JP2004335079A - Recording control unit, recording and reproducing device, and recording control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set optimum recording parameters most suitable to the most likelihood decoding method. <P>SOLUTION: The operation of a reliability value ¾Pa-Pb¾-Pstd of a result of the most likelihood of a part which corresponds to the start and final end parts of an edge of a recording mark and in which occurrence probability is higher in the most likelihood decoding method is performed by each combination of the prescribed mark length and space length immediately before, and each combination of the mark length and space length immediately after, recording parameters optimizing an edge shift position is obtained from the operation result, and recording in which the obtained recording parameter is reflected is performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a recording control device, a recording / reproducing device, and a recording control method using a maximum likelihood decoding method.

  In a recording / reproducing apparatus that records and reproduces original digital information on a portable recording medium, even if a recording pulse having the same shape is used, the shape of a mark formed on the medium varies due to individual differences between the apparatus and the recording medium. The quality of the reproduced signal can be large. In order to prevent a decrease in reliability due to such variations, a calibration operation is performed when a recording medium is attached or detached. Calibration is control for setting the characteristics of the reproduction system and optimizing the shape of the recording pulse and the like in order to ensure the reliability of the user data.

  A general information reproducing apparatus uses a PLL circuit that extracts clock information included in a reproduced signal and discriminates original digital information based on the extracted clock information.

  FIG. 14 shows a conventional optical disk drive. Light reflected from the optical disk 17 is converted into a reproduction signal by the optical head 18. The reproduced signal is shaped by the waveform equalizer 19. The waveform-shaped reproduced signal is binarized by the comparator 20. Normally, the threshold value of the comparator 20 is feedback-controlled so that the integration result of the binarized signal output becomes zero. The phase comparator 21 calculates a phase error between the output of the binary signal and the recovered clock. The phase error is averaged by the LPF 22, and the processing result becomes the control voltage of the VCO 23. The phase comparator 21 is feedback-controlled so that the phase error output from the phase comparator 21 is always zero. In a recording medium on which thermal recording is performed, the shape of the mark formed on the medium differs based on the thermal interference on the medium and the recording patterns before and after. Therefore, it is necessary to set the optimum printing parameters for printing the individual patterns.

  The index for evaluating the recording parameter is the error detection output as described above. The recording parameters are set so that the error detection output is minimized. Specifically, based on the recording pattern output from the pattern generating circuit 26 using the initially set recording parameters, the recording compensation circuit 27 generates a pulse having a predetermined waveform, and the laser driving circuit 28 Record When reproducing information from a track on which a predetermined pattern is recorded, the error detection circuit 24 obtains a detection signal by integrating the absolute value of the phase error between the output of the comparator 20 and the output of the VCO 23. This detection signal has a correlation with the jitter between the reproduction clock and the binarized pulse edge. Recording and reproduction are repeated by changing the recording parameters. The recording parameter when the detected value is minimized is optimized.

  FIG. 15 shows a specific operation of the error detection circuit 24. For example, when a recording pulse having a repetition pattern of 6T, 4T, 6T, and 8T is used, a case where the end edge of the mark corresponding to the combination pattern of the 4T mark and the 6T space is optimized is described. It is assumed that the start edge of the mark corresponding to the combination pattern of the 6T space and the 8T mark and the end edge corresponding to the combination pattern of the 8T mark and the 6T space are recorded with optimal recording parameters.

  When an NRZI signal having a cycle as shown in FIG. 15A is provided, the recording compensation circuit 27 generates a laser drive waveform pulse as shown in FIG. 15B. Tsfp is a parameter for setting the mark start position, and Telp is a parameter for setting the mark end position. The laser drive circuit modulates the light emission power according to a pattern as shown in FIG. By laser light emission, an amorphous region is physically formed on the track as shown in FIG. When Telp is changed to Telp1, Telp2, and Telp3, the shape of the mark to be formed changes as shown in FIG. Consider information reproduction from a track in such a recording state.

  When the recording parameter at the end of the 4T mark is set to the optimum value Telp2, a reproduced signal indicated by a solid line in FIG. 15D is obtained. The threshold value is determined so that the integrated value of the comparator output becomes zero. The phase difference between the comparator output and the reproduction clock is detected, and the reproduction clock (FIG. 15E) is generated so that the integrated value of the phase error becomes 0.

  Next, a case is considered where the recording parameter at the end of the 4T mark is smaller than the optimum value and is set to Telp1. At this time, a reproduced signal indicated by a solid line in FIG. Since the 4T mark end edge changes in the time axis direction, the threshold value Tv of the comparator becomes larger as shown by the dashed line in FIG. 15F than in FIG. 15D. Since the output of the comparator has changed, the phase of the reproduced clock is advanced as compared with FIG. 15E so that the integrated value of the phase error becomes 0, and a reproduced clock as shown in FIG. 15G is generated.

  Conversely, consider a case where the recording parameter at the end of the 4T mark is set to be larger than the optimum value and is set to Telp3. At this time, a reproduced signal indicated by a solid line in FIG. Since the end edge of the 4T mark changes in the time axis direction, the threshold value Tv of the comparator becomes smaller as shown by the one-dot chain line in FIG. 15H than in FIG. Since the output of the comparator has changed, the phase of the reproduced clock is delayed as compared with FIG. 15E so that the integrated value of the phase error becomes 0, and a reproduced clock as shown in FIG. 15I is generated.

  When a time difference (a so-called data-clock jitter) between a mark end edge (rising edge of a reproduced signal) and a reproduced clock is measured, distributions as shown in (j) to (l) of FIG. 15 are obtained. However, it is assumed that the end of the 4T mark and the end of the 8T mark have the same dispersion of the same variance.

  In the case of the reproduced signal and the reproduced clock as shown in FIGS. 15D and 15E, the distribution of the time difference between the comparator output and the reproduced clock at the rising edge (mark end edge) is obtained. become that way. The average value of the distributions at the end of the 4T mark and the end of the 8T mark is 0.

