| 摘要 |
PURPOSE:To perform the tracking servo easily and satisfactorily by detecting a position where no pit exists as a signal corresponding to the total reflection level and shifting equivalently a photodetector to set the detector at the center of a reflected beam. CONSTITUTION:Two output signals P1 and P2 are delivered from split regions which are combined variably and receive the peak wave detection through the 1st and 2nd peak wave detecting circuits 13 and 14 respectively. Then the position of a reflected beam spot is decided from the output of the 2nd comparator 16 to produce the switch signal needed for a switching control circuit 18. A synthetic switch circuit 12 is changed over to give an equivalent shift to a photodetector as a whole so that the spot of the reflected beam is aparently set at the center of the photodetector. The output of the 1st comparator 15 is supplied to the 3rd comparator 17 to be compensated by the output of the comparator 16, i.e., the detection signal for no-pit position. Thus the tracking error signal free from offset is supplied to the driving part of an optical system. Then the satisfactory tracking servo is possible. |
