JPH11126434A - Information recording and playback method - Google Patents

Abstract

(57) [Summary] [Purpose] To efficiently remove noise. In an information reproducing apparatus for reproducing data on a recording medium by using a predetermined encoding rule, a reproduction interval of a specific pattern which can be separately detected from the data inserted at regular intervals in the data is set. 1/2 of the reproduced signal when T seconds
It has a low frequency component cutoff filter that removes frequency components below THz. [Effect] It is possible to remove a low frequency component on which a lot of noise is superimposed without losing an information component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for recording information on a medium and reproducing the information, and particularly to an optical disk medium using a coding rule having no DC free property. This is an information recording / reproducing method that is effective for reducing fluctuations in the reproduced signal level that occur in such cases.

[0002]

2. Description of the Related Art In an optical disk file, to improve data reliability, that is, to reduce an error rate, it is effective to improve a signal-to-noise ratio of a reproduced signal and increase a data detection window. As a method of binarizing the reproduction signal, the following two methods are exemplified. As a first method, there is a method of directly binarizing a detection signal indicating the presence or absence of a recording mark recorded on an optical disk by an optical head at a certain slice level (hereinafter, referred to as an original waveform detection method). . As a second method, a method of detecting a position corresponding to a code word by differentiating the detection signal (hereinafter, referred to as a differential detection method)
There is.

In a system in which a code word is made to correspond to the center of a recording mark (hereinafter referred to as a mark position recording system), a detection signal from an optical head is first-order differentiated, and a zero crossing of the first-order differentiation signal is performed. It is common to detect points. Also,
In a method in which a code word is made to correspond to both ends of a recording mark (hereinafter, referred to as a mark edge recording method), a detection signal from an optical head is second-order differentiated, and a zero cross point of the second-order differentiation signal is detected. It is common to do this.

The reduction in the signal-to-noise ratio that occurs when the reproduced signal is binarized is smaller in the original waveform detection. In the case of the differential detection method, since the frequency band near the differential constant (cutoff frequency) increases, the original signal-to-noise ratio needs to be sufficiently ensured.

On the other hand, items that characterize the modulation method (coding rule) include DC freeness, self-clocking, and detection window width.

The DC free property means that the recording pattern on the medium after modulation and the average level of the reproduced signal obtained from the recording pattern are not dependent on the data pattern before modulation.
It is a property that it is always constant within a certain data length range (for example, one byte period).

As a method of evaluating the degree of DC freeness, accumulated charge may be used. The accumulated charge is the recording mark
The polarity corresponding to the mark side of the reproduced waveform obtained from the mark or the recorded mark is + (plus), and the polarity corresponding to the unrecorded portion between the marks, ie, the gap side, is-(minus). In this case, it means the cumulative value of the above code in a certain data period. When the DC free property is completely satisfied, the accumulated charge is always zero. In general, if the accumulated charge is 0 within an appropriate division of the data length, for example, within one byte, it is determined that the data has DC free property. The accumulated charge is also called DSV (Digital Sum Value).

When the coding rule having such a DC free property is used, the level of the reproduced signal does not fluctuate even when the reproduced signal system is connected by a coupling capacitor or the like. In the above-described differential detection method, since the same number of amplitude signals always occur in the upper and lower sides due to the nature of the differential waveform, the average level of the differential signal is kept substantially constant even when the modulation method itself has no DC freeness. .

Regarding the data detection window width, the wider is the data detection window.
The error occurrence rate in the case where the data detection position fluctuates becomes low. In NRZ (non-return-to-zero) modulation, the detection window width is the same as one bit of data before modulation, and the detection window width is the widest. However, it does not have the self-clocking property which is one of the characteristics of the modulation method. The self-clocking property is a characteristic in which a clock for reproduction can be generated from the data recorded on the medium itself. In the NRZ modulation, when "1" or "0" is continuous as data, "Self-clocking property" is used.
Since the transition point between 1 "and" 0 "disappears, a reproduced clock cannot be generated.As a modification of NRZ modulation, NRZI (non-return to zero inversion) in which a transition point is forcibly inserted is used.
S) There is modulation, but the problem of overhead and the problem of DC freeness remain.