  However, when the parameter at the end of the 4T mark is Telp1 (a value smaller than the optimum value Telp2), the average value of the distribution of the 4T mark end edge and the average value of the 8T mark end edge distribution are 0 as shown in FIG. And the distribution is the same distance from 0. Therefore, the total variance of the rising edge is larger than in the case of FIG. Similarly, when the parameter at the end of the 4T mark is Telp3 (a value larger than the optimum value Telp2), the average value of the distribution of the 4T mark end edge and the average value of the 8T mark end edge distribution are as shown in FIG. The distribution is not 0, but is the same distance from 0. 15 (l) and FIG. 15 (j), the distributions of the 4T mark end and the 8T mark end are interchanged. Also in this case, the total variance of the rising edge is larger than in the case of FIG.

  When the result of accumulating the absolute value of the phase error is used as the error detection output, the error detection value changes as shown in FIG. 15M according to the change of the recording parameter Telp. Therefore, the recording parameter is changed, and the parameter that minimizes the output of the error detection circuit 24 is set as the optimum value.

  In the above example, the procedure for optimizing the parameter Telp at the end of the 4T mark has been described. However, test recording is performed for other parameters using specific patterns corresponding to the parameters, and the optimal parameters are determined based on the error detection output. Find out.

FIG. 16 is a flowchart showing the operation for obtaining all the recording parameters according to the above procedure. The area of the medium on which the test recording is to be performed is accessed (S161), and the test recording is performed while changing the recording parameters at the start and end of the mark for each predetermined area (for example, sector) (S163). Information is reproduced from the test recording area, and an error detection output is obtained for each area where the parameter is changed (S164). A parameter that minimizes the error detection output is obtained (S165). The above operation is repeated until all parameters are obtained in order to obtain the next parameter (S162) (see Patent Documents 1 and 2).
JP 2000-200418 A JP 2001-109597 A

  However, in the method of setting the recording parameter so as to minimize the jitter as described above, the probability that an error occurs may not be minimized in a system employing the maximum likelihood decoding method. In the maximum likelihood decoding method, typically, a signal pattern is preliminarily estimated from a reproduced signal waveform, and the reproduced signal is decoded into a signal having the most probable signal pattern while comparing the reproduced signal waveform with the estimated signal waveform. How to In the maximum likelihood decoding method, the smaller the difference between the reproduced signal waveform and the estimated signal waveform, the smaller the probability that an error will occur.

  An object of the present invention is to provide a recording control device, a recording / reproducing device, and a recording control method for optimizing recording parameters when recording information so that the probability of occurrence of an error when performing maximum likelihood decoding is minimized. And

  The recording control device of the present invention receives a digital signal generated from an analog signal indicating information reproduced from an information recording medium, and shapes a waveform of the digital signal. A maximum likelihood decoding unit that performs maximum likelihood decoding and generates a binary signal indicating the result of the maximum likelihood decoding, and a result of the maximum likelihood decoding based on the digital signal whose waveform has been shaped and the binary signal A reliability calculation unit that calculates the reliability of the information recording medium, based on the calculated reliability, comprising an adjustment unit that adjusts the shape of a recording signal for recording the information on the information recording medium, whereby the Objective is achieved.

  The adjusting section may adjust a shape of a predetermined portion of the recording signal.

  The adjusting section may adjust the position of the edge of the recording signal.

  The maximum likelihood decoding unit may perform maximum likelihood decoding using a state transition rule determined from a recording code having a minimum polarity inversion interval of 2 and an equalization scheme PR (C0, C1, C0).

  The maximum likelihood decoding unit may perform maximum likelihood decoding using a state transition rule determined from a recording code having a minimum polarity inversion interval of 2 and an equalization scheme PR (C0, C1, C1, C0).

  The maximum likelihood decoding unit may perform maximum likelihood decoding using a state transition rule determined from a recording code having a minimum polarity inversion interval of 2 and an equalization scheme PR (C0, C1, C2, C1, C0). .

  The reliability calculation unit may calculate the reliability based on a digital signal and a binary signal corresponding to an end of a recording mark formed on the information recording medium.

  The adjusting unit may adjust the shape of the recording signal so as to increase the reliability.

  The adjusting unit calculates one of the integrated value of the calculated reliability and the average value of the calculated reliability, and determines the shape of the recording signal based on one of the integrated value and the average value. It may be adjusted.

  The adjusting unit may calculate one of the integrated value and the average value for each combination of the recording mark length and the space length.

  The recording / reproducing apparatus of the present invention includes: a reproducing unit that generates a digital signal from an analog signal indicating information reproduced from an information recording medium; a shaping unit that receives the digital signal and shapes the waveform of the digital signal; A maximum likelihood decoding unit that performs maximum likelihood decoding on the shaped digital signal and generates a binarized signal indicating the result of the maximum likelihood decoding, based on the shaped digital signal and the binary signal A reliability calculation unit that calculates the reliability of the result of the maximum likelihood decoding, and an adjustment unit that adjusts the shape of a recording signal for recording the information on the information recording medium based on the calculated reliability, A recording unit for recording the information on the information recording medium based on the adjustment result of the shape of the recording signal, whereby the object is achieved.

  A recording control method according to the present invention includes the steps of: receiving a digital signal generated from an analog signal indicating information reproduced from an information recording medium, shaping the waveform of the digital signal; Performing a likelihood decoding to generate a binary signal indicating the result of the maximum likelihood decoding, and determining the reliability of the result of the maximum likelihood decoding based on the digital signal whose waveform has been shaped and the binary signal. Calculating, and adjusting the shape of a recording signal for recording the information on the information recording medium based on the calculated reliability, whereby the object is achieved.

  The adjusting step may include adjusting a shape of a predetermined portion of the recording signal.

  The adjusting may include adjusting an edge position of the recording signal.

  According to the present invention, the reliability of the result of the maximum likelihood decoding is calculated based on the digital signal whose waveform is shaped and the binary signal generated by the maximum likelihood decoding unit, and the information is calculated based on the calculated reliability. The shape of a recording signal for recording information on a recording medium is adjusted. Thus, the shape of the recording signal can be adjusted so that the reliability of the result of the maximum likelihood decoding becomes high, so that the probability of occurrence of an error when performing the maximum likelihood decoding can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, a method for evaluating the quality of a reproduced signal when the maximum likelihood decoding method is used will be described. As an example, a recording code having a minimum polarity reversal interval of 2 is used as the recording code, and the signal waveform is such that the frequency characteristics of the signal during recording and reproduction are PR (1, 2, 2, 1) equalization. A method for evaluating the quality of a reproduced signal in the case where is shaped will be described.

