Re: gEDA-user: bypass caps

[John Doty <jpd@xxxxxxxxxxxxx>]

On Aug 21, 2006, at 5:10 AM, Stuart Brorson wrote:

> For your furnace controller, you probably won't see any difference
> between 1.0uF and 0.1 uF; either one will work for you.  It's not
> necessarily in the  same class as the GHz server motherboards or 10
> GHz router boards that the SI gurus argue about.

It's not the *application* that matters: it's the *parts*! A chip  
capable of 500 MHz operation needs layout and bypassing appropriate  
to that speed. Otherwise, you're asking for double clocking,  
oscillation, crosstalk, etc. This can be a real problem with  
specialized aerospace chips (so-called "high reliability". Yeah  
right...), where things like clock rates are grossly derated on the  
spec sheet already, and you can be burned by things that are a *lot*  
faster than you expect. I've seen this cost millions of dollars when  
at the last moment it was found that the circuit didn't work cold,  
because a chip ran too fast for its bypass arrangements...

John Doty              Noqsi Aerospace, Ltd.
jpd@xxxxxxxxxxxxx




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