Does someone has good measures to separate analog GND and digitao GND?

 

You can split the ground plane, one for analog and one for digital. Only connect them at the connector leaving the PCB.

 

Like retched said, I also split (not separate) the ground plane. You should still have one ground plane, but keep the analog signals with the analog, same thing with the digital signals.

 

try to keep the point where the 2 meet or connect together as close to the source as possible, and this is the only point where the 2 join....




B. Morse

 

Opinions vary. I like a single ground plane, but am careful to make sure the return current paths in the plane don't get the analogue and digital signals mixed up, which is easy enough to avoid with thoughtful component placement. Sometimes mini-planes in switched-mode power supplies can be useful, but they're joined to a master plane at a judicious point.

If you're thinking of splitting ground planes because of an ADC or DAC, then remember that the AGND and DGND pins should both see exactly the same reference, so if you really feel the need to split a plane then the point where they join should be as close as possible to these two ground pins. The AGND and DGND pins of an IC are brought out separately for fabrication reasons (the analogue and digital circuit grounds in the IC can't easily be joined internally), not because there's a functional need for isolation; just the opposite.

It's a complex field, much depends upon the application, and often there is no right answer, just a solution that is least-wrong. Here's some quotes from top signals expert Henry Ott on the subject, over at EDN.