| 摘要 |
PURPOSE:To suppress track jump even when a scratched or contaminated optical disk is used, by controlling servo gains in such a way that the larger scratch detecting signals become, the smaller the servo gains becomes and the smaller the servo gains beome, the smaller return time constants become. CONSTITUTION:When a scratch detecting signal 19 produced from the envelope detection of a reflecting signal 18 from a disk is inputted in a servo gain controlling circuit, a control A signal 20 is outputted from an inversional amplifier 15 and, when the control A signal 20 is ''L'', a switch 13 is closed and a servo gain is lowered. When a large scratch or contamination is detected while the servo gain is descending, a control B signal 21 is outputted from another inversional amplifier 16. When the signal 21 is outputted, another switch 14 is closed and the servo gain 22 is further lowered and a further stronger condition is established against the scratch or contamination. After the scratch or contamination passes, the switch 14 is immediately opened and the servo gain is raised by one step. When the disk makes another several turns, the switch 13 is opened and the servo gain is returned to the original high state. |
