From: Zabinski, Patrick J. ([email protected])
Date: Wed Apr 19 2000 - 11:40:18 PDT
> > > Case in point: we just ran the onchip capacitance extraction
> > > for a customer
> > > device. 200nm technology, before adding intentional bypass
> > > devices, the
> > > assorted sources of supply capacitance came to ~230 nF in the
> > > 100-1000 MHz
> > > range.
> > D.C.
> > Can you shed some light as to what you mean by "assorted
> > sources of supply capacitance"? It's hard for me to believe
> > 230 nF of trace/grid-capacitance, so I'm struggling to figure
> > out where it's coming from.
> Most of your logic is quiescent. RAMs especially. And when
> you get down to it, that means that you have a great deal
> of gate-source capacitance in series with fully-on source-drain
> paths. The net effect is a truly enormous amount of charge
> reservoir, damped by parallel high-ESR drain-well and
> well-substrate capacitance.
Thanks; this helps.
I can understand and reasonably-estimate the effects of the "gate-source
capacitance in series with fully-on source-drain paths" without
too much difficulty with Spice. However, I have yet to see an effective
model within Spice/Hspice that acocunts for the "high-ESR
drain-well and well-substrate capacitance"; how do you
determine the effective capacitance for these well-capacitances
and the associated ESR?
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