Re: gEDA-user: basic anti-EMI design q

[Karel Kulhavy <clock@xxxxxxxxxxxxx>]

On Thu, Mar 23, 2006 at 10:43:45PM -0800, Steve Meier wrote:
> Digital ground and analog ground have to get tied together some where.
> Think of the ground path being the return of an electrical circuit. All
> seperating the grounds out does is to have the single ended analog
> signals return signals not getting mixed in with the digital return
> signals. Yes noise on one side will propigate through to the other
> but.... an inductor along with the capacitance between the planes will

As the ground is thought as a zero point, nothing can propagate through
it.

Unless the ground has resistance or inductance, but then it's not a ground.

CL<
> significantly lower the short term amplitude.
> 
> So the operative word is immediately... remember the idea of an inductor
> is that the current flowing through it can not change instantly.
> 
> Steve Meier
> 
> Phil Taylor wrote:
> >Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> >  
> >>I also use seperate
> >>ground plains (the return path) and tie the analog ground to the digital
> >>ground with a power inductor.
> >>    
> >
> >Steve, how does this work?  It'd seem like any spikes getting into the analog
> >side (or even an analog signal transient) would return thru this  inductor
> >(that ties gnda to gndd) and immediately cause the entire analog ground to go
> >high?  This seems contradictory.
> >
> >pt
> >
> >
> >
> >