JPS56129479A - Detector for changing point - Google Patents

Abstract

PURPOSE:To simplify a device, by preventing the production of an unnecessary black signal in an intermediate tone signal, by detecting the minimum point of facsimile signal in a given level or lower, and assuming this detection point as a changing point signal. CONSTITUTION:The facsimile signal from the input terminal 1 is input to the A/D conversion circuit 3, it is sampled with a given period of sampling clock given to the input terminal 2 and analog signal is converted into digital signal. The output of the conversion circuit is fed to the delay circuit 4 and to the comparator 5 with a delay of one clock's share, and the result is compared with the output of the conversion circuit 3. Further, the output of the conversion circuit 3 is fed to the comparator 6, it is compared with a preset given level, to output the output X2. Further, the output of the comparator 6 is delayed at the delay circuit 7 by one clock's share and fed to the minimum point detection circuit 8 as the output X3 together with the outputs X1, X2 of the comparators 5, 6. Further, the first point where the facsimile signal is smaller than a given level is detected with the detection circuit 8, avoiding the production of unnecessary black signal in the intermediate tone signal.