JP2004241102A - Method for correcting aberration in optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently correcting a spherical aberration by utilizing the phenomenon that, if there is the spherical aberration generated by a light spot due to a thickness error of a transparent substrate of an optical disk, the maximum amplitude relating to the reproduced signals of a long period and a short period shifts backward around the focusing point of an objective lens in an optical disk device. <P>SOLUTION: If there is certain recorded information in the optical disk 5, that information is reproduced and the focusing position of the objective lens 4 is determined (S21 and S22). Next, the objective lens 4 is moved forward and backward by an equal distance (α) around the position and the maximum amplitude (LA, SA), (LA', SA') of the reproduced signals of the long period and the short period are determined in the respective positions. The difference of the maximum amplitude: ΔGa(=LA-SA), ΔGb(=LA'-SA') is determined (S23 to S26). Further, the difference thereof: ΔGa-ΔGb is determined and an aberration correcting section 3 is feedback-controlled by the value thereof as control data (S27 to S29 → S22). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an aberration correction method for an optical disk device, and in particular, corrects spherical aberration occurring in a light spot due to a thickness of a transparent substrate of an optical disk deviating from a standard value, and records and corrects the light with an appropriate light spot. It relates to an improvement for causing reproduction.
[0002]
[Prior art]
In recent years, various types of optical disks such as CDs (Compact Disks) and DVDs (Digital Versatile Disks) have been put into practical use as high-density information recording media. This is performed by irradiating the information recording layer of the optical disk with a minute light spot through the system.
More specifically, as shown in FIG. 28, the optical disc 101 generally has an information recording layer 102 formed along the surface of the optical disc 101, and the information recording layer 102 has a structure covered with a transparent substrate 103. The optical disc apparatus guides the recording / reproducing laser beam to the front of the optical disc 101 by a light guide system, and a light spot on the surface of the information recording layer 102 by the final condensing optical system (objective lens in the figure) 104. 105 is formed.
Here, information is written concentrically or spirally in the information recording layer 102 with recording pits on the order of micrometers, and the transparent substrate 103 is made of a transparent resin such as polycarbonate. In addition to protecting the optical disk, the optical disk itself has a function of providing mechanical strength.
Although the optical disc 101 shown in FIG. 28 has a configuration in which the front and back surfaces of the information recording layer 102 are covered with a transparent substrate 103 (in the case of a double-sided recording optical disc, such a configuration is inevitably used). In a single-sided recording optical disk, a transparent substrate may be provided only on the recording surface side.
[0003]
By the way, recently, a large capacity of an optical disc and a corresponding high density are remarkable, and a numerical aperture of an objective lens 104 for forming a light spot tends to be further increased. For example, a numerical aperture corresponding to a conventional CD Is 0.45, compared to 0.6 for a DVD capable of high-density recording, and the use of an objective lens having a numerical aperture of 0.8 or more is also being studied.
[0004]
Under such circumstances, the accuracy of the thickness t of the transparent substrate 103 on the optical disc 101 has extremely important significance in recording / reproducing information.
This is because the transparent substrate 103 naturally has a constant refractive index, and when the light spot 105 is formed by the objective lens 104 as described above, it is difficult to determine if the thickness t of the transparent substrate 103 is out of the allowable value. This is because the influence of the aberration generated in the spot 105 increases, and particularly, when the numerical aperture of the objective lens 104 increases, the range of the aberration also increases, and the possibility that an error occurs in recording and reproduction increases.
For example, when the numerical aperture becomes 0.85, the tolerance of the thickness t of the transparent substrate is considered to be several μm or less in a general optical disk. It is quite difficult even with technology.
[0005]
FIG. 29 shows a change in the light intensity distribution around the optical axis of the light spot 105 with respect to the defocus amount when the thickness t of the transparent substrate 103 is within the allowable value. There is a tendency that the beam diameter changes substantially symmetrically before and after the focal point.
On the other hand, if the deviation of the thickness t of the transparent substrate 103 exceeds the allowable value, spherical aberration causing concentric wavefront fluctuation centering on the optical axis occurs, and as shown in FIG. Changes asymmetrically before and after the focal point. In addition, the light intensity distribution tends to exhibit irregular changes due to an increase in side lobes or an increase in beam diameter with respect to the defocus amount.
[0006]
Therefore, in the optical disk device, when the thickness t of the transparent substrate 103 exceeds the allowable value, the amount of aberration is detected by any method, and the optical system is adjusted based on the detected information. It is necessary to correct the light intensity distribution of the light spot 105 so that proper recording / reproduction can always be performed.
[0007]
Regarding the problem, Patent Literature 1 below proposes the following aberration correction method and an optical disk apparatus that executes the method.
First, FIG. 31 shows a plan view (A) and a cross-sectional view (B) of an optical disc 101 similar to the above, and a specific area (lead-in area in the figure) 106 of the optical disc 101 for detecting the spherical aberration. Specific pattern information is recorded.
Specifically, as shown in FIG. 32A, a specific pattern in which two types of pit rows 107 and 108 having different periods are formed alternately is formed. The period is longer than the period of the column 108.
The specific pattern may be recorded on the optical disk 101 in advance, or may be written by an optical disk device before the original recording / reproduction is performed.
[0008]
Then, the optical disk device reads the specific pattern information of the specific area 106 when performing normal recording / reproduction.
In this case, the reproduced signal read from each of the pit rows 107 and 108 has a signal waveform as shown in FIG. 32B, and the amplitude of the reproduced signal is large in the section of each pit row 107. It becomes smaller in the section.
That is, reproduced signals having different amplitudes are obtained from the specific pattern information according to the cycles of the pit strings 107 and 108.
[0009]
Here, the vertical axis indicates the maximum amplitude of the reproduction signal, and the horizontal axis indicates the amount of defocus from the focal point of the objective lens 104. The relationship between them will be as shown in FIG.
10A shows a case where the thickness t of the transparent substrate 103 is within the allowable value, FIG. 10B shows a case where the thickness t exceeds the allowable value, and a solid line shows a change related to the long-period pit row 107. The dashed line corresponds to the change tendency of the short-period pit row 108.
As is clear from the figures, in the case of (A), in which almost no aberration occurs, the amplitude of the reproduction signal obtained from the light spot 105 becomes almost symmetrical before and after the focal point, but the aberration occurs. In the case (B), the amplitude of the reproduction signal in a state shifted from the focal point of the objective lens 104 becomes asymmetric before and after the focal point.
In the latter case (B), the spherical aberration occurs on the (+) side, and the maximum amplitude of the reproduction signal of the long-period pit row 107 is obtained on the far side from the focal point, and conversely, The maximum amplitude of the reproduction signal of the periodic pit train 108 is obtained on the near side from the focal point.
This is because, as shown in FIG. 30, when the thickness t of the transparent substrate 103 exceeds the allowable value, the light intensity distribution of the light spot 105 changes asymmetrically before and after the focal point, and the maximum of the reproduction signal It is considered that the conditions for forming the light spot 105 for obtaining the amplitude are based on the period of the pit row.
[0010]
Accordingly, the defocus amounts (focus offset amounts) fo1 and fo2 giving the maximum amplitudes of the long-period pit row 107 and the short-period pit row 108 in FIG. This corresponds to spherical aberration generated by an error exceeding.
The change in the amplitude of the reproduced signal of each of the pit rows 107 and 108 shown in FIG. Since the signs of the defocus amounts fo1 and fo2 giving the maximum amplitude are inverted, not only the correction amount relating to the aberration but also the correction direction can be confirmed.
Therefore, in the invention of Patent Literature 1, aberration correction is performed by correcting the difference (fo1−fo2) between the defocus amounts fo1 and fo2 that give the maximum amplitudes related to the pit rows 107 and 108 to be minimum. An appropriate light spot 105 is obtained.
[0011]
In Patent Literature 1, the aberration correction operation performed by the optical disk device is described with a simple flowchart. However, it is presumed that aberration correction is actually performed based on the operation procedure shown in the flowchart of FIG.
First, when the optical disk 101 is set, it is checked whether the optical disk 101 is read-only or rewritable, and it is checked whether a specific pattern is recorded in a specific area (S51 to S54).
Here, if the specific pattern is recorded in the specific area, the optical disc apparatus immediately starts reading the recorded information (S53, S54 → S57), but the rewritable optical disc 101 is not recorded. In this case, the reading is started after the specific pattern is recorded in the specific area (S53, S54, S55).
On the other hand, when the optical disk 101 is a read-only optical disk and the above-described recording is not performed, it is determined that the optical disk 101 cannot correct the aberration, and the aberration correction operation is not performed (S54 → S56).
[0012]
When reading is started, a reproduction signal is obtained from the specific pattern while moving the objective lens 104 in the optical axis direction around the focal point.
Then, the reproduction signal is sampled at a predetermined cycle for each set position of the objective lens 104, and an amplitude change with respect to the defocus amount of the reproduction signal of each of the pit rows 107 and 108 is obtained (S58, S59).
Further, based on each amplitude change obtained for each set position of the objective lens 104, the defocus amounts fo1 and fo2 giving the maximum value of the amplitude change for each of the pit rows 107 and 108 are obtained (S60).
[0013]
Next, the difference (fo1-fo2) between the defocus amounts fo1 and fo2 is obtained. If the difference (fo1-fo2) is not within the allowable range, the aberration correction unit (not shown) provided in the optical system is used by (fo1-fo2). Steps S57 to S60 are executed again while controlling to be smaller (S61, S62 → S57 to S60).
Here, the aberration correction unit has a function of adjusting the divergence or convergence angle of the incident light beam using the defocus amount (fo1-fo2) as control data.
Thereafter, by repeating the control operation after the start of the reading to make (fo1−fo2) fall within the allowable range, spherical aberration in the case where the thickness t of the transparent substrate 103 exceeds the allowable value is corrected and the appropriateness is obtained. The light spot 105 is configured.
The amount of defocus can be detected using a conventional optical head and a signal processing system, so that it is not necessary to newly provide hardware.
[0014]
[Patent Document 1]
JP-A-2002-150569
[0015]
[Problems to be solved by the invention]
According to the spherical aberration correction method and the optical disk apparatus according to the invention of Patent Document 1, although the spherical aberration based on the thickness error of the transparent substrate can be corrected, a specific pattern must be recorded in a specific area of the optical disk in advance. Must.
Therefore, there is a fatal problem that a read-only optical disk that has already been standardized cannot be handled (see steps S52 → S54 → S56 in FIG. 34). In the case of a rewritable optical disk, it is only necessary to record a long-period and a short-period pit train, but it is necessary for the optical disk device to prepare such recording information in advance, and the optical disk has aberrations. Since a special recording area for correction must be provided, there arises a problem that the original information recording area is narrowed to reduce the capacity of the optical disk.
[0016]
Further, in Patent Document 1, the specific area is not limited to the lead-in area of the optical disk, but the specific area is set at a fixed position on the optical disk.
Therefore, even if the thickness of the transparent substrate in the specific area falls within the range of the allowable value, the thickness may exceed the allowable value in the other information recording areas or vice versa. Even if the optical system is uniformly controlled only by the obtained control information, there is a possibility that the spherical aberration cannot be accurately corrected.
Patent Document 1 proposes a method of recording a specific pattern in a lead-in area and a lead-out area of an optical disc and interpolating and estimating a shift amount of an intermediate area. However, the degree of freedom for correcting spherical aberration is proposed. Is small.
