JP3811258B2 - Information reproducing method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an information reproducing method and apparatus for reproducing information recorded on a high-density recording medium.
[0002]
[Prior art]
In recent years, high-density DVDs (Digital Versatile Disk or Digital Video Disk) have attracted attention as next-generation large-capacity optical disks. As this DVD, a DVD-RAM (Random Access Memory), a DVD-ROM (Lead Only Memory), a DVD-R (Recordable) and the like are known. In the next generation of DVD, it is necessary to further improve the recording density. As a processing system for the reproduction system for improving the recording density, it has been studied to introduce a PRML (Partial Response Maximum Likelihood) system used in the field of HDD and communication.
[0003]
Here, a general recording / reproducing system for DVD that leads to the examination of the introduction of the PRML system will be described with reference to FIG. First, the recording system will be described. An interface unit (I / F unit) 1 that controls an interface with a host device such as a personal computer (not shown) separates data and commands and controls the recording / reproducing apparatus. Among these, the data is temporarily stored in the RAM 3 from the I / F unit 1 through the buffer manager 2. Data stored in the RAM 3 is sent to the digital modulation unit 4. The digital modulation unit 4 adds an error correction code and a synchronization signal to the user data, and converts it into bit string data according to a predetermined modulation method, for example, EFM (Eight-Fourteen Modulation). The modulated signal is output to the optical pickup 6 through the analog recording system 5 that controls the emission intensity and the like, and is stored in the optical pickup 6 with respect to the optical disk (information recording medium) 8 that is rotationally driven by the spindle motor 7. Recording is performed using light emitted from an LD (semiconductor laser).
[0004]
Next, the reproduction 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 the analog reproduction system 9. A binarizing circuit 11 converts a synchronizing signal synchronized with an analog signal obtained from the analog reproducing system 9 into a binary digital signal while taking it with a PLL (Phase Locked Loop) circuit 10. The digital signal converted to binary is subjected to synchronization detection and modulation demodulation processing by the digital demodulation unit 12 or error correction processing based on the error correction code, and is 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 through the I / F unit 1.
[0005]
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 reference signal for offset cancellation, and 2 depending on whether the analog signal is larger or smaller than the voltage value of the reference signal. It is configured to be valuated. Reference numeral 14 denotes a D-type flip-flop that latches the output of the comparator 13 in accordance with the synchronous clock of the PLL circuit 10.
[0006]
However, in such a general binarization circuit 11, the PRML method is being studied because a problem such as intersymbol interference is insufficient as a reproduction process for high-density recording over DVD. This PRML system is introduced in, for example, the document “NIKKEI ELECTRONICS 1994.1.17 (no.599)” “Signal Processing System PRML Supporting Next Generation Mass Storage” (p.71-p.97) Yes. In this PRML system, the binarization circuit 11 shown in FIG. 8 is replaced with a waveform equalizer 15, an n-value quantization circuit (for example, a ternary circuit) 16, and a maximum likelihood decoding circuit 17 as shown in FIG. Are connected in order. Thus, when binarizing an analog signal obtained by reading information recorded by a predetermined modulation method from the optical disc 8, the amplitude of one or more analog signals is an integral multiple of a clock synchronized with the analog signal. The waveform equalization circuit 15 performs a process of delaying and adding the value obtained by multiplying the coefficient corresponding to the delay amount and the value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient to obtain an added signal. Processing for obtaining quantized data by quantizing the number corresponding to the added delay amount using a threshold between quantization is performed by the n-value quantization circuit 16, and this quantized data and a modulation rule of a predetermined modulation scheme are performed. Basically, the maximum likelihood decoding circuit 17 performs maximum likelihood decoding that prohibits transitions that are not present.
[0007]
Among these, the waveform equalization circuit 15 and the n-value equalization circuit 16 influence the performance of the PRML processing method. Here, the waveform equalization circuit 15 is configured as shown in FIG. 11, for example. First, an A / D converter 18 is provided that converts the reproduced analog signal into a digital signal in synchronization with the synchronization clock of the PLL circuit 10. The A / D converter 18 quantizes the 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. The D-type flip-flop 19 has a number of bits that matches the multivalue (for example, eight values) output from the A / D converter 18. The data delayed by one clock by the D flip flop 19 and the current data obtained from the A / D converter 18 are added by the adder 20 to obtain an addition signal output to the n-ary circuit 16. It is done.
