JP2010140519A - Maximum likelihood decoding method of reproduction signal, optical disk device, integrated circuit, and optical disk - Google Patents

Abstract

To provide a reproducing method capable of adjusting the recording condition of an optical disc to an optimum condition in a state deviated from an ideal PR equalization level.
A β designation value that matches an optimum recording condition of an optical disk is acquired, and a signal expectation value of maximum likelihood decoding is calculated from the β designation value by a predetermined conversion formula. By setting the calculated expected signal value in the maximum likelihood decoding circuit, the reproduction error rate or the signal quality evaluation index value becomes better as it is closer to the β designated value, and the optimum recording condition of the optical disc can be adjusted. It becomes possible.
[Selection] Figure 1

Description

  The present invention relates to a technique for reproducing digital information recorded on an optical disc by a maximum likelihood decoding method.

  In recent years, with the increase in the density of optical discs, the shortest mark length of recording marks approaches the limit of optical resolution, the increase in intersymbol interference and the deterioration of SNR (Signal Noise Rate) become more prominent. As a signal processing method, PRML It is becoming common to use the (Partial Response Maximum Likelihood) method or the like.

  The PRML system is a technique that combines partial response (PR) and maximum likelihood decoding (ML), and is a system that selects the most probable signal sequence from a reproduced waveform on the assumption that known intersymbol interference occurs. For this reason, it is known that decoding performance is improved as compared with the conventional level determination method (for example, Non-Patent Document 1).

The signal reproduced from the recording medium is subjected to partial response equalization so as to have a predetermined frequency characteristic using a waveform equalizer or digital filter, and then the most probable state transition sequence is selected using Viterbi decoding or the like. Thus, the corresponding binarized data is decoded. In general, an amount L representing the probability of state transition to state S _n (where n is the number of states) up to time k is defined by equation (1).

In equation (1), y _i is the value of the reproduced signal at time i, and E _i is the expected ideal reproduced signal value. In the maximum likelihood decoding method, a state transition sequence that minimizes the amount L representing the probability obtained by Expression (1) is selected and decoded into corresponding binarized data (for example, Patent Document 1).

In addition, the value L obtained by equation (1) increases with respect to the asymmetry and level fluctuation of the reproduction signal caused by fluctuations in recording conditions, fluctuations in focus servo and tracking servo during recording / reproduction, and the decoding performance is increased. May deteriorate. On the other hand, adaptive maximum likelihood decoding has also been proposed in which the expected value level E _i is subjected to follow-up control in accordance with changes in the signal level y _i to improve decoding performance (for example, Patent Document 2).

As the density of optical discs further increases, intersymbol interference and SNR degradation become more problematic. Non-patent document 1 describes that it is possible to maintain the reproduction performance by changing the PRML method to a higher order method. For example, in the case where the recording capacity per recording layer of a 12 cm optical disk is 25 GB, the reproduction performance can be maintained by adopting the PR (1, 2, 2, 1) ML system. It is described that when the recording capacity per layer is 33.3 GB, it is necessary to adopt the PR (1, 2, 2, 2, 1) ML system. As described above, it is expected that the tendency to adopt the higher-order PRML system will continue in proportion to the increase in the density of the optical disk.
JP 2003-141823 A JP-A-10-261272 Illustrated Blu-ray Disc Reader Ohm

  However, a higher-order PRML method with high performance at the time of reproduction is adopted so that the error rate of the reproduced binarized data becomes small, or the value of the evaluation index of the reproduction signal quality described in Patent Document 1 is When recording adjustment (particularly edge position adjustment of the recording mark) is performed so as to be small, depending on the recording density of the optical disc, recording that can fully exhibit the recording performance of the optical disc is performed (recording under recording conditions that maximize the SNR). ) Was not possible, and the margin during playback was reduced. For example, when optimum recording adjustment is performed in the reproduction signal processing of the PR (1, 2, 2, 2, 1) ML system, a 2T mark (T is a channel width (channel clock cycle)) mark that is a short recording mark In addition, the size of the 3T mark becomes very small, which greatly deviates from the original optimum recording condition of the optical disk, and there is a problem that the characteristics of repeated recording and the aging deterioration characteristics are lowered.

  If the adaptive maximum likelihood decoding described above is used, the binarized data can be recorded even if recording is performed in a state deviating from the expected value level corresponding to the ideal PR (1, 2, 2, 2, 1). However, the error rate is the same regardless of whether the amount of deviation from the expected value level corresponding to the ideal PR (1, 2, 2, 2, 1) is large or small. Therefore, it becomes difficult to match the recording conditions between different optical disk devices, and in the worst case, the conditions recorded on one optical disk change variously, and the fluctuation becomes large during reproduction. Therefore, there is a problem in that it is necessary to make the responsiveness for adaptive control very high and the stability is lacking.

  In order to solve the above problems, the maximum likelihood decoding method of the present invention is a maximum likelihood decoding method for decoding most probable digital information from a sampling signal of a reproduction signal obtained by reproducing information recorded on a track of an optical disc with marks and spaces. The difference between the sampling signal sequence of the reproduction signal in a predetermined period and the expected value sequence of the sampling signal of the reproduction signal corresponding to each digital information sequence is detected, and the digital information sequence having the smallest difference is detected as the digital information sequence. A maximum likelihood decoding step that is selected as a decoding result of the reproduction signal, an index value designation step that designates an expected value of an index value indicating a ratio between the energy center of the reproduction signal and the amplitude center of the longest mark and the longest space; A calculation step of calculating each expected value of the sampling signal used in the maximum likelihood decoding step according to the expected value of the index value, Serial The maximum likelihood decoding step, which comprises using the respective expected value of the sampling signal calculated in the calculation step.

