JP2001266382A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk device capable of detecting relative tilting of a disk and an optical head in a wide band precisely and capable of detecting tilting in radial and tangential directions simultaneously. SOLUTION: The device has equalizing means 14, 15 and 16 for correcting the frequency characteristic of the signals of three tracks reproduced by using three beams and a control means 17 for controlling the characteristics of the equalizing means. The device optimizes the tap coefficients of the equalization means from a signal system reproduced in a learning data area where previously fixed data is recorded on an optical disk and an ideal value system corresponding to this learning data reproducing signal by batch processing so as to remove crosstalk components by using a method of least squares and calculates the tap coefficient values of these to detect relative tilting of the disk and the optical head.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for determining a relative inclination between an optical disk and an optical head for irradiating the optical disk with a light beam.

[0002]

2. Description of the Related Art As the density of optical disks increases, an optical system for reproducing the disks is required to reduce the beam spot diameter. The beam spot diameter is proportional to the wavelength of the light source and inversely proportional to the numerical aperture (NA) of the objective lens. Therefore, it is necessary to shorten the wavelength of the light source as the density increases. Also,
Assuming that the substrate thickness of the disk is constant, the coma aberration generated at the time of the disk tilt increases in inverse proportion to the wavelength, so that the coma aberration increases by the shortened wavelength. Therefore, since the distortion of the reproduction signal due to the disc tilt tends to increase with the increase in the density, a technique for correcting the relative tilt between the disc and the optical head to cancel the influence of the aberration has been attracting attention. I have. As an element supporting such a technique, a technique for detecting a relative tilt amount and a direction of a disc and an optical head becomes important.

Attempts have been made to detect such disc tilt. For example, JP-A-11-27
There is a tilt detection device disclosed in 3113. In this method, an error value between a signal read from a central recording track among three recording tracks adjacent to each other and a predetermined value is obtained, and the read value read from a track adjacent to the center recording track on the inner peripheral side of the disk is determined. A first coefficient is obtained from a correlation between a signal and the error value, and a second coefficient is obtained from a correlation between a read signal read from a recording track adjacent to the center recording track on the outer peripheral side of the disk and the error value. The inclination occurring between the recording disk and the information reading means is detected based on the magnitude balance between the first coefficient and the second coefficient.

In this tilt detecting device, successive processing is used to obtain the first and second coefficients for the reproduction signals of adjacent tracks on the inner and outer circumferences. Such a method is called an adaptive algorithm of the least squares method, and is characterized in that coefficients are sequentially obtained.

[0005]

However, in the above tilt detecting device, there is a problem in the convergence of tap coefficients, and a signal sequence of a sufficient length is required until the tap coefficients converge to an appropriate value. . In particular, in order to detect a signal such as a disc tilt that shows a small change while constantly changing, it is important for the tilt detection performance that the tap coefficient converges to an appropriate value in a short section.

In this known example, a coefficient is updated using a zero-cross signal, and the coefficient is updated only when the target track reproduction signal takes a value near zero. Therefore, the influence of the level fluctuation of the target track signal cannot be taken into consideration, so that even after learning with a sufficient signal sequence length, the convergence value of the coefficient itself cannot secure sufficient accuracy for tilt detection. .

This tilt detecting device is effective only for detecting a radial tilt corresponding to the radial direction of the disk, and does not detect the tilt in the track tangential direction which is always mixed with the radial tilt in the disk. The device has a narrow application range to this system.

An object of the present invention has been made in view of the above circumstances, and it is possible to accurately detect a relative inclination between a disk and an optical head over a wide band, and to realize radial and tangential. An object of the present invention is to provide an optical disk device capable of simultaneously detecting tilts in directions.

[0009]

In order to solve the above-mentioned problems and achieve the object, an optical disk apparatus according to the present invention is configured as follows.

