JP2006313631A - Reproduced signal evaluating method, information recording medium, and information reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reproduced signal evaluating method in which a reproduced signal obtained from an information recording medium in which the prescribed information is recorded at high density can be evaluated accurately. <P>SOLUTION: The method is provided with a step (ST11) in which a reproduced signal is obtained from the information recording medium in which digital information is recorded by recording marks of different size, a step (ST12) in which amplitude of a first reproduced signal in which digital information recorded by the largest size recording mark is reflected is obtained, a step (ST13) in which amplitude of a second reproduced signal in which digital information recorded by a recording mark being small after the smallest size is reflected is obtained out of signals included in the reproduced signal, a step (ST14) in which an evaluation value is obtained from a ratio of amplitude of the first and the second reproduced signals, and a step (ST15) in which a property of the reproduced signal is evaluated by the evaluation value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reproduction signal evaluation method for evaluating the quality of a reproduction signal reproduced from an information recording medium on which digital information is recorded. The present invention also relates to an information recording medium on which digital information is recorded. Furthermore, the present invention relates to an information reproducing apparatus for reproducing digital information from an information recording medium on which digital information is recorded.

  In a digital recording / reproducing apparatus for writing / reading digital data such as an optical disk and a magnetic disk, the storage capacity per unit area is increased due to the improvement of the high-density recording technique, and the margin of the reproduction signal quality is reduced. Therefore, it is necessary to determine the recording state accurately. In particular, when a replaceable medium is used, there is a compatibility problem when the same medium is used in a plurality of apparatuses or when a plurality of media are used in the same apparatus. Therefore, from the viewpoint of ensuring compatibility, it is necessary to define characteristics when a signal is reproduced from a medium by a predetermined device.

  A conventional optical disc apparatus will be described below with reference to FIG.

  Digital data is recorded on the optical disc 100 by forming a signal track. In addition to the recordable / reproducible type, the optical disc may be a read-only disc in which data is recorded on the irregularities of the disc surface at the time of manufacture, or a disc in which a recordable area and a read-only area are mixed.

  To perform reproduction, the optical disk 100 is rotated by a motor 101, and a signal recorded on the optical disk 100 is read by an optical head 102 using laser light. In the optical head 102, a light beam emitted from an LD (laser diode) is recorded on a track formed on the optical disc 100 by an objective lens (a pit on which data is recorded by unevenness and a mark recorded by a change in reflectance). (Including both). The light beam reflected by the optical disc 100 is condensed on a photodetector by a condenser lens to obtain a reproduction signal.

  The signal output from the optical head 102 is subjected to waveform equalization by the waveform equalization unit 104 after the signal is amplified by the reproduction amplifier 103. The waveform equalization unit 104 is configured by a filter having characteristics such as high-frequency emphasis in order to easily identify digital data recorded continuously along the track.

  In order to restore the recorded digital data to the original data, it is necessary to make the equalized reproduction signal binary data of 0 or 1, and to identify the data by synchronizing the clock. Since no clock signal is recorded on the optical disc, the PLL circuit 105 generates a clock signal from the reproduced signal. On the other hand, the waveform slice identification circuit 106 outputs binary data in synchronization with the clock signal output from the PLL circuit 105. The discriminating method uses a waveform slicing method in which 0 and 1 are distinguished by a level comparator based on the center level of the reproduction signal.

  The waveform slicing method will be described with reference to the operation waveform diagram of FIG. On the optical disc, for example, recording marks are formed as shown in FIG. 11 (c) according to the recording waveform shown in FIG. 11 (b) corresponding to the recording data shown in FIG. 11 (a). When reproducing the information recorded on the optical disk in this way, a reproducing light beam is irradiated onto the optical disk from the LD in the optical head as a minute beam spot as shown by the oblique lines in FIG. A reproduction signal is obtained by reading the mark. The waveform of the reproduced signal (reproduced waveform) is not a rectangular wave as shown in FIG. 11 (b) due to the characteristics of the recording / reproducing system, but is obtained as a dull waveform as shown in FIG. 11 (d).

  Therefore, the equalizer equalizes the waveform such that the intersection of the equalized waveform and a set threshold value (indicated by a one-dot chain line) is the center of the discrimination point with respect to the reproduced waveform as shown in FIG. Is given. Specifically, the high frequency component of the reproduction signal is amplified. The discriminator outputs binary data as ‘1’ if the level of the equalization waveform is high and ‘0’ if the level of the equalization waveform is low, with respect to the equalization waveform and threshold value at the discrimination point. As a result, decoded data is obtained as shown in FIG.

  As evaluation criteria for optical disks and drives, jitter after waveform equalization, modulation amplitude and asymmetry before waveform equalization are used.

  A method for defining jitter will be described. The intersection of the equalized waveform and the threshold is not necessarily the center of the window due to noise or the like. Therefore, the intersections of the equalized waveform and the threshold value are distributed as shown in FIG. 12 with respect to the interval (window) of the identification points. At this time, jitter is expressed by the standard deviation of the intersection data when normalized by the window width.

