**From:** Steve Corey (*steve@tdasystems.com*)

**Date:** Wed Dec 22 1999 - 16:03:58 PST

**Next message:**Ron Miller: "Re: [SI-LIST] : Frequency dependence and all that jazz"**Previous message:**D. C. Sessions: "Re: [SI-LIST] : Clean sheet of paper"**In reply to:**Shah, Nilesh N: "RE: [SI-LIST] : Frequency dependence and all that jazz"**Next in thread:**Ron Miller: "Re: [SI-LIST] : Frequency dependence and all that jazz"**Reply:**Ron Miller: "Re: [SI-LIST] : Frequency dependence and all that jazz"**Maybe reply:**Erik Daniel: "Re: [SI-LIST] : Frequency dependence and all that jazz"

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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*

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*

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*

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**Next message:**Ron Miller: "Re: [SI-LIST] : Frequency dependence and all that jazz"**Previous message:**D. C. Sessions: "Re: [SI-LIST] : Clean sheet of paper"**In reply to:**Shah, Nilesh N: "RE: [SI-LIST] : Frequency dependence and all that jazz"**Next in thread:**Ron Miller: "Re: [SI-LIST] : Frequency dependence and all that jazz"**Reply:**Ron Miller: "Re: [SI-LIST] : Frequency dependence and all that jazz"**Maybe reply:**Erik Daniel: "Re: [SI-LIST] : Frequency dependence and all that jazz"

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