The optical disk apparatus of the present invention irradiates a target track on an optical disk and a track adjacent to both sides of the target track with three light beams at the same time, and detects reflected light reflecting information recorded on these three tracks. A reproducing means for converting information reflected on the reflected light detected by the optical means into an electric signal and providing the electric signal as a reproducing signal; and a three-track reproducing signal provided from the reproducing means for a predetermined time delay. A delay means for causing the delay means, an equalizing means comprising a transversal filter for respectively correcting the frequency characteristics of the three-track reproduced signal provided from the delay means, a control means for controlling a tap coefficient group of the transversal filter, Tilt calculating means for calculating the tilt of the disk based on a signal from the control means. A signal value sequence reproduced from the target track as an observation value sequence, and a predetermined signal value sequence corresponding to the signal value sequence reproduced from the target track as an ideal value sequence. A tap that satisfies a condition that minimizes the sum of squares of a measured value series obtained by a relational expression expressed by a linear combination of the tap coefficient group and a residual of the ideal value series over a plurality of channel bits. The coefficient group is obtained by batch processing, and the tilt calculating means detects the relative inclination between the optical disk and the optical means by calculating between the tap coefficient groups.

Here, the superiority of the tilt detection method of the optical disk device according to the present invention as compared with the conventional example will be described.

FIG. 1 is a graph showing the difference in convergence of tap coefficients according to the processing algorithm of the least squares method.

The horizontal axis represents the length (number of channel bits) of the signal sequence used for calculating the tap coefficient, and the vertical axis represents the tap coefficient value. In theory, when the signal sequence length is infinite, both the batch processing and the adaptive processing converge to the same value.

It can be seen from the figure that the batch processing algorithm approaches the convergence value (about 1.75 in this case) with a smaller signal sequence length than the adaptive algorithm. Therefore, the use of the collective processing algorithm can derive the optimum tap coefficient with a signal sequence in a small range, which means that wideband tilt detection is possible.

In the example shown in FIG. 1, in the batch processing, the tap coefficient value within ± 2% of the final convergence value is established with a signal sequence length of 75 channel bits, while the tap coefficient value falls within the same range in the adaptive algorithm. Requires 1000 channel bits to establish. That is, the collective processing increases the detection band by about 13 times.

In the conventional tilt detecting device, the tap coefficient is updated using a zero-cross signal, and the tap coefficient is updated only when the target track signal takes a value near zero.

Therefore, since the tap coefficients are updated by extracting only the zero-crossing points in the entire signal sequence, a long signal sequence is required for the tap coefficient value to converge to a sufficient value also in this sense. This means that only an average tilt in a physically long range can be detected in tilt detection. On the other hand, in the present method, since the tap coefficient is obtained by using all the channel bits in the signal sequence, the amount of tilt at a short physical length can be detected. Therefore, from this point as well, the tilt detection band of the optical disk device of the present invention is expanded. On the other hand, in the case where a learning data sequence is provided for tilt detection, even if the batch processing is used, even if the learning data sequence length is shortened, the same tilt detection performance as that of the adaptive processing can be secured. Therefore, a decrease in the user data capacity due to the learning data sequence is suppressed, which leads to a substantial improvement in the capacity.

Further, in the method of extracting only when the target track reproduction signal has a value near 0 and updating the tap coefficient,
The value itself that converges differs from the method of extracting all possible levels of the signal sequence and optimizing the tap coefficients. It is known that the influence of crosstalk is also correlated with the signal level of the target track, and it is clear that it is desirable to optimize the tap coefficient in consideration of the possible level of the target track reproduction signal. Therefore, the convergence value of the tap coefficient is better when optimized using all possible levels of the signal sequence than when zero cross points are used.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing a schematic configuration of a disc tilt detecting device corresponding to an example of the optical disc device of the present invention.

The disc tilt detecting device is roughly divided into:
An optical head 10 for detecting reflected light reflecting information recorded on an optical disc; a crosstalk canceller 20 for processing a reproduction signal to remove crosstalk and intersymbol interference components contained in the reproduction signal from the target track; And a tilt detection circuit 22 for calculating a tap coefficient of a filter circuit in the crosstalk canceller to detect a relative tilt between the disc and the reproduction optical system.

The light beam emitted from the laser light source 1 becomes parallel light by the collimator lens 2 and enters the diffraction grating 3. The three beams of the 0th order light and ± 1st order light diffracted by the diffraction grating are transmitted through a polarizing beam splitter (PBS) 4, a quarter wavelength plate 5 and an optical disk by an objective lens 6. The light is condensed on the information recording surface 7.

The condensed beam is controlled by a focus servo / tracking servo system (not shown) so that the best minute spot can be obtained on the recording surface.

FIG. 3 shows an example of the arrangement of the beam spots on the recording surface of the optical disk at this time.

