JP2613199B2 - Information reproducing method and optical disk - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk file device, and particularly to a recording / reproducing method suitable for improving data recording density.

[Conventional technology]

As a multi-level amplitude signal discriminating circuit, Japanese Patent Application Laid-Open No. 61-94416 discloses a configuration example for a multi-level modulation signal used in a general communication channel. The identification circuit described above is A / D
By properly controlling the DC offset of the input signal of the converter, there is an effect that the threshold value of the identification circuit is always kept optimal. However, it is difficult to apply the method to a reproduced signal detected from an optical disk or the like because the assumed signal form is different. That is, it is necessary to consider an identification method in consideration of the recording film characteristics of the optical disk. When a reproduced signal obtained from a pit recorded on an optical disk is detected by a photodetector and amplified by an AC amplifier, the average level fluctuates up and down due to the density of the recorded data. A recording scheme in which recording pits are uniformly recorded in advance over the entire area like a compact disc, and the average level is essentially kept substantially constant (referred to as a DC-free modulation scheme).
Then, the fluctuation of the average level is small. However, when an unrecorded area exists as in a write-once optical disk, a level fluctuation occurs due to the presence or absence of a pit. In the case of amplifying a signal using a DC amplifier, if the temperature drift of the amplifier itself is large, it becomes difficult to accurately identify many threshold values. This phenomenon also exists in the reproduction system of a compact disk.

In general, on optical disks, as shown in "Introduction to Video Disks and DADs", Iwamura, Corona, P212-P215, the zero cross point of the eye pattern (usually half the level of the maximum amplitude of the reproduced signal). , Has been binarized. If the signal-to-noise ratio of the reproduced signal is sufficiently high and the fluctuation of the DC level of the signal is small, it can be quantized to a value of three or more by a threshold of two or more. However, since most recording films currently used are intended to obtain binarized information, recording is performed using only a saturation region where the amplitude of a reproduction signal with respect to a recording optical pattern is maximized. Therefore, at present, recording is performed in the unsaturated region,
It is difficult to detect the peak value of the pit and use it as reproduction data unless some correction means or an accurate reference level is obtained.

[Problems to be solved by the invention]

In the prior art, in order to detect a difference in the amplitude of a reproduction signal and obtain multi-valued data, the recording medium itself does not have a level serving as a reference for a threshold value. It was generally handled as binary data.
It is conceivable that one information point (pit) has three or more values of information (for example, 0, 0.5, 1, or 0, 1, 2,...) As a direction of high density.

An object of the present invention is to form a recording pit at a saturation level in advance as a prepit at the time of producing a disc master or before recording user data, and to set a peak level of a reproduction signal of the recording pit and a level of an unrecorded area ( Alternatively, by setting a plurality of thresholds using a mirror surface level having no track guide groove as a reference, multi-level recording is performed to achieve high density. In addition, the pre-pit of the reference level is also used as a fixed clock, and is used as reference data for generating a recording (modulation) clock and generating a reproduction (demodulation) clock when recording information in an area between the pre-pits. Is also possible.

[Means for solving the problem]

The object of the present invention is to provide a pit having a predetermined saturation level as a pre-pit, generally a quarter of the wavelength of the laser light source used, in the header pit of each sector or at a constant interval in the data area. At the time of reproduction, the peak level obtained from the pre-pit is regarded as the maximum amplitude value of the recording pit, the level of the reproduction signal from the unrecorded area is regarded as the minimum amplitude value, and the level therebetween is divided by several threshold values. In addition, this is achieved by enabling handling as multi-valued data by the threshold value. At the time of recording, a pit is generated using an unsaturated region where the amplitude of the reproduction signal changes with respect to the recording power.

As described above, multi-value recording of information can be realized.

