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mosfet multipliers & fingers

Analog layout

 Why they mention multipliers & fingers seperately?

ex:- m=10, f=10

but why they mention like this

f=100.

So please any body tell me why we need to place multipliers insted of using only fingers?

 Thank you,

  Sivaji

  • Quek

    Hi Sivaji

    In mosfet bsim models (version 3v3 and above), m and nf affects how other parameters (e.g. stress parameters) are calculated and so affects circuit behaviour. It is not really correct to say that we should place m instead of nf. You can use either depending on your needs. The only thing to take note is that both schematic and layout must be consistent. E.g. if m=3 and nf=1 is used in schematic, then layout should have 3 unabutted mos devices with 1 finger each. Having 3 abutted mos devices mean m=1 and nf=3. This can result in wrong results for sensitive circuits like bandgaps.


    Best regards
    Quek

  • Analog layout

     just go through attachment and let me know. Why we need to specify m and nf. insteed of using m we can use only nf.?

  • Andrew Beckett

    Quek already answered this in a general way so it's unclear what else you need to know. Your question is rather vague and a more specific answer would require understanding of the particular choices for the specific design kit/technology you're using. Such questions would be best placed to the provider of the design kit.

    Regards,

    Andrew.

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