  The maximum likelihood decoding step may be Viterbi decoding.

  A DC control step of detecting an energy center level of the sampling signal of the reproduction signal and controlling a DC level of the sampling signal so that the detected energy center level becomes a center level of the processing of the maximum likelihood decoding step; You may have.

  Further, it may further include a partial response equalization step for equalizing the sampling signal of the reproduction signal so as to have a predetermined frequency characteristic, and an output signal of the partial response equalization step may be input to the maximum likelihood decoding step. .

  The equalization characteristic of the partial response equalization step may be PR (1, 2, 2, 2, 1) equalization.

  The expected value of the sampling signal used in the maximum likelihood decoding step may be a 9-level value corresponding to PR (1, 2, 2, 2, 1) equalization.

  The information recorded on the optical disk is recorded according to the 1-7 modulation method, and there are 16 types of patterns in PR (1, 2, 2, 2, 1) equalization, and sampling used in the maximum likelihood decoding step. The expected value of the signal may be a value corresponding to the 16 types of patterns.

  An optical disk apparatus according to the present invention is an optical disk apparatus for reproducing information recorded on a track of an optical disk with marks and spaces, and irradiates the optical disk with a laser and outputs a reproduction signal corresponding to the amount of reflected light. An optical head, a reproduction clock generation circuit that generates a reproduction clock from the reproduction signal, an A / D conversion circuit that outputs a sampling signal obtained by sampling the reproduction signal with the reproduction clock, and most probable digital information from the sampling signal A maximum likelihood decoding circuit that decodes the difference between the sampling signal sequence in a predetermined period and the expected value sequence of the sampling signal of the reproduction signal corresponding to each digital information sequence And a decoding circuit that selects a digital information sequence having a minimum difference as a decoding result of the reproduction signal; An index value designating circuit for designating an expected value of an index value indicating a ratio between the energy center of the reproduction signal and the amplitude center of the longest mark and the longest space; and the maximum likelihood decoding step according to the expected value of the index value The decoding circuit uses each expected value of the sampling signal calculated by the calculation circuit.

  The decoding circuit may be a Viterbi decoding circuit.

  And a DC control circuit that detects an energy center level of the sampling signal of the reproduction signal and controls the DC level of the sampling signal so that the detected energy center level becomes the center level of the processing of the decoding circuit. May be.

  In addition, a partial response equalization circuit that equalizes the sampling signal of the reproduction signal so as to have a predetermined frequency characteristic may be further provided, and an output signal of the partial response equalization circuit may be input to the decoding circuit.

  The equalization characteristic of the partial response equalization circuit may be PR (1, 2, 2, 2, 1) equalization.

  The expected value of the sampling signal used in the maximum likelihood decoding circuit may be a 9-level value corresponding to PR (1, 2, 2, 2, 1) equalization.

  The information recorded on the optical disc is recorded according to the 1-7 modulation method, and there are 16 types of patterns in PR (1, 2, 2, 2, 1) equalization, and sampling used in the maximum likelihood decoding circuit. The expected value of the signal may be a value corresponding to the 16 types of patterns.

  In addition, information on the expected value of the index value is recorded in advance on the optical disc, and the index value designating circuit may use the acquired information on the expected value as the expected value of the index value.

  An integrated circuit of the present invention is an integrated circuit that decodes a reproduction signal obtained by reproducing information recorded on a track of an optical disc with marks and spaces, and a reproduction clock generation circuit that generates a reproduction clock from the reproduction signal, and the reproduction An A / D conversion circuit that outputs a sampling signal obtained by sampling a signal with the reproduction clock; and a maximum likelihood decoding circuit that decodes the most probable digital information from the sampling signal. The difference between the sampling signal sequence in the period and the expected value sequence of the reproduction signal corresponding to each digital information sequence is detected, and the digital information sequence that minimizes the difference is selected as the decoding result of the reproduction signal The ratio of the decoding circuit that performs the energy center of the reproduction signal and the amplitude center of the longest mark and the longest space An index value designating circuit for designating an expected value of the standard value, and a calculation circuit for calculating each expected value of the sampling signal used in the maximum likelihood decoding step according to the expected value of the index value, Each of the expected values of the sampling signal calculated by the calculation circuit is used.

  When reproducing information recorded with marks and spaces on a track, the optical disc of the present invention expects the sampling signal of the reproduction signal corresponding to each digital information sequence with respect to the sampling signal sequence of the reproduction signal in a predetermined period. A sampling used for the maximum likelihood decoding, wherein the digital information is decoded by a maximum likelihood decoding method that detects a difference from the sequence and selects a digital information sequence that minimizes the difference as a decoding result of the reproduction signal. Information on each expected value of the signal is recorded in advance.

  Further, the information of each expected value recorded in advance may be a 9-level value corresponding to PR (1, 2, 2, 2, 1) equalization.

  The information recorded on the optical disk is recorded in accordance with the 1-7 modulation method, and there are 16 types of patterns in PR (1, 2, 2, 2, 1) equalization. The value information may be values corresponding to the 16 types of patterns.

  The information of each expected value recorded in advance may be recorded by wobbling the track.

  The information of each expected value recorded in advance may be recorded by marks and spaces on the track.

