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I am designing a 4 layers PCB with the following stack-up:

  • Signal flooded with GND
  • Solid GND plane
  • POWER plane
  • Signal flooded with GND

For the top Layer I want to divide the GND plane (flooded) into 3 parts and connect them to the solid GND plane through vias.

Can this decrease the noise from the digital circuits (digital sensors) and the power supply that can affect the analog circuit? {J6, J13 } (ADC + PASSIVE FILTER)

Would it be better to connect all the GND pads to the solid GND plane directly or should I split the ground plane?

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  • \$\begingroup\$ Looks like you have a pretty good stackup. Why do you think you need or want the 3 individual GND pours on the top layer? \$\endgroup\$
    – SteveSh
    Dec 8, 2020 at 15:33
  • \$\begingroup\$ Also, it would be good if you could annotate one of your pictures to give us an idea where the sensitive analog components are, like the ADC and any associated signal conditioning circuits. \$\endgroup\$
    – SteveSh
    Dec 8, 2020 at 15:34
  • \$\begingroup\$ @SteveSh All the components are on top Layer So when I flood the top layer with Gnd I won't add many vias to connect the pads to the GND plane. \$\endgroup\$
    – PCB-ABBS
    Dec 9, 2020 at 7:27

1 Answer 1

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In most cases, it's a bad idea to separate GND planes. What happens is that you have high-frequency noise going around and you end up having your 3 planes behaving as 3 capacitors coupled to your inner plane.

It is also very difficult to guess where the high-frequency noise/current goes as it doesn't necessarily follow shorter paths.

Another issue is that it is a bad idea to have traces running through a plane gap (which would be the case in your design). This couples the trace between the planes.

If you want to make a low noise plane for analog, the best method is to split the plane in half (and not having several planes across the board), filtering from GND to AGND, and connect the plane beneath what does the AGND to GND link like ADC and the power lines (through R-L-C filtering).

Overall, in most real-life cases, you will end up with less noise using a single plane, well done multiple planes can be better but they can be tricky.

It is also better to have all the connectors on one side of the board to avoid cross current flow.

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  • \$\begingroup\$ Thank you for your answer, If I will rely only on the Solid ground, I will end up putting a lot of vias ( all my components are SMD and placed on the top layer ). I am thinking of connecting all my AGND on top ( I will add keep out areas on digital components uSD connector, USB connector, ...) and I will connect them to the solid ground via vias. In this way the two grounds will act like global capacitor \$\endgroup\$
    – PCB-ABBS
    Dec 10, 2020 at 9:47

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