JP2004022156A - Signal reproducing method and signal reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal reproducing method and a signal reproducing device in which a genuine change in signal quality corresponding to the change in an equalized modulus can be detected and optimization of the equalized modulus with high precision is made possible. <P>SOLUTION: The method is constituted with a step 1(S1) to reproduce an optical disk, a step 2(S2) to store digital reproducing data which is an A/D converted reproducing signal for the optical disk, a step 3(S3) to change the equalized modulus for waveform equalization, a step 4(S4) to read out stored digital reproducing data to perform the waveform equalization with the equalized modulus, a step 5(S5) to evaluate an error rate regarding the waveform equalized digital reproducing date and a step 6(S6, S7) to decide the optimum equalization modulus based on corresponding relationships between the equalization modulus and the error rate after iterating the steps ranging from the step 3(S3) through the step 5(S5) more than once. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a signal reproducing method and a signal reproducing apparatus for optimally equalizing a reproduced signal when reproducing a signal from a recording medium.
[0002]
[Prior art]
In recent years, a PRML (Partial Response Maximum Likelihood) method has been adopted as a data detection method for realizing a higher recording density of an information recording medium. That is, the PRML system is a type of signal processing technology, and is a system that combines a waveform equalization technology called PR equalization and a Viterbi decoding system that selects and reproduces a most likely (most probable) data sequence. It is applied to high-density magnetic disks and optical video disks.
[0003]
In the PRML system, it is necessary to perform waveform equalization on a reproduced signal waveform reproduced from a recording medium so as to approach a predetermined frequency characteristic assumed in the PR class. Therefore, an adaptive equalization technique for adaptively updating the equalization characteristic of waveform equalization with respect to the reproduction characteristic fluctuation is used because there is a reproduction characteristic fluctuation caused by the characteristic fluctuation of.
[0004]
As an example of the conventional adaptive equalization technique, for example, as described in Japanese Patent Application Laid-Open No. H11-16279 [publication date: January 22, 1999 (1999), January 22, 1999], the reproduced signal waveform, the current There is a method of detecting an equalization error from the relationship between the equalization characteristics and the frequency characteristics assumed in the PR class, and adaptively changing the equalization characteristics so as to reduce the equalization error. According to this method, the frequency characteristic of the reproduced waveform after the equalization can be gradually brought closer to the frequency characteristic assumed in PRML.
[0005]
[Problems to be solved by the invention]
However, in general, the waveform equalization process simultaneously enhances the high frequency components of the noise. Therefore, in the above-described conventional signal reproducing method and signal reproducing apparatus, when adaptive equalization is performed with the frequency characteristic assumed in the PR class as a target, the error rate is not always the best due to the influence of the deterioration of the S / N ratio. Often, it does not have chemical properties. Therefore, in order to optimize the error rate with higher accuracy, it is necessary to determine the optimum equalization characteristic after actually evaluating the correlation between the equalization characteristic and the error rate.
[0006]
However, when performing a process of changing the equalization characteristics in various ways and repeating the error rate measurement each time, for example, if the reproduction is performed by changing the equalization characteristics for each sector, the individual equalization characteristics are different. The error rate is measured using the reproduction signal of the area. For this reason, there is a problem in that the difference in the equalization characteristics is buried in the fluctuation in the quality of each reproduction signal, and it is difficult to find the optimum equalization characteristics. Further, even if the same region is repeatedly reproduced for each equalization characteristic, the reproduction signal characteristic fluctuates with time due to a servo residual error and the like, and in any case, it is difficult to optimize the equalization with high accuracy. have.
[0007]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to detect a change in a pure signal quality corresponding to a change in an equalization coefficient, and to realize a highly accurate equalization coefficient. It is an object of the present invention to provide a signal reproducing method and a signal reproducing device that can be optimized.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the signal reproducing method of the present invention includes a step 1 for reproducing a recording medium such as an optical disk, and a step 2 for storing digital reproduction data obtained by A / D converting a reproduction signal of the recording medium. Step 3 of changing the equalization coefficient of waveform equalization, step 4 of reading out the stored digital reproduction data and performing waveform equalization using the equalization coefficient, and For example, Step 5 of evaluating signal quality such as an error rate, and Step of determining the optimum equalization coefficient based on the correspondence between the equalization coefficient and the signal quality after repeating Steps 3 to 5 a plurality of times. 6 is provided.
[0009]
According to another aspect of the present invention, there is provided a signal reproducing apparatus which reproduces a recording medium such as an optical disk and outputs digital reproduction data by A / D converting a reproduction signal of the recording medium. A / D conversion means, memory means such as a semiconductor memory for storing the digital reproduction data, waveform equalization means for reading the digital reproduction data stored in the memory means and performing waveform equalization, and waveform equalization The signal quality evaluation means for evaluating the signal quality of the digital reproduction data thus obtained, and the signal quality evaluation means evaluates the signal quality such as an error rate while changing the equalization coefficient of the waveform equalization means. An equalization optimization control unit that determines an optimum equalization coefficient based on a correspondence relationship between the coefficient and the signal quality is provided.
