JPH117727A - Method and apparatus for reproducing information - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a threshold value for quantizing an output from a waveform equalization means to be an optimum value in order to utilize a PRML(partial response maximum likelihood) process system. SOLUTION: An appearance frequency to a quantized value of an amplitude of an addition signal is obtained for a threshold value of quantizations during processing. Valley parts 23a, 23b between a ridge 22a of a highest appearance frequency and ridges 22b, 22c adjacent to the ridge 22a are set as threshold values -Xth, Xth of the quantizations. The threshold values -Xth, Xth can be accordingly set at a part where as few errors as possible are brought about, and eventually even information recorded with high density to an information recording medium can be reproduced properly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an information reproducing method and apparatus for reproducing information recorded on a high-density recording medium.

[0002]

2. Description of the Related Art In recent years, high-density DVDs (Digital Versatile Disks or Digi-
tal Video Disk) is attracting attention. This DVD includes a DVD-RAM (Random Access Memor).
y), DVD-ROM (Read Only Memory), DV
DR (Recordable) and the like are known. And D
In the next generation of VD, it is necessary to further improve this recording density. As a processing method of a reproduction system for improving the recording density, PRML (Partial Response Matrix) used in fields such as HDDs and communications has been used.
ximum Likelihood) is being considered.

Here, a general recording / reproducing method for a DVD which leads to the study of the introduction of the PRML method will be described with reference to FIG. First, the recording system will be described. An interface unit (I / F unit) 1 for controlling an interface with a host machine such as a personal computer (not shown) separates data and commands and controls the recording / reproducing apparatus. Of these,
The data is temporarily stored in the RAM 3 from the I / F unit 1 through the buffer manager 2. The data stored in the RAM 3 is sent to the digital modulator 4. The digital modulator 4 adds an error correction code or a synchronization signal to the user data, and determines a predetermined modulation scheme, for example, EF.
It is converted into bit string data according to M (Eight-Fourteen Modulation). The modulated signal is output to an optical pickup 6 via an analog recording system 5 for controlling the light emission intensity and the like, and is applied to an optical disc (information recording medium) 8 which is rotationally driven by a spindle motor 7. Recording is performed using light emission of an LD (semiconductor laser).

Next, a reproducing system will be described. Information recorded on the optical disk 8 is read by the optical pickup 6, and a DC fluctuation component or the like in the analog signal is removed by an analog reproduction system 9. And analog playback system 9
The PLL outputs a synchronization signal synchronized with the analog signal obtained from
A (Phase Locked Loop) circuit 10 converts the signal into a binary digital signal by a binarization circuit 11 while taking it. The digital signal converted into binary is subjected to synchronization detection and modulation demodulation processing by the digital demodulation unit 12, error correction processing based on an error correction code, and the like, and temporarily stored in the RAM 3 through the buffer manager 2. Is done. Thereafter, the data is sent from the RAM 3 to the personal computer or the like via the I / F unit 1.

Here, the binarization circuit 11 is generally configured as shown in FIG. That is, a comparator 13 is used which receives an analog signal obtained from the analog reproduction system 9 and a preset offset cancellation reference signal, and determines whether the analog signal is larger or smaller than the reference signal voltage. It is configured to be valued. Reference numeral 14 denotes a D-type flip-flop that latches the output of the comparator 13 in synchronization with the synchronization clock of the PLL circuit 10.

However, such a general binarization circuit 11 is insufficient in reproduction processing for high-density recording of DVD or more due to problems such as intersymbol interference, so that a signal processing method called a PRML method has been studied. ing. This PRML method is described in, for example, the document "NIKKEIELECTRONICS 1994.1.17 (n
o.599) in “Supporting the Next-Generation Mass Storage Devices of PRML Signal Processing Systems” (p.71-p.97).
In the PRML system, the binarization circuit 11 shown in FIG. 8 is replaced with a waveform equalizer 15, an n-level conversion circuit (for example, a ternary conversion circuit) 16, and a maximum likelihood decoding circuit 17 as shown in FIG. Are connected in order. Accordingly, when binarizing an analog signal obtained by reading information recorded in a predetermined modulation format from the optical disc 8, the amplitude of one or more analog signals is set to an integral multiple of a clock synchronized with the analog signals. The waveform equalizing circuit 1 performs a process of delaying and adding a value obtained by multiplying a coefficient corresponding to the delay amount and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient to obtain an added signal.
5, the added signal is quantized to a number corresponding to the added delay amount using a threshold value between quantizations to obtain quantized data by an n-level quantization circuit 16. Basically, the maximum likelihood decoding circuit 17 performs maximum likelihood decoding that prohibits transitions that are not in the modulation rule of the determined modulation method.

The waveform equalizer 15 and the n-valuer 1
6 affects the performance of the PRML processing method. Here, the waveform equalization circuit 15 is configured, for example, as shown in FIG. First, the reproduced analog signal is supplied to the PLL circuit 10.
A / A that converts to a digital signal in synchronization with the synchronization clock of
A D converter 18 is provided. This A / D converter 18
Quantizes an analog signal into, for example, an 8-bit digital signal. By inputting this quantized data to the D-type flip-flop 19, the data one clock before is held. This D-type flip-flop 19 has an A / D
The number of bits is adjusted to a multi-valued (for example, 8-valued) output from the converter 18. This D-type flip flop 19
The data delayed by one clock and the current data obtained from the A / D converter 18 are added in the adder 20, and an addition signal output to the n-value conversion circuit 16 is obtained.

