| 摘要 |
PURPOSE:To execute a focus control with high accuracy, by mixing focus information detected by a level variation of a reproducing RF signal, and executing the focus control. CONSTITUTION:A laser light 1' emitted from a laser light emitting body 1 is irradiated on a track of a disk 5 through a collimating lens 2, a half-mirror 3 and an objective lens 4, and a reflected light from the disk 5 is reflected by the half-mirror 4, and is made incident to the photodetecting surfaces of 4-split photosensors 100-103 of a photosensor 7 through a prism 8. Each photoelectric converting output of the photosensors 100-103 is added by analog adders 9, 10, is supplied to high-pass filters HPFs 18, 19, respectively, and a reproducing RF signal by bit information is detected. Outputs of the HPFs 18, 19 are added to an output of a differential amplifier 11, being focus information, through envelope detectors 13, 14 and a differential amplifier 15, and drive a moving coil 6, by which a distance from on the disk surface of an objective lens 4 is controlled. |
