| 摘要 |
PURPOSE:To control a tracking phase by a negative feedback loop similarly to the stable point by enabling the pseudo stable point to be detected and by inverting the control polarity of the tracking phase. CONSTITUTION:In case of descent into the pseudo stable point, either one of the signals of the frequencies of 2fH, 4fH is extracted by a band-pass filter 27 from a mixed output of a reference signal R and a pilot signal P of a reproduc ing track. After detection at a level detector 28, a waveform shaping is performed at a Schmitt trigger circuit 29 and the connecting state of a switch 30 is changed over. In case of descent into the pseudo stable point, the switch 30 selects an output pulse (-SWP) of an inversion circuit 31 and otherwise, selects a head switching pulse (SWP). At the pseudo stable point, the relation of the frequency of the differential frequency signals relative to the leading and lagging of the tracking phase is the reverse to that of the stable point. In such a case, the stable point can be obtained by reversing the relation of the two without moving the relative position between the track and the head even though there is caused the descent into the pseudo stable point.
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