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FAQ. In AD7124-4/AD7124-8, Can I use a single AIN pin as analog input pin and shared this pin as bias voltage (VBIAS) pin to bias the analog input at mid supply?

Answer: Yes, that should work Vbias can be brought out to AIN-. However, if there are large RC values connected to AIN- then AIN+ sees a filtered version of the bias voltage. The difference between the bias voltage at AIN+ and AIN- results in a voltage error that can be detected by the ADC, so it adds an error to the measurements. To use a shared pin approach, limited RC values must be use. To use unlimited RC values, it is recommended to use a dedicated pin for Vbias and applied Vbias as the common mode voltage on the outer side of the anti-aliasing filter.