  Next, modulation amplitude and asymmetry will be described. Due to the resolution (MTF) characteristics of the optical system, the amplitude of a signal having a small recording mark on the optical disk and a high density is small, and the amplitude of a signal having a large recording mark and a low density is large. Further, when the size of the recording mark exceeds the size corresponding to the spot size on the optical disk, the reproduction signal amplitude becomes substantially constant. As a result, the reproduction signal from the optical disc on which the recording marks having a plurality of types of sizes are formed is as shown in FIG.

  At this time, the modulation amplitude (MA) is defined by the ratio between the amplitude of the signal with the highest density (closest signal amplitude: I0) and the amplitude of the signal with the lowest density (most coarse signal amplitude: I1). The densest signal amplitude is the amplitude of the signal with the highest density, and has the shortest signal level change period and the smallest signal amplitude. The coarsest signal amplitude is the amplitude of the signal with the lowest density, has the longest signal level change period, and has the largest signal amplitude. Since the signal amplitude having a low density more than a certain level is almost equal, it can be considered as the maximum value of the amplitude of the entire reproduction signal. From the ratio of these two values, the modulation amplitude can be expressed by the following equation.

MA = I0 / I1 ・ ・ ・ Equation 1
Asymmetry (SA) is defined by the amount of deviation between the center level of the densest signal and the center level of the coarsest signal. The asymmetry can be expressed by the following equation from the low level side (L0L) and the high level side (L0H) of the densest signal, and from the low level side (L1L) and the high level side (L1H) of the coarsest signal amplitude.

SA = ((L1H + L1L)-(L0H + L0L)) / 2 (L1H-L1L) ・ ・ ・ Equation 2
These definition systems functioned when the amplitude of the closest signal was sufficiently secured and at the same time sufficient SN was also secured in terms of quality. Actually, even when the data is identified by the binary waveform slice, if the error rate is sufficiently good, it is possible to measure the amplitude of the densest signal.

  However, when the recording density is increased, the amplitude of the most dense signal is reduced, making it difficult to identify by binary waveform slices, and interference occurs between adjacent data, making it difficult to separate the data. These phenomena cause the error rate to deteriorate and the stored data cannot be read.

  There is a PRML method as a means for dealing with the phenomenon accompanying such high density. PRML is a data identification means that replaces a binary waveform slice, removes the influence of interference between data, and can reproduce more probable data from the data before and after it even if the quality of the densest signal is somewhat degraded.

  Thus, even when new means for increasing the density are introduced, a decrease in the density of the closest signal and a decrease in the quality of the reproduced signal are inevitable. Under such circumstances, it is difficult to accurately evaluate the reproduction signal with the conventional definition of modulation amplitude and asymmetry depending on the densest signal. In addition, in the conventional evaluation method based on the binary waveform slice, although the identification method has changed, the correspondence between the evaluation result and the error rate after identification cannot be sufficiently obtained. Cannot be reflected correctly.

  As described above, in the method for defining the reproduction signal such as modulation amplitude and asymmetry based on the conventional definition, the reproduction signal is accurately evaluated when the density of the closest signal decreases as the density increases and the quality deteriorates. There was a problem that made it difficult.

  Further, when the PRML method is introduced in correspondence with the higher density, there is a problem that the definition based on the binary waveform slice does not correctly correspond to the evaluation result and the error rate after identification.

  The inability to accurately evaluate the playback signal means that it becomes impossible to specify a storage medium for ensuring compatibility, particularly in a system in which the storage medium can be exchanged. It is necessary to specify a good evaluation method.

  An object of the present invention is to provide a reproduction signal evaluation method, an information recording medium, and an information reproduction apparatus described below in view of the above-described circumstances.

  (1) A reproduction signal evaluation method capable of accurately evaluating a reproduction signal obtained from an information recording medium on which predetermined information is recorded at high density.

  (2) An information recording medium on which predetermined information is recorded at a high density so that a reproduction signal satisfying a predetermined evaluation condition is obtained.

  (3) An information reproducing apparatus for reproducing an information recording medium on which predetermined information is recorded at a high density so that a reproduction signal satisfying a predetermined evaluation condition is obtained.

  In order to solve the above problems and achieve the object, a reproduction signal evaluation method, an information recording medium, and an information reproduction apparatus of the present invention are configured as follows.

  (1) A reproduction signal evaluation method according to the present invention includes a step of reproducing an information recording medium on which digital information is recorded with recording marks of various sizes by an optical means, and obtaining a reproduction signal reflecting the digital information; Obtaining the amplitude of a first reproduction signal (that is, the reproduction signal having the lowest recording density) reflecting the digital information recorded by the recording mark having the largest size among the signals included in the reproduction signal; and Second reproduction signal reflecting digital information recorded by a recording mark of a predetermined size excluding a recording mark having the smallest size among signals included in the signal (that is, a predetermined recording density excluding a reproduction signal having the highest recording density) And the step of obtaining the evaluation value based on the ratio of the amplitudes of the first and second reproduction signals. , And a step of evaluating the characteristics of the reproduced signal in the evaluation value.

  (2) A reproduction signal evaluation method according to the present invention includes a step of reproducing an information recording medium on which digital information is recorded with recording marks of various sizes by an optical means, and obtaining a reproduction signal reflecting the digital information; Obtaining an amplitude center level of a first reproduction signal (that is, a reproduction signal having the lowest recording density) in which digital information recorded by a recording mark having the largest size among the signals included in the reproduction signal is reflected; Of the signals included in the reproduction signal, a second reproduction signal reflecting digital information recorded by a recording mark of a predetermined size excluding a recording mark having the smallest size (that is, a predetermined reproduction signal excluding a reproduction signal having the highest recording density). And a difference between the amplitude center levels of the first and second reproduction signals. A step of obtaining an evaluation value based on, and a step of evaluating the characteristics of the reproduced signal in the evaluation value.

