JP2006236441A - Method and apparatus for recording and reproducing multi-level information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine multi-level information by simultaneously using a reproducing signal having a small influence of intercode interference rather than determining multi-level information only from a cell center value sampled at the center of a conventional cell. <P>SOLUTION: Cell multi-level information is judged by using both of a reproducing signal (value between cells) sampled when the center of an optical spot comes to a boundary between the cell and its subsequent cell and a reproducing signal (cell center value) sampled when the optical spot comes to the center of the cell. Thus, an erroneous detection is reduced, and a high-density multi-level recording/reproducing are performed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multilevel information recording / reproducing method and apparatus for recording or reproducing multilevel information on an information recording medium such as an optical disc, and more particularly to a multilevel data processing method capable of reducing a data error rate in multilevel data processing. is there.

  Conventionally, in an optical disk, binary digital data is formed on a spiral or concentric track by forming embossed uneven pits (ROM disk), holes in inorganic / organic recording films (recordable disk), and crystal state. (Phase change disk), magnetization direction (magneto-optical disk), etc. When reproducing these recorded data, a track is irradiated with a laser beam to detect a difference in intensity of reflected light, a difference in polarization direction due to the magnetic Kerr effect, and the like to obtain a reproduced RF signal. Then, binary data is detected from the obtained reproduction RF signal.

  In recent years, research and development for increasing the recording capacity of these optical discs has been promoted. As a technique for miniaturizing a light spot related to information recording / reproduction, the wavelength of a light source ranges from red (650 nm) to blue-violet (405 nm). ) Is becoming. The numerical aperture of the objective lens is also being increased from 0.6 or 0.65 to 0.85. On the other hand, a more efficient multilevel recording / reproducing technique using the same light spot size has been proposed.

  For example, as a multi-level recording / reproducing technique, the applicant of the present application disclosed in Japanese Patent Laid-Open No. 5-128530, the width of the information pit in the track direction on the information track of the optical information recording medium, and the light spot for reproducing the information pit. A recording method for recording multi-value information by combining the shift amounts in the track direction with respect to the detection signal, and a detection signal obtained from a light spot and a detection signal learned in advance when reproducing the multi-value recorded information pit. And a reproduction method for reproducing multi-value information based on the correlation between the two (Patent Document 1).

  In addition, in ISOM2003 (Write-once Disks for Multi-level Optical Recording: Proceedings Fr-Po-04), which is an international conference in the research on the optical disc field, a blue-violet light source (405 nm) and an optical system of NA 0.65 are used. For an optical disk with a track pitch of 0.46 μm, the width in the track direction of an area (hereinafter referred to as a cell) for virtually recording one information pit is set to 0.26 μm, and multilevel of 8 levels. An announcement has been made on recording and reproduction (Non-Patent Document 1).

  Eight-level information pits are recorded in each cell after being converted from binary data to eight levels when recording on an information recording medium. In the case of 8-level recording, one cell corresponds to 3-bit binary data. For example, for 3-bit information, as shown in FIG. 2, (0, 0, 0) is 0 level, (0, 0, 1) is 1 level, (0, 1, 0) is 2 level, ( (0, 1, 1) is 3 levels, (1, 0, 0) is 4 levels, (1, 0, 1) is 5 levels, (1, 1, 0) is 6 levels, (1, 1, 1) Corresponds to 7 levels.

  In addition, as shown in FIG. 2, for example, as shown in FIG. 2, the 8-level information pit is divided into 16 equal widths in the track direction of the cell, no information pit is recorded at level 0, and 1/16 is equivalent to 2/16 cells. , Level 2 is 4/16 cells wide, Level 3 is 6/16 cells wide, Level 4 is 8/16 cells wide, Level 5 is 10/16 cells wide, Level 6 is The width for 12/16 cells and the level 7 for 14/16 cells.

  The information pits thus selected are recorded randomly, the amount of reflected light is received by a photodetector, and the reproduction signal obtained from the multi-value information pits is obtained with the center of the light spot having a width in the cell track direction. When sampling is performed at the timing when it comes to the center, a distribution as shown in FIG. 3 is obtained as the amplitude of the reproduction signal for each level.

  Here, the amplitude of the reproduction signal when level 0 continues where no information pits are written is “1”, and the amplitude of the reproduction signal when level 7 information pits are continuously recorded. The size is standardized as “0”.

  The value of the reproduction signal corresponding to each level has a width because it receives an influence (intersymbol interference) from information pits written before and after the information pit of interest. As shown in FIG. 3, it can be seen that separation detection cannot be performed with a fixed threshold when the amplitude distribution of the reproduction signal and the adjacent level overlap.

