LOW_NOISE_AND_DRIFT_COMPOSITE_AMP

Published:2009/6/24 3:13:00 Author:May | From:SeekIC

This circuit offers the best of both worlds, It can be combined with a low input offset voltage and drift without degrading the overall system's dynamic performance. Compared to a standalone FETinput operational amplifier, the composite amplifier circuit exhibits a 20-fold improvement in voltage offset and drift. In this circuit arrangement, A1 is a highspeed FET input op amp with a closed-loop gain of 100 (the source impedance was arbitrarily chosen to be 100 kΩ). A2 is a SuperBeta bipolar input op amp. It has good dc characteristics, biFET-level input bias current, and low noise. A2 monitdrs the voltage at the input of Al and injects current to Al's null pins. This forces A1 to have the input properties of a bipolar amplifier while maintaining its bandwidth and low-inputbias-current noise.



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