Is there any specific impedance that should be used on the Differential inputs on the AD7781 ADC.
Also is their any requirement for differential impedance.
As mentioned in the datasheet, AD7781 differential input channel feeds into high impedance input stage of the amplifier. Thus, the input can tolerate any significant source impedances. You can also refer to the EVAL-AD7781 schematic and layout. Please see link below for details.