Center out of the three beam spots
The beam is irradiated onto a target track (Track n) on which data to be reproduced is recorded, and Le is applied to both adjacent tracks (Track n-1, Track n + 1).
ft and Right beams are irradiated.

The light reflected by these beam spots passes through the objective lens 6 in the opposite direction and becomes parallel light again.

The reflected light passes through the quarter-wave plate 5, has a polarization perpendicular to the incident light, and is reflected by the PBS 4. The beam reflected by the PBS 4 is converged by the condenser lens 8 and is incident on the photodetector 9. The photodetector 9 is divided into a plurality of regions, and signals by three beams are detected independently. At this time, the reflected light by the Center beam is photoelectrically converted into a signal Sc, and the reflected lights by the Left beam and the Right beam are respectively converted into the signal S.
1 and Sr.

The signals Sl, Sc, and Sr are sent to delay circuits 11, 12, and 13, respectively, to correct the time shift of the irradiation position of each beam in the track scanning direction. That is,
The signal after passing through the delay circuits 11, 12, and 13 is a signal when the three beams scan right next to each other.

Therefore, the amount of delay with respect to the beam (Left beam in FIG. 3) reproducing the most preceding position on the optical disk is the longest, and the beam reproducing the rearmost position (FIG. 3).
In this case, the delay amount for the right beam is the shortest. At this time, the delay circuit that gives the shortest delay amount among the delay circuits 11 to 13 may be omitted.

The signals Sl ', Sc' and Sr 'whose phase shifts have been corrected by the delay circuits 11, 12 and 13 have their frequency characteristics corrected independently by the waveform equalizing circuits 14, 15 and 16, respectively. The waveform equalizing circuits 14, 15, 16 are composed of, for example, a 5-tap transversal filter. The equalization characteristics of all waveform equalization circuits are controlled by a control signal from the tap coefficient calculation circuit 17, for example, a tap coefficient value. The tap coefficient calculating circuit 17 includes waveform equalizing circuits 14, 15, 16
The tap equalization circuit 1 receives as input a waveform equalization circuit 1 so that a crosstalk component included in the signal Sc ′ of the Center beam is efficiently removed by a method described later.
Control signals for controlling the equalization characteristics of 4, 15, and 16 are output to waveform equalization circuits 14, 15, and 16. Waveform equalization circuit 1
The signals Sl ″, Sc ″, and Sr ″ whose frequency characteristics have been appropriately corrected by 4, 15 and 16 are crosstalk by subtracting Sl ″ and Sr ″ from Sc ″ in the subtractor 18. The components are removed, and the signal SE is obtained.
User data is generated by the signal SE undergoing a predetermined data demodulation operation in the demodulation circuit 19.

Next, the internal configuration of the crosstalk canceller 20 will be described in detail.

The waveform equalizing circuits 14, 15, 16 are composed of, for example, transversal filters as shown in FIG. This figure shows a 5-tap transversal filter,
In particular, there is no theoretical limit to the number of taps, and the more the number of taps, the more precise the frequency characteristics can be corrected. However, it should be noted that if the number of taps is too large, the circuit scale becomes large and the cost increases.

FIG. 4 shows the signal S from the Center beam.
It is an example of a transversal filter applied to c ′. This transversal filter has a delay circuit 3
It comprises 0, coefficient multipliers 35 to 39 and an adder 40. The signal Sc ′ from the delay circuit 12 in FIG. The delay circuit 30 includes a plurality of stages, in this example, four stages of unit delay elements 31, 32, 33, and 34 cascade-connected, and a plurality of taps C1, C2, C3,
C4 and C5. Each delay element is constituted by, for example, a delay line when the signal Sc 'is an analog signal. When the signal is a digital signal, it can be constituted by, for example, a D flip-flop. In this example, all the delay elements are elements having a delay time of τ, but they may have different delay times.

