| 摘要 |
PROBLEM TO BE SOLVED: To realize an easy digital solving method especially using the direct interpolation between samples for calculating a positional error of a beam by making a track of a rotating movable carrier to the reference, particularly in the case the maximum frequency of a band required for information is equal to a half of the sampling frequency. SOLUTION: A secondary signal A+C, (B+D) passing through the sampling and the filtering by a filter LPF (the cut-off frequency is 1/4 of the sampling frequency at the most) is produced from the signals A to D which are outputted from a photodetector while being corresponded to the beam reflected by the movable carrier. The phase deviation between these signals shows the positional deviation TE of the beam with respect to the track of the carrier. In the decision of a phase deviation value, the attainment to sort at least one pair of samples ECHm, ECHM at the outside of the range +TH as to each of signals A+C and B+D and to discriminate two transitions ECH12, 20 such that the direction crossing with the threshold SE is the same and the threshold SE is the reference, the decision of two transitions by means of interpolating from the sorted sample and the decision of time difference Ti between these two transitions, are included.
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