| 摘要 |
PURPOSE:To fix the opening loop gain of a focus servo system by providing an optical recording and reproducing device with an amplifier for changing the opening loop gain of a focus servo system, a detecting means for detecting whether information is recorded on a track of a recording medium and a gain adjusting means for the amplifier. CONSTITUTION:Light from an optical head 4 is irradiated on an optical disc 3 and the light reflected by the disc 3 and returned to the head 4 is branched to a detector 5 in an automatic focusing system and a detector 10 in a tracking system. A signal 6 converted into a voltage by the detector 5 is sent to a detecting circuit 7 for detecting defocusing and converted into a servo error signal voltage by the circuit 7 and the voltage is amplified by an amplifier 8 and applied to a driving circuit 9, which drives an automatic focusing actuator in the optical head 4 to compensate its defocusing. On the other hand, information from the detector 10 is A-D converted by a reproducing circuit 11, the digital signals are counted, and when the number of sector mark signals coincides with a previously fixed value, the recording of information in the data part is decided and the gain of the amplifier 8 is changed on the basis of a switching signal 14 outputted from a gain switching signal generating part 13. |
