JP4303184B2 - Multilevel information reproducing method, information reproducing apparatus, multilevel information recording method, information recording apparatus, and optical information recording medium - Google Patents

Description

The present invention relates to a multilevel information reproducing method, an information reproducing apparatus, a multilevel information recording method, an information recording apparatus, and an optical information recording medium.

  2. Description of the Related Art An optical disc apparatus that records and reproduces information using a laser beam has attracted attention as a high-density and large-capacity information recording apparatus. Optical disc apparatuses are roughly classified into three types: a read-only type, a write-once type, and a rewritable type. For playback only, CD-ROM and DVD-ROM, and write-once and rewritable types, such as CD-R, CD-RW, DVD + R, and DVD + RW, have a length of 0.4 on a track separated by a constant pitch interval. Recording is performed by forming pits or recording marks having a concavo-convex shape of about 1 μm, and reproduction is performed by irradiating a weak laser beam at the time of recording and reading the presence or absence of the mark by the difference in the amount of reflected light. In this case, information is recorded as the presence / absence of a mark, and binary recording / reproduction is performed.

  On the other hand, in order to increase the recording density of the optical disc, multi-value recording methods such as ternary recording have been studied. For example, Patent Documents 1 to 3 and the like describe a ternary recording optical information recording / reproducing apparatus. This is done by changing the amount of laser beam applied to the recording medium to selectively form pits (holes) with different depths, or selectively form pits or bubbles (recesses) with different sizes. Thus, ternary information data is recorded. In this case, the reproduction is basically performed by utilizing the difference in the amount of reflected light, and comparing the reproduction signal output obtained by the photodetector with a multi-level reference level (threshold). The threshold for determination of multi-value data is determined based on the result of learning the recording / reproduction characteristics of the recording medium in advance.

  However, since the difference in the amount of reflected light corresponding to each level of multi-value information data is very small, the reproduction signal level fluctuation or offset due to slight differences in recording film composition or non-uniformity from disk to disk, rotational system jitter, etc. Therefore, the level judgment is wrong. That is, if the offset or amplitude of the reproduction signal fluctuates, an error from the threshold value for determining the multi-value information occurs, which causes an increase in erroneous determination of multi-value data. FIG. 11 shows a state in which the offset amount changes while the signal amplitude varies.

  In this regard, for example, according to Patent Document 4, in a signal detection circuit of a binary recording type optical disc apparatus, an AGC circuit that controls a signal amplitude reproduced from a medium to a predetermined level, and an output signal of the AGC circuit are differentiated. A configuration including a differentiation circuit and a peak position detection type binarization circuit that generates an information pulse signal using only the output signal of the differentiation circuit is shown.

  According to Patent Document 5, in an optical information recording / reproducing apparatus that records and reproduces multi-value information data of three or more values by irradiating a recording medium with a laser beam, in a predetermined area of the recording medium, A reference signal of three or more values representing the recording level of all values of the multi-value information data is recorded, and a reproduction signal of the multi-value information data is based on the reproduction signal level of three or more levels corresponding to each value of the reference signal. It has been proposed to set a plurality of threshold values for determining the level and to record the reference signal on a recording medium when recording multi-value information data.

JP 58-371378 A JP 58-66546 A JP 58-215735 A JP-A-6-103581 Japanese Patent No. 2602860

  According to Patent Document 4, since feedback is applied to AGC using a differential signal, noise mixed in the DC component of the reproduction signal is removed, and feedback is applied to AGC so that the differential signal amplitude has a desired magnitude. Thus, the accuracy of AGC control can be improved.

  Further, according to Patent Document 5, a reference level against a variation or offset of a reproduction signal level of multilevel information data caused by a slight difference or non-uniformity of a recording film composition for each disk, a jitter of a rotating system, or the like. Is optimized, and even if the relationship of the playback signal level of each value of multi-value information data changes, the reference level also changes accordingly, so that multi-value information data can be determined accurately. Thus, highly reliable recording and reproduction can be performed. Furthermore, by recording the reference signal on the recording medium when recording the multi-value information data, the irradiation state of the laser beam, such as focus deviation, tracking deviation, aberration, medium tilt, etc., is the same as when the multi-value information data is recorded. Therefore, it is possible to reliably and easily determine the reproduction signal level of the multi-value information data without being affected by the temporal change in the laser beam irradiation state.