  (3) In addition to the description in (1) or (2) above, the reproduction signal evaluation method of the present invention includes a third reproduction signal (that is, the most reproduced digital information recorded with the smallest recorded mark). The amplitude of the reproduction signal having a high recording density is 15% or less of the amplitude of the first reproduction signal (that is, the reproduction signal having the lowest recording density) reflecting the digital information recorded by the recording mark having the largest size. Alternatively, in the case of 20% or less, the third reproduction signal (that is, the reproduction signal having the highest recording density) is excluded from the evaluation target.

  (4) In addition to any one of the above (1) to (3), the reproduction signal evaluation method of the present invention is adapted to reproduce the second reproduction signal (that is, reproduction with a predetermined recording density excluding the reproduction signal with the highest recording density). As the signal, a reproduction signal reflecting the digital information recorded by the second smallest recording mark (that is, the second highest density reproduction signal) is used.

  (5) A reproduction signal evaluation method according to the present invention comprises a step of reproducing an information recording medium on which digital information is recorded by optical means to obtain a reproduction signal reflecting the digital information; Equalizing on the basis of response characteristics, obtaining a multi-level equalized signal, obtaining an amplitude level distribution of the equalized signal, obtaining a plurality of actually measured peak values from the level distribution, and the predetermined partial response An evaluation value based on a step of obtaining a plurality of ideal peak values from characteristics, a step of obtaining a difference value between each measured peak value and each ideal peak value, and a sum or average value of absolute values of the difference values of each peak value And a step of evaluating characteristics of the reproduction signal with the evaluation value.

  (6) In the reproduction signal evaluation method of the present invention, an information recording medium on which digital information is recorded is reproduced by optical means to obtain a reproduction signal reflecting the digital information; Equalizing on the basis of response characteristics, obtaining a multi-level equalized signal, obtaining an amplitude level distribution of the equalized signal, obtaining a plurality of actually measured peak values from the level distribution, and the predetermined partial response An evaluation value based on a step of obtaining a plurality of ideal peak values from characteristics, a step of obtaining a difference value between each measured peak value and each ideal peak value, and a sum or an average value of square values of the difference values of each peak value And a step of evaluating characteristics of the reproduction signal with the evaluation value.

  (7) In addition to the above description (5) or (6), the reproduced signal evaluation method of the present invention multiplies the difference value by a weighting factor corresponding to the peak of each level distribution to obtain a corrected difference value. A step of obtaining, and adopting the corrected difference value instead of the difference value.

  (8) In addition to the description in (7) above, the reproduction signal evaluation method of the present invention obtains the weighting factor from the variance value for each level distribution peak.

  (9) In addition to the description in (7) above, the reproduction signal evaluation method of the present invention obtains the weighting coefficient from the occurrence frequency for each level distribution peak.

  (10) In addition to the description in (7) above, the reproduction signal evaluation method of the present invention is based on the degree of influence on the peak of each level distribution with respect to an error when identifying the equalized signal by Viterbi decoding. Find the weighting factor.

  (11) In the reproduced signal evaluation method according to the present invention, in addition to any one of the above (5) to (10), the partial response characteristic is PR (1, 2, 2, 1).

  (12) In addition to the description in any one of (5) to (11) above, the reproduction signal evaluation method of the present invention obtains an evaluation value for a difference value for at least a part of the level distribution when obtaining the evaluation value. Remove from the subject.

  (13) In the reproduced signal evaluation method according to the present invention, in addition to any of the above (1) to (12), the shortest bit length of the digital information recorded on the information recording medium is 2 bits.

  (14) With the information recording medium of the present invention, when the reproduction signal is evaluated by the reproduction signal evaluation method described in any one of (1) to (13) above, a reproduction signal that satisfies a predetermined evaluation condition is obtained. Record digital information as required.

  (15) The information reproducing apparatus of the present invention reproduces the information recording medium described in the above (14), and obtains a reproduced signal that satisfies a predetermined evaluation condition.

  According to the present invention, the following reproduction signal evaluation method, information recording medium, and information reproduction apparatus can be provided.

  (1) A reproduction signal evaluation method capable of accurately evaluating a reproduction signal obtained from an information recording medium on which predetermined information is recorded at high density.

  (2) An information recording medium on which predetermined information is recorded at a high density so that a reproduction signal satisfying a predetermined evaluation condition is obtained.

  (3) An information reproducing apparatus for reproducing an information recording medium on which predetermined information is recorded at a high density so that a reproduction signal satisfying a predetermined evaluation condition is obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

  An embodiment in which the present invention is applied to a digital optical disc apparatus will be described with reference to the drawings.

  FIG. 1 shows reproduction signal processing of an optical disc apparatus adopting a PRML (Partial Response and Maximum Likelihood) method corresponding to a high-density optical disc.

