Homebrew PCBs

On Fri, 25 Aug 2006 10:54:40 +0200, Adrian <adicont2@...> wrote:

> I read some articles about this problem and all talk about star
> groundind, but nothing about power supply line.
> Let's supose we have a simple transformer-bridge-cap-regulator power
> supply and two circuits, one analog and one digital. What is the best
> layout in this case. I mean, what is the principle? A longer power
> line and a shorter ground line for the digital section? It's OK to
> connect the digital power line at the same single point whith analog
> and the digital ground between transformer and bridge.
> Or simply two ground and two power lines conected at the power supply
> entry, after the filter cap?
> Adrian


Usually you have some sort of interface between digital and alalog, like a  
AD converter. Then you will connect the grounds right at that component.  
If you don't then right at the supply is fine. Power is not such a problem  
as long as you decouple things well. You may need inductors as additional  
filters for sensitive circuits, with caps both sides. The inductor blocks  
ac as you know.

When doing ground layout i like to think in voltage drops.

ST