On a board with separate analog and digital ground planes connected at one place, the connection is often made with an inductor. How is this inductor chosen? Obviously it has to be able to handle enough current, but what other factors are important?
I'm more interested in the type of inductor rather than the value, since I would expect to try different values.
Best Answer
Another school of thought is to forget the inductor and split ground plane. Instead use a solid plane, but use careful placement and routing to ensure the digital/analogue signals stay in their respective portions of the PCB.
According to the figure below, you can see (for high speed signals) most of the return current flows very close to the trace (x is distance from centre of trace, h is trace height above plane):
No time to go into more detail right now (will try and add more later) but here are a couple of excellent links on the subject:
Henry Ott - Mixed Signal Layout
TI - High speed Layout Guidelines