I am measuring differential voltage +-1v (always) using AIN4(+1V), AIN5(-1V) channels and to measure offset voltage I connected AIN3 and AIN2 to AGND. Now when I power-on my system, first I measure the offset voltage (AIN3 and AIN2) and then I switch to channels AIN4,5 to measure +-1V continuously. When I measure offset voltage with global chop mode enabled using channels AIN3, AIN2 my output is oscillating between 5LSBs (more or less) to 16777216LSBs(Max code of ADC). If I disable global chop mode I get around 80LSBs of offset and the output is not oscillating. My question is why my output is oscillating if global chop mode is enabled when measuring the AGND signal? This behavior is not seen if I measure +-1V with global chop mode enabled or disabled.
FYI: AVDD=+2.5V, AVSS=-2.5V
Reference: internal reference