[0008]
The movement of the 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 waveform equalization output, that is, the output of the adder 20, takes either a value around 0V or a value around ± 2V when the output level changes. Therefore, ternarization is performed using values of −2V, 0V, and + 2V to obtain three state signals, which are output to the maximum likelihood decoding circuit 17 so that final binarization processing is appropriately performed. .
[0009]
[Problems to be solved by the invention]
By the way, the actual reproduction waveform is not a rectangular wave as shown in FIG. 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. If there are two threshold values for ternarization between the intervals d as shown by the broken line, it is accurate. Can be ternarized. In particular, if the distance d is wide, it is possible to cope with fluctuations in the position of the mountain in the amplitude distribution due to amplitude fluctuations. 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 analog signal to be reproduced is sampled at each predetermined timing X as shown in FIG. The frequency expression is expressed as described above, and the frequency expression is normalized as an appearance frequency of each amplitude value.
[0010]
However, in reality, when the optical disk 8 recorded at a higher density is reproduced by the same recording / reproducing system, interference occurs between the signals to be reproduced at each timing, so that an error occurs, and the adder 20 Also, the amplitude distribution due to the output does not show clear characteristics as shown in FIG. 13, and there is a possibility that the quantization threshold is set at a place with many errors. That is, if the part of the PRML process that quantizes the output of the waveform equalization circuit does not work well, an error occurs in the reproduction process, and as a result, it is meaningless to improve the recording density of the optical disc 8. End up.
[0011]
Therefore, the present invention can set the threshold for quantizing the output from the waveform equalization means to the optimum value when using the PRML processing method, thereby improving the recording density in the information recording medium. It is an object of the present invention to provide an information reproducing method and apparatus that can make the information meaningful.
[0017]
[Means for Solving the Problems]
  The invention described in claim 1When 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 delayed by an integral multiple of a clock synchronized with the analog signal. Waveform equalization means for 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 a threshold between quantization of the added signal Quantization means for obtaining quantized data by quantizing to a number corresponding to the added delay amount by using the maximum likelihood decoding for prohibiting transitions not included in the modulation rule and the modulation rule of the modulation scheme In an information reproducing apparatus including a decoding unit, in order to obtain a threshold value between quantizations when performing quantization, an appearance frequency is obtained for a value obtained by quantizing the amplitude of the addition signal, and the number of appearance frequencies is large. Mountain By threshold value determining means that uses a valley portion between mountains adjacent to the mountain as a threshold value between quantizations, a first memory having an address equal to or longer than a period for which an appearance frequency is determined by the threshold value determining means, and a waveform equalizing means A second memory having an address equal to or greater than a value obtained by quantizing the amplitude of the addition signal, and the information recording medium is a disk-shaped medium that is rotationally driven. If the medium is a period shorter than the time for which the medium rotates once, 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 the first value. 1 is written at the address indicated by the pointer p, the data at the address x of the second memory is incremented by 1, and the data xx at the address (pt) of the first memory is incremented. Read out, and to be incremented by 1 the pointer p with decrements the data of the address xx of the second memory.
[0018]
  Therefore, the threshold value for quantization can be set as much as possible in a portion with few errors, and as a result, even if information is recorded on the information recording medium at high density, it can be reproduced properly. Also,The fluctuation of the peak position in the amplitude distribution due to the amplitude fluctuation can be caused by the temperature change of the semiconductor laser or the like, or the birefringence of the substrate of the information recording medium. In this case, by changing the time for obtaining the amplitude distribution (appearance frequency) to be shorter than the time for one rotation, the fluctuation due to the rotation can be removed in determining the threshold value.
[0019]
  Also,By using a so-called ring buffer memory, it is possible to appropriately determine a threshold value for quantization with a small apparatus scale.
[0020]
  Claim2The described invention is claimed.1In the described information reproducing apparatus, when the appearance frequency is represented by Q (x) where x is a value obtained by quantizing the amplitude of the addition signal by the waveform equalization means,
R (x) = k (−n) * Q (x−n) +... + K (0) * Q (x) + k (n) * Q (x + n)
An intermediate value R (x) for obtaining a threshold value is obtained, and a threshold value between each quantization is obtained from the intermediate value R (x). Therefore, even if the amplitude distribution is not represented by a smooth curve and is jagged, it is possible to appropriately detect the valley that should be the threshold value by applying digital filtering using the previous and subsequent values. be able to.
