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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,

    So if the two independent axes (VGS and VDS) are "x" and "y", you want a slice which is in the z axis - i.e. the dependent axis - thus giving you a true contour map (at least for a single value).

    There's not really an capability to do that - there's the xval function if there's a single crossing, but if there are multiple regions that won't help you. 

    So right now you're probably best doing this in Matlab, say. You could use the spectre toolbox for Matlab (covered in the MMSIM documentation, and in app notes in the <MMSIMinstDir>/tools/spectre/examples directory hierarchy).

    I just used this simple example:

    // example of sweeping id curves
    model nch mos1 type=n vto=1 kp=16u gamma=1.3 lambda=0.01 \
           phi=0.7 pb=0.80 mj=0.5 mjsw=0.3 cgbo=200p cgso=350p cgdo=350p \
           cj=300u cjsw=500p ld=0.1u tox=80n \
           af=1 kf=3.1e-24


    m1 (drain gate 0 0) nch w=20u l=0.8u
    vgs (gate 0) vsource dc=2.5
    vds (drain 0) vsource dc=1

    voff (off 0) vsource dc=20m
    vcvs (gate2 off gate 0) vcvs gain=1
    rload (gate2 0) resistor r=10k

    save m1:ids m1:gm rload:1

    sweepvgs sweep dev=vgs param=dc start=0 stop=2 step=20m {
        dc dc dev=vds start=0 stop=5 step=20m
    }

    And ran (from command line) "spectre idcurvesw.scs" which produced idcurvesw.raw (the PSF results).

    Then I did this in Matlab:

    gm=cds_srr('./idcurvesw.raw','sweepvgs_dc-sweep','m1:gm');
    contour(getfield(gm,'vgs:dc'),gm.dc,gm.S);

    (could use mesh instead of contour to see a graph). Similarly could look at m1:ids:

    id=cds_srr('idcurvesw.raw','sweepvgs_dc-sweep','m1:ids')
    mesh(getfield(id,'vgs:dc'),id.dc,id.A)

    So this means you then don't have to load it and then export it to CSV to read back into Matlab; it can directly read the PSF results into Matlab.

    Regards,

    Andrew.

Reply

  • Michele,

    So if the two independent axes (VGS and VDS) are "x" and "y", you want a slice which is in the z axis - i.e. the dependent axis - thus giving you a true contour map (at least for a single value).

    There's not really an capability to do that - there's the xval function if there's a single crossing, but if there are multiple regions that won't help you. 

    So right now you're probably best doing this in Matlab, say. You could use the spectre toolbox for Matlab (covered in the MMSIM documentation, and in app notes in the <MMSIMinstDir>/tools/spectre/examples directory hierarchy).

    I just used this simple example:

    // example of sweeping id curves
    model nch mos1 type=n vto=1 kp=16u gamma=1.3 lambda=0.01 \
           phi=0.7 pb=0.80 mj=0.5 mjsw=0.3 cgbo=200p cgso=350p cgdo=350p \
           cj=300u cjsw=500p ld=0.1u tox=80n \
           af=1 kf=3.1e-24


    m1 (drain gate 0 0) nch w=20u l=0.8u
    vgs (gate 0) vsource dc=2.5
    vds (drain 0) vsource dc=1

    voff (off 0) vsource dc=20m
    vcvs (gate2 off gate 0) vcvs gain=1
    rload (gate2 0) resistor r=10k

    save m1:ids m1:gm rload:1

    sweepvgs sweep dev=vgs param=dc start=0 stop=2 step=20m {
        dc dc dev=vds start=0 stop=5 step=20m
    }

    And ran (from command line) "spectre idcurvesw.scs" which produced idcurvesw.raw (the PSF results).

    Then I did this in Matlab:

    gm=cds_srr('./idcurvesw.raw','sweepvgs_dc-sweep','m1:gm');
    contour(getfield(gm,'vgs:dc'),gm.dc,gm.S);

    (could use mesh instead of contour to see a graph). Similarly could look at m1:ids:

    id=cds_srr('idcurvesw.raw','sweepvgs_dc-sweep','m1:ids')
    mesh(getfield(id,'vgs:dc'),id.dc,id.A)

    So this means you then don't have to load it and then export it to CSV to read back into Matlab; it can directly read the PSF results into Matlab.

    Regards,

    Andrew.

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