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 AC vs. PZ analysis  

Last post Sun, Apr 24 2011 12:22 PM by Andrew Beckett. 3 replies.
Started by ASICnm 20 Apr 2011 01:26 PM. Topic has 3 replies and 2132 views
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  • Wed, Apr 20 2011 1:26 PM

    • ASICnm
    • Not Ranked
    • Joined on Sun, Sep 7 2008
    • Linkoping, Sweden
    • Posts 10
    • Points 255
    AC vs. PZ analysis Reply

    I have a complex opamp model built using ideal sources (no transistors models). I am interested in frequency response, so tried both AC and PZ analysis, to check the dominant pole (-3 dB), resulting as:

    AC @ 59.24 MHz , and PZ @ 60.18 MHz. This is fairly close, then i compensate the model (miller compensation with nulling resistor) to stretch this pole from another nondominant pole. The resulting dominant pole reported by AC: 130 KHz, while PZ reports: 226 MHz (which is more convcingly a value for nondominant pole).

    I want to know why are the values so different. Assuming there are no frequency dependent components used either (so freq eval may not help much) why does PZ misses the dominant pole altogether ?

    Finally would jumping to IC 6.15 help for this particular issue ?  I am currently on IC 5.1.14, Spectre ver. 6.1.1.565

    Regards,

     

    • Post Points: 20
  • Thu, Apr 21 2011 10:14 PM

    Re: AC vs. PZ analysis Reply

    I think the best thing would be to contact customer support with a testcase that shows the problem - hard to imagine why this is happening without actually seeing the data.

    IC615 won't make any difference - the results come from the simulator. You might want to try using a more recent MMSIM version, because that's probably a good 5 years or so old - maybe it's a bug that's been fixed. So try MMSIM101 (the latest MMSIM release) first before reporting it.

    Best Regards,

    Andrew.

    • Post Points: 20
  • Sun, Apr 24 2011 10:24 AM

    • ASICnm
    • Not Ranked
    • Joined on Sun, Sep 7 2008
    • Linkoping, Sweden
    • Posts 10
    • Points 255
    Re: AC vs. PZ analysis Reply

    Thanks Andrew,

    I tried it MMSIM101 and yet the result is still the same. So I will now go forward with customer support. BTW, im interested to know the additions in various MMSIM versions.

    • Post Points: 20
  • Sun, Apr 24 2011 12:22 PM

    Re: AC vs. PZ analysis Reply
    There is a "what's new" document (or documents) that you can access via "cdnshelp" (cdsdoc in older releases) which summarizes the major changes and innovations in each new release.

    Regards,

    Andrew
    • Post Points: 5
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Started by ASICnm at 20 Apr 2011 01:26 PM. Topic has 3 replies.