In order to solve this problem, in the example of the announcement of ISO 2003, a reproduction signal from a pit row in which the value of the information pit of interest and the values of the information pits before and after the information are known is read and stored. (Learning) describes a method of separating and detecting a reproduction signal from an actual information pit and a recorded value (see a correlation).
Japanese Patent Laid-Open No. 5-128530 ISO2003 (Write-once Disks for Multi-level Optical Recording: Proceedings Fr-Po-04)

  In optical discs, level fluctuations and amplitude fluctuations occur due to various factors such as differences in reflectivity between various optical discs and differences in reproduction frequency characteristics between the inner and outer circumferences within a single optical disc. Therefore, even if the separation detection method as described above is used, the reproduced signal may be detected with an incorrect value.

In particular, if a blue-violet light source (405 nm) and an NA 0.85 optical system are used to reduce the light spot and aim to increase the density to about 30 Gbit / inch ² , the amount of inter-code interference increases further. The overlap of the amplitude distribution of the reproduction signal with respect to each level shown in FIG.

  An object of the present invention is to provide a multi-value information recording / reproducing method and apparatus capable of reducing false detection by determining multi-value information with higher accuracy than the conventional separation detection method and capable of high-density multi-value recording or reproduction. It is in.

  In order to achieve the above-mentioned object, the present invention uses a light spot to provide cells at virtually constant intervals on a track of an optical information recording medium, and the information pit width or information pit in the track direction is provided in the cell. In the multi-value information recording / reproducing method for recording or reproducing multi-value information by changing the area of the cell, the inter-cell value obtained by sampling the reproduction signal when the center of the light spot comes to the boundary between the cell and the subsequent cell. And multivalue information of the cell is determined based on both the cell median sampled at the cell center.

  In addition, the present invention provides an optical spot on a track of an optical information recording medium by using a light spot, and virtually changes the width of the information pit or the area of the information pit in the track direction. A multi-value information recording / reproducing apparatus for recording or reproducing multi-value information by means for detecting an inter-cell value obtained by sampling a reproduction signal when the center of the light spot comes to the boundary between a cell and a subsequent cell; Means for detecting a cell median value obtained by sampling a reproduction signal when the center of the light spot comes to the cell center, and means for determining multi-value information of the cell based on the inter-cell value and the cell median value. It is characterized by having.

  In the present invention, the number of cells is based on both the inter-cell value obtained by sampling the reproduction signal when the center of the light spot comes to the boundary between the cell and the subsequent cell and the cell median value sampled at the center of the cell. Determine value information. That is, erroneous detection is reduced by determining multi-level information using not only the cell median value but also the inter-cell value where the effect of intersymbol interference is slight.

  According to the present invention, the multi-value information is not determined only from the cell median sampled at the center of the conventional cell, but between the cells obtained at the boundary between the cell where the influence of intersymbol interference is slight and the subsequent cell. By simultaneously determining the multi-value information by using the value, it is possible to reduce erroneous detection and to perform high-density multi-value recording / reproduction.

  In addition, in the candidate value of the multi-value information obtained from the inter-cell value and the cell median value, the absolute value of the difference from the learning pattern information is calculated, and the multi-value information of the target cell is determined by comparing this. The accuracy of the multi-value information of the cell of interest can be improved.

  Further, by storing candidate values of multi-value information obtained from inter-cell values and cell median values in a cell series, and determining and correcting multi-value information of the cell of interest by constantly monitoring the mutual relationship, The accuracy of determination of the cell of interest can be improved.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram showing an embodiment of a multi-value information recording / reproducing apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes an optical disk as an information recording medium on which spiral or concentric tracks are formed, and 2 denotes a spindle motor that rotationally drives the optical disk 1. As described with reference to FIG. 2, this optical disk 1 is provided with cells at virtually constant intervals in the track direction, and the multi-value information is recorded and reproduced by changing the width of the information pit (or the area of the information pit) in the cell. It is.

  Reference numeral 3 denotes an optical head for recording or reproducing multi-value information with respect to the optical disc 1, and condenses laser light from a semiconductor laser as a light source with an objective lens and irradiates the optical disc 1 with a light spot. The reflected light from the optical disk 1 of the light spot is detected by a photodetector in the optical head 3 and sent to the operational amplifier circuit 4.

  The operational amplifier circuit 4 processes the signal of the photodetector of the optical head 3 to detect a focus error signal / tracking error signal for controlling the optical spot to scan along a desired track of the optical disc 1. . The servo circuit 5 performs focus control and tracking control by controlling the focus actuator / tracking actuator in the optical head 3 based on the signal. The servo circuit 4 controls the spindle motor 2 to control the rotation of the optical disk 1 such as constant linear velocity or constant angular velocity.