The operation of waveform equalization in the waveform equalization circuit 15 will be described with reference to FIG. The reproduction waveform in the illustrated example shows an ideal waveform example corresponding to the recording waveform. The output of this waveform equalization, that is, the output of the adder 20 is
The place where the output level changes is a value near 0V and ± 2.
It takes one of the values near V. Therefore, -2V, 0
The signal is ternarized using values of V and + 2V, three state signals are obtained and output to the maximum likelihood decoding circuit 17, so that final binarization processing is properly performed.

[0009]

By the way, the actual reproduced waveform is not a rectangular wave as shown in FIG. 12, but a blunt waveform. Even in this case, if there is no error, the distribution of the appearance frequency of the amplitude of the added signal as shown in FIG. 13 is shown. Can be ternarized. In particular, if the interval d is large, it is possible to cope with a change in the position of a mountain in the amplitude distribution due to an amplitude change. The appearance frequency of the amplitude of the addition signal shown in FIG. 13 is shown in FIG. 15 by replacing the amplitude value when the reproduced analog signal is sampled at every predetermined timing X with the horizontal axis as shown in FIG. In this manner, the frequency expression is used, and such a frequency expression is normalized as the appearance frequency of each amplitude value.

However, in reality, when the same recording / reproducing system reproduces data from the optical disk 8 on which high-density recording has been performed, interference occurs between signals to be reproduced at each timing, and an error occurs. The amplitude distribution due to the output of the adder 20 also does not show a clear characteristic as shown in FIG. 13, and there is a possibility that the threshold value of quantization is set to a place where there are many errors. That is, in the PRML processing, if the portion for quantizing the output of the waveform equalization circuit does not operate well, an error occurs in the reproduction process, and as a result, it becomes meaningless even if the recording density of the optical disc 8 is improved. I will.

Therefore, according to the present invention, when using the PRML processing method, the threshold value for quantizing the output from the waveform equalizing means can be set to an optimum value.
It is an object of the present invention to provide an information reproducing method and an information reproducing apparatus capable of improving the recording density of an information recording medium.

[0012]

According to the first aspect of the present invention,
When binarizing an analog signal obtained by reading information recorded in a predetermined modulation format from an information recording medium, the amplitude of one or more analog signals is delayed by an integral multiple of a clock synchronized with the analog signal. A sum signal obtained by adding a value obtained by multiplying a coefficient corresponding to the delay amount and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient is obtained, and the sum signal is added using a threshold between quantization. Quantization is performed in an information reproducing method in which quantized data quantized to a number corresponding to the delay amount is obtained, and the quantized data is subjected to maximum likelihood decoding that prohibits a transition that is not in a modulation rule of the modulation scheme. In order to obtain a threshold between each quantization, the frequency of appearance of the value obtained by quantizing the amplitude of the addition signal is obtained, and a valley between a mountain having a large number of appearance frequencies and a mountain adjacent to the mountain is obtained. Between each quantization It was set as the value. Therefore, the threshold value for quantization can be set to a portion having as few errors as possible. As a result, even if information is recorded at high density on the information recording medium, it can be properly reproduced.

According to a second aspect of the present invention, in the information reproducing method according to the first aspect, the information recording medium is a disk-shaped medium that is driven to rotate, and the period for which the appearance frequency is obtained is one rotation of the disk-shaped medium. The period is shorter than the time. Therefore, the fluctuation of the peak position in the amplitude distribution due to the fluctuation of the amplitude may be caused by a change in the temperature of the semiconductor laser or the like, or by a double refraction of the substrate of the information recording medium. In the case of a disk-shaped medium, by making the time for obtaining the amplitude distribution (appearance frequency) shorter than the time for one rotation, fluctuations due to rotation can be removed in determining the threshold value.

According to a third aspect of the present invention, in the information reproducing method of the first or second aspect, when the value obtained by quantizing the amplitude of the added signal is x and the appearance frequency is represented by Q (x), R (x )
= K (-n) * Q (x-n) + ... + k (0) * Q (x) + k (n)
An intermediate value R (x) for obtaining a threshold value of * Q (x + n) is obtained, and a threshold value between each quantization is obtained from the intermediate value R (x). Therefore, even when the amplitude distribution is not represented by a smooth curve and is jagged, by performing digital filtering using the values before and after, a valley portion to be a threshold portion is properly detected. be able to.

According to a fourth aspect of the present invention, in the information reproducing method of the first, second or third aspect, the information recording medium has a signal reproduced from the information recording medium having a different amplitude depending on the length of the mark / space. The medium is a medium in which the amplitude of one analog signal is one of the clocks synchronized with this analog signal.
A delay signal is obtained by adding a value obtained by multiplying a coefficient corresponding to a delay amount of one clock and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient, and quantizing the added signal into three values. In order to obtain a threshold value between each quantization when obtaining quantized quantized data, an appearance frequency with respect to a value obtained by quantizing the amplitude of the addition signal is obtained. The valley between the peaks is set as the threshold between the quantizations. Therefore, in an information recording medium such as an optical disk, it is well known that the reproduction amplitude of a short mark or space is small, and if the length of the mark or space changes, it affects the determination of the threshold value for quantization. In the case of quantizing to ternary values, a valley between a central mountain having the highest frequency of occurrence and peaks on both sides thereof is set to a threshold value in an amplitude distribution in which five peaks can be formed in accordance with the amplitude of the length. Therefore, an appropriate threshold can be determined irrespective of a change in amplitude.

