Cmod A7 massive GND noise in FPGA Posted January 6 · Edited January 6 by hamster On this topic I've been making an audio DSP board using the CMOD A7, where additional noise is a real pain. My initial prototype board had some audio noise problems - I couldn't hear it but I could measure it. I initally thought was due to the CMOD-A7 and could not be fixed, but eventually put down to quite a few different causes: - I had nearly shorted the output of one of the DAC to GND, which as causing spikes on the power rail. Once fixed things were a lot better, but not perfect/ - I had not made any real attempt to stitch the top fill to the ground plain on the bottom - after all it was a hack. - I didn't have any series resistors in the I2S lines. I added 50 ohm ones (just picked a random value out of the air - might look at this again) - I had a few capacitor bodges standing up in the air, which could only make things worse - I was measuring very close to the FPGA, with a high impedance scope probe So I addressed all of these in the next prototype, and made up a test jig allowing me to measure 30cm from the board and things are much better - to the point I can't reliably measure any additional noise in the audio band. I guess what I am trying to say is that even with just one GND pin the CMOD-A7 can be part of a low noise audio system, but you have to put some extra thinking and work in to make it happen. This may or may not be of use to your use-case.