Electronic – Avoiding noise coupling by power switching to ground plane in multilayer PCB

ground-planemulti-layer

I've a 4 layer PCB in which I've to layout a power switching supply mixed with digital signal circuit.

My stack up is:

  • Top Layer: component and routing (power net and signals)

  • Internal plane 1: GND

  • Internal plane 2: +3V3

  • Bottom Layer: routing (power net and signals)

Now the question is: what's the better way to layout the GND internal plane?

I've thought of three possibilities:

  1. use all the PCB area with GND plane

  2. clear out both planes on the PCB area in which is present the power switching circuit and use the only what remains with GND

  3. split GND planes and make a dedicated analog GND internal plane only for power switching circuit

I was thinking to proceed with solution 1), but I'm wondering if the power switching circuit may inject noise to the GND plane by coupling.

Is solution 1 OK? How should I modify it?

Best Answer

As suggested, you want to separate your ground plane into regions to reduce noise coupling between the different functions of the circuit, in your case: switched supply and signals. The regions should be connected with each other in a single point only (see image below).

Google Image for "pcb ground plane switch" gave the following result:

enter image description here

(Note that the borders between the ground plane regions apply for ALL the layers. If signal traces run over multiple ground planes you might get large current loops.)

To sum up, you should go for a combination of 1) and 3).

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