  However, in Patent Document 4, the shift of the peak position of the differential detection signal is fed back to AGC in order to perform AGC control accurately. This is a method applicable to any binary recording method in which an edge is detected by a differentiated signal and information is detected by the length of a mark. However, in the multi-value recording method for recording and reproducing so that the amount of reflected light is in multiple stages, information is recorded on the signal level (signal output magnitude) indicating multi-value information itself, so that the DC component itself is also recorded. Contains information. In multi-level recording, a method such as Patent Document 4 that applies feedback to AGC using a result obtained by differentiating and removing a DC component cannot be applied. Therefore, some means for improving AGC accuracy is required as a multi-level recording method. . In addition to the fact that information is recorded in the signal level (signal output magnitude) itself indicating multilevel information, in addition to the amplitude correction (gain correction) of the method as in Patent Document 4, some offset correction is also performed. A countermeasure is required.

  In Patent Document 5, the reference recording mark is set under the condition that no intersymbol interference originally occurs. In FIG. 5 of Patent Document 5, the reference signal portion is composed of a combination of 0, 1, and 2. However, the signal value is the same as the amount of reflected light 0 in the intermediate period that changes from 0 to 1 or 1 to 2. It has become. This shows a state in which the recording data is sufficiently long with respect to the beam spot diameter and there is no intersymbol interference. This is because if the intersymbol interference component enters the reference signal, an error occurs and the threshold value cannot be determined with high accuracy. In addition, the reference signal is recorded as known data, and is recorded as existing data in an area different from the data area or for each block in which the data area is configured in order to learn and determine unknown data. A reference signal has been inserted. However, since a long reference signal is added in addition to user data, there is a problem of reducing the recording capacity. In addition, if the line density is increased to increase the capacity, the quality of the reference signal and the clock signal also deteriorates, so it is necessary to take improvement measures.

  The object of the present invention is to enable the AGC processing to accurately detect and appropriately correct the fluctuation of the offset component and the amplitude component while minimizing the recording mark added to the user data for the reference signal and the synchronization signal. Is to do.

  An object of the present invention is to further improve the quality of the reference signal and the clock signal.

The multi-value information reproducing method of the present invention is a multi-value information reproducing method for an optical information recording medium on which a recording mark is recorded so that the mark occupancy per cell changes according to multi-value data of three or more values. Detecting a reference signal by a reference mark for AGC (Auto Gain Control) periodically inserted in a data area after removing an intersymbol interference component from a reproduction signal obtained from the optical information recording medium, and detecting A step of sequentially normalizing fluctuations of an offset component and an amplitude component included in the reproduction signal with reference to the maximum value Max and the minimum value Min of the reference signal, and a plurality of values based on the normalized reproduction signal. Determining value data.

According to the present invention, in the multi-value information reproducing method described above , the sequential normalization step calculates an offset component by an operation of (Max + Min) / 2, and (Max−Min) / [(Max + Min) / 2. ], The amplitude component is calculated by the following calculation, and the reproduction signal is sequentially corrected so that fluctuations of these offset component and amplitude component become zero.

The information reproducing apparatus of the present invention is an information reproducing apparatus for an optical information recording medium on which a recording mark is recorded so that a mark occupancy per cell changes according to multi-value data of three or more values, An A / D converter that converts a reproduction signal obtained from an optical information recording medium into digital data, a waveform equalizer that removes an intersymbol interference component from the reproduction signal converted into digital data, and an intersymbol interference component is removed Means for detecting a reference signal by a reference mark for AGC (Auto Gain Control) periodically inserted in the data area from the reproduced signal, and a maximum value Max and a minimum value Min of the detected reference signal Means for calculating the amount of fluctuation between the offset component and amplitude component included in the reproduction signal, means for removing the amount of fluctuation between the offset component and amplitude component from the reproduction signal, Comprising means for determining multi-level data based on the amount min the reproduced signal has been removed, the.

