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low noise DC amplifier design

Question asked by jk4556 on Dec 5, 2011
Latest reply on Dec 8, 2011 by jk4556



I am trying to design a circuit which will apply a gain and offset (Vout = (Vin * A) + B) to a DC reference signal. The reference signal is specified to have a voltage noise of < 3nV/Hz^.5. The signal range is -10V to +10V. The gain and offset will be variable via a potentiometer (the offset will be derived from another reference source and varied through a divider circuit).


What would be a good amplifier to choose for this design? I think all of the in-amps I have looked at have an input noise spec greater than 3nV/Hz^.5, i.e.: the AD8222 has an input noise of 8nV/Hz^.5 and .25uVp-p noise at .1Hz-10Hz.


An instrumentation amplifier would be convenient to use because the offset voltage could be applied to the reference pin. My other thought was to use regular op-amps and build a gain stage and a summing stage for the gain and offset. It looked like, in general, the low-noise op-amps had better noise specs than the in-amps, I imagine that a more complicated circuit would be more susceptible to noise sources though.


What would be a good amplifier for this application? Which approach would be better (the instrumentation amplifer or the multi-stage op-amp design) in terms of noise performance, or is there a different approach that would also be better?