| 摘要 |
PURPOSE:To obtain a stable tracking signal with excellent linearity and without changing detection sensitivity by using a level of a sum signal adding all output signal from a photodetector split into plural portions to normalize a tracking error signal. CONSTITUTION:Output signals of photodetectors 9a, 9c and 9c, 9d being 4 divisions are added by adder circuits 14, 15 and the signal from the circuits 14, 15 is fed to an adder circuit 16 and a subtraction circuit 17. A tracking error signal detection circuit 23 samples and holds a difference signal S8 from the circuit 17 at a zero cross point of leading edge trailing edge of a sum signal S7 from the circuit 18 and takes the difference to form a tracking error signal S13. An amplitude detection circuit 24 detects the amplitude of a signal S7 and a division circuit 25 divides the signal S13 by an amplitude S14 of the signal S7. Thus, a stable tracking signal S15 with good linearity and without change in the detection sensitivity is outputted in such a way.
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