| 摘要 |
PURPOSE:To properly operate an A/F servo system, by eliminating disturbances in address areas, sectors, separator areas, etc., contained in focusing error signals. CONSTITUTION:A focusing error signal 19 containing a disturbance is obtained when signals Ia and Ic of external photodetector elements 15a and 15c of a three-division photodetector 15 are impressed in an adder 30 and the output of the adder 30 and the signal Ib of an internal photodetector element 15b are inputted in a differential amplifier 17. On the other hand, the signals Ia and Ic are also impressed to a subtractor 31 and a full-wave rectified output 36 is obtained by passing the output 35 of the subtractor 31 through a full-wave rectifying circuit 32. The output 36 is further passed through an LPF33 and a correcting signal 37 is obtained. The signals 19 and 37 then become a focusing error signal 38 whose disturbance is corrected in a mixer 34. |
