I am working on a Data acquisition system. The input range is +/-10V and common mode range of +/2V. So, the total signal range could be +/-12V. Inorder to remove the common mode I am using an instrumentation amplifier. Since my system is 16 bit precise and allowed drift error is less, I have selected AD8421. Its gain drift is 1 ppm/DegC.
The problem which I am facing is the input and output range of AD8421. I used a architecture given in Fig 70 of AD8421 data-sheet. With this architecture the output of IA is limited to +/-5V. But, The Fig 10 which depicts the range of input with respect to the output voltage, indicates that the IA's input can't be < -10V and >+11V. But my input is +/-12V with common mode shift.
So, I am thinking of using the same architecture shown in Fig 70 with higher inverting gain for reference generator. The attachment has the schematic of this. I have planned for a gain of -4. With this architecture the voltage at the output of IA is +/-2V and at the reference pin of IA +/-8V. The absolute difference between these two is +/10V. Since the IA's output has +/-2V, input head room of IA is increase by a significant amount.
Is there any ADC( >16 Bit with <+/- 2LSB INL ) which can process this signals deferentially.
Note: Please refer the attachment for the schematic and signal range.