Hi Kai,

Thanks for your reply, I was desparately waiting for it.

Pick two separate and arbitrary points on your digital plane. Now assume, that a ground return current flows between these two points. And now think about, whether there's any possibility, that a certain portion of this current is ALSO flowing on analog ground plane. That's the important question here. Now analyze your layout and this above and you will see, that with your design a digital ground return current can flow from the one point to +5V power supply, traverse the barrier of secondary windings via interwinding capacitance, run back to analog plane and through the connection of analog and digital ground plane (under your ADC) back to the other point on digital ground plane! That's what I meant with 'ground loop' here.

Ok, I think I understood your point and below is the illustration of what I understood.



That is about the problem but whats the solution to feed this circuit two separate transformers??? or something else.

Thanks & Regards,
Prahlad Puorhit