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Abstract

A pulse modulation operation circuit includes a current bus, a plurality of switch current sources connected parallel to each other and commonly connected to the current bus for generating current pulses corresponding to external input signals, charge conversion element connected to the current bus for integrating the current pulses and converting them into a charge, and an output for converting the charge into a binary digital signal and outputting the binary digital signal. Each pulse width modulation signal is input to a corresponding one of the switch current sources, which in turn generates a constant current for a period corresponding to the width of each pulse of the signal, to convert each signal pulse into a current pulse. The thus-obtained current pulses are added on the common current bus, thereby obtaining, by capacitive integration, a total charge Q.sub.total proportional to the sum of the widths of the current pulses. To this end, a reference charge counter circuit has a function for integration and a function for digitizing the total charge Q.sub.total in units of a reference charge Q.sub.std in real time.

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First Claim