Homebrew PCBs

I can't offer all the reasons, but high frequency stuff will effect 
the low frequency stuff.  you have 2 choices, physical seperation or 
an antenna that will adsorb that HF stuff.   Often, you'll see the 
circuit board is cut with a physical seperation.

AC on the board can and will effect low voltage ADC circuits and low 
voltage logic.  putting a ground plane around the lines reducies 
noise on those lines.

long traces runnning next to HF stuff will be effected so keeping the 
traces sperated 1/4 wavelenght is a minimum, more is better, a ground 
inbetween even better.

I put moats around my ADC stuff.  the terminals, filters, ADC are all 
surrounded by a ground line.   My outputs by another, and my power 
supply by another and if needed, the micro gets one too.

There are impedance reasons for the ground plane and RF and emf 
reasons for a ground ring.  Also a ground matrix is sometiems used.  
this is a cross hatched area, not just solid copper.

Hope this helps.
and I hope others fill in the blanks.

Dave



--- In Homebrew_PCBs@yahoogroups.com, "ghidera2000 
<ghidera2000@y...>" <ghidera2000@y...> wrote:
> I often see ground traces expanding out to cover large areas of 
> PCBs. I have a half-idea that this is to clean up the ground when 
> using analog parts, is this correct? If not, whats the actual 
> reason? How much does it really help?