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

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From: Steve Corey (steve@tdasystems.com)
Date: Wed Dec 22 1999 - 16:03:58 PST


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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