METHOD AND APPARATUS OF REPRODUCING MULTILEVEL INFORMATION

Abstract

In a method of reproducing multilevel information, cell-boundary values are obtained. Each of the cell-boundary values is obtained when the center of a light spot comes at a boundary between adjacent cells. Then, on the basis of the cell-boundary values and prestored reference values for the cell-boundary value, cell-boundary-value metrics are calculated. Furthermore, on the basis of the cell-boundary-value metrics, path metrics are calculated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining widths in a direction of tracks and corresponding combinations of 3 bits based on different levels of multilevel information pits.

FIG. 2 is a diagram for explaining a distribution of the amplitudes of cell-center values.

FIG. 3 is a diagram for explaining positional relationship between preceding and succeeding cells and a light spot in a case where a cell-center value is being sampled.

FIG. 4 is a diagram for explaining positional relationship between preceding and succeeding cells and a light spot in a case where a cell-boundary value is being sampled.

FIG. 5 is a histogram showing results of simulation of the levels of reproduced signals of cell-center values before waveform equalization in a case where 8-ary multilevel data is reproduced.

FIG. 6 is a histogram showing results of simulation of the levels of reproduced signals of cell-boundary values before waveform equalization.

FIG. 7 is a block diagram of an optical disk drive according to a first embodiment of the present invention.

FIGS. 8A and 8B are diagrams showing a binary-to-multilevel converter circuit in the first embodiment.

FIG. 9 is a diagram showing a convolutional encoder in the first embodiment.

FIG. 10 is a table showing bit conversion by a mapping circuit in the first embodiment.

FIG. 11 is a table for converting binary data to 8-ary data by the binary-to-multilevel converter circuit in the first embodiment.

FIG. 12 is a diagram showing sampling points relevant to processing executed by a multilevel-data determining circuit in the first embodiment.

FIG. 13 is a block diagram showing the configuration of the multilevel-data determining circuit in the first embodiment.

FIG. 14 is a diagram showing a cell-center-value-metric calculating circuit and a minimum-cell-center-value-metric selecting circuit in the first embodiment.

FIG. 15 is a table showing an example of reference values used in the cell-center-value-metric calculating circuit.

FIG. 16 is a diagram showing a cell-boundary-value-metric calculating circuit and a minimum-cell-boundary-value-metric selecting circuit in the first embodiment.

FIGS. 17A to 17D show tables showing examples of reference values used in the cell-boundary-value-metric calculating circuit.

FIG. 18 is a diagram showing a branch-metric calculating circuit in the first embodiment.

FIG. 19 is a diagram showing combinations of multilevel values of left and right cells of cell-boundary values.

FIG. 20 is a trellis diagram corresponding to a convolutional encoder in the first embodiment.

FIG. 21 is a diagram showing an example of state transition in the trellis diagram corresponding to the convolutional encoder in the first embodiment.

FIG. 22 is a table showing decoded information and associated branch metrics in the first embodiment.

FIG. 23 is a diagram showing a binary-to-multilevel converter circuit in a second embodiment of the present invention.

FIG. 24 is a diagram showing the relationship between multilevel values of cell-center values and cell-boundary values in the form of a convolutional encoder.

FIG. 25 is a diagram showing sampling points where processing is executed by a multilevel-data determining circuit in the second embodiment.

FIG. 26 is a block diagram showing the configuration of the multilevel-data determining circuit in the second embodiment.

FIG. 27 is a trellis diagram in the second embodiment.

FIG. 28 is a trellis diagram showing results of calculation of branch metrics in the second embodiment.

FIG. 29 is a trellis diagram showing results of calculation of path metrics in the second embodiment.

FIG. 30 is a trellis diagram showing results of calculation of path metrics in the second embodiment.

FIG. 31 is a trellis diagram showing results of calculation of path metrics in the second embodiment.

FIG. 32 is a block diagram showing the configuration of a multilevel-data determining circuit in a third embodiment of the present invention.

FIG. 33 is a trellis diagram of the multilevel-data determining circuit in the third embodiment.

FIG. 34 is a trellis diagram showing results of calculation of path metrics by the multilevel-data determining circuit in the third embodiment.

Claims

1. A method of reproducing multilevel information using a light spot, the multilevel information being recorded by defining virtual cells at regular intervals on tracks of an optical information recording medium and varying sizes of information pits in the cells, the method comprising the steps of: obtaining cell boundary values, each of the cell boundary values being obtained by performing sampling when the center of the light spot reaches a boundary between adjacent cells;calculating cell boundary value metrics on the basis of the cell boundary values and prestored reference values for the cell boundary values; andcalculating path metrics on the basis of the cell boundary value metrics.

2. The method according to claim 1, wherein, in the step of calculating the cell boundary value metrics, with a plurality of successive cells being considered as a unit, possible values of individual cell boundary values are classified as even numbers or odd numbers, and in each combination of the even numbers and/or the odd numbers, metrics are calculated for the individual cell boundary values on the basis of the cell boundary values and the reference values associated with the combination, calculation is performed using the metrics of the cell boundaries, and a minimum value among results of the calculation is selected and output.

3. The method according to claim 1, further comprising the steps of: calculating cell center value metrics on the basis of cell center values and prestored reference values for the cell center values, each of the cell center values being obtained by performing sampling when the light spot reaches the center of a cell; andcalculating branch metrics on the basis of the cell center value metrics and the cell boundary value metrics associated with the cell center value metrics;wherein, in the step of calculating the path metrics, the path metrics are calculated on the basis of the branch metrics.

