| 摘要 |
PURPOSE:To optimize focusing of an optical disk by giving an offset to a focus error output of an objective lens in an optical output circuit and switching an offset to a specific value respectively at signal reproduction and signal recording so as to eliminate a delicate difference between the recording and reproduction. CONSTITUTION:A light reflected in an optical disk and returned in received by a sensor 11 to obtain a couple of complementary outputs. The outputs Sa, Sb in pairs are processed by a subtracter 15 and an adder 16, the result is given to an automatic gain control circuit via amplifiers 15a, 16a to obtain a focus error. Then a phase compensation circuit 18 applies phase compensation, an adder 19 adjusts the offset, then the result is fed to a focus coil 22a, where focus control is applied so that the focus error is made zero. Then a switch 23 is used to select an optimum offset depending at signal reproduction and recording respectively and the focus control of the optical disk is applied always under the optimum condition. |