  When multi-value information is recorded on the optical disc 1, the binary data input 6 is converted into multi-value data by the multi-value conversion circuit 7, and a signal corresponding to the multi-value data is output by the modulation circuit 8. The laser drive circuit 9 drives the semiconductor laser in the optical head 3 according to the signal, and records a mark according to the multi-value information on the track of the optical disc 1.

  When reproducing multi-value information, a light spot for reproduction is irradiated onto the optical disk 1 from the optical head 3, and the reflected light is received by a photodetector. The detection signal is signal-processed by the operational amplifier circuit 4, the obtained signal is converted into a digital signal by the AD conversion circuit 10, and the cell median value / inter-cell value separation detection circuit 12 separates the cell median value and the cell-cell value. To do.

  These processes are performed using the clock generated by the PLL circuit 11. The cell median values separated by the cell median value / intercell value separation detection circuit 12 are subjected to waveform equalization processing by the cell median value waveform equalization circuit 13, and the intercell values are obtained by the intercell value waveform equalization circuit 14. Waveform equalization processing is performed. Then, the reference value of the learning table data is read from the learning memory 17, and the multi-value data determination circuit 15 determines the multi-value level based on both values as will be described later. Further, it is converted into binary data by the multi-value-to-binary conversion circuit 16 and outputted as a binary data output 18.

  Next, a method for reproducing multilevel information will be described in detail. As described above, the cell center value / inter-cell value separation detection circuit 12 detects the sampled digital signal separately into the cell center value and the inter-cell value. Here, the difference between the sampling positions of the cell median value and the inter-cell value and their characteristics will be described with reference to FIGS.

  FIG. 4 shows the positional relationship between the front and rear cells and the light spot when sampling the cell median value. As an example, the track pitch is 0.32 μm, the light spot size is 0.405 μm (wavelength 405 nm, the numerical aperture of the objective lens: NA 0.85), and the cell size is 0.2 μm. In this parameter, it is experimentally found that the cell median value of the target cell does not take the same value because the level of the preceding cell and the succeeding cell changes from 0 to 7, and has a width due to the influence of intersymbol interference. ing.

  This is intuitively understood from the fact that the bottom of the light spot on the middle cell in FIG. 4 is on the left and right cells. The influence of the intersymbol interference on the cell median value increases as the cell becomes smaller with respect to the size of the light spot.

  FIG. 5 shows the positional relationship when the light spot comes to the boundary between the left and right cells when sampling the inter-cell value. The width of two cells is 0.4 μm with respect to the light spot size of 0.405 μm, and most of the light spots are on the left and right cells. That is, the inter-cell values sampled at the boundary between the left and right cells have almost no influence from the outside, and the influence of intersymbol interference from the outside is smaller than that of the left and right cells.

  The cell median and intercell values as described above are obtained by sampling each of the cell median / intercell value separation detection circuit 12 with a clock synchronized with the multi-value data generated by the PLL circuit 11. The cell median sampling clock and the inter-cell sampling clock have the same frequency and are different in phase from each other by 1/2 period (one cell is defined as 1 period).

  Thereafter, waveform equalization is performed by the cell median value waveform equalization circuit 13 and the intercell value waveform equalization circuit 14 corresponding to the reproduction signals of the cell median value and the intercell value. First, the cell median waveform equalization circuit 13 will be described. The inter-symbol interference from the information pits written before and after the information pit reproduction signal focused by the cell median waveform equalization circuit 13 is suppressed. Here, an example of the effect of suppressing intersymbol interference will be described with reference to FIG.

  FIG. 6 uses a blue-violet light source (405 nm) and an optical system of NA 0.85, and the size of a cell for recording one information pit virtually provided on an optical disc having a track pitch of 0.32 μm is set to 0. This is a simulation result showing a histogram of the reproduction signal level of the cell median before and after waveform equalization when 8-level multilevel data is reproduced at 20 μm. FIG. 6A shows a cell median reproduction signal before waveform equalization, and FIG. 6B shows a cell median reproduction signal after waveform equalization. As can be seen from FIG. 6, the reproduced signal is subjected to waveform equalization, so that it is separated into 0 to 7 levels and can be easily detected as multi-value data.

  Next, the inter-cell value waveform equalization circuit 14 will be described. The inter-cell value waveform equalization circuit 14 suppresses intersymbol interference from information pits written on the left and right outer sides of the inter-cell values at the boundary between the left and right cells. Similar to the cell median value, an example of the effect of suppressing intersymbol interference will be described with reference to FIG.