[0021]
  Claim3The described invention is claimed.1In the information reproducing apparatus described above, the information recording medium is a medium in which a signal reproduced from the information recording medium has an amplitude that differs depending on the length of the mark / space, and the waveform equalizing means converts the amplitude of one analog signal to this Delay by one clock of the clock synchronized with the analog signal, and obtain an addition signal 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; The threshold value determining means obtains an appearance frequency for a value obtained by quantizing the amplitude of the addition signal in order to obtain a threshold value between quantizations when quantizing the addition signal into three values to obtain quantized data. The valley portion between the central mountain with the highest frequency and the mountains on both sides is set as a threshold between quantizations. Therefore, it is well known that in an information recording medium such as an optical disc, the reproduction amplitude of a short mark or space is small, and if the length of the mark or space changes, it also affects the determination of the threshold for quantization. In the case of quantization to ternary values, the threshold value is the valley portion between the central mountain with the highest frequency of appearance and the mountain on both sides in the amplitude distribution that can be formed by five peaks according to the long and short amplitudes. Therefore, it is possible to determine an appropriate threshold value regardless of the change in amplitude.
[0022]
  Claim4The described invention is claimed.1In the described information reproducing apparatus, the threshold value determining unit has a counting unit that counts the number of binary transitions subjected to maximum likelihood decoding when quantizing into three values, and starts from the peak of the central mountain having the highest appearance frequency. The threshold between each quantization is determined so that the range including the number of transitions becomes the center value of the three values. Therefore, since the threshold for quantization is determined by the transition of the state of maximum likelihood decoding, the appropriate threshold is determined.
[0023]
  Claim5The described invention is claimed.1In the information reproducing apparatus described above, suppose that the third memory having an address equal to or greater than the period for which the threshold value is determined by the threshold value determining unit, t is the period for determining the appearance frequency, and p is the current pointer of the third memory. Write either the first value indicating that the maximum likelihood decoded binary value has changed or the second value indicating that there is no change to the address indicated by the pointer p to the third memory; When the first value is written, the value of the counting means for counting the number of binary transitions subjected to maximum likelihood decoding is incremented by 1, and the data xx at the third memory address (pt) is read out. When 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. Therefore, by using a so-called ring buffer memory, it is possible to appropriately determine the threshold for quantization with a small apparatus scale.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS. Note that this embodiment is a playback system for an optical disc for DVD or further generation, for example, and is based on the premise that the PRML processing method is used, and is the same as the portion shown in FIGS. Parts are denoted by the same reference numerals and description thereof is omitted (the same applies to the following embodiments). In the present embodiment, a threshold value determination circuit (determining a threshold value for quantization in the n-value quantization circuit (quantization means) 16 based on the output (= addition signal) of the waveform equalization circuit (waveform equalization means) 15. Threshold determination means) 21 is added. This threshold value determination circuit 21 is configured as an analysis processing means such as a DSP (Digital Signal Processing) or a CPU (Central Processing Unit), and an adder 20 is used to obtain a threshold value between quantizations when performing quantization. Determine the appearance frequency for the value obtained by quantizing the amplitude of the added signal obtained from the above, and determine the threshold value using the valley between the mountain with the most frequent appearance frequency and the mountain adjacent to the mountain as the threshold between each quantization. Has a function to perform processing.
[0025]
That is, when there are many errors in the addition output from the adder 20 in the waveform equalization circuit 15, when the appearance frequency with respect to a value obtained by quantizing the amplitude is obtained, the distribution characteristics as shown in FIG. As shown in FIG. 1, the crests of the normalized distribution characteristic peaks are connected, the interval d portion is eliminated, and basically a threshold value for quantization cannot be obtained. At the same time, fluctuations in the peak position of the amplitude distribution due to amplitude fluctuations cannot be dealt with. In this regard, in the present embodiment, when information is reproduced from the optical disc 8, an amplitude distribution (appearance frequency distribution 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. Even in such a distribution, the threshold value is determined so that the valleys 23a and 23b between the mountain 22a having a high frequency of appearance and the mountains 22b and 22c adjacent to the mountain 22a have threshold values −Xth and Xth. Is. As a result, it is possible to determine the optimum threshold values -Xth and Xth that minimize the error, and appropriately reproduce information recorded at high density.
