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R extraction in Assura

TIGRESS

Has anyone done R  extraction and verfied their designs ?

I dont understand how RCX extraction in Assura works?

I verified my opamp's gain through simulations and and after C extraction,the magnituded matched well except for the change in bandwidth .

but with R extraction,the magnitude of the gain of the opamp increased by 10db.How is that possible???parasitic R's will be in the range of ten's of ohms,how can they cause such huge change in the output impedanance??? 

Is the R extraction analysis correct??

 

  • Andrew Beckett

    With correct technology data, R extraction should be very accurate.

    Did the addition of the parasitics cause it to move into a different operating region? Maybe it wasn't biassed right in the schematic case, and addition of the parasitics have moved some transistors into the saturation region (assuming it's MOS) and are then working more as intended? It's very hard to know what the cause could be without seeing the circuit.

    Regards,

    Andrew.

  • TIGRESS

     Tell me if this is the right way to see the parasitic R .In extracted layout, under the PARASITICS ---> Report Parasitics----> All Nets option is present.I click this and it shows the cumulative parasitic R and C of each wire..

    Addition of parasitics does not change the operating range of the transistor..

    The circuit i am testing now is a Telescopic PMOS input Differential amplifier with triode region transistor common mode feedback.Parameters such as gain and offset were the same when  simulated with the schematics and C extracted ciruit.But when R extracted circuit is simulated,there is a difference in gain as well there is offset in the output .The Gm's and Gds's of the transistors do not vary in all the 3 cases,but there is a change in the output impedance in the R extracted circuit which seems to be the reason in the increase in the gain.

     

     

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