In the data format of the optical disk,
In addition to user data, address information indicating a position on the disk, a pattern for pulling in a phase-locked loop (PLL) for generating a reproduction clock, and insertion at a certain interval in the data. Specific data such as a resynchronization pattern to be recorded is recorded. Of these, the address information is generally created in advance as pits (holes) at the time of manufacturing the disk. 130m as an example of the disc format
Discs of the continuous servo type having a diameter of m are defined by the ISO (International Standardization) standard.

Here, the ISO standard will be described as an example.
As a modulation method, a mark position recording method of 2-7 RLL (run length limit) modulation is used, and a 1-byte resynchronization mark is inserted for every 20 bytes of data. The resynchronization mark (RESYNC) is a function to correct the phase relationship between the reproduction clock generated by the PLL and the reproduction data by one bit or more due to a defect on the disk or the like, thereby correcting the phase by the resynchronization mark. have. The number of data bytes between resynchronization marks is set within an error-correctable range by ECC (error correction code).

In this ISO format, the resynchronization mark
There is only one type, and no change is made by the data pattern. In this format, a mark position recording method is used, and since the mark position is usually detected by differential detection, the need for DC freeness is not so strong. Further, the function of the resynchronization mark is limited to only the correction of the data bit deviation.

[0013]

SUMMARY OF THE INVENTION Conventional disk players
In a mat, there is only one type of resynchronization mark.
Further, the 2-7 RLL modulation method is used as the data modulation method, and no special consideration is given to DC freeness. To increase the density of an optical disk, a mark edge recording method in which code words are made to correspond to both ends of a recording mark is effective.
According to the mark edge recording method, it is possible to expect a linear recording density improvement of about twice that of the mark edge recording method for marks of the same size.

In order to detect an edge position in a mark edge recording method, a differential detection method is generally used. Regarding the DC freeness, the DSV can be made close to 0 irrespective of the modulation method. However, considering the reduction of the signal-to-noise ratio in the reproduction system, the original waveform detection method is more advantageous than the differential detection method in which the level in the high frequency band increases.

In the case of the original waveform detection method, when an amplifier that can pass DC is not used, a fluctuation of the reproduction signal level due to the data pattern occurs except for the modulation method having the DC free characteristic. Accurate detection becomes difficult. DC amplifiers are more difficult to handle than AC amplifiers because they require a large dynamic range and are offset and drifting due to temperature and power supply fluctuations.
In the case where a modulation method having no DC free property is used and an original waveform detection method which is advantageous in terms of a signal-to-noise ratio is used, the above-described level fluctuation becomes a problem for stable data detection.

[0016]

As a means for solving the above-mentioned problem, a resynchronization mark existing in a format defined by the ISO standard is used to positively contribute to a reduction in reproduction level fluctuation. It may be used as a pattern. That is, in this case, a method is effective in which the accumulated charge is selected based on the resynchronization pattern sequence that brings the accumulated charge as close to 0 as possible and the sign of the accumulated charge in the data sequence of the resynchronization pattern.

At the time of data recording, the accumulated charge is obtained from the distance between the changing points in the code word data string (the length of the mark and the length of the gap in the mark edge recording system). A plurality of resynchronization patterns are prepared according to the sign of the accumulated charge.
This can be realized by selecting the one whose accumulated charge approaches 0 most.

Even when an AC amplifier is used for data reproduction, the frequency determined from the interval of twice or more the resynchronization pattern insertion interval is set sufficiently higher than the AC coupling cutoff frequency. By doing so, the level shift of the reproduction signal can be ignored, and stable binarization can be realized.

[0019]

The recording data system comprises a modulation circuit and a circuit for generating a specific pattern such as a resynchronization mark, a selection circuit, an accumulated charge detection circuit, a write laser drive circuit, and the like. The accumulated charge detection circuit can be realized by comparing the number of mark-side bits and the number of gap-side bits by a counter. The modulation circuit and the write laser drive circuit can be realized by a conventional configuration.

In the case of the mark edge recording system, the number of codeword bits corresponding to the mark side and the gap side is counted by the accumulated charge detection circuit based on the codeword generated by the modulation circuit. As the resynchronization mark, two types of patterns having an even number and an odd number of codeword bits are prepared, and the accumulated charge up to the resynchronization mark insertion timing is used to determine the accumulated charge up to that time. Select a resynchronization mark approaching zero.

