I have an analog circuit (A-D and filter) that has to get placed relatively close to an FPGA (0.3" between the nearest points on the FPGA to the closest component of the filter, generally about 1" for most parts). I'm concerned about picking up any noise from the digital stuff. My intuition tells me that (in the absence of a proper split plane, which isn't doable in this case) it would be useful to put a slit in the ground planes between the filter and the fpga.
Any opinions? Alternatives (can't move either block)?
Thanks,
Chris