[Action]

By setting the depth of the reference prepit provided in advance to a quarter of the laser wavelength of the light source used and by making it sufficiently large with respect to the diameter of the reproduction light spot, a maximum amplitude can be obtained as a reproduction signal. Can be. The peak value of the reproduction signal can be used as a reference level when generating a reproduction pulse. Since the recording film characteristics can be considered to be constant in a small area, for example, in one sector, it may be provided in the header area of each sector. Of course, the reference pits may be arranged uniformly in the data area.

If this reference level is used as a reference value for setting a threshold for data identification, a plurality of values can be converted into a single bit as long as the signal-to-noise ratio of the reproduced signal permits, without using a special correction means in the detection circuit. Can correspond. That is, it is possible to realize multi-value recording, which is one means of high-density recording. Further, if the reference bits are provided at regular intervals in the data area, it can be used as a clock phase reference at the time of modulation / demodulation, whereby the clock for data modulation / demodulation can be obtained stably and accurately.

〔Example〕

Hereinafter, an embodiment of the present invention will be described. Fig. 1 (a)
Is an optical disk 1, which is formed by a concentric or spiral track guide groove and a plurality of areas (sectors) formed by a header region 2 containing address information and the like.
It has a configuration divided into FIG. 1 (b) is a diagram showing an example of a format for a certain sector including the header region. In the format shown in FIG. 1B, an unrecorded area and an area in which the amplitude of the reproduced signal is maximum are provided as one area of the level detection signal 5 in the header area 2 of each sector. Sample and hold each level of the user data area 7 following
5 is a configuration example in the case of using as a reference of a quantization threshold value of multi-valued recording data recorded in. At the beginning of each header area, a sector mark 3 indicating the start of a sector is placed.
Next, a synchronization signal 4 indicating clock generation and demodulation start,
The level detection signal 5 and the address signal 6 correspond to the header area 2
As a pre-format. In FIG. 1B, the level detection signal 5 is placed immediately after the synchronization signal 4. However, even immediately after the sector mark 3 or immediately after the address signal 6, the area of the detection signal 5 is detected. If you decide, you can do it.

FIG. 1C shows an example of the pit arrangement of the level detection signal 5. The level detection pit 8 is preformatted so that the pit depth is about one-fourth of the wavelength of the laser light used, and the pit width and pit length are sufficient for the signal level sufficient for the reproduction light spot diameter. The size is such that it can be obtained. The reproduction signal level from the level detection pit 8 is sampled and held, and the held value is used as the maximum amplitude level. Following the level detection pit 8, an unrecorded area 9 is provided. Similarly, the reproduction signal level of the unrecorded area 9 is sampled and held to be used as an unrecorded reproduction level. FIG. 2 shows a circuit configuration example for sampling and holding each level. FIG. 3 shows a time chart of the circuit operation. In FIG. 2, a reproduction pulse 11 that has already been binarized is input to a synchronization signal detection circuit 10. The reproduction pulse 11 may be generated by a conventionally used generation circuit. Also, the detection of the synchronization signal 4 may be a conventionally used configuration. For example, a method is conceivable in which a pattern match is determined every several bits of a data pattern using a shift register, a majority decision is taken for the determined logic level, and a detection pulse is output. The detection pulse 12 detected by the detection circuit 10 is input to the delay circuit 13. The delay circuit 13 can be easily configured using a normal delay element or a shift register. The role of the delay circuit 13 is
Since the level detection pit 8 is later than the time at which the synchronization signal detection pulse 12 is output, a delay is made by this time difference to generate a sample pulse for sampling the reproduction signal level of the level detection pit 8. It is.
The sample pulse uses the delay pulse 14 and the hold pulse uses the delay pulse 14 as a monomultivibrator (MM) 15
Is used. Using these control pulses, the level of the reproduced signal 19 inverted and amplified by the amplifier 18 is held by the sample / hold circuit (S / H) 17. Here, it is desirable to use a DC amplifier having a small drift as the amplifier 18. Similarly, for the level of the unrecorded area 9 located immediately after the level detection pit 8, the delay circuit
20, a mono multivibrator (MM) 22 and a sample and hold circuit 24 hold the data. These elements are easily available as off-the-shelf elements. Next, the operation of the above circuit, including the following signal processing, will be described in detail with reference to the time chart of FIG.

