JPS6469960A - Detecting system of zero cross point of waveform having sawtooth distortion - Google Patents

Abstract

PURPOSE:To detect a zero cross point irrelevantly to the frequency of a waveform etc., by providing a means to measure a phase amount from a time point of starting measurement to a time point of rise of an output signal of a detector, a means to measure a phase amount up to the last time point of the rise etc. CONSTITUTION:A count circuit 4 is started at a point of phi=0 by a signal from a start signal terminal 7 and stopped at the first rise of an output of a detector 2, and a count value in this period is set at phi1. Next, in the same way as in the detection of the count value phi1, a count circuit 5 is started at the point of phi=0, and a count value of a counter is returned to 0 and restarted at every rise of the output of the detector 2. Moreover, the counting operation is stopped at a point of phi=H. By the above-stated operation, a phase amount phi2, from the last rise of the output of the detector 2 to phi=H is obtained. Subsequently phi1 data and phi2 data are subjected to arithmetic processing 9 and thereby a zero cross point can be detected.