Have been thinking about ADCs and doing a layout, which always brings me back to one of my favorite articles on the web about layout, thought I’d share it here. Also with resources like this, I do normally recommend you download and save them somewhere like a dropbox. This is knowledge that never goes out of style 
PDF version:
I also had the privilege of chatting with Hank Z on The Amp Hour a couple years ago, he’s a great engineer and was a joy to talk to:
Generally, use a single ground plane, and partition your layout to keep the analog and digital stuff separate.
Remember that the return current for a signal follows the path of least inductance. This means that the return current for a digital trace will be in the plane directly below (or above) it.
Thanks Chris,
Those are very helpful links. Of all of electronics, I find signal integrity stuff the hardest; it always seems to be shrouded in a veil of mystery, especially with book titles like: “High-speed digital design - a handbook of black magic”.
/Niels.