The recording code is b _k , the recording code one time before is b _k−1 , the recording code two times before is b _k−2, and the recording code three times before is b _k−3 . An ideal output value Level _v of PR (1, 2, 2, 1) equalization is represented by (Equation 1).
Level _v = b _k−3 + 2b _k−2 + 2b _k−1 + b _k (Equation 1)
Here, k is an integer representing time, and v is an integer from 0 to 6.

Assuming that the state at the time k is S (b _k−2 , b _k−1 , b _k ), a state transition table of (Table 1) is obtained.

For simplicity, state S (0,0,0) _k at time k is S0 _k , state S (0,0,1) _k is S1 _k , and state S (0,1,1) _k is S2 _k 2, the state S (1,1,1) _k is S3 _k , the state S (1,1,0) _k is S4 _k , and the state S (1,0,0) _k is S5 _k . A transition diagram is obtained. The state transition diagram shown in FIG. 2 shows a state transition rule determined from a recording code whose minimum polarity inversion interval is 2 and the equalization method PR (1, 2, 2, 1). When this state transition diagram is developed along the time axis, the trellis diagram of FIG. 3 is obtained. Attention is paid to the state S0 state of _k and time _{k-4 S0} k-4 at time k. FIG. 3 shows two possible state transition sequences between the state S0 _k and the state S0 _k-4 . Assuming that one possible state transition sequence is path A, path A transits states S2 _k-4 , S4 _k-3 , S5 _k-2 , S0 _k-1 , and S0 _k . Assuming that another state transition sequence is path B, path B transitions between states S2 _k-4 , S3 _k-3 , S4 _k-2 , S5 _k-1 , and S0 _k . When the maximum likelihood decoding result from time k-6 to time k is ( _Ck-6 , _Ck-5 , _Ck-4 , _Ck-3 , _Ck-2 , _Ck-1 , _Ck ). _{, (C k-6, C} k-5, C k-4, C k-3, C k-2, C k-1, C k) = (0,1,1, x, 0,0,0 ) Is obtained (x is a value of 0 or 1), it means that the state transition sequence of the path A or the path B is estimated to be most likely. Since the probability that the state at the time k-4 is the state S2 _k-4 is the same for both the path A and the path B, the reproduction signal y _k-3 from the time k-3 to the time k is the same. By calculating the cumulative value of the square of the difference between the value up to the reproduced signal y _k and the expected value of each of the path A and the path B, the state transition sequence of either the path A or the path B is likely to be certain. I understand. Assuming that the accumulated value of the square of the difference between the value of the reproduced signal y _k−3 to y _k from time k−3 to time k and the expected value of the path A is Pa, Pa is represented by (Equation 2). Is done. Assuming that the accumulated value of the square of the difference between the value of the reproduction signal y _k−3 to y _k from time k−3 to time k and the expected value of the path B is Pb, Pb is represented by (Equation 3). Is done.
Pa = (y _k−3 −4) ² + (y _k−2 −3) ² + (y _k−1 −1) ² + (y _k− 0) ² (Equation 2)
Pb = (y _k−3 −5) ² + (y _k−2 −5) ² + (y _k−1 −3) ² + (y _k− 1) ² (formula 3)
Here, the meaning of the difference Pa−Pb between Pa and Pb indicating the reliability of the maximum likelihood decoding result will be described. It can be said that the maximum likelihood decoding unit confidently selected the path A if Pa << Pb, and confidently selected the path B if Pa >> Pb. If Pa = Pb, either path A or path B can be selected, and it can be said that whether the decoding result is correct is 5 minutes and 5 minutes. When Pa-Pb is obtained from the decoding result for a predetermined time or a predetermined number of times, a distribution of Pa-Pb is obtained. FIG. 4 shows a schematic diagram of the distribution of Pa-Pb.

  FIG. 4A shows the distribution of Pa-Pb when noise is superimposed on the reproduced signal. The distribution has two peaks, one having a maximum frequency when Pa = 0, and another having a maximum frequency when Pb = 0. The value of Pa−Pb when Pa = 0 is expressed as −Pstd, and the value of Pa−Pb when Pb = 0 is expressed as Pstd. The absolute value of Pa-Pb is calculated to obtain | Pa-Pb | -Pstd. FIG. 4B shows the distribution of | Pa−Pb | −Pstd. The standard deviation σ and the average value Pave of the distribution shown in FIG. It is assumed that the distribution shown in FIG. 4B is a normal distribution, and when the value of the reliability | Pa−Pb | of the decoding result becomes −Pstd or less based on, for example, σ and Pave, an error occurs. , The error probability P (σ, Pave) is expressed as (Equation 4).

  From the average value Pave and the standard deviation σ calculated from the Pa-Pb distribution, the error rate of the binary signal indicating the maximum likelihood decoding result can be predicted. That is, the average value Pave and the standard deviation σ can be used as indexes of the reproduction signal quality. In the above example, it is assumed that the distribution of | Pa-Pb | is a normal distribution, but when the distribution is not a normal distribution, the number of times that the value of | Pa-Pb | -Pstd becomes equal to or less than a predetermined reference value Can be counted, and the counted number can be used as an index of the signal quality.

  In the case of a state transition rule determined from a recording code having a minimum polarity inversion interval of 2 and an equalization method PR (1, 2, 2, 1), a combination that can take two state transition sequences when a state transition occurs There are eight patterns in the range from time k-4 to time k, eight patterns in the range from time k-5 to time k, and eight patterns in the range from time k-6 to time k. When the range to be detected is further expanded, a combination that can take two state transition sequences has a reliability Pa-Pb pattern. What is important here is that if the reliability Pa-Pb is used as an index of the reproduction signal quality and only patterns with a high possibility of error (error rate) are detected without detecting all patterns, the detection is performed. The result can be used as an index correlated with the error rate. Here, the patterns having a high possibility of being erroneous are patterns in which the value of the reliability Pa−Pb is small, and are eight patterns in which Pa−Pb = ± 10. The eight patterns and Pa-Pb are summarized in (Table 2).

