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In my last question I found out that having two different layers for Ground and Analog Ground may induce capacitive coupling. Now I want to ask more generally if the idea I had is worse than connecting DGND and AGND on the same plane. May PCB stack-up is currently as follows:

Signal, DGND, AGND, Signal

My PCB looks like this:

enter image description here

So there is an ESP32-S3 (bottom right), MAX6675 temperature sensor (top right), camera interface (SCCB) working at 20 MHz (top mid), Li-po charging circuitry (top left), Li-po protection circuitry (top left), 3.3 V power supply (left mid), 1.5 V and 2.8 V power supplies (left of cam connector) and an ADC (ADS1110) above the battery connector.

To the AGND plane is only connected the AGND Pin of the 3.3 V power supply and the AGND pin of the camera.

If it is a bad idea, how can I make it better?

pipe
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Cem Pamir Bana
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1 Answers1

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My PCB Stackup is currently as follows:

Signal, DGND, AGND, Signal

Put DGND and AGND on the same layer to avoid the problem that you mentioned (capacitive coupling) and, to keep both GNDs close below the components they are acting as a GND-plane for.

You just need to figure out how and where you connect the AGND and DGND planes (hint a single point connection at the junction of some type of analogue to digital conversion I.C. is normally recommended).

Andy aka
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  • Okay but I have to have 4 layers, because you can only choose from 2 or 4. So should I switch to Signal - GND - GND - Signal or GND - Signal - Signal -GND? Or does it make sense to transform the Analog Plane into a power plane? (I have 1.5V, 2.8V, 3.3V power supplies, can I all put them in that power plane? – Cem Pamir Bana Mar 31 '23 at 07:57
  • I always have signal on the outer layers because, if I screw up, I can fix with track cuts. The DC stuff might conveniently go on the middle plane furthest from the component side. – Andy aka Mar 31 '23 at 09:36
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    @CemPamirBana are we done here now? – Andy aka Mar 31 '23 at 12:49