In FIG. 3A, a detection pulse 12 is output from a pulse train of the reproduction pulse 11 by a synchronization signal detection circuit. From the detection pulse 12, a delay pulse 14
Is generated. With the delay pulse 14, the level of the level detection pit 8 of the reproduction signal 19 is sampled by the sample and hold circuit 17. Next, the delay pulse 16 generated by the mono multivibrator 15 from the fall of the delay pulse 14
Thus, the reproduction level of the level detection pit 8 is held. The sampled and held level is the maximum level signal
As 25, it is input to the inverting input of the comparator 27 via the resistor 29. On the other hand, a delay pulse 21 is generated from the delay pulse 14 by the delay circuit 20. The delay pulse 21 samples the reproduction signal level of the unrecorded area 9. As a hold pulse, a minimum level signal 26 is obtained by using a delay pulse 23 obtained by delaying the delay pulse 21 by a monomultivibrator 22.
The level signal 26 is connected to an inverting input of a comparator 28 by a resistor.
Entered via 30. Resistors 29, 30, and 31 have a maximum level of 25
And the minimum level 26 to create two thresholds. FIG. 2 shows a case where there are two thresholds, but the same applies to a case where there are three or more thresholds. Only when the level of the reproduction signal 19 to the non-inverting input is higher than the input level to the inverting input of the comparator 27, the logical level of "H" level is output by the comparator 27. The same applies to the comparator 28. Next, a method of quantizing into multi-valued data will be described with reference to FIGS.
In FIG. 3 (b), the information signal is recorded with pits indicating ternary amplitudes of 0 (unrecorded), 1, and 2.
It is assumed that the user data is as shown in FIG. Resistance 29 ~
By the thresholds 34, 35 set by 31, the comparator 27,
The respective outputs 32, 33 of 28 are as shown in the figure.
Here, the output 41 of the AND gate 36 becomes "H" level only when both the outputs 32 and 33 become "H". AND gate 37
Is output from the inverter 39 to the comparator output 32.
Becomes “H” level only when both the inverted logic level and the comparator output 33 become “H”. AND gate 38
As the output 43, the level obtained by inverting the comparator outputs 32 and 33 by the inverters 39 and 40 is input, so that the output 43 becomes the “H” level only when the inverted logic levels are both “H”. Here, the configuration is such that when the data level is “0”, that is, when no recording is performed, the AND output 43 is set to “H”. Rather, when both of the AND outputs 41 and 42 are “L” level, It is more convenient to determine that the level is "0". In this case, if you use a NOR gate with AND outputs 41 and 42 as inputs,
Can be determined.

Next, a method of recording such multi-value information (for example, a case of ternary recording) will be described. FIG. 4 is a diagram showing a change in a reproduction signal amplitude (or a reproduction signal peak value from a pit) with respect to a recording light power;
It is a general characteristic curve of a write-once type recording film. Recording power in a small space than P _1, the pit is not formed. Small space than P ₂ recording power at greater than P ₁ is an unsaturated region, the reproduction signal amplitude increases with increasing write power. Large area recording power than P ₂ is a saturation region, even the reproduction signal amplitude recording power changes hardly changes. Generally, when binary data "0" and "1" are recorded, a recording bit of data "1" is formed by a recording power corresponding to the saturation area. Normally, in the non-saturated region, the reproduction signal amplitude changes with the fluctuation of the recording power. Therefore, this is not used in binary recording. However, if the recording pulse width and the recording power are set to appropriate values according to the recording radius on the disk, Multi-level recording of three or more values is possible. Currently, the signal-to-noise ratio of an additional optical disk is 60 dB at a measurement bandwidth of 30 kHz.
The above is adopted, and up to four-level recording can be realized even at the current level considering the margin of the signal-to-noise ratio.

