SERVO CIRCUIT FOR A MOTOR FOR REPRODUCING A PCM AUDIO DISK

摘要

A servo system for use with apparatus for reproducing a disk on which PCM pulse code modulation signals have been modulated by a run length limited code and which are recorded at a constant linear velocity and the circuit detects the length of a period during which a playback signal is inverted and produces an output corresponding to the detected length and has a peak value hold circuit for maintaining a peak value of the output and a bottom value hold circuit at a later stage of the peak value hold circuit which has a time constant which is larger than the charging time constant of the peak value hold circuit so as to produce an output which follows the output of the peak value hold circuit. A comparator compares the output of the bottom value hold circuit with a reference value so as to produce a signal for controlling a disk drive motor such that a maximum or minimum length during which the playback signal is inverted equals the length when the linear velocity is a reference value so that the linear velocity will be maintained constant during playback.