| 摘要 |
PURPOSE:To always obtain an error signal of a prescribed range irrespective of the reflection light quantity from an optical disk, by modulating an error detecting signal from a signal output means, based on an output of a comparing means, and allowing the modulated signal to pass through a second low-pass filter. CONSTITUTION:A light quantity signal L and a focus error detecting signal FED are supplied to pulse width modulating circuits 5, 6, respectively. In this case, the circuits 5, 6 are allowed to have an amplitude corresponding to the light quantity signal L or the detecting signal FED, and also, allowed to output a pulse signal of pulse width corresponding to an output of a comparator 8. Subsequently, the pulse signal from the circuit 5 is supplied to the comparator 8 through the first LPF 7, and compared with a reference voltage VR of a reference voltage generating circuit 9. Also, the detecting signal FED which has been modulated by the circuit 6 becomes a focus error signal FE by the second LPF 11, and by driving an objective lens of an optical system by using this signal, a focus-servo is executed. |
