How to create a mixed signal pcb

[nick]

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I want to create a board that has both high speed digital components (specifically the SAM3X8E - from arduino DUE) and an analog audio circuit.

The analog parts were originally a shield to the arduino. The reason i want to create a mixed mode board to combine the two circuits into one, is because i used to have a lot of noise. After searching, people suggested that this is noise from the digital circuit and i will have to remake the board.

This is a link with the original question. There you will also find a picture of the schematic of the shield. Proper Decoupling

My question is how do i ground the whole thing. I have seen many different approaches in threads like these:https://electronics.stackexchange.com/questions/128637/how-should-i-connect-agnd-and-dgnd (LINK 1)
https://electronics.stackexchange.com/questions/334735/star-point-in-schematics (LINK 2)
https://electronics.stackexchange.com/questions/194538/for-multiple-adc-circuits-pcb-layout-grounding-why-is-single-point-ground-imp (LINK 3)

So do i need to have different GND planes for digital and analog? I was considering using tha ‘Star ground approach’ but the first link said it is the least efficient. Trevor_G also said (in the second link): “For this kind of circuit, integral single ground and power planes with appropriate layout to keep the signal loops as short as possible is much better.” So i have only one common ground plane?

Then reading these two guidelines: https://www.maximintegrated.com/en/app-notes/index.mvp/id/5450 http://www.hottconsultants.com/techtips/split-gnd-plane.html

I found out that one GND plane is all that is needed. But many things were unclear and lost in theory. For example, do i have to separate the two planes? If yes, do they have to join in one place? Do i need to ‘cut’ the two planes? If yes, where exactly do i cut? What happens when the analog signals, enter the digital side of the board? Like when the analog information enters the ADC of the microcontroller? If there indeed is a cut, how am i supposed to route the traces? In general, how do i design the GND layer?

What i will do: *Keep the digital parts away from the analog parts - upper copper layer (thanks peufeu!) *Use two regiulators, one for the digital side and one for the analog side *Avoid digital power and digital signal to pass in the same area as the analog side (on all layers)

An extra question: *I saw in the stackexchange link 3 to keep the power sources on the digital side of the board. That includes the analog regulator as well? But the analog power trace will have to pass through the digital side… But when the analog signal enters the ADC of the microcontroller then the analog signal enters digital side as well. So is it impossible to separate them?

[InterestedTom]

You don’t have to physically cut the circuit board at the gaps in the ground plane.

Often a microcontroller will have all the analog pins in one small area of the package, this allows for that area to bridge the joint between the split ground plane. You are supposed to make the joint between the two ground planes large enough to route all the necessary signals on layer(s) above or below it.