According to a fifth aspect of the present invention, in the information reproducing method according to the fourth aspect, when quantizing into three values, the number of transitions of the maximum likelihood decoded binary is counted, and the frequency of occurrence is highest. The range including the number of transitions from the peak of the central mountain is 3
The threshold value between each quantization is determined so as to be the center value. Therefore, since the threshold value for quantization is determined by the transition of the state of maximum likelihood decoding, an appropriate threshold value is determined.

According to a sixth aspect of the present invention, when binarizing an analog signal obtained by reading information recorded by a predetermined modulation method from an information recording medium, the amplitude of one or more analog signals is converted to the analog signal. Waveform equalizing means for delaying by an integral multiple of a clock synchronized with a signal, adding a value obtained by multiplying a coefficient corresponding to the delay amount and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient to obtain an added signal And quantizing means for quantizing the added signal to a number corresponding to the added delay amount using a threshold value between quantization to obtain quantized data;
In an information reproducing apparatus including the quantized data and maximum likelihood decoding means for performing maximum likelihood decoding that prohibits transitions that are not included in the modulation rule of the modulation scheme, in order to obtain a threshold between each quantization when performing quantization. A threshold value determining means for determining a frequency of appearance of a value obtained by quantizing the amplitude of the addition signal, and setting a valley portion between a mountain having a high frequency of occurrence and a mountain adjacent to the mountain as a threshold between quantizations. With. Therefore, the threshold value for quantization can be set to a portion having as few errors as possible, and as a result,
Even if information is recorded at a high density on the information recording medium, it can be properly reproduced.

According to a seventh aspect of the present invention, in the information reproducing apparatus according to the sixth aspect, the information recording medium is a disk-shaped medium that is driven to rotate, and the period for which the appearance frequency is determined by the threshold value determining means is set in the disk-shaped medium. Is shorter than the time for one rotation. Therefore, the fluctuation of the peak position in the amplitude distribution due to the fluctuation of the amplitude may be caused by a temperature change of a semiconductor laser or the like, or a birefringence of the substrate of the information recording medium. In the case of a medium, the time for obtaining the amplitude distribution (appearance frequency) is set to 1
By making the time shorter than the rotation time, a variation due to the rotation can be removed in determining the threshold value.

According to an eighth aspect of the present invention, in the information reproducing apparatus of the seventh aspect, the first memory having an address longer than a period for which the appearance frequency is determined by the threshold value determining means, and the amplitude of the added signal by the waveform equalizing means. And a second memory having an address equal to or greater than a value obtained by quantizing the amplitude of the sum signal, where t is the period for which the occurrence frequency is to be obtained and p is the current pointer of the first memory. Value x
Is written into the address indicated by the pointer p in the first memory, the data at the address x in the second memory is incremented by 1, and the data xx at the address (pt) in the first memory is written. And read the second
Is decremented by one and the pointer p is incremented by one. Therefore, the threshold value for quantization can be properly determined in a state where the device scale is small, using a memory called a so-called ring buffer.

According to a ninth aspect of the present invention, in the information reproducing apparatus of the sixth, seventh or eighth aspect, the value obtained by quantizing the amplitude of the added signal by the waveform equalizing means is represented by x, and the appearance frequency is represented by Q
When represented by (x), the threshold value determining means is as follows: R (x) = k (−n) * Q (x−n) +... + k (0) * Q (x) +
An intermediate value R (x) for obtaining a threshold value of k (n) * Q (x + n) is obtained, and a threshold value between each quantization is obtained from the intermediate value R (x). Therefore, even when the amplitude distribution is not represented by a smooth curve and is jagged, by performing digital filtering using the values before and after, a valley portion to be a threshold portion is properly detected. be able to.

The invention according to claim 10 is the invention according to claims 6, 7,
10. In the information reproducing apparatus described in 8 or 9, the information recording medium is a medium in which a signal reproduced from the information recording medium has a different amplitude depending on the length of a mark / space, and the waveform equalizing means performs the conversion of one analog signal. An addition signal obtained by delaying the amplitude by one clock of a clock synchronized with the analog signal, and adding a value obtained by multiplying a coefficient corresponding to the delay amount of one clock and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient. And threshold value determination means obtains an appearance frequency with respect to a value obtained by quantizing the amplitude of the addition signal in order to obtain a threshold value between each quantization when obtaining the quantized data by quantizing the addition signal into three values. The valley between the central peak with the highest frequency of occurrence and the peaks on both sides of the central peak is set as the threshold between the quantizations. Therefore, in an information recording medium such as an optical disk, it is well known that the reproduction amplitude of a short mark or space is small, and if the length of the mark or space changes, it affects the determination of the threshold value for quantization. 3
When quantizing to a value, the valley between the central peak with the highest frequency of occurrence and the peaks on both sides of the peak in the amplitude distribution of five peaks corresponding to the long and short amplitudes is used as the threshold. Since the threshold value is used, an appropriate threshold value can be determined regardless of a change in amplitude.

According to an eleventh aspect of the present invention, in the information reproducing apparatus of the tenth aspect, the threshold value determining means includes a counting means for counting the number of transitions of the maximum likelihood decoded binary when quantizing to three values. The threshold between each quantization is determined so that the range including the number of transitions from the peak of the central mountain having the highest appearance frequency becomes the central value of the three values. Therefore,
Since the threshold for quantization is determined by the transition of the state of maximum likelihood decoding, an appropriate threshold is determined.

