Periodical signal detection circuit within a variable window length

Claim 1

A periodical signal detection circuit in an apparatus which reproduces an information signal and a periodical signal from a recording medium having both periodic signals and information signals recorded thereon, said periodical signal detection circuit comprising: separation circuit means coupled to receive signals reproduced from said recording medium for separating said periodical signal from the signals reproduced from said recording medium, said periodical signal being a series of pulses; reference pulse generating circuit means for generating reference pulses having a repetition frequency which is the same as the repetition frequency of said periodical signal; window signal forming circuit means for forming window signals respectively having different widths, with repetition period identical to the repetition frequency of said reference pulse and of said periodicl signals; first gate circuit means for producing said periodical signals, responsive to the separated periodical signal received from said separation circuit means and to the window signal received from said window signal forming curcuit means; first counter means coupled to said reference pulse generating circuit and reset in response to each of the pulses of said periodical signal, for continuing a count of said reference pules from said reference pulse generating circuit during an interval in which the pulse of said periodical signal is absent, said first counter producing a switching control signal according to the count therein; window signal supplying means responsive to the switching control signal from said first counter means for supplying to said first gate circuit means a window signal, among said window signals produced by said window signal forming circuit means at the repetition frequency of said periodic signals said supplied window signal having a width corresponding to the switching control signal; second gate circuit means coupled to said separation circuit means and to said first counter means for passing the periodic signal from said separation circuit means according to the output of said first counter means; and output circuit means for producing said reference pulses, the output of said first gate circuit means, or the output of said second gate circuit means as a detected periodical signal.