[0010]
According to the above invention, the digital reproduction data is stored in a memory means such as a semiconductor memory, and is read out repeatedly, thereby changing the equalization coefficient and changing the signal quality evaluation means for the same reproduction waveform data. It is possible to evaluate a signal quality such as an error rate, thereby detecting a change in a pure signal quality such as an error rate corresponding to a change in an equalization coefficient without being affected by a servo residual error or the like. This makes it possible to optimize the equalization coefficient with high accuracy.
[0011]
Therefore, it is possible to detect a change in signal quality, such as a pure error rate, corresponding to a change in the equalization coefficient, and to provide a signal reproduction method and a signal reproduction apparatus capable of optimizing the equalization coefficient with high accuracy. can do.
[0012]
Further, in the signal reproducing method according to the present invention, in the signal reproducing method described above, the step 6 is a step of determining an equalization coefficient having the best signal quality such as an error rate as an optimal equalization coefficient. It is characterized by.
[0013]
Further, in the signal reproducing apparatus according to the present invention, in the signal reproducing apparatus described above, the equalization optimization control means determines an equalization coefficient having the best signal quality such as an error rate as an optimal equalization coefficient. It is characterized by:
[0014]
According to the above invention, for example, the equalization coefficient with the best signal quality such as an error rate is determined as the optimum equalization coefficient, so that the equalization coefficient can be optimized with high accuracy.
[0015]
Further, in the signal reproducing method according to the present invention, in the signal reproducing method described above, in the step 6, the center of the range of the equalization coefficient where the signal quality such as an error rate becomes better than a predetermined quality is optimally equalized. It is characterized in that it is a step of determining as a coefficient.
[0016]
Further, in the signal reproducing apparatus according to the present invention, in the signal reproducing apparatus described above, the equalization optimization control means may control a center of a range of an equalization coefficient in which signal quality such as an error rate becomes better than a predetermined quality. Is determined as the optimal equalization coefficient.
[0017]
According to the above invention, for example, the center of the range of the equalization coefficient where the signal quality such as the error rate becomes better than the predetermined value is determined as the optimum equalization coefficient, so that the capacity of the memory for storing the digital reproduction data is reduced. Even if it is small, it is possible to easily determine the optimum equalization coefficient.
[0018]
Also, the signal reproducing method of the present invention, in the signal reproducing method described above, comprises a step of detecting an error rate of the digitally reproduced data whose waveform has been equalized, and a step of evaluating signal quality from the error rate. It is characterized by.
[0019]
Further, in the signal reproducing apparatus according to the present invention, in the signal reproducing apparatus described above, the signal quality evaluating means includes an error rate detecting means for detecting an error rate of the digitally reproduced data whose waveform has been equalized, An error rate signal quality evaluation means for evaluating signal quality is provided.
[0020]
According to the above invention, the optimum equalization coefficient is determined based on the actually measured error rate. Therefore, it is possible to determine the optimum equalization coefficient with high accuracy.
[0021]
Further, in the signal reproducing method according to the present invention, in the signal reproducing method described above, the step 5 detects a path metric difference between the two paths by performing PRML decoding on the digitally reproduced data whose waveform has been equalized. And evaluating the signal quality from the path metric difference.
[0022]
Further, in the signal reproducing apparatus according to the present invention, in the signal reproducing apparatus described above, the signal quality evaluation means performs PRML decoding on the digitally reproduced data whose waveform has been equalized to obtain a path metric difference between two paths. And a path metric difference signal quality evaluation means for evaluating signal quality from the path metric difference.
[0023]
According to the above invention, the optimum equalization coefficient is determined based on the path metric difference. As a result, even if the capacity of a memory means such as a semiconductor memory is reduced, the best value of the error rate can be detected, so that the optimum equalization coefficient can be determined with higher accuracy. Further, for example, the recording medium such as an optical disk is hardly affected by defects such as scratches and dirt, and the error rate can be predicted even if the recording bit string is unknown. Can be optimized. From this, it is also possible to realize a process of performing equalization optimization using the reproduction signal at that point in time at a predetermined time interval. It is possible to follow more accurately.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS.
[0025]
As shown in FIG. 2, an optical disk reproducing apparatus as a signal reproducing apparatus according to the present embodiment includes an optical disk 1 as a recording medium, an optical pickup 2, a reproduction clock extracting circuit 3, an A / D converter 4, a semiconductor memory 5, It includes a transversal filter 6, an error rate measurement circuit 7, and a controller 8.
[0026]
The optical pickup 2 includes a semiconductor laser (not shown), various optical components, a photodiode, and the like. The laser beam emitted from the semiconductor laser is reflected by an information bit string recorded on the optical disk 1, and the reflected light is electrically converted by the photodiode. The signal is converted into a signal and an analog reproduction signal is output.
[0027]
The transversal filter 6 includes two delay elements for a time T (T represents one channel bit time of a reproduced signal), two amplifiers having a gain α times, one amplifier having a gain 1 / (1 + 2α) times, and addition. This is a digital filter composed of a single device and has a function of emphasizing the high frequency component of the input signal. The reason why the gain is multiplied by 1 / (1 + 2α) in the final stage of the transversal filter 6 is that it is a condition for not amplifying the DC component (the component of frequency = 0) (amplification ratio = 1). Here, the gain α is an equalization coefficient, and by changing this value, the equalization characteristic of the transversal filter 6 can be changed.