[0026]
A second embodiment of the present invention will be described with reference to FIGS. 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 portion with the lowest appearance frequency is not necessarily the valley bottom portion, and it is difficult to determine that the threshold is appropriate. Therefore, in the present embodiment, the threshold value determination circuit 21 is provided with a digital filter 24 as shown in FIG. 4, and filtering is performed using values before and after the appearance frequency to obtain the threshold value −Xth and Xth portions. It is comprised so that the part used as a power valley may be detected appropriately in a smooth state.
[0027]
More specifically, when the appearance frequency is represented by Q (x) where x is a value obtained by quantizing the amplitude of the addition signal of the adder 20 by the waveform equalization circuit 15, the digital filter 24
R (x) = k (−n) * Q (x−n) +... + K (0) * Q (x) + k (n) * Q (x + n)
Is obtained so as to obtain an intermediate value R (x) for obtaining a threshold value, and a threshold value between quantizations is obtained from the intermediate value R (x). (x),..., Q (x + n), and a coefficient multiplier 26 for multiplying coefficients k (−n),..., k (0),. And an adder 27 for adding the multiplication results of the coefficient multiplier 26.
[0028]
Therefore, according to the present embodiment, even if the amplitude distribution is not represented by a smooth curve but is jagged, by performing digital filtering using the previous and subsequent values, the result is Thus, the amplitude distribution as shown in FIG. 1 can be corrected, and the threshold-Xth and Xth portions that should be valleys can be properly detected.
[0029]
A third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, as is well known in the optical disc 8, it is considered that the reproduction amplitude of short marks and spaces is small. That is, when the reproduction signal has a different amplitude depending on the length of the mark or space, the reproduction signal has, for example, a reproduction signal 27a for a short mark or space and a reproduction signal for a long mark or space as shown in FIG. 27b are mixed, and when the amplitude distribution at that time is taken, a characteristic divided into five peaks 28a to 28e is shown as shown in FIG. Therefore, in the present embodiment, assuming that the n-value quantization circuit 16 quantizes to ternary values, it is added to obtain a threshold value between quantizations when quantized to ternary values to obtain quantized data. An appearance frequency is obtained for the value obtained by quantizing the amplitude of the addition signal of the adder 20, and the valleys 29a and 29b between the central mountain 28a having the highest frequency of appearance and the mountain 28b and 28c on both sides thereof are obtained. The thresholds between the quantizations are determined as -Xth and Xth. That is, if the length of the mark or space on the optical disk 8 changes, it affects the determination of the threshold value for quantization, but if it is quantized to ternary values, five peaks can be made according to long and short amplitudes. 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 value can be determined.
[0030]
However, in this embodiment, when quantizing into three values in this way, the number of binary transitions subjected to maximum likelihood decoding by the maximum likelihood decoding circuit 17 is counted, and the central peak 28a having the highest appearance frequency is counted. The threshold value between the quantizations is determined so that the range including the number of transitions from the peak is the middle 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 0 to state 1 or from state 1 to state 0, so this edge is used as the number of transitions. If it is counted, it can be easily realized by setting the thresholds on both sides of the central mountain 28a so that the total number of amplitude distributions in between is equal to the number of edges. As described above, since the threshold for quantization is determined by the transition of the state of maximum likelihood decoding, the appropriate threshold is determined.
[0031]
A fourth embodiment of the present invention will be described with reference to FIG. First, in the present embodiment, the fluctuation of the peak position in the amplitude distribution due to the amplitude fluctuation or the like may be caused by a temperature change of the semiconductor laser or the like in the optical pickup 6 or the cause of birefringence of the substrate of the optical disk 8. Considered points. That is, in the present embodiment, for the disc-shaped optical disk 8 that is rotationally driven by the spindle motor 7, the period for determining the appearance frequency for calculating the amplitude distribution is set to be shorter than the time for which the optical disk 8 rotates once. Thus, in determining the threshold value, fluctuation due to rotation can be removed.
[0032]
As a configuration for this, a ring buffer may be used as shown in FIG. That is, when the amplitude data (value obtained by quantizing the addition signal) x is stored in the first memory 31, it is composed of a ring buffer (FILO; First-In Last-Out), and the length of the address is L. (L is longer than the period for determining the appearance frequency). In addition, a second memory 32 that stores the distribution of the appearance frequency of each quantized value (for example, the distribution shown in FIG. 6) is also provided. The second memory 32 has an address equal to or greater than the value obtained by quantizing the addition signal. Here, if the pointer by the address generator 33 for the first memory 31 that is a ring buffer is p, a new amplitude value is entered at the address indicated by the pointer p, and the corresponding appearance frequency is incremented by 1 (+1). If the holding period (period for obtaining the appearance frequency) is t, the appearance frequency corresponding to the data of (pt) is decremented by 1 (−1). However, since it has a ring buffer configuration, when (pt) is negative, the address is (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.
