| 摘要 |
PURPOSE:To attain a stable focus servo action by holding the signal level or the peak level at the position of a focus error signal when an objective lens is moved and using the holding output to correct the level of the focus error signal. CONSTITUTION:In an open mode of a servo loop an offset detecting circuit 4 holds the output level of an error amplifier 2 as the offset value at a position A where a sufficient distance is secured between an objective lens and the recording surface of a disk in response to a focus start command. Then said held offset value is used as the negative input of a subtractor 3. While a peak holding circuit 5 holds the positive peak level of the output of an error ramp 2 at a position B. The holding output of the circuit 5 is supplied to a multiplier 6 after a gain correction value arithmetic circuit 13 calculated the gain correction value A which is adversely proportional to the holding output of the circuit. While a zero-cross detecting circuit 8 corrects the signal level via the subtractor 3 and the multiplier 6 and then supplies this detection output to a switch control circuit 12. |