  FIG. 7 is a simulation result showing a histogram of reproduction signal levels of inter-cell values before and after waveform equalization, and is calculated using the same parameters as in FIG. FIG. 7A shows a reproduction signal of inter-cell values before waveform equalization, and FIG. 7B shows a reproduction signal of inter-cell values after waveform equalization. As can be seen from FIG. 7, it is understood that the reproduction signal of the inter-cell value is separated into 15 values of 0 to 14 without applying signal processing such as waveform equalization. Of course, if the waveform equalization is performed, the degree of separation can be further increased. Here, the reason why the reproduction signal is separated into 15 values is that if the sum of the multi-levels in two adjacent cells is the same, the inter-cell value also takes the same level.

  This will be described with reference to FIG. FIG. 8 is a diagram showing combinations of multi-value levels of left and right cells of inter-cell values. There are a total of 8 × 8 = 64 combinations of the left and right cells, but the level that the reproduction signal of the inter-cell value can take is 15. That is, it can be seen that the sum of the left and right multi-value levels is the value of the inter-cell value.

  From this, if the multilevel level of the previous cell is known, the level of the subsequent cell can be uniquely determined by detecting the inter-cell value. For example, if the level of the previous cell is known as “3” and the inter-cell value is detected as “7”, the level of the subsequent cell can be determined as “4” from 7−3 = 4. Generally, the level of the previous cell is “X” (0 ≦ X ≦ 7, X is an integer), the level of the subsequent cell is “Y” (0 ≦ Y ≦ 7, Y is an integer), and the inter-cell value Is “Z” (0 ≦ Z ≦ 14, Z is an integer), X + Y = Z (or Z−X = Y).

  After the waveform equalization of the cell median value and the inter-cell value is performed in this way, the multi-value data determination circuit 15 outputs the multi-value data of the determination result. Output after being converted to value data.

  Next, a multi-value data determination method in the multi-value data determination circuit 15 will be described in detail with reference to FIGS. In this embodiment, it is assumed that 8-level multi-value data of 0 to 7 is reproduced. FIG. 9 is a diagram for explaining a multi-value data determination method in the multi-value data determination circuit 15. The multi-value data determination circuit 15 is mainly divided into a cell median value determination unit 19, an inter-cell value determination unit 20, and a final value determination unit 21.

  First, the cell median value determination unit 19 will be described. The cell median value determination unit 19 performs determination in consideration of three consecutive cells (preceding cell, target cell, and succeeding cell) as described with reference to FIG. The multi-value data determination circuit 15 starts an operation in step 1 when a cell median reproduction signal is input.

  Next, in step 2, the value of the preceding cell is determined (this selects the value of the cell of interest obtained in the previous step). For example, if the value of the target cell determined one step before is “7”, the value of the preceding cell is selected as “7” (here, “selection” is not a final determination but a temporary determination) Meaning decision). Alternatively, as a method of selecting the value of the preceding cell, the cell median reproduction signal (sampling value when the light spot is located at the center of the preceding cell) is determined by level slicing with a plurality of thresholds corresponding to each level. May be.

  Next, in step 3, the value of the succeeding cell is selected by level-slicing the reproduction signal of the cell median value (sampling value when the light spot is located at the center of the succeeding cell) (the closest value in the level slice). choose). For example, assume that the value of the succeeding cell is selected as “7”. Up to this point, the values of the preceding cell and the succeeding cell among the three continuous cells are selected.

  Next, in step 4, the value of the target cell closest to the reproduction signal of the cell median value is selected from the cell median value learning table (FIG. 10) using the values of the preceding cell and the succeeding cell. Further, in step 5, the second closest value is selected. In step 6, the values selected in steps 4 and 5 are determined as the first candidate “a” and the second candidate “b”, respectively.

  Steps 4 to 6 in the cell median value determination unit 19 will be described in more detail with reference to FIGS. FIG. 10 shows a learning table used for determination of multi-value data. FIG. 10A shows a cell median value learning table, in which all combinations that can be taken by the preceding cell, the target cell, and the succeeding cell and a table of all 512 patterns (8 × 8 × 8) are created. The 512 pattern information is recorded at the beginning of the user data area on the optical disc 1, and before reproducing the user data area information, a reproduction signal of the cell median value of the target cell of each pattern is detected and the sampling is performed. The value is stored in the learning memory 17 as a reference value.

  Next, a method for determining a candidate value of a target cell using the cell median value learning table in steps 4 to 6 in the cell median value determination unit 19 in FIG. 9 will be described with reference to FIG. First, in step 11, the operation is started. In step 12, the sampled cell median reproduction signal is sequentially input to the cell median determination unit. Further, the learning memory 17 is accessed in step 13, and each time the cell median value is input in step 14, the reference values obtained from the cell median learning table of FIG. .

