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Modeling >> Transmission Lines and Other Distributed Devices >> Frequency dependent modeling
https://designers-guide.org/forum/YaBB.pl?num=1328548336

Message started by kylelyson on Feb 6^th, 2012, 9:12am

Title: Frequency dependent modeling
Post by kylelyson on Feb 6^th, 2012, 9:12am

Hello,
I'm trying to model an off-chip inductor that has frequency dependence. I'm simulating with Cadence spectre and need to run AC, tran, and SP simulations. For the AC/SP is there a way to model variance of the inductance with frequency? i.e. I'm not sure how to pull in the freq or AC sweep into the model. Please help, thanks.

Title: Re: Frequency dependent modeling
Post by aaron_do on Feb 14^th, 2012, 4:59pm

Hi,

what do you mean by "model variation of the inductance with frequency" in "AC/SP"? When we say we want to model an effect, it usually means we want to write out an equation to describe it, or maybe you want to create an LC model of the effect. If that's what you're trying to do, I don't see what it has got to do with AC/SP...

Or are you simply trying to plot inductance versus frequency using AC/SP analysis. If this is the case, you should be able to do it easily using SP analysis and the Z or Y parameters.

regards,
Aaron

regards,
Aaron

Title: Re: Frequency dependent modeling
Post by kylelyson on Feb 16^th, 2012, 4:37pm

Hey Aaron, thanks for your reply.

Yeah, so your first intuition is what I'm trying to do. Essentially model the variance of an "off-chip" inductor using spectre. For example, the inductance and parasitic R varies with freq and I have an equation for modeling this. Using spectre I personally do not know how to pull in the frequency sweep information into a model (w/o writing a VerilogA model) for example (i.e. Rvar= k1*sqrt(freq), etc etc). I was hoping to make this simple and have a lumped elements and in the Inductance and Resistance fields simply insert the model in the form of an equation utilizing the frequency swept in an AC or an SP simuation sweep. I've done this many time in ADS for example but never using spectre. Does this make sense?

Thanks again,
Kyle

Title: Re: Frequency dependent modeling
Post by aaron_do on Feb 16^th, 2012, 5:14pm

Hi kylelyson,

ok I kinda get what you're trying to do. If you're trying to model a frequency dependent resistance, you could use the fracpole component in analogLib. It is discussed in the modeling section in this website (it has been implemented since the document was written).

http://www.designers-guide.org/Modeling/ind.pdf

A frequency dependent inductance sounds like it can be modeled using inductors and capacitors, but I don't know how you could simply put the equation into the component with frequency dependence. Hopefully somebody else will reply with a more informative answer.

regards,
Aaron

Title: Re: Frequency dependent modeling
Post by sheldon on Feb 17^th, 2012, 4:39am

kylelson,

MMSIM 11.1 supports the $freq keyword for frequency domain
analysis so you can do what you would like to do for frequency domain
analysis. In addition to using the fracpole for transient analysis, you
can also generate an s-parameter file from frequency domain analysis
and use it with the n-port for transient analysis. You can contact your
support for more details.

Sheldon