[SI-LIST] Re: decoupling
- From: Doug Brooks <doug@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx, richard hill <richard2636@xxxxxxxxxx>
- Date: Tue, 10 Jul 2001 11:26:42 -0700
Richard,
You will get a lot of input on this for sure.
One type of input will say that you want Low ESR caps and that the minimum
of the impedance curve will be at the self resonant frequency point of the
capacitor and that the minimum impedance will be ESR.
THIS IS NOT NECESSARILY TRUE!
I point you to an article that proves this on the UltraCAD web site at
http://www.ultracad.com
Look for the article on ESR and bypass caps. It points out, among other
things, that moderate ESR can give a better response than low ESR, that the
minimum impedance point is not the self resonant frequency when there are
adjacent caps with similar, but not identical self-resonant frequencies,
and that the parallel influence of the caps results in an impedance that is
LESS than ESR.
I will be giving a seminar on this topic at PCB East in September.
Doug Brooks
At 12:03 AM 7/7/2001 -0700, richard hill wrote:
>I have come across 470 pF capacitors being used
>for decoupling. What frequency range is this
>capacitor effective for decoupling? How about .1 uF
>and .01 uF? What if you put all of them in parallel?
>Is there a good document describing this selection of
>capacitors, I have come across these values quite often.
>
>
***********************************************************
Doug Brooks' book, "Electrical Engineering for the Non-Degreed Engineer is
now in its 3rd printing. Learn about it at www.ultracad.com
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