  Here, since the value of the preceding cell and the succeeding cell is selected as “7” in the table to be read (refer to the description of FIG. 9), 8 patterns from all 512 patterns, that is, (7, 0, 7) to (7 , 7, 7). Next, in step 15, the absolute value of the difference between the cell median and the eight pattern reference values is calculated, and this is set as the M value. In step 16, the eight M values are compared, and when the value of the cell of interest is “a”, the M value (which is expressed as M (a)) is the smallest, and “a” is the cell median value. The determination unit 19 determines the first candidate value.

  Further, when the value of the cell of interest is “b”, the M value (represented as M (b)) is assumed to be the second smallest, and “b” is set as the second candidate value in the cell median value determination unit 19. decide. Then, it progresses to step 17 and complete | finishes operation. The above is the description of the cell median value determination unit 19.

  Next, returning to FIG. 9, a method for determining the value of the cell of interest in the inter-cell value determination unit 20 will be described in detail with reference to FIGS. 10 and 12. As shown in FIG. 9, the inter-cell value determination unit 20 uses the value of the preceding cell determined in step 2 in step 7, and pays attention to the reproduction signal of the inter-cell value from the inter-cell value learning table (FIG. 10). Select a cell value. Further, in step 8, the value selected in step 7 is determined as a candidate value “x”.

  Steps 7 and 8 in the inter-cell value determination unit 20 will be described in detail with reference to FIGS. FIG. 10B is an inter-cell value learning table in which all combinations that can be taken by the preceding cell and the cell of interest and a table of all 64 patterns (8 × 8) are created. Similarly, 64 patterns of information are recorded at the beginning of the user data area on the optical disc 1, and before reproducing the information of the user data area, the reproduction signal of the inter-cell value of the target cell of each pattern is detected, The sampling value is stored in the learning memory 17 as a reference value.

  Next, a method for determining a candidate cell candidate value using the inter-cell value learning table in steps 7 and 8 in the inter-cell value determination unit 20 in FIG. 9 will be described with reference to FIG. First, in step 18, the operation is started. In step 19, the sampled inter-cell value reproduction signal is sequentially input to the inter-cell value determination unit 20. In step 20, the learning memory 17 is accessed. In step 21, each time an intercell value is input, the reference value obtained from the intercell value learning table in FIG. Read sequentially.

  Here, since the value of the preceding cell is selected as “7” in the table to be read (see the description of FIG. 9), eight patterns out of all 64 patterns, that is, combinations of (7, 0) to (7, 7) It is narrowed down to. Next, in step 22, the absolute value of the difference between the inter-cell value and the 8-pattern reference value is calculated, and this is set as the M value. In step 23, the eight M values are compared, and when the value of the cell of interest is “x”, the M value (which is expressed as M (x)) is the smallest, and “x” is the inter-cell value. It is determined as a candidate value in the determination unit. Then, it progresses to step 24 and complete | finishes operation. The above is the description of the inter-cell value determination unit 20.

  Referring back to FIG. 9, the algorithm of the final value determination unit 21 that finally performs determination using the candidate values respectively obtained by the cell median value determination unit 19 and the inter-cell value determination unit 20 will be described with reference to FIGS. This will be described in detail with reference to FIG.

  FIG. 13 shows the flow of processing operations in the final value determination unit 21. First, in step 25, the operation is started. In step 26, “a”, “b”, “x”, which are candidates for the multi-value level, and M (a), M (b), M (x) corresponding to the M values are input. In step 27, the candidate values “a ′” and “x ′” selected in the preceding cell are read from the memory. “A ′” and “x ′” are obtained by storing “a” and “x” in the memory before the end of a series of final value determination operations one step before in step 30 described later. Using these parameters, the multilevel level of the target cell is finally determined in step 28, and then the multilevel level of the preceding cell is corrected in step 29. Further, after “a” and “x” are stored in the memory in step 30, the process proceeds to step 31 and the operation is terminated.

  Next, the algorithm of step 28 for finally determining the multi-value level of the cell of interest will be described in detail with reference to FIG. In step 32, the operation is started. Next, in step 33, consider the case where a = x. Since it is considered that the accuracy rate is considerably high, the process proceeds to step 35, the value of the cell of interest is determined to be “a”, and the operation is terminated in step 42. Next, proceeding to step 34, consider the case where a ≠ x and b = x.

  In this case, since it is difficult to determine whether the correct answer is “a” or “x”, it is necessary to determine in consideration of other parameters. In the present invention, M (a) and M (b) which are absolute values of differences between “a ′” and “x ′” which are candidate values selected one step before in the preceding cell and the reference value of the learning table. ), M (x) is considered as a parameter.

