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Get X-value from an expression that plots Frequency vs. Vtune

HoWei

In Assembler I am running a VCO in a transient simulation. I sweep the design-variable Vtune (0:0.5:1.5) --> 4 simulation points.

For each of these 4 different simulation pointss I calculate the frequency when the VCO is in steady state - thus I get 4 frequency values--> one frequency value per Vtune-voltage

This allows me to plot Freq vs. Vtune.

Now, from this plot/curve I want to interpolate the Vtune which is required to achieve e.g. Freq=480MHz.

Basically I need a "xval( signal y-val )", but it does not exist.

I tried "cross()" - but it requires a time dependend signal

I tried "xval()" - but it does not give the x-val for a specific y-val

How can I do that ?

Parents

  • cross doesn't require a time-dependent signal... so you should be able to use that. If it had been results from an ac analysis, then you might have had to do cross(mag(VF(...)) ...) but that's not the case here.

    So I'm not sure why you can't use cross?

    Andrew

  • in reply to Andrew Beckett

    Hi Andrew, 

    after using cross() properly over the "sweeps" (not "points") I got my "Vtune_480M" values.

    Now:

    1. It is displayed as a curve (not a constant) - maybe because I do a corner sweep and have different VDD values per corner

    2. I want to use this Vtune_480MHz value as the Vtune for my PSS+Pnoise simulations, but currently this does not work. The PSS says the value is NIL

    Any idea ?

  • in reply to HoWei

    This would be the corner setup - AVDD, temperature and the process-corners are changing

  • in reply to HoWei

    I'm a little busy today, so can't delve into this too much, so a quick suggestion to see if you can move forward. Perhaps just try adding ymax(expression ?overall t) around your expression - so ymax(cross(...) ?overall t) - I'm assuming that the graphs are single-point graphs but with the other corner variables showing up? This should then scalarize (if that's a word) the result...

    Andrew

  • in reply to Andrew Beckett

    Your proposal ymax( ... ?overall t)  "scalerized" the value and a number was given.

    And also the PSS+PNOISE simulations are running succesfully!

    Perfect ! Problem solved !

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