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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,

    There's no contour capability, although you can take a slice across the data using the value() function - so maybe that is sufficient. For example, if the inner sweep is VGS and outer sweep VDS, a slice of the inner sweep would be:

    value(getData("M1:gm" ?result 'dc) 0.5)

    or if you want to do it for the outer sweep (the value function works by default on the inner sweep), you could do:

    value(getData("M1:gm" ?result 'dc) 'VDS 0.6)  ; where 'VGS is the name of the swept variable

    Maybe that's what you want? 

    Otherwise you can save the data to a table - which version of Virtuoso are you using? (Help->About in the CIW)

    Potentially there's a print statement in spectre, but I'm not sure that's really the right solution. You could add this in your save.scs :

      print M1:gm, name=dc to="stuff%T.out"

    I made the filename have %T so that it has a timestamp in there for each point in the parametric sweep - but this is a bit clunky. The print statement in spectre is primarily there for compatibility with other SPICE simulators, and is rarely used with spectre syntax (spectre -h print for more details; for example, it must have a comma at the end of all the outputs, which is a little strange).

    Regards,

    Andrew.

Reply

  • Michele,

    There's no contour capability, although you can take a slice across the data using the value() function - so maybe that is sufficient. For example, if the inner sweep is VGS and outer sweep VDS, a slice of the inner sweep would be:

    value(getData("M1:gm" ?result 'dc) 0.5)

    or if you want to do it for the outer sweep (the value function works by default on the inner sweep), you could do:

    value(getData("M1:gm" ?result 'dc) 'VDS 0.6)  ; where 'VGS is the name of the swept variable

    Maybe that's what you want? 

    Otherwise you can save the data to a table - which version of Virtuoso are you using? (Help->About in the CIW)

    Potentially there's a print statement in spectre, but I'm not sure that's really the right solution. You could add this in your save.scs :

      print M1:gm, name=dc to="stuff%T.out"

    I made the filename have %T so that it has a timestamp in there for each point in the parametric sweep - but this is a bit clunky. The print statement in spectre is primarily there for compatibility with other SPICE simulators, and is rarely used with spectre syntax (spectre -h print for more details; for example, it must have a comma at the end of all the outputs, which is a little strange).

    Regards,

    Andrew.

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