  Next, a method for making a determination in consideration of “a ′” and “x ′” in steps 36 to 39 will be described. The purpose of this is to further increase the accuracy of the determination of the attention cell by examining the relationship between the candidate value in the preceding cell and the candidate value in the attention cell. That is, when the determination result in the preceding cell is different from the actual correct value, it is inevitably used that the rule having a candidate value for the target cell and the preceding cell has. First, consider a case where x ′ is erroneously determined as the final value of the preceding cell.

  For example, when the correct value of the preceding cell and the target cell is “3”, when the candidate value a ′ of the preceding cell is “3” and x ′ is “2”, “2” of x ′ is erroneously finalized. When selected as the determination value, the candidate value of the target cell has a high probability that a is “3” and x is “4”. This is because, as described above, the level of the previous cell is “X” (0 ≦ X ≦ 7, X is an integer), and the level of the subsequent cell is “Y” (0 ≦ Y ≦ 7, Y is an integer). If the interval value is “Z” (0 ≦ Z ≦ 14, Z is an integer), the relationship X + Y = Z (or Z−X = Y) is established (in this case, Z = 6). ).

Expressing this in general terms,
(A−x) <0 and (a′−x ′)> 0... Step 36 or
(A−x)> 0 and (a′−x ′) <0... Step 37
It becomes.

  If Steps 36 and 37 are satisfied, there is a high possibility that “x” is wrong. Therefore, the target cell is finally determined as “a” in Step 35, and the operation ends in Step 42.

  Conversely, consider a case where a 'is erroneously determined as the final value of the preceding cell. Assuming that the correct value of the preceding cell and the target cell is “3”, when the candidate value a ′ of the preceding cell is “4” and x ′ is “3”, the final determination value is “4” of a ′ by mistake. If you select as In that case, the candidate value of the target cell has a high probability that a is “3” and x is “2”.

Expressing this in general terms,
(A−x)> 0 and (a′−x ′)> 0... Step 38 or
(A−x) <0 and (a′−x ′) <0... Step 39
It becomes.

  If Steps 38 and 39 are satisfied, there is a high possibility that “x” is erroneous. Therefore, the target cell is finally determined as “a” in Step 35, and the operation ends in Step 42. The above is a method for determining in consideration of “a ′” and “x ′”.

Further, if none of the conditions in Steps 36 to 39 is satisfied, the second method is determined in consideration of M (a), M (b), and M (x). That is,
| M (b) −M (a) | <e and M (a)> M (x)...
If the condition is satisfied, the target cell is finally determined as “x (= b)” in step 41. Here, e is a certain constant, and is preferably set to a value of 1/2 to 1/4 of the reproduction signal level difference of the cell median value between each of the multilevel levels.

  That is, when the condition of | M (b) −M (a) | <e is satisfied, it is very difficult to determine whether “a” or “b” from the reproduction signal of the cell median value. Considering finally the case of | M (b) −M (a) | = 0, the probability of whether the cell of interest is “a” or “b” is 50%. Therefore, if the condition of M (a)> M (x) is satisfied, it is determined that the cell of interest has a high probability of “x (= b)”, and the operation is terminated in step 42.

  Finally, let us consider a case where the conditions of Steps 33 and 34 are not satisfied (when a ≠ x and b ≠ x). Since it is highly possible that “x” is incorrect, the value of the cell of interest is determined as “a” in step 35, and the operation is terminated in step 42. This is because, in the case of multi-level recording, it is known from the simulation results that errors during reproduction are generally within ± 1 level (“a” or “b” is correct), and “x” is correct. This is because the probability is extremely low.

  Next, returning to FIG. 13, after finally determining the multilevel level of the target cell in step 28, the multilevel level of the preceding cell is corrected in step 29.

  FIG. 15 shows an algorithm for correcting the multilevel level of the preceding cell in step 29. First, in step 43, the operation is started. Next, in steps 44 to 47, as described with reference to FIG. 14, the value finally determined in the preceding cell is corrected by examining the relationship between the candidate value in the preceding cell and the candidate value in the target cell.

  That is, when a rule with a candidate value for the target cell and the preceding cell has, it is determined that the determination result in the preceding cell is different from the actual correct value. For example, when the correct value of the preceding cell and the target cell is “3”, when the candidate value a ′ of the preceding cell is “3” and x ′ is “2”, “2” of x ′ is erroneously finalized. When selected as the determination value, the candidate value of the target cell has a high probability that a is “3” and x is “4”.

Expressing this in general terms,
(A−x) <0 and (a′−x ′)> 0... Step 44 or
(A−x)> 0 and (a′−x ′) <0... Step 45
It becomes.

