Re: [SI-LIST] : on-chip decoupling capacitance (and SI)

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From: D. C. Sessions (dc.sessions@vlsi.com)
Date: Tue Apr 18 2000 - 16:51:44 PDT


Sandy Taylor wrote:
>
> > I have heard rumors that modern microprocessors use 10s of nF of on-chip decoupling
> > (presumably provided by large areas of thin oxide) to keep the core supply noise in a
> > range where the flip-flops don't loose their minds.
>
> Chris
>
> For a solution running at 1GHz in a device drawing 80W in a 0.18u technology, look at:
> "An On-Chip Voltage Regulator Using Switched Decoupling Capacitors" in ISSCC 2000.
> I'll see if I can get a copy of the paper and slides for Ray to make available.
>
> The on chip problems can be severe. 100s of nF is a reasonable for a large microprocessor today. This helps provide a reservoir of charge for the surge of current with each clock tick within a clock
> cycle or for a step in the current due to an increase in activity over several cycles. With today's uP, the potential dI/dT is so severe that even using a flip chip ball grid array with hundreds of
> power/ground pins and a carefully designed package you have no chance of seeing significant current from the board for several clock cycles.

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. Sessions
dc.sessions@vlsi.com

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