Re: tiny inductor with every bypass cap?

On Sat, 21 Jun 2008 16:06:02 GMT, "Talal Itani" <titani@[EMAIL PROTECTED]
>
wrote:

>Hello,
>
>I was looking at the schematics for a DSP-based board, running at 100
MHz. 
>They have a tiny inductor with every bypass cap around the DSP.  Do you 
>think this is necessary?  This DSP has analog stuff built-in.  If we do
not 
>need analog, can the inductors be eliminated?
>
>Thanks,
>T.I. 
>

Inductors don't generally help digital chips, and may actually reduce
timing margins. We do use ferrite bead+capacitor filters on the supply
rails of some fast opamps and adc's, to keep switcher noise and
other-channel crosstalk from sneaking in.

The best way to power big digital chips is with solid power planes,
reasonably bypassed. That will present lower rail impedances than you
could get by isolating the bypass caps on a per-pin basis.

John