[0033]
That is, in general, when the period for obtaining the appearance frequency 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 expressed by the first memory 31. Is written at the address indicated by the pointer p, and on the second memory 32 side, the data at the address x is incremented by 1, and the data xx at the address (pt) of the first memory 31 is read out. The data at the address xx of the second memory 32 is decremented by 1 (the switching between the addresses x and xx is performed by the selector 34) and the pointer p is incremented by 1. In this way, according to the present embodiment, by using the first memory 31 that is a so-called ring buffer, it is possible to appropriately determine the threshold for quantization with a small apparatus scale.
[0034]
Although not particularly illustrated, in the case of the amplitude distribution as shown in FIG. 6, when quantizing into three values, the number of binary transitions subjected to maximum likelihood decoding by the maximum likelihood decoding circuit 17 is counted, Similarly to the case of FIG. 7, when the threshold value between the quantizations is determined so that the range including the number of transitions from the peak of the central peak 28a having the highest appearance frequency becomes the central value of the three values. Can be processed using a ring buffer. That is, when the data binarized by the maximum likelihood decoding circuit 17 is stored in a memory (third memory), it is constituted by a ring buffer and the length of the address is L. Here, if the pointer of the third memory serving as a ring buffer is p, the first value indicating that there is a change in the binary value as a result of the new maximum likelihood decoding, and that there is no change. Any value of the indicated second value is written to the address indicated by the pointer p in the third memory. 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. If the period for determining the appearance frequency is t, the number of transitions is decremented by 1 when the data of (pt) is the first value (-1), and if the data is the same, the number of transitions is decremented. Do not change. However, since the ring buffer is used, when (pt) is negative, the address is (pt + L). After this processing, the pointer is incremented (+1). Again, if p> L, then p = 0.
[0035]
That is, as a general theory, when the period for obtaining the appearance frequency 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, Any one of the second values indicating no change is written to the address indicated by the pointer p in the third memory, and when the first value is written, the maximum likelihood decoding number of binary transitions 1 is incremented by 1, and the data xx at the address (pt) of the third memory is read. If the read value is the first value, the count value of the counting means is set to 1. And the pointer p is incremented by 1 to obtain the count value of the central peak. Therefore, in this case as well, a so-called ring buffer memory can be used to appropriately determine the threshold for quantization with a small device scale.
[0041]
【The invention's effect】
  Claim1According to the described 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 delayed by an integral multiple of a clock synchronized with the analog signal. Waveform equalization means for 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 a threshold between quantization of the added signal Quantization means for obtaining quantized data by quantizing to a number corresponding to the added delay amount by using the maximum likelihood decoding for prohibiting transitions not included in the modulation rule and the modulation rule of the modulation scheme In an information reproducing apparatus including a decoding unit, in order to obtain a threshold value between quantizations when performing quantization, an appearance frequency is obtained for a value obtained by quantizing the amplitude of the addition signal, and the number of appearance frequencies is large. Mountain By threshold value determining means that uses a valley portion between mountains adjacent to the mountain as a threshold value between quantizations, a first memory having an address equal to or longer than a period for which an appearance frequency is determined by the threshold value determining means, and a waveform equalizing means A second memory having an address equal to or greater than a value obtained by quantizing the amplitude of the addition signal, and the information recording medium is a disk-shaped medium that is rotationally driven. If the medium is a period shorter than the time for which the medium rotates once, 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 the first value. 1 is written at the address indicated by the pointer p, the data at the address x of the second memory is incremented by 1, and the data xx at the address (pt) of the first memory is incremented. Read out, and to be incremented by 1 the pointer p with decrements the data of the address xx of the second memoryTherefore, the threshold value for quantization can be set as much as possible in a portion with few errors, and as a result, even if information is recorded on the information recording medium at high density, it can be reproduced properly.