According to a twelfth aspect of the present invention, in the information reproducing apparatus of the eleventh aspect, a third memory having an address equal to or longer than a period for which the appearance frequency is obtained by the threshold value determining means, and a period for which the occurrence frequency is obtained is t, Assuming that the current pointer of the third memory is p, one of the first value indicating that the maximum likelihood decoded binary value has changed and the second value indicating that there is no change is stored in the third memory. 3 is written to the address indicated by the pointer p, and when the first value is written, the value of the counting means for counting the number of transitions of the maximum likelihood decoded binary is incremented by one. The data xx at the address (pt) of the memory is read, and if the read value is the first value, the count value of the counting means is decremented by one, and the pointer p is incremented by one so that the central part is decremented. It was to obtain the count value worth of.
Therefore, the threshold value for quantization can be properly determined in a state where the device scale is small, using a memory called a so-called ring buffer.

[0024]

FIG. 1 shows a first embodiment of the present invention.
A description will be given based on FIG. In this embodiment,
For example, since it is a reproduction system for an optical disk for DVD or a next generation optical disk and it is assumed that the PRML processing method is used, the same parts as those shown in FIGS. 8 to 15 are denoted by the same reference numerals. The description is omitted (the same applies to the following embodiments). In the present embodiment, a threshold value determination circuit (which determines a threshold value for quantization in an n-value quantization circuit (quantization means) 16 based on an output (= addition signal) of a waveform equalization circuit (waveform equalization means) 15. A threshold value determining means 21 is added. This threshold determination circuit 21
Means DSP (Digital Signal Processing) or CPU
(Central Processing Unit) or the like, and is a frequency of appearance of a value obtained by quantizing the amplitude of an addition signal obtained from the adder 20 to obtain a threshold value between each quantization when performing quantization. And has a function of performing a threshold determination process in which a valley between a mountain having a high frequency of appearance and a mountain adjacent to the mountain is set as a threshold between quantizations.

That is, when there are many errors in the addition output from the adder 20 in the waveform equalizing circuit 15, the appearance frequency with respect to the value obtained by quantizing the amplitude is obtained. Is not shown, and as shown in FIG. 1, the tails of the peaks of the normalized distribution characteristics are connected, and there is no interval d, so that a threshold value for quantization cannot be basically obtained. At the same time, it is not possible to cope with a change in the position of the peak of the amplitude distribution due to a change in the amplitude. In this regard, in the present embodiment, when reproducing information from the optical disk 8, an amplitude distribution (a distribution of the frequency of appearance with respect to a value obtained by quantizing the amplitude of the addition signal obtained from the adder 20) is obtained as shown in FIG. The threshold value is determined so that the valleys 23a and 23b between the peak 22a having a high frequency of appearance and the peaks 22b and 22c adjacent to the peak 22a have the threshold values -Xth and Xth. Things. This makes it possible to determine the optimal threshold values -Xth and Xth so that errors are minimized, and it is possible to appropriately reproduce information recorded at high density.

FIGS. 3 and 4 show a second embodiment of the present invention.
It will be described based on. In the present embodiment, it is considered that the amplitude distribution is not actually represented by a smooth curve as shown in FIG. 1 but often becomes a jagged curve as shown in FIG. In this case, the part with the lowest appearance frequency is not necessarily the valley bottom part, and it is difficult to determine that the threshold is appropriate. Therefore, in the present embodiment, a digital filter 24 as shown in FIG. 4 is provided in the threshold value determining circuit 21 and filtering is performed using values before and after the appearance frequency, thereby forming the threshold values −Xth and Xth. It is configured so that a portion to be a power valley is properly detected in a smooth state.

More specifically, when the value obtained by quantizing the amplitude of the added signal of the adder 20 by the waveform equalizing circuit 15 is represented by x and the appearance frequency is represented by Q (x), the digital filter 24
R (x) = k (−n) * Q (x−n) +... + K (0) * Q (x) +
An intermediate value R (x) for obtaining a threshold value of k (n) * Q (x + n) is obtained, and a threshold value between each quantization is obtained from the intermediate value R (x). (x−n),..., Q (x),.
+ N) and a coefficient k (-
, k (0),..., k (n)
6 and an adder 27 for adding the multiplication results of these coefficient multipliers 26.

Therefore, according to the present embodiment, even if the amplitude distribution is not represented by a smooth curve but is jagged,
By applying digital filtering using the values before and after, it is possible to correct the amplitude distribution as shown in FIG. 1 as a result, and to properly detect the valleys which should be the thresholds -Xth and Xth. can do.

FIGS. 5 and 6 show a third embodiment of the present invention.
It will be described based on. In the present embodiment, the optical disk 8
As is well-known, the point that the reproduction amplitude of a short mark or space is small is taken into consideration. That is, when the amplitude of the reproduced signal differs depending on the length of the mark or the space, the reproduced signal has, for example, a short mark or space reproduced signal 27a and a long mark or space reproduced signal as shown in FIG. 27b are mixed, and the amplitude distribution at that time is taken. As shown in FIG.
The characteristic is divided into e. Therefore, in the present embodiment,
Assuming that the n-value quantization circuit 16 quantizes to three values, the amplitude of the addition signal of the adder 20 is calculated in order to obtain a threshold between each quantization when quantizing to three values and obtaining quantized data. The appearance frequency with respect to the quantized value is obtained, and the central mountain 28a having the largest number of appearance frequencies and the mountains 28b on both sides of the central mountain 28a,
The configuration is such that the valleys 29a and 29b between the valleys 28c and 28c are determined as thresholds -Xth and Xth between the respective quantizations. That is, if the length of the mark or space on the optical disk 8 changes, the determination of the threshold value for quantization is also affected. However, in the case of three-value quantization, five peaks can be formed according to the amplitude of the length. In the amplitude distribution, only the valleys 29a and 29b between the central peak 28a with the highest frequency of appearance and the peaks 28b and 28c on both sides thereof are used for the threshold value. Regardless of this, an appropriate threshold can be determined.

