| 摘要 |
PURPOSE:To attain always stable focus and tracking control by providing a differential amplifier circuit for detecting a differential signal of dividing photodetecting elements detecting focus or a tracking error, an additional amplifier circuit for detecting the signal summed up said dividing photodetecting element and a division circuit for dividing the differential signal by the sum signal. CONSTITUTION:When it is defined that a signal from the dividing photodetecting element 10a is (a) and a signal from the element 10b is (b), an output signal, i.e. a focus error signal, of the differential amplifier circuit 11 goes to (b-a) and an output signal 22 of the additional amplifier circuit 20 goes to (a+b). If the intensity of light detected by the dividing photodetecting elements at a recording time is k times that of reproducing, the error signal 21 goes to k(b-a). When the focus error signal 21 is divided by the sum signal 22 in the division circuit 23, the output signal 24 of the division circuit 23 goes to the formula I at a reproducing time and the formula II at a recording time, so that the values of the formulas I and II are always constant independently of the value of k. Consequently, the focus error signal 24 is not varied in both the recording and reproducing times. |