[0042]
  Claim1According to the described invention, EmotionThe information recording medium is a disk-shaped medium that is rotationally driven, and the period for determining the appearance frequency in the threshold value determination means is shorter than the time for which the disk-shaped medium rotates once. Minutes can be removed.
[0043]
  Claim1According to the described invention, ThresholdA first memory having an address equal to or longer than a period for which the appearance frequency is determined in the value determining means, and a second memory having an address equal to or larger than a value obtained by quantizing the amplitude of the addition signal by the waveform equalizing means. Assuming that the required period 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 written to the address indicated by the pointer p in the first memory, and the second The data at the address x of the first memory is incremented by 1, the data xx at the address (pt) of the first memory is read, the data at the address xx of the second memory is decremented by 1, and the pointer p is set to 1. The threshold value for quantization is appropriately determined using a so-called ring buffer memory with a small device scale. Door can be.
[0044]
  Claim2According to the described invention, the claims1In the described information reproducing apparatus, when the appearance frequency is represented by Q (x) where x is a value obtained by quantizing the amplitude of the addition signal by the waveform equalization means,
R (x) = k (−n) * Q (x−n) +... + K (0) * Q (x) + k (n) * Q (x + n)
Since the intermediate value R (x) for obtaining the threshold value is obtained, and the threshold value between each quantization is obtained from the intermediate value R (x), the amplitude distribution is not represented by a smooth curve, but in a jagged shape. Even if it exists, the part used as the threshold value part can be detected appropriately by performing digital filtering using the value before and behind.
[0045]
  Claim3According to the described invention, the claims1In the information reproducing apparatus described above, the information recording medium is a medium in which a signal reproduced from the information recording medium has an amplitude that differs depending on the length of the mark / space, and the waveform equalizing means converts the amplitude of one analog signal to this A sum signal obtained by adding a value obtained by delaying one clock of the clock synchronized with the analog signal, multiplying the coefficient corresponding to the delay amount by one clock, and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient is obtained. The determining means obtains an appearance frequency for a value obtained by quantizing the amplitude of the addition signal in order to obtain a threshold value between quantizations when quantizing the addition signal into three values to obtain quantized data. Since the valley between the central mountain having the highest number of times and the mountain on both sides thereof is set as a threshold between each quantization, as is well known in the information recording medium such as an optical disk, a mark or a space is used. If the length of the signal changes, the amplitude also changes and affects the determination of the threshold value for quantization. Since the valley between the central mountain with the highest frequency of occurrence and the mountain on both sides is used for the threshold, it is possible to determine an appropriate threshold regardless of the change in amplitude. it can.
[0046]
  Claim4According to the described invention, the claims1In the described information reproducing apparatus, the threshold value determining unit has a counting unit that counts the number of binary transitions subjected to maximum likelihood decoding when quantizing into three values, and starts from the peak of the central mountain having the highest appearance frequency. Since the threshold value between each quantization is determined so that the range including the number of transitions becomes the middle value of the three values, the threshold value for quantization is determined by the transition of the state of maximum likelihood decoding. The threshold value is determined.
[0047]
  Claim5According to the described invention, the claims1In the information reproducing apparatus described above, if the third memory having an address that is equal to or greater than the period for which the threshold value is determined by the threshold value determining means, t is the period for determining the appearance frequency, and p is the current pointer in the third memory, the maximum likelihood Either the first value indicating that the decoded binary value has changed or the second value indicating that there is no change is written to the address indicated by the pointer p in the third memory, and the first value When the value is written, the value of the counting means for counting the number of binary transitions subjected to maximum likelihood decoding is incremented by 1, and the data xx at the address (pt) of the third memory is read and read. When the value is the first value, the count value of the counting means is decremented by 1 and the pointer p is incremented by 1 so as to obtain the count value of the central mountain, so-called a ring buffer memo By using, it can be appropriately performed to determine the threshold value for quantization in small apparatus scale state.
[Brief description of the drawings]
FIG. 1 is a distribution characteristic diagram of appearance frequencies showing a first embodiment of the present invention.
FIG. 2 is a block diagram showing an outline of a PRML processing system.
FIG. 3 is a distribution characteristic diagram of appearance frequencies showing a second embodiment of the present invention.
FIG. 4 is a block diagram showing an outline of a digital filter.
FIG. 5 is a schematic diagram showing reproduction 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 illustrating a configuration example of the binarization circuit.
FIG. 10 is a block diagram showing an outline of a PRML processing system.
