Modulation abnormality detector for optical sound-recording system

Claim 1

An information recording apparatus in which an exposing beam scans a film, said exposing beam being formed by a scanning width control signal modulated in accordance with an input signal, to form on said film an exposing locus whereby said input signal is recorded on said film, characterized by a modulation abnormality detector circuit which compares said scanning width control signal with an upper limit setting signal and a lower limit setting signal and which detects when a scanning width indicated by said scanning width control signal becomes larger than an upper limit scanning width indicated by said upper limit setting signal or becomes smaller than a lower limit scanning width indicated by said lower limit setting signal and which produces a detection signal indicating a result of the detection, wherein said modulation abnormality detector circuit includes first and second comparator means having respective noninverting inputs connected to said scanning width control signal and respective inverting inputs connected to positive and negative voltage sources for producing an upper limit setting signal and a lower limit setting signal, respectively, and logic circuit means receiving said scanning width control signal modulated in accordance with said input signal and said upper and lower limit setting signals for producing said detection signal, and wherein said logic circuit means includes a first invertor receiving said scanning width control signal modulated in accordance with said input signal, a second invertor receiving said lower limit setting signal from said second comparator means, a first NAND gate receiving said upper limit setting signal from said first comparator means and an output from said first invertor, a second NAND gate receiving said scanning width control signal modulated in accordance with said input signal and an output of said second invertor, and first and second monostable multivibrator circuits connected to be triggered by respective outputs of said first and second NAND gates, the output of said first and second multivibrator circuits being added together to form said detection signal.