JP3776530B2 - Optical information reproducing device - Google Patents

Optical information reproducing device Download PDF

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JP3776530B2
JP3776530B2 JP27888096A JP27888096A JP3776530B2 JP 3776530 B2 JP3776530 B2 JP 3776530B2 JP 27888096 A JP27888096 A JP 27888096A JP 27888096 A JP27888096 A JP 27888096A JP 3776530 B2 JP3776530 B2 JP 3776530B2
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x1
x2
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binary data
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JPH10106161A (en
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裕 柏原
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株式会社東芝
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[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical information reproducing apparatus such as an optical disk apparatus, and more particularly to an optical information reproducing apparatus using a PRML system in a reproduction signal processing system.
[0002]
[Prior art]
PRML (Partial Response Maximum Likelihood) is a technique used for a reproduction signal processing system in a magnetic recording / reproducing apparatus and an optical recording / reproducing apparatus, and partial response equalization (PR equalization) for a reproduced waveform from a recording medium. In this method, after known intersymbol interference is intentionally added, the data is decoded into binary data by a maximum likelihood decoder (ML decoder) using a Viterbi decoding method or the like.
[0003]
An example in which this PRML method is applied to an optical disc apparatus will be described. FIG. 12 is a diagram showing a configuration of an optical disc apparatus using a conventional PRML system, and FIG. 13 is an operation waveform diagram thereof.
[0004]
At the time of recording on the optical disc 101, the binary input data is recorded in the recording / reproducing system 102 by, for example, modulation and coding, so that the continuous length of 0 or 1 is d or more and k or less (referred to as d constraint or k constraint, respectively). The data is converted into data after modulation consisting of (Length Limited) code, further converted into a recording waveform, and then recorded on the optical disc 1 as a pit sequence. The reproduced waveform from the optical disc 101 is not obtained as a rectangular wave due to the characteristics of the recording / reproducing system 102, but is obtained as a dull waveform as shown in FIG. Then, the data is decoded into binary data by the ML decoder 104.
[0005]
PR (1, 1), PR (1, 2, 1), PR (1, 2, 2, 1), PR (1, 1, etc.) are used as PR equalization methods in the PRML system that are being studied for use in optical disc apparatuses. 3, 3, 1) and the like. Here, PR (1, X1, X2,..., Xn, 1) equalization means that the discrimination point signal levels of the equalized waveform with respect to the 1T recording waveform are 1, X1, X2,. , 1 means equalization. In other words, the number in () represents what value of intersymbol interference is given at each sampling time by PR equalization.
[0006]
FIG. 15 shows an example of the equalized waveform of each PRML system listed above. As shown in the figure, for example, at PR (1, 1), data at a certain sampling time causes +1 interference with data at the next sampling time, and at PR (1, 2, 1), a certain sampling time. Is equalized so that +2 interference occurs in the next sampling time data, and +1 interference occurs in the next sampling time data. The same applies to PR (1, 2, 2, 1).
[0007]
In order to perform desired PR equalization, tap coefficients (C0, C1,..., Cm in FIG. 2) of the transversal filter 103 must be appropriately selected. As a tap coefficient selection method, for example, the least square error method (MSE method) is used. In the MSE method, an equalized target waveform is obtained from known binary data and a PR equalization method to be used, and an equalization square error is minimized from this and a reproduced waveform corresponding to the previous binary data. This is a method of selecting a tap coefficient.
[0008]
FIG. 12 shows an example in which a fixed value is used for the tap coefficient of the transversal filter 103, while FIG. 16 shows an example in which the tap coefficient is variable. In FIG. 16, a parameter setting unit 105 is provided in addition to the configuration of FIG. The parameter setting unit 105 includes a memory 106 storing binary data for parameter setting, a target waveform creation unit 108 after equalization, and a tap coefficient determination unit 109.
[0009]
The post-equalization target waveform creator 108 creates a post-equalization target waveform from the parameter setting binary data and the PR equalization method to be used. On the optical disc 101, pits corresponding to the binary data for parameter setting are recorded in advance, and the tap coefficient of the transversal filter 103 is determined from the reproduced waveform of this portion and the equalized target waveform.
