| 摘要 |
PURPOSE:To prevent a spot from being moved to another bit train by the influence of noise, external impact, or the like, by extending practically a control area of a tracking error control signal to an optional bit train. CONSTITUTION:When the spot is moved to the outside of a line l2 in the figure, a phase comparator 20 outputs a phase difference signal D because the outside of the line l2 is the control area to a bit train (N+1); but since this phase difference signal D is supplied to a non-inverted input terminal (+) of an operational amplifier 31 through an AND circuit 25, an OR circuit 27, and a low pass filter 29, a positive-polarity tracking error control signal shown by a solid line B is attained. When the spot is moved to the inside of a line l1, the tracking error control area is extended practically by components indicated by solid lines B and D similarly, that is, a hysteresis characteristic is given to the tracking error control signal; and thus, the spot is prevented from being moved to another track by noise, external impact, or the like. |
