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Working with DC sweeps and OP

MicheleA

Hi all,

I know it's not appealing to write one's first post in an RF focused group talking about DC but please bare with me :)

I am interested in plotting some MOS DC parameters like gm, gmoverid, Cgg, gds as they vary across VGS and VDS.

Keeping VDS fixed for the moment, I would expect to be able to DC sweep VGS and get a curve of - say - gm Vs. VGS. This is not the case. I actually get only one point, which is the point corresponding to the "static" value of VGS, in the design variables list.

Of course I could set up an equation in the Calculator for the derivative of Id but I think that "somewhere" the tool should calculate those parameters for me...And also because for some trickier parameters like Cgg the whole process would be more complicated.

The alternative to that is to run a parametric analysis, but this is way less effective timewise.

 Does anybody know of a way of overcoming this?

Thank you in advance,

 Michele

Parents

  • Michele,

    The way to do this is to create an ASCII file called "save.scs" and in that put:

      save M1:gm

    or

      save M1:oppoint

    or

      save *:gm sigtype=dev

    or

      save *:oppoint sigtype=dev

    (see "spectre -h save" for more details - particularly on wildcarding).

    Then reference this file using Setup->Model Libraries in ADE. What this is doing is telling it to additionally save the operating point data (or specifically gm) for a single transistor or set of transistors. Normally this doesn't happen for DC sweeps, just DC operating points - in order to prevent a huge amount of data being produced that most of the time you don't need. 

    Having done this, you should be able to access the resulting operating point data from the DC sweep from the results browser, and then you'll get a plot of it versus your sweep. Similarly if you did a transient you could plot the gm versus time using this approach.

    Hope that's clear,

    Regards,

    Andrew.

Reply

  • Michele,

    The way to do this is to create an ASCII file called "save.scs" and in that put:

      save M1:gm

    or

      save M1:oppoint

    or

      save *:gm sigtype=dev

    or

      save *:oppoint sigtype=dev

    (see "spectre -h save" for more details - particularly on wildcarding).

    Then reference this file using Setup->Model Libraries in ADE. What this is doing is telling it to additionally save the operating point data (or specifically gm) for a single transistor or set of transistors. Normally this doesn't happen for DC sweeps, just DC operating points - in order to prevent a huge amount of data being produced that most of the time you don't need. 

    Having done this, you should be able to access the resulting operating point data from the DC sweep from the results browser, and then you'll get a plot of it versus your sweep. Similarly if you did a transient you could plot the gm versus time using this approach.

    Hope that's clear,

    Regards,

    Andrew.

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