[0010]
The discrimination point signal level in the ML decoder 104 for the waveform after PR equalization is obtained from the PR equalization method used in the transversal filter 103. For example, in PR (1, X, X, 1) equalization, the discrimination point signal level is obtained as shown in FIGS. The ML decoder 104 decodes the equalized waveform from the transversal filter 3 into binary data using these discrimination point signal levels as parameters.
[0011]
By the way, unlike a magnetic disk device (particularly a hard disk device), an optical disk device often uses a so-called removable medium that can be attached to and detached from a drive device as a recording medium. Of course, the above-described optical disk apparatus using the PRML system is also desired to be compatible with a plurality of types of recording media having different specifications and characteristics. However, in the optical disk apparatus using the conventional PRML system, the values (intersymbol interference values) of X1, X2,..., Xn in PR (1, X1, X2,..., Xn, 1) equalization are fixed. When reproducing a plurality of types of recording media, if the values of X1, X2,..., Xn are optimized for a certain recording medium, the bit error rate is reduced when other recording media having different reproduction waveform characteristics are used. There is a problem that it cannot be reduced.
[0012]
That is, in PR (1, X1, X2,..., Xn, 1) equalization, the values of X1, X2,..., Xn are conventionally selected as integers, but depending on the type of the recording medium, after ML decoding, Although the values of X1, X2,..., Xn that minimize the data bit error rate are not always integers, integer values are conventionally selected.
[0013]
[Problems to be solved by the invention]
As described above, in the conventional optical disk apparatus to which the PRML system is applied, the correspondence to a plurality of types of recording media is not taken into consideration. When a recording medium is used, there is a problem that the bit error rate cannot be reduced.
[0014]
The present invention has been made to solve such problems, and an object of the present invention is to provide an optical information recording / reproducing apparatus capable of reproducing a plurality of types of recording media by the PRML method. .
[0015]
[Means for Solving the Problems]
The present invention optically reproduces information recorded as a mark string on a recording medium, performs partial response equalization with a transversal filter on the obtained reproduced waveform, and then decodes the binary data with a maximum likelihood decoder. In the optical information reproducing apparatus to perform, when the partial response characteristic is represented by PR (1, X1, X2,... Xn, 1), at least an error rate is obtained from binary data decoded by the maximum likelihood decoder. , X value selection means for selecting the values of X1, X2,... Xn according to the determination result of the determination means, and the identification point from the values of X1, X2,. And an identification point signal level determining means for determining the signal level .
[0016]
The present invention also optically reproduces information recorded as a mark string on a recording medium, and after the obtained reproduced waveform is subjected to partial response equalization by a transversal filter, it is decoded into binary data by a maximum likelihood decoder. In the optical information reproducing apparatus that performs the above, when the partial response characteristic is represented by PR (1, X1, X2,... Xn, 1), at least an error is detected from the binary data decoded by the maximum likelihood decoder. Determining means for determining the rate, X value selecting means for selecting the values of X1, X2,... Xn according to the determination result of the determining means, and the X1, X2, selected by the X value determining means ... Tap coefficients of the transversal filter are determined from the post-equalization target waveform creation means for creating the post-equalization target waveform from the value of Xn, and the post-equalization target waveform and the reproduced waveform And-up coefficient determination means, the X1, X2, characterized in that the value of · · · Xn and a decision point level determining means for determining the identification point signal level.
[0017]
In addition, the present invention optically reproduces information recorded as a mark string on a recording medium, performs partial response equalization with a transversal filter on the obtained reproduced waveform, and then decodes the binary data with a maximum likelihood decoder. In the optical information reproducing apparatus that performs, the intersymbol interference imparting value in the partial response equalization is selected according to the characteristics of the reproduced waveform, and the tap coefficient of the transversal filter and the maximum value are selected from the selected intersymbol interference imparting value. a parameter setting means for setting an identification point signal level of likelihood decoder as parameters, said parameter setting means includes storage means for storing binary data parameterization, parameter settings stored in the storage means An error rate determination method for determining an error rate by comparing binary data for use with binary data decoded by the maximum likelihood decoder X value selection means for selecting the values of X1, X2,... Xn according to the determination result of the error rate determination means, binary data for parameter setting stored in the storage means, and the X value A post-equalization target waveform creation means for creating a post-equalization target waveform from the values of X1, X2,... Xn selected by the selection means, and the transformer from the post-equalization target waveform and the reproduced waveform. a tap coefficient determining means for determining a tap coefficient of the transversal filter, the X1, X2, characterized in that the value of · · · Xn and a decision point level determining means for determining the identification point signal level.
