Joining analog and digital ground

Every chip maker thinks his chip is the center of the universe. So every power pin on their eval board has two ferrite beads and four caps ranging from 100uF to 100pF, and they want analog and digital grounds that meet only under their chip.

The fun begins when you have to lay out a non-trivial board with, say, more than one chip that wants the grounds to meet only under it.

Sometimes I think that the dumbest interns at some chip manufacturers are assigned to write the datasheets and do the eval boards.

And eval boards don't have to pass EMI tests.

Except for boards with truly isolated channels, I have never done a board with separate analog and digital grounds. I've never wanted to have two ground pours at different potentials.

John

So what you are saying is that chip makers are like politicians?

Seriously, I have seen a solution where you had this: DGND, AGDN1, AGND2, AGND3 ...

The channels were as "quiet" as Candlestick after the 49ers scored.

Which is kind of interesting since many of those are used by hobbyists at home.

Same here. My only split ground boards were for things like ECG, intravascular ultrasound, gear for markets where stuff can go kabloiue, and so on. Where standards usually prescribe the level of isolation and creepage distances. Even if not, because I always assumed that even seasoned doctors could panic and apply the defibrillator before unplugging stuff.

I'm sure you both are right.

I did anticipate the possibility of having to do modifications. I knew this board is my guinea pig and it was laid out with that in mind.:)