[0028]
Further, the error rate measuring circuit 7 has a function of calculating and outputting an error rate (bit error rate) from the equalized reproduced signal. The controller 8 is a sequencer composed of a microcomputer or the like. The controller 8 checks the correlation with the error rate calculated by the error rate measurement circuit 7 while changing the equalization coefficient of the transversal filter 6, and determines the optimum equalization coefficient α. Has a control function to determine.
[0029]
The optical pickup 2 has a function as a reproducing means of the present invention, the reproduced clock extracting circuit 3 and the A / D converter 4 have a function as an A / D converting means, and the semiconductor memory 5 has The transversal filter 6 has a function as a waveform equalizing means, the error rate measuring circuit 7 has a function as a signal quality evaluating means, and the controller 8 has a function as a memory means. Each has a function as optimization control means.
[0030]
Here, the error rate measurement circuit 7 will be described in more detail.
[0031]
The error rate measuring circuit 7 includes a Viterbi decoding circuit 9, a recording bit string register 10, a comparator 11, a counter 12, a sample number register 13, and a divider 14, as shown in FIG.
[0032]
In the error rate measuring circuit 7, the equalized waveform signal input from the transversal filter 6 is subjected to Viterbi decoding in the Viterbi decoding circuit 9, and is output as a binary reproduced bit string of 0 or 1. The reproduced bit string is compared with a recording bit string stored in the recording bit string register 10 in advance by the comparator 11, and when the two are different, a signal is sent to the counter 12. When this process is performed for a predetermined number of samples, the counter 12 outputs the number of reproduced bits different from the recording bits, that is, the number of error bits. The value divided by the number of samples is output to the controller 8 as the bit error rate. The Viterbi decoding circuit 9, the recording bit string register 10 and the comparator 11 have a function as an error rate detecting means of the present invention, and the counter 12, the sample number register 13 and the divider 14 function as an error rate detecting means of the present invention. It has a function as signal quality evaluation means.
[0033]
The reproducing operation of the optical disk reproducing device having the above configuration will be described based on the flowchart shown in FIG.
[0034]
First, in step 1, a light beam is irradiated from the optical pickup 2 onto the optical disk 1, and an analog reproduction signal of an information bit sequence recorded on the optical disk 1 is output (S1). Then, in step 2, the analog reproduction signal is converted into digital waveform data by the A / D converter 4 and stored in the semiconductor memory 5 (S2). Note that the A / D conversion here is performed at the timing of the clock extracted from the analog reproduction signal by the reproduction clock extraction circuit 3 composed of a PLL (Phase Locked Loop).
[0035]
Next, after the equalization coefficient α of the transversal filter 6 is changed under the control of the controller 8 in step 3 (S3), the digital waveform data read from the semiconductor memory 5 is changed in step 4 by the transversal filter 6. Performs a waveform equalization process (S4).
[0036]
In step 5, the digital waveform data after the waveform equalization is input to the error rate measuring circuit 7, and the error rate is calculated (S5). The controller 8 stores the error rate in association with the equalization coefficient α.
[0037]
In step 6, it is determined whether or not the equalization coefficient α is within the predetermined test range. If the equalization coefficient α is still within the test range, the controller 8 repeats the steps (but the equalization coefficient α is different) from step 3 (S3). 5 (S5) is performed. Thus, the processing from step 3 (S3) to step 5 (S5) is repeated until it is determined in step 6 that the equalization coefficient α has finished the predetermined test range. Finally, the controller 8 determines the optimal equalization coefficient α based on the correspondence between the stored equalization coefficients α and the error rates (S7).
[0038]
As described above, since the digital reproduction data is stored in the semiconductor memory and repeatedly read out, the error rate can be measured for the same reproduction waveform data while changing the equalization coefficient. It is possible to detect a change in a pure error rate corresponding to a change in the equalization coefficient without being affected by a residual error or the like, and to optimize the equalization coefficient with high accuracy.
[0039]
FIG. 4 is one of actual measurement examples of the correspondence between the equalization coefficient α obtained by the above processing and the error rate, and the processing for determining the optimum equalization coefficient α using this will be described in further detail.
[0040]
Assuming that the predetermined test range in step S6 is −0.4 ≦ α ≦ 0 and the change width of α is 0.02, α = −0.4, −0.38,. , 0, are obtained as shown in the graph of FIG. In step S8, if α at which the bit error rate becomes the best is determined as the optimum equalization coefficient, α = −0.32 can be easily determined as the optimum equalization coefficient.
[0041]
Note that FIG. 4 shows an actual measurement example in the case where the capacity of the semiconductor memory 5 is sufficient. However, in practice, the capacity of the semiconductor memory 5 cannot be so large in many cases. For example, assuming that the capacity of the semiconductor memory 5 is 240 Kbytes, the number of digital waveform data samples is 240 × 1000 = 240,000 samples, and if the bit error rate is 1/2400000 = 4.1E-6 or less, an error occurs. Since no bit is generated, it is not possible to distinguish a state having a better bit error rate.
