| 摘要 |
PURPOSE:To eliminate an offset due to external disturbance by controlling an output of a synthesis means in response to each direct current of a couple of detected outputs, an AC component level ratio, disc inclination and a bias of an objective lens to set the synthesis ratio to an optimum value. CONSTITUTION:A DC component by external disturbance is included respectively in a low frequency component difference C and a high frequency envelope component difference G of detecting elements 9a, 9b in the relation of in phase and an AC component being a tracking error component is included in opposite phase. Then both difference components G, C are synthesized by a desired synthesis ratio at a differential amplifier 21 to eliminate the DC component by external disturbance. The DC component (offset of tracking error) is cancelled by a value of a gain coefficient gamma of a gain variable amplifier 22. That is, DC offset component due to external disturbance included in a tracking error signal is corrected nearly completely by selecting the gamma having an equal DC offset when the inclination of the disc and the bias of lens are maximum. |