  The information of each expected value recorded in advance may be recorded in a BCA (Burst Cutting Area).

  Further, the wavelength of the laser irradiating the track is λ, the numerical aperture of the objective lens for condensing the laser on the track is NA, the shortest mark length recorded on the track is Tm, and the shortest space length is Ts, and (Tm + Ts) It may be <λ / (2NA).

  The wavelength λ of the laser may be 400 nm to 410 nm.

  The numerical aperture NA of the objective lens may be 0.84 to 0.86.

  The length Tm + Ts obtained by adding the shortest mark length Tm and the shortest space length Ts may be less than 238.2 nm.

According to the present invention, the target of the recording condition of the recording mark position and size so that the recording performance of the optical disk can be sufficiently exhibited is determined, and the energy center of the reproduction signal when reproducing the recording mark recorded according to the target is determined. The ratio (β value) between the longest mark and the center of the amplitude of the reproduction signal of the longest space is obtained, and an expected ideal reproduction signal value E _i used for maximum likelihood decoding is calculated based on this β value. Maximum likelihood decoding is performed using the calculated expected value E _i . Here, by adjusting the recording conditions so that the error rate of the binarized data subjected to maximum likelihood decoding is reduced, or the value of the reproduction signal quality evaluation index described in Patent Document 1 is reduced. It is possible to make adjustments so that the recording performance of the optical disk can be sufficiently exhibited.

  Further, if recording is performed by performing the recording adjustment as described above, it is easy to ensure reproduction compatibility performance when the optical disk is reproduced by an optical disk apparatus different from the recorded optical disk apparatus.

Also, in the reproduction of a reproduction-only optical disc (ROM disc) in which information is recorded in advance by pits, β value information corresponding to the reproduction signal of the optical disc is acquired, and maximum likelihood decoding is performed based on the acquired β value. By calculating the expected ideal reproduction signal value E _i used in the above and applying it to maximum likelihood decoding, it is possible to ensure stable reproduction performance at a low error rate.

  Embodiments of a maximum likelihood decoding method, an optical disc apparatus, and an optical disc according to the present invention will be described below.

(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of the optical disc apparatus according to Embodiment 1 of the present invention.

  The optical disc device 118 can reproduce data from the optical disc 100 and record data on the optical disc 100. Note that the function of recording data is not essential, and the optical disk device 118 may be a reproduction-only optical disk player. At this time, a data modulation circuit 114, a recording compensation circuit 115, and a laser control circuit 116 of the optical disk device 118 described later are not necessary.

  A physical configuration of the optical disc 100 is shown in FIG. A disk-shaped optical disk 1 has a number of tracks 2 formed in a spiral shape, for example, and each track 2 has a number of finely divided sectors. Data is recorded on each track 2 in units of blocks 3 having a predetermined size. The track 2 is meanderingly formed, and an address value corresponding to each block 3 is recorded by modulation of the meandering frequency or phase.

  The optical disk device 118 includes an optical head 101, a motor 102, a servo circuit 103, an A / D conversion circuit 104, a DC control circuit 105, a PLL circuit 106, a PR equalization filter 107, a Viterbi decoding circuit 108, a data demodulation circuit 109, and a quality evaluation. A circuit 110, a disc information reproduction circuit 111, a CPU 112, a data modulation circuit 114, a recording compensation circuit 115, and a laser control circuit 116 are provided.

  Servo circuit 103, A / D conversion circuit 104, DC control circuit 105, PLL circuit 106, PR equalization filter 107, Viterbi decoding circuit 108, data demodulation circuit 109, quality evaluation circuit 110, disk information reproduction circuit 111, CPU 112, data The modulation circuit 114, the recording compensation circuit 115, and the laser control circuit 116 are mounted as one chip circuit (optical disk controller) 117. All of these may not be integrated into one chip. For example, the servo circuit 103 may not be included. Alternatively, the laser control circuit 116 may be incorporated in the optical head 101. Furthermore, these may be provided separately as individual circuits without being integrated into one chip. It should be noted that the optical disc 100 described above is not an essential component of the optical disc device 118 because it can be removed from the optical disc device 118.

  The optical head 101 irradiates the optical disc 100 with a light beam, detects the amount of light reflected from the optical disc 100 while scanning the track, and outputs an electrical signal (reproduction signal) corresponding to the amount of reflected light. Although not shown, the optical head 101 includes a light source that emits a light beam, a lens that focuses the light beam, and a light receiving unit that receives the light beam reflected by the information recording layer of the optical disc 100 and outputs a reproduction signal. Is provided.

  The motor 102 rotates the optical disc 100 at a specified number of rotations.

  The servo circuit 103 generates and extracts a servo error signal corresponding to the light beam condensing state on the track of the light beam from the reproduction signal from the optical head 101, and from the optical head 101 in the track of the optical head 101 using the servo error signal. Control is performed so that the light beam condensing state and the track scanning state are optimal. Further, the radial position (for example, the track position) on the optical disc 100 that irradiates the light beam and the rotational speed of the motor 102 are optimally controlled.

  The A / D conversion circuit 104 outputs a sampling signal obtained by sampling the data reproduction signal corresponding to the mark / space recorded on the track from the reproduction signal from the optical head 101 with the reproduction clock.