The information reproducing apparatus of the present invention is an information reproducing apparatus for an optical information recording medium on which a recording mark is recorded so that a mark occupancy per cell changes according to multi-value data of three or more values, Means for detecting a peak position of a reference signal for AGC (Auto Gain Control) obtained from an optical information recording medium and generating a synchronizing signal; and a reproducing signal obtained from the optical information recording medium is generated by the generated synchronizing signal A / D converter that converts digital data at the center of the cell with reference to the above, a waveform equalizer that removes intersymbol interference components from the reproduction signal converted into digital data, and the intersymbol interference components removed A means for detecting a reference signal by a reference mark for AGC (Auto Gain Control) periodically inserted in the data area from the reproduction signal, and a maximum value Max and a minimum value Min of the detected reference signal. A means for calculating a fluctuation amount between an offset component and an amplitude component included in the reproduction signal, a means for removing a fluctuation amount between the offset component and the amplitude component from the reproduction signal, and a fluctuation amount removal. Means for determining multi-valued data based on the reproduced signal.

According to the present invention, after removing the intersymbol interference component from the reproduction signal, the reference signal for AGC periodically inserted in the data area is detected, and the maximum value Max and the minimum value Min of the detected reference signal are detected. Since the fluctuation of the offset component and the amplitude component included in the playback signal is sequentially normalized with reference to the above, the detected offset component and amplitude are not affected by the influence of intersymbol interference (effect as noise). The fluctuation component with the component can be removed from the reproduction signal, and the multi-level level can be accurately determined.

Further, according to the present invention, after removing the intersymbol interference component from the reproduction signal, the AGC reference signal periodically inserted in the data area is detected, and the maximum value Max and the minimum value of the detected reference signal are detected. Since the fluctuation between the offset component and amplitude component included in the playback signal is sequentially normalized with reference to Min, the offset component detected without being affected by intersymbol interference (influence as noise) The amplitude component and the fluctuation component can be removed from the reproduction signal, the multi-level level can be accurately determined, and the synchronization signal is generated by detecting the peak position of the mark for the reference signal. Therefore, the reference signal mark can also be used as the synchronization signal mark, and the capacity drop due to the reference mark can be minimized.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  First, prior to the description of the present embodiment, the principle of the multilevel recording / reproducing method which is the premise thereof will be described with reference to FIG. FIG. 1 is a schematic diagram showing the principle of a waveform example of a multilevel reproduction signal. Here, a recording mark is recorded on an optical information recording medium by irradiating a laser beam so that the mark occupancy per unit area called a cell changes (that is, area modulation). Recording of value data is realized. For example, by changing the mark occupancy rate to 8 gradations including the state where no recording mark exists (unrecorded cell), multi-value recording with 8 values can be performed. In the waveform example of the multilevel reproduction signal corresponding to the multilevel recording example shown in FIG. 1, for example, even in an unrecorded cell, as shown in A, B, and C, the mark of the recording mark of each adjacent cell It can be seen that the same signal value is not obtained under the influence of the occupation ratio. In order to increase the recording linear density, the relationship between the physical length (cell length) DL in the scanning direction of the beam spot of the recording mark and the beam spot diameter BD for recording / reproduction is expressed as DL = It is defined as BD / 2.

  FIG. 2 shows a schematic configuration example of the optical disc apparatus according to the present embodiment for realizing recording / reproduction of multi-value information on the optical disc (optical information recording medium) 1 under such conditions. This optical disc apparatus realizes the information reproducing apparatus and information recording apparatus of the present invention. In this case, the optical disc 1 may be of any recording method such as a write-once type or a rewritable type. FIG. 2 shows the minimum necessary components related to the present embodiment.

  The optical disk apparatus of the present embodiment includes a semiconductor laser (LD), an objective lens, an optical system, and the like, and an optical pickup 2 for irradiating the optical disk 1 with a laser beam. In addition, an information data generator 3, a multi-value data converter 4, and an LD drive signal generator 5 are provided as the configuration of the recording system. On the other hand, the configuration of the reproduction system includes a photodetector 6, a BPF / gain adjustment circuit 7, a synchronization signal detection circuit 8, a sampling signal generation circuit 9, a quantization A / D converter 10, a waveform equalizer 11, and a multi-value data memory 12. And an AGC processing circuit 13 is provided.

  First, when multi-value data is recorded on the optical disc 1, user data input to the information data generator 3 is converted into multi-value data by the multi-value data converter 4, and the multi-value data is converted by the LD drive signal generator 5. A recording mark is recorded by generating a recording pulse for recording by area modulation corresponding to the value data, modulating and driving the semiconductor laser, and condensing and irradiating the recording surface of the optical disc 1 with a laser beam.

