From what I've read in the datasheet, the AD7691 ADC (http://www.analog.com/static/imp...) can digitize a voltage ranging between +/-VREF.
A single-ended to differential driver is used to provide inputs at the IN+ and IN- pins.
However, I am wondering if it is possible to use ADA4841-2 amplifiers (http://www.analog.com/static/imp...) like shown on pg. 15 (Figure 29) of the AD7691 datasheet to measure the voltage drop across a resistor.
A sensor that can be considered as a resistor would be connected across the inputs of the ADA4841-2 amplifiers. The circuit would be the same as that on pg. 15.
Feeding the resistor with a constant current source, the AD7691 would measure the voltage drop across the resistor.
This should be possible, since according to pg. 1 of the AD7691 datasheet, "On the CNV rising edge, it samples the voltage difference between the IN+ and INâˆ’ pins."
According to pg. 14 of the datasheet: "Therefore, the differential voltage between the inputs IN+ and INâˆ’ captured at the end of the acquisition phase is applied to the comparator inputs, causing the comparator to become unbalanced."
My question is: does this application of the AD7691 change the transfer function of the ADC, and how would I interpret the digital output of the ADC as a voltage difference?
Because this is an SAR ADC, I would assume that the ADA4841-2 is required to act as a buffer for the analog inputs of the ADC.