[0042]
FIG. 5 is an actual measurement example of the correspondence between the equalization coefficient α and the bit error rate in such a case. The break in the graph when the equalization coefficient α is in the range of −0.32 to −0.28 indicates that no error bit has occurred. In such a case, in step S8, α at which the bit error rate becomes the best cannot be uniquely determined as the optimum equalization coefficient.
[0043]
Therefore, as another form of step S8, the center of the range of the equalization coefficient α falling below the predetermined error rate may be determined as the optimum equalization coefficient. That is, in the example of FIG. 5, if the predetermined bit error rate is set to 1E-5, the range of the equalization coefficient α at which the bit error rate becomes 1E-5 or less is -0.36 to -0.18. Therefore, the optimum equalization coefficient α = (− 0.36-0.18) /2=−0.27 can be determined as the average value of the range.
[0044]
As described above, even when the capacity of the semiconductor memory 5 is small, the optimum equalization coefficient α can be easily determined.
[0045]
As described above, according to the signal reproducing method of the present embodiment, step 1 for reproducing the optical disk 1, step 2 for storing digital reproduction data obtained by A / D conversion of the reproduction signal of the optical disk 1, and equalization of waveform equalization Step 3 for changing the coefficient α, Step 4 for reading out the stored digital reproduction data and performing waveform equalization using the equalization coefficient α, and Step 5 for evaluating the error rate of the waveform-equalized digital reproduction data. , After repeating Steps 3 to 5 a plurality of times, determining an optimal equalization coefficient based on the correspondence between the equalization coefficient α and the error rate.
[0046]
The optical disk reproducing apparatus according to the present embodiment includes an optical pickup 2 for reproducing the optical disk 1, a reproduction clock extracting circuit 3 for A / D converting a reproduction signal of the optical disk 1 and outputting digital reproduction data, and an A / D converter. , A semiconductor memory 5 for storing digital reproduction data, a transversal filter 6 for reading the digital reproduction data stored in the semiconductor memory 5 and performing waveform equalization, and a signal for the waveform-reproduced digital reproduction data. The error rate is measured by the error rate measurement circuit 7 for evaluating the quality and the error rate measurement circuit 7 while changing the equalization coefficient α of the transversal filter 6, and the optimum and the like are determined based on the correspondence between the equalization coefficient and the signal quality. And a controller 8 for determining a conversion coefficient.
[0047]
Therefore, by storing the digital reproduction data in the semiconductor memory 5 and repeatedly reading it, the error rate measurement circuit 7 evaluates the error rate of the same reproduction waveform data while changing the equalization coefficient α. It is possible to detect a change in the pure error rate corresponding to the change in the equalization coefficient α without being affected by the servo residual error, etc., and to optimize the equalization coefficient α with high accuracy. Become.
[0048]
As a result, it is possible to provide a signal reproducing method and an optical disk reproducing apparatus that can detect a change in a pure error rate corresponding to a change in the equalization coefficient α and enable highly accurate optimization of the equalization coefficient α. Can be.
[0049]
In the signal reproducing method according to the present embodiment, step 6 is a step of determining an equalization coefficient α having the best error rate as an optimum equalization coefficient.
[0050]
Further, in the optical disk reproducing device of the present embodiment, the controller 8 determines the equalization coefficient α that gives the best error rate as the optimum equalization coefficient.
[0051]
Therefore, by determining the equalization coefficient α with the best error rate as the optimum equalization coefficient, it is possible to optimize the equalization coefficient α with high accuracy.
[0052]
In the signal reproducing method according to the present embodiment, step 6 is a step of determining the center of the range of the equalization coefficient α at which the error rate becomes better than the predetermined quality as the optimum equalization coefficient.
[0053]
Further, in the optical disk reproducing device of the present embodiment, the controller 8 determines the center of the range of the equalization coefficient α in which the error rate becomes better than the predetermined quality as the optimum equalization coefficient.
[0054]
Therefore, by determining the center of the range of the equalization coefficient α in which the error rate becomes better than the predetermined value as the optimum equalization coefficient, even if the capacity of the memory for storing the digital reproduction data is small, the optimum It is possible to easily determine the equalization coefficient α.
[0055]
Further, the signal reproducing method of the present embodiment includes a step of detecting an error rate of digitally reproduced data whose waveform has been equalized, and a step of evaluating signal quality from the error rate.
[0056]
In the optical disk reproducing apparatus according to the present embodiment, the error rate measuring circuit 7 includes a Viterbi decoding circuit 9 for detecting an error rate of waveform-equalized digital reproduced data, a recording bit string register 10, a comparator 11, And a sample number register 13 and a divider 14 for estimating the signal quality.
[0057]
According to the above invention, the optimum equalization coefficient α is determined based on the actually measured error rate. Therefore, it is possible to determine the optimum equalization coefficient with high accuracy.
[0058]
[Embodiment 2]
Another embodiment of the present invention will be described below with reference to FIGS. For convenience of description, members having the same functions as those shown in the drawings of the first embodiment are given the same reference numerals, and descriptions thereof will be omitted.