  On the other hand, when reproducing multi-value data based on the recording marks recorded on the optical disc 1, the laser beam is focused and irradiated on the optical disc 1 that is rotationally driven, and the reflected return light is received by the photodetector 6 and photoelectrically reflected. A reproduction signal that is an electric signal is obtained by the conversion.

  This reproduction signal removes high-pass filter (HPF) for signal fluctuations of the rotation period (mainly due to reflectance fluctuations of the optical disc 1) and signal noise (caused by LD noise and circuit noise) above the data band. By performing a filtering process using a band pass filter (BPF) combined with a low pass filter (LPF) for the purpose, noise included in the reproduction signal is removed. The reproduced signal from which noise has been removed is corrected so as to correspond to the dynamic range of the A / D converter 10 in order to reduce the quantization error in the A / D converter 10. Specifically, if the dynamic range of the A / D converter 10 is, for example, 0V-5V, the amplitude of the reproduction signal is detected by envelope detection, and the gain is set such that the minimum is around 0V and the maximum value is around 5V. Adjust and amplify. The BPF / gain adjustment circuit 7 performs the BPF process and the gain adjustment process.

  Next, in order to sample and quantize the reproduction signal at the center of the cell, a synchronization signal is generated by the synchronization signal detection circuit 8 from the synchronization signal pattern recorded together with the multilevel data, and the sampling signal is based on this synchronization signal. In accordance with the sampling signal generated by the generation circuit 9, the reproduction signal in a multilevel signal state is quantized by the A / D converter 10 (A / D conversion = analog-digital conversion), and further, the waveform equalizer 11 Remove interference. As the waveform equalizer 11, for example, a known transversal type may be used. The waveform equalized reproduction signal is sequentially stored in the multilevel signal memory 12. The signals stored in the multilevel signal memory 12 are sequentially read out, and the AGC processing circuit 13 performs the characteristic AGC processing of the present embodiment.

  That is, the AGC processing circuit 13 of the present embodiment detects a reference signal based on the reference mark after waveform equalization (detection means), refers to the maximum value Max and the minimum value Min of the detected reference signal, and reproduces them. The offset component included in the signal is calculated by an operation of (Max + Min) / 2, and the amplitude component is calculated by an operation of (Max−Min) / [(Max + Min) / 2] (calculation means). Processing (removal means) for sequentially correcting the reproduction signal so that fluctuations of these offset component and amplitude component become zero is performed. This process corresponds to a process of sequentially normalizing fluctuations in the offset component and the amplitude component included in the reproduction signal with reference to the maximum value Max and the minimum value Min of the detected reference signal.

  Using the reproduction signal (multi-valued data) after receiving such AGC processing, the multi-value level is judged by a multi-value data judging circuit (not shown) to reproduce the recorded information. Such a multi-value data determination method is described in detail in, for example, Japanese Patent Application Laid-Open No. 2003-45035, and detailed description thereof is omitted here. However, as an example, FIG. 3 shows a reproduction signal waveform example in which eight values are recorded at a recording density of 6.4 bits / μm. The recording / reproducing conditions were as follows: laser beam wavelength λ: 650 nm, lens numerical aperture 0.65 NA, optical disc 1 = DVD + RW disc, and circumferential length DL of the data cell was 0.47 μm. In this case, if the multilevel signal of three consecutive data cells is T (i, j, k), T (0,1,0) and T (7,0,0) are close due to the influence of intersymbol interference. In the determination with the fixed threshold of 8 levels corresponding to each multi-level (hereinafter referred to as threshold determination), the distinction between T (0,1,0) and T (7,0,0) Is difficult. However, if the multi-value levels i (n−1) and k (n + 1) of the data cells positioned before and after the nth to be reproduced can be predicted, T (0,1,0) and T (7,0) , 0) can be distinguished. Such a multi-value data determination method is called DDPR (Data Detection using Pattern Recognition). Therefore, the DDPR method uses a method of selecting a candidate for j to be reproduced after predicting a pattern in units of three consecutive data cells.