[0017]
Further, regarding the procedure for creating control data for aberration correction (S57 to S60), the position of the objective lens 104 is sequentially moved around the focal point, and the amplitude value of the long-period and short-period signals is changed each time. Is obtained, and the defocus amount corresponding to the maximum value of the amplitude change in each cycle is obtained, and the difference between the defocus amounts is used as control data for the aberration correction unit.
Therefore, the procedure (S58) for obtaining the amplitude values of the long-period and short-period signals is performed many times, and the procedures of steps S57 to S60 are repeated until the difference between the defocus amounts converges on the allowable range. There is also a problem that the time required to complete the aberration correction becomes long.
[0018]
Therefore, the present invention does not target the special optical disk as described above, and reproduces the recording information of the normal optical disk without narrowing the information recording area of the optical disk, and generates a spherical surface caused by a deviation in the thickness of the transparent substrate. It has been created for the purpose of providing an optical disk device capable of accurately and quickly obtaining control data for correcting aberrations and capable of always performing appropriate recording / reproduction with an appropriate light spot.
[0019]
[Means for Solving the Problems]
According to a first aspect of the present invention, in an optical disk device, an aberration correction unit that adjusts a divergence or a convergence angle of an incident system light beam from a laser light source to an optical disk, and converges the incident system light beam to an information recording layer of the optical disk The objective lens forming the light spot is moved in the direction of the optical axis of the incident light beam, and at this time, the reflected light from the light spot is received and output by the photodetector, and the reproduced signal is processed and analyzed. A control unit that controls the aberration correction unit based on the result, and when a spherical aberration occurs in the light spot, the position of the objective lens is shifted from the focal point position with respect to the information recording layer in the optical axis direction. An aberration correction method for an optical disk device that corrects the spherical aberration by using the reproduction signal having a maximum amplitude in a state, wherein some information is stored on the optical disk. If the information is recorded, the information is reproduced, and the control unit performs a first procedure for obtaining the in-focus position of the objective lens and an optical axis direction from the in-focus position obtained in the first procedure. A second procedure for moving the front and rear by the same distance and calculating the maximum amplitude of the reproduced signal obtained from the photodetector at each moving position; and a third procedure for calculating the difference between the maximum amplitudes obtained in the second procedure. And a fourth step of controlling the aberration corrector so that the calculation result obtained in the third step approaches 0. A method of correcting a spherical aberration in an optical disk device, comprising the steps of:
[0020]
According to the present invention, the maximum amplitude of the reproduction signal is obtained at two points where the objective lens is moved by the same distance in the optical axis direction from the in-focus position in the second procedure, and the difference between the maximum amplitudes is obtained only in the third procedure. Thus, the amount of aberration correction at the light spot due to the thickness of the transparent substrate exceeding the allowable range can be obtained.
Further, according to the present invention, it is sufficient if there is some recording information on the optical disk (in the case of a rewritable optical disk, some recording information is written in advance). It is not limited to.
By the way, in the present invention, the maximum amplitude of the signal itself is obtained irrespective of various periods included in the reproduction signal. As a result, only the maximum amplitude of a long period signal is targeted. As shown in parentheses, if the optical disk has a spherical aberration that exceeds the allowable range, the maximum amplitude of both the long-period and short-period signals for the defocus of the objective lens will deviate from the focal point. , It is possible to obtain the aberration correction amount only for a long-period signal, and it is possible to secure practically sufficient correction accuracy.
When the refractive index of the transparent substrate of the optical disk is constant, the amount of defocus of the objective lens and the amount of aberration correction correspond uniformly, so that the difference between the maximum amplitudes obtained in the third procedure and the aberration correction It is possible to complete the aberration correction by one control by, for example, tabulating the correspondence relationship with the amount, but the first to fourth procedures are performed until the calculation result obtained in the third procedure falls within the allowable range. If the sequence control is repeated, accurate aberration correction can be realized regardless of the refractive index of the transparent substrate.
[0021]
Further, in the second procedure of the present invention, the following method can be adopted as means for obtaining the maximum amplitude of the reproduction signal at each moving position of the objective lens.
(1) A reproduction signal obtained from the photodetector is sampled at a predetermined cycle, and based on a time interval of a zero cross point and a state transition determined by a partial response characteristic and a run length limit, a signal of a short cycle or a long signal is determined. A method that determines whether the signal is a periodic signal, performs waveform equalization on a short-period reproduced signal, and separates only the long-period signal by filtering to obtain the maximum amplitude of the long-period signal.
(2) a gain control unit for controlling the amplitude of the input reproduction signal based on a gain error signal of an error detection unit, which will be described later, and a maximum of a maximum amplitude of the short-period signal in the reproduction signal obtained from the gain control unit; A first threshold value set at a central level and a second threshold value and a third threshold value set slightly larger on the positive and negative sides than the maximum amplitude level of the short-period signal are provided, and the number of times the reproduced signal crosses each threshold value is determined. A cross extracting unit that separately performs integration, repeatedly executes an operation of clearing all integrated values when any of the integrated values reaches a predetermined first set value, and a threshold value in the cross extracting unit. When the integrated value according to any of the above has reached the first predetermined value, the integrated value according to the first threshold value is compared with the integrated value according to the second and third threshold values, and the integrated value of the former is compared. Is larger than each of the latter integrated values An error detection unit that outputs a gain error signal in a case where the error is detected, and an envelope detection unit that detects an envelope of the reproduction signal obtained from the gain control unit and obtains a maximum amplitude thereof. When outputting an error signal, a second set value set to be smaller than the first set value is compared with each integrated value related to the second and third threshold values, and the second set value is determined by the second set value. When the second set value is smaller than each of the integrated values, the gain error signal is used as a gain error signal for decreasing the gain.
Each of the above methods suppresses an increase in the amplitude of a short-period signal due to crosstalk between signals, and enables accurate detection of only the amplitude of a long-period signal. Optimize the amplitude difference.
[0022]
Next, a second invention provides an optical disc apparatus, comprising: an aberration correction unit for adjusting a divergence or a convergence angle of an incident light beam from a laser light source to an optical disc; The objective lens forming the light spot on the recording layer is moved in the direction of the optical axis of the incident light beam, and at this time, the reflected light at the light spot is received and output by the photodetector, and the reproduced signal is processed and analyzed. A control unit that controls the aberration correction unit based on the analysis result, and when a spherical aberration occurs in the light spot, the position of the objective lens is shifted from a focal point position with respect to the information recording layer in the optical axis direction. An aberration correction method in an optical disk device that corrects the spherical aberration by using the reproduction signal having a maximum amplitude in a deviated state. When the information is recorded, the information is reproduced, and the control unit performs the first step of obtaining the in-focus position of the objective lens, and the control unit irradiates the objective lens from the in-focus position obtained in the first step. It is moved back and forth in the axial direction by the same distance, and at each moving position, a long-period signal and a short-period signal included in the reproduction signal obtained from the photodetector are separated, and a signal at each moving position at each moving position And calculating the difference between the maximum amplitudes of the signals in each cycle at each movement position, and calculating the difference between the calculation results for each movement position of the objective lens obtained in the second procedure. A spherical aberration correcting method for an optical disk device, comprising: executing a third procedure for obtaining the result and a fourth procedure for controlling the aberration correcting unit so that a difference between the calculation results obtained in the third procedure approaches zero. Related.
[0023]
The present invention is characterized in that, unlike the first invention, in the second procedure, control data of the aberration corrector is created based on the long-period signal and the short-period signal included in the reproduction signal.
Therefore, in the second procedure, a long-period signal and a short-period signal included in the reproduction signal obtained from the photodetector are divided at each moving position of the objective lens, and the signal of each period is moved at each moving position. , And a difference between the maximum amplitudes of the signals in each cycle is calculated for each moving position.
As shown in FIG. 33B, the change of the maximum amplitude of the long-period signal and the short-period signal with respect to the defocus amount of the objective lens is shifted in the opposite direction around the focal point. The calculation result in the second procedure of the invention shows a larger change rate with respect to the defocus amount of the objective lens as compared with the first invention.
That is, by using the calculation result in the second procedure, more precise and accurate aberration correction control can be performed.
In particular, in the present invention, similarly to the first invention, the sequence control of repeating the first to fourth procedures until the calculation result obtained in the third procedure falls within the allowable range is executed, and the refractive index of the transparent substrate is adjusted. The aberration correction can be performed irrespective of the above, but there is an advantage that the aberration correction can be completed in a short time by reducing the number of repetitions.
[0024]
In the second procedure of the present invention, the following method can be adopted as means for obtaining the maximum amplitude of the reproduction signal at each moving position of the objective lens.
(1) A reproduction signal obtained from the photodetector is sampled at a predetermined cycle, a zero cross point of the sampling signal is detected to detect a polarity inversion interval, and a peak value and a bottom value within the inversion interval are determined. Calculating and filtering based on the inversion interval information, the peak value and the bottom value are classified in association with long-period and short-period signals, and a peak value group and a bottom value classified according to each period are obtained. A method of obtaining the maximum amplitude of a signal in each cycle using a representative value of a group.
(2) The reproduction signal obtained from the photodetector is sampled at a predetermined cycle, and based on the time interval of the zero-cross point and the state transition determined by the partial response characteristic and the run-length limit, the signal is either a short-cycle signal or a long signal. Determine whether the signal is a periodic signal, and perform filtering based on the determination information to classify the signal in association with the long-period and short-period signals, and use the representative value of the signal group of each divided period. A method to find the maximum amplitude of the signal in each cycle.
[0025]
According to a third aspect of the present invention, in the optical disc apparatus, an aberration corrector for adjusting a divergence or a convergence angle of an incident system light beam from a laser light source to the optical disc, and an objective lens condensing the incident system light beam to obtain information on the optical disc A waveform equalizer that sets a boost amount and performs equalization processing on a reproduced signal that is received and output by a photodetector and that is reflected by a light spot formed on a recording layer, and the objective lens is connected to the incident system. A control unit that moves the light beam in the optical axis direction and controls the aberration correction unit based on a boost amount obtained from the waveform equalization unit at that time, and some information is recorded on the optical disc. If the information is reproduced, the control unit reproduces the information, and the control unit determines whether the objective lens is focused on the optical disc in a first procedure, and determines whether the objective lens is focused in the first procedure. A second procedure of moving the optical axis direction back and forth by the same distance and detecting each boost amount set by the waveform equalizing unit at each moving position, and calculating a difference between the boost amounts detected in the second procedure. A spherical aberration generated in the light spot is corrected by executing a third procedure and a fourth procedure of controlling the aberration corrector so that the calculation result obtained in the third procedure approaches zero. And a method for correcting spherical aberration in an optical disc device.
[0026]
Generally, in an optical disk device, a signal equal to or higher than a signal band reproduced from an optical disk is cut off by a low-pass filter to reduce noise, and a waveform equalization process for increasing a gain in a signal band having a small amplitude is performed. Done.
In this case, since the reproduced signal differs depending on the optical disc, it is necessary to adjust the signal transmission characteristic in the waveform equalization processing so as to adapt to the reproduced signal, and set the cutoff frequency of the low-pass filter and read the signal. A boost amount for increasing a gain of a specific frequency band related to a reproduction signal is adaptively set.
