Wobble signal demodulation method and wobble signal demodulator
Pseudo synchronization due to crosstalk is detected with a small circuit scale in decoding address information from an MSK-modulated wobble signal. An MSK mark detection unit detects MSK marks periodically placed as synchronization signals in a wobble signal. A first synchronization state determination unit determines synchronization establishment with a detection position of each MSK mark as a reference, or out-of-synchronization. A prediction timing generation unit periodically generates a timing at which each MSK mark is to be detected based on the synchronization position after the establishment of synchronization. A second synchronization state determination unit compares a detection timing with the prediction timing, after the MSK mark is detected at a predetermined position within a period a predetermined number of times in succession, and determines the synchronization position as a pseudo synchronization position due to crosstalk on condition that there is a shift between the detection timing and the prediction timing.
1 . A wobble signal demodulation method, comprising;
reading an MSK (Minimum Shift Keying)-modulated wobble signal from an optical recording disc having a track formed therein corresponding to the wobble signal;
detecting MSK marks periodically placed as a synchronization signal, from the wobble signal read;
establishing synchronization with a detection position of each of the MSK marks detected being set as a synchronization position;
continuously detecting the MSK marks after the establishment of synchronization and periodically generating a prediction timing indicating a timing at which each of the MSK marks is to be detected, based on the synchronization position;
comparing a timing at which each of the MSK marks is detected, with the prediction timing corresponding to the timing, after each of the MSK marks is detected at a predetermined position within a period a predetermined number of times in succession; and
determining, based on a result of the comparison, the synchronization position as a crosstalk pseudo synchronization position due to crosstalk, on condition that there is a shift between the timing and the prediction timing.
2 . The wobble signal demodulation method according to claim 1 , further comprising:
decoding address information provided in a position with a position of the synchronization signal within the period being used as a reference, based on the synchronization position, the address information indicating a physical position on the optical recording disc; and
correcting the synchronization position according to a direction and an amount of the shift obtained by the comparison, when the crosstalk pseudo synchronization position is determined, so as to obtain a normal synchronization position, and decoding the address information based on the normal synchronization position.
3 . A wobble signal demodulator, comprising:
a reading unit to read an MSK (Minimum Shift Keying)-modulated wobble signal from an optical recording disc having a track formed therein corresponding to the wobble signal;
an MSK mark detection unit to detect MSK marks periodically placed as a synchronization signal, from the wobble signal read by the reading unit;
a first synchronization state determination unit to determine, based on a detection result of the MSK mark detection unit, one of a synchronization locked state in which synchronization is established with a detection position of each of the MSK marks being set as a synchronization position, and an out-of-synchronization state in which out-of-synchronization occurs;
a prediction timing generation unit to periodically generate a prediction timing indicating a timing at which each of the MSK marks is to be detected, based on the synchronization position in the synchronization locked state; and
a second synchronization state determination unit to compare a timing at which each of the MSK marks is detected, with the prediction timing generated by the prediction timing generation unit so as to correspond to the timing, after each of the MSK marks is detected at a predetermined position within a period a predetermined number of times in succession by the MSK mark detection unit, and to determine, based on a result of the comparison, the synchronization position as a crosstalk pseudo synchronization position due to crosstalk, on condition that there is a shift between the timing and the prediction timing.
4 . The wobble signal demodulator according to claim 3 , further comprising a decoding unit to decode address information provided in a position with a position of the synchronization signal within the period being used as a reference, based on the synchronization position, the address information indicating a physical position on the optical recording disc, wherein:
the second synchronization state determination unit outputs, to the decoding unit, shift information indicative of a direction and an amount of the shift obtained by the comparison, when the crosstalk pseudo synchronization position is determined; and
the decoding unit corrects the synchronization position based on the shift information output from the second synchronization state determination unit so as to obtain a normal synchronization position, and decodes the address information based on the normal synchronization position.
5 . The wobble signal demodulator according to claim 3 , further comprising a stability determination counter to increment a count value when a detection position of the MSK mark currently detected by the MSK mark detection unit and the detection position previously detected are the same within the period, and to reset the count value when the detection position currently detected and the detection position previously detected are different from each other, in the synchronization locked state,
wherein the second synchronization state determination unit determines whether the synchronization position corresponds to the crosstalk pseudo synchronization position, after the count value of the stability determination counter reaches a predetermined threshold value.
6 . The wobble signal demodulator according to claim 4 , further comprising a stability determination counter to increment a count value when a detection position of the MSK mark currently detected by the MSK mark detection unit and the detection position previously detected are the same within the period, and to reset the count value when the detection position currently detected and the detection position previously detected are different from each other, in the synchronization locked state,
wherein the second synchronization state determination unit determines whether the synchronization position corresponds to the crosstalk pseudo synchronization position, after the count value of the stability determination counter reaches a predetermined threshold value.
7 . The wobble signal demodulator according to claim 3 , wherein:
the MSK mark detection unit detects, in the synchronization locked state, the MSK marks within a detection window serving as a section with a predetermined length and including the prediction timing generated by the prediction timing generation unit; and
the first synchronization state determination unit determines, in the synchronization locked state, the out-of-synchronization state on condition that the number of times the MSK mark detection unit fails to detect the MSK marks within the detection window reaches a predetermined threshold value.
8 . The wobble signal demodulator according to claim 4 , wherein:
the MSK mark detection unit detects, in the synchronization locked state, the MSK marks within a detection window serving as a section with a predetermined length and including the prediction timing generated by the prediction timing generation unit; and
the first synchronization state determination unit determines, in the synchronization locked state, the out-of-synchronization state on condition that the number of times the MSK mark detection unit fails to detect the MSK marks within the detection window reaches a predetermined threshold value.
9 . The wobble signal demodulator according to claim 5 , wherein:
the MSK mark detection unit detects, in the synchronization locked state, the MSK marks within a detection window serving as a section with a predetermined length and including the prediction timing generated by the prediction timing generation unit; and
the first synchronization state determination unit determines, in the synchronization locked state, the out-of-synchronization state on condition that the number of times the MSK mark detection unit fails to detect the MSK marks within the detection window reaches a predetermined threshold value.
10 . The wobble signal demodulator according to claim 6 , wherein:
the MSK mark detection unit detects, in the synchronization locked state, the MSK marks within a detection window serving as a section with a predetermined length and including the prediction timing generated by the prediction timing generation unit; and
the first synchronization state determination unit determines, in the synchronization locked state, the out-of-synchronization state on condition that the number of times the MSK mark detection unit fails to detect the MSK marks within the detection window reaches a predetermined threshold value.