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

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From: Shah, Nilesh N (
Date: Wed Dec 22 1999 - 15:10:29 PST

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
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
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 N Shah,
Package Electrical Design Engineer,
PCG, Folsom, CA.
Intel Corporation.
tel:916-356 1129.

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