Therefore, the amplitude of the reproduced signal after being processed by the waveform equalizing section has a constant value regardless of the long period or the short period, and the influence of spherical aberration and defocus amount does not appear in the reproduced signal. On the other hand, the boost amount is a control value for the waveform equalization process, and is a value reflecting each of the above conditions. That is, when the amplitude ratio of the short-period signal to the long-period signal is small, the boost amount increases, and conversely, the boost amount decreases.
Therefore, in the present invention, the aberration correction using the boost amount as the control value is performed, and the waveform equalization unit sets the objective lens while moving the objective lens from the in-focus position by the same distance back and forth in the optical axis direction. The aberration correction unit is controlled so that the difference between the boost amounts approaches zero.
Also in the present invention, if the sequence control of repeating the first to fourth steps is performed until the calculation result obtained in the third step falls within the allowable range, accurate control can be performed regardless of the refractive index of the transparent substrate. Aberration correction can be realized.
[0027]
According to a fourth aspect of the present invention, when the optical disc apparatus performs continuous recording or reproduction, the recording or reproduction is performed at a speed higher than a normal linear velocity to secure a time margin. The present invention relates to a method for correcting spherical aberration in a disk drive, wherein the method for correcting spherical aberration according to the first or second invention is executed within a margin time.
[0028]
Generally, in an optical disk device, when performing continuous recording or reproduction, the wavelength of a laser tends to be slightly shifted with a change in temperature.
In that case, in the optical disk, apart from the spherical aberration due to the thickness error of the transparent substrate, the spherical aberration accompanying the above-mentioned wavelength shift also occurs.
According to the present invention, since a sufficient time is secured in the normal recording or reproduction mode and the aberration correction is appropriately executed, the spherical aberration due to the laser wavelength shift can also be corrected.
When recording or reproduction is performed at a speed higher than the normal linear speed, for example, data transfer at the time of recording or reproduction is performed as fast as possible, and a margin time is secured by combining a buffering function. Can be adopted.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, each embodiment of the “aberration correction method for an optical disc” of the present invention will be described in detail with reference to FIGS. 1 to 23.
[Embodiment 1]
First, FIG. 1 shows a schematic configuration of an optical disk device to which this embodiment is applied. A beam splitter 2, an aberration corrector 3, and an objective lens 4 are sequentially arranged in the traveling direction of the laser light emitted from the laser light source 1, and a light spot 7 is formed on the information recording layer 6 of the optical disk 5 by the objective lens 4. Then, the reflected light from the optical disk 5 is returned from the objective lens 4 to the beam splitter 2 again through the aberration correction unit 3, and the beam splitter 2 reflects the returned light and makes it incident on the photodetector 8.
The laser light source 1 and the optical elements 2, 3, and 4 are mounted on the optical pickup 9, and move integrally in the radial direction of the optical disk 5.
In this embodiment, a general beam splitter 2 is used, but a configuration may be employed in which a polarized beam splitter and a quarter-wave plate are applied to efficiently separate reflected light.
[0030]
Here, the aberration corrector 3 has a function of changing the divergence angle or the convergence angle of the light beam incident on the objective lens 4.
For example, as shown in FIG. 1, it is composed of a combination of a concave lens 3a and a convex lens 3b, and one or both lenses 3a and 3b can be moved in the optical axis direction, and the distance between the two lenses 3a and 3b is changed to change the function. Can be adopted.
In addition, a variable focus lens composed of a liquid crystal element having a concentric electrode pattern centered on the optical axis is used to control the phase change amount of the liquid crystal transmitted light by a voltage applied to the electrode pattern, or two convex lenses Or a method using a hologram lens.
Further, a collimator lens can be used for the aberration corrector 3 and the objective lens 4 which are condensing optical systems, and the divergence angle or convergence angle of the light beam can be changed by moving the collimator lens in the optical axis direction. It is.
[0031]
On the other hand, the reproduction signal output from the photodetector 8 is amplified by the high-frequency amplifier 10 and input to the signal processing circuit 11, which processes the reproduction signal and outputs each control signal to the servo circuit 12. Focus control for moving the objective lens 4 in the optical axis direction, tracking control for finely adjusting the optical axis in the radial direction, slide control for coarsely moving the entire optical pickup 9 in the radial direction of the optical disc, and a spindle motor. 13 spindle control is executed.
Although the focus, tracking, and slide control is performed via an actuator, the actuator is not shown in FIG.
[0032]
The feature of this embodiment is that, as described above, the aberration correction unit 3 is provided on the optical axis, the servo circuit 12 has a built-in aberration correction control unit 14, and the aberration correction control unit 14 The point is that the divergence angle or convergence angle of the light beam in the aberration correction unit 3 is controlled via an actuator (not shown) based on the analysis result of the reproduction signal of the optical device 8 by a predetermined algorithm.
[0033]
By the way, in this embodiment, the purpose of forming a proper light spot 7 by correcting the spherical aberration caused by the deviation of the thickness t of the transparent substrate 15 of the optical disk 5, and obtaining the same from the photodetector 8. The basic operation of performing the control by controlling the aberration correction unit 3 based on the reproduced signal to be performed is the same as the technology disclosed in Patent Document 1 described above.
However, the present invention does not target the optical disc 101 on which the specific pattern is formed in the specific area 106 as in Patent Literature 1, but performs the above-described aberration correction operation on the normal optical disc 5.
Therefore, in this embodiment, the procedure for checking the optical disk 5 in advance and the signal analysis algorithm by the aberration correction control unit 14 incorporated in the servo circuit 12 are different from those in Patent Document 1, and the aberration correction control unit The method of controlling the aberration corrector 3 using the analysis result obtained by the analysis algorithm is also different, and the control procedure is simplified to realize more efficient aberration correction.
[0034]
Next, the aberration correction procedure in this embodiment is shown in the flowcharts of FIGS.
First, when the optical disk 5 is set in the optical disk device, it is confirmed whether or not there is any record information on the optical disk 5 (S1, S2).
Here, if the optical disk 5 is a read-only disk, or if it is a rewritable disk and some information has already been written, the read mode is set and the focus adjustment function is set to the ON state. (S2 → S5, S6).
A rewritable disc in which information is recorded in a pre-recorded area, or a rotation at the time of recording in a wobbling groove such as a CD-R (Compact Disc recordable) or an MD (Mini Disc). When the control information and the address management information of the sector are recorded, they may be regarded as the record information.
On the other hand, when the optical disk 5 is a rewritable disk and information has not been written, the recording mode is set, information is recorded for a certain period of time, and after the recording is completed, the mode is switched to the reading mode. The focus adjustment function is set to the ON state (S2, S3 to S6).
Here, the recording information does not need to be a specific pattern, but may be any data having randomness in accordance with a normal run-length limit.
The above-described recording is performed in a state where the aberration correction is not performed. However, even if the recording is executed by performing the servo control in the correction state corresponding to the appropriate preset value, the aberration correction procedure described later is hardly affected. .
[0035]
When the above procedure is completed, the process proceeds to the reproduction of the recorded information, and the servo circuit 12 obtains the in-focus position of the objective lens 4 with respect to the optical disk 5 (S7, S8).
Then, the servo circuit 12 moves the objective lens 4 from the in-focus position by + α in the optical axis direction, and samples a reproduction signal obtained in that state at a predetermined cycle (S9).
Here, the amplitude of the reproduction signal changes at various frequencies according to the recording information, but the aberration correction control unit 14 obtains the maximum amplitude Ga from the change of the sampling signal (S10).
It is optional whether the maximum amplitude Ga is obtained as a peak-to-peak value or as one of positive and negative peak values.
When the maximum amplitude Ga is obtained, the servo circuit 12 moves the objective lens 4 by the focus adjustment function by an equal distance to the opposite side around the focal point (moves by −α from the focal point in the optical axis direction), The aberration correction controller 14 obtains the maximum amplitude Gb of the sampling signal in the same procedure as described above (S11, S12).
Then, the aberration correction controller 14 calculates the difference (Ga-Gb) between the maximum amplitudes of the reproduced signals obtained at the respective positions of the objective lens 4, and when the absolute value | Ga-Gb | of the difference is equal to or less than the predetermined threshold value Ea1, It is determined whether or not there is (S13, S14).
[0036]
By the way, as is clear from FIG. 32 (B) in the prior art, the amplitude of the reproduced signal is larger in the long-period portion than in the short-period portion, and thus the maximum amplitudes Ga and Gb are obtained from the long-period reproduced signal. It is considered to have been obtained.
Further, as shown in FIG. 33B, if the thickness t of the transparent substrate 103 of the optical disk 101 exceeds the allowable range and spherical aberration occurs, the reproduced signal is shifted from the focal point of the objective lens 104. Take the maximum amplitude value.
More specifically, in light of this embodiment, as shown in FIG. 4, a change in the maximum amplitude of the long-period reproduction signal with respect to the defocus amount is indicated by a two-dot chain line. That is, when (A) spherical aberration occurs on the (-) side, it becomes maximum on the near side of the focal point, and (C) when spherical aberration occurs on the (+) side, on the far side from the focal point. (B) when spherical aberration does not occur, it tends to be maximum at the focal point.
[0037]
From this, the sign of the maximum amplitude difference (Ga-Gb) indicates whether spherical aberration occurs on the (+) / (-) side, and the absolute value | Ga-Gb | Control amount for this purpose.
Therefore, in this embodiment, the value of Ea1 is set as a threshold value for the absolute value | Ga−Gb | for satisfying the condition (condition that the spherical aberration falls within the allowable range) substantially in the state of FIG. 4B. When the absolute value | Ga−Gb |> Ea1, the aberration correction controller 14 controls the aberration corrector 3 with (Ga−Gb) as an error value (S14, S15).
In other words, since Ga = Gb in the state of FIG. 4B, the threshold value Ea1 is set to a value close to 0.
[0038]
Then, after controlling the aberration corrector 3 based on the error value (Ga-Gb), steps S8 to S14 are repeated and executed again, and the procedure is repeated until | Ga-Gb | ≦ Ea1 is satisfied in step S14. (S14, S15 → S8-S14).
The above-described repetition procedure is shown in the timing chart of FIG. 5, in which (A) shows the switching state of the position of the objective lens 4 and (B) shows the change in the maximum amplitude Ga, Gb of the reproduction signal by the repetition control. It can be seen that the absolute value | Ga−Gb | converges to 0 by the repetitive control of the aberration corrector 3.
[0039]
In this embodiment, steps S8 to S14 are repeatedly executed as described above. However, when the refractive index of the transparent substrate 10 of the optical disk 5 is constant, an error value (Ga-Gb) is set in advance. If the amount of correction by the aberration corrector 3 is stored in a table, and the table is used to perform optimal correction by one control, aberration correction can be completed very quickly.
In addition, if the original focus shift of the objective lens 4 is corrected and optimized together with the above-described aberration correction, a more ideal light spot 7 can be formed.
In this case, a method of optimizing the aberration correction procedure and the defocus correction alternately and alternately, and a method of executing both corrections simultaneously to drive to the optimum condition can be considered.
[0040]
According to this embodiment, the aberration can be corrected regardless of the conditions of the optical disc as described above, and the maximum of the reproduction signal can be obtained with the objective lens 4 moved by an equal amount α before and after the focal point. Since the control data of the aberration corrector 3 can be obtained only by obtaining the amplitude value, the aberration correction can be completed in a very short time as compared with the optical disc device and the aberration correction method of Patent Document 1.
