| 摘要 |
PURPOSE:To prevent jump of a track and defocusing due to a defect of a disk, etc., by substituting the control signal in a servo circuit for the output of a low- pass filter which extracts a low frequency component from detection signal used for a focusing or tracking error. CONSTITUTION:When the level of the noise N in a tracking error detection signal VA exceeds an upper-limit reference voltage VB+VL or a lower-limit reference voltage VB-VL, a high-level comparison output is obtained at the output terminal of the 1st or the 2nd comparator 25 or 26. This high-level comparison output is supplied as a comparison output pulse (a) shown by a solid line in a figure C to the input terminal of a control part 23 through an OR gate 19. During a high-level period t1 of a switching pulse (b), a switch 24 is operated to make a connection between the normally open contact NO and common contact COM, switching a control signal VC supplied to a servoamplifier 7 from the tracking error detection signal VA to the low-pass filter output voltage VB. |