The output signals from the taps C1, C2, C3, C4, C5 are supplied to multipliers 35, 36, 37, 38, 3 respectively.
After multiplication by weighting factors β1, β2, β3, β4, and β5 at 9, the adder 40 adds them up to obtain a waveform-equalized signal Sc ''. The tap signals C1 to C
5 is output to the tap coefficient calculation circuit 17 and used for calculating the tap coefficient. The coefficients in the multipliers 35 to 39 are variable coefficients, and each coefficient β1, β2, β3, β4, β5 is
It is controlled and determined by the tap coefficient calculation circuit 17.
The frequency response of the transversal filter can be freely changed by the tap coefficient. According to the present invention, the tap coefficient calculation circuit 17 is eventually replaced by the waveform equalization circuit 1.
That is, the equalization characteristics of 4, 15, and 16 are controlled.

The transversal filters for the signals Sl 'and Sr' from the Left and Right beams have basically the same configuration as that shown in FIG. 4, and the tap coefficients are controlled by the tap coefficient calculation circuit 17 respectively. As a result, signals Sl ″ and Sr ″ corresponding to crosstalk components from adjacent tracks are obtained. Note that Sl ′, S
The specification can be changed such that the number of taps of only the transversal filter for r 'is set to 7 taps.

Next, the internal configuration of the tap coefficient calculation circuit 17 will be described with reference to FIG.

The tap coefficient calculation circuit 17 has an ideal value sequence table 52 corresponding to the data pattern of the learning data area where predetermined data on the optical disk 7 is recorded. As the ideal value, for example, a value obtained by sampling an ideal waveform when data in the learning data area is reproduced under the condition that there is no crosstalk may be used. This can be done by storing the reproduced waveform under ideal conditions in the optical disk apparatus maker in advance, or the learning data is stored in the data area on the optical disk 7 where there is no crosstalk in the lead-in area, that is, there is no mark row in both adjacent tracks. A pattern may be recorded, and a waveform obtained when the data area is reproduced may be fetched as an ideal value and recorded in the ideal value series table 52.

FIG. 6 shows an example of a mark sequence in the learning data area and an ideal value sequence corresponding thereto. An ideal reproduced signal corresponding to a specific pattern in the learning data area of Track n is sampled, for example, for each channel bit, and data for m channel bits is held as discrete data. In this case, assuming that the resolution is 8 bits per one channel bit, an area of m × 8 bits on the memory 51 is occupied for storing the ideal value series.

On the other hand, the tap coefficient calculation circuit 17 generates tap signals L1 to L5 and C1 from the waveform equalization circuits 14, 15, 16 when the learning data area on the optical disk 7 is reproduced.
To C5, R1 to R5 are stored in the memory 51 as observation values. At this time, a tap signal having 5 × 3 = 15 taps is sampled in the same cycle as the sampling cycle of the ideal value series, for example, for each channel bit. The data length is the same as the ideal value sequence length, for example, data for m channel bits is stored in the memory 51. In this case, assuming a resolution of 8 bits per channel bit, an area of 15 × m × 8 bits on the memory 51 is required for a reproduced signal sequence of three beams.

In the above example, when m = 1000, the memory 51 occupies a capacity of 128 Kbits for the ideal value sequence and the reproduced signal value sequence.

After the learning data area has been reproduced in this way, if the data length of the learning data area is m channel bits, for example, a 3-beam reproduced signal value (observed value) sequence (15 × m) for m channel bits And the ideal value series (1 ×
m) is stored in the memory 51.

Now, the operation of the timing detection circuit 21 for transmitting a timing signal to the tap coefficient calculation circuit 17 will be described. The timing detection circuit 21
The reproduction signal Sc ′ by the ter beam is monitored, the end of the learning data area is detected, and the timing signal is transmitted to the bus 54 inside the tap coefficient calculation circuit 17. Since known data is recorded in the learning data area, it is possible to detect the end of the learning data area. The microcomputer 53 is connected to the bus 5
4, a timing signal is detected, and at the same time when the reproduction of the learning data area is completed, the squared sum of the residuals of the observed value series multiplied by the tap coefficient and the ideal value series by a linear least squares algorithm described in detail below. Is minimized, that is, the optimal solution of the tap coefficient that makes the observed value sequence closest to the ideal value sequence is obtained and output.

In the microcomputer 53, the timing detection circuit 2
Each time the timing signal from 1 is detected, the memory 51 is accessed to calculate the tap coefficient and update the tap coefficient. Further, between the timing signals, the value of the tap coefficient group of the previous calculation result is held and output. That is, when reproducing user data from one learning data area to the next learning data area, the tap coefficient values calculated in the previous learning data area are held, and the waveform equalization circuits 14, 15, and 16 are held. Is output to This is because when unknown user data is reproduced, better results can be obtained by holding the tap coefficient values obtained in the learning data area.

