[SI-LIST] Re: Decoupling capacitors
- From: "Martin Euredjian" <martin@xxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 21 Jun 2002 11:51:02 -0700
I just signed-up to this list read through most of this thread in the
archives. I was intrigued by Istan Novak's post, and the approach he
suggests:
"One of the published examples replaced about 250 pieces of different-size
different-value bypass capacitors with 50 pieces of controlled-ESR 2.2uF
capacitors on a CPU card. Apart of two bulks, there was only this single
value of bypass capacitor on the board, achieving the minimum number of
bypass capacitors, and at the same time effectively suppressing
capacitor-to-capacitor, capacitor-to-plane, and modal plane resonances."
....
"Measured data supporting the claims/statements (except the last item) on
the above list, including more details about implementations, have already
been published and is available on line."
Can someone (Istan?) post a link to further information on this approach?
I am trying to decide on an approach to take on a simple design I'm working
on; just a couple of XC2V1000's, some 133MHz SDRAM and half a dozen other
devices. HD video processing. Data rates from 74MHz to 165MHz, if you
ignore GHz in/out section.
What I've read so far from other sources has me a bit confused as to which
approach might be the safest. One camp goes for a lot of caps and a
half-dozen or more values. Some of my own -basic- simulations tell me that
a bunch of 0402 (low ESL, ~0.6nH?) 0.01uF's right on the power pins and a
generous number of 150uF, 0.1ohm (~3.4nH?) tantalums distributed throughout
the board might do just as well.
Frankly, I'm having trouble deciding which way to go. And, now, of course,
I read that a valid solution may exist --if I understand it correctly--
without the use of hundreds of small caps. This, of course, is very
attractive from many perspectives and I'd like to learn more about it.
Finally, a question:
How do large valued (>1uF) multilayer chip caps compare to tantalums for
high-speed and bulk decoupling? Panasonic has values all the way up to
about 100uF but very little performance data (ESR, ESL, SRF?)
Thanks,
Martin Euredjian
eCinema Systems, Inc.
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