JP4213632B2 - Data playback device - Google Patents

Description

  The present invention relates to a data reproducing apparatus that reproduces data (recording codes) on a recording medium such as an optical disk, and more particularly to a technique for performing reproduction processing using a PRML method.

  For recordable disc media including optical discs such as CD (Compact Disc) and DVD (Digital Versatile Disc) and magnetic discs, intersymbol interference and noise in the playback waveform as recording density increases and recording / playback processing speeds up. However, a technique called PRML is known as a means for performing highly reliable reproduction processing under such conditions.

  PRML is a combination of multi-value convolutional code generation processing based on PR (Partial Response) equalization and maximum likelihood decoding such as Viterbi decoding, so that a digital code (recorded on a recording medium (disk)) ( Recording code).

  In the PR equalization process, the amount of intersymbol interference is adjusted by waveform equalization using an FIR filter for the sample value obtained by subjecting the reproduction signal from the disk to analog-digital conversion by an A / D converter. Then, a multi-level convolutional code sequence (PR code) having several amplitude values corresponding to the permutation pattern of continuous recording codes is generated. There are innumerable forms of PR equalization depending on the number of recording codes (constraint length) used to generate one sample of PR codes and how amplitude values are given.

  In the maximum likelihood decoding process, a plurality of reference values (PR code reference values) corresponding to each code value are set as ideal PR code values that do not include disturbance factors such as noise and variation in the reproduced signal. Then, based on distance information calculated between these and a PR code (PR equalization value) including a disturbance component obtained by an actual device, a soft decision between the PR equalization value and the PR code reference value is performed. Then, the recording code pattern determined to be the maximum likelihood based on the result is decoded.

  By the way, in a recordable disc medium, there may be a plurality of areas having different reproduction characteristics on the same medium. That is, there are a case where an area in which non-rewritable information such as a physical address is recorded on the disk coexists with an additionally writable area, and a case where areas additionally written by different data recording apparatuses coexist. In such a case, the amplitude level of the PR equalization code deviates from the initially set PR code reference value due to the difference in the reproduction signal amplitude before and after the switching of the reproduction characteristics, so that there is a problem that the reliability of the decoding process is lowered. .

As a technique that can be a solution to the above problem, Patent Document 1 describes an apparatus having means for giving an appropriate PR code reference value to each region having different reproduction characteristics in a recording medium. In this apparatus, a PR code reference value calculation pattern (training pattern) recorded in advance on a recording medium is divided into several areas centered on each PR code reference value with respect to the magnitude of the PR equalization value. The PR equalized value samples that are reproduced are grouped for each sample that applies to each region. By calculating the average for each group, it is possible to set a PR code reference value suitable for the area to be reproduced.
JP-A-9-245432

  In order to achieve high reliability of the decoding process in the PRML process, the distribution of the PR equalized value and the PR code reference value coincide with each other, that is, an appropriate distribution of the PR equalized value centered on the PR code reference value. Formation is necessary. In the case where a non-rewritable area and an additionally writable (rewritable) area coexist on the disk, or in the case where an area that has been additionally written by different data recording devices coexists, the reproduction characteristics are recorded on the same recording medium. Since there are a plurality of different data areas, it is desired to perform decoding processing by switching to an appropriate PR code reference value for each data area.

  In the level determination and grouping process of the PR equalization value using the apparatus described in Patent Document 1, accurate determination is easy when the number of levels of the PR code reference value is small, and an appropriate PR code reference value is determined. Calculation is possible. However, in general, a complicated PR code system having a large constraint length has a large number of levels of the PR code reference value, and the interval between the levels is narrow, making accurate determination difficult. In the technique described in Patent Document 1, when a PR code system having a large number of PR code reference value levels is applied, accurate determination becomes difficult.

