Hi,
I don't know what you want to achieve with your circuit.
Please tell us your ideas.
My view:
You overcomplicate things ... and sadly this way you reduce performance.
* Using the same reference for both sensor and ADC has some benefits:
- initial accuracy as well as drifts of the reference is cancelled out, thus you may use a really cheap reference.
- you just have to focus not to introduce much noise and that both sensor and ADC really see the same signal.
Thus the use of "U$A" does nothing but introduce errors. It's offset drift and noise is sent to the ADC only and thus can't be cancelled out in ratiometric style.
The same applies to "U$B"(because it's errors ar only sent to the sensor).
The use of R2, R3, R4 do nothing useful but introducing initial errors, drift and noise to the ADC only and thus can't be cancelled out.
And it makes the signal high impedance = weak ... and thus prone for external influence
It reduces VRef to the ADC, which makes no sense, since the noise of the ADC is higher than it's resolution.
U$B makes the sensor to be supplied with "constant current" (and not constant voltage).
Is this really a benefit?
Here you need to consult the datasheet if there is some benefit ... and whether this benefit is not cancelled out by the additional errors like noise and drift which is introduced by the circuit.
******
My recommendation: keep it simple and use the benefit of a ratiometric system:
The simplest way with very good performance is to use a well low pass filtered signal derived from VCC
A simple zener could give additional benefit to decouple from VCC
--> R, zener, C
Use the capacitor voltage as sensor supply.
The use 4 identical R C low pass filters to feed the signals to the ADC.
* capacitor_GND to ADC_Ref-
* capacitor_+ to ADC_Ref+
* sensor_out- to ADC_in-
* sensor_out+ to ADC_in+
--> 4 x R, 4 x C
(If the wiring to the sensor is lengthy, then consider to use kelvin wiring: feed back the sensor supply to the ADC with extra wires. No additional electronic components needed.)
That's all. And I'm sure it gives more accurate and more precise ADC results than your expensive and complicated circuit.
Klaus