  The DC control circuit 105 detects the energy center level of the sampling signal, and controls the DC level of the sampling signal so that the energy center level becomes the zero level of the subsequent processing circuit (center level of signal processing). FIG. 2 is a block diagram showing the configuration of the DC control circuit. The DC control circuit 105 includes an adding circuit 200, an integrating circuit 201 including an adder and a delay circuit, and a gain circuit 202. The adding circuit 200 subtracts the detected energy center level from the input sampling signal, thereby removing the DC offset component so that the energy center becomes zero level. The integrating circuit 201 detects the energy center level by integrating the values of the sampling signals after DC control. The gain circuit 202 determines the responsiveness of feeding back the energy center level detected by the integrating circuit 201 to the DC control level input to the adder 200. Since the frequency component of the data reproduction signal should not be affected, it is usually desirable to set a value smaller than 1/1000.

  The PLL circuit 106 uses the sampling signal after DC control to generate a reproduction clock that is synchronized with the channel frequency of the data reproduction signal. The recovered clock is also used as a processing clock by sampling in the A / D conversion circuit 104, DC control circuit 105, PR equalization filter 107, Viterbi decoding circuit 108, and data demodulating circuit 109. In addition, although it was set as the structure which produces | generates the reproduction | regeneration clock synchronized with the reproduction | regeneration signal and it samples by the A / D conversion circuit 104, it is not limited to this. For example, the A / D conversion circuit 104 is a PLL circuit of an ITR (Interpolated Timing Recovery) system that samples at a frequency higher than the reproduction clock and then converts the sampling signal into a digital signal synchronized with the channel frequency by a digital filter or the like. May be.

  The PR equalization filter 107 is a digital filter that performs PR equalization processing on the sampling signal after DC control so as to have a frequency characteristic suitable for intersymbol interference that occurs according to the recording density of the optical disc 100. For example, as shown in FIG. 9A, in the case of a conventional BD having a recording density (25 GB per information recording layer), the laser wavelength 904 is 405 nm, and the numerical aperture (Numerical Aperture; NA) of the objective lens 903 is 0. .85, the length of the shortest recording mark 2T902 recorded on the track 900 is 149 nm, and in this case, PR (1, 2, 2, 1) equalization is most suitable. As shown in FIG. 9B, when the recording density is further increased to 33.4 GB per information recording layer, the length of the shortest recording mark 2T906 recorded on the track 900 is 111.5 nm. In this case, PR (1, 2, 2, 2, 1) equalization is most suitable. Hereinafter, PR (1, 2, 2, 2, 1) equalization will be described as an example. The PR equalizing filter 107 may be a digital filter with a fixed coefficient, or adaptively controlling the coefficient so as to be close to the frequency characteristic of PR (1, 2, 2, 2, 1). It may be a digital filter.

  As described above, the Viterbi decoding circuit 108 is a state transition sequence that minimizes the cumulative value L of the square of the difference from the signal expected value obtained by the equation (1) with respect to the output signal of the PR equalization filter 107. Is selected and decoded into corresponding binary data. The signal expectation value in the case of PR (1, 2, 2, 2, 1) ML will be described with reference to FIGS. FIG. 3 shows a signal expectation value level 302 for the bit pattern 300 of binarized data for 5T. For example, in the case of BD, since the 1-7 modulation method is used, the length of the shortest mark / space is 2T, and there are 32 5T bit patterns 300 in total. As shown in state 301 in FIG. 3, the pattern is narrowed down to 16 patterns. When these 16 bit patterns 300 are convolved with the frequency characteristics of PR (1, 2, 2, 2, 1), 9 levels from 0 to 8 are obtained, and the signal expectation value 302 is set to the center level 4 The value of -4 to +4 with 0 being 0. FIG. 4 shows ideal reproduction signals from 2T to 9T based on the bit pattern 300 and the signal expectation value 302 obtained in FIG. The signal 400 has a 2T waveform, the signal 401 has a 3T waveform, the signal 402 has a 4T waveform, the signal 403 has a 5T waveform, the signal 404 has a 6T waveform, the signal 405 has a 7T waveform, the signal 406 has an 8T waveform, and the signal 407 has a 9T waveform. The signal level 408 is the expected signal level +4, the signal level 409 is the expected signal level +3, the signal level 410 is the expected signal level +2, the signal level 411 is the expected signal level +1, and the signal level 412 is the expected signal level 0 ( Signal level 413, signal level 414 is signal expected value level-2, signal level 415 is signal expected value level-3, and signal level 416 is signal expected value level-4. Here, if the signal amplitude is changed from −0.5 to +0.5, the interval between the signal expected value levels is 0.125. As shown in FIG. 4, the Viterbi decoding circuit 108 normally performs maximum likelihood decoding using 9-level signal expected values at intervals of 0.125 from −0.5 to +0.5.

  The data demodulating circuit 109 demodulates the binarized data decoded by the Viterbi decoding circuit 108 according to the 1-7PP modulation method, and outputs reproduced data.

  The quality evaluation circuit 110 is a circuit that calculates an evaluation index value indicating the quality of a reproduction signal, as described in Patent Document 1, for example.

  The disc information reproducing circuit 111 reproduces address information and disc control information recorded in advance on the optical disc 100 from the reproduction signal from the optical head 101.

  The data modulation circuit 114 outputs a modulation signal obtained by modulating the recording data according to the 1-7PP modulation method when recording the recording data in a predetermined block on the track of the optical disc 100.

  The recording compensation circuit 115 generates a recording compensation signal for controlling the timing of the edge position of the recording mark and the recording power level from the modulation signal so that the recording mark is appropriately formed on the track of the optical disc 100.

