Question We are now trying to design a PCB for the three AD7633s and associated circuitry. Our customer has asked us to look at your reference design as detailed in document, EVAL-AD76XXCBZ. However, I would like to ask you (or your colleagues) about the peculiarness with the ground planes. From what I can see, there are four layers, and layer 2 is ground. The only issue I have regarding your board are the connections to ground from layers 1 and 3, as the multiple connections from these layers will cause ground looping problems within the PCB. I'm therefore reluctant to start using this grounding scheme due the grounding issues. Finally, if we were to go forward with this type of grounding scheme, our customer actually wants to use all 4 layers as ground - I wonder whether you could comment on this please. Answer The EVAL-AD76XXCBZ has been designed, layout and have been tested for optimum performance by our product line and layout group. I have a good confidence that there is no foreseeable issues. And if there is any issues we would have found it by now (fingers cross). The EVAL-AD76XXCBZ doc and layout gives a good explanation as to this. See page 3, "power supply and grounding" page 4. Fig 2 to fig 10 give all info wrt to the board. If you are referring to layer 1 and 3 to top_side_layer and shield_layer respectively. As far as I know it, the shielded layer need not be connected to ground, (hence as the name implies). But you need to double check this, as I do not have the Gerber files and appropriate cad viewer. As for your customers request in using all 4 layers of ground will have routing issues (if it were based from our eval board design). From design and layout experience, pending on one's design & complexity, i.e. components, speeds etc. do and will dictate the layers and grounding requirements. I believe for this EVAL-AD76XXCBZ is sufficient. But for your design which may have more additional components/complexity and extra parts, could well be differ. Therefore (maybe) you may in fact need to increase your layers and also increase your ground layers. As your client may feel there is an issue as your design may differ from our ref design as suggested above. Therefore as an independent reviewer. I would consider the above first before deciding and maybe looking at the option in increase to 6-8 layers.

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AD7663 Production
Based on the Pulsar core, the AD7663 is a bipolar 16-bit, 250 kSPS, charge redistribution SAR Analog-to-Digital Converter that operates from a single 5...
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