Digital information reproducing apparatus including a circuit for detecting frequency deviation of a synchronism clock

摘要

A digital information reproducing apparatus includes a reading device to read out digital information recorded on a recording medium; a first clock generator to produce a first clock synchronized with the digital information read out by the reading device; a second clock generator to generate a second clock of a predetermined frequency; a processing circuit to process the digital information read out by the reading device on the basis of the first clock produced by the first clock generator; and a switching circuit for switching from the first clock produced by the first clock generator to the second clock generated by the second clock generator and for outputting the second clock to the processor in a case when the frequency of the first clock produced by the first clock generator deviates from a predetermined range. The first clock generator includes a PLL circuit for inputting the digital information read out by the reading device and producing the first clock. The switching circuit includes a frequency comparison judging circuit which determines that the frequency of the first clock has deviated from the predetermined range when a predetermined number of first clocks are not counted by a first counter until a predetermined number of second clocks are counted by a second counter.