Now consider the case of ternary recording. The level of the threshold 35 and 34 respectively S _A, when the S _B, when data "0", may be recorded with a small power than P _A, originally, the data "0"
Therefore, at this time, the recording power is not normally irradiated. The data "2" when, although may be recorded with greater power than P _B, better saturation recording was line summer in this case P ₂ or more power is stable. P _A and P _B when the data "1"
Will be recorded at the intermediate power. Next, an embodiment of the recording power setting circuit is shown in FIG. In FIG. 5, the user data (recording data) 50 to be recorded enters the serial data input of the shift register 51. The shift register
The 51 data shift clock 52 is also input to the counter 53 at the same time. 2 ¹ of the output 54 of the counter 53 is connected to the data Raţ cyclamate poke input latch 55. That is, when the value of the counter 53 is "2", the data from the shift register 51 is latched to perform serial / parallel conversion every three bits. The output of the latch 55 is a ROM in which power data based on a preset recording radius is written.
(Read only memory) Connected to address inputs 56 to 58, recording power information corresponding to data is stored in the ROM 56.
Output from ~ 58. In the example of Fig. 5, RO with 8-bit output
Although M is used, an arbitrary bit may be used depending on the required precision. The output of ROM56-58 is 3
The D / A converter 62 is connected to state buffers 59 to 61 and activates only one of the buffers in accordance with the recording radius position or other condition parameters to activate only one of the buffers. Can be entered. The D / A
The analog level of the (digital-to-analog) converter 62 is connected to the power setting input of the laser driver. The recording data 50 is also input to the delay circuit 64, and a pulse delayed by the operation time of the recording power setting circuit is connected to the data input of the laser driver 63. The delay circuit 64 can use a shift register. In this case, the clock 52 is used as a shift clock. In FIG. 5, the contents of the ROMs 56 to 58 are values determined in advance by test recording. 6, one embodiment of the laser driver 63 is shown in FIG. The power setting level 70 from the D / A converter 62 is input to the base of a transistor 74 that determines the value of the current source of the current switch composed of the transistors 72 and 73. In the example of FIG. 6, the case where the semiconductor laser 75 is driven at a negative potential is shown. Therefore, the power setting level
70 is also given as a negative potential, and if it is not within a predetermined voltage range, a level shift circuit may be used. The current value is set to a value obtained by dividing the emitter potential of the transistor 74 and the potential difference of the negative power supply -V by the value of the resistor 76. Also transistors
In the current switch composed of 72 and 73, since the transistor having the higher base potential is turned on, the current set to the semiconductor laser is applied when the data input 71 is at the “H” level. Here, the OR gate 77 sets the logic level
It has the function of converting TTL to ECL (Emitter, Coupled Logic) level, and has Zener diodes 78,7.
9 causes a level shift in the negative potential direction. Resistance 80, 81
ECL termination (pull-down) resistor. With the above operation, a recording pulse corresponding to the data input 71 can be generated with the recording power set at the power setting level 70. In addition, a light emission current of 82 for the purpose of emitting a reproduction light level for reproduction.
During playback, the laser power is weaker than during recording.
Is allowed to emit light. The resistor 83 is a resistor for preventing an overcurrent from flowing when the input of the power setting level 70 is opened for some reason, and has a relatively high resistance value (for example, 100 kΩ or more).

Next, in the case of 2-7 modulation, the effect of improving the bit density will be described by taking four-level recording as an example. 2-7 modulation refers to an RLL (run-length-length) with a density ratio of 1.5 that allows two to seven "0s" to be included between "1" and "1" of the modulated codeword.
Limit) code. FIG. 7 shows a code word pattern after modulation. The recording word generation circuit shown in FIG. 5 converts the code word 100 from serial data to parallel data every three bits. In each of the divided block data 101 to 105, at most one "1" can exist. This is evident from the rules for 2-7 modulation. The position of "1" in each block is "3" at the beginning, "2" at the center, "1" at the end, and "0" at the end. Since the example shown in FIG. 7 is a quaternary recording, it can be reproduced by adding another level threshold to the embodiment of FIG. As described above, 4
Can be valued. Coded quaternary data
If expressed as the same bit length as 100, it will be like the quaternary code word 106 shown in FIG. Although the quaternary code word can be recorded on the disk as it is, if there is a concern about the interference of adjacent bits, the quaternary code is always inserted with "0" between the quaternary bits. The code word 107 may be generated and recorded. Even in the latter case, the original code word
The bit density can be increased by a factor of 1.5 compared to recording 100 as it is.