To determine tap coefficients by the linear least squares method, first, a measured value y is obtained for each channel bit from a relational expression f between an observed value series and an unknown number series (in this case, tap coefficients). At this time, the relational expression f may be any expression as long as it is a linear combination of unknowns. However, when a transversal filter as shown in FIG. 4 is considered, the relational expression is obtained by multiplying each tap by a tap coefficient for weighting. It is represented as (1).

[0045]

(Equation 1)

Here, q _{i1 to} q _i15 are observation values at the i-th channel bit, that is, tap signals L1 to L1.
L5, C1 to C5, and R1 to R5. Also, x _{1 to} x
₁₅ is an unknown number, that is, tap coefficients α _{1 to} α ₅ , β ₁ to
β ₅ , γ _{1 to} γ ₅ .

With respect to the measured value sequence y and the ideal value sequence y0 over m channel bits, the least square condition is given by the following equation (2).

[0048]

(Equation 2)

In order for (2) to be minimized with respect to each parameter _xj , its derivative only needs to be 0. That is, the following equation (3) is obtained.

[0050]

(Equation 3)

Equation (3) is converted to an unknown parameter x _{j ′} (j ′ =
When rearranging regarding 1 to 15), the following equation (4) is obtained.

[0052]

(Equation 4)

Equation (4) is the following simultaneous linear equation (5).

[0054]

(Equation 5)

However, the simultaneous temporary equation (5) satisfies the following equations (6) and (7).

[0056]

(Equation 6)

The above are all constants represented by known quantities. Therefore, a tap coefficient satisfying the least square condition based on the equation (2) is obtained by solving the above simultaneous linear equations. That is, the tap coefficient desired to be obtained by the following equation (8) can be described.

[0058]

(Equation 7)

Therefore, in the microcomputer 53, the memory 5
The optimal solution of the tap coefficients can be obtained by solving the problem of obtaining the solution of the above simultaneous equations from the observation value sequence and the ideal value sequence on 1. That is, a tap coefficient is obtained by collective processing on a reproduction signal sequence covering m channel bits.

By applying the tap coefficients thus obtained to the taps of the waveform equalizing circuits 14, 15, and 16, the equalizing coefficients are adjusted so that the data in the learning data area approaches the waveform ideal value when there is no crosstalk. Is done. That is, the crosstalk component is removed.

The three-track reproduced signal waveform equalizing circuit 1 is designed to remove the crosstalk component in this manner.
When the tap coefficients of 4, 15, and 16 are controlled, what value each tap coefficient value takes is examined in consideration of the beam spot shape on the disk and the physical position of the tap.

FIGS. 7 (a) to 7 (c) show a contour map of a track and a beam spot shape on a disk and a physical position of each tap of a three-track reproduction signal. The tap shows a case where five taps are applied as an example.

FIG. 7A is a diagram showing a beam spot shape when there is no relative tilt between the disk and the optical system. At this time, the beam spot is symmetrical with respect to the center (target) track and vertically symmetrical with respect to the radial center line (straight line L3R3).

On the other hand, FIG. 7B is a diagram showing a beam spot shape when a radial tilt occurs on the disk. At this time, the beam spot is Left
A trailing side is formed on the track side, and a crescent-shaped side lobe is formed on one Right track side. On the other hand, when the disk is tilted in the tangential direction as shown in FIG. 7C, the beam spot shape in the radial direction is shaped by rotating the beam spot by 90 degrees.

When the tap coefficients are optimized to cancel the crosstalk, the tap coefficient value varies depending on the magnitude of the crosstalk amount at each tap position. That is, when the beam spot shape changes due to the tilt, the influence of the crosstalk from each tap position changes, and the tap coefficient value changes accordingly.

Therefore, the tap coefficient optimized to remove the crosstalk component roughly reflects the beam spot shape on the disk.

For example, when there is no tilt as shown in FIG. 7 (a), the beam spot shape is symmetrical in the vertical and horizontal directions. Therefore, taps (C2 and C4) symmetrical in the vertical and horizontal directions with respect to the center tap C3 of the Center track. , R3 and L3
) Are considered to have almost the same value. On the other hand, when there is a radial tilt as shown in FIG. 7B, the tap (L
3, R2, R4, etc.) (α3, γ
2, γ4, etc.) become large, and taps (R3, L2, L4, etc.) at positions where the side lobe intensity is relatively low
, The absolute value of the tap coefficient (γ3, α2, α4, etc.) becomes smaller.