After the aberration correction is completed, it is needless to say that the in-focus position is obtained again, the objective lens 4 is controlled to move to that position, and normal recording or reproduction is executed thereafter.
[0041]
[Embodiment 2]
In this embodiment, similarly to Patent Document 1, aberration correction is performed using long-period and short-period reproduction signals.
However, as in the case of the first embodiment, since a normal optical disc is targeted, a specific analysis algorithm is applied in order to obtain the maximum amplitude related to the reproduction signal in each cycle.
Another characteristic is a control procedure for performing aberration correction in a shorter time.
[0042]
The schematic configuration of an optical disk device to which this embodiment is applied is the same as that shown in FIG. 1, and the procedure shown in the flowchart of FIG.
Therefore, a description thereof will be omitted here, and a description will be given of a signal processing procedure and a control procedure for aberration correction in the aberration correction control unit 9 after the reproduction of the recorded information is started.
[0043]
FIG. 6 is a functional block diagram relating to signal processing of the aberration correction control unit 14, and FIG. 7 is a flowchart showing the signal processing / aberration correction control procedure. However, the optical system control means 26 in FIG. 6 controls the objective lens 4 mounted on the optical pickup 9 side and the actuator of the aberration correction unit 3, and is a control means which performs both focus adjustment and aberration correction. .
First, when the reproduction of the recorded information on the optical disk 5 is started, the servo circuit 12 executes the focus control on the optical system control means 26 to obtain the in-focus position of the objective lens 4 on the optical disk 5 (S21, S22). .
Then, the servo circuit 12 moves the objective lens 4 by + α from the in-focus position by the optical system control means 26, and the aberration correction control unit 14 uses the A / D converter 21 to convert the reproduction signal input in that state for a predetermined period. (S23).
In this case, even if the clock in the A / D converter 21 is a self-running fixed frequency clock, it is synchronized with a signal bit using a PLL (phase-locked loop) circuit. Is also good.
[0044]
Steps S21 and S22 are the same as those in the first embodiment, but in this embodiment, a zero-cross detector 22, a peak / bottom value detector (hereinafter, referred to as a “PB value detector”) 23, and an inversion interval detection The amplitudes LA and SA of the long-period and short-period signals included in the reproduced signal are obtained by the section 24 and the filtering means 25 (S24).
Hereinafter, this signal processing method will be specifically described.
[0045]
The sampled reproduction signal is input to the zero-cross detector 22 and the PB value detector 23.
Here, the zero-cross detecting unit 22 sets a zero level with a predetermined level as a threshold, finds a difference between the reproduced signal and the zero level, and detects the time point as a zero-cross point each time the polarity of the difference is reversed. .
Then, the zero-cross information is given to the PB value detection unit 23, and the PB value detection unit 23 detects the peak value Pn and the bottom value Bn of the reproduced signal obtained in the intermediate time zone of the preceding and following zero cross points. (However, “n” is an integer that is incremented by one each time two zero cross points are obtained.)
[0046]
The zero-cross information obtained by the zero-cross detecting unit 22 is given to the inversion interval detecting unit 24, and the inversion interval detecting unit 24 detects the inversion interval Tn corresponding to the time interval between the preceding and following zero cross points. That is, the number of clocks is counted from the time when the zero-cross information is received, and the count value at the time when the zero-cross information is received next is detected as the inversion interval Tn.
Each information of the peak value Pn and the bottom value Bn obtained by the PB value detection unit 23 and the inversion interval Tn obtained by the inversion interval detection unit 24 is provided to the filtering unit 25.
[0047]
The filtering unit 25 includes a table for classifying the inversion interval Tn related to the zero cross point into a long cycle and a short cycle. Each time the inversion interval Tn is obtained from the inversion interval detection unit 24, the filtering unit 25 uses the table. Then, the peak value Pn and the bottom value Bn are separated for each period and saved in a memory.
Then, a representative value (average value or median) of the peak value Pn and the bottom value Bn for each cycle saved based on the reproduction signal for a certain time is obtained, and the representative value of the peak value Pn and the bottom value Bn for each cycle. , The amplitude LA of the long-period reproduction signal and the amplitude SA of the short-period reproduction signal are obtained.
[0048]
In the above case, both the peak value Pn and the bottom value Bn are obtained and the amplitude is obtained as a peak-to-peak value. However, the PB value detection unit 23 is used as a peak value detection unit or a bottom detection unit. Alternatively, only one of the bottom values Bn may be obtained, and the peak value Pn or the bottom value Bn for each cycle may be directly used as the amplitude.
The method using both the peak value Pn and the bottom value Bn has the advantage of being unaffected by the asymmetry of the reproduced signal. However, the method using either one can ensure sufficient accuracy in some cases. There is an advantage that the procedure is simplified.
[0049]
The above signal processing method can be more specifically understood with reference to FIG.
In the figure, the horizontal axis represents the time axis, and the vertical axis represents the signal level of the reproduced signal, and the waveform of the reproduced signal is shown.
The zero-crossing detector 22 outputs zero-crossing information Z each time the reproduction signal crosses a zero level, using the time as a zero-crossing point.
The zero-cross information Z is given by the following equation, and gives a polarity corresponding to the timing of the zero-cross point and the positive or negative slope of the reproduced signal at that point.
Z = Pole (Sn-1) ∧Pole (Sn)
Here, Sn: signal level at the sampling point
∧: EX-OR operation
Pole: Polarity indicated by 0, 1
[0050]
The inversion interval detection unit 24 counts the sampling points at each timing when the zero-cross detection unit 22 outputs the zero-cross information Z to obtain the inversion interval Tn related to the preceding and following zero-cross points.
The PB value detection unit 23 detects the peak value Pn and the bottom value Bn until the next zero-cross information Z is obtained every time the zero-cross detection unit 22 outputs the zero-cross information Z. In FIG. For each inversion interval Tn, P0, P1, P2, P3, P4, P5, P6,... Indicated by ● correspond to the peak values, and B0, B1, B2, B3, B4,.
The peak value Pn and the bottom value Bn can be searched using a hill-climbing method.
That is, for the sampling signal at each inversion interval Tn, the maximum value or the minimum value is obtained by calculating M by the following equation, and the peak value Pn-1 is obtained at the immediately preceding inversion interval Tn-1. Is the extreme value (maximum value) as the bottom value Bn. Conversely, if the bottom value Bn-1 is obtained, the extreme value (minimum value) is the peak value Pn.
M = MAX (Sn-1, Sn) or M = MIN (Sn-1, Sn)
Here, Sn: signal level at the sampling point
MAX: Select the larger of the two arguments
MIN: Select the smaller of the two arguments
In the case where the amplitude is obtained from only the peak value Pn or the bottom value Bn as described above, a method of selecting the one having the larger absolute value in the preceding and following reversal intervals Tn can be adopted.
[0051]
Next, the filtering unit 25 divides the inversion interval Tn into a long cycle and a short cycle. In the example of FIG. 8, the long cycle is set to Tn: 6 to 8, and the short cycle is set to Tn: 3.
Then, the peak value Pn and the bottom value Bn are divided for each period, and a representative value regarding the divided peak value Pn and the bottom value Bn is obtained.
In FIG. 8, for the long period (Tn: 6 to 8), P1, P5,... Are included as peak values, and B1, B2, B4,. ... are included as peak values, and B0, B3, ... are included as bottom values, and PL, B1, B2 represent representative values of signal levels indicated by P1, P5, ... over a long period range. , B4,..., The representative signal level represented by P0, P2, P4,... In the short cycle range is PS, and the representative signal level represented by B0, B3,. Then, a value after filtering is obtained in the following relationship.
Filtered value
Peak long period range Tn: 6-8 → PL
Peak short period range Tn: 3 → PS
Bottom Short period range Tn: 3 → BS
Bottom Long period range Tn: 6-8 → BL
[0052]
Then, the filtering means 25 calculates the amplitude LA of the long-period reproduction signal and the amplitude SA of the short-period reproduction signal by the following equation.
LA = PL-BL
SA = PS-BS
The amplitudes LA and SA of each cycle are obtained as peak-to-peak values. However, when the peak value or the bottom value itself is obtained as the amplitude, the amplitudes may be determined as follows.
LA = PL, SA = PS or LA = -BL, SA = -BS
[0053]
Here, returning to the flowchart of FIG. 7, the respective amplitudes LA and SA relating to the long-period and short-period reproduction signals obtained by the above-described processing are output to the optical system control unit 26. Finds the difference ΔGa = (LA−SA) between the amplitudes LA and SA in each cycle (S24).
[0054]
Next, the optical system control means 26 moves the objective lens 4 by -α from the in-focus position, contrary to step S23 (S25).
Then, the reproduced signal obtained in that state is sampled at a predetermined period by the A / D converter 21, and the amplitudes LA 'and SA' of the long-period and short-period reproduced signals are obtained based on the same signal processing method as described above. , And their difference ΔGb = (LA′−SA ′) (S26).
[0055]
Incidentally, the optical system control means 26 moves the position of the objective lens 4 by ± α around the focal point in the optical axis direction to obtain the amplitudes LA, SA, LA ′, SA ′ of the long-period and short-period reproduction signals. When these are made to correspond to the relationship between the defocus amount and the signal amplitude similarly to FIG. 4 verified in the first embodiment, the respective amplitudes LA, SA, LA ′, and SA ′ are positioned as shown in FIG. It becomes.
As shown in the figure, the amplitudes of the long-period and short-period reproduction signals with respect to the amount of defocus depend on the spherical aberration states (A), (B), and (C) due to the thickness t of the transparent substrate 10 of the optical disc 5. Exhibit different changes. However, in the figure, the solid line corresponds to the change in the amplitude of the long-period reproduction signal, and the broken line corresponds to the change in the amplitude of the short-period reproduction signal.
When spherical aberration occurs, the defocus amount at which the amplitude change in each cycle becomes the maximum value is shifted in the opposite direction around the focal point, which is the conventional technique shown in FIG. Corresponds to the content described in.
Specifically, (A) when the spherical aberration occurs on the (−) side, the maximum amplitude related to the long-period reproduction signal is on the near side from the focal point, and the maximum amplitude related to the short-period reproduction signal is When the spherical aberration occurs on the (+) side, the relationship becomes opposite to the above, and when (B) the spherical aberration does not occur, each reproduction is performed. The maximum amplitude of the signal is obtained at the focal point.
Therefore, as is clear from FIG. 9, when (A) spherical aberration occurs on the (−) side, ΔGa <ΔGb, and (C) when spherical aberration occurs on the (+) side, ΔGa> ΔGb. ΔGb, and (B) when no spherical aberration occurs, ΔGa = ΔGb.
[0056]
Therefore, returning to FIG. 7, the optical system control means 26 calculates (ΔGa−ΔGb) and determines whether or not the absolute value | ΔGa−ΔGb | of the difference is equal to or smaller than a predetermined threshold value Ea2 (S27, S28).
Here, the sign of (ΔGa−ΔGb) indicates whether spherical aberration occurs on the (+) / (−) side, and the absolute value | ΔGa−ΔGb | gives a control amount for aberration correction. become.
Therefore, the optical system control means 26 sets the value of Ea2 as a threshold value for the absolute value | Ga−Gb | for satisfying the condition (condition where the spherical aberration falls within the allowable range) substantially in the state of FIG. 9B. Then, the aberration correction unit 3 is controlled using (ΔGa−ΔGb) as an error value (S28, S29).