However, when quantizing to ternary values in this way, in the present embodiment, the number of transitions of binary values subjected to maximum likelihood decoding by the maximum likelihood decoding circuit 17 is counted, and the center frequency of the highest occurrence frequency is calculated. The threshold between the quantizations is set so that the range including the number of transitions from the peak of the peak 28a becomes the central value of the three values. That is, referring to FIG. 12, the central mountain 28a appears once at the edge when the state transitions from state 0 to state 1 or when the state transitions from state 1 to state 0. If counting is performed, it can be easily realized by setting thresholds on both sides of the central mountain 28a so that the total number of amplitude distributions between them becomes equal to the number of edges. As described above, since the threshold value for quantization is determined by the transition of the state of maximum likelihood decoding,
An appropriate threshold value is determined.

A fourth embodiment of the present invention will be described with reference to FIG. First, in the present embodiment, the fluctuation of the position of the peak in the amplitude distribution due to the fluctuation of the amplitude is caused by the temperature change of the semiconductor laser or the like in the optical pickup 6 or the like.
Consideration is given to possible causes such as birefringence of the substrate of the optical disk 8. That is, in the present embodiment, with respect to the disk-shaped optical disk 8 driven to rotate by the spindle motor 7, the period for calculating the appearance frequency for calculating the amplitude distribution is set to a period shorter than the period of one rotation of the optical disk 8. Thus, when determining the threshold value, it is possible to remove the fluctuation due to rotation.

As a configuration for this, a ring buffer may be used as shown in FIG. That is, when the amplitude data (the value obtained by quantizing the added signal) x is stored in the first memory 31, a ring buffer (FILO; First-In) is stored.
Last-Out), and the length of the address is L (L is longer than the period for which the appearance frequency is obtained). Further, a second memory 32 is provided for storing a distribution of the appearance frequency of each quantized value (for example, a distribution as shown in FIG. 6). The second memory 32 has an address equal to or greater than a value obtained by quantizing the addition signal. Here, assuming that a pointer by the address generator 33 for the first memory 31 as a ring buffer is p, a new amplitude value is inserted into the address pointed to by the pointer p, and the corresponding appearance frequency is incremented by 1 (+1). Then, assuming that the retention period (period for which the appearance frequency is obtained) is t, the appearance frequency corresponding to the data of (pt) is decremented by 1 (-1). However,
Because of the ring buffer configuration, if (pt) is negative, the address will be (pt + L). After the end of this process, the value of the pointer p is incremented by 1 (+1). At this time, if p> L, p = 0.

That is, as a general theory, assuming that the period for which the appearance frequency is obtained is t and the current pointer of the first memory 31 is p, the value x obtained by quantizing the amplitude of the current addition signal by the adder 20 is represented by the first value. In the second memory 32, the data at the address x is incremented by one, and the data x at the address (pt) of the first memory 31 is written to the second memory 32.
x is read, the data at the address xx in the second memory 32 is decremented by 1 (the switching of the addresses x and xx is performed by the selector 34), and the pointer p is incremented by 1. As described above, according to the present embodiment, by using the first memory 31 which is a so-called ring buffer, it is possible to appropriately determine the threshold value for quantization with a small device scale.

Although not particularly shown, in the case of the amplitude distribution as shown in FIG.
The number of binary transitions subjected to the maximum likelihood decoding by the maximum likelihood decoding circuit 17 is counted, and a range including the number of transitions from the peak of the central mountain 28a having the highest appearance frequency becomes the central value of the three values. When the threshold between the quantizations is determined, the processing can be performed using the ring buffer as in the case of FIG. That is, when the data binarized by the maximum likelihood decoding circuit 17 is stored in a memory (third memory), a ring buffer is used.
Let L be the length of the address. Here, assuming that a pointer of a third memory serving as a ring buffer is p, here,
As a result of the new maximum likelihood decoding, one of the first value indicating that the binary value has changed and the second value indicating that there is no change is pointed to the third memory. Write to the address pointed to by p. Here, if there is a change (in the case of the first value), the number of transitions is incremented by 1 (+1), and if they are the same, the number of transitions is not changed.
Assuming that the period for which the appearance frequency is obtained is t, if the data of (pt) is the first value, the number of transitions is decremented by 1 (-1). Do not change. However, since a ring buffer is used,
If (pt) is negative, the address is (pt + L). After this processing, the pointer is incremented (+1). Also in this case, if p> L, p = 0.

That is, as a general theory, assuming that the period for which the appearance frequency is obtained is t and the current pointer of the third memory of the ring buffer configuration is p, the first value indicating that the binary value subjected to maximum likelihood decoding has changed. Is written into the third memory at the address indicated by the pointer p, and when the first value is written, the maximum likelihood decoded binary value is written to the third memory. The value of the counting means for counting the number of transitions is incremented by one, and the address (p−
The data xx of t) is read, and if the read value is the first value, the count value of the counting means is decremented by 1 and the pointer p is incremented by 1 to obtain the count value of the central mountain. What should I do? Therefore, also in this case, using a so-called ring buffer memory,
The threshold value for quantization can be properly determined in a state where the device scale is small.