  Therefore, if Steps 44 and 45 are satisfied, the process proceeds to Step 48 where the preceding cell is corrected to “a ′” and the operation is terminated at Step 51. In this case, it is considered that the preceding cell is determined to be “2” of x ′, and is corrected to “3” of a ′.

  Conversely, consider a case where a 'is erroneously determined as the final value of the preceding cell. Assuming that the correct value of the preceding cell and the target cell is “3”, when the candidate value a ′ of the preceding cell is “4” and x ′ is “3”, the final determination value is “4” of a ′ by mistake. If you select as In that case, the candidate value of the target cell has a high probability that a is “3” and x is “2”.

Expressing this in general terms,
(A−x)> 0 and (a′−x ′)> 0... Step 46 or
(A−x) <0 and (a′−x ′) <0 Step 47,
It becomes.

  If Steps 46 and 47 are satisfied, the process proceeds to Step 49 where the preceding cell is corrected to “x ′”, and the operation is terminated at Step 51. In this case, it is considered that it is wrong to determine the preceding cell as “4” of a ′, and it is corrected to “3” of x ′.

  The above is the details of the final value determination unit in FIG. 13 and the determination method of multivalue data in the multivalue data determination circuit 15 which is a feature of the present invention.

  As a supplement, in the optical disc apparatus according to the present invention, an error correction data adding circuit for adding data for performing error correction to input binary data, and a synchronization signal for indicating a delimiter of a predetermined amount of data are provided. Although there is no mention of a synchronization signal addition circuit or the like to be added, the essence of the present invention is not changed at all. The above is the description of the multi-value information recording / reproducing method and apparatus for recording or reproducing multi-value information in the present invention.

It is a block diagram which shows one Embodiment of the multi-value information recording / reproducing apparatus which concerns on this invention. It is a figure explaining the combination of the width | variety of the track direction by the difference in the level of a multi-value information pit, and 3 bits corresponding to it. It is a figure explaining the amplitude distribution of a cell median. It is a figure explaining the positional relationship of the cell and light spot before and behind at the time of sampling the cell median. It is a figure explaining the positional relationship of the cell before and behind and the light spot at the time of sampling the value between cells. It is a figure which shows the simulation result which shows the histogram of the reproduction signal level of the cell median value before and after performing the waveform equalization in the case of reproducing multilevel data of 8 levels. It is a figure which shows the simulation result which shows the histogram of the reproduction signal level of the value between cells before and behind performing waveform equalization. It is a figure which shows the combination of the multi-value level of the cell on either side of the value between cells. It is a figure explaining the determination method of the multi-value data in a multi-value data determination circuit. It is a figure which shows the learning table used for determination of multi-value data, (a) is a cell median value learning table, (b) is a figure which shows an inter-cell value learning table. It is a figure explaining the method of determining the candidate value of the attention cell using the cell median value learning table of the cell median value determination part in FIG. It is a figure explaining the method of determining the candidate value of the attention cell using the intercell value learning table of the intercell value determination part in FIG. It is a figure explaining the algorithm of the final value determination part in FIG. It is a figure explaining the algorithm which determines the multi-value level of the attention cell in FIG. It is a figure explaining the algorithm which corrects the multi-value level of the preceding cell in FIG.

Explanation of symbols

1. Optical disc (information recording medium)
2 Spindle motor 3 Optical head 4 Operational amplifier circuit 5 Servo circuit 6 Binary data input 7 Multi-level circuit 8 Modulation circuit 9 Laser drive circuit 10 AD conversion circuit 11 PLL circuit 12 Cell median value / inter-cell value separation detection circuit 13 cell Waveform equalization circuit for median value 14 Waveform equalization circuit for cell-to-cell value 15 Multi-value data determination circuit 16 Multi-value-to-binary conversion circuit 17 Memory for learning 18 Binary data output 19 Cell median value determination unit 20 Inter-cell value determination Part 21 Final value judgment part

Claims (17)

