Phase Margin analysis using spectre ?
Reply #65 - Oct 29th, 2016, 5:13am
 
AMSA,

    Will say that if you want stability information, then you should use
periodic stability analysis not pac. PSTB is intended for this problem,
you can use PAC for audio susceptability and other measurements. It
is possible, see the attached picture for an example.

  There was a paper a while ago on using pac before pstb became
available.
Frequency response analysis for switching converters  in SPICE
without averaging, H. Deng, A. Q. Huang, Y. Ma, PESC 2004

  The pstb example is from an AE-ware workshop of dc-to-dc converter
simulation with Spectre RF, contact your local Cadence AE for details.

                                                                               Sheldon
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