[0036]

According to the first aspect of the present invention, when binarizing an analog signal obtained by reading information recorded by a predetermined modulation method from an information recording medium, one or more analog signals can be converted. The amplitude is delayed by an integral multiple of the clock synchronized with the analog signal, and a sum signal obtained by adding a value obtained by multiplying a coefficient corresponding to the delay amount and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient is obtained. This addition signal is quantized to a number corresponding to the added delay amount using a threshold value between quantizations to obtain quantized data, and maximum likelihood decoding for prohibiting a transition that is not in the modulation rule of the quantized data and the modulation scheme. In the information reproducing method in which the amplitude of the addition signal is quantized to obtain a threshold value between each quantization when performing the quantization, the frequency of occurrence of the frequency of the frequency of the frequency is calculated. Next to the mountain Since the valley between the peak and the valley is used as the threshold between the quantizations, the threshold for the quantization can be set to a part with few errors as much as possible. Even if information is recorded at high density, it can be properly reproduced, and can be adapted to high density recording.

According to the second aspect of the present invention, in the information reproducing method according to the first aspect, the information recording medium is a disk-shaped medium that is driven to rotate, and the period for which the appearance frequency is obtained is one rotation of the disk-shaped medium. Since the time period is shorter than the time period, the fluctuation due to rotation can be removed in determining the threshold value.

According to the third aspect of the present invention, in the information reproducing method according to the first or second aspect, when a value obtained by quantizing the amplitude of the added signal is represented by x and an appearance frequency is represented by Q (x), (x) = k (-n) * Q (x-n) + ... + k (0) * Q (x) +
An intermediate value R (x) for obtaining a threshold value of k (n) * Q (x + n) is obtained, and a threshold value between each quantization is obtained from the intermediate value R (x). Even in the case of a jagged shape that is not represented by a curve, by applying digital filtering using the values before and after, it is possible to properly detect a valley portion that should be a threshold portion.

According to the fourth aspect of the present invention, the first aspect is provided.
In the information reproducing method according to Item 2 or 3, the information recording medium is a medium in which a signal reproduced from the information recording medium has a different amplitude depending on the length of a mark / space, and the amplitude of one analog signal is added to this analog signal. Delayed by one clock of the synchronized clock, an added signal is obtained by adding a value obtained by multiplying a coefficient corresponding to the delay amount of one clock and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient. In order to obtain a threshold between each quantization when obtaining quantized data by quantizing to three values, an appearance frequency with respect to a value obtained by quantizing the amplitude of the addition signal is obtained. Since the valley between the peaks on both sides is set as the threshold between the quantizations, as is well known, the amplitude of the mark or space changes when the length of the mark or space changes, as is well known. This also affects the determination of the threshold value for quantization, but in the case of three-valued quantization, among the amplitude distributions that can be generated in five peaks according to the long and short amplitudes, Since the valley between the central peak and the peaks on both sides is used for the threshold, an appropriate threshold can be determined regardless of the change in the amplitude.

According to the fifth aspect of the present invention, in the information reproducing method according to the fourth aspect, when quantizing into three values, the number of transitions of the maximum likelihood decoded binary is counted, and the appearance frequency is calculated. Since the threshold between each quantization is determined so that the range including the number of transitions from the peak of the most central mountain becomes the middle value of the three values, the threshold for quantization is determined by the maximum likelihood decoding. Since it is determined by the state transition, an appropriate threshold value is determined.

According to the sixth aspect of the present invention, when binarizing an analog signal obtained by reading information recorded in a predetermined modulation method from an information recording medium, the amplitude of one or more analog signals is changed. Waveform equalization that delays by an integer multiple of the clock synchronized with this analog signal, adds a value obtained by multiplying a coefficient corresponding to the delay amount, and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient to obtain an added signal. Means, quantizing means for quantizing the sum signal to a number corresponding to the added delay amount by using a threshold value between quantization to obtain quantized data, and the quantizing data and the modulation rule of the modulation method are not included. In an information reproducing apparatus having maximum likelihood decoding means for performing maximum likelihood decoding for prohibiting transition, an appearance frequency with respect to a value obtained by quantizing the amplitude of an addition signal in order to obtain a threshold value between each quantization when performing quantization. Ask for this Since the threshold value determining means is provided with a valley between a peak having a high frequency of occurrence and a peak adjacent to the peak as a threshold between the quantizations, the threshold for quantization is minimized and the error is minimized. The information can be set appropriately, and as a result, the information can be properly reproduced even if the information is recorded at a high density on the information recording medium.

According to the seventh aspect of the present invention, in the information reproducing apparatus according to the sixth aspect, the information recording medium is a disk-shaped medium which is driven to rotate, and the threshold value determining means determines the appearance frequency in the disk-shaped medium. Since the period is shorter than the time for the medium to make one rotation, fluctuations due to rotation can be removed in determining the threshold value.

According to an eighth aspect of the present invention, in the information reproducing apparatus according to the seventh aspect, the first memory having an address longer than the period for which the appearance frequency is determined by the threshold value determining means, and the addition signal by the waveform equalizing means. And a second memory having an address equal to or greater than the value obtained by quantizing the amplitude of the signal, where t represents the period for which the appearance frequency is obtained and p represents the current pointer of the first memory. The written value x is written to the address indicated by the pointer p in the first memory, the data at the address x in the second memory is incremented by 1, and the address (p−
Since the data xx of t) is read and the data of the address xx of the second memory is decremented by one and the pointer p is incremented by one, the memory of a so-called ring buffer is used to reduce the device scale. In this state, the threshold value for quantization can be properly determined.