  The laser control circuit 116 controls the irradiation power of the light beam from the optical head 101 according to the recording compensation signal. Thereby, a recording mark is formed on the track of the optical disc 100.

  The CPU 112 obtains the address information reproduced by the disk information reproducing circuit 111, instructs the servo circuit 103 to search for a block for recording and reproducing data, and performs a recording operation on each circuit at the searched block position. Instruct the playback operation. Thereby, each circuit controls the optical head 101 to irradiate the light beam with the irradiation power of the light beam suitable for the recording operation or the reproducing operation to be performed.

  Further, the CPU 112 obtains a β designated value included in the disc control information reproduced by the disc information reproducing circuit 111, and sets expected signal values of the Viterbi decoding circuit 108 based on the obtained β value. Processing 113 is included. FIG. 7 shows the process steps of the expected value calculation process 113. First, in step 700, an instruction is issued to the servo circuit 103 and the disc information reproducing circuit 111 to search for a track on which disc control information is recorded, and to reproduce the disc control information. In step 701, a β designation value is extracted from the reproduced disc control information according to a predetermined format. Next, in step 702, each signal expected value used in the Viterbi decoding circuit 108 is calculated according to a predetermined calculation formula based on the β designated value. In step 703, the calculated signal expected values are set in the Viterbi decoding circuit. After the above, in step 704, an instruction is issued to the servo circuit 103 and the disc information reproducing circuit 111 to search for a track for reproducing data and reproduce the data. Although the CPU 112 performs the process of calculating the expected signal value, the calculation process may be performed by the Viterbi decoding circuit 108 or the disc information reproducing circuit 111.

  Next, the method for calculating the expected signal value in step 702 in the expected value calculation process 113 will be described with reference to FIGS.

  FIG. 5 shows the waveform of the data reproduction signal. Here, since the data reproduction signal 500 is controlled by the DC control circuit 105 so that the energy center becomes zero level, the reproduction signal energy center level 501 is zero level. When the maximum amplitude level 502 of the data reproduction signal 500 is A and the minimum amplitude level 503 is B, the β value is a value defined as (A + B) / (A−B) × 100. For example, when A is +0.45 and B is −0.55, the β value is 10%.

  FIG. 6 shows an example in which the 9 levels of the signals shown in FIGS. 3 and 4 described above are equally spaced in the output signal after the PR signal is subjected to PR equalization by the PR equalization filter 107 with respect to the β value. This shows a relationship that deviates from the general state. The signal level 600 is the expected signal level +4, the signal level 601 is the expected signal level +3, the signal level 602 is the expected signal level +2, the signal level 603 is the expected signal level +1, and the signal level 604 is the expected signal level 0 ( Signal level 605, signal level 606 corresponds to signal expected value level-2, signal level 607 corresponds to signal expected value level-3, and signal level 608 corresponds to signal expected value level-4. . When the signal amplitude is changed from -0.5 to +0.5, an equal level of 0.125 intervals is ideal when the β value is 0%. In a state where the energy center is controlled to be zero level, the signal level 604 of the center level has a feature that the level decreases as the β value increases and shifts so that the level increases as the β value decreases. For the other levels, as the β value increases, the interval between the levels above the center level increases, and the interval between the lower levels decreases. On the contrary, when the β value becomes small, the interval between the levels above the center level is narrowed, and the interval between the levels below is widened. From the above, the relationship in which the value of each level changes according to the β value can be approximated by a linear expression such as Vn = Pn · β + Qn. Here, n is each level from -4 to +4, Vn is a signal expectation value of level n, Pn is a coefficient indicating a slope with respect to the β value of level n, β is a β value, Qn is a β value of level n of 0% Represents the expected signal value. Using this relational expression, the expected signal value of each level can be calculated from the acquired β designated value.

  Although the relationship is a linear equation, it may be a quadratic or higher polynomial approximation.

Further, the expected signal value Qn when the β value is 0% is set to an ideal equal level of 0.125 intervals. However, in high-density recording of 33.4 GB per information recording layer, it is as short as 2T or 3T. The amplitude of the mark is very small and may not reach a uniform level as the output signal of the PR equalizing filter 107. In such a case, for example, a signal expectation indicating the amplitude of the 3T signal when the β value is 0%. The values Q ₊₂ and Q ₋₂ may be +0.220 and −0.220 instead of +0.250 and −0.250, respectively.

Further, for example, when the relationship is a linear expression, it is known that the coefficient Pn is experimentally in the following range.
−0.526 <P ₋₄ <−0.283
−0.158 <P ₋₃ <−0.085
+0.072 <P ₋₂ <+0.133
+0.005 <P ₋₁ <+0.009
+0.183 <P ₀ <+0.138
−0.005 <P ₊₁ <+0.005
+0.087 <P ₊₂ <+0.162
−0.236 <P ₊₃ <−0.127
−0.380 <P ₊₄ <−0.706

  As described above, the β designation value designated as the optimum recording condition that can maximize the repetitive recording characteristics and the aging deterioration characteristics of the optical disc 100 is acquired, and the expected signal value in the Viterbi decoding circuit 108 is calculated according to the β designation value. In this state, recording is performed on the optical disc 100, reproduction is performed, the quality index value by the quality evaluation circuit 110 is referred to, and the timing of the edge position of the recording mark in the recording compensation circuit 115 is set so that the quality index value becomes small. By appropriately adjusting the recording power level and the irradiation power of the light beam in the laser control circuit 116, it is possible to perform recording under the optimum recording conditions of the optical disc 100.

