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PZ analysis - DC Op. point not recomputed at each point

PNadeau

Hi all,

I am using the PZ analysis and sweeping a design variable that affects the DC operating point of my circuit (using the sweep variable feature of PZ).

It seems I cannot get PZ to recompute the DC solution at each sweep point, despite trying various combinations of options I saw in the help regarding this (prevoppoint, restart, useprevic). One clue is that the oppoint=screen option only prints one operating point in the log. Also, the poles do not move according to the circuit design insight.

This is the command in the netlist with all those options specified:

pz ( in out ) pz iprobe=V0 freq=100M param=Rd start=3k stop=27k step=3k oppoint=screen prevoppoint=no restart=yes useprevic=no

If I instead run a single-point PZ, and use ADEXL to sweep the same parameter over the exact same points, I get a different results, but these in fact correspond to the expected pole motion behaviour. 

Curious if this might be a bug or if I am not using the parameter sweep properly.

Thanks in advance,

Phil

  • PNadeau
    Forgot to add:
    IC: 6.1.7-64b.78
    MMSIM: 15.1.0.284.isr1 32bit
    RHEL6
  • awesome1
    Phil, thank you for posting your comments. I am struggling with the same issue in ADEXL.
  • Andrew Beckett

    Hi Philip,

    The oppoint=screen doesn't prove anything - it would only ever output the initial operating point anyway, and not per point in the sweep.

    This should just work without you having to set any special parameters. The parameters are to control what it does at the beginning - much of the time, the sweeps in these analyses don't cause a change in the operating point, but if they do, it should recompute the operating  point. Other small-signal analyses do this.

    So if this is not working, it's a bug. I don't have the time today or tomorrow to put together an example where the poles and zeros are dependent upon the operating point and to try this out, so please contact customer support with something that reproduces the problem - that way we can investigate and get it fixed.

    Kind Regards,

    Andrew.

  • PNadeau

    Hi Andrew,

    Thanks for the additional details.  This clarifies for me how it is supposed to work.  I'll try to set up something that can be sent to customer support.

    Cheers,
    Phil

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