  (Equation 5) is obtained by summarizing the reliability Pa-Pb of the above eight decoding results.

Here, Ak = (yk-0) ² , Bk = (yk-1) ² , Ck = (yk-2) ² , Dk = (yk-3) ² , Ek = (yk-4) ² , Fk = ( yk-5) ² and Gk = (yk-6) ² . Determine the Pa-Pb which satisfies the maximum likelihood decoding result _{c k} (number 5), obtains the average value Pave ₁₀ and the standard deviation sigma ₁₀ from the distribution of Pa-Pb. The probability P ₁₀ the distribution of Pa-Pb causes a assume the errors to be normal distribution is expressed by (Equation 6).

The eight patterns are patterns that cause a one-bit shift error, and the other patterns are patterns that cause a shift error of two or more bits. When the error pattern after the PRML processing is analyzed, most of the error patterns are 1-bit shift errors. Therefore, the error rate of the reproduced signal can be estimated by obtaining (Equation 6). As described above, the standard deviation σ ₁₀ and the average value Pave ₁₀ can be used as indices indicating the quality of the reproduced signal.

  In the embodiment of the present invention, the above-mentioned eight patterns are detected for each recording pattern described later (for each pattern of a combination of the mark length and the immediately preceding space length and a pattern of the combination of the mark length and the immediately succeeding space length). The recording parameters for optimizing the position of the edge of the recording signal are determined by paying attention to the shape of the recording signal, particularly the start and end portions of the edge. Focusing only on the pattern with the minimum value of | Pa-Pb | among the reliability | Pa-Pb | of the maximum likelihood decoding results of all the patterns means focusing on only the edge portion of the recording mark. means. As described above, a pattern in which the value of Pa-Pb is small is a pattern in which the error occurrence probability is large. That is, if the position of the edge of the recording mark is partially optimized so as to increase the reliability of the maximum likelihood decoding result, it means that the overall optimization is achieved. The method will be described below.

FIGS. 5A to 5H show sample values of the above eight patterns (Pattern-1 to Pattern-8). The horizontal axis represents time (one division represents one channel clock cycle (Tclk)), the vertical axis represents signal level (0 to 6), and the dotted and solid lines represent path A and path B, respectively. Each sample value corresponds to an input expected value Level _v of 0 to 6 in the maximum likelihood decoding described in (Table 1). As shown in FIGS. 15C and 15D, the recorded portion (amorphous region) is reproduced as a waveform whose signal level is lower than the comparator threshold because the reflected light is reduced. On the other hand, the unrecorded portion (non-amorphous area) is reproduced as a waveform above the comparator threshold. In addition, all eight patterns shown in FIG. 5 correspond to reproduced waveforms that are boundary portions (start and end edges of marks) between a recorded portion (mark) and an unrecorded portion (space). Therefore, of the eight patterns in FIG. 5, Pattern-1, Pattern-2, Pattern-3, and Pattern-4 correspond to the starting edge portion of the mark, and Pattern-5, Pattern-6, Pattern-7, and Pattern-n. 8 corresponds to the end edge portion of the mark.

Focusing on Pattern-1, a description will be given of a method of detecting a shift deviation of the start edge of a mark. FIG. 6 shows a correlation between a reproduction waveform and a shift of a recording mark in Pattern-1. In FIG. 6, the solid line symbol △ indicates an input signal, and a path A indicated by a dotted line is a correct state transition path. The input signal is generated based on the recording mark B1. It is assumed that the recording mark A1 has an ideal starting edge. FIG. 6A shows a case where the starting edge position of the recording mark is shifted backward compared to the ideal starting edge position. The sample values (y _k−3 , y _k−2 , y _k−1 , y _k ) of the input signal are set to (4.2, 3.2, 1.2, 0.2), and (Equation 2) and (Eq. 2) From Expression 3), the distance Pa between the path A and the input signal and the distance Pb between the path B and the input signal are obtained as in (Expression 7) and (Expression 8).
Pa = (4.2-4) ² + (3.2-3) ² + (1.2-1) ² + (0.2-0) ²
= 0.16 (Equation 7)
Pb = (4.2-5) ² + (3.2-5) ² + (1.2-3) ² + (0.2-1) ²
= 7.76 (Equation 8)
The shift amount and the shift direction of the start end edge can be obtained by calculating | Pa−Pb | −Pstd described above.
E1 = | Pa−Pb | −Pstd = | 0.16−7.76 | −10 = −2.4 (Equation 9)
The absolute value of E1 obtained from (Equation 9) is the shift amount, and the sign thereof is the shift direction. That is, in the case of FIG. 6A, since it is possible to detect that E1 = −2.4, it can be determined that the start end edge position is shifted behind the reference by 2.4.

Similarly, FIG. 6B shows a case where the start edge position of the recording mark B1 is shifted forward compared to the ideal start edge position. Sample values of the input signal _{(y k-3, y k} -2, y k-1, y k) (3.8, 2.8, 0.8, -0.2) and then, E2 (= | Pa -Pb | -Pstd), E2 = 2.4 can be calculated. Therefore, in the case of FIG. 6B, it can be determined that the starting edge position is shifted by 2.4 by a value before the reference.