  High-density digital data is recorded on the optical disc 100 by forming a signal track. In addition to the recordable / reproducible type, the optical disc may be a read-only disc in which data is recorded on the irregularities of the disc surface at the time of manufacture, or a disc in which a recordable area and a read-only area are mixed.

  To perform reproduction, the optical disk 100 is rotated by a motor 101, and a signal recorded on the optical disk 100 is read by the optical head 102 using laser light. The signal read out by the optical head 102 is amplified by the reproduction amplifier 103 and then sampled by the A / D converter 107 to be converted into digital data. As the clock used for sampling, the PLL circuit 105 detects the phase error signal from the equalized signal, and operates so that the reproduced signal and the generated clock signal are synchronized.

  The reproduction signal converted to digital is then PR-equalized by the PR equalizer 108. The conventional waveform equalization unit 104 shown in FIG. 10 has a high-frequency emphasis characteristic that amplifies a close-packed signal having a small amplitude in order to facilitate binary waveform slicing. On the other hand, the PR equalization unit 108 shown in FIG. 1 has a characteristic that the output waveform is a waveform that receives a predetermined interference pattern.

  The reproduction signal waveform and PR equalization will be described with reference to FIG. 2A to 2D show recording data, a recording waveform, a recording mark, and a reproduction waveform, respectively, as in FIGS. 11A to 11D. FIG. 2E shows waveforms after equalization when the equalizer is based on the PR (1, 2, 2, 1) characteristic with respect to the reproduced waveform of FIG. The PR (1, 2, 2, 1) characteristic is a characteristic in which an impulse response appears at a ratio of 1: 2: 2: 1 at four consecutive identification points. Although not shown, the same applies to other PR characteristics such as PR (1, 2, 1). In the PRML system, signal deterioration in an equalizer can be suppressed by performing waveform equalization to a PR characteristic close to the characteristic of an actual reproduction waveform reproduced from an optical disc. For example, as shown in FIG. 3, the PR equalization unit 108 multiplies the output of each delay unit 201 of one sample time connected in cascade by a predetermined coefficient in the multiplier 202, and outputs the output of each multiplier 202. It can be constituted by a transversal filter in the form of adding by the adder 203.

  In the PRML playback signal processing system, a Viterbi decoder 109, which is a typical maximum likelihood decoder, is generally used as a discriminator disposed after an equalizer. Assuming that the reproduction signal is equalized to the PR (1, 2, 2, 1) characteristic by the PR equalization unit 108, the Viterbi decoder has to include all the sequences satisfying the PR (1, 2, 2, 1) characteristic. A sequence having the smallest error from the sample sequence of the equalized waveform is selected, and binary data (decoded data) corresponding to the selected sequence is output. This is shown in FIG. In FIG. 4A, the points indicated by circles indicate the sample series of the equalized waveform, and the lines connected by the solid lines indicate the signal series selected by Viterbi decoding. Since the selected signal sequence level is as shown in FIG. 4B, the decoded data is identified as shown in FIG. 4C from the PR (1, 2, 2, 1) characteristics.

  In the PRML system, since decoding is performed not from one sample value but from a plurality of sample values and is identified as the most probable signal sequence, resistance to signal degradation components having no correlation between the sample values is strong.

  In an optical disc apparatus, the resolution (MTF: Modulation transfer function) is restricted by the characteristics of the optical system. The MTF has a characteristic that the reproduction signal amplitude decreases as the recording mark becomes smaller. If the resolution is high, smaller recording marks can be reproduced. On the other hand, since the resolution is limited by the wavelength of the LD used and the aperture ratio of the objective lens, the resolution cannot be increased freely. Therefore, when the recording density is increased under the condition where the resolution is limited, the reproduction signal amplitude of the portion where the recording mark is small decreases.

  An example of the MTF characteristic is shown in FIG. The vertical axis represents the amplitude value of the reproduction signal, and the horizontal axis represents the size of the recording mark normalized by 1 bit. When data is recorded by RLL (1, 7) modulation, the densest mark with the highest density (recording mark with the smallest size) is 2 bits (2T), and the coarsest mark with the lowest density (the smallest size). A large recording mark) is 8 bits (8T). Therefore, the 2T reproduction signal with the highest density can obtain only a very low amplitude. In the actual playback waveform, noise is added to this low-amplitude signal, and it is also affected by interference from adjacent signals, and it is difficult to record the densest signal stably. Signal quality is significantly degraded. Therefore, it is difficult to accurately obtain the correct value of the conventional definition of the reproduction signal using the amplitude of the most dense signal.

  FIG. 6 shows an example of a reproduction signal waveform when random data modulated with RLL (1, 7) is recorded on a high-density optical disk. The waveform shown in FIG. 6 can be obtained by observing the output of the reproduction amplifier 103 with an oscilloscope. From this observation result, the lowest density 8T signal can be measured as I8 in FIG. 6 from the maximum amplitude of the measurement result. On the other hand, the amplitude of the 2T signal with the highest density seems to be I2 in FIG. 6. However, since the signal amplitude is small and affected by noise and interference, it is difficult to measure with high accuracy, so it was reproduced from the disc. Not suitable for signal evaluation.

