High accuracy mosfet-switched sampling circuit

Abstract

A high-accuracy MOSFET-switched sampling circuit feeds charge feedthrough error to a load as well as to a dummy load during DC input signal sampling by a switching MOSFET, thereby reducing storage of the charge feedthrough error on the load to the extent that the charge feedthrough error is rather stored on the dummy load. During AC input signal sampling, the high-accuracy MOSFET-switched sampling circuit isolates the AC input signal from the dummy load. Charge feedthrough error produced by an isolating MOSFET that isolates the AC input signal from the dummy load is exactly compensated by a phase-opposed compensating MOSFET positioned in the DC input signal path. The dummy load and the load may be active as well as passive and may be selected to have equal and unequal electrical characteristics. The compensating current produced by the compensating MOSFET may be selected not only to exactly compensate the charge feedthrough error of the isolating MOSFET but also to compensate the charge feedthrough error of the switching MOSFET in the DC input signal path. High sampling accuracies are achieved by the instant invention in a wide variety of applications including an exemplary auto-zeroed CMOS comparator.