| 摘要 |
PURPOSE:To attain stable control of a tracking error signal by delivering a signal obtained by delaying the output of a photodetecting element corresponding to a preceding beam and a signal corresponding to the difference of the output of a photodetecting element corresponding to a following beam as error signals. CONSTITUTION:In a normal working mode the output A' of a variable delay element 8 is supplied selectively as a positive phase input of a differential amplifier 6. Here no time difference exists between the output A' and the adverse phase input of the amplifier 6. Therefore the disturbance of waveforms having substantially same phases, if produced to outputs A' and B due to the injuries on a recording surface, can be eliminated by the amplifier 6. This reduces the disturbance level of a signal K (A'-B) which is delivered from the amplifier 6 as a tracking error signal. In addition, the level of noises due to mixture of the RF signal component is also reduced. This secures the stable tracking control.
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