| 摘要 |
PURPOSE:To compensate the offset voltage regardless of the variance of a disk itself and to detect the best focal point by detecting the offset compensation voltage for each disk. CONSTITUTION:The HF signal delivered from a photodetector 3 is amplified through a high-frequency band amplifier 7 and then converted into a sound signal. This sound signal is detected by a wave detecting circuit 8, and the peak of the wave detection output is detected by a peak detecting circuit 9. This detection output is delivered in the form of a memory command signal. While the clock pulses delivered from a clock pulse generating circuit 10 are counted by a counter circuit 11. This count output is converted into an analog signal by a D/A converting circuit 12 to obtain the output voltage which increases in steps in proportion to the count value of clock pulses. This output voltage is supplied to a memory circuit 15, and at the same time the output voltage shifted down by a level shifting circuit 14 is supplied to a focus error detecting circuit 4 in the form of the offset compensation voltage. Then the focus control is performed in the direction where the focus voltage is set at 0. |
