JP2738700B2 - Signal reproducing method, information recording medium, information recording / reproducing method, and optical disk apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a signal reproducing system, and more particularly to a signal reproducing system used for reading an optical recording medium such as an optical disk or an optical tape. The present invention relates to a signal reproducing method suitable for detecting data stably and accurately irrespective of reflectivity fluctuation or the like. Further, the present invention relates to an information recording medium, an information recording / reproducing method, and an optical disk device used therein.

[Conventional technology]

A method of providing a servo byte area for the purpose of performing data modulation / demodulation, focus servo, and tracking servo on a recording medium is described as a sample servo format, SPIE Procedures, Vol. 695, Optical Mass Data Storage, 2 (1986)
(SPIEProceedings Vol.695, Optical Mass Data Storge
2,1986). This paper does not specifically mention a data modulation method, but at present, a modulation method having a high DC-free property in which the average value does not easily change due to the density of the data pattern is recommended. Generally, the data modulation method is evaluated based on the self-clocking property, the density ratio, the detection window width, and the like in addition to the DC-free property described above. For example, in an MFM (Modified FM) system used for a magnetic disk or the like, a "1" is generated at the back of a bit cell in response to a "1" of a data bit, and the "0" of a data bit is generated. When two or more "0" s are consecutive, "1" is generated in front of the bit cell for the second and subsequent "0" s. Therefore, even when “0” or “1” continues in the data bit, “0” and “1” are not necessarily included in the recording pulse.
Inversion occurs at an appropriate frequency. Therefore, the DC free property is high, and the demodulation clock can be generated from the recorded data itself. (On the other hand, self-clocking is possible.) On the other hand, in order to accurately demodulate data, it is necessary to check the presence or absence of a recording bit for a half detection window width of the data bit. On the other hand, NRZ (non-
Return-to-zero) modulation is based on the data bits "1",
This method records "0" as it is as a code word, and has essentially no DC-free property or self-clocking property. However, since the detection window width is the same as the data bit width, it is a method that is strong against jitter fluctuation. Conceivable. According to the sample servo format as described above or a format of the same type, the modulation method can be determined regardless of the presence or absence of the self-clocking property of the data itself. However, it is difficult to perform DC-free demodulation in an AC-coupled amplification system unless some means is used. For example, the case where a considerable number of "0" s are continuous and the case where "1" s are continuous are such that the signal level becomes the same in the amplification system in which the DC component is cut. "And" 1 "cannot be distinguished.

Further, even when a method having DC-free property is used as a modulation method, a change in the reflectivity of a disk or a change in a reproduction signal level occurs due to the influence of retardation.

As described above, in order to obtain accurate information from the reproduction signal of the optical disc, it is necessary to suppress the fluctuation of the reproduction signal itself while improving the DC-free property in the reproduction process.

[Problems to be solved by the invention]

In the above-mentioned prior art, usable modulation systems are limited to those having good DC-free property and self-clocking property. However, even with a modulation method that does not have the above characteristics, there is a modulation method that has a wide detection window width and is stable against jitters and the like. Also, fluctuations in the reproduction signal level that occur depending on the disk characteristics pose a problem in accurate information reproduction.

An object of the present invention is to generate a modulation / demodulation clock using a sample servo format, and at the same time, clamp a signal level near a servo pit or a signal level in a specially provided unrecorded area to a specific level by a clamp circuit. Therefore, it is an object of the present invention to enable stable demodulation by compensating for DC-free characteristics and suppressing signal level fluctuations that occur depending on disk characteristics. As a method of clamping, it is also possible to detect an unrecorded area existing in the data recording area at the time of reproduction and clamp the signal level of the unrecorded area. This method can be applied even if it is not a sample servo format.

[Means for solving the problem]

The above object can be achieved both when using the sample servo format and when not using it. When a sample servo format is to be used, it is achieved by using a region near the servo pit or a dedicated clamp region and clamping the reproduced signal level corresponding to this portion to a specific level by a clamp circuit. . When the sample servo format is not used, that is, in the continuous groove format, an unrecorded area in the data recording area is determined at the time of reproduction, and the reproduction signal level in this area may be similarly clamped. As the unrecorded area in the data recording area, it is convenient to use the area before or after the preformatted header section or immediately after the resynchronization mark (RESYNC) pattern inserted in the data.

