| 摘要 |
PURPOSE:To prevent a track jump even if a light spot strikes a flaw or stain part to cuase the disorder of a tracking error signal, by detecting the level of envelopes of a high frequency signal reproduced from a disk, and substituting it with a signal which is held at a potential in an envelope level drop. CONSTITUTION:The tracking error signal 12 is supplied to a phase compensating circuit 13 through the 2nd analog switch 24b to put a tracking servo system in operation. When, however, the envelope 18 of the high frequency signal 17 detected on a track drops below a preset value Vref, the 1st and the 2nd switches 24a and 24b are changed over for a specific period determined by a pulse signal 30. The mean value of the tracking error signal right after the envelope drop is supplied from a holding circuit 25 and a phase compensating circuit output having a specific level based upon the input signal is generated, so that a tracking actuator 15 keeps on holding the position. |
