Robert:
If you look at the curves that you included you will see that the 0.1uf
capacitor has lower impedance at 10000 KHz then the 1uf capacitor. This
is because the inductance of larger value capacitors is larger than
smaller value capacitors.

Also I think that the value of 1 ohm is somewhat arbitrary and does not
apply well in many cases, especially high gain or high power circuits.

-- Rich


"Robert A. LaBudde" wrote:
>
> At 10:49 AM 6/2/00 -0700, Dave wrote:
> > >Has anyone found/experimented with the optimum size capacitance
> > >value and/or physical size for use in/around a microprocessor?
> >
> >You want the caps to absorb well at the third harmonic of the clock.
> >0.1uF does well at 3 MHz, 0.01 at 30. 0.001 at 300.
> >It's a broad response, so dont think that there's one specific value.
> >However, if you use 0.1uF on a 20 MHz part, you won't get the supression
> >that you could if you used 0.047uF.
>
> This suggests that lower capacitance a priori works better at higher speeds.
>
> My understanding of the specifications suggests the opposite: for any make
> of capacitor, higher capacitance always works better at any frequency.
>
> What might be true is that certain types of capacitors are only available
> in small denominations, and these types have lower ESR and ESI so they work
> better at higher frequencies.
>
> What's important is that the impedance of the capacitor be only 1 ohm or so
> at the frequency of interest to reduce ripple at the current draw required.
>
>   ------------------------------------------------------------------------
>                                       Name: capacitor impedance vs freq.gif
>    capacitor impedance vs freq.gif    Type: GIF Image (image/gif)
>                                   Encoding: base64
>
>   ------------------------------------------------------------------------
> ================================================================
> Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral@lcfltd.com
> Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
> 824 Timberlake Drive                            Tel: 757-467-0954
> Virginia Beach, VA 23464-3239                   Fax: 757-467-2947
>
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