Hi Osamu,
The plot is not incorrect it’s just not very clear.
No matter what the resolution you set on the AD2S1210, you can still read back 16 bits, accuracy is at the resolution you set however.
The histograms are for 16, 14, 12 and 10 bit resolution with hysteresis enabled and for 16, 14, 12 and 10 bit resolution with hysteresis disabled.
The histogram plots when hysteresis is disabled are all reading in the full 16-bits of data. For example for 10-bits of resolution you can’t get codes between 8191 and 8194. If you scaled the plot back to the 10-bit level you would get a 2 or 3 code spread.
This is why the 10-bit resolution shows such a wide spread.
Regards,
Jarwin