  The present invention has been made in view of the above problems, and an object of the present invention is to perform data reproduction processing of digital data (recording code) by the PRML method on a recording medium in which a plurality of data areas having different reproduction characteristics coexist. Even if a PR encoding method having a large number of PR code reference value levels is applied to the playback apparatus, it is possible to realize a highly reliable decoding process by setting an appropriate PR code reference value for each data area having different playback characteristics. To provide technology.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  In order to achieve the above object, a data reproducing apparatus of the present invention detects data (recording code) by a PRML method using a PR equalizer and a maximum likelihood decoder for a reproduction signal from a recording medium such as an optical disk. A playback device characterized by the following. The recording medium to be reproduced is of a format having an area where a known data pattern is recorded corresponding to a data area having different reproduction characteristics. The data reproducing apparatus of the present invention uses the sample value or PR equalized value of the reproduction signal from the recording medium as an input signal as means for calculating the PR code reference value, and uses the data without using maximum likelihood decoding. A code identification circuit for identifying (decoding) (recording code), a code identification value holding circuit for sequentially inputting a code identification value as a result of the identification and holding a code identification value pattern within a predetermined period, and a reproduction signal PR equalized value samples, which are PR equalized outputs, are sequentially input, and a plurality of consecutive PR equalized value samples (PR equalized value patterns) in the same period as the code identification value holding circuit are held together. For each PR equalized value sample and amplitude level stored in the PR equalized value holding circuit according to the PR equalized value holding circuit and the code identification value pattern held by the code identification value holding circuit. An equalization value-ideal value determination circuit for determining a correspondence relationship for similar groups, and an equalization for grouping PR equalization value samples stored in the PR equalization value holding circuit based on the determination result A value grouping circuit; and an average value calculation circuit that calculates an average value for each group of the grouped PR equalized value samples. The data reproducing apparatus of the present invention uses the area of the known data pattern as a learning data area for calculating a PR code reference value during the reproduction process of the recording medium, and the code identification value holding circuit An output value of the code identification circuit for a reference value calculation area is held, and the PR equalization value holding circuit holds a PR equalization value for the PR code reference value calculation area, and the equalization value− The ideal value determination circuit determines a correspondence relationship between each PR equalization value sample and a PR code value reference value level based on the code identification value pattern held in the code identification value holding circuit, and performs the equalization value grouping The circuit performs grouping based on a determination result of the equalization value-ideal value determination circuit, calculates a total value in each group, and counts the number of samples, and the average value calculation circuit The average value is calculated for the loop, by setting the PR code reference value for the data area following in response to the learning data area based on the calculated value, to perform maximum likelihood decoding by this setting.

  The recording medium to be reproduced is of a format in which a data pattern area known to the data reproducing apparatus of the present invention is provided at the boundary of an area where reproduction characteristics are switched, for example, at the head of the user data area immediately after that. The known data pattern is used as learning data for calculating the PR code reference value in the means for calculating the PR code reference value including the code identification circuit. In the known data pattern area on the recording medium, a data pattern designed so that the amplitude of the PR equalization value for this area takes the level of all PR code ideal values is recorded in advance at the time of recording the reproduction target data, for example. The The code identification circuit is a circuit for code identification processing provided separately from the PRML processing circuit. The data reproducing apparatus of the present invention performs grouping on the PR equalized value for the learning known data pattern region and calculation of an average value in each group at the time of reproducing data on the recording medium. A PR code reference value suitable for the characteristics of each data area following the known data pattern area is calculated and set. The maximum likelihood decoder performs a highly reliable decoding process based on the setting of the PR code reference value.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  According to the present invention, even if a PR encoding method having a large number of PR code reference value levels is applied to a data reproducing apparatus that performs data reproduction processing by the PRML method for a recording medium in which a plurality of data areas having different reproduction characteristics coexist. Therefore, it is possible to realize a highly reliable decoding process by setting an appropriate PR code reference value for each data area of the reproduction characteristics. In particular, even in a scene where it is difficult to set the PR code reference value level in advance, for example, in an optical disc reproduction process in which a plurality of areas having different optical characteristics coexist due to differences in recording conditions, the reproduction signal is changed from the reproduction signal in that area. A decoding process can be realized by calculating and setting an appropriate PR code reference value level.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  FIG. 1 shows a configuration of a data reproducing apparatus according to an embodiment of the present invention. The present embodiment shows a configuration example as an optical disk reproducing apparatus (disk drive apparatus). The data reproduction apparatus according to the present embodiment includes a laser unit 102, a photodetector 103, an AGC circuit 104, an A / D conversion circuit 105, a PRML processing circuit 106, a demodulation circuit 116, and a PR code reference value calculation circuit 109. Configured. The PR code reference value calculation circuit 109 includes a code identification circuit 110, a code identification value holding circuit 111, a PR equalization value holding circuit 112, an equalization value-ideal value determination circuit 113, an equalization value grouping circuit 114, and an average value. A calculation circuit 115 is included. As a system configured to include the data reproducing apparatus of the present embodiment, the optical disk 101 and a host device (not shown) are included.

