Re: gEDA-user: Edge ringing filtering

[John Doty <jpd@xxxxxxxxxxxxx>]

On Mar 7, 2006, at 1:22 AM, Karel Kulhavy wrote:

> > ESR of capacitors is usually negligible in problems like this.
>
> Isn't - if you neglect the ESR and assume it's zero, then you get that
> two connected capacitors will have infinite impedance between their
> zeroes and will always fail to filter at that frequency no matter how
> hard you try. So if the clock frequency hits that point you can throw
> the device away - it will not only enormously radiate but stop working
> because the noise on the power line will build up until the gates burn
> out from overvoltage.

Usually the dissipation that prevents this is elsewhere. Wires and  
traces have resistance, especially at microwave frequencies (skin  
effect). If it's really radiating, that's dissipation. Inductive  
coupling to surrounding dissipative circuits may also be important.  
The usual approach to suppressing the problem you have involves  
ferrite beads, which are highly dissipative. So, forget ESR and model  
the other stuff first, then check to see if ESR matters.

John Doty              Noqsi Aerospace, Ltd.
jpd@xxxxxxxxxxxxx