When the reproduced data system is constituted by an AC-coupled amplifier, the low cut-off frequency of the amplifier is set sufficiently lower than the frequency corresponding to the resynchronization mark interval. The correction of the accumulated charge effectively works. When the low cut-off frequency of the reproduction system is increased, resynchronization is performed in consideration of the average level fluctuation amount of the reproduction signal so that the edge detection position shift caused by the level fluctuation falls within the detection window width. It is necessary to shorten the mark interval. However, when the resynchronization mark interval is shortened, the overhead increases.

On the other hand, the shorter the resynchronization mark interval is, the more effective it is from the original purpose of the resynchronization mark, which is the function of correcting the bit deviation between the reproduction clock and the reproduction data.
It is necessary to select an appropriate interval from the increase in heads. 130
In a continuous servo type magneto-optical disk having a diameter of mm, a resynchronization mark of 1 byte is inserted for every 20 bytes of data. In order to enable the resynchronization mark to be detected from only one side edge in the mark edge recording method, a slight increase in the resynchronization pattern length occurs. For example, 1-7
When the mark edge recording method is used in the RLL modulation method,
By inserting a 2-byte resynchronization mark for every 30 bytes of data, the level fluctuation of the reproduced signal (with the self-clocking property maintained) even for a modulation method that originally has no DC freeness. The deviation of the accumulated charge amount from 0) can be reduced, and stable recording and reproduction can be realized.

[0023]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of one embodiment in which the present invention is applied to an optical disk device.

In FIG. 1, an optical disk 101 is rotated at a constant speed by a spindle motor 102, and a recording / reproducing laser beam is focused on a recording film surface of the optical disk 101 by an optical head 103 by a focusing lens. The optical head 103 moves the optical disk 10 in accordance with the information recording position.
1 in the radial direction.

The detection signal 104 detected by the photodetector in the optical head 103 is applied to the low frequency component cutoff filter 10.
5 removes the DC component. This is the detection signal 10
This is because a lot of noise generated from the focal spot tracking mechanism of the light spot is superimposed on the low frequency region of No. 4, and it is necessary to remove this noise component in order to reliably reproduce information.

The signal that has passed through the low frequency component cutoff filter 105 is amplified to a desired signal level by an amplifier 106 and converted to a digital signal 108 by a binarization circuit 107. A clock component is extracted from the digital signal 108 by a PLL (phase locked loop) circuit 109, and the digital signal 10 is
From 8, the reproduction data 111 is generated by the demodulation circuit 110.

At the time of recording information, the recording data 112 is converted through a modulation circuit 113 into a recording code sequence 114 adapted to the optical disk recording / reproducing characteristics. Then, a resynchronization signal 116 generated by the resynchronization signal generation circuit 115 is added at regular intervals in the recording code sequence 114, and the laser driving circuit 117 responds to the signal by the optical head 103.
The laser inside is modulated. The laser light is applied to the optical head 10
The focusing lens in 3 is focused on the recording film surface of the optical disk 101, and recording is performed by forming a recording mark according to the intensity of the light spot.

Next, the format of data recorded on the optical disk 101 will be described with reference to FIG.

Recording and reproduction of information on the optical disk are performed for each unit called a sector. These sectors exist along the information track spirally provided from the inner circumference to the outer circumference of the optical disk, and about 100,000 or more, and each sector is physically identified by an identification number called a sector address. FIG. 2 shows the recording format of one sector on which information is recorded on the optical disc.

A sector head section 201 is provided at the head of the sector.
There is. The sector head 201 includes a sector mark for recognizing the start of a sector, a synchronization signal for starting the generation of a clock signal by the PLL circuit 109, and information such as the above-mentioned sector address as pre-pits at the time of manufacturing an optical disc. It is a part that is made in advance.