In FIG. 4, an A / D converter 10 and a waveform equalizer 11 are used, and after an average calculation processing step by calculation means, a combination pattern (eight values) of three consecutive data cells configured by known combinations. At the time of recording, it is composed of steps of learning a multi-value signal distribution of 8 ³ = 512, which is described as a test pattern in FIG.

  In FIG. 5, the A / D converter 10 and the waveform equalizer 11 are used to temporarily determine the multi-value data from the reproduction signal result of the unknown multi-value data, and compare with the result by the learning table as shown in FIG. Thus, the step consists of the step of calculating the reproduction signal error δs between the multi-value data candidate j and the learning table.

  In such a DDPR method, it has been confirmed that the error rate of multi-value data candidates is reduced to 1/10 or less of threshold determination by learning the tendency of intersymbol interference in advance.

  Next, reference marks used for reference signals in the AGC processing circuit 13 will be described.

  In general, when there is no waveform equalization processing and an intersymbol interference component is included in the reference signal, an error occurs and the threshold cannot be determined with high accuracy. Under the condition of DL = BD / 2, in order to perform the AGC correction process with the signal before waveform equalization, as shown in FIG. 6B, a mark row pattern having a combination of a reference mark length of 8 cells or more is required. I need it. By combining eight cells, the maximum value Max and the minimum value Min shown in FIG. 6B can be accurately detected without being affected by the recording state of the cells positioned before and after the reference mark. Can do.

  On the other hand, in the present embodiment, since the waveform equalizer 11 performs waveform equalization processing in advance, the reference mark length may be a mark row pattern composed of a combination of at least three cells. In this case, since the influence of the cells positioned before and after the reference recording mark can be removed by waveform equalization, the maximum value Max and the minimum value Min can be detected with high accuracy as shown in FIG. With this effect, the capacity drop due to the reference mark can be reduced to 3/8 = 38%.

  In general, a combination of one cell indicating the maximum value Max included in the reference signal and a plurality of cells indicating the minimum value Min may be used. However, it is necessary to generate a detection window in order to detect the reference mark, and the peak position can be detected because the cell of the reference mark exists in the window. Therefore, by providing an even number of cells indicating the minimum value Min before and after the peak position so as to be within the window width, it is possible to arrange a cell indicating a peak at the center position of the reference mark.

  The reference mark length can play the same role even if it is an inverted type in which the signal waveform of the mark row pattern shown in FIG. 6A is inverted. That is, as shown in FIG. 7, the mark row pattern may be a combination of at least three cells, one cell indicating the minimum value Min and a plurality of cells indicating the maximum value Max. Also in this case, since the influence of the cells located before and after the reference recording mark can be removed by waveform equalization, the maximum value Max and the minimum value Min can be detected with high accuracy as shown in FIG. With this effect, the capacity drop due to the reference mark can be reduced to 3/8 = 38%.

  In general, a combination of one cell indicating the minimum value Min included in the reference signal and a plurality of cells indicating the maximum value Max may be used. However, as described above, when the cell center and the peak position of one cell indicating the minimum value Min are matched, it is desirable that the number of cells indicating the maximum value Max is an even number.

At this time, the physical length of the cell in the scanning direction of the beam spot is DL, the recording / reproducing beam spot diameter defined by 1 / e ² is BD, and the reference signal is composed of a plurality of cells. When the number of reference mark cells for use is n (a positive integer), the relationship satisfies DL ≦ BD, n ≧ (BD / DL) * 2 + 1, and the cell indicating the maximum value Max included in the reference signal and the minimum If one of the cells indicating the value Min is one, it can serve as a reference mark. That is, FIG. 6A shows an example in which there are two (a plurality of) cells indicating the maximum value Max (unrecorded cells) and one cell (the cell having the maximum mark occupancy) indicating the minimum value Min. On the contrary, as shown in FIG. 7, there are two (plural) cells indicating the minimum value Min (cells with the largest mark occupancy) and one cell (unrecorded cell) indicating the maximum value Max. May be.