  The optical disc 101 is a recording medium such as a CD or a DVD included in a playback process target in the data playback apparatus of the present embodiment, and data (record code) to be played back is recorded in a predetermined recording format. The optical disc 101 has a plurality of data areas having different reproduction characteristics, and correspondingly has an area in which a known data pattern for calculating a PR code reference value is recorded at a boundary where the characteristics are switched. The format of the optical disc 101 is, for example, a DVD-RAM. The DVD-RAM has a VFO area, which is an area in which a known data pattern is recorded, as a sector format at a location where the reproduction characteristics are switched on the disk. The data recorded in this VFO area can be used as learning data for calculating the PR code reference value.

  The laser unit 102 is a unit that emits coherent light to obtain a reflected light signal corresponding to a recording code from the optical disc 101. The photodetector 103 is a photodetector that converts the intensity of the reflected light signal into an electrical signal. The AGC circuit 104 controls the maximum value and the minimum value of the electric signal output from the photodetector 103 to be constant. The A / D converter 105 is a circuit that performs sampling and analog-digital conversion of the reproduction signal (analog) output from the AGC circuit 104 at a timing synchronized with the reproduction signal by a clock generated by a PLL circuit (not shown). is there. Due to the phase difference detection processing in the PLL, the DC offset of the ADC (A / D converter) output is compensated.

  The PRML processing circuit 106 includes a PR equalization circuit 107 and a Viterbi decoding circuit 108, and is a circuit that performs processing by PRML. The PR equalization circuit 107 is a circuit that performs PR equalization processing on the reproduction signal sample value (digital) output from the A / D converter 105. The Viterbi decoding circuit 108 uses the output from the PR equalization circuit 107, that is, the PR equalization value, and the ideal value, that is, the PR code reference value set by the PR code reference value calculation circuit 109 described later, on the optical disc 101. It is a circuit that performs maximum likelihood determination and output of data (recording code). The demodulation circuit 116 is a circuit that performs processing such as decoding and error correction on the binarized code obtained by the PRML processing circuit 106 and converts it into a data format handled by the host.

  The PR code reference value calculation circuit 109 is a circuit that performs a PR code reference value calculation process that is a characteristic process in the data reproducing apparatus of the present embodiment. The data reproduction apparatus according to the present embodiment performs optical disk reproduction processing by PRML processing using the PR code reference value calculation circuit 109. The PR code reference value calculated by the PR code reference value calculation circuit 109 is set in the Viterbi code circuit 108.

  The code identification circuit 110 is a circuit for identifying a recording code by using the reproduction signal sample value or the PR equalized value as an input signal and not using a PR code reference value. What is the PRML processing circuit 106? A separate code identification circuit. In particular, the present embodiment shows a configuration in which the code identification circuit 110 uses a reproduction signal sample value that is an output of the A / D converter 105 as an input signal. As another configuration, the code identification circuit 110 may use a PR equalization value that is an output of the PR equalization circuit 107 as an input signal. Detailed configuration will be described later.

  The code identification value holding circuit 111 is a holding circuit that stores and shifts the code value, which is the identification result of the code identification circuit 110, and outputs an identification code pattern within a predetermined period.

