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Offset nulling a Fully differential Amplifier

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OldRFguy

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Continuous offset nulling of a Fully Differential Amplifier

I am thinking of using a precision low frequency op-amp to null the offset voltage of a wide bandwidth fully differential amplifier (LT6600) by sensing the closed loop offset voltage across the input terminals and driving a suitable correction current into one or other of the virtual earths to correct the offset.

Has anyone tried this technique and, if so, can you offer any suggestions on its implementation?

Many thanks

OldRFguy
 
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The "sensing of closed loop offset voltage across the input terminals" part already implies some sort of differential input stage, which will likely suffer offset of the same order as that of your main opamp.
 

Yes, of course that is correct; the composite amplifier now inherits the offset characteristics of the precision op-amp but precision op-amps can have offsets measured in microvolts whereas a Fully Differential Amplifier has offsets that typically fall between about 5mV and 30mV so the composite amplifier has the scope to improve the offset of the FDA very substantially.
 

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