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Aug 22nd, 2019, 7:42am
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How to find the over-all worst-case? (Read 3407 times)
weber8722
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How to find the over-all worst-case?
May 22nd, 2015, 4:08am
 
Hi,

to check a design, you can run MC and corners (like on Vdd, T, RL, CL, fclk, etc.), but doing a MC at each corner combination is far too time-consuming. To simplify the verification or doing an optimization (by hand or automated) it would be much better to know (or 1st to find) the worst-case for each performance within the allowed range of parameters.

But how to find the over-all WC?
Doing 1st a corner analysis is not working well, because some effects only show up once you include mismatch. However, is just doing MC at nominal and then doing a WC corner finding already the full solution? Or would we still miss some WC combinations of statistical and deterministic parameters?

A simple example where "Corners 1st, then MC" fails would be a balanced Op-Amp. Here Voffset over ALL corners is zero due to symmetry, so you cannot find a WC corners set all all. So MC 1st is obviously the better solution. But is this all, end of story?

Bye Stephan
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Frank Wiedmann
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Re: How to find the over-all worst-case?
Reply #1 - May 26th, 2015, 4:02am
 
If you do not want to check all possible combinations, you always have to make certain assumptions about the behavior of your circuit, which will define your simulation strategy. If these assumptions are not correct, your simulation results may not be correct either. Such is life.

In your specific case, I would probably use a dcmatch analysis in Spectre instead of Monte-Carlo to find the worst-case corner for Voffset.
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sheldon
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Re: How to find the over-all worst-case?
Reply #2 - Jun 25th, 2015, 10:57pm
 
Stephan,

  Not really a simulation question. If you have access to Cadence
tools, then you can access these functions in ADE GXL. For more info
please see the Variation Aware Design RAK on the Cadence support
site. Or if you can read Japanese, you can read the series of articles
I have written on the topic on Sound of Cadence Smiley Worst case
corners will be in the June version, soon to be released.

         https://www.cadence.co.jp/soc/

                                                                        Sheldon
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