| 摘要 |
PURPOSE:To obtain a stable driving output of an optical head in both reproduction and recording modes regardless of variation of the total reflected light quantity, by providing a changeover switch which switches the gains of both amplifiers with switch signals of recording and reproduction modes and a control means which stabilizes the outputs of both amplifiers approximately at the same level regardless of a recording or reproduction mode. CONSTITUTION:The servo gain is decided by amplifiers 2 and 3, and the gain of the amplifier 3 is decided from the equivalent drain-source resistance value of an FET4 as well as resistances R18 and R19. Then the gain of the amplifier is decided based on the mean value of laser power of a recording mode. Thus the servo gain is liable to have a shortage despite the gain setting of an amplifier 16 since the level of the laser power is low in a reproduction mode. In this respect, an analog switch 14 is controlled by a recording/reproduction gate to obtain the drive voltage approximately equal between recording and reproduction modes in order to compensate a track shift. For this purpose, the values of resistances R18 and R19 are properly selected. In such a way, the optimum servo gain is obtained. |