Note that in the state of FIG. 9B, ΔGa = ΔGb, so the threshold value Ea2 is set to a value close to 0.
[0057]
Thereafter, after controlling the aberration correction unit 3 based on (ΔGa−ΔGb), steps S22 to S28 are repeated and executed again, and the procedure is repeated until | ΔGa−ΔGb | ≦ Ea2 is satisfied in step S28. This is the same as in the first embodiment (S28, S29 → S22 to S28).
As a result, the aberration corrector 3 gradually adjusts the divergence or convergence angle of the incident light beam, and | ΔGa−ΔGb | converges to 0, thereby finally | ΔGa−ΔGb | ≦ Ea2. At this stage, the aberration correction is completed.
In this embodiment, steps S22 to S28 are repeatedly executed as described above. However, when the refractive index of the transparent substrate 10 of the optical disc 5 is constant, the error value (ΔGa−ΔGb) is determined in advance. If the correction amount of the aberration corrector 3 is tabulated and the table is used to perform the optimum correction in one control, the aberration correction can be completed very quickly, and As in the first embodiment, a more ideal light spot 7 can be formed by performing the correction of the original defocus of the objective lens 4 simultaneously or alternately with the correction procedure.
[0058]
Here, as apparent from a comparison between FIG. 9 according to this embodiment and FIG. 4 according to the first embodiment, | ΔGa−ΔGb | in FIG. 9 with respect to the moving amount ± α of the objective lens 4 is | in FIG. Is larger than Ga-Gb |, and the rate of change of | ΔGa-ΔGb | with respect to the defocus amount is larger than the rate of change of | Ga-Gb |.
Therefore, according to this embodiment, the aberration correction control is executed using (ΔGa−ΔGb) as an error value after obtaining the amplitudes of the long-period and short-period reproduction signals by the signal processing method described above. More accurate and efficient control becomes possible.
[0059]
[Embodiment 3]
In the first and second embodiments, the maximum amplitude of the reproduction signal at each position of the objective lens 4 is basic information for obtaining control data for the aberration corrector 3, and the aberration correction controller 14 for obtaining the maximum amplitude. Has a very important significance in securing the accuracy of aberration correction.
Further, the processing method of the reproduction signal (steps S24 and S26 in FIG. 7) described in the second embodiment is merely an example, and other various signal processing methods can be applied.
Thus, in this embodiment, various signal processing methods applicable to the first and second embodiments will be specifically described as the following examples.
Note that the signal processing method itself of the following embodiment can also be applied to a case where the change in the amplitude of the reproduced signal in each cycle is obtained while changing the position of the objective lens 104 in the aberration correction method of Patent Document 1 according to the related art.
[0060]
<Example 1>
The signal processing method in the aberration correction control unit 14 according to this example is applicable to the second embodiment, and a functional block diagram relating to the signal processing executed by the control unit 9 of the optical disk device is shown in FIG.
First, as in the case of the second embodiment, a reproduction signal obtained by reading recorded information on the optical disk 5 is input from the photodetector 8 to the control unit 9 and is sampled by the A / D converter 31.
However, the clock supplied to the A / D converter 31 in this case is synchronized with the signal bit rate using a PLL circuit, and sampling is performed at that bit rate.
[0061]
The sampled reproduction signal is output to the zero-cross detection unit 22 and the interpolation unit 32.
The zero-cross detection unit 22 detects the zero-cross information Z in the same procedure as in the second embodiment, and outputs it to a partial response determination unit (hereinafter, referred to as a “PR determination unit”) 33.
On the other hand, the interpolation unit 32 delays the reproduction signal by 180 degrees, calculates the average of the immediately preceding sampling signal and the current sampling signal, and outputs the average to the filtering unit 34 and the PR discrimination unit 33.
[0062]
The PR discriminating unit 33 discriminates a target value based on the run-length limit (RLL) of the reproduction signal and a state transition determined by the PR characteristic using the zero-cross information and the average data.
Here, the partial response (PR) characteristics will be described.
When the characteristics of PR (a, b, b, a) are imparted to the solitary wave and equalized, the equalized waveform is (1, 7) RLL, 0, a, a + b, 2a, 2b, a + 2b, 2a + 2b Take the seven values of
When the seven values are input to the Viterbi decoder, the original signal (input value) and the reproduced signal after PR equalization (output value) are restricted by the past signal. By using the fact that the input signal "1" does not continue more than twice, it can be represented by a state transition diagram as shown in FIG.
In the drawing, S0 to S5 indicate a state determined by the immediately preceding output value.
From this state transition diagram, for example, when in the state S2, when the input value is a + 2b, the output value becomes 1 and the state transits to the state S3. When the input value is 2b, the output value becomes 1 and the state moves to the state S4. Transitions, but no other input values are entered.
When the zero-cross information Z is "1", it corresponds to a zero-cross point, which is represented by a value "a + b" in the state transition diagram of FIG. → It occurs during the transition to S5.
In this case, the right half states S2, S3, and S4 in FIG. 11 follow a path of a positive value (a + 2b, 2a + 2b, or 2b when normalized to a + b = 0), and the left half states S5, S0 , S1 are positive paths by referring to values before or after the zero crossing point to follow a path of a negative value (either 0, a, or 2a when normalized to a + b = 0). Or a negative route.
Moreover, if the interval from a certain zero cross point to the next zero cross point is known (that is, if the number of transitions from state S2 to state S5 or from state S5 to state S2 is known), the route is determined. And the possible values become clear for each sample point.
Further, in the state transition diagram of FIG. 11, when the value is other than “a + b”, that is, when it is not the zero cross point, the zero cross information Z is “0”.
From this state transition diagram, two consecutive zero cross points (Z = “1”) are not taken out consecutively, and in the case of RLL (1, X), adjacent zero cross points (Z = “1”) There is at least one “0” between them (when the zero point information Z changes from “1” → “0” → “1”, that is, state S1 → S2 → S4 → S5 or state S4 → When the transition is made from S5 to S1 to S2).
In the case of RLL (2, X), there are at least two “0” s between adjacent Z = “1”.
In an actual signal, it is fully expected that the detection of the zero cross point itself will be erroneously detected due to the influence of noise or the like.However, in the case of feedback control, if the probability of making a correct determination exceeds the probability of making an error, the signal converges in the correct direction. In addition, due to sufficient integration processing, single-shot noise is considered to be practically acceptable.
[0063]
Based on the partial response (PR) characteristics described above, the PR determination unit 33 sets the minimum run-length limit of the reproduction signal to 2 (the minimum inversion interval is 3) for the PR (a, b, b, a) characteristics, for example. In FIG. 11, there is no path of S2.fwdarw.S4 and S5.fwdarw.S1 in FIG. 11, and there is only a circuit path transition. Since the zero crossing state is S2 and S5, the interval between the polarity and the zero crossing point is divided For example, the target value at each sampling point can be determined.
When the minimum run-length limit of the reproduction signal is 1 (the minimum inversion interval is 2), the state transition is performed as shown in FIG. 11 and the zero-crossing states are S2 and S5. The target value at can be determined.
That is, the PR determination unit 33 calculates the average value based on the zero-cross information Z (including the polarity and the interval between the zero-cross points) of the zero-cross detection unit 22 and the average value data of the adjacent sampling signals output from the interpolation unit 32. Discrimination data of which target value the data corresponds to is created.
[0064]
Next, the filtering unit 34 classifies each average value data obtained from the interpolation unit 32 for each target value using the determination data obtained from the PR determination unit 33.
However, the zero level is omitted because it is not used.
Specifically, as shown in FIG. 12, the filtering means 34 divides each average value data corresponding to the target value; 2a + 2b, a + 2b, a, 0 obtained from the PR discriminator 33, and The average value PL, PS, BS, BL is obtained for each group.
[0065]
In the figure, the average value data group indicated by ○ belongs to the target value; 2a + 2b, 0, and the average value data group indicated by ● belongs to the target value: a + 2b, a, but the average value belongs to the target value: 2a + 2b. The value data group is a value close to the peak value of the long-period signal, the average value data group belonging to the target value; 0 is a value close to the bottom value of the long-period signal, and the average value data group belonging to the target value: a + 2b is The average value data group belonging to the target value; a has a value close to the peak value of the short-period signal and a value close to the bottom value of the short-period signal.
Therefore, the average values PL and BL are values approximating the peak value and the bottom value of the long-period signal, respectively, and the average values PS and BS are values approximating the peak value and the bottom value of the short-period signal. .
[0066]
Then, as in the case of the second embodiment, the filtering means 34 calculates the amplitude LA of the long-period reproduction signal and the amplitude SA of the short-period reproduction signal as a peak-to-peak value by the following equation.
LA = PL-BL
SA = PS-BS
Further, when the amplitudes LA and SA are obtained using the peak value or the bottom value itself as the amplitude, the following expression may be used as in the case of the second embodiment.
LA = PL, SA = PS or LA = -BL, SA = -BS
[0067]
<Example 2>
The signal processing method in the aberration correction control unit 14 according to this example is applicable to the second embodiment, and a functional block diagram related to the signal processing is shown in FIG.
In the figure, an A / D converter 41 operates with a free-running clock of a fixed frequency, samples a reproduction signal input from a photodetector 8, and converts the sampled signal into a digital phase locked loop (DPLL) unit 42. Output to
[0068]
Here, the DPLL unit 42 has a self-contained PLL function, interpolates an input signal by itself and generates a resampling signal, and controls a timing of interpolation by extracting a phase error and feeding it back. It has the function to do.
More specifically, the resampling / interpolating unit 42a resamples the sampling signal of the A / D converter 41 based on the timing signal obtained from the timing generating unit 42b, and has a configuration as shown in FIG. The average of the immediately preceding sampling signal and the current sampling signal is obtained, and the average is output to the phase error detection unit 42c as a resampling signal obtained by performing interpolation processing.
In the phase error detection unit 42c, the resampling signal after the interpolation processing is output to the filtering unit 34 in the next stage, and the phase error is detected and output to the loop filter 42d. Therefore, the zero cross information Z is also output to the filtering means 34.
The loop filter 42d extracts a low-frequency component of the phase error signal and outputs it as error level information to the resampling / interpolating unit 42a.
Therefore, according to the DPLL unit 42, it is possible to obtain a resampling signal obtained by interpolating the output of the A / D converter 41 operating with the free-running clock at an accurate timing, and to obtain a zero-crossing signal from the phase error detection unit 42c. Information Z is also obtained.
[0069]
Next, the resampling signal of the DPLL section 42 and the zero-cross information Z are output to the PR discriminating section 33, and the PR discriminating section 33 uses the zero-cross information and the resampling signal to reproduce the reproduced signal as in the case of the first embodiment. Of the target value based on the run-length limit (RLL) and the state transition determined by the PR characteristic.
Then, the resampling signal of the DPLL section 42 and the target value discrimination data of the PR discrimination section 33 are input to the filtering section 34, and thereafter, the long-period reproduction signal is reproduced in the same procedure as in the first embodiment. The amplitude LA and the amplitude SA of the short-cycle reproduced signal are obtained.
[0070]
<Example 3>
The signal processing method according to this example is applicable to the first embodiment, and a functional block diagram related to the signal processing is shown in FIG.