  Although the signal expectation value is set at 9 levels, the present invention is not limited to this. For example, in the case of PR (1, 2, 2, 2, 1), it may be set for each of the 16 patterns in the state 301 shown in FIG. 3, or signal levels related to 2T and 3T that are likely to change. May be set for each state 301 and other signal levels may be set together.

  The optical disk device 118 includes the CPU 112, the data demodulation circuit 109, the data modulation circuit 114, and the disk information reproduction circuit 111, but is not limited thereto. For example, it may be an optical disk evaluation apparatus in which the CPU 112, the data demodulation circuit 109, the data modulation circuit 114, and the disk information reproduction circuit 111 are not provided and a host computer is connected separately.

(Embodiment 2)
FIG. 8 shows an area configuration of the optical disc according to the second embodiment of the present invention.

  The optical disc 800 includes an information recording layer. Data is recorded on the optical disc 800 by forming recording marks in the information recording layer. On the optical disk 800, tracks are formed concentrically.

  Optical disc 800 includes a BCA (Burst Cutting Area) area 810, a lead-in area 820, a user area 830, and a lead-out area 840.

  In the BCA area 810, a barcode-like signal is recorded in advance, and includes a unique number for identifying a medium that is different for each disc, copyright information, and disc characteristic information. This disc characteristic information includes the number of information recording layers and identification information of an address management method. The disk characteristic information includes, for example, information indicating the number of information recording layers, predetermined bit information corresponding to the number of permitted layers, and information on recording density. Examples of the information relating to the recording density include information indicating the recording capacity of the optical disc and information indicating the channel bit length (recording line density).

  In addition, in the case of a read-only disc, the storage location of the information related to the recording density may be the BCA area and / or the inside of the recording data (uneven pits) (recorded as a data address added to the data). In the case of a write-once or rewritable recording disc, a BCA area and / or PIC area and / or wobble (recorded as sub-information superimposed on the wobble) can be considered.

  The user area 830 is configured so that the user can record arbitrary data. For example, user data is recorded in the user area 830. User data includes, for example, audio data and visual (video) data.

  Unlike the user area 830, the lead-in area 820 is not configured to allow the user to record arbitrary data. The lead-in area 820 includes a PIC (Permanent Information and Control data) area 821, an OPC (Optimum Power Calibration) area 822, and an INFO area 823.

  The PIC area 821 includes disc characteristic information. In this disk characteristic information, for example, the number of information recording layers, identification information of an address management method, and access parameters described above are recorded. The access parameter is, for example, a parameter relating to laser power for forming / erasing a plurality of recording marks on the optical disc 800 and a parameter relating to a recording pulse width for recording a plurality of recording marks.

  In the optical disc 800, each value of a signal expected value level used for maximum likelihood decoding when reproducing a state recorded under an optimum recording condition capable of maximizing repetitive recording characteristics and aging deterioration characteristics is recorded in the BCA area and / or Alternatively, it is recorded in the PIC area. By acquiring this value and setting it as the expected signal level of maximum likelihood decoding as shown in the first embodiment, it is possible to reproduce the signal in an optimal state.

  In the present embodiment, it is assumed that disk characteristic information including each value of the expected signal level used for maximum likelihood decoding is stored in both the BCA area 810 and the PIC area 821. However, this is an example and is not limited to this example. For example, any of a BCA area, a PIC area, the inside of recording data, a wobble, or any two or more of these areas may be used. If the same disc characteristic information is recorded in a plurality of locations, it can be read out from either one. Therefore, it is possible to ensure the reliability of the disk characteristic information. Even if the type of the disc is unknown, the optical disc apparatus can know the number of information recording layers of the disc by storing the disc characteristic information in these pre-positioned areas. Can do.

  When there are a plurality of information recording layers, the information recording layer (reference layer) on which the disk characteristic information is arranged is, for example, the layer farthest from the optical head, in other words, the laser beam is incident. It may be a layer at the deepest position from the surface on the side to be processed.

  In addition, although each value of the signal expected value level used for maximum likelihood decoding is included in the disk characteristic information, the present invention is not limited to this. For example, it may be an interval between each signal expected value level, or may be a coefficient of a calculation formula for obtaining each signal expected value level from a β designated value.

  In the above-described embodiment, the expected signal value of maximum likelihood decoding (Viterbi decoding circuit 108) is changed. However, a range in which the expected signal value can be changed may be determined. For example, FIG. 11A corresponds to two bit patterns with a small Euclidean distance that are relatively likely to be erroneous in the maximum likelihood decoding in the case of the PR (1, 2, 2, 2, 1) ML system. An example of an ideal signal waveform is shown. In the case of these two signal waveforms, the square of the Euclidean distance is 14. FIG. 11B shows an example of the signal waveform when the expected signal value calculated with the β value of −10% is used in these two bit patterns. At this time, the square of the Euclidean distance is 13.71, which is about 2% smaller than the original 14, and changes to the side where decoding errors are likely to occur. FIG. 12 shows a change in the square value of the Euclidean distance with respect to the β value in the above bit pattern. The larger the square of the Euclidean distance, the greater the margin for decoding errors. For example, the range of the β designated value (or the corresponding signal expectation value) may be set to −15% or more.

  Finally, BD (Blu-ray Disc) will be briefly explained as an example of the optical disc of the present invention. The main optical constants and physical formats of Blu-ray Discs can be found on the white papers posted on the Blu-ray Disc Reader (Ohm Publishing) and the Blu-ray Association website (http://www.blu-raydisc.com/). It is disclosed.