According to the ninth aspect of the present invention, the sixth aspect is provided.
In the information reproducing apparatus described in 7 or 8, when the value obtained by quantizing the amplitude of the added signal by the waveform equalizing means is represented by x and the appearance frequency is represented by Q (x), the threshold value determining means: R (x) = k (-N) * Q (x-n) + ... + k (0) * Q (x) +
An intermediate value R (x) for obtaining a threshold value of k (n) * Q (x + n) is obtained, and a threshold value between each quantization is obtained from the intermediate value R (x). Even in the case of a jagged shape that is not represented by a curve, by applying digital filtering using the values before and after, it is possible to properly detect a valley portion that should be a threshold portion.

According to the tenth aspect of the present invention, in the information reproducing apparatus according to the sixth, seventh, eighth or ninth aspect, the information recording medium has a signal reproduced from the information recording medium having a mark / space length. Is a medium whose amplitude varies depending on
The waveform equalizing means delays the amplitude of one analog signal by one clock of a clock synchronized with the analog signal,
An addition signal is obtained by adding a value obtained by multiplying the coefficient corresponding to the delay amount of one clock and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient.
In order to obtain a threshold value between each quantization when obtaining quantized data by quantizing to a value, an appearance frequency with respect to a value obtained by quantizing the amplitude of the addition signal is obtained. Since the valley between the peaks on both sides is set as the threshold between the quantizations, as is well known, the amplitude changes when the length of the mark or space changes, and the quantum This also affects the determination of the threshold value for quantization, but when quantizing to ternary values, the central peak with the highest frequency of appearance is selected from among the five peaks that can be generated according to the long and short amplitudes. Since the valley between the peaks on both sides is used for the threshold value, it is possible to determine an appropriate threshold value irrespective of a change in amplitude.

According to the eleventh aspect, according to the first aspect,
0, the threshold value determining means has a counting means for counting the number of maximum-likelihood decoded binary transitions when quantizing to three values, and the peak of the central mountain having the highest frequency of appearance is provided. Since the threshold between the quantizations is determined so that the range including the number of transitions becomes the central value of the three values, the threshold for the quantization is determined by the transition of the state of the maximum likelihood decoding. An appropriate threshold value is determined.

According to the twelfth aspect, according to the first aspect,
In the information reproducing apparatus described in Item 1, if the third memory having an address equal to or longer than the period for which the appearance frequency is determined by the threshold value determining means, the period for which the appearance frequency is determined is t, and the current pointer of the third memory is p, A first value indicating that the likelihood decoded binary value has changed and a second value indicating that there is no change
Is written to the address indicated by the pointer p in the third memory, and when the first value is written, the value of the counting means for counting the number of transitions of the maximum likelihood decoded binary is calculated. The data xx at the address (pt) of the third memory is read out by incrementing by 1, and if the read value is the first value, the count value of the counting means is decremented by 1 and the pointer p is set to 1 In this case, the threshold value for quantization is obtained by using only a so-called ring buffer memory, so that the threshold value for quantization can be appropriately determined in a state where the apparatus scale is small. .

[Brief description of the drawings]

FIG. 1 is a distribution characteristic diagram of an appearance frequency according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating an outline of a PRML processing system.

FIG. 3 is a distribution characteristic diagram of an appearance frequency according to the second embodiment of the present invention.

FIG. 4 is a block diagram illustrating an outline of a digital filter.

FIG. 5 is a schematic diagram showing reproduced signals having different amplitudes.

FIG. 6 is a distribution characteristic diagram of the appearance frequency.

FIG. 7 is a block diagram showing a third embodiment of the present invention.

FIG. 8 is a block diagram showing an outline of a general optical information recording / reproducing apparatus.

FIG. 9 is a block diagram showing a configuration example of the binarization circuit.

FIG. 10 is a block diagram illustrating an outline of a PRML processing system.

FIG. 11 is a block diagram showing a configuration example of the waveform equalization circuit.

FIG. 12 is a time chart showing an example of waveform equalization processing in the case of an ideal reproduced waveform.

FIG. 13 is a distribution characteristic diagram showing an output example of the waveform equalization circuit when there are few errors, by replacing the output example with an appearance frequency.

FIG. 14 is a time chart showing the sampling operation.

FIG. 15 is a characteristic diagram showing a principle of replacement with an appearance frequency.

[Explanation of symbols]

 Reference Signs List 8 information recording medium 15 waveform equalizing means 16 quantizing means 17 maximum likelihood decoding means 21 threshold value determining means 22 peak 23 valley 28 peak 29 valley 31 first memory 32 second memory

Claims (12)