In the same figure, the components denoted by the same reference numerals as those in FIG. 13 of the second embodiment are the same functional units.
The feature of this embodiment is that the PR discriminating / equalizing unit 51 in the second embodiment is a PR discriminating / equalizing unit 51, and the PR discriminating / equalizing unit 51 uses the resampling signal input from the DPLL unit 42 and the zero-cross information. Tentative determination of the target value from the state transition determined by the PR equalization and the run-length limit based on the Eq. (1), and whether or not to equalize the error of the actual resampled signal with respect to the target value is selected.
That is, as described with reference to FIGS. 11 and 12 of the first embodiment, the states S2 and S5 correspond to the zero point, 2a + 2b becomes the maximum target value on the positive side, and 0 becomes the maximum target value on the negative side. However, error equalization is not selected for the resampling signals related to those target values, and error equalization is selected only for the other target values a + 2b, a + b, and a.
[0071]
In this case, the waveform equalization processing is performed on the short-period resampling signals related to the target values a + 2b, a + b, and a, and in particular, crosstalk between signals when the period changes from a long period to a short period is suppressed. .
Accordingly, the long-period resampling signal relating to the target value 2a + 2b, 0 changes according to the input signal, but the other short-period resampling signals relating to the target values a + 2b, a + b, a are equalized and substantially constant. The value is close to the value.
Specifically, the resampling signals (signals of ●) belonging to a + 2b and a shown in FIG. 12 and the resampling signals (signals near the zero cross) belonging to a + b in FIG. Only the resampling signal related to 2a + 2b, 0 reflects the actual amplitude.
[0072]
Therefore, when the processing is performed by the filtering means 34, the peak value PL and the bottom value BL of the long-period signal can be detected without being affected by the crosstalk between the signals. The signal amplitude LA (= PL-BL) can be accurately obtained.
In this embodiment, SA (= PS-BS) corresponding to the amplitude of a short-period signal has a substantially constant value.
[0073]
Next, although the amplitude data LA and SA of the signal of each cycle obtained by the filtering means 34 are output to the optical system control means 26, the amplitude SA of the signal of the short cycle becomes a constant value as described above. FIG. 17 shows the amplitude change of the signal in each cycle with respect to the defocus amount as in FIG. 9 in the second embodiment.
Therefore, as is apparent from FIG. 6, the control data ΔGa (= LA−SA) and ΔGb (= LA′−SA ′) output from the filtering means 34 to the optical system control means 26 are mainly composed of long-period reproduced signals. Only the changes in the amplitudes LA and LA ′ of the current data are reflected.
However, since SA and SA 'have the same value, as shown in FIG. 18, the amplitudes LA and LA' of the long-period reproduced signal are directly used as control data ΔGa (= LA) and ΔGb (= LA ′). May be used.
[0074]
In this embodiment, the resampling / interpolation is performed by the DPLL unit 42. However, when the resampling is not performed, the clock is synchronized with the bit rate of the input signal by the PLL circuit as shown in FIG. A / D converter 31 is applied, and the sampling signal is output to a PR discriminating / equalizing unit 51 and a zero-crossing detecting unit 22. The PR discriminating / equalizing unit 51 uses the zero-crossing information Z from the zero-crossing detecting unit 22 to perform PR. The provisional determination of the target value may be performed from the state transition determined by the equalization and the run-length limit.
[0075]
<Example 4>
FIG. 19 shows a circuit configuration relating to signal processing of the aberration correction control unit 14 in this embodiment.
In the figure, a signal sampled by an A / D converter 31 operating with a free-running clock of a fixed frequency is input to an ATC (Automatic Threshold Level Control) circuit 61, and the center level (DC level) is set to an optimum threshold. DC control is performed so as to match.
The output of the ATC circuit 61 is input to an AGC (Automatic Gain Control) circuit 62, which controls the gain so that the relatively short inversion interval signal has a constant magnitude. As shown in (2), the amplitude components of the upper envelope La and the lower envelope Lb are detected, and the maximum amplitude G is obtained as the difference between them, and is output to the optical system control means 26.
Therefore, the signal processing method of this example is suitable for obtaining the amplitude of a long-period signal as in the case of the first embodiment, and the GA and GB shown in FIG. 4 can be obtained with high accuracy.
[0076]
However, the AGC circuit 62 in this embodiment is not provided with a normal gain control function, but has a function of making a relatively short inversion interval signal a constant magnitude. Therefore, as shown in FIG. A cross extraction unit 62b and an error detection unit 62c are incorporated together with the circuit 62a.
Hereinafter, the function and operation of the AGC circuit 62 will be specifically described.
[0077]
As shown in FIG. 20, the cross extraction unit 62b sets the first threshold level Th0 of the intermediate level set near the center level of the level difference of the reproduction signal S at the minimum inversion interval of the reproduction signal S to a value higher than Th0. A total of three threshold levels, a second large threshold level Th1 and a third threshold level Th2 smaller than Th0, are preset, and reproduction is performed for each of the three threshold levels Th0, Th1, and Th2. The number of times when the signal crosses is independently integrated, and when any of these three integrated values reaches a preset value, all three integrated values are cleared and the same operation is repeated again. I have.
[0078]
FIG. 21 shows a circuit diagram of the cross extraction unit 62b.
As shown in the drawing, the cross extraction unit 62b includes three cross detectors 71-0 to 71-2 to which the reproduction signal S output from the gain control circuit 62a is input, and each of the cross detectors 71-0 to 71-2. The comparators 72-0 to 72-2 are provided in correspondence with each other, and a three-input OR circuit 73 to which output signals of the comparators 72-0 to 72-2 are input.
[0079]
Each of the cross detectors 71-0 to 71-2 has its threshold level (threshold) set in advance to the values of Th0, Th1, and Th2 shown in FIG. 20, and each time the reproduction signal S crosses the set threshold level. The counted integrated values (cross count values) C0, C1, and C2 are output.
Here, the level difference between the threshold levels Th0 and Th1 and the level difference between Th0 and Th2 are set to be equal to P, and the level difference P is set to be smaller than the minimum value Q of the amplitude related to the minimum inversion interval. I have.
Accordingly, any one of the three threshold levels Th0, Th1, and Th2 always indicates a correct zero-cross value (threshold level Th0 in the example of FIG. 20).
[0080]
Returning to FIG. 21 again, the cross count value detected by each of the cross detectors 71-0 to 71-2 is output to the comparators 72-0 to 72-2, and separately from the common setting value in each of the comparators 72-0 to 72-2. Are compared in size.
This set value is set to the original average zero-cross count value in a period sufficiently long with respect to the minimum inversion interval, and the comparators 72-0 to 72-2 respectively determine “H” when they match the set value. It is configured to output a signal.
[0081]
Therefore, a coincidence signal “H” is extracted from the comparator whose input integrated value (cross count value) of the comparators 72-0 to 72-2 has reached the set value earliest, and this is used as a reset pulse by the OR circuit 73. The signals are commonly supplied to the detectors 71-0 to 71-2 and reset the respective integrated values (cross count values).
As described above, since any one of the three threshold levels Th1, Th0, and Th2 always indicates a correct zero-cross value, the integrated value that has reached the set value earliest always includes the minimum inversion interval. Which is used for error calculation.
Normally, the number of times that the reproduced signal crosses the center threshold level Th0 within a predetermined time among the three threshold levels Th1, Th0, and Th2 should be the largest, and therefore, the number of crossings of the center threshold level Th0 is large. The integrated value C0 should reach the above set value earliest.
[0082]
Therefore, the error detecting unit 62c in FIG. 19 calculates the integrated value C0 of the number of crossings of the center threshold level Th0 in the cross extracting unit 62b, the integrated value C1 of the number of crossings of the upper threshold level Th1, and the lower threshold value. Based on the comparison result of the integrated value C2 of the number of crosses of the level Th2, the integrated value C0 of the number of crosses at the center threshold level Th0 in a predetermined unit time is set to be larger than the integrated values C1 and C2. A DC error signal is generated so that the balance between C1 and C2 is equal, and a gain error signal is output so that the integrated values C1 and C2 have a fixed ratio to the integrated value C0.
[0083]
The flowchart of FIG. 22 shows the operation procedure of the error detection unit 62c more specifically.
First, when the output reset signal of the cross extraction unit 62b becomes “H” level, that is, when the above-mentioned set value is reached, it is determined whether or not the integrated values are in the states of C0 ≧ C1 and C0 ≧ C2. (S31, S32).
Here, when the above-mentioned state is established, that is, when the integrated value C0 of the number of crossings related to the central threshold level Th0 in a predetermined unit time is larger than the other integrated values C1 and C2, the reproduced signal is It will be in the amplitude range.
[0084]
When the integrated values C1 and C2 are both larger than a predetermined value (for example, a value of about 70% of C0 in consideration of the influence of noise), it is determined that the amplitude of the reproduced signal is large, and the gain error in the direction of decreasing the gain is determined. A signal is output (S33, S34).
On the other hand, when the integrated values C1 and C2 are both smaller than the predetermined value, it is determined that the amplitude of the reproduced signal is small, and a gain error signal in the direction of decreasing the gain is output (S33 → S35, S36).
In addition, in cases other than the states of C0 ≧ C1 and C0 ≧ C2, or in the case of C1 ≧ predetermined value ≧ C2 or C2 ≧ predetermined value ≧ C1 even if C0 ≧ C1 and C0 ≧ C2, the gain The error signal is not output (S32 → S37, S35 → S37).
[0085]
As a result, the short-period signal in the reproduced signal shown in FIG. 23A has a nearly constant amplitude as shown in FIG. 23B, and the long-period signal is clearly separated from the short-period signal and accurately detected. Therefore, there is an advantage similar to the case where the waveform equalization processing is performed in the third embodiment.
Also, as described above, if the long-period signal is detected by the envelope detection circuit 63, the level difference between the upper envelope La and the lower envelope Lb in FIG. And the optical system control unit 26 can execute aberration correction using the control data as control data.
In this embodiment, since the operation is performed without using the PLL circuit, accurate aberration correction data can be obtained even when tracking servo is not performed.
[0086]
[Embodiment 4]
This embodiment relates to a method for performing aberration correction using a boost amount obtained when performing waveform equalization in signal processing of an optical disc device as control data.
First, FIG. 24 shows a schematic configuration of an optical disk device to which this embodiment is applied, which is basically the same as the configuration shown in FIG. The characteristic is that the calculated value of the boost amount obtained by the waveform equalizer 16 of the signal processing circuit 11 is input to the signal processing circuit 11.
That is, in this embodiment, the aberration correction control unit 14 ′ obtains the boost amount from the waveform equalization unit 16 without using the reproduction signal of the photodetector 8 as in each of the above-described embodiments, and controls the aberration correction unit 3. Control.
[0087]
Here, the waveform equalizing section 16 is usually provided at the first stage of the signal processing circuit of the optical disk device, and has a boost amount for increasing the gain of a signal band having a small amplitude in accordance with the characteristics of a reproduced signal that differs depending on the optical disk. Is set, and a signal transmission characteristic is adjusted to prevent an error from occurring in a later signal processing process.
There are various methods for obtaining the boost amount in the waveform equalization process in the optical disk device. Basically, the boost amount is calculated by obtaining the maximum amplitude and the minimum amplitude of the reproduced signal. The waveform equalizer 16 may be configured by providing each signal processing method and the boost amount calculation circuit described in the second and third embodiments.