[0023]
As described above, according to the present invention, the type of the recording medium is indirectly detected from the characteristics of the reproduction waveform, or directly detected, and the tap coefficient of the transversal filter and the maximum likelihood decoder according to the type of the recording medium. By setting the discrimination point signal level in, it becomes possible to perform good reproduction on a plurality of types of recording media by the PRML method.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0025]
(First embodiment)
FIG. 1 is a block diagram showing a configuration of an optical disc apparatus according to the first embodiment of the present invention.
This optical disc apparatus includes an optical disc 1 which is a recording medium for optically recording and reproducing information by a light beam, a recording / reproducing system 2 including an optical head, and a reproduction waveform output from the recording / reproducing system 2 at the time of reproduction. A transversal filter 3 that performs PR equalization (partial response equalization), and an ML decoder (maximum likelihood decoder) 4 that decodes a reproduced waveform after equalization by the transversal filter 3 into binary data, and It comprises a parameter setting unit 5 that sets the tap coefficient and discrimination point signal level of the transversal filter 3 as parameters. Hereinafter, a case where PR (1, X, X, 1) equalization is used as PR equalization in the transversal filter 3 will be described.
[0026]
The transversal filter 3 is configured, for example, as shown in FIG. This transversal filter 3 cascades unit delay elements 18a, 18b,..., 18c having a predetermined delay time, and with respect to the signals at the input / output terminals (referred to as taps) of the delay elements 18a, 18b,. The weighting units 19a, 19b,..., 19c multiply the weighting coefficients (referred to as tap coefficients) C0, C1,..., Cm to perform weighting. It is the composition which obtains.
[0027]
In this case, the reproduced waveform can be PR-equalized by appropriately selecting the tap coefficients C0, C1,. As a tap coefficient selection method, for example, a target waveform after equalization is obtained from known binary data and a PR equalization method to be used, and an equalization square error is obtained from this and a reproduced waveform corresponding to the previous binary data. The least square error method (MSE method) is used in which the tap coefficient is selected so that is minimized.
[0028]
The parameter setting unit 5 includes a memory 6 storing binary data for parameter setting, an X value setting unit 7, a post-equalization target waveform creation unit 8, a tap coefficient determination unit 9, and a discrimination point signal level determination unit 10. And an error rate determiner 11.
[0029]
In this embodiment, the X value selector 7 determines the value of X, which is the intersymbol interference value in the PR (1, X, X, 1) equalization in the transversal filter 3, as a characteristic of the reproduced waveform, here the error rate determination. First, the initial value X0 is output, then Xi is sequentially obtained from the determination result of the error rate determination unit 11, and the error rate (bit error rate) is finally allowed. A value of X that satisfies the value is selected.
[0030]
As described above, when considering PR (1, X1, X2,..., Xn, 1) equalization, X1, X2,..., Xn that minimize the bit error rate of binary data obtained by ML decoding. The value of is not necessarily an integer depending on the recording medium that is the optical disc 1. For example, the relationship between the value of X in the PR (1, X, X, 1) equalization of this embodiment and the bit error rate of binary data after ML decoding is as shown in FIG. Points 22a and 22b in FIG. 3 indicate X values XA and XB that minimize the bit error rate when different media A and B are used as the optical disc 1, respectively, and these are not necessarily integers. In the example of FIG. 3, the X value XA of the high density medium A is greater than 0 and less than 1, and the X value XB of the low density medium B is greater than 1 and less than 2.
