I inherited a poor design that uses the ADuC834. fADC is 105 Hz. One aux channel, 16-bit sigma-delta converter, always shows an exponentially converging series [V0 * (1 - exp(-k * n)] when N conversions are executed successively. The first measurement is the most accurate, and after 10 or so readings the value is erroneously high by about 100 counts. I can interleave my measurements with other channels, and the artifact disappears, but I would like to take successive readings and average them.
** Why is this happening? **
I have no details on PCB construction or grounding.
I have not verified if this happens on other channels.
SF = 0x0D;
ADC0CON = 0x47;
ADC1CON = 0x70;
ADCMODE = 0x31;
Here is a typical series: 8099, 80bc, 80da, 80ea, 80f3, 80fd, 8100, 8107, 8109, 810b