4. The method according to claim 3, wherein, in the step of calculating the cell center value metrics, with a plurality of cells being considered as a unit, possible values of the individual cell center values in the unit are classified as even numbers or odd numbers, and in each combination of the odd numbers and/or the even numbers, metrics are calculated for the individual cell center values on the basis of the cell center values and the reference values associated with the combination, calculation is performed using the metrics of the cell centers, and a minimum value among results of the calculation is selected and output.

5. The method according to claim 3, wherein the cell boundary value metric associated with the cell center value metric is calculated on the basis of either one of the cell boundary values sampled at the cell boundaries of the cell having the cell center associated with the cell center value metric, which is calculated on the basis of the cell center value sampled at the cell center.

6. An apparatus for reproducing multilevel information using a light spot, the multilevel information being recorded by defining cells at regular intervals on tracks of an optical information recording medium and varying sizes of information pits in the cells, the apparatus comprising: an optical head with a photodetector, the optical head producing a light spot; anda multilevel data determining circuit, wherein said multilevel data determining circuit obtains cell boundary values, each of the cell boundary values being obtained by performing sampling when the center of the light spot reaches a boundary between adjacent cells, said multilevel data determining circuit calculating cell boundary value metrics on the basis of the cell boundary values and prestored reference values for the cell boundary values, and said multilevel data determining circuit calculates path metrics on the basis of the cell boundary value metrics.

7. An apparatus according to claim 6, wherein said multilevel data determining circuit calculates the cell boundary value metrics with a plurality of successive cells considered as a unit, possible values of individual cell boundary values are classified as even numbers or odd numbers, and in each combination of the even numbers and/or the odd numbers, said multilevel data determining circuit calculates metrics for the individual cell boundary values on the basis of the cell boundary values and the reference values associated with the combination, the calculation being performed using the metrics of the cell boundaries, said multilevel data determining circuit further selecting and outputting a minimum value among the results of the calculation.

8. The apparatus according to claim 6, wherein said multilevel data determining circuit further calculates cell center value metrics on the basis of cell center values and prestored reference values for the cell center values, each of the cell center values being obtained by performing sampling when the light spot reaches the center of a cell, and wherein said multilevel data determining circuit calculates branch metrics on the basis of the cell center value metrics and the cell boundary value metrics associated with the cell center value metrics.

9. An apparatus according to claim 8, wherein said multilevel data determining circuit calculates the cell center value metrics with a plurality of successive cells considered as a unit, possible values of individual cell center values in the unit are classified as even numbers or odd numbers, and in each combination of the even numbers and/or the odd numbers, said multilevel data determining circuit calculates metrics for the individual cell center values on the basis of the cell center values and the reference values associated with the combination, the calculation being performed using the metrics of the cell centers, said multilevel data determining circuit further selecting and outputting a minimum value among the results of the calculation.

10. The apparatus according to claim 8, wherein the cell boundary value metric associated with the cell center value metric is calculated by said multilevel data determining circuit on the basis of either one of the cell boundary values sampled at the cell boundaries of the cell having the cell center associated with the cell center value metric, which is calculated on the basis of the cell center value sampled at the cell center.

11. The apparatus according to claim 6, wherein said optical head can record the multilevel information on the optical information recording medium.

12. An apparatus for reproducing multilevel information using a light spot, the multilevel information being recorded by defining cells at regular intervals on tracks of an optical information recording medium and varying sizes of information pits in the cells, the apparatus comprising: means for obtaining cell boundary values based on a sampling when the center of the light spot reaches a boundary between adjacent cells;means for calculating cell boundary value metrics on the basis of the cell boundary values and prestored reference values for cell boundary values; andmeans for calculating path metrics on the basis of the cell boundary value metrics.

13. The apparatus according to claim 12, wherein said means for calculating cell boundary metrics uses a plurality of successive cells being considered as a unit, possible values of individual cell boundary values are classified as even numbers or odd numbers, and in each combination of the even numbers and/or the odd numbers, said means for calculating cell boundary metrics calculates metrics for the individual cell boundary values on the basis of the cell boundary values and the reference values associated with the combination, the calculation being performed using the metrics of the cell boundaries, said means for calculating cell boundary metrics further selects and outputs a minimum value among the results of the calculation.

14. The apparatus according to claim 12, further comprising: means for calculating cell center value metrics on the basis of cell center values and prestored reference values for the cell center values;means for calculating branch metrics on the basis of the cell center value metrics and cell boundary value metrics associated with the cell center value metrics; andmeans for calculating path metrics on the basis of the branch metrics.

15. The apparatus according to claim 14, wherein said means for calculating cell center value metrics uses a plurality of successive cells considered as a unit, possible values of individual cell center values are classified as even numbers or odd numbers, and in each combination of the even numbers and/or the odd numbers, said means for calculating cell center value metrics calculates metrics for the individual cell center values on the basis of the cell center values and the reference values associated with the combination, the calculation being performed using the metrics of the cell center, said means for calculating cell center value metrics further selects and outputs a minimum value among the results of the calculation.

16. The apparatus according to claim 14, wherein the cell boundary value metric associated with the cell center value metric is calculated by said means for calculating cell boundary value metrics on the basis of either one of the cell boundary values sampled at the cell boundaries of the cell having the cell center associated with the cell center value metric which is calculated on the basis of the cell center value sampled at the cell center.

17. The apparatus according to claim 12, further comprising means for recording the multilevel information on an optical information recording medium.