[0031]
As shown by the curves 21a and 21b in FIG. 3, since the relationship between the X value and the error rate is a downward convex function in both media A and B, the values of XA and XB can be easily obtained. That is, it is possible to obtain a change in the bit error rate by changing the value of X, and obtain the values of X immediately before the error rate starts to decrease and increase as XA and XB. Further, the convergence value of X does not necessarily have to be an integer from FIG. 3, and in particular, in a high-density optical disc as shown in the medium A, it is good by setting the value of X to a value larger than 0 and smaller than 1 Playback is possible. The X value selector 7 supplies the X value thus selected to the target waveform generator 8 and the discrimination point signal level determiner 10 after equalization.
[0032]
The post-equalization target waveform creator 8 creates a post-equalization target waveform from the binary data given from the parameter setting binary data memory 6 and the X value selected by the X value selector 7. . The post-equalization target waveform indicates a waveform that should be taken by the reproduced waveform after being equalized correctly by the transversal filter 3.
[0033]
This equalized target waveform is given to the tap coefficient determiner 9. A pit corresponding to the binary data for parameter setting is recorded in advance on the optical disc 1, and the tap coefficient determiner 9 equalizes the reproduced waveform from the reproduced waveform corresponding to the pit and the equalized target waveform. A tap coefficient that matches the subsequent target waveform is obtained and given to the transversal filter 3.
[0034]
The discrimination point signal level determiner 10 obtains the discrimination point signal level based on the value of X given from the X value selector 7 and supplies this to the ML decoder 4. In this embodiment, PR (1, X, X, 1) equalization is performed in the transversal filter 3, but the discrimination point signal level in this PR (1, X, X, 1) equalization is X. It can be easily obtained from the values according to, for example, FIGS.
[0035]
5 to 7 are diagrams showing state transition diagrams at the time of PR (1, X, X, 1) equalization, and symbols used in the diagrams are defined as shown in FIG. The discrimination point signal level is determined from the history of the input bits up to 3 bits before and the current input bit.
[0036]
When the modulated data modulated by the RLL (d, k) code is subjected to NRZI conversion, the shortest pit (blank) length is (d + 1) T. FIG. 5 shows a state transition diagram when there is no d constraint, FIG. 6 shows a state transition diagram when the d constraint is 1, and FIG. 7 shows a state transition diagram when the d constraint is 2.
[0037]
When the d constraint is 1, the shortest pit (blank) length is 2T, and as a result, state S2 (010) and state S5 (101) disappear. When the d constraint is 2, the shortest pit (blank) length is 3T. As a result, in addition to the absence of the state S2 (010) and the state S5 (101), the state transition from the state S3 to the state S6, There is no state transition from state S4 to state S1.
[0038]
The ML decoder 11 performs maximum likelihood decoding such as Viterbi decoding on the equalized waveform from the transversal filter 3 using the discrimination point signal level thus obtained, and outputs decoded data of binary data. To do. The decoded binary data is output to the next stage circuit and also supplied to the error rate determination unit 11.
[0039]
In the error rate determination unit 11, the binary data from the ML decoder 11 and the parameter setting binary data from the memory 6 are compared to determine the error rate of the binary data, that is, the bit error rate. It is determined whether or not the error rate satisfies an allowable value, and the determination result is output to the X value selector 7. When the error rate determination unit 11 determines that the bit error rate satisfies the allowable value, the PR (1, X, X, 1) ML method using the tap coefficient and the discrimination point signal level at that time, PR equalization and maximum likelihood decoding are performed.
[0040]
As described above, according to the present embodiment, X of the intersymbol interference giving value in PR equalization is determined according to the characteristics (bit error rate) of the reproduction waveform from the optical disc 1 depending on the type of medium used as the optical disc 1. By selecting the value and obtaining the tap coefficient of the transversal filter 3 and the discrimination point signal level in the ML decoder 11 from the value of X, reproduction is correctly performed even if the type of medium used as the optical disc 1 is different. Is possible.
[0041]
(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 8 is a block diagram showing the configuration of the optical disc apparatus according to the second embodiment. The same reference numerals are assigned to elements corresponding to those in FIG. 1 to describe differences from the first embodiment. In the present embodiment, the parameter setting unit 5 uses the X value selector 7 in FIG. A medium type discriminator 12 and an X value memory 13 are provided in place of the device 11.