[Action]

The clamp circuit is turned on intermittently for a time corresponding to the aforementioned clamp area. When the clamp circuit is turned on, the signal level is clamped to a preset DC potential for that section. In a section other than the clamp region, the signal level is off, and the signal level is held by a time constant determined by a capacitor inserted in series with the signal line and a resistor inserted between the signal line and the ground. Since the clamp area has an unrecorded signal level, if the level is clamped to a predetermined DC potential, the DC component can be compensated even for the non-clamp area and a reproduced signal with little fluctuation can be obtained. it can.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First
FIG. 2 is a block diagram showing an embodiment of a signal reproducing system according to the present invention, FIG. 2 is a diagram showing an example of a disk format of the above embodiment, and FIG. 3 (a) shows a case where MTF modulation is recorded as position data. 3 (b) is an MFM
FIG. 3 (c) is a signal waveform diagram of each component when recording the modulation as edge data, FIG. 3 (c) is a signal waveform diagram of each component when the NRZ modulation is performed,
FIG. 4 is a diagram showing a configuration example of the binarization circuit of FIG. 1, FIG. 5 is a diagram showing an operation of the binarization circuit, FIG. 6 is a diagram showing a configuration example of a clamp signal generation circuit, FIG. 7 is a diagram showing the operation of the generation circuit, FIG. 8 is a diagram showing a configuration example of the level clamp circuit, and FIG. FIGS. 10 (a) to 10 (c) show an example of the configuration of the binarization circuit after the level clamp processing, and FIGS. 11 (a) to 11 (c).
FIG. 10 is a diagram showing the operation in each case of FIG. 10, FIG. 12 is a diagram showing the operation of the reproduction clock generation circuit, and FIG. 13 is a configuration example of a level clamp circuit for generating a clamp pulse by the reproduction clock. FIG.

FIG. 1 shows only the detection optical system and the detection electric system among the components of the optical disc apparatus, and the control system of the optical spot, the recording electric system and the like are omitted. In FIG. 1, a disk 1 is rotated by a spindle motor 2. The laser light emitted from the semiconductor laser 3 is
After being converted into a parallel light beam by the collimating lens 4, it passes through the beam splitter 5, is reflected by the galvanometer mirror 6, and is condensed on the recording film on the disk 1 by the objective lens 7. The position of the objective lens 7 is controlled so as to always focus on the recording film surface by moving the position of the objective lens 7 up and down in accordance with the vertical movement of the disk 1. With respect to the fluctuation of the disk 1 in the radial direction, by controlling the rotation angle of the galvanometer mirror 6 and controlling the position of the entire optical head, the light spot is always positioned on the target track. . The objective lens 7 may be moved in the vertical and radial directions by using a fixed mirror as the galvanometer mirror 6. The detection system shown in FIG. 1 shows a configuration in which a perpendicular magnetization film (magneto-optical medium) is used as the recording film of the optical disk 1.

