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AC vs. PZ analysis

ASICnm

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,

 

  • 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.

  • 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.

  • 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

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