[0042]
In the present embodiment, identification information indicating the type of medium is recorded on the optical disc 1, and the medium type discriminator 12 determines the medium of the optical disc 1 from the identification information in the reproduction waveform reproduced by the recording / reproduction system 2. The type is determined, and the determination result is supplied to the X value memory 13. As shown in FIG. 9, the X value memory 13 stores X values (XA, XB,...) Determined in advance separately for a plurality of types of recording media A, B,. Data of the X value corresponding to the medium type determined by the medium type determiner 12 is read from the X value memory 13 and supplied to the post-equalization target waveform generator 8 and the discrimination point signal level determiner 10. .
[0043]
As described above, according to the present embodiment, it is possible to set the tap coefficient and the discrimination point signal level that are optimum for the type of the recording medium used as the optical disc 1.
[0044]
(Third embodiment)
Next, a third embodiment of the present invention will be described. FIG. 10 is a block diagram showing a configuration of an optical disc apparatus according to the third embodiment. In the present embodiment, the parameter setting unit 5 includes a medium type discriminator 12, a tap coefficient memory 14, and a discrimination point signal level memory 15. As shown in FIG. 11, the tap coefficient memory 14 and the discrimination point signal level memory 15 respectively have tap coefficients CA0, CA1,... Corresponding to a plurality of types of recording media A, B,. Data of CAm, CB0, CB1,..., CBm... And discrimination point signal levels LA0, LA1,..., LAm, LB0, LB1,. Then, the tap coefficient and the data of the discrimination point signal level corresponding to the discrimination result of the medium type discriminator 12 are read from these memories 14 and 15, and are supplied to the transversal filter 3 and the ML decoder 4, respectively.
[0045]
As described above, according to this embodiment, it is possible to set the tap coefficient and the discrimination point signal level that are optimum for the type of the recording medium used as the optical disc 1.
[0046]
In the above embodiment, PR (1, X, X, 1) equalization has been described as an example. However, the present invention is not limited to this, and PR (1, X1, X2,..., Xn, 1) The present invention is applicable to any case of equalization (n is 1 or more).
[0047]
【The invention's effect】
As described above, according to the present invention, the intersymbol interference imparting value in the partial response equalization according to the characteristics of the reproduction waveform and the type of the recording medium, that is, PR (1, X1, X2,..., Xn, 1), etc. X1, X2,..., Xn values are selected, and the tap coefficient of the transversal filter and the discrimination point signal level of the maximum likelihood decoder are set or recorded from the selected intersymbol interference giving value. The PRML method is applied to a plurality of types of recording media by reading out the tap coefficients of the transversal filter and the identification point signal level of the maximum likelihood decoder that have been obtained and stored in advance according to the type of the medium and setting them as parameters. It is possible to make playback possible.
[0048]
In particular, since the values X1, X2,..., Xn can be set to values larger than 0 and smaller than 1, high-density media can be reproduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical disc apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram showing a configuration of a transversal filter. FIG. 3 shows a PR (1, X, X, 1) ML. FIG. 4 is a diagram showing the relationship between the value of X and the bit error rate of decoded data when used. FIG. 4 is a diagram for explaining the relationship between the value of X and the discrimination point signal level in PR (1, X, X, 1) equalization. FIG. 5 is a state transition diagram when there is no d constraint for explaining the relationship between the value of X and the discrimination point signal level in PR (1, X, X, 1) equalization. FIG. 6 is a state transition diagram when d constraint = 1 for explaining the relationship between the value of X and the discrimination point signal level in PR (1, X, X, 1) equalization. X, X, 1) State when d constraint = 2 to explain the relationship between the value of X and the discrimination point signal level in equalization FIG. 8 is a block diagram showing a configuration of an optical disc apparatus according to a second embodiment of the present invention. FIG. 9 is a diagram showing a configuration of an X-value memory in FIG. 8. FIG. FIG. 11 is a block diagram showing a configuration of an optical disc apparatus according to the embodiment of the present invention. FIG. 11 is a diagram showing configurations of a tap coefficient memory and an identification point signal level memory in FIG. FIG. 13 is a diagram showing an example of modulated data, a recording waveform, a pit sequence, and a reproduction waveform in the optical disc apparatus. FIG. 14 is a diagram illustrating PR (1, X1, X2,..., Xn, 1) equalization. FIG. 15 is a diagram showing a relationship between a 1T recording waveform and an equalized waveform at the time of performing. FIG. 15 is a diagram showing examples of post-modulation data, reproduced waveform and various PR equalized waveforms in an optical disc apparatus. Other light di Diagram illustrating the configuration of a click device [Description of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical disk 2 ... Recording / reproducing system 3 ... Transversal filter 4 ... ML decoder 5 ... Parameter setting device 6 ... Parameter setting binary data memory 7 ... X value setting device 8 ... Equalized target waveform creation device 9 ... Tap coefficient determiner 10 ... Discrimination point signal level determiner 11 ... Error rate determiner 12 ... Medium type discriminator 13 ... X value memory 14 ... Tap coefficient memory 15 ... Discrimination point signal level memory 16 ... 1T recording waveform 17... PR (1, X1, X2,..., Xn, 1) equalized waveform after 1T equalization 18a, 18b, 18c... Unit delay elements 19a, 19b, 19c. , 21b... Functions 22a, 22b indicating the relationship between the X value of each medium and the bit error rate.

