[SI-LIST] Re: PDN sim: why not IFFT ?
- From: Istvan Novak <istvan.novak@xxxxxxxxxxx>
- To: hreidmarkailen@xxxxxxxxx
- Date: Tue, 16 Jul 2013 09:20:17 -0400
Hello Agathon,
Theoretically there is nothing wrong with the process. Practical
details may make a
generic implementation challenging. We need to assume that the entire
PDN is
linear and time invariant and in this case (from power source to bump),
this means
not only the capacitors and the DC source, but also the silicon. Another
practical
challenge is the very wide relative bandwidth: DC sources may have
signatures
in the kHz frequency range, the package and silicon have features in the GHz
frequency range. The usual FFT processes require equidistant spacing of
samples,
which can result in millions of points to transform. Doable today, but
just a
little while back this was a major hurdle. And there is the uncertainty
of the
excitation waveform. When people do the same process in signal
integrity, the
signal is much better known; with PDN noise generated by the silicon,
many users
would be left to wild speculations.
Best regards,
Istvan Novak
Oracle
On 7/16/2013 2:33 AM, agathon wrote:
> Hello all,
> For obtaining a time domain response at IC bumps, V(t), given the die
> current stimulus I(t) which is already assured to be steady state itself in
> a single record, not a repeated concatenation with a constant moving avg.,
> then dc suppressed, the following seems straightforward:
>
> 1. Convert stimulus I(t) to the freq. domain with FFT, using sufficient
> points. Make sure, with Hilbert's help, it's causal.
>
> 2. Vi(f) = Sum[ Zij(f) x Ij(f) ]. Zij(f) is already on hand from pkg,
> pcb model extraction. Here, i= response bump port & j= other bump ports.
> The pcb end (vrm) is @gnd.
>
> 3. Then Vi(t) = IFFT{Vi(f)} for bump port i. Look, ma ! No time
> domain simulation required.
>
> Please, somebody explain why I never see this in the literature and major
> simulator vendors just want to change the subject (for the most part). Is
> this a conspiracy? :-) More likely, I'm ignorant of something.
>
> Thanks,
> Agathon
> ----------------------
>
>
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