FIG. 7 shows the correlation between the reproduced waveform in Pattern-1 and the deviation of the recording mark. In FIG. 7, path B is the correct state transition path. FIG. 7A shows a case where the starting edge of the recording mark is shifted behind as compared with the ideal starting edge. The sample values (y _k−3 , y _k−2 , y _k−1 , y _k ) of the input signal are set to (5.2, 5.2, 3.2, 1.2), and E3 (= | Pa− When Pb | -Pstd) is calculated, E3 = 2.4 can be calculated. Therefore, in the case of FIG. 7A, it can be determined that the starting edge position is shifted behind the reference by 2.4. FIG. 7B shows a case where the starting edge position of the recording mark is shifted forward compared to the ideal starting edge position. Sample value of the input signal _{(y k-3, y k} -2, y k-1, y k) and (4.8, 4.8, 2.8, 0.8) and, E4 (= | Pa- When Pb | −Pstd) is calculated, E4 = −2.4 can be calculated. Therefore, in the case of FIG. 7B, it can be determined that the starting edge position is shifted by 2.4 by a value before the reference. When the path A in FIG. 6 is a correct answer and when the path B in FIG. 7 is a correct answer, the expression of the sign indicating the deviation direction of the start edge of the recording mark is opposite. This depends on the relationship between the expected value sequence of each of the correct answer path and another candidate path and the sequence of the input signal. As shown in FIG. 6B and FIG. 7A, when the sequence of the input signal has a large error from the expected value sequence of the path that is not the correct answer, the value calculated by (Equation 9) is positive. The value has a sign. In other words, the larger the difference between the sequence of the input signal and the expected value sequence of the path that is not the correct answer, the less likely it is that errors will occur in maximum likelihood decoding. In this case, in (Equation 9), it is calculated as a positive sign value. In consideration of this feature, the deviation direction of the start edge position of the recording mark may be detected. In Pattern-1, when Path A is correct, Pattern-1 is a pattern used when detecting the leading edge of a combination of a 2T space and a mark longer than a 4T mark, and when Path B is correct. Is a pattern used at the time of detecting the start edge of a combination of a 3T space and a mark having a length of 3T mark or more. By using the method described above, an integrated value or an average value for each start / end pattern of each recording mark is obtained, and recording parameters are set so that the deviation amount of the edge position approaches 0, which is most suitable for the maximum likelihood decoding method. Recording control becomes possible.

  Here, optimization of the recording parameters will be described. The minimum polarity reversal interval of the recording code is m (m = 2 in the present embodiment). The starting position of the mark formed on the information recording medium depends on the width of the space immediately before the mark and the width of the mark itself. For example, when the immediately preceding space width is from mT to (m + b) T, the starting position of the mark depends on the immediately preceding space width. If the immediately preceding space width is larger than (m + b) T, the start position of the mark does not depend on the immediately preceding space width. When the own mark width is from mT to (m + a) T, the starting position of the mark depends on the own mark width. When the own mark width is larger than (m + a) T, the starting position of the mark does not depend on the own mark width.

  The end position of the mark formed on the information recording medium depends on the width of the mark itself and the width of the space immediately after the mark. For example, when the own mark width is from mT to (m + a) T, the end position of the mark depends on the own mark width. When the own mark width is larger than (m + a) T, the end position of the mark does not depend on the own mark width. If the subsequent space width is from mT to (m + b) T, the end position of the mark depends on the subsequent space width. If the subsequent space width is larger than (m + b) T, the end position of the mark does not depend on the subsequent space width. Here, a and b are integers of 0 or more, and the maximum polarity inversion of the recording code is larger than m + a and m + b.

  Considering the dependence of the start position and the end position of the mark as described above, it is necessary to optimize the start parameter Tsfp for a mark having a space whose width is equal to or less than (m + b) T. Further, it is necessary to optimize the termination parameter Telp for a mark having a width of (m + a) T or less. Assuming that m = 3 and a = b = 3 for simplicity, it is simply necessary to optimize parameters corresponding to the 32 recording patterns shown in FIG. In FIG. 8, for example, 2Ts2Tm means that the pattern has a 2T space immediately before the 2T mark.

  FIG. 9 shows which of the eight patterns (Pattern-1 to Pattern-8) is to be used to detect each of the recording patterns (that is, edge patterns) shown in FIG. For example, 2Ts3Tm in FIG. 8 means that the shift amount of the signal corresponding to the start / end pattern of the recording mark is detected in the P3A pattern. P3A is Pattern-3 and means a pattern in which path A is a correct state transition path. Further, 3Ts3Tm in FIG. 8 means that the shift amount is detected in the pattern of P1B or P4A. P1B indicates a pattern in which the path B is a correct state transition path in Pattern-1, and P4A indicates a pattern in which the path A is a correct state transition path in Pattern-4. From the above, the method of controlling the recording parameters optimal for the maximum likelihood decoding means that the recording parameters are changed so that the shift amounts of the signals corresponding to the respective start and end patterns of the recording marks in FIG. It is to let.

  In FIG. 9, 2Ts2Tm (2T mark rising and 2T space immediately preceding pattern) and 2Tm2Ts (2T mark falling and 2T space immediately following pattern) correspond to the eight patterns (Pattern-1 to Pattern-8). In (2), since the detection is not possible, it is necessary to optimize the edge shift amount by another method. However, a pattern including 2Ts2Tm and 2Tm2Ts is a pattern in which the value of the reliability Pa-Pb is relatively large, and is not included in the eight patterns. In other words, it can be said that even if the edge portions of 2Ts2Tm and 2Tm2Ts are not strictly optimized, there is a low possibility that an error will occur in maximum likelihood decoding. Therefore, instead of optimizing each disk, an appropriate initial value may be used. When optimizing 2Ts2Tm and 2Tm2Ts, optimization may be performed so that the integrated value of the phase error of the reproduction signal is minimized.

  FIG. 1 shows a recording / reproducing apparatus 100 according to an embodiment of the present invention. The recording / reproducing apparatus 100 executes the above-described recording parameter optimizing method.

  The recording / reproducing device 100 includes a reproducing unit 101, a recording control device 102, and a recording unit 103. The information recording medium 1 is mounted on the recording / reproducing device 100. The information recording medium 1 is an information recording medium for optically recording and reproducing information, and is, for example, an optical disk.

  The reproducing unit 101 includes an optical head unit 2, a preamplifier 3, an AGC 4, a waveform equalizer 5, an A / D converter 6, and a PLL circuit 7. The reproducing unit 101 generates a digital signal from an analog signal indicating information reproduced from the information recording medium 1.

  The recording control device 102 includes a shaping unit 8, a maximum likelihood decoding unit 9, a reliability calculation unit 10, and an adjustment unit 104. The adjustment unit 104 includes a pattern detection circuit 11, an edge shift detection circuit 12, and an information recording medium controller 13. The recording control device 102 is manufactured, for example, as a semiconductor chip.