Therefore, for example, when the difference calculation α3-γ3 of the center tap coefficients of the right and left adjacent tracks is performed, a value of almost 0 is output when there is no radial tilt, whereas the absolute value is output when there is radial tilt. Will be output. Therefore, the radial tilt can be detected by such an operation. FIG. 8 shows a plot of the change in α3-γ3 with respect to the radial tilt amount. It can be seen that α3-γ3 well reflects radial tilt. When a radial tilt occurs, the side lobe shapes in the right and left adjacent tracks change greatly. Therefore, when the calculation between the tap coefficients (between α1 to α5 and γ1 to γ5) in the right and left adjacent tracks is performed, the radial tilt is detected. Easy to say.

FIGS. 9 and 10 show examples of radial tilt detection by other calculations. FIG. 9 shows (γ2 + γ4) − (α2
+ Α4), and FIG. 10 shows (γ2)
+ Α3 + γ4)-(α2 + γ3 + α4). It can be seen that both signals are signals that well reflect radial tilt.

On the other hand, the tilt can be detected also in the tangential direction as shown in FIG. When there is a tangential tilt as shown in FIG. 7 (c), taps (C
4, C1, L2, R2, etc.)
4, β1, α2, γ2, etc.), and the taps (C5, C
2, L4, R4, etc.) tap coefficients (β5, β
2, α4, γ4, etc.) become smaller.

Therefore, for example, when the difference calculation β2−β4 of the tap coefficients before and after the beam center of the center track is performed, a value of almost 0 is output when there is no tangential tilt, but there is a tangential tilt. In this case, a value having a large absolute value is output. Therefore, the tangential tilt can be detected by such an operation. FIG. 11 shows a plot of the change in β4-β2 with respect to the tangential tilt amount. It can be seen that β4-β2 well reflects tangential tilt.

When a tangential tilt occurs, the side lobe shape at the front and rear taps on the same track changes greatly, so that the tap coefficients between the tap coefficients (between α1 and α5 or between β1 and β5, Alternatively, it can be said that the tangential tilt is easily detected by performing the calculation of (γ1 to γ5).

FIGS. 12 and 13 show examples of tangential tilt detection by other calculations. FIG. 12 shows (β1 + β
4) shows the result of the calculation of-(β2 + β5), and FIG.
3 shows the result of the calculation of (α2 + β4 + γ2) − (α4 + β2 + γ4). It can be seen that both are signals that well reflect the tangential tilt.

In an actual optical disk drive, there are many cases where the tilt in the radial direction and the tilt in the tangential direction are mixed as shown in FIG. 14 (in the example of the figure, the same amount of tilt in the radial direction and the tangential direction). Is shown). In such a case, the above-described calculation of the radial tilt detection and the calculation of the tangential tilt detection may be performed simultaneously. That is, for example, by performing the above-described calculations α3-γ3 and β4-β2, it is possible to simultaneously detect the radial component and the tangential component of the tilt from each calculation. FIG. 15 is a diagram plotting changes in α3-γ3 with respect to the radial tilt amount and changes in β4-β2 with respect to the tangential tilt amount when radial tilt and tangential tilt coexist. It can be seen that each signal reflects radial tilt and tangential tilt well. However, it is conceivable that the radial tilt detection sensitivity of the α3-γ3 signal and the tangential tilt detection sensitivity of β4-β2 are not necessarily the same. In such a case, a sensitivity correction coefficient is assigned to one or both of these signals. And adjust the sensitivity of both.

FIG. 16 shows an example of a tilt detection circuit that performs the above-described calculations and detects a tilt. The coefficient value α3 at the center tap L3 of the Left track and the coefficient value γ3 at the center tap R3 of the Right track of the tap coefficient group optimized to reduce the crosstalk component in the tap coefficient calculation circuit 17 are input to a subtractor. By taking the difference, a radial tilt signal is obtained. On the other hand, among the tap coefficient groups optimized to reduce the crosstalk component in the tap coefficient calculation circuit 17 at the same time, Cent
The tangential tilt signal is obtained by inputting the coefficient values β2 and β4 at the taps C2 and C4 of the er track to the subtractor and taking the difference.

