| 摘要 |
PURPOSE:To prevent a tracking servo system oscillating phenomenon by providing a negative fly-back loop at an amplifier to drive a tracking member. CONSTITUTION:The light reflected by a pre-group 2 is made incident through an objective lens 5 and a beam splitter 8 onto light detecting devices 9 and 10. The output of the light detecting devices 9 and 10 is inputted to a differential amplifier 11, a far field tracking error signal is obtained to the output of the differential amplifier 11 and through an equalizer 12, an adder 13 and a driving amplifier 14, a tracking driving device 6 is driven and controlled. In such a case, a tracking position detecting device 7 detects the position of the radial direction of an objective lens 5. A filter 15 and an amplifier 16 is provided. In order to operate a fly-back system, a switch 17 is set to an ON position, a differential circuit is used as the filter 15 and then, the oscillating character of the radial direction of the objective lens 5 comes to be the characteristic with an effective damping and the gain of the positive fly-back comes to be <='1'.
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