passive device modelling in HSPICE

[OpAmp]

passive device modeling

Hi,

How can I define a passive element in HSPICE with the following impedance: 1/(Y(j*2*pi*f)^0.5) where Y is a constant and f is frequency. Note that this is an impedance of a Warburg element. It is very similar to the impedance of a capacitor but it is inversely proportional to the root-squared of frequency.

Thanks
OpAmp

 

[rfsystem]

Because HSpice is a time domain simulator only discrete component approximations or FFT translation could simulate irrational frequency transfer functions. The second principle is used by ADS where frequency domain models are translated into time domain and are simulated together with the nonlinear time domain models. The approximation of the frequency domain function f^(1/2) is best described by Ken Kundert:

https://www.designers-guide.org/Modeling/fracpole.zip

So he uses rational components s^1 or s^(-1) to approximate irrational function over a greater frequency range.

I have tried in the past to approximate s^(1/2) or s^(-1/2) by an rational function is s but the order should get very high to get about a frequency decade approximation. So Ken's approach is more effective.