Multi-value information is recorded by changing the width of the information pit or the area of the information pit in the track direction by virtually arranging cells at regular intervals on the track of the optical information recording medium using the light spot. Alternatively, in the multi-value information recording / reproducing method for reproducing, the inter-cell value obtained by sampling the reproduction signal when the center of the light spot comes to the boundary between the cell and the subsequent cell, and the cell median value sampled at the center of the cell. A multi-value information recording / reproducing method characterized in that multi-value information of a cell is determined based on both. The multi-value information recording / reproducing method according to claim 1, wherein the cell median value is determined from candidate values obtained by level slicing with a plurality of thresholds corresponding to each level. The multi-value information recording / reproducing method according to claim 2, wherein the threshold value is adjusted based on multi-value information of preceding and following cells, or the inter-cell value and the cell median value. The cell median is determined from a candidate value obtained by referring to a preceding cell preceding the target cell of interest, a succeeding cell to follow, or a multi-value determination value of the preceding cell and succeeding cell. The multi-value information recording / reproducing method according to claim 1, wherein   The reproduction signal of the cell median value of the cell of interest corresponding to all combination patterns in which the marks of three consecutive preceding cells, the cell of interest, and the succeeding cell are grouped as one group is learned in advance as the learning pattern information, 5. The multi-value information recording / reproducing method according to claim 4, wherein the multi-value information recording / reproducing method is used as a reference value for multi-value determination of a cell. 5. The multilevel information recording / reproducing according to claim 2, wherein the multilevel determination value of the preceding cell is determined by a level slice based on a plurality of thresholds corresponding to each level for obtaining the candidate value. Method. The multi-value information recording / reproducing according to claim 4, wherein the multi-value determination value of the preceding cell is multi-value information finally determined using both the inter-cell value and the cell median value. Method. 5. The multi-value information recording according to claim 2, wherein the multi-value determination value of the succeeding cell is determined by a level slice based on a plurality of thresholds corresponding to each level for obtaining the candidate value. Playback method. The multi-value information recording / reproducing method according to claim 1, wherein the inter-cell value is determined from a candidate value obtained by referring to a multi-value determination value of a preceding cell preceding a target cell of interest. . The multi-information recording / reproducing method according to claim 9, wherein the multi-value determination value of the preceding cell is multi-value information finally determined using both the inter-cell value and the cell median value. . The multi-value determination value of the preceding cell uses a multi-value determination value determined by a level slice based on a plurality of thresholds corresponding to each level for obtaining the candidate value, or both the inter-cell value and the cell median value. 10. The multi-value information recording / reproducing method according to claim 6, 7 or 9, wherein the multi-value determination value is finally determined. Learning the reproduction signal of the inter-cell value of the preceding cell and the target cell corresponding to all the combination patterns with the marks of two consecutive cells (previous cell, target cell) as one group as learning pattern information, The multi-value information recording / reproducing method according to claim 9, wherein the multi-value information recording / reproducing method is used as a reference value for multi-value determination of the cell of interest. The first candidate value obtained from the cell median is “a”, the second candidate value is “b”, the candidate value obtained from the inter-cell value is “x”, and when a = x, there are many cells of interest. The multi-value information recording / reproducing method according to claim 9, wherein the value information is determined as “a”. When x = b, M (a), M (b), and M (x) that are absolute values of the difference between the cell median value and the inter-cell value and the learning pattern information are
| M (b) −M (a) | <e and M (a)> M (x) e: When the condition of the constant is satisfied, the multi-value information of the cell of interest is determined as “x (= b)” The multi-value information recording / reproducing method according to claim 13. In the preceding cell preceding the target cell, the first candidate value obtained from the cell median is “a ′”, the candidate value obtained from the inter-cell value is “x ′”,
(A−x) <0 and (a′−x ′)> 0,
(Ax)> 0 and (a′−x ′) <0,
Or
(A−x)> 0 and (a′−x ′)> 0,
(A−x) <0 and (a′−x ′) <0
The multi-value information recording / reproducing method according to claim 13, wherein the multi-value information of the cell of interest is determined as “a” when the above condition is satisfied. In the preceding cell preceding the cell, the first candidate value obtained from the cell median is “a ′”, the candidate value obtained from the inter-cell value is “x ′”,
(A−x) <0 and (a′−x ′)> 0, or
When the condition (a−x)> 0 and (a′−x ′) <0 is satisfied, the multi-value information of the preceding cell is corrected to “a ′”,
(A−x)> 0 and (a′−x ′)> 0, or
The multi-value information of the preceding cell is corrected to “x ′” when the condition of (a−x) <0 and (a′−x ′) <0 is satisfied. Multi-value information recording / reproducing method. Multi-value information is recorded by changing the width of the information pit or the area of the information pit in the track direction by virtually arranging cells at regular intervals on the track of the optical information recording medium using the light spot. Or in a multi-value information recording / reproducing apparatus for reproducing, means for detecting an inter-cell value obtained by sampling a reproduction signal when the center of the light spot comes to the boundary between a cell and a subsequent cell, and the center of the light spot. Characterized in that it comprises means for detecting a cell median value obtained by sampling a reproduction signal when it reaches the center of the cell, and means for judging multi-value information of the cell based on the inter-cell value and the cell median value. Multi-value information recording / reproducing apparatus.