Periodical signal detection circuit within a variable window length

Abstract

A periodical signal detection circuit in a reproducing apparatus which reproduces an information signal and a periodical signal from a recording medium recorded with the information and periodical signals comprises a separation circuit for separating the periodical signal from the reproduced signal, a reference pulse generating circuit for generating a reference pulse having a same repetition frequency as the periodical signal, a window signal forming circuit for forming window signals respectively having differing widths, with a repetition period identical to that of the reference pulse, a first gate circuit for producing the periodical signal from the periodical signal obtained from the separation circuit and the window signal obtained from the window signal forming circuit, a first counter for generating a switching control signal every time the reference pulse is counted N (N is an integer including zero) times, to produce an output when counting is performed for a predetermined number of times, a window signal supplying circuit responsive to the switching control signal obtained from the first counter of the window signals from the window signal forming circuit, for supplying a window signal having a width corresponding to the switching control signal to the first gate circuit, a second gate circuit for passing the signal from the separation circuit according to the output of the first counter, and an output circuit for producing the reference pulse, the output of the first gate circuit, or the output of the second gate circuit as a detected periodical signal.