  The PR equalization value holding circuit 112 stores and shifts the output of the PR equalization circuit 107 as needed to hold a continuous PR equalization value pattern within the same fixed period as the period in the code identification value holding circuit 111. Circuit.

  The equalization value-ideal value determination circuit 113 is a plurality of PR equalization values stored in the PR equalization value holding circuit 112 and a plurality of PR equalization methods determined according to the identification code pattern held by the code identification value holding circuit 111. This is a circuit for determining the correspondence with the ideal value level.

  The equalization value grouping circuit 114 groups PR equalization values corresponding to each ideal value level (PR code group A, PR code group B,...) According to the processing result of the equalization value-ideal value determination circuit 113. ).

  The average value calculation circuit 115 calculates the average value of each group in the equalization value grouping circuit 114, and uses the calculated average values (group A average value, group B average value,...) In the Viterbi decoding circuit 108. It is a circuit that outputs as a PR code reference value used for decoding processing. In the following, data targeted for the optical disc 101 recorded with the restriction of the shortest mark length 2T (T is the transfer period of 1-bit data) by the PR equalization format represented as “PR (a, b, b, a)”. This embodiment will be described by taking a reproduction process as an example.

  FIG. 2 is a diagram showing an example of an optical disk reproduction signal (eye pattern) in the data reproduction apparatus according to the embodiment of the present invention. This shows an example of an eye pattern for a reproduction signal waveform input to the PRML processing circuit 106. Each vertical line indicates a strobe time, and each horizontal line indicates a multilevel (for example, 7 values) reference value level. Determination is performed in a predetermined time interval. In an optical disc recorded with high density, slice processing for identifying a code for each sample on the basis of a single amplitude level is small because the amplitude of a reproduction signal for a code having a short recording mark length is reduced due to intersymbol interference. Then, accurate reproduction becomes difficult. In contrast to this, PRML is called PRML that multi-values the reference amplitude level, collects the soft decision results between each sample value and the reference amplitude level, and performs code identification by maximum likelihood pattern determination for a series of sample strings. It is known that the technique is effective. In the PRML system, a reference value level is set based on a convolutional coding rule called a PR code, and waveform equalization (PR equalization) targeting the reference value level is performed.

  FIG. 3 is an explanatory diagram showing the configuration (digital code input) of the PR code circuit 301 that performs the processing by the PRML method. The configuration of the PR equalization circuit 107 corresponds to the configuration of the PR code circuit 301. As shown in FIG. 3, the PR code Y (n) in the format of “PR (a, b, b, a)” is a code string composed of binary values of “1” and “−1”, for example. It is generated by a convolutional encoder having a recording code X (n) as an input, a constraint length of 4, a tap number of 4, and a register (delay circuit) number of 3. The transfer function of this convolutional encoder is expressed by the following equation (1).

^{H (z -1) = a +} bz -1 + bz -2 + az -3 ··· (1)
FIG. 4 is an explanatory diagram showing a pulse response of the PR code circuit 301. The unit pulse response (PR equalization value Y (n)) of the PR code circuit 301 has a 4-step width as shown in FIG. 4 and interferes with a code adjacent to the input code string (recording code X (n)). give.

  FIG. 5 shows a correspondence table between the recording code X (n) and the PR code Y (n) in the PR code circuit 301. Under the condition of the shortest mark length 2T, there are 10 combinations of the input code X (n) and the PR code Y (n) as shown in FIG. 5, and the PR code Y (n) has a total of 7 values. is there. X (n) takes “1” and “−1” as values. Here, in a disk drive apparatus as a data reproducing apparatus, the input code X (n) corresponds to a mark and a space recorded on the disk. Further, the original code string X (n) can be decoded from the PR code Y (n) by the decoder having the inverse characteristic of the equation (1).

  On the other hand, the signal input to the PRML circuit (in the present embodiment, the PRML processing circuit 106) in the disk drive device is not a binary signal, as shown in FIG. / This is a multilevel reproduction signal to which intersymbol interference is added due to space or the spot shape of laser light. This type of intersymbol interference characteristic is called an MTF (Modulation Transfer Function) characteristic.