Next, the principle of recording, erasing, and reproducing information will be briefly described. When recording information, the light intensity of the semiconductor laser 3 is modulated in accordance with the recording data to locally increase the temperature of the recording film. It is assumed that the magnetization direction of the perpendicular magnetization film on the disk 1 is set to one of the upper and lower directions in advance. When the temperature of the recording film reaches the Curie point, the magnetization of the recording film is lost due to the thermomagnetic effect. At this time,
If a magnetic field in a direction opposite to that in the unrecorded state is applied by the external electromagnetic coil 8, a region where the temperature rises locally in the cooling process and a region where the magnetization is locally opposite to the surroundings is formed.
This is the record. To delete the information once recorded,
This can be achieved by setting the light intensity of the semiconductor laser 3 to the same level as during recording in the area to be erased, and setting the externally applied magnetic field in the direction opposite to that during recording.
In the above-described recording / erasing example, the case where the light intensity is modulated is described. However, the light intensity may be fixed, and a magnetic field modulation method by inverting the externally applied magnetic field in accordance with the recording data may be used. . Information is reproduced by detecting the rotation angle of the plane of polarization of the reflected light. The reflected light from the disk 1 passes through the objective lens 7 again, is reflected by the beam splitter 5, and is guided to the half-wave plate 9. The light whose main axis of the polarization plane is rotated by 45 degrees by the half-wave plate 9 transmits the P-polarized light component by the beam splitter 10 and
The polarization component is reflected. The component light on the transmission side is focused on the photodetector 14 by the lens 12. The component light on the reflection side is a lens
The light is condensed on the photodetector 13 at 11. The ratio between the P-polarized component and the S-polarized component changes according to the change in the magnetization direction of the recording film.
Therefore, if the difference between the signals detected by the photodetector 13 and the photodetector 14 is calculated, a change in the magnetization direction can be detected. The amplifier 16 is a differential amplifier, and the output of the amplifier 16 becomes a magnetization signal (data signal) 104. Meanwhile, Disk 1
Since the reflected light from the upper hole pit does not involve rotation of the plane of polarization, the change in the amount of light incident on the photodetectors 13 and 14 is theoretically the same. Therefore, no signal due to the hole pit appears in the data signal 104. To detect the pit signal 102,
The sum of the signals detected by the photodetectors 13 and 14 may be obtained by the amplifier 18. At this time, the change in the magnetization direction is P
Since the polarization component and the S-polarization component appear with opposite phase intensities, the pit signal 102 does not show a change in the magnetization direction as a signal. As described above, a signal accompanied by a change in the amount of reflected light due to a pit or the like on the disk 1 is the pit signal.
Signals appearing only at 102 and accompanied by a rotation change in the plane of polarization appear only in the data signal 104. The pit signal 102 becomes a pit pulse 106 binarized by the binarization circuit 22. The level clamp circuit 26 is a circuit for clamping the pit position on the disk 1 or the level of the magnetization signal in a clamp-only area to a certain constant value. The correction data signal 110 is converted into a data pulse 112 by the binarization circuit 28, and the original demodulated data 116 is reproduced by the demodulation circuit 32 by using the clock 114 generated by the reproduction clock generation circuit 30. The detailed configuration and operation of the main components in the reproduction circuit 20 will be described later.

Next, an embodiment of a disk format for carrying out the present invention will be described. FIG. 2 is an enlarged view of a part of the disk 1. Tracks for recording information are indicated by dashed lines, and are provided on the disc 1 in concentric circles or spirals. Track 20 above
Pits 210 to 212 for tracking and clocking are provided alternately on the left and right with respect to 0 to 202. Briefly explaining the actual tracking operation, in a disk format as shown in FIG. 2, the pits 210 to 212 are formed at regular intervals or with a certain regularity.
If the light spot is positioned exactly on the tracks 200-202, the signal amplitude of the pit signal obtained from the pit 210 and the pit signal obtained from the pit 211 will be equal. However, when the position of the optical spot is shifted left or right with respect to the normal track center, the signal amplitude from the pit located on the shifted side becomes large, and conversely, the signal amplitude from the pit located on the opposite side becomes small. Become. For this reason, the pit
The signal amplitudes of 210 and 211 become unbalanced. If the position of the light spot is controlled so as to correct the imbalance, the light spot can always be positioned on the target track. The format shown in FIG. 2 is an example, and the present invention can be implemented using a generally known sample servo format. About the sample servo format, SPIE Procedure, Vol. 695, 1986, Optical
Mass Data Storage (SPIE Proceedings Vol.69
5, P239-242, 1986, Optical Mass Data Storage 2).

