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I am designing 4-layer mixed signal PCB and it is totally crowded (with components).

I know how analog and digital grounds should be separated below components. But I do not have enough room in some places to do this properly.

So I came up with the idea to have AGND on a second layer below analog parts (on the top layer) and have digital tracks at the bottom layer and below that a DGND.

What would be the main cons of that kind of solution?

This is going to be only in some places where I am lacking the board space. But something like this.

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Jüri Bogatkin
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  • I use separate grounds *extremely rarely* as it can, in many situations, do more harm than good. See (for example) https://electronics.stackexchange.com/questions/185306/analog-power-ground-planes-doubts/185320#185320 Why do you believe they need to be completely separate? – Peter Smith Jan 25 '20 at 16:11
  • I need separate grounds, because this is and audio mixed-signal device. Meaning that there is audio electronics part and digital signal part. These definitely need separate grounds - analog and digital ground. I have used similar separation in my previous designs and it has worked well. – Jüri Bogatkin Feb 03 '20 at 21:38

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Your solution seems right to me. If you really need to separate AGND and DGND (which is not so obvious), then keeping DGND near the digital components and AGND near the analog ones is the best you can do.

Short answer: There are no cons without further Specs.

Stefan Wyss
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