Kost, Looking at the buffer using R89, it looks like this should just be removed. It's possible that it was intended for some gain in the buffer with R87, but in the end, this should just be a unity gain buffer. If you've replaced this with a 10kΩ resistor, it should be ok. This only adds a small load to the buffer. As for the noise, I'm not sure what this problem is. What data rate are you using? Is this waveform 50Hz or 60Hz as the power line cycle in your region? Line cycle could couple into the signal with the input or the reference, but if the buffer helps, it's more likely a problem with the input. If this is a problem with the input voltage, I would check the output of the source to make sure that the signal stays within AVDD and AVSS, also, I'd check the grounding between the signal source and the EVM. Joseph Wu
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