Fig. 3 uses a format as shown in Fig. 2,
FIG. 5 is a diagram showing signals when data recording / reproduction is performed.
Modulation methods include Modified FM (MF
M) is used in FIGS. 3 (a) and 3 (b), and the case where NRT (NRZ) modulation is used is shown in FIG. 3 (c).
These are given as examples. Referring to FIG. 3, a case where recording data 222 is recorded in a data recording area 220 between clock pits will be described. The MFM outputs a pulse of 1/2 bit behind the bit cell for the data bit "1", and outputs two or more "0" s for the data bit "0". With respect to the second and subsequent "0", a pulse corresponding to 1/2 bit is output in front of the bit cell. As described above, in the MFM, even if “1” or “0” continues in the data bit, “1” or “0” is always inverted as a recording pulse. Therefore, the average level of the modulated recording pulse and the reproduced signal sequence for an arbitrary data bit sequence is kept substantially constant. The above modulation scheme is called a DC-free modulation scheme. FIG. 3A shows a case where the MFM-modulated codeword “1” is directly recorded in the data recording area 220 on the track 220 in correspondence with the recording pulse 224. The recording domain 231 indicated by oblique lines is a region having a magnetization opposite to that of the surroundings, and a reproduced signal as shown in the figure is obtained as the data signal 104. FIG. 3B shows a case where the edge of the recording pulse 228 is made to correspond to "1" of the MFM-modulated codeword. FIG. 3C shows a case where the recording data 222 is subjected to NRZ modulation and recorded. In FIG. 3, the recording pulse is returned to the "0" level in the area where the pits 210 to 212 exist. The reason is that the pits 210 to 212
This is because the level of the magnetization signal (data signal) is clamped at the place where the magnetic field exists, and the magnetization direction near the pit is set to the unrecorded state. The pit signal 102 can be obtained as a signal corresponding to the pits 210 to 212. In FIGS. 3 (a) and 3 (b), the fluctuation of the reproduction signal with respect to the average level 226 is relatively small because a modulation method having a good DC-free property is used. Therefore, even if the electric system for detecting the reproduction signal is AC-coupled and only the signal change is transmitted, relatively stable data recognition can be performed with a fixed threshold value. In general, a magneto-optical signal has a smaller degree of modulation than a DC level. Therefore, when amplified by DC coupling,
The problem that the output is easily saturated by the DC level easily occurs. Therefore, it is desired to use AC coupling to extract only the modulated component and amplify it. In the MFM shown in FIGS. 3A and 3B, the detection window width is 1/2 of the data bit. That is, to accurately demodulate the data, the peak position of the reproduced signal 104,
Or it must be possible to determine the presence or absence of an edge position. Therefore, a modulation scheme having a wider detection window width is more advantageous for peak shift or edge shift. In the NRZ modulation recording shown in FIG. 3 (c), the average level changes depending on the duty ratio of the reproduced signal. Average level in the figure
Reference numeral 226 denotes a constant value, and the level of the reproduction signal varies. In the NRZ modulation, the time of the detection window width is equal to the data bit width, which is equivalent to twice the MFM. However, since there is no DC-free property, when “0” or “1” continues,
In the AC coupling, the same level is obtained, so that accurate demodulation is difficult. Therefore, if a clock signal for recording / reproduction can be generated by any means and a DC component can be realized, the advantage of NRZ modulation can be utilized even when it is desired to amplify by AC coupling. The format shown in FIG. 2 can be tracked by clock pits 210 to 212, and a clock signal for modulation and demodulation can be generated by a reproduction clock generation circuit 30. Therefore, even if the modulation method itself has no self-clocking property, recording and reproduction can be performed. When a band including a DC component such as NRZ modulation is used, the DC component is simply lost by AC coupling and amplification, so that the demodulation cannot be performed. As a means for solving such a problem, a clock clamp 210 to 2 is used by using a level clamp circuit.
An effective method is to clamp the reproduced signal level at a place corresponding to 12 or a place corresponding to an unrecorded area provided exclusively or the like to a certain potential to restore the DC component. The specific method will be described later.

In the example shown in FIG. 3, the data signal 104 and the pit signal 1
02 is separated at the stage of the detection system. However, in the case of an optical disc in which data is also recorded in a hole pit, it is necessary to separate the clock pit from the data pit by another method. As an optical method, for example, it is conceivable that the depth of the clock pit is set to around 1/4 of the wavelength of the reproduction laser, and the clock is treated as a phase pit. This method is the same as the conventional method in which the header signal is treated as a phase pit and the data pit is treated as a light and shade pit. In order to selectively detect only the phase pit, there is a method of arranging a two-segment type photodetector in a far field along a track and detecting the difference based on a difference signal between the two. By taking the sum signal of both, only the light and dark pits can be detected. As an electrically performed method, it is conceivable to select and detect by pattern matching using an individual pattern that cannot occur in a data pit row as a pattern of a clock pit row. This method is already known as a method for detecting a servo pit area in a sample servo format.