  In the BD, a laser beam having a wavelength of 405 nm (400 to 410 nm if the tolerance of the error range is ± 5 nm) and NA = 0.85 (0.84 to if the tolerance of the error range is ± 0.01). 0.86) objective lens is used. The track pitch is 0.32 μm, the channel clock frequency is 66 MHz (66.000 Mbit / s) at the BD standard transfer rate (1 ×), 264 MHz (264.000 Mbit / s) at the transfer rate of BD4x, and the transfer rate of BD6x Is 396 MHz (396.000 Mbit / s), and the transfer rate of BD8X is 528 MHz (528.000 Mbit / s). The standard linear velocity (reference linear velocity, 1X) is 4.917 m / sec.

  As for the thickness of the protective layer (cover layer), a thinner protective layer than 0.6 mm of DVD so that the influence of spot distortion due to tilt can be suppressed as the numerical aperture is increased and the focal length is shortened. For example, out of the total thickness of the medium of about 1.2 mm, the protective layer has a thickness of 10 to 200 μm (more specifically, a substrate of about 1.1 mm, a transparent protective layer of about 0.1 mm for a single-layer disc, two In the case of a layered disc, a protective layer of about 0.075 mm may be used as an intermediate layer (Spacer Layer) of about 0.025 mm, and in the case of three or more discs, the thickness of the protective layer and / or the intermediate layer is further reduced.

  INDUSTRIAL APPLICABILITY The present invention is useful for increasing the recording density of an optical disc, and can be used for a large-capacity optical disc, a reproducing method thereof, an optical disc apparatus, and an integrated circuit.

1 is a block diagram illustrating a configuration of an optical disc device according to Embodiment 1. FIG. It is a block diagram which shows the structure of the DC control circuit of an optical disk apparatus. It is a figure which shows the signal expected value of the maximum likelihood decoding with respect to the bit pattern in the case of PR (1, 2, 2, 2, 1). It is a figure which shows the signal level of the reproduction | regeneration signal which performed the ideal equalization process in the case of PR (1, 2, 2, 2, 1). It is a figure which shows (beta) value of a data reproduction signal. It is a figure which shows the example of the relationship between (beta) value and the signal expectation value of maximum likelihood decoding. It is a figure which shows the process of calculating | requiring the signal expectation value of maximum likelihood decoding from (beta) designation | designated value. FIG. 6 is a diagram showing an area configuration of an optical disc according to a second embodiment. (A) is a figure which shows the example of BD of the conventional recording density, (B) is a figure which shows the example of the high density disc of recording density higher than BD. It is a figure which shows the physical structure of an optical disk. (A) is an ideal waveform of two bit patterns in which the square of the Euclidean distance is 14, and (B) is a diagram showing an example of a waveform when the β value becomes −15%. It is a figure which shows the example of the relationship between the square of the Euclidean distance of two bit patterns, and (beta) value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100, 800, 1 Optical disk 101 Optical head 102 Motor 118 Optical disk apparatus 200 Adder circuit 201 Integration circuit 202 Gain circuit 500 Data reproduction signal 900, 2 tracks 901, 902, 905, 906 Recording mark 3 blocks

Claims (26)

