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Cadence spectre save options are confusing

jasongong

Hi All,

I found that the save options in ADE-> save all are very confusing.

there is no clear documentation on difference between nestlvl and subcktprobelvl.

i got an impression that nestlvl is for voltage probes, and subcktproblvl is for terminal currents.

consider following requirement: 

i try to save selected voltage signals and top to "top-2" level terminal currents.

if i choose "select signal to output(save)" to be "selected",  the subcktprobelvl = 2, select device current (currents) = all,

then simulation output selected voltage (which is correct) but output the terminal current from very bottom transistor to terminal

current which are 2-3 levels up.

if i choose  "select signal to output(save)" to be "lvlpub",  the nestlvl = 2,  the subcktprobelvl = 2, select device current (currents) = all,

then simulation output selected voltage and the terminal currents from top level down 2 level currents.

so it seems that nestlvl do affect the terminal current output but it is never specified in ADE or spectre manual in detail.

i am hoping that expert here can give a explanation on how different save options affect the voltage and current output.

thanks

jason

  • Jason, 

    It's not that complicated. From "spectre -h options" (with some lines removed to shorten it):

    Output parameters
9       save=selected     Signals to output  public. Possible values are all,
                          lvl, allpub, lvlpub, selected, none, and nooutput.
11      nestlvl=infinity  Levels of subcircuits to output.
12      subcktprobelvl=0  Level up to which the subcircuit terminal currents
                          are to be computed.
16      currents=selected
                          Terminal currents to output. (See important note in
                          the description below the parameter descriptions
                          about saving currents by using probes). Possible
                          values are all, nonlinear, selected, and none.

    The currents option (device currents) saves the terminal currents from the primitive devices - everywhere (if set to all). subcktprobelvl adds current probes to the pin of each subckt instance (for that number of levels of hierarchy), and save=lvl/lvlpub tells it to save signals (voltages usually) from nestlvl levels of hierarchy. 

    The currents are pretty much separately controlled from the voltages. There are some slightly unusual cases here and there, but in general it's quite simple.

    Regards,

    Andrew.

  • Hi Andrew,

    thanks for your reply. i think that the question is :

    whether the subckt terminal current is controlled by switch "subcktprobelvl" alone, or it is overridden

    by "nestlvl" switch? 

    from my test, it seems that if "save=selected", "subcktprobelvl" has no effect. i.e. simulation won't output subckt terminal current.

    Only when i use "save=lvl or lvlpub or all", and set nestlvl = n, n > subcktprobelvl, i can get subckt terminal current.

    the nestlvl option never tells it controls voltage only, or both voltage and current from manual. if it controls current too, then subcktprobelvl 

    seems redunant.

    thanks

    jason

  • Jason,

    My limited checks seemed to show it was working OK. If you're seeing what you perceive as incorrect behaviour, you should contact customer support with a testcase that illustrates the problem, then we can work on getting it fixed (or we can clarify if it is indeed correct behaviour).

    Regards,

    Andrew.

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