| 摘要 |
PURPOSE:To fetch always a stable main signal from an optical disk by correcting an error of an error signal outputted from a circuit for detecting a shift of a focus on the optical disk, in case when the accuracy of said circuit is deteriorated due to influence of temperature, etc. CONSTITUTION:A correcting signal is synthesized with an output signal of a low-frequency oscillating circuit 12, and thereafter, added to an output signal of a subtracting circuit 9, namely, an error signal which is not corrected yet, by the fourth adding circuit 14. In case when the focus is matched completely, the values of two points (a), (b) of an envelope of a held main signal become equal to each other, and no output signal appears. On the other hand, in case when the focus is shifted, a difference is generated in values of two points (c), (d). This difference is derived together with a code so that the direction of a shift of the focus can also be judged, and outputted to a correcting signal generating circuit 13. In this case, a correcting signal corresponding to a difference of values of the points (c), (d) is generated, added to the error signal outputted by the subtracting circuit 9 in the fourth adding circuit 14, this error signal is corrected, and an output of a lens driving circuit 17 is controlled so that the amplitude of the envelope of the main signal always becomes maximum. |