Next, the main parts of the components shown in FIG. 1 will be described.
FIG. 4 is a configuration example of the binarization circuit 22, and FIG. 5 is a diagram for explaining the operation. FIG. 4 shows a circuit for detecting a pit center position from the pit signal 102 and generating a pit pulse 106. The pit signal 102 is converted to a low impedance by the buffer 50 and input to the differentiating circuit 52 and the comparator 54. A reference level 120 is applied to the other input of the comparator 54. When the pit signal 102 exceeds the reference level 120, the gate pulse 134 becomes "H". Differentiator 52
Converts the signal 102 'into a differentiated signal 126,
126 is input to the comparators 56 and 58. The comparator 56 outputs the differential signal 12
Set pulse when 6 is higher than reference level 122
“H” is output as 128. On the other hand, the comparator 58 outputs the differential signal 1
When "26" is higher than the reference level 124, "H" is output as the reset pulse 130. The output (Q) of the flip-flop 60 becomes “H” when the rising edge of the pulse is input to the set (S) terminal, and the output (Q) becomes “L” when the rising edge of the pulse is input to the reset (R) terminal. "Behave. Thus, the resulting set pulse 12
8 and the reset pulse 130 generate a peak detection pulse 132. The peak detection pulse 132 may be used as it is as the pit pulse 106.
By taking the logical product of the AND 34 and the AND gate 62, it is possible to prevent a pit detection pulse from being output at a place where the pits 210 to 212 do not exist due to the influence of signal noise.

FIG. 6 is an example of a configuration for generating a clamp pulse 108 from a pit pulse 10, and FIG. 7 is a diagram showing an operation. FIG. 6 (a) shows a circuit in which the pit pulse 106 is input to the trigger (T) terminal of the monomultivibrator 140, and the clamp pulse 108 which becomes "H" for an arbitrary time from the rising edge of the pit pulse 106 is generated. In this case, the clamp pulse 108 necessarily occurs at a time later than the pit center position and near the pit. FIG. 6 (b) is an example of a circuit that solves the above problem and can generate a clamp pulse 108 at an arbitrary position. That is, the first monomultivibrators 142 and 146 use the first monomultivibrator 142 to generate an output which becomes "H" for an arbitrary time from the rising edge of the pit pulse 106, and the second monovibrator 142 is triggered by the fall of the output. Multi-vibrator 146 allows final clamp pulse 108
Generate In FIG. 6 (b), an inverted signal () 148 is used as the output of the first mono-multivibrator 142, and this is used as the trigger input (T) of the mono-multivibrator 146 of FIG. In this way, the clamp pulse 10
8 can be generated at any position on the track 200. In the figure, the case where the clamp pulse 108 is generated in an area gradually lowering the data recording area 220 centered on the positions of the pits 210 to 212 is shown. According to the method of FIG. 6B, for example, even when an unrecorded portion is provided as a clamp-dedicated area other than the pits 210 to 212, it is possible to easily realize the generation of a clamp pulse in the dedicated area.

FIG. 8 shows a configuration example of the level clamp circuit 26, and FIG.
The figure shows the operation. The data signal 104 is input to an amplifier 150 and amplified to an appropriate level. After that, it is input to the CR circuit composed of the capacitor 152 and the resistor 154,
The signal processed here is again amplified to an appropriate level by the amplifier 156, and becomes the correction data signal 110. On the other hand, the portion mainly configured by the transistor 158 is a switching circuit, and only when the transistor 158 is turned on,
The signal level is clamped to approximately the same potential as the emitter potential (clamp level) 164. Clamp pulse 108 is “H”
At this time, the base potential of the transistor 158 increases and the transistor 158 is turned on. The diode 162 is for accelerating discharge and stopping reverse current when the transistor 158 is turned off.
The variable resistor 160 is for setting a clamp level. In the disk format shown in Fig. 9, pits 210-2
A clamp-dedicated area 232 is provided in an area not including 12. In the above description, when a magnetization signal is obtained by differential detection, it is stated that the reflected light from the pit is canceled out. However, in actuality, the imbalance of the optical system and the electric system and the magnetization of the slope around the pit are described. Since the direction is not necessarily vertical, a slight disturbance of the signal occurs at the pit portion. Therefore, in order to clamp at an accurate level, it is desirable to provide a dedicated clamping area as shown in FIG. FIG. 9 shows a case where the recording data 222 is recorded in the data recording area 220 by NRZ modulation. The clamp pulse 108 is generated in the clamp dedicated area 232 by the circuit described with reference to FIG. Although the average value of the data signal 104 before the clamping process fluctuates due to the density of the duty ratio, by performing the clamping process, the correction data signal 110 is a signal having a small variation in the average value based on the clamp level 164. be able to.

