Re: [SI-LIST] : Frequency dependence and all that jazz

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From: Ron Miller (rmiller@Brocade.COM)
Date: Wed Dec 22 1999 - 16:23:24 PST


Nilesh

Please contact Art Frasier at Intel, Santa Clara. He has HP MDS/ADS which
can used measured S-parameters together with other frequency dependent elements
and transfer them back into the time domain.

Ron Miller

Steve Corey wrote:

> Nilesh -- SPICE-like simulators doing time-domain analyses solve their differential equations in the time domain, based on the charge/flux stored in
> capacitors/inductors and the derivatives of the voltage/current variables at each node/branch. A time-domain simulator has no concept of frequency.
>
> It is quite possible to get frequency dependence included in a model for a time-domain simulator, since L's and C's are frequency-dependent
> impedances/admittances and can be shown, when used in conjunction with R's (and inductance coupling coeffficients) to accurately represent any well-behaved
> function if used in the correct topology and with the correct values. However, for certain structures (e.g., long cables used at high frequencies) a large
> number of lumped elements is required to represent the delay.
>
> A full wave solver is one of many approaches to getting a frequency dependent model. Other approaches, such as 2-D solvers, may be quite sufficient
> without going to such great lengths -- you have to evaluate what frequency-dependent effects you are trying to model. /* begin brazen advertising */ We
> offer a tool which extracts models from measured data and handles some effects, such as non-uniform impedance and next-door coupling, quite well. /* end
> brazen advertising */ General full-wave modeling from measurement is on the horizon, and is a current research topic in academia, but we do not offer it at
> this time.
>
> Hope this helps,
>
> -- Steve
>
> -------------------------------------------
> Steven D. Corey, Ph.D.
> Time Domain Analysis Systems, Inc.
> "The Interconnect Modeling Company."
> http://www.tdasystems.com
>
> email: steve@tdasystems.com
> phone/fax: (206) 417-3439
> -------------------------------------------
>
> "Shah, Nilesh N" wrote:
>
> > Hi:
> > I have a question:
> > It's all well and fine to build frequency dependent MODELS,
> > but what about the simulator(ex Hspice) itself?
> > For example, if I feed the output of a simple inverter to an
> > L,C, R network, (and I'm doing a simple time domain transient analysis)
> >
> > INVERTER------LRC NETWORK----OUTPUT
> >
> > does the simulator decompose the output waveform of the inverter
> > into it's frequency components before feeding it into the LC network?(i
> > don't think so)
> > For example, if the output of my buffer looks like a repeating square pulse
> > running at 400Mhz 50% duty cycle with a finite rise time, does the LRC
> > network "see"
> > the input wave as
> > Asin(w1t)+Bsin(w2t)+..... etc
> > where w1=400Mhz and w2,w3 etc are the harmonics?Or does one have to
> > explicitly
> > take the output of the waveform, decompose it and then feed it artificially
> > to the LRC network?
> >
> > or does the LRC network "see" as it's input,a bunch of dc points for
> > which the simulator solves the nodal matrix using difference or differential
> > equations? i.e. does the LRC network "see" only 1 frequency coming in which
> > is the fundamental?
> >
> > How does this work?How is the frequency content of the output waveform of
> > the buffer conveyed to the LCR network?
> > I was planning to investigate this but I thought some of
> > you experts out there might have the answer at the top of your head...
> >
> > Also, tools like Ansoft Q3d extract models only at 1 frequency(I think), so
> > unless you use HFSS, how do you get a true frequency dependent model?
> > I've generated R,L versus frequency and other parameter versus frequency
> > curves, but this is with 2 d models using TEM assumptions.what about 3-d
> > models?
> > is ther ANY way at all except for using a full wave solver like HFSS to
> > generate true frequency
> > dependent models and simulate in the time domain?
> >
> > Thanks for your ideas in advance.
> > Nilesh
> >
> >
> > Nilesh N Shah,
> > Package Electrical Design Engineer,
> > PCG, Folsom, CA.
> > Intel Corporation.
> > tel:916-356 1129.
> >
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--
Ronald B. Miller  _\\|//_  Signal Integrity Engineer
(408)487-8017    (' 0-0 ') fax(408)487-8017
     ==========0000-(_)0000===========
Brocade Communications Systems, 1901 Guadalupe Parkway, San Jose, CA  95131
rmiller@brocade.com,  rbmiller@sjm.infi.net

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