A maximum likelihood decoding method for decoding the most probable digital information from a sampling signal of a reproduction signal obtained by reproducing information recorded in a mark and a space on an optical disc track,
The difference between the sampling signal sequence of the reproduction signal in a predetermined period and the expected value sequence of the sampling signal of the reproduction signal corresponding to each digital information sequence is detected, and the digital information sequence having the smallest difference is determined as the reproduction signal. A maximum likelihood decoding step to select as a decoding result;
An index value designating step for designating an expected value of an index value indicating a ratio between the energy center of the reproduction signal and the center of amplitude of the longest mark and the longest space;
A calculation step of calculating each expected value of the sampling signal used in the maximum likelihood decoding step according to the expected value of the index value,
In the maximum likelihood decoding step, each expected value of the sampling signal calculated in the calculation step is used.   The maximum likelihood decoding method according to claim 1, wherein the maximum likelihood decoding step is Viterbi decoding.   A DC control step of detecting the energy center level of the sampling signal of the reproduction signal and controlling the DC level of the sampling signal so that the detected energy center level becomes the center level of the processing of the maximum likelihood decoding step; The maximum likelihood decoding method according to claim 1, wherein:   The method further comprises a partial response equalization step for equalizing the sampling signal of the reproduction signal so as to have a predetermined frequency characteristic, and an output signal of the partial response equalization step is input to the maximum likelihood decoding step. The maximum likelihood decoding method according to claim 1.   5. The maximum likelihood decoding method according to claim 4, wherein the equalization characteristic of the partial response equalization step is PR (1, 2, 2, 2, 1) equalization.   6. The maximum likelihood according to claim 5, wherein the expected value of the sampling signal used in the maximum likelihood decoding step is a 9-level value corresponding to PR (1, 2, 2, 2, 1) equalization. Decryption method.   The information recorded on the optical disc is recorded according to the 1-7 modulation method, and there are 16 types of patterns in PR (1, 2, 2, 2, 1) equalization, and the sampling signal used in the maximum likelihood decoding step 6. The maximum likelihood decoding method according to claim 5, wherein the expected value is a value corresponding to the 16 types of patterns. An optical disc apparatus for reproducing information recorded with a mark and a space on an optical disc track,
An optical head for irradiating the optical disc with a laser and outputting a reproduction signal corresponding to the amount of reflected light;
A reproduction clock generation circuit for generating a reproduction clock from the reproduction signal;
An A / D conversion circuit for outputting a sampling signal obtained by sampling the reproduction signal with the reproduction clock;
A maximum likelihood decoding circuit for decoding the most probable digital information from the sampling signal,
The maximum likelihood decoding circuit includes:
A difference between the sampling signal sequence in a predetermined period and an expected value sequence of the sampling signal of the reproduction signal corresponding to each digital information sequence is detected, and a digital information sequence having the smallest difference is obtained as a decoding result of the reproduction signal. A decoding circuit to select;
An index value designating circuit for designating an expected value of an index value indicating a ratio between the energy center of the reproduction signal and the center of the amplitude of the longest mark and the longest space;
A calculation circuit that calculates each expected value of the sampling signal used in the maximum likelihood decoding step according to an expected value of the index value,
The optical disc apparatus characterized in that the decoding circuit uses each expected value of the sampling signal calculated by the calculation circuit.   9. The optical disc apparatus according to claim 8, wherein the decoding circuit is a Viterbi decoding circuit.   A DC control circuit that detects an energy center level of the sampling signal of the reproduction signal and controls a DC level of the sampling signal so that the detected energy center level becomes a center level of processing of the decoding circuit; The optical disc apparatus according to claim 8.   A partial response equalization circuit for equalizing the sampling signal of the reproduction signal so as to have a predetermined frequency characteristic, and an output signal of the partial response equalization circuit is input to the decoding circuit. Item 9. The optical disk device according to Item 8.   12. The optical disc apparatus according to claim 11, wherein the equalization characteristic of the partial response equalization circuit is PR (1, 2, 2, 2, 1) equalization.   13. The optical disc apparatus according to claim 12, wherein an expected value of the sampling signal used in the maximum likelihood decoding circuit is a 9-level value corresponding to PR (1, 2, 2, 2, 1) equalization. .   Information recorded on the optical disc is recorded according to the 1-7 modulation method, and there are 16 types of patterns in PR (1, 2, 2, 2, 1) equalization. The sampling signal used in the maximum likelihood decoding circuit 13. The optical disc apparatus according to claim 12, wherein the expected value is a value corresponding to the 16 types of patterns.   9. The expected value of the index value is recorded in advance on the optical disc, and the index value designating circuit sets the acquired expected value information as the expected value of the index value. Optical disk device. An integrated circuit that decodes a reproduction signal obtained by reproducing information recorded in a mark and a space on an optical disc track,
A reproduction clock generation circuit for generating a reproduction clock from the reproduction signal;
An A / D conversion circuit for outputting a sampling signal obtained by sampling the reproduction signal with the reproduction clock;
A maximum likelihood decoding circuit for decoding the most probable digital information from the sampling signal,
The maximum likelihood decoding circuit includes:
A difference between the sampling signal sequence in a predetermined period and an expected value sequence of the sampling signal of the reproduction signal corresponding to each digital information sequence is detected, and a digital information sequence having the smallest difference is obtained as a decoding result of the reproduction signal. A decoding circuit to select;
An index value designating circuit for designating an expected value of an index value indicating a ratio between the energy center of the reproduction signal and the center of the amplitude of the longest mark and the longest space;
A calculation circuit that calculates each expected value of the sampling signal used in the maximum likelihood decoding step according to an expected value of the index value,
The integrated circuit, wherein the decoding circuit uses each expected value of the sampling signal calculated by the calculation circuit. When playing back information recorded on a track with marks and spaces, the difference between the sampling signal sequence of the playback signal and the expected value sequence of the playback signal sampling signal corresponding to each digital information sequence is detected. The digital information is decoded by a maximum likelihood decoding method that selects a digital information sequence having a minimum difference as a decoding result of the reproduction signal,
An optical disc in which information on each expected value of a sampling signal used in the maximum likelihood decoding is recorded in advance.   18. The optical disc according to claim 17, wherein the information of each expected value recorded in advance is a 9-level value corresponding to PR (1, 2, 2, 2, 1) equalization.   Information recorded on the optical disc is recorded according to the 1-7 modulation method, and there are 16 types of patterns in PR (1, 2, 2, 2, 1) equalization. 18. The optical disc according to claim 17, wherein the information is a value corresponding to the 16 types of patterns.   18. The optical disc according to claim 17, wherein the information of each expected value recorded in advance is recorded by track wobbling.   18. The optical disc according to claim 17, wherein the information of each expected value recorded in advance is recorded by a mark and a space on a track.   18. The optical disc according to claim 17, wherein the information of each expected value recorded in advance is recorded in a BCA (Burst Cutting Area).   The wavelength of the laser that irradiates the track is λ, the numerical aperture of the objective lens that focuses the laser on the track is NA, the shortest mark length recorded on the track is Tm, and the shortest space length is Ts, and (Tm + Ts) <λ The optical disc according to claim 17, which is / (2NA).   The optical disk according to claim 23, wherein the wavelength λ of the laser is 400 nm to 410 nm.   The optical disk according to claim 23, wherein the numerical aperture NA of the objective lens is 0.84 to 0.86.   The optical disk according to claim 23, wherein a length Tm + Ts obtained by adding the shortest mark length Tm and the shortest space length Ts is less than 238.2 nm.

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