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ADC7762 on board differentail amplifier

Question asked by B3Brad on Nov 29, 2013
Latest reply on Jan 8, 2014 by ChrisD.Rama

I am seeking performance specification for the on-chip differential amplifier on the ADC7762, in particular the maximum and recommended voltages for VinA+ (Pin 19) and VinA- (pin 20).  The data sheet appears to be silent in this regard.

 

In previous designs using AD7678 I have used an AD8139 to level shift and generate the differential input signal, but presumably the on-chip diff amp will provide a more precise level shift.

 

I am also curious about the recommendation (at fig 27 of the data sheet) to use an AD8021 to derive a differential input for the on chip amplifier A1 from a single ended signal.  Since A1 is going to level shift the input signal anyway, why not just apply the signal  to one input and ground reference to the other?  Does A1 perform better if the differential inputs are balanced?

 

My signal input is a single ended bipolar output from a current to voltage conversion circuit.  The gain can be adjusted as required, currently the measurement range is +/- 3.275V.   However I would like to allow the voltage to exceed this range in the overload condition.  Currently the signal can range up to +/- 15V which I presume would damage the input?  Would the input be safe over voltage ranges of say +/- 5V? 

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