[sdiy] Various GND planes in PCB layout..

[Bert Schiettecatte]

Hi Jay,

> I don't know if I would put an inductor on the ground. What 
> I've done before when working with audio converters is the following:
> 
> 1) Connect the digital and analog ground at one and only one 
> point. Make sure the trace is big enough to handle the 
> current. Put this near where the power comes into the board 
> and before it is used by the digital section.
> 
> 2) The system that I was working with shared +5V for both the 
> analog and digital components on the board. The primary was 
> analog +5V. To get the digital +5V we would use either a 
> ferrite or a small value resistor (10 to 20 ohms) between the 
> analog and digital +5V. Then we would bypass the +5 at the 
> resistor or ferrite with a larger value cap (4.7uf to 22uf) 
> and each digital chip had a smaller 0.1uf bypass cap. Also 
> make sure the resistor/ferrite can handle the current.
> 
> Might want to get some of the application notes and/or audio 
> converter data sheets from Analog Devices, Crystal or AKM and 
> check out their PCB layout notes.

Thanks for the tips. So if there are several different audio 
Circuits distributed around the PCB and around the digital 
Section (which is in the middle of the board), do they all have 
To share the same analog ground copper pour on the top? I also 
have a Ground plane since this is a 4 layer board, but I'm not 
sure I  Should split that up into an analog ground section and 
a digital Ground. 

Since the analog sections are all around the digital section 
In a circle, if I all give them the same analog ground copper 
Pour on the top layer, they will form 75% of a full circle 
Around the digital section. People told me making loops with 
Pcb traces is a bad idea so that's why the idea came up to give
Each analog section its own ground copper pour on the top layer. 

Thanks!
Bert