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Is it a real breakthrough to remove the input voltage range limitation of IA

Question asked by jebaspaul on Mar 18, 2014
Latest reply on Mar 19, 2014 by jcolao

Hi,

 

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.

 

Thanks,

Jebas.

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