Differential phase error detector using dual arm correlation for servo tracking in an optical disk storage device
First Claim
1. In an optical storage device for recording digital data, a differential phase error detector for generating a tracking error signal in response to a light-beam reflected off of an optical storage medium, the light-beam generated by an optical transducer, the differential phase error detector comprising:
- (a) a photodetector, responsive to the light-beam, for generating a first and second position signals S1 and S2; and
(b) a correlator for correlating the first and second position signals S1 and S2 to generate a position error signal indicative of the optical transducer'"'"'s position relative to a centerline of a selected trackwherein;
the first and second position signals S1 and S2 are discrete-time signals S1(n) and S2(n); and
the correlator computes a correlation corr(Δ
) according to ##EQU5## where L is an integer representing the length of the correlation and Δ
is an integer representing a time shift between S1(n) and S2(n).
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Abstract
In an optical disk storage device, a differential phase detector is disclosed for generating a position error signal independent of the frequency content of the recorded data. A pair if diagonal signals S1 and S2 are generated by adding a pair of respective quadrants of a four-quadrant photodetector, where the phase offset between the diagonal signals represents the position error of the pit image as it passes over the photodetector. The position error is determined in the present invention by computing the difference between a positive and negative correlation of the diagonal signals S1 and S2, otherwise referred to as a dual arm correlation (DAC) ##EQU1## where Δ is the correlation offset and L is the correlation length. In the preferred embodiment, the correlation offset Δ is adaptively adjusted to maximize the correlation between S1 and S2. In this manner, the position error estimate is substantially insensitive to the frequency content of the recorded data. Furthermore, this method extends the position error over a range of plus or minus one-half a track, which facilitates generating a quadrature signal for use in counting track crossings during seek operations.
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Citations
27 Claims
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1. In an optical storage device for recording digital data, a differential phase error detector for generating a tracking error signal in response to a light-beam reflected off of an optical storage medium, the light-beam generated by an optical transducer, the differential phase error detector comprising:
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(a) a photodetector, responsive to the light-beam, for generating a first and second position signals S1 and S2; and (b) a correlator for correlating the first and second position signals S1 and S2 to generate a position error signal indicative of the optical transducer'"'"'s position relative to a centerline of a selected track wherein; the first and second position signals S1 and S2 are discrete-time signals S1(n) and S2(n); and the correlator computes a correlation corr(Δ
) according to ##EQU5## where L is an integer representing the length of the correlation and Δ
is an integer representing a time shift between S1(n) and S2(n). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. In an optical storage device for recording digital data, a differential method of detecting a phase error for generating a tracking error signal in response to a light-beam reflected off of an optical storage medium, the light-beam generated by an optical transducer, the method comprising the steps of:
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(e) detecting a first and second position signals S1 and S2 from the light-beam; and (f) correlating the first and second position signals S1 and S2 to generate a position error signal indicative of the optical transducer'"'"'s position relative to a centerline of a selected track wherein; the first and second position signals S1 and S2 are discrete-time signals S1(n) and S2(n); and the step of correlating comprises the step of computing a correlation corr(Δ
) according to ##EQU8## where L is an integer representing the length of the correlation and Δ
is an integer representing a time shift between S1(n) and S2(n). - View Dependent Claims (16, 17, 18, 19, 20)
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21. In an optical storage device for recording digital data, a differential phase error detector for generating a tracking error signal in response to a light-beam reflected off of an optical storage medium, the light-beam generated by an optical transducer, the differential phase error detector comprising:
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(a) a photodetector, responsive to the light-beam, for generating a first and second position signals S1(n) and S2(n); and (b) a correlator for correlating the discrete-time position signals S1(n) and S2(n) to generate a position error signal indicative of the optical transducer'"'"'s position relative to a centerline of a selected track, the correlator computing a correlation value corr(Δ
) according to;
##EQU9## where L is an integer representing the length of the correlation and Δ
is an integer representing a time shift between S1(n) and S2(n). - View Dependent Claims (22, 23, 24)
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25. In an optical storage device for recording digital data, a differential phase error detector for generating a tracking error signal in response to a light-beam reflected off of an optical storage medium, the light-beam generated by an optical transducer, the differential phase error detector comprising:
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(i) a photodetector, responsive to the light-beam, for generating four quadrant analog signals; (j) at least one sampling device for sampling the four quadrant analog signals to generate four quadrant discrete signals; (k) a first summing circuit for summing a first two of the four quadrant discrete signals to generate a first discrete position signal S1(n); (l) a second summing circuit for summing a second two of the four quadrant discrete signals to generate a second discrete position signal S2(n); and (m) a discrete time phase offset detector for detecting a phase offset between the first and second discrete position signals S1(n) and S2(n) wherein; the discrete time phase offset detector comprises a correlator for correlating the first and second discrete position signals to generate the phase offset; and the correlator computes a correlation value corr(Δ
) according to;
##EQU10## where L is an integer representing the length of the correlation and Δ
is an integer representing a time shift between S1(n) and S2(n). - View Dependent Claims (26, 27)
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Specification