There is an information in AD7794 Data Sheet: RMS noise: 80 nV (Gain = 64). And
there is an information in Product Description and presentation about AD779x:
40 nV (Gain = 64). What is true?
The rms noise is 80nV when the gain equals 64 and the update rate is 16.7 Hz
(default value). When the update rate is reduced to 4.17Hz, the rms noise is
reduced to 40nV with the gain at 64.