FREQUENCY DETECTING CIRCUIT

摘要

The circuit is fed with a digital information signal obtained from an optical disc and having an inverting period falling within a range of a max. inverting period, with the min. inverting period predetermined by the modulation system. An edge detection circuit detects the logical level changing points on a waveform of a pulse component of the digital signal. A counter receives the edge detecting signal(107) and a demodulating clock signal (108) to count intervals between adjacent pulse edges. The counter output is fed to a comparator.