[0059]
In the error measuring circuit 7 according to the first embodiment, the bit error rate is obtained by directly comparing the reproduction bit string decoded by the Viterbi decoding circuit 9 with the recording bit string. However, according to this method, there is a problem that the recording bit string needs to be known in advance, a problem that the bit error rate cannot be detected correctly when the optical disc 1 includes a defect such as a scratch or dirt, or the number of samples. There are many issues such as the need for large quantities.
[0060]
Therefore, a configuration in which a bit error rate is predicted by using a path metric difference in Viterbi decoding is added, and a configuration in which an optimal equalization coefficient is determined based on the obtained error rate is effective.
[0061]
Here, as a method of evaluating signal quality using a path metric difference in Viterbi decoding, a method called SAM (Sequenced Amplitude Margin) has been proposed (T. Perkins, “A Window Martin Like Procedure for Living Promotion PR Marketing Evaluating PR). Performance "; IEEE Transactions on Magnetics, Vol. 31, No. 2, 1995, p1109-1114). A method of predicting a bit error rate using a SAM has also been proposed (T. Okumura, "A Method for Evaluating PRML System Reliability Using Sequential Amplitude Collection Annual, Annual Meeting, International, International, International, Convention, International, International, International, International, Convention, Momentary, International, International, International, Convention, International, International, Convention, International Momentary, International Conventions, International Conventions, International Conventions, International Conventions, International Conventions, International Conventions, International Conventions, International Conventions, International Conventions, International Conventions, International Conventions, International Conventions, Conventions, and International Publications)." ).
[0062]
When the above SAM is applied to the error rate measuring circuit 7, as shown in FIG. 6, the error rate measuring circuit 7 as the signal quality evaluation means is replaced by a path metric calculating circuit 15, a surviving path determining circuit 16, and a threshold. It comprises a value register 17, a comparator 18, a counter 19, a sample number register 20, and a divider 21. The path metric calculation circuit 15, the surviving path determination circuit 16, the threshold register 17, and the comparator 18 have a function as a path metric difference detecting means of the present invention, and include a counter 19, a sample number register 20, and a division register. The device 21 has a function as a path metric difference signal quality evaluation means of the present invention. The description of the same configuration as that of the first embodiment is omitted.
[0063]
A reproducing operation by the optical disk reproducing device having the above configuration will be described. The analog reproduction signal of the information bit string recorded on the optical disk 1 is stored in the semiconductor memory 5 through A / D conversion, subjected to waveform equalization by the transversal filter 6, and input to the error rate measurement circuit 7. The processing up to this point is the same as in the first embodiment.
[0064]
After that, in the present embodiment, the error rate measurement circuit 7 measures the path metric difference and predicts the error rate from this, instead of actually measuring the error rate as in the first embodiment. This processing will be described in detail.
[0065]
First, the path metric calculation circuit 15 calculates a path metric difference ΔM for the input digital waveform data after equalization. Here, consider a trellis diagram as shown in FIG. Here, in the figure, S (00), S (01), S (10), and S (11) represent states.
[0066]
For example, state S (00) indicates that the previous bit was 0 and the current bit was 0. The line connecting the states is called a branch, and represents a state transition. For example, a bit string “001” can be represented by a branch of S (00) → S (01). In FIG. 7, letters a to f are assigned as identifiers of the branches, and the ideal waveform level expected in each state transition is attached beside the letters. For example, since a represents a bit string of "000", -1 and b represents a bit string of "100", -0.5 is an ideal level. Here, the branch of S (01) → S (10) and S (10) → S (01) does not exist when there is a run length limit of d = 1 such as a (1,7) RLL code. Is assumed, which reflects that the bit strings “010” and “101” cannot exist.
[0067]
In the trellis diagram, considering a path that is a combination of all branches generated from an arbitrary state through an arbitrary state is equivalent to considering all possible bit strings. Therefore, comparing the ideal waveform expected for all the paths with the reproduced waveform actually reproduced from the optical recording medium, if the path having the closest waveform, that is, the path having the smallest path metric is searched for as the surviving path. , The most probable maximum likelihood path can be determined as a decoded bit string.
[0068]
The path metric is obtained by accumulating the square of the difference between the digital waveform data and the ideal level of each branch (branch metric) for all branches constituting the path. The surviving path determination circuit 16 has a function of detecting a path with the minimum path metric as a decoded bit string and feeding it back to the path metric calculation circuit 15. The path metric calculation circuit 15 knows the correct state of the trellis diagram from the decoded bit string input from the surviving path determination circuit 16, and calculates the path metric difference ΔM between the two paths input to each correct state, that is, the SAM value. can do.
[0069]
Next, the path metric difference ΔM output from the path metric calculation circuit 15 is compared with a predetermined threshold SL stored in the threshold register 17 by the comparator 18. The comparator 18 outputs a signal when ΔM <SL, that is, when the SAM value is smaller than a predetermined threshold.