  The shaping unit 8 is, for example, a digital filter, and receives the digital signal generated by the reproducing unit 101 and shapes the waveform of the digital signal so that the digital signal has a predetermined equalization characteristic.

  The maximum likelihood decoding unit 9 is, for example, a Viterbi decoding circuit, and performs maximum likelihood decoding on a digital signal whose waveform is output from the shaping unit 8 and generates a binary signal indicating a result of the maximum likelihood decoding.

  The reliability calculation unit 10 is, for example, a difference metric detection circuit, and performs maximum likelihood decoding based on a digital signal whose waveform is output from the shaping unit 8 and a binary signal output from the maximum likelihood decoding unit 9. Calculate the reliability of the result. In one embodiment of the present invention, the reliability calculation unit 10 determines the reliability of the maximum likelihood decoding result based on the digital signal and the binary signal corresponding to the start and end of the recording mark formed on the information recording medium 1. Calculate gender.

  The adjusting unit 104 adjusts the shape of a predetermined portion of the recording signal for recording information on the information recording medium 1 based on the reliability calculated by the reliability calculating unit 10 (for example, adjusts the position of the edge of the recording signal). Do). The adjustment unit 104 adjusts the shape of the recording signal so that the reliability of the result of the maximum likelihood decoding increases. The information recording medium controller 13 is, for example, an optical disk controller.

  The recording unit 103 includes a pattern generation circuit 14, a recording compensation circuit 15, a laser driving circuit 16, and the optical head unit 2. The recording unit 103 records information on the information recording medium 1 based on the result of adjusting the shape of the recording signal. In the present embodiment, the optical head unit 2 is shared by the reproducing unit 101 and the recording unit 103 and has both functions of a recording head and a reproducing head. Note that the recording head and the reproducing head may be provided separately. The operation of the recording / reproducing device 100 will be described in more detail below.

  The optical head 2 generates an analog reproduction signal indicating information read from the information recording medium 1. The analog reproduction signal is amplified by the preamplifier 3 and AC-coupled, and then input to the AGC 4. In the AGC 4, the gain is adjusted so that the output of the waveform equalizer 5 at the subsequent stage has a constant amplitude. The analog reproduced signal output from the AGC 4 is shaped by the waveform equalizer 5. The waveform-shaped analog reproduction signal is output to the A / D converter 6. The A / D converter 6 samples the analog reproduction signal in synchronization with the reproduction clock output from the PLL circuit 7. The PLL circuit 7 extracts a reproduction clock from the digital reproduction signal sampled by the A / D converter 6.

  The digital reproduction signal generated by the sampling of the A / D converter 6 is input to the shaping unit 8. The shaping unit 8 sets the frequency characteristics of the digital reproduction signal at the time of recording and reproduction to the characteristics assumed by the maximum likelihood decoding unit 9 (PR (1, 2, 2, 1) equalization characteristics in the present embodiment). Then, the frequency of the digital reproduction signal is adjusted (that is, the waveform of the digital reproduction signal is shaped).

  The maximum likelihood decoding section 9 performs maximum likelihood decoding on the digitally reproduced signal whose waveform has been output from the shaping section 8 to generate a binary signal. The reliability calculator 10 receives the waveform-shaped digital reproduction signal output from the shaping unit 8 and the binarized signal. The reliability calculation unit 10 determines a state transition from the binary signal, and indicates | Pa−Pb | −Pstd (Expression 9) indicating the reliability of the decoding result based on the determination result and the branch metric, and is hereinafter referred to as Pabs. Do). The pattern detection circuit 11 generates a pulse signal for allocating the above eight patterns (Pattern-1 to Pattern-8) to each of the start and end edges of the recording mark shown in FIG. 9 based on the binarized signal. And outputs it to the edge shift detection circuit 12. The edge shift detection circuit 12 accumulatively adds the above-mentioned reliability Pabs for each pattern, and obtains a deviation from the optimum value of the recording compensation parameter (hereinafter referred to as an edge shift). The information recording medium controller 13 changes the recording parameter (the waveform of the recording signal) determined to need to be changed from the edge shift amount for each pattern. The pattern generation circuit 14 outputs a recording compensation learning pattern.

  The recording compensation circuit 15 generates a laser emission waveform pattern according to the recording compensation learning pattern based on the recording parameters from the information recording medium controller 13. The laser drive circuit 16 controls the laser emission operation of the optical head unit 2 according to the generated laser emission waveform pattern.

  Next, the operation of the edge shift detection circuit 12 according to the embodiment of the present invention will be described in detail. FIG. 10 shows a pattern detection circuit 11 and an edge shift detection circuit 12. The pattern detection result of the pattern detection circuit 11 and the reliability Pabs calculated by the reliability calculation unit 10 are input to the edge shift detection circuit 12. In consideration of the delay in the pattern detection circuit 11, the input reliability Pabs data is delayed by a flip-flop (FF). The pattern detection output and reliability Pabs data corresponding to the detection output point are input to the adder, and at the same time, the pattern detection result is input to the selector. The selector selects the cumulative addition result so far according to the detection pattern and inputs the result to the adder. The adder adds the cumulative addition result to the newly input reliability Pabs data and outputs the result. Upon receiving the enable signal, the specific register corresponding to the detection pattern stores the addition result.

  For example, when information is recorded on an information recording medium in which information is managed in address units, it is assumed that an addition section gate signal and a register enable signal as shown in FIGS. 11B and 11C are used. FIG. 11A shows an address unit. When test recording is performed in the user area for each address unit to determine the edge shift amount, control for defining an addition section is required. When the addition section gate signal as shown in FIG. 11B is input to the edge shift detection circuit 12, the addition section gate signal passes through two stages of flip-flops as shown in FIG. Will be entered. The flip-flop is reset in the Low period of the addition period gate signal shown in FIG. 11B, and the addition result is stored in the High period. A register enable signal as shown in FIG. 11C is generated from the addition section gate signal. The register enable signal is an enable signal for storing the addition result in the registers REG29 to REG0 at the end of the addition section gate signal. is there. Data indicating the edge shift amount for each address unit is stored in the registers REG29 to REG0. The edge shift detection circuit 12 having such a circuit configuration can obtain all the edge shift amounts necessary for optimizing the recording parameters using one adder.