FIG. 6 is a diagram showing a configuration (analog signal input) of the PR equalization circuit 107. The PR equalization circuit 107 that performs PR equalization is an FIR filter as shown in FIG. 6 that receives the reproduction signal quantized and sampled by the A / D converter 105 as an input. An input reproduction signal X ′ (t) is composed of an ADC (A / D converter), a delay circuit (Z ⁻¹ ), a multiplier for each coefficient (A to D), and an adder (Σ). A PR equalized value Y ′ (n) is output through the convolution process. This circuit gives a frequency characteristic so that the transfer characteristic combined with the MTF characteristic matches the characteristic of the PR code circuit shown in the equation (1), so that the recording code on the optical disc 101 and the PR equalization circuit 107 The relationship with the output is brought close to the relationship between the input code and the PR code value shown in FIG. The PR equalization value obtained from the PR equalization circuit 107 forms a wide distribution due to noise or the like included in the reproduction signal, and does not necessarily match the ideal PR code value. Therefore, the Viterbi decoding circuit 108 uses the PR code values that are the ideal values as reference values (PR code reference values) to summarize the distance calculation results for each PR equalized value sample, and according to the determined maximum likelihood pattern of the PR code optical disc The data (recording code) on 101 is decoded.

  The PRML process described above is a method based on the premise that the amplitude level of the PR code reference value and the distribution of the PR equalized value amplitude match. On the other hand, the MTF characteristic necessary for setting the characteristic of the PR equalizer depends on the characteristics of both the data recording / reproducing apparatus and the recording medium to be reproduced, and the area additionally recorded by the different data recording apparatus even within the same reproducing medium. Are different MTF characteristics and cause inconsistencies. This causes a decrease in decoding accuracy. For this reason, in the data reproducing apparatus of the present embodiment, a known data pattern region for calculating the PR code reference value is provided on the optical disc 101 to be reproduced, and this region is used for learning, for each reproducing region. The PR code reference value suitable for the value of the reproduced signal waveform is calculated and set.

  FIG. 7 is an explanatory diagram showing an example of a recording format of the optical disc 101 that is handled as a reproduction process target by the data reproduction apparatus of the present embodiment. In particular, a configuration example of sectors on the optical disc 101, which is the minimum data unit of recording / reproduction by the disc drive apparatus, is shown. In a track on the optical disc 101, a header area and a user data area exist. The header area is an area in which non-rewritable information such as a physical address is recorded, and the user data area is an area in which user data to be output to the host device is mainly recorded. Since the reproduction characteristics differ between the physical address area and the user data area, a known data pattern area is provided at the boundary. In FIG. 7, as a data configuration example, the header area further includes a PR code reference value calculation pattern area R1, an end instruction pattern area R2, and a physical address area R3. Further, the user data area further includes a PR code reference value calculation pattern area R4, an end instruction pattern area R5, and a user data area R6 in this order. The hatched areas R1 and R4 are areas where data patterns known to the data reproducing apparatus are recorded, and this data area is used as a learning data area for calculating the PR code reference value. The end instruction pattern areas R2 and R5 are small areas indicating the end of the PR code reference value calculation pattern areas R1 and R4, respectively. The area R1 is used for reproducing the data in the header area that follows, that is, the physical address information in the physical address area R3 here. That is, the PR code reference value calculated by learning by the PR code reference value calculation circuit 109 based on the reproduction signal from the PR code reference value calculation pattern region R1 is set in the PRML processing circuit 106, and the decoding process is performed based on the set value. Is done. Similarly, the area R4 is used for reproducing user data in the subsequent user data area, that is, user data in the user data area R6 here. As described above, as the format of the recording medium, the PR code for the data area immediately following the boundary of the area where the reproduction characteristic changes in the track on the optical disc 101, in other words, at the beginning of the area where the reproduction characteristic is switched. A reference value calculation pattern is recorded.