[0070]
Since this signal is input to the counter 19, the output of the counter 19 indicates the number of SAM values smaller than a predetermined threshold. On the other hand, since the output of the sample number register 20 indicates the total number of samples, the value obtained by dividing the output of the counter 19 calculated by the divider 21 by the output of the sample number register 20 is the frequency distribution of the SAM value. Indicates the relative frequency of the portion smaller than the predetermined threshold SL (the ratio to the total frequency). This value corresponds to the error rate and accurately represents the signal quality. From this value, the corresponding bit error rate can be derived by calculation. Since the detailed derivation calculation is already known, the detailed description is omitted.
[0071]
After the bit error rate is measured by the error rate measuring circuit 7 in this manner, the processing until the controller 8 determines the optimum equalization coefficient α based on the correspondence between each equalization coefficient α and the error rate is performed. Same as in the first embodiment.
[0072]
FIG. 8 is one of the actual measurement examples of the correspondence between the equalization coefficient α obtained by the above processing and the error rate. The capacity of the semiconductor memory 5 in this process is 240 Kbytes, which is the same as in the first embodiment when the capacity shown in FIG. 5 is small.
[0073]
From this graph, α = −0.32 when the bit error rate becomes the best can be determined as the optimum equalization coefficient. As a result, the problem that α at the time when the bit error rate becomes the best cannot be uniquely determined as the optimum equalization coefficient due to the existence of the equalization coefficient α in which no error bit occurs in FIG. Is found to be resolved.
[0074]
As described above, the error rate is predicted using the path metric difference, and the optimum equalization coefficient is determined based on the predicted error rate. Can be detected, so that the optimal equalization coefficient can be determined with higher accuracy. In addition, since the error rate can be predicted even if the recording bit string is unknown because it is hardly affected by the defect of the optical disc 1, it is possible to optimize the equalization coefficient using the reproduction signal at an arbitrary position on the optical disc 1. It becomes. Thus, for each predetermined time, a process of performing equalization optimization using the reproduction signal at that time can also be realized. Therefore, even with respect to the fluctuation of the optimal equalization coefficient due to the fluctuation of the reproduction characteristic over time, It is possible to follow more accurately.
[0075]
Note that jitter may be used as a signal quality evaluation value instead of the error rate.
[0076]
In this case, a configuration for detecting temporal fluctuation of an edge obtained by binarizing digital waveform data stored in the semiconductor memory 5 with a predetermined threshold value is required. In this configuration, for example, the position of an edge is detected by interpolation from two continuous digital waveform data in which one is larger than a predetermined threshold and the other is smaller, and the variance thereof is calculated to derive jitter. And the like.
[0077]
By determining the optimum equalization coefficient based on the jitter, even if the capacity of the semiconductor memory 5 is reduced, the best value of the signal quality can be detected, so that the optimum equalization coefficient can be determined with higher accuracy. It becomes. Further, since the signal quality is hardly affected by the defect of the optical disc 1 and the signal quality can be detected even if the recording bit string is unknown, the equalization coefficient can be optimized using the reproduction signal at an arbitrary position on the optical disc 1. It becomes. This makes it possible to realize a process of performing equalization optimization using the reproduction signal at that point in time at a predetermined time interval. It is possible to follow accurately.
[0078]
In the description of the present embodiment, the (1,7) RLL code is used as the run-length limited code of d = 1, but it is needless to say that the present invention is not limited to these.
[0079]
In each of the above embodiments, the optical disk reproducing apparatus has been described as an example of the reproducing apparatus. However, the present invention is not limited to this, and the same effect can be exerted in an apparatus that performs PRML signal reproduction. It is a kimono. That is, the present invention is applicable to all magnetic recording / reproducing devices, communication data receiving devices, and the like.
[0080]
As described above, in the signal reproducing method according to the present embodiment, in the step 5, the step of detecting the path metric difference between the two paths by performing the PRML decoding on the digitally reproduced data whose waveform has been equalized; Evaluating the signal quality from the path metric difference.
[0081]
The optical disc reproducing apparatus according to the present embodiment includes a path metric calculation circuit 15 that performs PRML decoding on digitally reproduced data whose waveform has been equalized to detect a path metric difference between two paths, and determines a surviving path. The circuit includes a circuit 16, a threshold register 17, a comparator 18, a counter 19 for evaluating signal quality from a path metric difference, a sample number register 20, and a divider 21.
[0082]
Therefore, the optimum equalization coefficient is determined based on the path metric difference. As a result, even if the capacity of the semiconductor memory 5 is reduced, the best value of the error rate can be detected, so that the optimum equalization coefficient can be determined with higher accuracy. Further, since the optical disk 1 is hardly affected by defects such as scratches and dirt, and the error rate can be predicted even if the recording bit string is unknown, the optimization of the equalization coefficient using a reproduction signal at an arbitrary position on the optical disk 1 is performed. Can be performed. From this, it is also possible to realize a process of performing equalization optimization using the reproduction signal at that point in time at a predetermined time interval. It is possible to follow more accurately.
[0083]
It should be noted that the present invention is not limited to the above-described embodiments, and various changes can be made within the scope of the claims, and the technical means disclosed in different embodiments can be appropriately combined. Embodiments included in the invention are also included in the technical means of the present invention.
