On the AD4170-4, two different coding options exist: unipolar and bipolar coding. Unipolar coding is used to represent positive voltages only, and bipolar coding can be used to represent both negative and positive differential voltages applied to the analog inputs of the ADC.
For the ADC operating in unipolar mode, the input range to the ADC is from 0V to Full scale, where the full-scale value is equal to VREF/Gain (reference input voltage/PGA Gain setting). The output coding is straight binary which means that
a zero differential input voltage applied to the analog inputs results in an output code of 00...00 (0x000000)
a midscale voltage (VREF/(2*Gain)) applied to the analog inputs results in an output code of 100...000 (0x800000)
a full-scale input voltage (VREF/Gain) results in an output code of 111...111. (0xFFFFFF)
When the ADC is operated in bipolar mode, the input range is from negative Full Scale (-FS) to positive Full Scale (+FS) where Full Scale (FS) equals VREF/Gain (reference input voltage/selected PGA gain). The output coding for bipolar operation is two’s complement with
a negative full-scale voltage applied to the analog inputs results in an output code of 100...00 (0x800000)
a zero differential input voltage applied to the analog inputs results in an output of 00...000 (0x000000)
a positive full-scale input voltage applied to the analog inputs results in an output code of 011...111 (0x7FFFFF)