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ip changer software free download full versionThis invention relates to an optical pickup for use with an optical disk recording and reproducing apparatus and more particularly to a focus servo control technique.
Generally, the laser beam from the light source of an optical pickup is focused on the optical disk in order to read data recorded on the disk or to record data on the disk. The light source, the objective lens and other component parts of the optical pickup constitute an optical system of the pickup. The pickup includes a photodetector which detects the light reflected by the disk.
The focus of the pickup is controlled on the basis of the output of the photodetector and also on the basis of the signal supplied from the disk drive.
The focus error detection is performed by making use of a diffraction grating which is formed on the disk or on the objective lens.
In general, it is difficult to adjust the focus of the pickup while the disk is rotating. Accordingly, a focus servo control method has been developed which makes use of the fact that the focus error signal changes depending on the rotation of the disk and makes the pickup focus on the disk by detecting the change of the focus error signal. In the focus servo control method, the focus servo control is performed on the basis of the zero-cross points of the focus error signal. In order to determine the zero-cross points accurately, the rotational speed of the disk is determined, and an optimum focus error signal is selected from a plurality of focus error signals obtained at different rotational speeds.
However, this focus servo control method requires much time for determining the zero-cross points accurately and further the optical pickup has to be stopped in order to perform the adjustment of the zero-cross points.
Further, even when a certain zero-cross point is determined accurately, if the rotational speed of the disk varies during the period of the focus error signal, the zero-cross point varies accordingly. Accordingly, it is impossible to obtain an optimum focus error signal and the focus servo control operation is performed in the worst case.# RUN: yaml2obj %s > %t.o
# RUN: llvm ac619d1d87
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