[0084]
【The invention's effect】
As described above, according to the signal reproducing method of the present invention, step 1 for reproducing a recording medium, step 2 for storing digital reproduction data obtained by A / D conversion of a reproduction signal of the recording medium, and equalization of waveform equalization Step 3 of changing a coefficient, Step 4 of reading out the stored digital reproduction data and performing waveform equalization using the equalization coefficient, and Evaluation of signal quality of the waveform-reproduced digital reproduction data 5 and a step 6 of determining an optimal equalization coefficient based on the correspondence between the equalization coefficient and the signal quality after repeating steps 3 to 5 a plurality of times.
[0085]
Further, as described above, the signal reproducing apparatus of the present invention includes: a reproducing unit for reproducing a recording medium; an A / D converting unit for A / D converting a reproduction signal of the recording medium to output digital reproduction data; Memory means for storing the digital reproduction data; waveform equalization means for reading the digital reproduction data stored in the memory means to perform waveform equalization; and evaluating the signal quality of the waveform-equalized digital reproduction data. The signal quality evaluator and the signal quality evaluator evaluate the signal quality such as an error rate while changing the equalization coefficient of the waveform equalizer, and optimize the signal quality based on the correspondence between the equalization coefficient and the signal quality. And an equalization optimization control means for determining an equalization coefficient.
[0086]
Therefore, by storing the digital reproduction data in the memory means and repeatedly reading the same, the signal quality can be evaluated by the signal quality evaluation means for the same reproduction waveform data while changing the equalization coefficient. . Therefore, a pure change in signal quality corresponding to a change in the equalization coefficient can be detected without being affected by a servo residual error or the like, and the equalization coefficient can be optimized with high accuracy.
[0087]
Therefore, it is possible to detect a change in signal quality, such as a pure error rate, corresponding to a change in the equalization coefficient, and to provide a signal reproduction method and a signal reproduction apparatus capable of optimizing the equalization coefficient with high accuracy. It has the effect that it can be done.
[0088]
Further, in the signal reproducing method according to the present invention, in the signal reproducing method described above, the step 6 is a step of determining an equalization coefficient having the best signal quality such as an error rate as an optimum equalization coefficient. It is.
[0089]
Further, in the signal reproducing apparatus according to the present invention, in the signal reproducing apparatus described above, the equalization optimization control means determines an equalization coefficient having the best signal quality such as an error rate as an optimal equalization coefficient. Things.
[0090]
Therefore, by determining the equalization coefficient with the best signal quality as the optimum equalization coefficient, there is an effect that the equalization coefficient can be optimized with high accuracy.
[0091]
Further, in the signal reproducing method according to the present invention, in the signal reproducing method described above, in the step 6, the center of the range of the equalization coefficient where the signal quality such as an error rate becomes better than a predetermined quality is optimally equalized. The method is a step of determining as a coefficient.
[0092]
Further, in the signal reproducing apparatus according to the present invention, in the signal reproducing apparatus described above, the equalization optimization control means may control a center of a range of an equalization coefficient in which signal quality such as an error rate becomes better than a predetermined quality. Is determined as the optimal equalization coefficient.
[0093]
Therefore, by determining the center of the range of the equalization coefficient in which the signal quality is better than the predetermined value as the optimum equalization coefficient, even if the capacity of the memory for storing the digital reproduction data is small, the optimum There is an effect that the equalization coefficient can be easily determined.
[0094]
Further, the signal reproducing method of the present invention, in the above signal reproducing method, comprises a step of detecting an error rate of the digitally reproduced data whose waveform has been equalized, and a step of evaluating a signal quality from the error rate. It is.
[0095]
Further, in the signal reproducing apparatus according to the present invention, in the signal reproducing apparatus described above, the signal quality evaluating means includes an error rate detecting means for detecting an error rate of the digitally reproduced data whose waveform has been equalized, Error rate signal quality evaluation means for evaluating signal quality.
[0096]
Therefore, since the optimum equalization coefficient is determined based on the actually measured error rate, it is possible to determine the optimum equalization coefficient with high accuracy.
[0097]
Further, in the signal reproducing method according to the present invention, in the signal reproducing method described above, the step 5 detects a path metric difference between the two paths by performing PRML decoding on the digitally reproduced data whose waveform has been equalized. And estimating the signal quality from the path metric difference.
[0098]
Further, in the signal reproducing apparatus according to the present invention, in the signal reproducing apparatus described above, the signal quality evaluation means performs PRML decoding on the digitally reproduced data whose waveform has been equalized to obtain a path metric difference between two paths. And a path metric difference signal quality evaluation means for evaluating the signal quality from the path metric difference.
[0099]
Therefore, the optimum equalization coefficient is determined based on the path metric difference. As a result, even if the capacity of a memory means such as a semiconductor memory is reduced, the best value of the error rate can be detected, so that the optimum equalization coefficient can be determined with higher accuracy. Further, since the recording medium is hardly affected by defects such as scratches and dirt, and the error rate can be predicted even if the recording bit string is unknown, the optimization of the equalization coefficient using a reproduction signal at an arbitrary position on the recording medium is performed. Can be performed. Thus, for each predetermined time, a process of performing equalization optimization using the reproduction signal at that time can also be realized. Therefore, even with respect to the fluctuation of the optimal equalization coefficient due to the fluctuation of the reproduction characteristic over time, There is an effect that it is possible to more accurately follow.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating an embodiment of a signal reproducing method by a signal reproducing apparatus according to the present invention.