The area following the sector head section 201 is a section for recording a recording mark when information is actually recorded.
First, a synchronization signal 202 for locking the frequency of the clock signal generated by the PLL circuit 109 is recorded. A signal having the same function as the synchronization signal 202 also exists in the sector head unit 201, but the signal in the sector head unit 201 is not recorded at the time of actual recording. Therefore, the same clock information as the clock used to record the actual information is recorded in this part, and there is a slight deviation between the clock component in the sector head unit 201 and the clock component at the time of recording. For this purpose, the synchronization signal 202 is used to finely adjust the clock signal generated by the PLL circuit 109 to perform resynchronization.

After the synchronization signal 202, a signal obtained by code conversion of actual user information by the modulation circuit is recorded. The amount of information to be recorded in one sector is determined for each optical disc.
Bytes or 512 bytes. After this predetermined amount of user information, an error correction code (ECC) for detecting and correcting the error when the user information is erroneously detected due to noise or the like during reproduction is recorded. The above-mentioned user information signal 203 and ECC 204 are blocks of a fixed amount; data (1), data (2),..., Data (N), and ECC (1), ECC (2),.
It is divided into C (M) (N and M represent certain integer values), and recorded with a resynchronization signal 205 added to each block.

The resynchronization signal 205 is a portion (defect portion) where recording marks due to scratches on the optical disk cannot be recorded continuously at all (defect portion) while the clock signal in the PLL circuit 109 is not detected at all during reproduction. It is provided in order to cope with a phenomenon in which a shift of an integer period occurs and all subsequent signal detections are erroneous. That is,
By adding a signal that can be identified even if the clock is shifted at regular intervals as a resynchronization signal, detection of the clock signal shift and resynchronization are performed based on the signal during playback, and subsequent information detection is performed. Return to normal operation again. Detection errors in the section from the defective portion to the resynchronization signal are corrected using the error correction signal. After this, the data (K)
(K represents a certain integer value) and the resynchronization signal 205 added between the data (K + 1) and Resync (K), E
The resynchronization signal 205 added between CC (K) and ECC (K + 1) is called Resync (N + K).

The above user information signal 203 and EC
After C204, a buffer unit 206 for adjusting the variation of one sector time caused by rotation jitter or the like follows, and then continues to the head of the next sector.

Next, the configuration of the recording signal pattern of the user information signal 203 will be described with reference to FIG.

The recording code sequence 114 is a signal sequence obtained by obtaining the recording data 112 through a modulation circuit. Generally, the modulation rule used for converting the recording data of the optical disk is RLL (Run-Length Limited) in which the number of "0" s between "1" and "1" of the code symbol obtained by the conversion is in a certain range. System. Since the clock information is extracted from the reproduced signal itself during data decoding during reproduction, the polarity inversion that is the source of the clock information in the reproduced signal must be constant in the reproduced signal in order to stably perform the clock information extraction operation. For example, it must be within the time interval.

The laser drive circuit 117 that has received the recording code sequence 114 modulates the laser emission intensity as a recording signal pattern sequence 301. That is, the recording code sequence 114
Intensity / weakness of the light emission intensity of the laser is inverted corresponding to “1”. A recording mark 302 is formed on an information track of the optical disc 101 during a period in which the light emission intensity is high according to the modulation of the laser light.

Then, at the time of reproduction, a reproduction signal 303 is obtained in which the electric signal potential changes according to the presence or absence of a recording mark. Since a large amount of noise is superimposed on the low frequency component of the reproduction signal 303, the low frequency component cutoff filter 10
5 is used to remove the noise, but if the recording signal pattern sequence 301 contains a signal component in the same frequency domain as the above noise, the information component is lost in the low-frequency cutoff filter 105, This may cause an error during signal decoding. Therefore, in order to realize highly reliable recording and reproduction, it is necessary to devise a method that does not include a low-frequency component in the recording signal pattern sequence 301.

One of the simple calculation methods for detecting the low-frequency component in the recording signal pattern sequence 301 is a method using the accumulated charge (DSV) 304. This means that the weight of the “Low” level of the recording signal pattern sequence is set to −1 and “Hig”
This is a method in which a weight (DSV) obtained by cumulatively adding the weight of each bit is calculated by setting the weight of the h ″ level to +1 and the determination is made based on the magnitude. For example, from the beginning to the end of a recording signal pattern sequence of one sector. When the absolute value of the DSV value is large, this means that the recording data contains a large amount of DC components, that is, the entire duty greatly deviates from 50%.