  Further, in the detection of the maximum value Max and the minimum value Min shown in FIG. 6A, a cell indicating the maximum value Max is an unrecorded cell, and a cell indicating the minimum value Min is a record with the maximum mark occupancy rate indicating 8 values. It consists of a mark row pattern based on a combination of marks. Here, in order to prevent the signal output of the cell indicating the maximum value Max from being affected by intersymbol interference from the front side of the reference mark (leftward in FIG. 6A), the cell output indicating the maximum value Max It is necessary to set the number of taps for waveform equalization to eliminate the influence of the previous four cells. For this purpose, at least 9 taps are required, and the relationship between the configuration of the recording mark length and the number of taps m (where m is a positive integer) of the waveform equalizer 11 is a relationship represented by m ≧ 2n−1. It becomes.

  FIG. 8 shows a basic configuration example of a general transversal type waveform equalizer 11 that can also be applied to this embodiment. The waveform equalizer 11 includes, for example, a plurality of delay circuits 21a to 21d that sequentially delay an input signal, multipliers 22a to 22e that respectively weight the signals before and after the delay, and adjacent front and rear stage multipliers. It is configured by a combination with adders 23a to 23d that sequentially add outputs. In FIG. 8, it consists of five taps.

  Incidentally, the reference mark for AGC as shown in FIG. 6A is inserted into the data area of the optical disc 1. An example of the configuration is shown in FIG. 9 as a reference mark format example. The sector mark located at the head is a unique pattern that does not exist in the data. For example, in the present embodiment, a pattern composed of a combination of mark rows having a multilevel level of (00000007777777) is used. The role of the sector mark is used to indicate the head of a sector, which is composed of a combination of a plurality of data blocks (see FIG. 9). The reference marks are arranged at equal intervals between data blocks using a mark row pattern having a combination of multi-value levels (00700) as shown in FIG. 6A. As an operation flow in sampling at the time of A / D conversion, first, a sector mark is detected, a window signal for detecting a reference mark is generated from the sector mark position, and only the reference mark is generated using this window signal. A synchronization signal that is extracted and synchronized with the peak position of the reference mark is generated in a cell cycle, and the signal is A / D converted at the center of the cell in accordance with the synchronization signal.

  Such a reference mark can also be used as a clock mark for a synchronization signal for sampling and quantizing the reproduction signal at the center of the cell as shown in FIG. That is, since the center position of the cell can be detected by detecting the peak using the minimum value Min shown in FIG. 6A as the peak position of the signal, it can be used as a synchronization signal for sampling. Thus, by combining the reference signal reference mark and the synchronization signal clock mark, information to be added in addition to data can be reduced, so that the recording capacity can be increased.

  In order to perform multi-level recording including such a reference mark, a plurality (two) of unrecorded cells as shown in FIG. 6A for generating a reference mark of a reference signal for AGC are used. A mark string pattern formed by a combination with one cell maximizing the mark occupancy is periodically inserted into the user multi-value data and encoded by the multi-value data converter 4 (encoding means). If the intensity of the laser beam is modulated by the LD drive signal generator (laser beam driving means) 5 according to the data, and the laser beam is focused on the optical disk 1 by the optical pickup 2 to record multi-value data. Good. The reference mark pattern may be a reverse pattern, that is, a mark row pattern including a combination of a plurality (two) of cells having the maximum mark occupancy and one unrecorded cell.

  Incidentally, a modification of the present embodiment is shown in FIG. In this modification, a first waveform equalizer 14 is added between the BPF / gain adjustment circuit 7 and the A / D converter 10, and the synchronization signal detection circuit 8 is connected to the first waveform equalizer 14. Is connected to. The first waveform equalizer 14 is a transversal type waveform equalizer in which, for example, an equalization coefficient is fixed, and is used to remove an intersymbol interference component of a reproduction signal before A / D conversion. It is done. That is, the role of the first waveform equalizer 14 is to remove the noise component due to intersymbol interference added to the reproduction signal for the synchronization signal pattern, thereby improving the signal quality and reducing the synchronization deviation at the time of sampling. It plays a role to reduce. Thereby, the precision of the synchronization at the time of sampling can be improved.