Claims (4)

  1. Optical information that optically reproduces the information recorded as a mark string on the recording medium, performs partial response equalization by a transversal filter on the obtained reproduced waveform, and then decodes it to binary data by a maximum likelihood decoder In the playback device,
    When the partial response characteristic is represented by PR (1, X1, X2,... Xn, 1), determination means for determining an error rate from at least binary data decoded by the maximum likelihood decoder;
    X value selection means for selecting values of X1, X2,... Xn according to the determination result of the determination means;
    And an identification point signal level determining means for determining the identification point signal level from the values of X1, X2,... Xn .
  2. Optical information that optically reproduces information recorded as a mark string on a recording medium, performs partial response equalization with a transversal filter on the obtained reproduced waveform, and then decodes the binary data with a maximum likelihood decoder In the playback device,
    When the partial response characteristic is represented by PR (1, X1, X2,... Xn, 1), determination means for determining an error rate from at least binary data decoded by the maximum likelihood decoder;
    X value selection means for selecting values of X1, X2,... Xn according to the determination result of the determination means;
    A post-equalization target waveform creation means for creating a post-equalization target waveform from the values of X1, X2,... Xn selected by the X value determination means;
    Tap coefficient determining means for determining a tap coefficient of the transversal filter from the equalized target waveform and the reproduced waveform;
    An optical information reproducing apparatus comprising: discrimination point level determining means for determining the discrimination point signal level from the values of X1, X2,... Xn .
  3. Optical information that optically reproduces information recorded as a mark string on a recording medium, performs partial response equalization with a transversal filter on the obtained reproduced waveform, and then decodes the binary data with a maximum likelihood decoder In the playback device,
    Select an intersymbol interference giving value in the partial response equalization according to the characteristics of the reproduced waveform, and from the selected intersymbol interference giving value, a tap coefficient of the transversal filter and an identification point signal level of the maximum likelihood decoder Parameter setting means for setting as a parameter,
    The parameter setting means includes storage means for storing parameter setting binary data;
    Error rate determination means for comparing the binary data for parameter setting stored in the storage means and the binary data decoded by the maximum likelihood decoder to determine an error rate;
    X value selection means for selecting the values of X1, X2,... Xn according to the determination result of the error rate determination means;
    Creating an equalized target waveform from the binary data for parameter setting stored in the storage means and the values of X1, X2,... Xn selected by the X value selection means Means,
    Tap coefficient determining means for determining a tap coefficient of the transversal filter from the equalized target waveform and the reproduced waveform;
    An optical information reproducing apparatus comprising: identification point level determining means for determining the identification point signal level from the values of X1, X2,... Xn.
  4. 4. The optical information reproducing apparatus according to claim 3, wherein at least one of the values of X1, X2,... Xn has a value larger than 0 and smaller than 1.
JP27888096A 1996-09-30 1996-09-30 Optical information reproducing device Expired - Fee Related JP3776530B2 (en)

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