Hi,
Have you looked at the op amp output range and checked to see if it's exceeding the 7107 input range in some way?
I don't see why it would be that though, the 7107/7106 are 200mV or 2V input as far as I recollect and your op amp input to the ADC is only 100mV (surely?).
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The LM358N datasheet says input to 0V (-0.3) and input offset voltage only 3mV max, so wouldn't that only be 6mV + bit more in case so say 10mV "noise" at the output only, meaning maybe 110mV at ADC input?