Difference between AGND and DGND

[Tom Davis]

Hello All,

It looks to me in case of using split GND plane for AGND and DGND, one probably places components like A/D, and D/A directly above and across the split of the 2 GND planes with the digital and analog interfaces point to the right direction respectively.

What really happen here ? It looks like inside the ICs, we still possibly violate routing analog traces over digital GND plane and vice-versa since this is unknown ? How large the split should be or should not be ?

Also any method in selecting ferrites to connect these GND together like what parameters values ?

 

[Singapura]

Hi Tom

Some manufacturers provide chip topology and PCB layout consideration information in their IC datasheets and these should be useful for your consideration.

I'm not a PCB designer so I can't advise you on the other issues that you raised. Perhaps some other in the forum can help.

Best regards

 

[is_razi]

hi,
because there are fast and sharp switching signals on digital side which can generate noise on precise analog signals the digital ground and analog ground are separated and the analog ground connected directly to the main ground of supply to avoid noising of it. usually the mixed signal ic manufacturers seprate the grounds internally and they give you the chance to seprate them on your PCB. for more technical information i recommend you to visit analog device semiconductor site and look for it between the app notes.also see this:
https://www.anadigm.com/_doc/AP020800-U202.pdf
hope to be useful