  FIGS. 8A to 8C are explanatory diagrams showing an example of data reproduction processing by the data reproduction apparatus according to the embodiment of the present invention. FIG. 8A shows a recording code X (n) as an example of a known data pattern recorded in the PR code reference value calculation pattern area in the sector configuration. FIG. 8B shows the waveform of the reproduction signal X ′ (n) of the recording code X (n) in the PR code reference value calculation pattern region. FIG. 8C shows a PR equalization value Y ′ (n) that is a PR equalization value pattern of the reproduction signal X ′ (n).

  A recording code X (n) as an example of a known data pattern for calculating the PR code reference value is a code sequence {1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0}. It is a repeated data structure. The present invention is not limited to this, and the VFO area data in the DVD-RAM can be used as the known data pattern, for example. The data structure of the VFO area is a format in which marks and spaces having a 4-channel bit length are alternately repeated, that is, a data structure of a code sequence {1, 1, 1, 1, 0, 0, 0, 0}.

  In the header area shown in FIG. 7, sector information including a physical address is pre-pitted at the time of production, and the area has optical characteristics different from those of the user data area. Therefore, the PR code reference value calculation pattern areas (R1, R4) are provided at the heads of the header area and the user data area in order to perform data reproduction processing corresponding to the change in the characteristics. The data pattern for calculating the PR code reference value is a repetitive pattern in which the value Y ′ (n) after PR equalization satisfies all the seven levels shown in FIG. 5 as shown in FIG. 8C. Stipulated in

  9A and 9B show a configuration example of the code identification circuit 110. FIG. The circuit shown in FIG. 9A calculates the difference between the sample value of the reproduced signal and the 0 level and outputs the sign bit, and is equivalent to a slicer based on the level comparison of the reproduced signal. This circuit corresponds to the configuration shown in FIG. The code identification circuit 110 a is configured to include an inverter, and receives the reproduction signal sample value code bit from the A / D converter 105 and outputs a code identification value. Further, the circuit shown in FIG. 9B has a different configuration. This circuit obtains the average of two adjacent PR equalization values, inverts the sign bit, and outputs it, and a recording code can be obtained as shown in the correspondence table of FIG. FIG. 10 is a correspondence table between recording codes and PR codes in decoding by the code identification circuit 110b. The code identification circuit 110b receives the PR equalization value from the PR equalization circuit 107, processes the addition value code bit of the reproduction signal sample through a register, an adder, and an inverter, and outputs a code identification value. The PR code reference value does not need to be set in any of the code determinations of the circuit configurations shown in FIGS. 9A and 9B.

  FIG. 11 shows a configuration example of the code identification value holding circuit 111 and the PR equalized value holding circuit 112. These are both constituted by shift registers, and each hold a code value and a PR equalized value for a certain period with each time as a reference. In this configuration example, the register length is 12 stages, which is the same as the period of the PR code reference value calculation pattern. Here, since the PR code reference value calculation pattern is known to the data reproducing apparatus and the PR code reference value can be obtained in advance, if a specific portion in the recording code pattern can be detected correctly, the detection position is used as a reference. Subsequent decoding values can be estimated. For example, in the recording code pattern shown in FIG. 8 (a), it is known that if a mark and space portion continuous for 4T periods can be detected correctly, the subsequent code pattern will be a 2T long mark and space. The PR code reference value pattern during this period can be estimated.

  FIGS. 12A and 12B show a configuration example related to the equalization value grouping circuit 114. As shown in FIG. 12A, the equalization value grouping circuit 114 has a signal (pattern matching) obtained by discriminating the code identification value pattern stored in the code identification value holding circuit 111 by the equalization value-ideal value determination circuit 113. A determination signal) and a PR code group circuit provided for each PR code reference value with a plurality of samples of PR equalization value holding values (PR equalization value patterns) stored in the PR equalization value holding circuit 112 as inputs. It is the structure which has a part. In this configuration example, the equalization value grouping circuit 114 includes circuit portions of PR code group # 1 to PR code group # 12 corresponding to each PR code reference value. FIG. 12B shows a configuration of a circuit portion corresponding to one PR code group.