  Therefore, in the case of a high-density disk in which the amplitude of the most dense signal is 20% or less (or 15% or less) of the signal having the lowest density, the 3D signal having the next density next to the 2T signal (ie, the most dense signal) Attention is paid to the amplitude of the signal reflected by the recording mark having a size one rank larger than the recording mark having a small size. The 3T signal amplitude indicated by I3 in FIG. 6 is suitable for evaluation of a high-density optical disk because a sufficient amplitude can be ensured as compared with the case of the 2T signal.

  Next, a method for evaluating a reproduction signal in a high-density optical disk using the second highest density quasi-closest signal and the lowest density roughest signal will be described with reference to FIG.

  There is a modulation amplitude as an evaluation item of the reproduction signal. When the resolution of the optical system of the optical disk device is deteriorated, the MTF characteristic is lowered, so that the influence on the signal having a low density is small, but the signal amplitude having a high density is greatly reduced. Therefore, by comparing the signal amplitude with high density with the signal amplitude with low density, and determining the modulation amplitude, whether the resolution of the optical system satisfies the regulations, or whether the optical disc was recorded normally with a device with a predetermined resolution It becomes possible to evaluate whether or not.

  In the case of a high-density optical disc recorded by RLL (1, 7) modulation, the second highest density 3T signal amplitude (I3) is used as the semi-closest signal, and the lowest density 8T signal amplitude (I8) is used as the coarsest signal. By defining the modulation amplitude (MA) using the following equation, the optical disc and the reproduction signal can be stably evaluated.

MA = I3 / I8 ・ ・ ・ Equation 3
Another evaluation item of the reproduction signal is asymmetry. In order to perform identification by waveform slice, the center level of the reproduced signal needs to be constant regardless of the signal density, and asymmetry has been added to the evaluation items. When the identification method is changed to the PRML method for high density, the signal level corresponding to each density becomes important in addition to the center level, so asymmetry continues to be an important evaluation item. . Asymmetry is affected by the shape of the mark formed on the optical disk and the beam spot shape.

  In the case of a high-density optical disc recorded by RLL (1, 7) modulation, the difference between the center level of the second highest density 3T signal as the quasi-closest signal and the center level of the lowest density 8T signal as the coarsest signal. In quantity, asymmetry can be considered. In other words, the asymmetry (SA) is defined by the following expression from the low level side (L3L) and high level side (L3H) of the 3T signal, and from the low level side (L8L) and high level side (L8H) of the coarsest signal amplitude. By doing so, the optical disc and the reproduction signal can be stably evaluated.

SA = ((L8H + L8L)-(L3H + L3L)) / 2 (L8H-L8L) Equation 4
As described above, in the definition of modulation amplitude and asymmetry using the densest signal in a high-density optical disk, stable evaluation becomes difficult due to a decrease in the level and quality of the densest signal. By using a quasi-closest density signal having a density lower than that of the dense signal, stable evaluation can be performed. A signal having the second highest density is suitable for the quasi-closest signal, but other level signals may be used as long as there is a sufficient level difference from the coarsest signal.

  Here, the reproduction signal evaluation method described above will be summarized with reference to the flowchart shown in FIG. As shown in FIG. 8, first, a reproduction signal is detected (ST11). That is, an information recording medium on which digital information is recorded with recording marks of various sizes is reproduced by optical means, and a reproduction signal reflecting the digital information is detected. Of the signals included in the detected reproduction signal, the amplitude of the first reproduction signal (that is, the reproduction signal having the lowest recording density) reflecting the digital information recorded by the recording mark having the largest size is obtained (ST12). ). In addition, the second reproduction signal (that is, the reproduction signal having the highest recording density) that reflects the digital information recorded by the recording mark having a predetermined size, excluding the recording mark having the smallest size, among the signals included in the reproduction signal is excluded. The amplitude of the reproduction signal having a predetermined recording density is obtained (ST13). Then, an evaluation value is calculated based on the ratio between the amplitudes of the first and second reproduction signals or the difference value between the amplitude center levels (ST14). The characteristics of the reproduction signal are evaluated with this evaluation value (ST15).

  It is also possible to provide an information recording medium on which digital information is recorded so that a reproduction signal that satisfies a predetermined evaluation condition can be obtained by evaluating the reproduction signal by the above-described reproduction signal evaluation method. Furthermore, an information reproducing apparatus capable of obtaining a reproduction signal that satisfies a predetermined evaluation condition when reproducing such an information recording medium can be provided. When the information recording medium described above is reproduced by a reproducing apparatus, a reproduced signal that reliably satisfies a predetermined evaluation condition can be obtained, so that not only a specific model but also a stable reproduction result can be obtained.

  So far, the evaluation method using the output signal of the reproduction amplifier before waveform equalization has been described, but it is also possible to evaluate with the signal after waveform equalization. Next, an evaluation method using a signal after waveform equalization will be described.

  An example of a sample sequence of a reproduced signal waveform and an equalized waveform having PR (1, 2, 2, 1) characteristics is shown in FIG. FIG. 7 shows an example of a histogram collected by classifying the sample values after equalization in the level direction. In the case of the PR (1, 2, 2, 1) characteristic, six distribution peaks appear. The value of each level distribution peak is P0 to P6. When modulation amplitude and asymmetry are good and waveform equalization is appropriately performed, values from P0 to P6 are calculated from C0 to C6 calculated from PR (1, 2, 2, 1) characteristics, respectively. Is equal to the ideal value of. The ideal value has the following relationship because the intervals of adjacent level distribution peaks are all equal.

