| 摘要 |
PURPOSE:To decrease a high area noise due to secondary resonance by forming an LPF, which has a cut-off frequency <= the secondary resonance frequency of an optical pick-up device, with a tertiary active filter. CONSTITUTION:For a driving part 9, a secondary active filter by voltage control voltage source type normal feed-back is composed of an arithmetic circuit 10, resistors 11 and 12 and capacitors 13 and 14. Then, a tertiary LPF is formed together with a primary RCLPF3. This tertiary LPF has the prescribed cut-off frequency to the secondary resonance frequency of the optical pick-up device. Thus, in a focus servo circuit 1, attenuation is sharp in a frequency band >=the cut-off frequency. Then, since the high area noise is decreased and it is not necessary to narrow a servo area, a gain in a servo characteristic or a margin concerning phase rotation can be enough secured. |