FIG. 2 is a block diagram showing an overall configuration of the signal reproducing apparatus.
FIG. 3 is a block diagram showing in detail a configuration of an error rate measuring circuit in the signal reproducing apparatus.
FIG. 4 is a graph showing a relationship between a bit error rate and an equalization coefficient in a signal reproducing method by the signal reproducing apparatus.
FIG. 5 is a graph showing a relationship between a bit error rate and an equalization coefficient when the signal reproducing method by the signal reproducing apparatus has a period in which no error bit occurs.
FIG. 6 is a block diagram showing an error rate measuring circuit according to still another embodiment of the signal reproducing apparatus and the signal reproducing method according to the present invention.
FIG. 7 is a trellis diagram used in a signal reproducing method by the signal reproducing device.
FIG. 8 is a graph showing a relationship between a bit error rate and an equalization coefficient in a signal reproducing method by the signal reproducing apparatus.
[Explanation of symbols]
1 Optical disk (recording medium)
2 Optical pickup (reproduction means)
3. Reproduction clock extraction circuit (A / D conversion means)
4 A / D converter (A / D conversion means)
5 Semiconductor memory (memory means)
6. Transversal filter (waveform equalization means)
7 Error rate measurement circuit (signal quality evaluation means)
8 Controller (Equalization optimization control means)
9 Viterbi decoding circuit (error rate detection means)
10. Record bit string register (error rate detection means)
11 Comparator (error rate detection means)
12 counter (error rate signal quality evaluation means)
13 Sample number register (error rate signal quality evaluation means)
14. Divider (error rate signal quality evaluation means)
15. Path metric calculation circuit (path metric difference detection means)
16. Surviving path determination circuit (path metric difference detecting means)
17 threshold register (path metric difference detecting means)
18 Comparator (path metric difference detection means)
19 counter (path metric difference signal quality evaluation means)
20 sample number register (path metric difference signal quality evaluation means)
21 Divider (path metric difference signal quality evaluation means)
α equalization coefficient

Claims (10)

Step 1 of playing the recording medium;
Storing digital reproduction data obtained by A / D converting the reproduction signal of the recording medium;
Step 3 of changing the equalization coefficient of waveform equalization;
Reading the stored digital reproduction data and performing waveform equalization using the equalization coefficient;
Step 5 of evaluating the signal quality of the digitally reproduced data whose waveform has been equalized;
A step of determining the optimum equalization coefficient based on the correspondence between the equalization coefficient and the signal quality after repeating steps 3 to 5 a plurality of times. 2. The signal reproducing method according to claim 1, wherein said step 6 is a step of determining an equalization coefficient having the best signal quality as an optimum equalization coefficient. 2. The signal reproducing method according to claim 1, wherein said step 6 is a step of determining, as an optimum equalization coefficient, a center of a range of the equalization coefficient at which the signal quality is better than a predetermined quality. Step 5 is:
Detecting an error rate of the digitally reproduced data whose waveform has been equalized;
2. The signal reproducing method according to claim 1, further comprising the step of evaluating a signal quality from said error rate. Step 5 is:
Performing PRML decoding on the waveform-reproduced digital reproduction data to detect a path metric difference between two paths;
2. The signal reproducing method according to claim 1, further comprising the step of evaluating the signal quality from the path metric difference. Reproducing means for reproducing the recording medium;
A / D conversion means for A / D converting a reproduction signal of the recording medium and outputting digital reproduction data;
Memory means for storing the digital reproduction data;
Waveform equalizing means for reading the digital reproduction data stored in the memory means and performing waveform equalization;
Signal quality evaluation means for evaluating the signal quality of the digitally reproduced data whose waveform has been equalized,
Equalization optimization control means for evaluating the signal quality by the signal quality evaluation means while changing the equalization coefficient of the waveform equalization means and determining an optimum equalization coefficient based on the correspondence between the equalization coefficient and the signal quality A signal reproducing device comprising: 7. The signal reproducing apparatus according to claim 6, wherein said equalization optimization control means determines an equalization coefficient having the best signal quality as an optimum equalization coefficient. 7. The signal reproducing apparatus according to claim 6, wherein the equalization optimization control means determines the center of the range of the equalization coefficient where the signal quality is better than a predetermined quality as the optimum equalization coefficient. The signal quality evaluation means,
Error rate detecting means for detecting an error rate of the digitally reproduced data having the waveform equalized;
7. The signal reproducing apparatus according to claim 6, further comprising: an error rate signal quality evaluation unit that evaluates a signal quality from the error rate. The signal quality evaluation means,
Path metric difference detecting means for performing PRML decoding on the digitally reproduced data whose waveform has been equalized to detect a path metric difference between two paths;
7. The signal reproducing apparatus according to claim 6, further comprising: a path metric difference signal quality evaluation means for evaluating a signal quality from the path metric difference.

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