Therefore, in order to suppress the DC component of the recording signal pattern sequence, it is only necessary to calculate the DSV value and make it as close to 0 as possible. That is, a plurality of patterns for the user information signal 203 and the resynchronization signal 205 to be added between each block of the ECC 204 are prepared, and each resynchronization signal 205 is selected from among them based on the DSV value of each block. I do. Specifically, the K-th (K represents an integer) resynchronization signal 205 (Res
yn (K)), the DSV value during the period from data (1) to data (K) and the level of the recording signal pattern sequence immediately before Resync (K) (hereinafter referred to as signal level) (“Low” / “High”) and data (K +
1) Select using the DSV value alone. However, the calculation of the DSV value for the data (K + 1) alone is performed on the assumption that the first signal level is “Low”.

For example, the DSV value from data (1) to data (K) is a positive number α, the last signal level up to that is “Low”, and the DSV value of data (K + 1) alone is If it is a positive number β (however, the DSV value of the resynchronization signal alone is all 0) (1) If the number of inversions of the signal level during Resync (K) is even, the data (K ) Becomes “Low”, the DSV values from data (1) to data (K + 1) are α + β. When used, the first signal level of the data (K) becomes “High”, so that the DSV values from the data (1) to the data (K + 1) are α−β. ) To data (K + 1) The absolute value of the V value is small (2),
In other words, an odd number of signal level inversions is selected for Resync (K).

Table 1 shows the results of these selections for all cases. Table 1 shows selection criteria for the resynchronization signal.

[0044]

[Table 1]

By selecting the resynchronization signal 205 for the ECC 204 based on the same criterion, low frequency component suppression of the entire recording signal pattern sequence can be realized.

Next, a specific example of the resynchronization signal 205 will be described. However, since the resynchronization signal 205 uses a pattern that is not generated from the modulation rule so that it can be detected even when the clock is shifted by an integer period during reproduction as described above, it depends on the modulation rule used in the modulation circuit 113. I do. Therefore, here, as an example, the (1-7) modulation which is one of the RLL systems (for example, Japanese Patent Laid-Open No. 58-119273).
An example of the configuration of the resynchronization signal 205 in the publication is described below.

First, Table 2 shows the modulation rules for (1-7) modulation. This modulation method is a method of converting a 2-bit data word into a 3-bit code word, and a code word generated by converting data according to this modulation rule always has a symbol "
One or more and seven or less "0" always enter between "1" and "1".

[0048]

[Table 2]

FIG. 4 shows an example of a code word pattern (prohibition pattern) that is not generated by this modulation rule.

(1) and (2) deviate from the rule that one or more and seven or less "0" always enter between "1" and "1". In addition, in the case of this modulation rule, the following prohibition patterns exist in addition to this. First, "1" as in (3)
If there are six “0” s between “1” and “1”, there are no seven “0s” between the next “1”. Also,
As in (4) and (5), "0" is 7 between "1" and "1".
If there is one, “0” is 6 between it and the next “1”.
No more than pieces.

Further, from the prohibitions from (2) to (5), there is an error between "1" including one "1" and "1".
The rule that no symbol of more than bits is entered is established. Therefore, when the pattern of (3) to (5) is included in the resynchronization signal, the interval between successive falling edges or the rising edge from successive rising edges in the binarized reproduction signal. Since the resynchronization signal can be identified because the edge interval is longer than a certain time, the apparatus configuration can be simplified in the case of a reproducing system using the front and rear edge independent detection method (for example, see Japanese Patent Application Laid-Open No. 2-183471).

FIG. 5 shows a specific example of the structure of the resynchronization signal 205 using the prohibition pattern (5) shown in FIG. Since this pattern includes three bits of the code word immediately before the synchronization signal, the number of signal level inversions in each pattern changes according to the immediately preceding code word, but the number of signal level inversions in (pattern 1) is (pattern 1). The resynchronization signal 205 for suppressing the low-frequency component of the recording signal pattern sequence can be constituted by these two types, which are always once more than that of 2) and always have different evenness. In addition, the resynchronization signal 2
05 is also convenient in the case of a reproducing system using the leading and trailing edge independent detection method.

