| 摘要 |
PURPOSE:To obtain the titled device which is low in its cost and small in size by executing a focus detection by utilizing an interference of each diffracted beam from an optical recording medium. CONSTITUTION:The titled device has the first-the fourth photodetectors 1-4 for outputting signals S1-S4, and an AC coupling circuit AC-couples a signal (S1+S2+S3+S4), a signal (S1+S2)-(S3+S4) and a signal (S2+S4)-(S1+S3), respectively. A zero cross detecting circuit 21 detects a zero cross point of the signal (S1+S2+S3+S4). Sampling circuits 25, 32 sample the signal (S2+S4)-(S1+S3), based on a detecting output of the zero cross detecting circuit 21. Multiplying circuits 22, 23 and 26 multiply the signal (S2+S4)-(S1+S3) by the polarity of the signal (S1+S2)-(S3+S4) in its time point. In this way, a result of this multiplication becomes an out-of-focus quantity. |