(Cn)-(Cn-1) = (C6-C0) / 6 Equation 5
If the optical disc is not properly manufactured or if the apparatus is poorly adjusted, the modulation amplitude and asymmetry will shift, and the peak value in these level distributions will deviate from the ideal value. When the sample value deviates from the ideal value, an error occurs at the stage of calculating the optimum data sequence in the Viterbi decoder, and an identification error occurs when the error increases. Therefore, the optical disc and the reproduction signal can be evaluated by obtaining the deviation from the ideal value for each peak.

  Next, a method for obtaining the evaluation value from the peak of the level distribution obtained for the sample series of the equalized waveform shown in FIG. 7 will be described.

As a first method, a difference from the ideal value is obtained for each peak value of each level distribution, and the characteristics are evaluated by the sum of the absolute values. At that time, the signal characteristic (S1) is expressed by the following Equation 6.

  As described above, the characteristics may be evaluated not only with the sum of the absolute values but also with the average value of the absolute values.

Alternatively, as a second method, a difference from the ideal value is obtained for each peak value of each level distribution, and the characteristics are evaluated by the sum of the squares. At that time, the signal characteristic (S2) is expressed by the following Expression 7.

  As described above, the characteristics may be evaluated not only by the sum of the squares but also by the average value of the squares.

The evaluation method using the equalized waveform shown above is useful as an evaluation method including the equalizer performance relatively easily. On the other hand, in order to reflect the error rate after the identification more accurately in the measurement result, the difference value relating to the peak of each level distribution is weighted in consideration of the nature of the signal and the identification method. It is desirable. At that time, Expression 6 and Expression 7 can be additionally modified as Expression 8 and Expression 9, assuming that the weighting coefficients for the peaks of each level distribution are W0 to W6, respectively.

  Next, an example of parameters related to the weight coefficient determination method will be described.

  If attention is paid to the distribution of each peak appearing in the histogram, the distribution of each distribution is not necessarily the same because it is influenced by the generation factor of the noise component and the frequency characteristics of waveform equalization. Even if the amount of deviation from the ideal value of the peak value is the same, if the variance is large, the sample value at the end of the distribution will be far away from the ideal value and overlap with the adjacent distribution, which may cause an error at the identification stage. Increases nature. Therefore, the relationship between the evaluation result and the error rate can be made closer by increasing the weighting for a peak with a large variance and decreasing the weighting for a peak with a small variance.

  Also, the frequency of occurrence of each level distribution is not necessarily equal due to the modulation characteristics of the recording data. It can be considered that the influence on the overall error rate is higher when the peak of the level distribution having a high occurrence frequency is shifted. In general, recorded data is often randomized to eliminate signal bias. Therefore, if the modulation method is determined, it can be considered that the actual occurrence frequency distribution is substantially equal to the occurrence frequency when random data is modulated. Therefore, the relationship between the evaluation result and the error rate can be made closer by using the ratio of the occurrence frequency of each level to the random data as a weighting coefficient.

  Further, due to the characteristic of Viterbi decoding at the subsequent stage, the degree of influence on the error after identification is not always the same depending on the signal level. For example, in the case of the PR (1, 2, 2, 1) characteristic, even if the minimum level P0 of the equalized waveform is smaller than the ideal value C0 or the maximum level P6 is slightly larger than the ideal value C6, Viterbi decoding It is hard to become an error. On the other hand, intermediate level deviations such as P1, P2, P4, and P5 are relatively likely to cause errors. The degree of influence on the error after identification in consideration of such characteristics of Viterbi decoding can be obtained by measuring the level of the equalized waveform when an error actually occurs. The relationship between the evaluation result and the error rate can be made closer by increasing the weighting for the level having a large influence on the error and decreasing the weighting for the small level.

  Either method is based on the addition of all peaks according to the number of peaks defined by the PR characteristics. However, for the sake of simplification, only some peaks are added and are representative as evaluation values. You may let them. Of course, the total weight coefficient may be finally determined by combining the degree of influence on the plurality of parameters.

  In this way, the level distribution peak is obtained from the histogram obtained by classifying the sampled waveform of the equalized waveform in the level direction, and the difference from the ideal value is weighted and added. Compared with the case where the evaluation is performed by the rate, it is possible to perform an evaluation that can more easily correspond to the error rate including the equalizer performance.

  Here, the reproduction signal evaluation method described above will be summarized with reference to the flowchart shown in FIG. As shown in FIG. 9, first, a reproduction signal is detected (ST21). That is, an information recording medium on which digital information is recorded with recording marks of various sizes is reproduced by optical means, and a reproduction signal reflecting the digital information is detected. The detected reproduction signal is equalized based on a predetermined partial response characteristic, and a multi-level equalized signal is generated (ST22). The level distribution of the amplitude of the equalized signal is obtained, and a plurality of actually measured peak values are calculated from this level distribution (ST23). A plurality of ideal peak values are calculated from predetermined partial response characteristics (ST24). A difference value between each measured peak value and each ideal peak value is obtained (ST25). An evaluation value is calculated based on the sum or average value of absolute values of difference values of peak values, or the sum or average value of square values (ST26). The characteristics of the reproduction signal are evaluated with this evaluation value (ST27).

