Hi,
The differential input voltage range of the AD7780 is equivalent to AIN(+) - AIN(-) = ±VREF/gain.
Given a VREF=1V & gain=128, the part can allow a differential input of AIN(+) - AIN(-) = 7.8mV, hence , if the full-scale output range of your transducer equals 6mV, a VREF of 1V is applicable.
The analog inputs, AIN(+) & AIN(-), can be biased at a certain level, between GND+450mV to AVDD-1.1 @ gain=128, as long as its difference, AIN(+) - AIN(-), would not exceed VREF/gain.
For ex. AIN(+)=2.506V; AIN(-)=2.5V, the differential input voltage would be , 2.506V – 2.5V = 6mV.
To reduce the reference to 1V, external resistors would be needed to attenuate the 5V excitation voltage. These resistors will add some noise. So, the overall noise may increase alittle.
Thanks and Best Regards,
Chris