Laplace s_xfer question

  • dillon

    dillon - 2010-08-10

    I'm using the s_xfer code model to implement an S-Domain (Laplace) Transfer Function that will ultimately be incorporated into a non-linear dependent current source.

    The problem is that the transfer function is not a simple ratio of polynomials in s.

    The transfer function is in the form of
    1 /  ((abs(s))^x) or 1 / pwr(abs(s),x)

    where x is a real, but non-integer value.

    I've done this successfully with PSPICE, but don't know if NGSPICE can handle it. Is it possible to implement this with s_xfer? The num_coeff and den_coeff parameters don't really support this.

    If this isn't doable with s_xfer, does anyone have any ideas for a workaround?



  • dillon

    dillon - 2010-08-31

    Thanks for your response!

    I have some additional info that may simplify this problem somewhat.

    In the scenario here, the stimulus in this analysis is a pure tone. Therefore, at steady state, s will just have the imaginary component j*omega. A real component would indicate some sort of exponential growth/decay. Therefore, abs(s) is just the frequency of the stimulus tone for my case.

    This lead me down the path of trying to use the "hertz" variable that is available when using a B source. However, this does not appear to be available outside of a B source.    

    So my next train of thought is:

    Can "hertz" variable be made available for use outside of a B source? … Such as in an expression defining laplace model coeffs for each frequency iteration of an AC analysis. I could see this requiring a code change. I'm not familiar enough with the source code to know.



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