  Such a first waveform equalizer 14 only needs to have a minimum function of using the reference mark as a synchronization mark. That is, the peak position of the cell is detected by using the minimum value Min shown in FIG. 6A as the peak position of the signal (in the case of FIG. 7, the peak value is detected using the maximum value Max as the peak position of the signal). Therefore, the reference mark can be used as a synchronization signal for sampling. To fulfill this role, the signal value indicating the peak position does not have to include an intersymbol interference component. Referring to FIG. 6A, the signal output of the cell indicating the minimum value Min indicating the peak position is not affected by intersymbol interference from the front side of the reference mark (leftward in FIG. 6A). In order to achieve this, it is necessary to use the number of taps for waveform equalization that eliminates the influence of the cell three cells before the cell having the minimum value Min. For this purpose, at least seven taps are required, and waveform equalization is required. The number of taps is less than that of the container 11 by 2 taps. That is, if the number of taps of the waveform equalizer 14 is m1 and the number of taps of the waveform equalizer 11 is m2, Dl ≦ BD, n ≧ (BD / DL) * 2 + 1, m2 ≧ 2 * n−1, m1 ≦ The relationship m2-2 is established.

  In the following, an example in which an AGC operation is actually performed using the reference mark format configuration example shown in FIG. 9 will be described in accordance with the above-described embodiment.

[Example 1]
In this embodiment, the number of blocks in one sector is 33. The number of cells in one block is 32 cells. In this embodiment, 33 reference marks for AGC are inserted and recorded in the data area at equal intervals in one sector. Therefore, the maximum value Max and the minimum value Min of the 33 reference marks are averaged and treated as representative values indicating the amplitude component and offset component of the sector. Here, the maximum value Max is the signal output value of (0) located at the fourth position in (00700), and the minimum value Min is the signal output value of 7 in (00700) (see FIG. 6A). The maximum value Max may be the second (0) signal output value in (00700). In this way, averaging using a plurality of reference mark signals also changes the reference mark signal output due to noise in the vicinity of the cell generation frequency. This is because it cannot be handled. Also, considering the effects of clock shift and defects during A / D conversion, it is clear that AGC accuracy can be improved by averaging.

  In addition, when the fluctuation component (amplitude component and offset component) included in the reproduction signal is lower than the frequency generated in the sector, the signal correction in the sector unit becomes a rapid response, and the effect of the AGC correction is sufficiently exhibited. May not be. Therefore, it is also effective to reduce the change due to abrupt correction by further averaging the signal value of the reference mark averaged in the sector unit in the scanning direction to obtain a representative value indicating the signal fluctuation of each sector. . Table 1 shows an experimental example in which the moving average number and the effect of AGC were measured. Note that the level fluctuation values in Table 1 indicate low-frequency fluctuation components corresponding to the sector period. According to the experimental example shown in Table 1, it can be understood that AGC correction can be performed with high accuracy by setting the moving average number to 3 sectors or more and 9 sectors or less.

[Example 2]
In this embodiment, the number of blocks in one sector is 33. The number of cells in one block is 32 cells. In addition, 33 AGC reference marks are recorded in one sector at regular intervals in one sector. Therefore, the maximum value Max and the minimum value Min of the 33 reference marks are handled as representative values of each block indicating the amplitude component and offset component of the sector. Here, the maximum value Max is the signal output value of (0) positioned fourth in (00700), and the minimum value Min is the signal output value of 7 in (00700). The maximum value Max may be the second (0) signal output value in (00700).

  As in the case of the first embodiment, considering the influence of noise near the cell generation frequency, clock shift at the time of A / D conversion, defects, etc., it is clear that averaging improves AGC accuracy. It is. Therefore, it is effective to reduce the change caused by abrupt correction by averaging the signal value of the reference mark of each block in the scanning direction to obtain a representative value indicating the signal fluctuation of each block. This embodiment is a more effective method than the first embodiment when the frequency of the fluctuation component included in the signal is high. Table 2 shows an experimental example in which the moving average number and the effect of AGC were measured. Note that the level fluctuation values in Table 2 indicate low-frequency fluctuation components corresponding to the sector period. According to the experimental example shown in Table 2, it can be seen that AGC correction can be performed with high accuracy by setting the moving average number to 7 sectors or more.

[Example 3]
According to the first and second embodiments, the AGC correction effect of the method of the present invention was confirmed, but in this embodiment, the clock accuracy is improved by the first waveform equalizer 14 as shown in the modification. The signal quality was compared. The jitter value aggregated in cell units (the signal amplitude value that can be taken by 8 values is 1) is 3.2% in the case where the first waveform equalizer 14 is not provided, but the first waveform equalizer 14. It was found that the signal quality can be improved by about 0.4% to 2.8%. Further, the first waveform equalizer 14 is not an adaptive automatic equalization type and needs to have a fixed equalization coefficient. By fixing the equalization coefficient, the first waveform equalizer 14 can be realized by an analog circuit, and therefore can be realized as a sampling processing circuit before A / D conversion.