FIG. 10 is a diagram showing a configuration example of the binarization circuit 28 of the correction data signal 110. FIG. 11 is a diagram showing the operation of each circuit in FIG. The binarization circuit 28 in FIG. 10 (a) binarizes the correction data signal 110 based on a fixed slice level 169 set by a variable resistor to obtain a data pulse 112.

The binarization circuit 28 shown in FIG.
The data pulse 112 is obtained by using the level of the portion corresponding to the clamp-dedicated area 232 as a reference for the threshold. Clamp pulse 108 is delayed pulse by delay element 180
It will be 181. This delayed pulse 181 and the original clamp pulse 10
By taking the logical product of 8 by the AND circuit 178, a sample pulse 179 is generated in the latter half of the clamp dedicated area 232.
In the first half of the clamp region, there is a concern that the clamp level is still insufficient due to the time constant of the level clamp circuit. Therefore, the latter half of the clamp region where a sufficiently stable level can be obtained is used as a threshold reference. Is desirable. The sample-and-hold circuit 170 has a function of sampling the level of the correction data signal 110 when the sample pulse 179 is "H" and holding the level when the sample pulse 179 is "L". Since the held level 171 may slightly fluctuate depending on the characteristics at the time of holding, the fluctuation is absorbed by the low-pass filter 172. The output 173 of the filter 172 is changed to a desired slice level 175 by the level shifter 174. When the slice level 175 may be smaller than the output 173 of the low-pass filter 172, a resistance voltage dividing circuit may be used. Also output 17
If it is larger than 3, it can be easily realized by using a DC amplifier. When the correction data signal 110 is binarized by the slice level 175, a data pulse 112 is obtained. FIG. 10 (c) shows a case where the clamp level 164 in the level clamp circuit 26 is used as a reference for the threshold value. A slice level 183 is generated by a level shifter 182 and binarized by a comparator 184 to obtain a data pulse 112 as in FIG. 10B.

FIG. 12 is a diagram showing the operation of the reproduction clock generation circuit 30. The reproduced clock 114 is generated from the pit pulse 106 by a phase lock loop (PLL) circuit in the clock generation circuit. Pit pulse 10 and playback clock 1
The phase of the 14 rising edges is matched by the PLL circuit. The PLL circuit may be of a type conventionally used in a reproducing circuit such as a magnetic disk, and the detailed circuit will not be described. In the clamp signal generating circuit shown in FIG. 6, a clamp pulse 108 is generated by directly using the pit signal 106. As a method of generating the clamp pulse 108, it is conceivable to generate the clamp pulse 108 by counting the reproduction clock 114. The circuit shown in FIG.
This is a configuration example of a level clamp circuit 26 to which a circuit for generating a clamp pulse 108 'is added between the count values "1" and "4" as shown in FIG. The reproduction clock 114 is input to the clock (c) terminal of the N-ary counter 190. The pit pulse 106 is input to the reset (R) terminal of the counter 190. When the pit pulse 106 is input, the counter is reset to "0". Comparator 192, 196 each start of the clamp pulse 108 'is intended for determining the end, the comparator 192 match determination when has decreased to the output Q ₀ to Q ₃ is "1" in the counter 190 (E) terminal is "H And the comparator 196 sets the counter 1
When the outputs Q _{0 to} Q _{3 of the} 90 become “4”, the coincidence determination (E) terminal becomes “H”. Therefore, the output from the coincidence determination (E) terminal of the comparator 192 is input to the set (S) terminal of the flip-flop 194, and the output from the coincidence determination (E) terminal of the comparator 196 is input to the reset (R) terminal of the flip-flop 194. Upon input, a pulse as shown in FIG. 12 can be generated as the clamp pulse 108 '.

In the embodiments described above, a sample servo format is used as a disk format, and in the case of magneto-optical recording, a magnetizing signal level corresponding to a sample pit portion or a magnetizing signal level corresponding to a clamp-dedicated area is clamped. In the case of recording, the latter example in which the signal level of the clamp-only area is clamped is shown.

As another embodiment, a method of clamping the signal level of an unrecorded area existing in the data portion can be considered. Although this method does not require a special clamp-only area, the data modulation method must have some degree of DC-free property. That is, since the unrecorded area is a portion corresponding to “0” of the modulated codeword, it is required that “0” appears at a certain frequency of 4. NRZ
In order to apply the above method to modulation, it is necessary to positively insert a part in which a code word is "0" into a data string.
To use NRZ modulation, it is necessary to obtain a reproduction clock separately from the data stream. For this purpose, a method using a sample servo format, a method for positively inserting a transition point between "1" and "0" in a data string and equivalently enabling self-clocking can be considered.