  In the circuit example of FIG. 10, the frequency of occurrence differs depending on a combination of a mark and a space of a predetermined length necessary for optimizing parameters in a recording pattern (for example, a random pattern) used for test recording. The detected 30 edge shift amounts (R23T, R33T,..., R45L, R55L) depend on the occurrence frequency of each pattern.

  Further, the PLL circuit 7 in FIG. 1 automatically detects the threshold value of the slicer using the DC component (low frequency component included in the reproduction signal), and synchronizes the reproduction signal with the clock signal. Therefore, it is desired that the test recording pattern has a small DC component so that the feedback control does not affect the clock generation in the PLL circuit 7. Also, in consideration of the time and accuracy required for optimization, a highly accurate detection result is desired in as few recording areas as possible. Therefore, a combination of a mark and a space necessary for parameter optimization occurs in a recording pattern at the same frequency, the DC component (DSV) included in the code becomes 0, and the unit length of the combination required for optimization is per unit length. It is necessary to use a recording pattern that increases the frequency of occurrence of the pattern. FIG. 12 shows an example of such a recording pattern.

  In FIG. 12, 2M means a 2T mark, and 2S means a 2T space. In the example of FIG. 12, 30 patterns, which are combinations of 2T to 5T marks and 2T to 5T spaces, occur once for each 108-bit recording pattern. The number of symbols “0” and “1” including the 108-bit recording pattern is 54, which is the same number, and the DSV of the recording pattern is 0. When this recording pattern is applied to the edge shift detection circuit 12 in FIG. 10, each pattern can be detected the same number of times, and a more accurate shift amount detection result can be obtained. In this embodiment, it is assumed that marks or spaces having a width of 5T or more can be recorded with the same recording parameters.

  FIG. 13 shows a modification of the edge shift detection circuit 12. In the edge shift detection circuit 12a shown in FIG. 13, a random pattern (a pattern having a different occurrence frequency depending on a combination pattern necessary for optimization) is used as a recording pattern used for test recording.

  In the edge shift detection circuit 12a of FIG. 13, the pattern detection circuit 11 detects the edge of the specific pattern (30 patterns) shown in FIG. 9, and individually integrates the edge shift amount and the number of times of pattern detection corresponding to each pattern. I do. The average edge shift amount is calculated for each specific pattern by dividing the addition result of the edge shift amount by the number of times of pattern detection. As a result, even if a test recording pattern having a different occurrence probability for each specific pattern is used, it is possible to determine which pattern corresponds to the start / end position of the recording mark to be changed.

  As described above, the edge shift detection circuit 12 included in the adjustment unit 104 calculates one of the integrated value or the average value of the reliability of the maximum likelihood decoding result for each combination of the recording mark length and the space length, The shape of the recording signal is adjusted based on the calculated integrated value or average value.

  In the above embodiment, the case where the maximum likelihood decoding unit performs maximum likelihood decoding using a state transition rule determined from a recording code whose minimum polarity inversion interval is 2 and the equalization scheme PR (1, 2, 2, 1) However, the present invention is not limited to this. For example, when a state transition rule determined from a recording code having a minimum polarity inversion interval of 3 and the equalization method PR (C0, C1, C1, C0) is used, or a recording code having a minimum polarity inversion interval of 2 or 3 is used. When a state transition rule determined from the equalization method PR (C0, C1, C0) is used, or a recording code having a minimum polarity inversion interval of 2 or 3 and the equalization method PR (C0, C1, C2, C1, C1) The present invention can be applied even when a state transition rule determined from C0) is used. C0, C1, and C2 are arbitrary positive numbers.

  Table 3 shows a state transition table representing a state transition rule determined by the recording code having the minimum polarity inversion interval of 2 and the equalization scheme PR (a, b, a), and FIG. 17 shows a state transition diagram. Here, a and b are arbitrary positive numbers.

  Also, Table 4 shows a state transition table representing a state transition rule determined by a recording code having a minimum polarity inversion interval of 2 and the equalization method PR (a, b, c, b, a), and FIG. Shown in Here, a, b, and c are arbitrary positive numbers.

  In the embodiment of the present invention, maximum likelihood decoding section 9 may perform maximum likelihood decoding using a state transition rule as shown in Tables 3 and 4 and FIGS.

  In the present embodiment, the recording parameter is a parameter for controlling the start and end positions of the edge of the recording mark, but the present invention is not limited to this. For example, when performing laser emission using multi-pulses described with reference to FIG. 15, parameters for controlling the width of the leading pulse, the width of the ending pulse, and the cooling pulse width are adjusted based on the reliability of the maximum likelihood decoding result. May be.

  Further, each component of the recording / reproducing apparatus 100 of the present invention may be realized by hardware or software. For example, the operations executed by at least one of the shaping unit 8, the maximum likelihood decoding unit 9, the reliability calculation unit 10, and the adjustment unit 11 may be realized by a program executable by a computer.

  According to the present invention, the reliability of the result of the maximum likelihood decoding is calculated based on the digital signal whose waveform is shaped and the binary signal generated by the maximum likelihood decoding unit, and the information is calculated based on the calculated reliability. The shape of a recording signal for recording information on a recording medium is adjusted. Thus, the shape of the recording signal can be adjusted so that the reliability of the result of the maximum likelihood decoding becomes high, so that the probability of occurrence of an error when performing the maximum likelihood decoding can be reduced.

  In the present invention, an optimal recording parameter is set for the maximum likelihood decoding method so that the probability of an error occurring when decoding a signal using the maximum likelihood decoding method is minimized. For the signal portion corresponding to the start and end portions of the edge of the recording mark and having a high error occurrence probability in the maximum likelihood decoding method, the reliability of the result of the maximum likelihood decoding is calculated. This calculation is performed for each combination of a predetermined mark length and space length. A recording parameter for optimizing the edge shift position is obtained from the calculation result, and recording is performed by reflecting the obtained recording parameter. As described above, the readability can be improved by optimizing the recording parameters of the signal portion where the probability of occurrence of an error increases during maximum likelihood decoding.

  As described above, the present invention is particularly useful in a recording control device, a recording / reproducing device, and a recording control method using the maximum likelihood decoding method.