It is a wave form diagram which shows typically the feature of the reproduction signal to multi-value recording data. It is a block diagram which shows the structural example of the principal part of the optical disk apparatus of one embodiment of this invention. It is explanatory drawing which shows the example of a pattern in which the multi-value determination in a multi-value data determination process is ambiguous. It is a figure which shows a learning table creation algorithm. It is a figure which shows a multi-value candidate selection algorithm. It is explanatory drawing which shows the example of a reference signal and a corresponding reproduction signal waveform example which are required with and without waveform equalization processing. It is explanatory drawing which shows the modification of the example of a reference mark. It is a block diagram which shows the structural example of a general transversal type | mold waveform equalizer. It is explanatory drawing which shows the format structural example of a reference | standard mark. FIG. 11 is a block diagram illustrating a modified configuration example of a main part of an optical disc device. It is explanatory drawing which shows the mode of an amplitude fluctuation | variation and an offset fluctuation | variation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical information recording medium 2 Optical pick-up 4 Encoding means 5 Laser beam drive means 10 A / D converter 11 Waveform equalizer

Claims (4)

A multi-value information reproducing method for an optical information recording medium on which a recording mark is recorded so that a mark occupancy per cell changes according to multi-value data of three or more values,
Detecting a reference signal by a reference mark for AGC (Auto Gain Control) periodically inserted in a data area after removing an intersymbol interference component from a reproduction signal obtained from the optical information recording medium;
Sequentially normalizing fluctuations in the offset component and the amplitude component included in the reproduction signal with reference to the detected maximum value Max and minimum value Min of the reference signal;
Determining multi-value data based on the normalized reproduction signal;
A multi-value information reproducing method comprising: The sequential normalization step includes:
The offset component is calculated by the calculation of (Max + Min) / 2, and the amplitude component is calculated by the calculation of (Max−Min) / [(Max + Min) / 2], and fluctuations in these offset component and amplitude component become zero. The multi-value information reproduction method according to claim 1, wherein the reproduction signal is sequentially corrected as described above. An information reproducing apparatus for an optical information recording medium on which a recording mark is recorded so that a mark occupancy per cell changes according to multi-value data of three or more values,
An A / D converter for converting a reproduction signal obtained from the optical information recording medium into digital data;
A waveform equalizer that removes intersymbol interference components from the reproduced signal converted into digital data;
Means for detecting a reference signal by a reference mark for AGC (Auto Gain Control) periodically inserted in the data area from the reproduced signal from which the intersymbol interference component has been removed;
Means for calculating a fluctuation amount of an offset component and an amplitude component included in the reproduction signal with reference to the detected maximum value Max and minimum value Min of the reference signal;
Means for removing a fluctuation amount of the offset component and the amplitude component from the reproduction signal;
Means for determining multi-valued data based on the reproduction signal from which the fluctuation amount has been removed;
An information reproducing apparatus comprising: An information reproducing apparatus for an optical information recording medium on which a recording mark is recorded so that a mark occupancy per cell changes according to multi-value data of three or more values,
Means for detecting a peak position of a reference signal for AGC (Auto Gain Control) obtained from the optical information recording medium and generating a synchronization signal;
An A / D converter that converts a reproduction signal obtained from the optical information recording medium into digital data at the center of a cell with reference to the generated synchronization signal;
A waveform equalizer that removes intersymbol interference components from the reproduced signal converted into digital data;
Means for detecting a reference signal by a reference mark for AGC (Auto Gain Control) periodically inserted in the data area from the reproduced signal from which the intersymbol interference component has been removed;
Means for calculating a fluctuation amount of an offset component and an amplitude component included in the reproduction signal with reference to the detected maximum value Max and minimum value Min of the reference signal;
Means for removing a fluctuation amount of the offset component and the amplitude component from the reproduction signal;
Means for determining multi-valued data based on the reproduction signal from which the fluctuation amount has been removed;
An information reproducing apparatus comprising:

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