FIG. 14 is an example of the configuration of the reproducing circuit 20 by clamping a data signal level corresponding to an unrecorded portion in the data, and FIG. 15 is a diagram showing the operation of FIG. The example of FIG. 15 shows a case where a pit 422 is formed by a pit edge recording in which a code word is made to correspond to a front edge and a rear edge in a space between continuous track guide grooves 420. The width of the track guide groove 420 shown in FIG. 15 is narrower than the track width, and the width of the gap between the grooves is larger than the width of the groove. In this way, even if the reproduction light spot slightly deviates from the data track, the reflected light level of the portion where no pit is recorded hardly varies. Therefore, if the level of the unrecorded portion is used, stable clamping can be performed. In FIG. 14, 2
The binarizing circuit 400 may be configured as shown in FIG. 10 (a), and rough binarization is performed by the slice level 520 to generate the data pulse 500. The binarization processing in the binarization circuit 400 is for discriminating a portion where no pit is recorded. The pattern determination circuit 402 has a function of outputting the pattern detection pulse 502 when the section in which the data pulse 500 is at "H" is somewhat long. Such processing is necessary because the amplitude of the reproduced signal is reduced in a portion where the data pattern is dense. Specifically, the recording clock is input to the counter, the data pulse 500 is counted only during the "H" section, and the count value is judged by the comparator to be larger or smaller. If the counted value is larger than the set value, the detection pulse 502 is output. You should do it. The clamp pulse 504 is generated from the detection pulse 502 by the clamp signal generation circuit 404. The configuration shown in FIG. 6 may be used as the clamp signal generation circuit. On the other hand, the data signal 401 is the delay element 4
In accordance with 08, the data is delayed by the delay of the counting time of the pattern discrimination circuit 402, and becomes a delayed data signal 508. The level clamp circuit 406 clamps the level of the delayed data signal 508 on the side where the pits are not recorded by the clamp pulse 504 to become a correction data signal 506.
In the figure, the polarity of the correction data signal 506 and the polarity of the delay data signal 508 are inverted. This can be realized by using the level clamp circuit 26 shown in FIG. 8 and changing the amplifier 150 to an inverting amplifier. The correction data signal 506 is converted into a data pulse 510 by a binarization circuit 410 similar to that shown in FIG. Subsequent processing proceeds in the same manner as shown in FIG. 1, and demodulated data 116 is obtained.

FIG. 16 is a diagram showing an example of setting an unrecorded area in the case of a continuous group format. In FIG. 16A, an unrecorded area is provided as a clamp area 624 between a data area 622 and a prepit area (header area) 620 constituted by prepits 600 created in advance on the disk. In the method shown in FIG. 16 (a), since there is only one header area 620 for each sector, the number of overhead areas in which data cannot be recorded is small, but the variation of the reproduction signal can be regarded as constant within one sector. If not, the problem is that the fluctuation of the correction data signal after the clamp processing cannot be suppressed completely. In FIG. 16 (b), a clamp area 630 immediately follows a plurality of resynchronization areas (RYSYNC) 628 existing in the data area.
Is shown. The resynchronization pattern is inserted into the data stream as appropriate, and is used to generate a playback clock.
It has the purpose of resynchronizing the L system. Accordingly, although the overhead slightly increases in FIG. 16 (b), the number of clamp areas increases as compared with the case of FIG. 16 (a), so that the effect of suppressing the fluctuation of the reproduction signal level is large. No.
Although the area between the track guide grooves is used as the data recording area in FIG. 16, the area above the guide grooves may be used. However, the method shown in FIG. 16 is recommended as the reference level at the time of the clamping process because the level variation is smaller when the inter-groove region is used.