FIG. 1 shows a recording / reproducing apparatus according to an embodiment of the present invention. FIG. 4 is a diagram showing a state transition rule determined from a recording code having a minimum polarity reversal interval of 2 and an equalization method PR (1, 2, 2, 1) in the embodiment of the present invention. FIG. 4 is a diagram showing a trellis diagram corresponding to the state transition rule shown in FIG. 2 according to the embodiment of the present invention. FIG. 10 is a diagram showing a distribution of Pa-Pb indicating reliability of the maximum likelihood decoding result in the embodiment of the present invention. The figure which shows the specific 8 pattern in embodiment of this invention. FIG. 6 is a diagram showing a correlation between a reproduced waveform and a deviation of a recording mark in Pattern 1 (when path A is a correct answer) of a specific pattern according to the embodiment of the present invention. FIG. 4 is a diagram showing a correlation between a reproduced waveform and a deviation of a recording mark in Pattern 1 (when path B is a correct answer) of a specific pattern according to the embodiment of the present invention. Diagram showing a list of recording parameters that require optimization Diagram showing which of the eight specific patterns to detect the recording parameters that require optimization FIG. 2 is a diagram illustrating an edge shift detection circuit according to the embodiment of the present invention. 4 is a timing chart showing the operation of the edge shift detection circuit according to the embodiment of the present invention. FIG. 4 is a diagram showing a recording pattern for learning according to the embodiment of the present invention. FIG. 2 is a diagram illustrating an edge shift detection circuit according to the embodiment of the present invention. Diagram showing the configuration of a conventional optical disk drive Diagram showing the operation of a conventional error detection circuit Flowchart showing an operation for obtaining a conventional recording parameter FIG. 4 is a diagram showing a state transition rule determined by a recording code having a minimum polarity reversal interval of 2 and an equalization method PR (a, b, a) in the embodiment of the present invention. FIG. 3 is a diagram showing a state transition rule determined by a recording code having a minimum polarity inversion interval of 2 and an equalization method PR (a, b, c, b, a) in the embodiment of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Information recording medium 2 Optical head part 3 Preamplifier 4 AGC
Reference Signs List 5 waveform equalizer 6 A / D converter 7 PLL circuit 8 shaping section 9 maximum likelihood decoding section 10 reliability calculation section 11 pattern detection circuit 12 edge shift detection circuit 13 information recording medium controller 14 pattern generation circuit 15 recording compensation circuit 16 Laser drive circuit 20 Comparator 21 Phase comparator 22 LPF
23 VCO

Claims (14)

A shaping unit that receives a digital signal generated from an analog signal indicating information reproduced from the information recording medium, and shapes a waveform of the digital signal;
A maximum likelihood decoding unit that performs maximum likelihood decoding on the digital signal whose waveform is shaped, and generates a binary signal indicating a result of the maximum likelihood decoding;
A reliability calculation unit that calculates the reliability of the result of the maximum likelihood decoding based on the digital signal whose waveform is shaped and the binary signal,
A recording control device comprising: an adjusting unit that adjusts a shape of a recording signal for recording the information on the information recording medium based on the calculated reliability.   The recording control device according to claim 1, wherein the adjustment unit adjusts a shape of a predetermined portion of the recording signal.   The recording control device according to claim 1, wherein the adjustment unit adjusts a position of an edge of the recording signal.   2. The maximum likelihood decoding unit according to claim 1, wherein the maximum likelihood decoding unit performs maximum likelihood decoding using a state transition rule determined from a recording code having a minimum polarity inversion interval of 2 and an equalization scheme PR (C0, C1, C0). Recording control device.   2. The maximum likelihood decoding unit according to claim 1, wherein the maximum likelihood decoding unit performs maximum likelihood decoding using a state transition rule determined from a recording code having a minimum polarity inversion interval of 2 and an equalization scheme PR (C0, C1, C1, C0). The recording control device according to the above.   The maximum likelihood decoding unit performs maximum likelihood decoding using a state transition rule determined from a recording code having a minimum polarity inversion interval of 2 and an equalization scheme PR (C0, C1, C2, C1, C0). 2. The recording control device according to 1.   The recording control device according to claim 1, wherein the reliability calculation unit calculates the reliability based on a digital signal and a binary signal corresponding to an end of a recording mark formed on the information recording medium.   The recording control device according to claim 1, wherein the adjustment unit adjusts the shape of the recording signal so that the reliability is improved.   The adjusting unit calculates one of the integrated value of the calculated reliability and the average value of the calculated reliability, and calculates the shape of the recording signal based on one of the integrated value and the average value. The recording control device according to claim 1, wherein the adjustment is performed.   The recording control device according to claim 9, wherein the adjustment unit calculates one of the integrated value and the average value for each combination of a recording mark length and a space length. A reproducing unit that generates a digital signal from an analog signal indicating information reproduced from the information recording medium,
Receiving the digital signal, a shaping unit for shaping the waveform of the digital signal,
A maximum likelihood decoding unit that performs maximum likelihood decoding on the digital signal whose waveform is shaped, and generates a binary signal indicating a result of the maximum likelihood decoding;
A reliability calculation unit that calculates the reliability of the result of the maximum likelihood decoding based on the digital signal whose waveform is shaped and the binary signal,
An adjusting unit that adjusts the shape of a recording signal for recording the information on the information recording medium based on the calculated reliability,
A recording unit that records the information on the information recording medium based on a result of adjusting the shape of the recording signal. Receiving a digital signal generated from an analog signal indicating information reproduced from the information recording medium, and shaping the waveform of the digital signal,
A step of performing maximum likelihood decoding on the digital signal whose waveform is shaped, and generating a binary signal indicating a result of the maximum likelihood decoding;
Calculating the reliability of the result of the maximum likelihood decoding based on the digital signal whose waveform is shaped and the binarized signal;
Adjusting the shape of a recording signal for recording the information on the information recording medium based on the calculated reliability.   The recording control method according to claim 12, wherein the adjusting step includes adjusting a shape of a predetermined portion of the recording signal.   13. The recording control method according to claim 12, wherein the adjusting step includes adjusting an edge position of the recording signal.

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