  It is also possible to provide an information recording medium on which digital information is recorded so that a reproduction signal that satisfies a predetermined evaluation condition can be obtained by evaluating the reproduction signal by the above-described reproduction signal evaluation method. Furthermore, an information reproducing apparatus capable of obtaining a reproduction signal that satisfies a predetermined evaluation condition when reproducing such an information recording medium can be provided. When the information recording medium described above is reproduced by a reproducing apparatus, a reproduced signal that reliably satisfies a predetermined evaluation condition can be obtained, so that not only a specific model but also a stable reproduction result can be obtained.

  The present embodiment will be summarized below.

  (1) The reproduction signal evaluation method according to the present embodiment is a step of reproducing an information recording medium on which digital information is recorded with recording marks of various sizes by optical means, and obtaining a reproduction signal reflecting the digital information. Determining the amplitude of the first reproduction signal reflecting the digital information recorded by the largest recording mark among the signals included in the reproduction signal, and among the signals included in the reproduction signal, Based on the ratio of the amplitude of the first and second reproduction signals, the step of obtaining the amplitude of the second reproduction signal reflecting the digital information recorded by the recording mark of a predetermined size excluding the recording mark of the smallest size Obtaining an evaluation value; and evaluating a characteristic of the reproduction signal with the evaluation value.

  (2) The reproduction signal evaluation method according to the present embodiment is a step of reproducing an information recording medium on which digital information is recorded with recording marks of various sizes by optical means, and obtaining a reproduction signal reflecting the digital information. Determining the amplitude center level of the first reproduction signal reflecting the digital information recorded by the record mark having the largest size among the signals included in the reproduction signal; and the signal included in the reproduction signal A step of obtaining an amplitude center level of a second reproduction signal reflecting digital information recorded by a recording mark of a predetermined size excluding a recording mark having the smallest size; and amplitudes of the first and second reproduction signals Obtaining an evaluation value based on a difference value of the center level, and evaluating a characteristic of the reproduction signal with the evaluation value. Eteiru.

  (3) In the reproduction signal evaluation method according to the present embodiment, an information recording medium on which digital information is recorded is reproduced by optical means to obtain a reproduction signal reflecting the digital information; Based on the partial response characteristics, obtaining a multi-level equalized signal, obtaining an amplitude level distribution of the equalized signal, obtaining a plurality of actually measured peak values from the level distribution, Based on a total or average value of absolute values of the difference values of each peak value, a step of obtaining a plurality of ideal peak values from partial response characteristics, a step of obtaining a difference value between each of the measured peak values and each ideal peak value Obtaining an evaluation value; and evaluating a characteristic of the reproduction signal with the evaluation value.

  (4) A reproduction signal evaluation method according to this embodiment reproduces an information recording medium on which digital information is recorded by optical means to obtain a reproduction signal reflecting the digital information; Based on the partial response characteristics, obtaining a multi-level equalized signal, obtaining an amplitude level distribution of the equalized signal, obtaining a plurality of actually measured peak values from the level distribution, Based on a step of obtaining a plurality of ideal peak values from partial response characteristics, a step of obtaining a difference value between each measured peak value and each ideal peak value, and a sum or an average value of the square values of the difference values of each peak value Obtaining an evaluation value; and evaluating a characteristic of the reproduction signal with the evaluation value.

  (5) The information recording medium according to the present embodiment records digital information so that a reproduction signal that satisfies a predetermined evaluation condition is obtained when the reproduction signal is evaluated by the reproduction signal evaluation method of (1) above. ing.

  (6) The information recording medium according to the present embodiment records digital information so that a reproduction signal that satisfies a predetermined evaluation condition is obtained when the reproduction signal is evaluated by the reproduction signal evaluation method of (2) above. ing.

  (7) The information reproducing apparatus according to the present embodiment records digital information so that a reproduction signal satisfying a predetermined evaluation condition is obtained when the reproduction signal is evaluated by the reproduction signal evaluation method of (1) above. When the recorded information recording medium is reproduced, a reproduction signal satisfying a predetermined evaluation condition is obtained.

  (8) The information reproducing apparatus according to the present embodiment records digital information so that a reproduction signal satisfying a predetermined evaluation condition is obtained when the reproduction signal is evaluated by the reproduction signal evaluation method of (2) above. When the recorded information recording medium is reproduced, a reproduction signal satisfying a predetermined evaluation condition is obtained.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention in the implementation stage. In addition, the embodiments may be appropriately combined as much as possible, and in that case, the combined effect can be obtained. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effect described in the column of the effect of the invention Can be obtained as an invention.