  In FIG. 12, the equalization value-ideal value determination circuit 113 compares the code identification value pattern identified through the code identification circuit 110 with a part or the entire pattern capable of determining the repetitive pattern of the recording code. I do. Then, the values stored in the PR equalization value holding circuit 112 are distributed to PR code groups set for each predicted value of the PR code in the equalization value grouping circuit 114 at the timing of matching in the coincidence determination. In the coincidence determination of the equalization value-ideal value determination circuit 113 shown in the figure, a pattern coincidence determination signal is output to the equalization value grouping circuit 114 as “0” when there is a coincidence and “1” when there is no coincidence. ing. In the example of the PR code reference value calculation pattern shown in FIG. 8A, the code stored in the code identification value holding circuit 111 is compared with the PR equalization value pattern shown in FIG. PR when the identification value pattern matches {1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0} in order from the right register, that is, the older code identification value sample The stored value levels of the equalized value holding circuit 112 are estimated to be {−2a, 2b, 2a + 2b, 2b, 0, −2b, − (2a + 2b), −2b, 0, 2a, 2a, −2a}, respectively. . At this timing, the value of each stage of the shift register constituting the PR equalization value holding circuit 112 is assigned to the PR code group for each PR code value. In this example, from the result estimated above, PR code group # 1 (code value: -2a), PR code group # 2 (code value: 2b), PR code group # 3 (code value: 2a + 2b), PR code group # 4 (code value: 2b), PR code group # 5 (code value: -2b), ..., PR code group # 12 (code value: -2a). This distribution process is performed for each period of the PR code reference value calculation pattern as long as the identification result of the code identification circuit 110 is correct. In addition, when the identification result of the code identification circuit 110 causes an error, there may be a case where an abnormality has occurred in the reproduction signal and is not suitable for the calculation of the PR code reference value. Can be excluded from the calculation.

  As shown in FIG. 12B, in the PR code groups # 1 to # 12, a counter and a total for counting the number of samples (number of PR equalization value samples) with respect to the allocated PR equalization values. And a circuit portion for holding and outputting a value (PR equalized value total value). This is composed of a register, a selector, an adder and the like. The circuit corresponding to each PR code group outputs the PR equalized value total value and the number of PR equalized value samples to the average value calculating circuit 115. The average value calculation circuit 115 calculates the average of these PR code group values. This absorbs the variation of each sample value derived from the noise component of the reproduction signal. The average value of each PR code group calculated in this way can be used as a PR code reference value reflecting an error in PR equalizer characteristics caused by a characteristic difference between the recording medium and the data recording / reproducing apparatus. . The reproduction process of the data (recording code) following the PR code reference value calculation pattern is performed immediately after the reproduction and recognition of the end instruction pattern (R2, R5) in FIG. This is switched to Viterbi decoding processing in the Viterbi decoding circuit 108 using the value as a set value.

  By the data reproduction process based on the PR code reference value setting using the PR code reference value calculation circuit 109 described above, a PR code reference value that matches the characteristics of the optical disc 101 to be reproduced and the data reproduction device can be obtained. A highly reliable decoding process can be realized by the Viterbi decoding circuit 108 in which the PR code reference value is set.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention can be used as a data reproducing device (disk drive device) for a recording medium such as a CD or a DVD.