[0088]
By the way, when the reproduction signal of the optical disk 5 has randomness due to the ordinary run-length limit, if the thickness t of the transparent substrate 15 of the optical disk 5 exceeds the allowable range and spherical aberration occurs, a long period As described above, each maximum amplitude of the short-cycle reproduction signal changes with respect to the defocus amount of the objective lens 4 in the relationship as shown in FIG. 9 in the second embodiment.
On the other hand, the boost amount is a control value for equalizing the waveform by increasing the gain of a signal band having a small amplitude as described above. When the amplitude ratio of a short-period signal to a long-period signal is small, the boost amount is increased. Increases, and vice versa, the boost amount decreases.
[0089]
Therefore, as shown in FIG. 25, when each of the states (A), (B), and (C) in FIG. 9 described above is made to correspond to the boost amount, each of the long period and the short period The maximum amplitudes LA and SA of the reproduced signal are constant irrespective of spherical aberration and defocus amount as shown in (A '), (B') and (C '). The boost amounts Ba and Bb thus obtained are values indicating the amplitude ratio of the short-cycle signal to the long-cycle signal.
That is, if there is no spherical aberration, and if the boost amounts Ba and Bb in each state where the objective lens 4 is shifted from the focal point by ± α in the optical axis direction are (medium), the spherical aberration becomes (−). Side, the boost amount Ba when the objective lens 4 is shifted from the in-focus position by + α in the optical axis direction is (small), and the boost amount Bb when the objective lens 4 is shifted by −α is ( When the spherical aberration occurs on the (+) side, the boost amount Ba when shifted by + α is (large), and the boost amount Bb when shifted by -α is (large). Small).
From this, the boost amounts Ba and Bb obtained from the waveform equalizer 16 are equal to ΔGa and ΔGb in Embodiment 2 (the difference between the maximum amplitudes of the long-period and short-period signals when the objective lens 4 is at each position). The boost amounts Ba and Bb have the same meaning, and can be used as control data of the aberration corrector 3.
[0090]
Based on the above premise, in this embodiment, the optical disc device executes aberration correction in the procedure shown in the flowchart of FIG.
As is apparent from a comparison between the figure and the correction procedure (FIG. 3) in the first embodiment, in the first embodiment, the objective lens 4 is moved by ± α from the in-focus position and the maximum value Ga of the reproduction signal is obtained. , Gb are calculated to generate an error value. In this embodiment, however, an error value is generated by detecting the boost amounts Ba and Bb from the waveform equalizer 16, which is different only in that point. It is.
[0091]
First, as in the case of the first embodiment, the optical disk 5 is checked and the focus adjustment function is turned on (FIG. 2). Then, the process shifts to the reproduction of recorded information, and the in-focus position of the objective lens 4 is obtained (S41, S41). S42).
Next, in each state in which the objective lens 4 is moved by ± α from the in-focus position as described above, the aberration correction control unit 14 ′ detects the boost amounts Ba and Bb from the waveform equalization unit 16 (Ba−Bb). ) Is obtained, and unless | Ba−Bb | ≦ Eb, the aberration correction unit 3 is controlled using (Ba−Bb) as an error value (S43 to S49). Here, Eb is a threshold value related to the magnitude of | Ba−Bb | at which the spherical aberration falls within the allowable range, and is a value close to 0.
The above-described procedure (S42 to S49) is repeatedly executed until the condition of | Ba-Bb | ≦ Eb is satisfied (S48 → S49 → S42 to S48).
[0092]
Therefore, the error value (Ba-Bb) converges to a value close to 0 as shown in FIG. 27 by the repetitive control of the aberration correction unit 3 by the aberration correction control unit 14 '. As a result, even if the thickness t of the transparent substrate 15 of the optical disk 5 exceeds the allowable range and spherical aberration occurs, the state changes from (A ′) and (C ′) to (B ′) in FIG. However, this corresponds to the fact that the reproduction by the photodetector 8 (the reproduction signal before being processed by the signal waveform equalizing unit 16) has changed from the state shown in FIGS. 25A and 25C to the state shown in FIG. This means that the spherical aberration has been corrected.
[0093]
According to this embodiment, since the control data can be generated by obtaining the boost amount from the waveform equalization unit 16 provided in the signal processing circuit 11 of the optical disc device, the circuit configuration of the aberration correction control unit 14 'is simplified, There is an advantage that aberration correction can be realized with an inexpensive configuration.
[0094]
[Embodiment 5]
The aberration correction methods of the first and second embodiments (including the case where the method of obtaining the maximum amplitude of the reproduction signal shown in each example of the third embodiment is applied) and the aberration correction method of the fourth embodiment are independent of each other. Not only can it be executed as the aberration correction mode, but it can also be executed while the optical disk device is performing normal recording or reproduction.
That is, continuous recording or reproduction is performed at a linear velocity as fast as possible, and a margin is appropriately secured, and the procedure of the first, second, or fourth embodiment is executed during the secured margin. You can also.
[0095]
In the optical disk device, the wavelength of the laser slightly shifts with the temperature change during continuous recording or reproduction, which also causes spherical aberration on the optical disk 5. However, according to the method of this embodiment, a continuous aberration occurs. Since aberration correction can be appropriately performed during recording or reproduction, it is possible to adaptively correct spherical aberration caused by a shift in laser wavelength.
In the case of this embodiment, it is a condition that a time margin for aberration correction is secured during recording or reproduction, as described above, but it is optional whether to perform it periodically or irregularly. .
[0096]
【The invention's effect】
The aberration correction method in the optical disk device of the present invention has the following effects due to the above configuration.
The invention according to claim 1 is a method for correcting a spherical aberration that occurs in a light spot due to an error in a thickness of a transparent substrate of an optical disk exceeding an allowable value, without using a specific optical disk, and Irrespective of the type, the amount of aberration correction is accurately obtained from a long-period signal included in a reproduction signal by a simple procedure, and more rapid correction control is enabled.
In addition, an optical disk having an aberration correction unit does not require a special optical system, so that there is an advantage in that the optical disk device does not increase in size or increase in manufacturing cost, and is easily commercialized.
The invention of claim 2 realizes more accurate aberration correction control in the invention of claim 1.
According to the third and fourth aspects of the present invention, in the first aspect of the invention, crosstalk between signals is suppressed, and only long-period signals included in a reproduced signal are accurately detected, and aberrations due to more appropriate correction data are obtained. Enables correction.
The invention of claim 5 has the same effect as that of the invention of claim 1, and also obtains control data having a large rate of change from long-period and short-period signals included in the reproduction signal, thereby enabling more accurate aberration correction. To
The invention according to claim 6 realizes more accurate aberration correction control in the invention according to claim 5.
The inventions of claims 7 and 8 provide a method for obtaining control data by rationally finding the maximum amplitudes of long-period and short-period signals in the invention of claim 5. Further, in the invention of claim 8, there is an advantage that the PLL circuit is not required and the aberration correction control can be performed even when the tracking servo is off.
The ninth and tenth aspects of the present invention have the same effect as the first aspect of the present invention, and perform aberration correction using the boost amount obtained from the waveform equalizer provided in the signal processing circuit of the optical disk device. Therefore, the configuration of the aberration correction control unit can be simplified, and a more inexpensive aberration correction system is realized.
According to an eleventh aspect of the present invention, in the first to tenth aspects of the present invention, even if the wavelength of the laser shifts due to a temperature change or the like when the optical disc apparatus performs continuous recording or reproduction, the shift of the spherical aberration accompanying the shift also occurs. In addition, it is possible to adaptively correct.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an optical disk device to which Embodiments 1 to 3 relating to an aberration correction method in an optical disk device of the present invention are applied.
FIG. 2 is a flowchart (steps S1 to S6) showing an aberration correction procedure according to the first embodiment.
FIG. 3 is a flowchart (steps S7 to S15) showing an aberration correction procedure according to the first embodiment.
FIG. 4 is a diagram showing a change (a two-dot chain line) of the maximum amplitude of a long-period signal included in a reproduction signal with respect to a defocus amount, and a maximum obtained at a position obtained by moving the objective lens by ± α from the in-focus position. It is a graph which shows an amplitude. However, (A) shows a case where spherical aberration occurs on the (−) side, (B) shows a case where spherical aberration does not occur, and (C) shows a case where spherical aberration occurs on the (+) side.
FIG. 5 is a timing chart showing a position (A) of an objective lens and a change (B) in a maximum amplitude of a reproduction signal in a state where the aberration correction procedure is repeatedly executed.
FIG. 6 is a functional block diagram relating to signal processing executed by a control unit in a second embodiment.
FIG. 7 is a flowchart illustrating an aberration correction procedure according to the second embodiment.
FIG. 8 is a graph for specifically explaining a procedure (steps S24 and S26 in FIG. 7) for obtaining the maximum amplitudes of the long-period and short-period reproduction signals in the second embodiment.
FIG. 9 shows changes in the maximum amplitude of the long-period and short-period signals included in the reproduction signal with respect to the defocus amount (solid line; long period, dotted line; short period), and ± α from the in-focus position with respect to the objective lens. 6 is a graph showing the maximum amplitude of a signal in each cycle obtained at a position shifted by only one. However, (A) shows a case where spherical aberration occurs on the (−) side, (B) shows a case where spherical aberration does not occur, and (C) shows a case where spherical aberration occurs on the (+) side.
FIG. 10 is a functional block diagram relating to a signal processing method of Example 1 (related to Embodiment 2) in Embodiment 3 (Example relating to various signal processing methods executed by the control unit of the optical disc apparatus).
FIG. 11 is a state transition diagram defined by a run-length limit and a partial response characteristic [a characteristic in the case of PR (a, b, b, a)] in a partial response determination unit.
FIG. 12 is a block diagram illustrating an example of a configuration of a filtering unit according to an embodiment of the present invention. It is a graph for specifically explaining a procedure.
FIG. 13 is a functional block diagram relating to a signal processing method of Example 2 (related to Embodiment 2) in Embodiment 3 (Example relating to various signal processing methods executed by the control unit of the optical disc apparatus).
FIG. 14 is a functional block diagram illustrating a configuration of a DPLL unit.
FIG. 15 is a functional block diagram relating to a signal processing method of Example 3 (related to Embodiment 1) in Embodiment 3 (Example relating to various signal processing methods executed by the control unit of the optical disc device).
FIG. 16 is a functional block diagram illustrating another configuration example according to the signal processing method of the third embodiment.
FIG. 17 shows changes in the maximum amplitude of the long-period and short-period signals included in the reproduced signal with respect to the defocus amount (solid line; long period, dotted line; short period) in the signal processing method according to the third embodiment; 5 is a graph showing the maximum amplitude of a signal in each cycle obtained at a position where the objective lens is moved from the focal point by ± α. (ΔGa and ΔGb correspond to the difference between the maximum amplitudes of the signals in each cycle when the objective lens is at each position.) However, (A) indicates that spherical aberration occurs on the (−) side, and (B) indicates (B). () Shows a case where spherical aberration does not occur, and (C) shows a case where spherical aberration occurs on the (+) side.