It is a figure which shows schematic structure of the reproduction | regeneration signal processing system of the optical disk apparatus using PRML. It is a figure which shows the operation | movement of a reproduction signal waveform and PR equalization. It is a figure which shows PR equalization circuit by a transversal filter. It is a figure which shows the identification operation | movement by a PRML system. It is a figure which shows the example of the MTF characteristic of an optical disk device. It is a figure which shows the reproduction signal waveform of a high-density optical disk apparatus. It is a figure which shows the frequency distribution of the sample value of the reproduction signal after PR equalization. It is a flowchart which shows the outline | summary of the reproduced signal evaluation method using the signal before waveform equalization. It is a flowchart which shows the outline | summary of the reproduction signal evaluation method using the signal after waveform equalization. It is a figure which shows schematic structure of the reproduction | regeneration signal processing system of the optical disk apparatus using the conventional level slice. It is a figure which shows the identification operation | movement by the conventional reproduction signal waveform and a level slice. It is a figure which shows the reproduction signal evaluation by the conventional jitter. It is a figure which shows the reproduction signal waveform of the conventional optical disk apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Optical disk 101 ... Motor 102 ... Optical head 103 ... Reproduction amplifier 105 ... PLL circuit 107 ... A / D converter 108 ... PR equalization part 109 ... Viterbi decoder

Claims (6)

Reproducing an information recording medium on which digital information is recorded by recording marks of various sizes by optical means, and obtaining a reproduction signal reflecting the digital information;
Obtaining the amplitude of the first reproduction signal reflecting the digital information recorded by the recording mark having the largest size among the signals included in the reproduction signal;
Obtaining the amplitude of the second reproduction signal reflecting the digital information recorded by the second smallest recording mark among the signals included in the reproduction signal;
Obtaining an evaluation value based on a ratio of amplitudes of the first and second reproduction signals;
Evaluating the characteristics of the reproduction signal with the evaluation value;
A reproduction signal evaluation method comprising: Reproducing an information recording medium on which digital information is recorded by recording marks of various sizes by optical means, and obtaining a reproduction signal reflecting the digital information;
Obtaining the amplitude center level of the first reproduction signal reflecting the digital information recorded by the recording mark having the largest size among the signals included in the reproduction signal;
Obtaining the amplitude center level of the second reproduction signal reflecting the digital information recorded by the second smallest recorded mark among the signals included in the reproduction signal;
Obtaining an evaluation value based on a difference value between amplitude center levels of the first and second reproduction signals;
Evaluating the characteristics of the reproduction signal with the evaluation value;
A reproduction signal evaluation method comprising: Reproducing an information recording medium on which digital information is recorded by recording marks of various sizes by optical means, and obtaining a reproduction signal reflecting the digital information;
Obtaining the amplitude of the first reproduction signal reflecting the digital information recorded by the recording mark having the largest size among the signals included in the reproduction signal;
Obtaining the amplitude of the second reproduction signal reflecting the digital information recorded by the second smallest recording mark among the signals included in the reproduction signal;
Obtaining an evaluation value based on a ratio of amplitudes of the first and second reproduction signals;
Evaluating the characteristics of the reproduction signal with the evaluation value;
An information recording medium, wherein digital information is recorded so that a reproduction signal satisfying a predetermined evaluation condition is obtained when the reproduction signal is evaluated by a reproduction signal evaluation method comprising: Reproducing an information recording medium on which digital information is recorded by recording marks of various sizes by optical means, and obtaining a reproduction signal reflecting the digital information;
Obtaining the amplitude center level of the first reproduction signal reflecting the digital information recorded by the recording mark having the largest size among the signals included in the reproduction signal;
Obtaining the amplitude center level of the second reproduction signal reflecting the digital information recorded by the second smallest recorded mark among the signals included in the reproduction signal;
Obtaining an evaluation value based on a difference value between amplitude center levels of the first and second reproduction signals;
Evaluating the characteristics of the reproduction signal with the evaluation value;
An information recording medium, wherein digital information is recorded so that a reproduction signal satisfying a predetermined evaluation condition is obtained when the reproduction signal is evaluated by a reproduction signal evaluation method comprising: Reproducing an information recording medium on which digital information is recorded by recording marks of various sizes by optical means, and obtaining a reproduction signal reflecting the digital information;
Obtaining the amplitude of the first reproduction signal reflecting the digital information recorded by the recording mark having the largest size among the signals included in the reproduction signal;
Obtaining the amplitude of the second reproduction signal reflecting the digital information recorded by the second smallest recording mark among the signals included in the reproduction signal;
Obtaining an evaluation value based on a ratio of amplitudes of the first and second reproduction signals;
Evaluating the characteristics of the reproduction signal with the evaluation value;
A reproduction signal satisfying a predetermined evaluation condition from an information recording medium on which digital information is recorded so that a reproduction signal satisfying a predetermined evaluation condition can be obtained when the reproduction signal is evaluated by a reproduction signal evaluation method comprising An information reproducing apparatus characterized by reading the information. Reproducing an information recording medium on which digital information is recorded with recording marks of various sizes by optical means, and obtaining a reproduction signal reflecting the digital information;
Obtaining the amplitude center level of the first reproduction signal reflecting the digital information recorded by the recording mark having the largest size among the signals included in the reproduction signal;
Obtaining the amplitude center level of the second reproduction signal reflecting the digital information recorded by the second smallest recorded mark among the signals included in the reproduction signal;
Obtaining an evaluation value based on a difference value between amplitude center levels of the first and second reproduction signals;
Evaluating the characteristics of the reproduction signal with the evaluation value;
A reproduction signal satisfying a predetermined evaluation condition from an information recording medium on which digital information is recorded so that a reproduction signal satisfying a predetermined evaluation condition can be obtained when the reproduction signal is evaluated by a reproduction signal evaluation method comprising An information reproducing apparatus characterized by reading the information.

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