Tracking error correction apparatus utilizing phase difference information derived from four photocells
First Claim
1. An optical information reproducing apparatus for optically reading an information recorded as a succession of pits formed on an information track on a recording medium, comprising:
- means for forming a light spot on said recording means;
converging means for collecting a reflected light from said light spot to form a far field image of said light spot;
a photodetector for receiving said far field image, said photodetector comprising first through fourth photocells respectively disposed at first through fourth quadrants defined by a first straight line parallel to a direction in which said information track is projected and a second straight line perpendicular to said first straight line, where said first straight line defines a border between said first and fourth quadrants and between said second and third quadrants, and said second straight line defines a border between said first and second quadrants and between said third and fourth quadrants;
means for producing an information signal corresponding to said information from an output signal of said photodetector;
tracking error detecting means comprising;
first delaying means for delaying an output signal of said first photocell for a specified time;
second delaying means for delaying an output signal of said second photocell for said specified time;
first adding means for adding an output signal of said first delaying means and an output signal of said third photocell;
second adding means for adding an output signal of said second delaying means and an output signal of said fourth photocell; and
phase comparison means for producing, as a tracking error signal, a phase difference signal corresponding to a difference of phases of output signals of said first and second adding means; and
means responsive to said tracking error signal for driving said light spot forming means to correct a tracking error.
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Accused Products
Abstract
Disclosed herein is an optical information reproducing apparatus having a phase difference tracking system which is free from an influence of a tangential phase difference of output signals from a photodetector. The photodetector comprises first through fourth photocells which are respectively disposed at first through fourth quadrants defined by a first straight line parallel to an information track image and a second straight line perpendicular to the first straight line. Output signals of the first and second photocells are delayed for a specified time by respective first and second delaying circuits. Output signals of the first delaying circuit and the third photocell are added by a first adder, and output signals of the second delaying circuit and the fourth photocell are added by a second adder. A phase comparator produces a tracking error signal from a phase difference between output signals of the first and second adders. Alternatively, a first phase comparator produces a phase difference between the output signals of the first and second photocells, and/or a second comparator produces a phase difference between the output signals of the third and fourth photocells. At least one of output signals of the first and second comparator is used for producing a tracking error signal.
38 Citations
10 Claims
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1. An optical information reproducing apparatus for optically reading an information recorded as a succession of pits formed on an information track on a recording medium, comprising:
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means for forming a light spot on said recording means; converging means for collecting a reflected light from said light spot to form a far field image of said light spot; a photodetector for receiving said far field image, said photodetector comprising first through fourth photocells respectively disposed at first through fourth quadrants defined by a first straight line parallel to a direction in which said information track is projected and a second straight line perpendicular to said first straight line, where said first straight line defines a border between said first and fourth quadrants and between said second and third quadrants, and said second straight line defines a border between said first and second quadrants and between said third and fourth quadrants; means for producing an information signal corresponding to said information from an output signal of said photodetector; tracking error detecting means comprising;
first delaying means for delaying an output signal of said first photocell for a specified time;
second delaying means for delaying an output signal of said second photocell for said specified time;
first adding means for adding an output signal of said first delaying means and an output signal of said third photocell;
second adding means for adding an output signal of said second delaying means and an output signal of said fourth photocell; and
phase comparison means for producing, as a tracking error signal, a phase difference signal corresponding to a difference of phases of output signals of said first and second adding means; andmeans responsive to said tracking error signal for driving said light spot forming means to correct a tracking error. - View Dependent Claims (2, 3, 4, 5)
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6. An optical information reproducing apparatus for optically reading an information recorded as a succession of pits formed on an information track on a recording medium, comprising:
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means of forming a light spot on said recording means; converging means for collecting a reflected light from said light spot to form a far field image of said light spot; a photodetector for receiving said far field image, said photodetector comprising first through fourth photocells respectively disposed at first through fourth quadrants defined by a first straight line parallel to a direction in which said information track is projected and a second straight line perpendicular to said first straight line, where said first straight line defines a border between said first and fourth quadrants and between said second and third quadrants, and said second straight line defines a border between said first and second quadrants and between said third and fourth quadrants; means for producing an information signal corresponding to said information from an output signal of said photodetector; tracking error detecting means for producing a tracking error signal from at least one of a phase difference between output signals of said first and second photocells and a phase difference between output signals of said third and fourth photocells; and means responsive to said tracking error signal for driving said light spot forming means to correct a tracking error. - View Dependent Claims (7, 8, 9, 10)
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Specification