In addition to the specific configuration example of the resynchronization signal 205 shown here, a plurality of resynchronization signals 20 are used for suppressing low frequency components of the recording signal pattern sequence.
It is possible to form a set of five.

Finally, FIG. 6 shows the transfer characteristic of the low-frequency cutoff filter 105 used when reproducing a recording mark recorded by a recording signal using the resynchronization signal 205. Assuming that the interval between the resynchronization signals is T seconds, the reproduction signal obtained by reproducing this recording mark hardly contains recording signal information at a frequency of 1/2 THz or less. Therefore, since only the noise component is contained in the region below this frequency in the reproduced signal, the noise component can be efficiently removed by the low frequency component cutoff filter 105. Therefore, it is necessary to design the interval T of the resynchronization signal in consideration of the recording density and the frequency domain of the noise component added to the reproduction signal.

[0055]

By using this information recording / reproducing method,
It is possible to suppress the low frequency component of the recording signal by the modulation method which does not originally have the DC-free property, and it is possible to remove the low frequency component where much noise is superimposed on the reproducing side without losing the information component. High recording and reproduction can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an implementation example in which the present invention is applied to an optical disk device.

FIG. 2 is a conceptual diagram showing an information sector on an optical disc and its recording format.

FIG. 3 is a waveform diagram showing a recording signal pattern sequence configuration of a user information signal.

FIG. 4 is a conceptual diagram showing a code word pattern (prohibition pattern) that is not generated by the modulation rule (1-7).

FIG. 5 is a conceptual diagram showing a specific configuration example of a resynchronization signal.

FIG. 6 is a graph showing a transfer characteristic of a low-frequency component cutoff filter;

[Explanation of symbols]

101: optical disk, 102: spindle motor, 10
3 optical head, 104 detection signal, 105 low frequency component cutoff filter, 106 amplifier, 107 binarization circuit, 108 digital signal, 109 PLL circuit, 1
10 demodulation circuit, 111 reproduction data, 112 recording data, 113 modulation circuit, 114 recording code sequence, 11
5 resynchronization signal generation circuit, 116 resynchronization signal, 117
... Laser drive circuit, 201 ... Sector head section, 202 ...
Synchronization signal, 203: user information signal, 204: ECC,
205: resynchronization signal, 206: buffer unit, 301: recording signal pattern sequence, 302: recording mark, 303: reproduction signal, 304: accumulated charge (DSV)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Fumiyoshi Kirino 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. Central Research Laboratory

Claims (4)

[Claims] 1. An information reproducing apparatus for reproducing data on a recording medium by using a predetermined encoding rule, wherein a specific pattern which can be separated and detected from the data inserted at regular intervals in the data is reproduced. When the interval is T seconds, 1
An information reproducing apparatus having a low-frequency component cutoff filter for removing a frequency component equal to or lower than / 2 THz. 2. The information reproducing apparatus according to claim 1, wherein
The specific pattern includes a first group in which the number of appearances of the code word “1” is an even number and the number of elements is 1 or more, and a first group in which the number of appearances of the code word “1” is an odd number and the number of elements is 1 or more. 2
An information reproducing apparatus, comprising: 3. An information recording / reproducing apparatus for recording data on a recording medium by using a predetermined encoding rule, wherein the information includes a code word "1" which can be detected separately from the recorded data. 1st with an even number of occurrences and 1 or more elements
And a specific pattern generation circuit that inserts a specific pattern having a code word “1” in which the number of appearances of the code word “1” is an odd number and the number of elements is 1 or more at regular intervals, and reproduction of the specific pattern. An information recording / reproducing apparatus comprising: a low-frequency component cutoff filter for removing a frequency component equal to or lower than 1/2 THz in a reproduced signal when an interval is T seconds. 4. The information recording / reproducing apparatus according to claim 3, further comprising a cumulative charge detecting circuit for counting the number of codeword bits corresponding to the mark side and the gap side based on the codeword. An information recording / reproducing apparatus, wherein one of the first group and the second group in which the accumulated electric charge is reduced to 0 is selected according to an output of a circuit and inserted into the recording data.