FIG. 11 is a block diagram illustrating 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 reproduction waveform.
FIG. 13 is a distribution characteristic diagram in which an output example of a waveform equalization circuit when there are few errors is replaced with an appearance frequency.
FIG. 14 is a time chart showing the sampling operation;
FIG. 15 is a characteristic diagram showing the principle of replacement with appearance frequency.
[Explanation of symbols]
8 Information recording media
15 Waveform equalization means
16 Quantization means
17 Maximum likelihood decoding means
21 Threshold determination means
22 mountains
23 Valley
28 mountains
29 Valley
31 First memory
32 Second memory

Claims (5)

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 delayed by an integral multiple of a clock synchronized with the analog signal. Waveform equalization means for 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 a threshold between quantization of the added signal Quantization means for obtaining quantized data by quantizing to a number corresponding to the added delay amount by using the maximum likelihood decoding for prohibiting transitions not included in the modulation rule and the modulation rule of the modulation scheme In an information reproducing apparatus comprising a decoding means,
  In order to obtain a threshold between quantizations when performing quantization, an appearance frequency is obtained with respect to a value obtained by quantizing the amplitude of the addition signal, and a mountain between the frequency of the appearance frequency and a mountain adjacent to the mountain is determined. Threshold value determining means for setting a valley portion of
  A first memory having an address equal to or greater than a period for which the appearance frequency is determined in the threshold value determining means;
  A second memory having an address equal to or greater than a value obtained by quantizing the amplitude of the addition signal by the waveform equalization means;
  The information recording medium is a disk-shaped medium that is rotationally driven, and the period for which the appearance frequency is determined in the threshold value determination means is a period that is shorter than the time for which the disk-shaped medium rotates once,
  If 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 set to the address indicated by the pointer p with respect to the first memory. At the same time, the data at the address x of the second memory is incremented by 1, the data xx at the address (pt) of the first memory is read, and the data at the address xx of the second memory is read. An information reproducing apparatus characterized in that the pointer p is decremented by 1 and the pointer p is incremented by 1. The frequency of appearance is defined as x, where x is the value obtained by quantizing the amplitude of the added signal by the waveform equalization means ( x ) The threshold value determining means
R ( x ) = K ( -N ) * Q ( xn ) + ... + k ( 0 ) * Q ( x ) + K ( n ) * Q ( x + n )
Intermediate value R for obtaining the threshold value ( x ) This intermediate value R ( x ) 2. The information reproducing apparatus according to claim 1, wherein a threshold value between quantizations is obtained from the information. The information recording medium is a medium in which the amplitude of a signal reproduced from the information recording medium differs depending on the length of the mark / space, and the waveform equalizing means has a clock in which the amplitude of one analog signal is synchronized with the analog signal. A value delayed by one clock, a value obtained by multiplying a coefficient corresponding to the amount of delay by one clock, and a value obtained by multiplying the amplitude of the analog signal by an arbitrary coefficient are obtained to obtain an added signal. In order to obtain a threshold value between quantizations when quantizing the addition signal into three values to obtain quantized data, an appearance frequency is obtained with respect to a value obtained by quantizing the amplitude of the addition signal, and this appearance frequency is the highest. 2. The information reproducing apparatus according to claim 1, wherein a valley portion between the central mountain and the mountain on both sides thereof is set as a threshold between quantizations. The threshold value determining unit has a counting unit that counts the number of binary transitions subjected to maximum likelihood decoding when quantized into three values, and includes a range including the number of transitions from the peak of the central mountain having the highest appearance frequency. 2. The information reproducing apparatus according to claim 1, wherein a threshold value between each quantization is determined so that becomes a middle value of three values. A third memory having an address equal to or greater than a period for which the appearance frequency is determined in the threshold value determining means;
  When the period for obtaining the appearance frequency is t and the current pointer of the third memory is p, the first value indicating that the binary value subjected to maximum likelihood decoding has changed and the second value indicating no change. The value of the counting means for writing one of the above values to the address indicated by the pointer p in the third memory and counting the number of binary transitions subjected to maximum likelihood decoding when the first value is written. Is incremented by 1, the data xx at the address (pt) of the third memory is read, and when the read value is the first value, the count value of the counting means is decremented by 1 and the pointer 2. The information reproducing apparatus according to claim 1, wherein p is incremented by 1 to obtain a count value of a central peak.

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