〔The invention's effect〕

According to the present invention, the DC component can be stabilized by clamping the reproduction signal level in the unrecorded area. If a sample servo format is used as the format or recording is performed by actively inserting an unrecorded part in the data string, there is no DC free property or self-clocking property, but a modulation method with a wide detection window width, such as NRZ modulation , Stable data recognition becomes possible. If the width of the detection window is increased, there is a margin for jitter fluctuation due to noise, so that the reliability of data recognition can be improved.
Even in the case of a general modulation method, a section where data is not recorded, for example, an area where the code word “0” is so continuous or a specific unrecorded area is provided, and this area is used as a clamp area. Variations can be suppressed and the same effect as in the above case can be obtained. In addition, since the DC component can be reproduced in the AC coupling amplification system by the clamp process, the influence of the drift of the circuit system is reduced, and the fluctuation of the reflectance over one round of the disk and the fluctuation of the signal level due to the retardation are also reduced. There is an effect that can be suppressed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical disc signal reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of a disc format,
FIG. 3 is a diagram showing signal waveforms of respective parts, FIGS. 4 and 5 are diagrams showing a configuration diagram and operation of a binarization circuit, and FIGS. 6 and 7 are a configuration diagram and operation of a clamp signal generation circuit. 8 and 9 are diagrams showing a configuration diagram and operation of the level clamp circuit.
10 and 11 are diagrams showing the configuration and operation of the binarization circuit after the clamping process, FIG. 12 is a diagram showing the operation of the reproduction clock generation circuit, and FIG. 13 is another embodiment of the level clamp circuit. ,
FIGS. 14 and 15 are diagrams showing a configuration and operation of a reproducing circuit for detecting and clamping an unrecorded area in the data area, and FIG. 16 is an example of a clamp area setting in the case of a continuous group format. FIG.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-204433 (JP, A) JP-A-61-233470 (JP, A) JP-A-61-216166 (JP, A) JP-A-61-216166 258335 (JP, A) JP-A-59-8111 (JP, A) JP-A-58-83317 (JP, A) JP-A-61-45470 (JP, A) JP-A-61-246960 (JP, A) JP-A-61-233471 (JP, A)

Claims (10)

(57) [Claims] A servo area is provided at predetermined intervals along a track direction of a recording medium, and while tracking control is performed based on a signal obtained from the servo area, data is recorded in a data area between the servo areas. A signal reproducing method for reproducing information, wherein a reference reproduction signal level equivalent to a reproduction signal level from an unrecorded portion of the data recording area is obtained from a recording medium, and the reference reproduction signal level is clamped. Method. 2. The signal reproducing method according to claim 1, wherein the reference reproduction signal level is detected from a dedicated clamp area provided in a specific portion on the medium. 3. The signal reproducing method according to claim 1, wherein the reference reproduction signal level is detected from an unrecorded area in the data area. 4. An information recording medium having a recording film on which information is recorded along a track, a pre-pit area having phase bits provided at a predetermined interval along the track direction, and an information area located between the pre-pit areas. An information recording medium, comprising: a data area in which a data signal is recorded, and a clamp area in which a reproduction signal level equivalent to a reproduction signal level from an unrecorded portion of the data recording area is obtained. 5. The information recording medium according to claim 4, wherein said clamp area is provided periodically along said track. 6. The information recording medium according to claim 4, wherein said clamp area is adjacent to said pre-pit area. 7. Servo areas are provided at predetermined intervals along a track direction of a recording medium, and information is recorded in a data area between the servo areas while performing tracking control based on a signal obtained from the servo area. Alternatively, in the information recording / reproducing method for reproducing, the modulation method of the information recorded in the data area is a modulation method in which a reproduction signal of the information reproduced from the data area changes an average level according to a duty ratio of the reproduction signal. At the time of reproduction, a reference reproduction signal level equivalent to a reproduction signal level from an unrecorded portion of the data recording area is obtained from a recording medium, and the information is compensated for a change in the average level of the reproduction signal by using the reference reproduction signal level. An information recording / reproducing method characterized by reproducing. 8. The information recording / reproducing method according to claim 7, wherein said modulation method is an NRZ modulation method. 9. The information recording / reproducing method according to claim 7, wherein a threshold value for binarizing the reproduced signal is formed using the reference reproduced signal level. 10. A spindle for rotating an optical disk, an optical head for irradiating a laser to the optical disk, a photodetector for detecting laser reflected from the optical disk, and a light beam recorded on the optical disk based on an output of the photodetector. Optical disc device having a reproduction circuit for reproducing the information
A clamp signal generation circuit for detecting a clamp area where information is not recorded from a mark arranged at a predetermined position on the optical disc; and a reproduction signal level from the clamp area based on an output of the clamp signal generation circuit. An optical disc device having a level clamp circuit for clamping.