Tokyo Shibaura Denki Kabushiki Kaisha

Yukio Nakamura

Tadashi Kojima

Meisei Nishikawa

A circuit is disclosed which is applied for a digital audio disk (DAD) system for detecting a maximum inverting period of a digital audio signal optically read out from the DAD. The audio signal is prestored in the DAD so as to have the maximum and minimum inverting periods specially set by an eight to fourteen modulation (EFM). The detection circuit includes an edge detector for detecting pulse edges of the digital audio signal, a counter for counting pulse edge intervals on the basis of a modulating clock signal, a counter type register, and a comparator. When the register contents of the counter type register is smaller than the count value of the counter, the comparator produces a pulse signal by which said register updates the contents of the register by '1'. Repeating this operation, a maximum inverting period value of the digital audio signal is obtained in a fixed period of time.

Frequency detecting circuit for digital information reproducing system

A phase locked loop control circuit for a digital audio disk system is disclosed which has a voltage-controlled oscillator (VCO), a reference signal generator for generating a reference signal corresponding to the phase state of a digital audio signal when the digital audio signal is reproduced or read out and which is recorded on a digital audio disk (DAD) to have a maximum or minimum inverting period value predetermined by the eight to fourteen modulation method, a phase comparator connected to the output terminal of the reference signal generator and the VCO, a detector for detecting the maximum inverting period value included in the digital audio signal; and an adder for adding outputs from the phase comparator and the detector and for supplying a sum result as an oscillation control signal to the VCO.

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Yokohama, Japan

Yukio Nakamura