In the embodiment shown in FIG. 5, there is no particular circuit for generating the quaternary code sequence 106 and the corrected quaternary code sequence 107 as shown in FIG. In order to generate the code string 106, the transfer rate of the recording data 50 and the clock 52 shown in FIG. 5 is increased by three times, and the time corresponding to the current three bits becomes one bit of the quaternary code word. . At this time, it is necessary to input the data to the laser driver 63 for each bit of the code word 106. This can be dealt with by inputting the clock of the original frequency as the data input 71. FIG. 8 shows a time chart of the above operation. Clock 110 is the original frequency clock, and code word 111 has a transfer rate corresponding to clock 110. Here, the clock 52 in FIG.
A clock 112 having a frequency three times that of the clock 110 is used instead of the clock 110, and a code word 1 corresponding to the clock 112 is used instead of the recording data 50.
Enter 13. In this way, the output of the latch 55 input to the ROMs 56 to 58 is given by the quaternary code word 114. If the code word 114 is recorded by the original clock 110, pits can be formed at the recording rate of the quaternary code word 106 shown in FIG.

According to the above embodiment, multi-value recording / reproduction can be realized. The present invention may be implemented by a conventional configuration such as an optical system (optical head) and a detection system. Also the recording characteristic shown in Fig. 4, to perform multi-value recording, the recording power range of the non-saturation region, that is, towards the large difference medium P ₁ and P _2, the slope of the characteristic curve becomes gentle Therefore, stable recording can be performed even if the recording power setting accuracy is low. The present invention can be applied to, for example, a magneto-optical disc and a phase-change disc other than the optical disc using the perforated recording film. In magneto-optical recording, in particular, information on concavo-convex pits detected by a direct change in the amount of reflected light and magnetization domain information to be reproduced by detecting a change in the plane of polarization of the reflected light can be optically separated. Detection is easy when the level detection pits are dispersed and arranged with uneven pits in the area.

In the case of optical recording, since the recording characteristics are generally nonlinear with respect to the recording power, the threshold values set in the circuit of FIG. This point is considered to be a significant difference from the transmission path.

In the embodiment shown in FIG. 1, the level detection signal 5 is provided in the header area 2 and it is assumed that the recording characteristics are uniform in one sector. A level detection pit 8 may be provided.
FIG. 9 shows a detection method when a data pit is recorded between the level detection pits. In FIG. 9, pits 120-123
Is a pit train for level detection, and a recording pit 124 is recorded between the level detecting pits at a multi-level level. Now, for the level detection pits 120 to 123, by setting the pit depth to about 1/8 of the laser beam wavelength and preformatting, the photodetectors are arranged in the direction that receives the light quantity change in the linear velocity direction, and the difference between the two. Can be detected as a differential signal. In FIG. 9, a signal 125 is a front-back differential signal detected by the above-described front-back differential system. If the recording pits 124 are recorded as dark and light pits, the level detection pits can be separated and detected with almost no appearance in the differential signal 125. Playback signal 126
Is a signal obtained by directly detecting the amount of reflected light from the pit. As a method of detecting the level detection bits 120 to 123, the differential signal 125 is directly binarized by a slice level provided above and below to generate pulses 127 and 128, and the flip-flop is set at the rising edge of the pulse 127 and reset at the rising edge of the pulse 128. If used, the position of the level detection signal can be detected. By sampling the level of the reproduction signal 126 using the detection pulse 129, a reference level can be obtained. Thereafter, demodulation can be performed by the same circuit configuration as in FIG. In addition, by using the detection pulse 129 as a phase reference for generating a recording / reproducing clock, data can be recorded in a modulation method that does not allow self-clocking. Further, it can be used as an encoder signal for rotation control.
In the case of FIG. 9, the polarity of the data signal is
Although the signal polarity is in the same direction as the signal polarity from 0 to 123, if a pit is formed, the medium may have a high reflectance and reverse polarity. By dispersing the level detection pits in this way, the number of reference level sample points increases, the effect of fluctuations in recording film sensitivity and recording power can be reduced, and level clamping is facilitated. Thus, the fluctuation of the average level due to the density of the data pattern can be suppressed. Therefore, multi-level recording is possible without using a DC-free modulation method.