FIG. 18 shows changes in the maximum amplitude of the long-period and short-period signals included in the reproduction signal with respect to the defocus amount (solid line; long period, dotted line; short period) in the signal processing method of the third embodiment; 5 is a graph showing the maximum amplitude of a signal in each cycle obtained at a position where the objective lens is moved from the focal point by ± α. (ΔGa and ΔGb correspond to the maximum amplitude of a long-period signal when the objective lens is at each position.) However, (A) indicates that spherical aberration occurs on the (−) side, and (B) indicates In the case where no spherical aberration has occurred, (C) is the case where spherical aberration has occurred on the (+) side.
FIG. 19 is a block diagram illustrating a signal processing system according to a fourth embodiment (related to the first embodiment) in a third embodiment (an embodiment related to various signal processing systems executed by a control unit of an optical disc device).
FIG. 20 is a graph for explaining a setting mode of three threshold levels Th0, Th1, and Th2 with respect to a reproduction signal waveform.
FIG. 21 is a circuit configuration diagram of a cross extraction unit.
FIG. 22 is a flowchart illustrating an error signal generation procedure by an error detection unit.
FIG. 23 is a graph showing signal waveforms of an input signal (A) and an output signal (B) to a gain control unit.
FIG. 24 is a schematic configuration diagram of an optical disk device to which Embodiment 4 is applied.
FIG. 25 is a diagram illustrating the state of the boost amount obtained by the waveform equalization unit according to the fourth embodiment [(A ′), (B ′), (C ′)]. Here, Ba and Bb are boost amounts, and (large), (medium) and (small) indicate the tendency of the magnitude.
FIG. 26 is a flowchart illustrating an aberration correction procedure according to the fourth embodiment.
FIG. 27 is a timing chart showing a position (A) of the objective lens and a change (B) of the boost amount in a state where the aberration correction procedure is repeatedly executed.
FIG. 28 is a cross-sectional view of a general optical disc and a diagram showing a configuration of a light spot formed by an objective lens.
FIG. 29 is a diagram illustrating a change in light intensity distribution about the optical axis of the light spot with respect to the amount of defocus when the thickness deviation of the transparent substrate is within an allowable value.
FIG. 30 is a diagram showing a change in light intensity distribution about the optical axis of the light spot with respect to the amount of defocus when the thickness deviation of the transparent substrate exceeds an allowable value.
FIGS. 31A and 31B are a plan view (A) and a cross-sectional view (B) of an optical disc applied to the invention of Patent Document 1 according to the related art.
FIG. 32 is a diagram showing pit strings (A) having a long period and a short period of a specific pattern and a signal waveform (B) of a reproduction signal obtained from the pit strings.
FIG. 33 is a graph showing a change (solid line; long period, dotted line; short period) with respect to the defocus amount of the objective lens according to the maximum amplitude of each signal reproduced from the long-period and short-period pit strings. However, (A) shows a case where spherical aberration does not occur in the light spot, and (B) shows a case where spherical aberration occurs.
FIG. 34 is a flowchart showing an aberration correction procedure assumed in the invention of Patent Document 1.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... laser light source, 2 ... beam splitter, 3 ... aberration correction part, 3a ... concave lens, 3b ... convex lens, 4,104 ... objective lens, 5,101 ... optical disk, 6,102 ... information recording layer, 7 ... light spot, 8 photodetector, 9 optical pickup, 10 high frequency amplifier, 11 signal processing circuit, 12 servo circuit, 13 spindle motor, 14, 14 'aberration correction control unit, 15, 103 transparent substrate of optical disk , 16: waveform equalizer, 21, 31, 41, A / D converter, 22: zero cross detector, 23: peak / bottom value detector, 24: inversion interval detector, 25, 34: filtering means, 26 ... Optical system control means, 32 ... Interpolation unit, 33 ... Partial response discrimination unit, 42 ... DPLL (Digital Phase Locked loop) unit, 42a ... Resump Ring interpolator, 42b timing generator, 42c phase error detector, 42d loop filter, 51 partial response discriminator / equalizer, 61 ATC (Automatic Threshold level Control) circuit, 62 AGC (Automatic Gain Control) ) Circuit, 62a: gain control circuit, 62b: cross extractor, 62c: error detector, 63: envelope detector, 71-0-2: cross detector, 72-0-2: comparator, 106: specific area , 107... A long-period pit row, 108.

Claims (11)

In an optical disk device, an aberration correction unit that adjusts the divergence or convergence angle of an incident system light beam from a laser light source to an optical disk, and an objective that condenses the incident system light beam to form a light spot on an information recording layer of the optical disk The lens is moved in the direction of the optical axis of the incident light beam, and at that time, a reflected signal at the light spot is received and output by a photodetector, and a reproduction signal is processed and analyzed. A control unit for controlling the correction unit,
When the spherical aberration occurs in the light spot, the position of the objective lens is shifted in the optical axis direction from the focal position with respect to the information recording layer, and the reproduction signal has a maximum amplitude. An aberration correction method for an optical disk device that corrects aberration, comprising:
If any information is recorded on the optical disc, the information is reproduced,
The control unit includes:
A first procedure for determining the in-focus position of the objective lens;
A second procedure of moving the objective lens in the optical axis direction back and forth from the in-focus position obtained in the first procedure by an equal distance, and calculating a maximum amplitude of a reproduction signal obtained from the photodetector at each of the movement positions;
A third procedure for calculating a difference between the maximum amplitudes obtained in the second procedure;
And a fourth step of controlling the aberration corrector so that the calculation result obtained in the third step approaches zero. 2. The method according to claim 1, wherein the first to fourth steps are repeatedly performed until the calculation result obtained in the third step falls within an allowable range. In the second step, means for obtaining the maximum amplitude of the reproduction signal at each moving position of the objective lens is:
The reproduction signal obtained from the photodetector is sampled at a predetermined period, and based on the time interval of the zero cross point and the state transition determined by the partial response characteristic and the run length limit, the signal is a short period signal or a long period signal. And performing waveform equalization on a short-period reproduced signal, filtering and separating only the long-period signal to obtain the maximum amplitude of the long-period signal. 3. The method for correcting spherical aberration in the optical disc device according to 2. In the second step, means for obtaining the maximum amplitude of the reproduction signal at each moving position of the objective lens is:
A gain control unit that controls the amplitude of the input reproduction signal based on a gain error signal of an error detection unit described below,
The first threshold value, which is set to approximately the center level of the maximum amplitude of the short-period signal in the reproduced signal obtained from the gain control unit, and a value slightly larger to the positive and negative sides than the maximum amplitude level of the short-period signal. The second threshold and the third threshold are provided, and the number of times the reproduction signal crosses each threshold is separately integrated. When one of the integrated values reaches a predetermined first set value, all integrated values are obtained. A cross extraction unit that repeatedly executes an operation of clearing
When the integrated value related to any one of the threshold values in the cross extraction unit reaches the first predetermined value, the integrated value related to the first threshold value and the integrated value related to the second and third threshold values are calculated. An error detection unit that compares and outputs a gain error signal when the former integrated value is larger than each of the latter integrated values;
An envelope detector for detecting the envelope of the reproduction signal obtained from the gain controller and obtaining the maximum amplitude thereof,
Further, when outputting the gain error signal, the error detection unit compares a second set value smaller than the first set value with each of the integrated values related to the second and third threshold values. When the second set value is larger than each of the integrated values, the gain error signal is used to decrease the gain. Conversely, when the second set value is smaller than each of the integrated values, the gain is increased. 3. The method according to claim 1, wherein the gain error signal is used as a gain error signal. In an optical disk device, an aberration correction unit that adjusts the divergence or convergence angle of an incident system light beam from a laser light source to an optical disk, and an objective that condenses the incident system light beam to form a light spot on an information recording layer of the optical disk The lens is moved in the direction of the optical axis of the incident light beam, and at that time, a reflected signal at the light spot is received and output by a photodetector, and a reproduction signal is processed and analyzed. A control unit for controlling the correction unit,
When the spherical aberration occurs in the light spot, the position of the objective lens is shifted in the optical axis direction from the focal position with respect to the information recording layer, and the reproduction signal has a maximum amplitude. An aberration correction method for an optical disk device that corrects aberration, comprising:
If any information is recorded on the optical disc, the information is reproduced,
The control unit includes:
A first procedure for determining the in-focus position of the objective lens;
The objective lens is moved by the same distance back and forth in the optical axis direction from the focal point position obtained in the first procedure, and a long-period signal included in a reproduction signal obtained from the photodetector at each movement position. A second procedure of classifying the short-period signal, obtaining the maximum amplitude of the signal of each cycle at each movement position, and calculating the difference between the maximum amplitudes of the signals of each cycle at each movement position;
A third procedure for calculating a difference between the calculation results for each moving position of the objective lens obtained in the second procedure,
And a fourth step of controlling the aberration corrector so that the difference between the calculation results obtained in the third step approaches zero. 6. The method according to claim 5, wherein the first to fourth steps are repeatedly performed until the calculation result obtained in the third step falls within an allowable range. In the second procedure, means for obtaining a maximum amplitude related to a signal of each cycle at each movement position of the objective lens,
The reproduction signal obtained from the photodetector is sampled at a predetermined cycle, a zero cross point of the sampling signal is detected to detect a polarity inversion interval, and a peak value and a bottom value within the inversion interval are obtained. By performing filtering based on the inversion interval information, the peak value and the bottom value are classified in association with long-period and short-period signals, and a representative of the peak value group and the bottom value group divided for each period. 7. The method according to claim 5, wherein a maximum amplitude of a signal in each cycle is obtained using the value. In the second procedure, means for obtaining a maximum amplitude related to a signal of each cycle at each movement position of the objective lens,
The reproduction signal obtained from the photodetector is sampled at a predetermined period, and based on the time interval of the zero cross point and the state transition determined by the partial response characteristic and the run length limit, the signal is a short period signal or a long period signal. And performing filtering based on the discrimination information to classify the signals in association with the long-period and short-period signals, and to use the representative value of the divided signal groups in each period for each period. 7. The method according to claim 5, wherein a maximum amplitude of the signal is obtained. In an optical disk device,
An aberration corrector that adjusts the divergence or convergence angle of the incident light beam from the laser light source to the optical disk,
An objective lens condenses the incident light beam and sets a boost amount with respect to a reproduction signal received and output by a photodetector at a light spot formed on an information recording layer of the optical disc. A waveform equalization unit for performing an equalization process;
A control unit that moves the objective lens in the optical axis direction of the incident system light beam, and controls the aberration correction unit based on a boost amount obtained from the waveform equalization unit at that time.
If any information is recorded on the optical disc, the information is reproduced,
The control unit includes:
A first procedure for determining a focal point position of the objective lens with respect to the optical disc;
A second procedure of moving the objective lens in the optical axis direction back and forth by an equal distance from the in-focus position obtained in the first procedure, and detecting each boost amount set by the waveform equalizer at each movement position;
A third procedure for calculating a difference between the boost amounts detected in the second procedure,
And a fourth step of controlling the aberration corrector so that the calculation result obtained in the third step approaches 0, thereby correcting spherical aberration generated in the light spot. Spherical aberration correction method. 9. The method according to claim 8, wherein the first to fourth steps are repeatedly performed until the calculation result obtained in the third step falls within an allowable range. When the optical disc apparatus performs continuous recording or reproduction, a time margin is secured by executing the recording or reproduction at a speed higher than a normal linear velocity, and the time margin is secured within the secured margin time. 11. A method for correcting spherical aberration in a disk device, wherein the method for correcting spherical aberration according to claim 1 is executed.

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