It is a figure which shows the structure of the data reproduction apparatus in one embodiment of this invention. It is a figure which shows the example of an optical disk reproduction | regeneration signal (eye pattern) in the data reproduction apparatus in one embodiment of this invention. It is explanatory drawing which shows the structure of the PR code | cord | chord circuit which performs the process by a PRML system. It is explanatory drawing which shows the pulse response of PR code | symbol circuit. It is a figure which shows the correspondence table | surface of the recording code-PR code in a PR code circuit. It is a figure which shows the structure of PR equalization circuit of the data reproduction apparatus in one embodiment of this invention. It is explanatory drawing which shows the example of the recording format of the optical disk which the data reproducing device of one embodiment of this invention handles as a process target, and shows the example of a structure of a sector especially. (A)-(c) shows the processing example by the data reproduction apparatus of one embodiment of this invention, and the description which each shows the recording code in the pattern area | region for PR code reference value calculation of an optical disk, its reproduction signal, and PR code | cord | chord FIG. (A), (b) is a figure which shows the structural example of the code | symbol identification circuit of the data reproducing | regenerating apparatus in one embodiment of this invention. 4 is a correspondence table between a recording code and a PR code indicating decoding by a configuration example of a code identification circuit in the data reproduction device according to the embodiment of the present invention. (A), (b) is a figure which shows the structural example of the code | symbol identification value holding circuit and PR equalization value holding circuit of the data reproducing | regenerating apparatus in one embodiment of this invention. (A), (b) is a figure which shows the structural example of the equalization value grouping circuit of the data reproducing | regenerating apparatus in one embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Optical disk, 102 ... Laser part, 103 ... Photo detector, 104 ... AGC circuit, 105 ... A / D converter, 106 ... PRML processing circuit, 107 ... PR equalization circuit, 108 ... Viterbi decoding circuit, 109 ... PR Code reference value calculation circuit, 110, 110a, 110b ... code identification circuit, 111 ... code identification value holding circuit, 112 ... PR equalization value holding circuit, 301 ... PR code circuit, R1, R4 ... PR code reference value calculation pattern Area, R2, R5 ... End instruction pattern area, R3 ... Physical address area, R6 ... User data area.

Claims (3)

A data reproducing apparatus for detecting data by a PRML method using a PR equalizer and a maximum likelihood decoder for a reproduction signal from a recording medium,
The recording medium to be reproduced has an area where a known data pattern is recorded corresponding to the data area having different reproduction characteristics,
A code identifying circuit for identifying the data without using maximum likelihood decoding using a sample value or PR equalized value of a reproduction signal from the recording medium as an input signal;
A code identification value holding circuit for inputting a code identification value as a result of the identification and holding a code identification value pattern within a predetermined period;
A PR equalization value holding circuit that collectively holds a plurality of consecutive PR equalization value samples in the same period as the code identification value holding circuit;
An equalized value-ideal value determining circuit for determining a correspondence relationship between each PR equalized value sample stored in the PR equalized value holding circuit and a PR code reference value level that is an ideal value of the PR equalized value; ,
An equalization value grouping circuit for grouping PR equalization value samples stored in the PR equalization value holding circuit;
An average value calculating circuit for calculating an average value for each group of the grouped PR equalized value samples,
During the reproduction process of the recording medium, the area of the known data pattern is used as a learning data area for calculating the PR code reference value,
The code identification value holding circuit holds an output value of the code identification circuit for the learning data area,
The PR equalization value holding circuit holds a PR equalization value for the learning data area,
The equalization value-ideal value determination circuit determines a correspondence relationship between each PR equalization value sample and a PR code reference value level based on a code identification value pattern held in the code identification value holding circuit,
The equalization value grouping circuit performs grouping based on the determination result of the equalization value-ideal value determination circuit, calculates the total value in each group, and counts the number of samples.
The average value calculation circuit calculates an average value for each group, sets a PR code reference value for a subsequent data area corresponding to the learning data area based on the calculated value, and performs maximum likelihood decoding by this setting. A data reproducing apparatus characterized in that processing is performed. The data reproducing apparatus according to claim 1, wherein
The data recorded on the recording medium is “a code with a run length of 2”,
The process of the PRML method used in the reproduction process is “PR code generation constraint length is 4”.
A data reproducing apparatus characterized in that the data structure of the learning data area for calculating the PR code reference value is "a format in which marks and spaces having a 4-channel bit length are alternately repeated". The data reproducing apparatus according to claim 2, wherein
The format of the recording medium is “DVD-RAM”,
A data reproducing apparatus, wherein the learning data area for calculating the PR code reference value is "VFO".

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