〔The invention's effect〕

According to the present invention, a plurality of threshold values can be generated based on the value of the level detection bit at which the reproduced signal pre-formatted is maximum and the value of the unrecorded area, so that multi-valued recorded data can be stably recorded. It can be handled and is effective in improving the bit density of data.

[Brief description of the drawings]

FIG. 1 is a diagram showing a format configuration of an optical disc for carrying out the present invention, FIG. 2 is an example of a circuit for reproducing a multi-valued information pit signal using a plurality of threshold values, and FIG. 3 is a circuit shown in FIG. 4 is a recording characteristic, FIG. 5 is an example of a recording circuit for performing multi-value recording, FIG. 6 is a configuration example of a laser driver, and FIGS. 7 and 8 are binary codewords. FIG. 9 is a diagram showing a process of generating a multi-level code word from the data, and FIG. 9 is a diagram showing a method of increasing the density by multi-level recording. 1 ... optical disk, 8 ... level detection pit, 17,24 ...
… Sample hold circuit, 27, 28 …… Comparator, 75
…… Semiconductor laser.

Claims (6)

(57) [Claims] 1. A reproducing method for reproducing a recording medium on which a multilevel data signal identified by an amplitude or a peak value of a reproduced signal is recorded along a track, wherein a reference mark is provided on the track, A maximum level of the data signal is set based on a signal obtained from the reference mark, and a minimum level of the data signal is set based on a signal obtained from an unrecorded area of the track, and a plurality of levels are set between the maximum level and the minimum level. An information reproducing method for setting a threshold value, and quantizing the data signal using the plurality of threshold values to identify a multilevel level. 2. The track is divided into a plurality of sectors,
2. The information reproducing method according to claim 1, wherein each of the sectors has a header area and a data area, and the fiducial mark is provided in the header area. 3. The information reproducing method according to claim 1, wherein the reference marks are formed at equal intervals along a track, and the reference marks are used as a reference for forming a clock. 4. The information reproducing method according to claim 1, wherein an optical disk is used as the recording medium, and the reference mark is a bit having a quarter depth of a signal reproducing laser wavelength. 5. An optical disk having substantially concentric tracks, wherein the tracks are divided into a plurality of sectors, each of which has a header area and a data area, wherein the header area is formed by phase pits. Address signal area, and a level detection signal area provided separately from the address area. The level detection signal area has a spot of the signal reproducing laser at a quarter depth of the signal reproducing laser wavelength. An optical disc having a phase pit whose length in the track direction is longer than its diameter and an unrecorded area whose length in the track direction is longer than the spot diameter of the laser for signal reproduction. 6. An optical disk having substantially concentric tracks is irradiated with a laser, a laser beam reflected by the optical disk is detected, a reproduction signal is obtained, and information recorded on the optical disk is reproduced based on the reproduction signal. In the information reproducing method, the track is divided into a plurality of sectors, each of which has a header area and a data area, wherein the header area has a phase of a quarter depth of a signal reproducing laser wavelength. A reproduction signal level obtained from the phase pit is sampled and held as a first level; a reproduction signal level obtained from the unrecorded area is sampled and held as a second level; An information reproducing method for forming a threshold having an intermediate level between the first and second levels and discriminating the reproduction signal based on the threshold.