[Claims] When an analog signal obtained by reading information recorded in a predetermined modulation format from an information recording medium is binarized, the amplitude of one or more analog signals is adjusted by a clock synchronized with the analog signal. Delayed by an integer multiple, a sum signal obtained by adding a value obtained by multiplying a coefficient corresponding to the delay amount and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient is obtained. To obtain quantized data quantized to a number corresponding to the added delay amount,
In the information reproducing method in which the maximum likelihood decoding is performed to prohibit a transition which is not in accordance with the modulation rule of the modulation data and the modulation scheme, in order to obtain a threshold value between each quantization when performing the quantization, The frequency of appearance for a value obtained by quantizing the amplitude is obtained, and a valley between a mountain having a high frequency of occurrence and a mountain adjacent to the mountain is set as a threshold between quantizations. Information reproduction method. 2. The information recording medium according to claim 1, wherein the information recording medium is a rotationally driven disk-shaped medium, and a period for which the appearance frequency is obtained is a period shorter than a time for rotating the disk-shaped medium once. Information reproduction method. 3. The appearance frequency is represented by Q (x), where x is a value obtained by quantizing the amplitude of the addition signal, and R (x) = k (−n) * Q (x−n) +... + K ( 0) * Q (x) +
An intermediate value R (x) for obtaining a threshold value of k (n) * Q (x + n) is obtained, and a threshold value between each quantization is obtained from the intermediate value R (x). 3. The information reproducing method according to 1 or 2. 4. An information recording medium, wherein a signal reproduced from the information recording medium has a different amplitude depending on the length of a mark / space, and the amplitude of one analog signal is one of a clock synchronized with the analog signal. A delay signal is obtained by adding a value obtained by multiplying a coefficient corresponding to a delay amount of one clock and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient, and quantizing the added signal into three values. In order to obtain a threshold value between each quantization when obtaining quantized quantized data, an appearance frequency with respect to a value obtained by quantizing the amplitude of the addition signal is obtained. 4. The information reproducing method according to claim 1, wherein a valley portion between the peaks is used as a threshold between quantizations. 5. When quantizing into ternary values, the maximum likelihood decoded 2
The number of transitions of the values is counted, and the threshold between each quantization is determined so that the range including the number of transitions from the peak of the central mountain having the highest frequency of appearance becomes the central value of the three values. 5. The information reproducing method according to claim 4, wherein the information is reproduced. 6. When binarizing an analog signal obtained by reading information recorded in a predetermined modulation method from an information recording medium, the amplitude of one or more analog signals is changed by a clock synchronized with the analog signal. Waveform equalizing means for delaying by an integral multiple, adding a value obtained by multiplying a coefficient corresponding to the delay amount and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient to obtain an added signal, A quantizing means for quantizing to a number corresponding to the added delay amount by using a threshold value between quantization to obtain quantized data, and a maximum likelihood for prohibiting a transition which is not in a modulation rule of the quantized data and the modulation scheme. In an information reproducing apparatus having maximum likelihood decoding means for performing decoding, an appearance frequency with respect to a value obtained by quantizing the amplitude of the added signal is obtained in order to obtain a threshold value between each quantization when performing quantization. Frequency times Often mountainous and information reproducing apparatus of the valleys, characterized in that it comprises a threshold value determining unit that the threshold between the quantized between mountain adjacent to the mountain. 7. The information recording medium is a disk-shaped medium that is rotationally driven, and a period in which the threshold value determining means determines an appearance frequency is a period shorter than a time period in which the disk-shaped medium makes one rotation. Item 7. An information reproducing apparatus according to Item 6. 8. A first memory having an address equal to or longer than a period for which an appearance frequency is determined by a threshold value determining means, and a second memory having an address equal to or greater than a value obtained by quantizing the amplitude of an addition signal by a waveform equalizing means. When the period for obtaining the appearance frequency is t and the current pointer of the first memory is p, a value x obtained by quantizing the amplitude of the current addition signal is indicated by the pointer p with respect to the first memory. At the same time, the data at the address x in the second memory is incremented by one, and
8. The data xx at the address (pt) of the second memory is read, and the data at the address xx of the second memory is decremented by one and the pointer p is incremented by one. The information reproducing apparatus according to the above. 9. When the value obtained by quantizing the amplitude of the added signal by the waveform equalizing means is represented by x and the appearance frequency is represented by Q (x),
The threshold value determining means is as follows: R (x) = k (−n) * Q (x−n) +... + K (0) * Q (x) +
An intermediate value R (x) for obtaining a threshold value of k (n) * Q (x + n) is obtained, and a threshold value between each quantization is obtained from the intermediate value R (x). An information reproducing apparatus according to 6, 7, or 8. 10. An information recording medium is a medium in which a signal reproduced from the information recording medium has a different amplitude depending on the length of a mark / space, and a waveform equalizing means converts the amplitude of one analog signal into the analog signal. A value obtained by multiplying a value obtained by multiplying a coefficient corresponding to one clock of the delay amount and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient to obtain a sum signal is obtained. The determining means obtains an appearance frequency with respect to a value obtained by quantizing the amplitude of the addition signal in order to obtain a threshold value between each quantization when obtaining the quantized data by quantizing the addition signal into three values. 10. The information reproducing apparatus according to claim 6, wherein a valley between the central peak having the largest number of times and the peaks on both sides thereof is set as a threshold value between quantizations. apparatus. 11. The threshold value determining means includes counting means for counting the number of binary transitions subjected to maximum likelihood decoding when quantizing to ternary values. 11. The information reproducing apparatus according to claim 10, wherein the threshold value between the quantizations is determined so that a range including the number of times becomes a central value of the three values. 12. A maximum likelihood where a third memory having an address equal to or longer than a period for which the appearance frequency is determined by the threshold value determining means, a period for which the appearance frequency is determined is t, and a current pointer of the third memory is p, A first value indicating that the decoded binary value has changed and a second value indicating that there has been no change
Is stored in the pointer p to the third memory.
When the first value has been written, the value of the counting means for counting the number of transitions of the maximum likelihood decoded binary is incremented by one, and the address (pt) of the third memory is written. ) Is read, and if the read value is the first value, the count value of the counting means is decremented by 1 and the pointer p is incremented by 1 to obtain the count value of the central peak. The information reproducing apparatus according to claim 11, wherein: