Sensing circuit for a multi-level signal charge

Abstract

This multi-level signal charge sensing circuit includes a first capacitor for holding inspected charge, a second capacitor for holding a plurality of reference charge levels and a comparator for comparing potentials produced at the first and second capacitors. As the plurality of reference charge levels, (N-1) charge levels of different known values are prepared. The inspected charge is given to the first capacitor which is reset, and the (N-1) reference charge levels are successively given from the highest or lowest level to the second capacitor which is also reset. The comparator is operated for every step of supplying each reference charge level. Of the successive reference charge supplying steps at an instant between the steps corresponding to 0 and (N-1), the output state of the comparator is inverted, thus supplying digital information representing the inspected charge level. This sensing circuit permits discrimination and sensing or detection of N different inspected charge levels with a single circuit construction.