The learning data area used for disc tilt detection described above only needs to record known data only on the target track, and ordinary user data may be recorded on both adjacent tracks. In this case, the capacity of the learning data area is reduced and the user data area of the entire disc is increased as compared with a method in which known data needs to be recorded on both adjacent tracks.

It is conceivable that the learning data area is set to a fixed area on the optical disk 7 for tilt detection. For example, a synchronization pattern (SYNC code) included in normal user data of a DVD is used as the learning data area. Can also be used. In DVD, one sector is composed of 2 KB, and a 26 × 32-bit SYNC code exists in one sector. Since 16 types of predetermined patterns are repeatedly used in the SYNC code, by preparing in advance ideal value sequences for all of these patterns, the SYNC code itself can be learned to optimize tap coefficients. Available as data. By doing so, since a new data area for tilt detection is not required, a disc tilt detection device can be realized without a decrease in user storage capacity.

The learning data includes, for example, DVD-R
An ID code or an address mark included in the header area of the AM can also be used. The learning data area may be provided at a fixed interval (for example, one sector) in the user data area of the disk, or provided only in the innermost lead-in area and the outermost lead-out area of the disk. You may leave.

According to the present invention, a signal reproduced by three beams in a learning data area where predetermined data is recorded on an optical disk and an ideal value sequence corresponding to the learning data are used to generate a three-beam reproduced signal. The tap coefficients of the waveform equalization circuit are optimized using the least squares method to reduce the crosstalk, and by calculating these optimized tap coefficients, the relative tilt between the disk and the optical head can be accurately determined over a wide band. Thus, it is possible to provide a disk tilt detection device capable of simultaneously detecting the tilt in the radial and tangential directions.

[0080]

According to the present invention, in the learning data area on the optical disc where predetermined data is recorded,
From the signal reproduced by the beam and the ideal value sequence corresponding to the learning data, the tap coefficients of the waveform equalization circuit for the three-beam reproduced signal are optimized using the least squares method so that the crosstalk is reduced. The present invention provides an optical disc device capable of detecting the relative tilt of a disc and an optical head with high accuracy over a wide band by calculating the converted tap coefficients, and capable of simultaneously detecting the tilt in the radial and tangential directions. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a difference in convergence of tap coefficient values between an adaptive algorithm and batch processing.

FIG. 2 is a diagram showing an overall schematic configuration of a disc tilt detection device corresponding to an example of the optical disc device of the present invention.

FIG. 3 is a diagram showing an arrangement of three beams on an optical disc.

FIG. 4 is a diagram illustrating a schematic configuration of a waveform equalization circuit.

FIG. 5 is a diagram illustrating a schematic configuration of a tap coefficient calculation circuit.

FIG. 6 is a diagram showing an ideal value sequence in a learning data area.

FIG. 7 is a diagram illustrating a relationship between a beam spot shape on an optical disc and a track.

FIG. 8 is a diagram illustrating radial tilt dependence of an (α3-γ3) signal.

FIG. 9 is a diagram showing the radial tilt dependency of a (γ2 + γ4)-(α2 + α4) signal.

FIG. 10: (γ2 + α3 + γ4) − (α2 + γ3 + α
4) A diagram showing radial tilt dependence of a signal.

FIG. 11 is a diagram showing the tangential tilt dependency of the (β4-β2) signal.

FIG. 12 is a diagram showing the tangential tilt dependency of a (β1 + β4)-(β2 + β5) signal.

FIG. 13: (α2 + β4 + γ2) − (α4 + β2 + γ
4) A diagram showing the tangential tilt dependency of a signal.

FIG. 14 is a diagram showing a relationship between a beam spot shape on an optical disc and a track.

FIG. 15 is a diagram illustrating tilt dependency of the (α3-γ3) signal and the (β4-β2) signal.

FIG. 16 is a diagram illustrating a configuration example of a tilt detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Collimating lens 3 ... Diffraction grating 4 ... Polarization beam splitter 5 ... Quarter wavelength plate 6 ... Objective lens 7 ... Optical disk 8 ... Condensing lens 9 ... Photodetector 11-13 ... Delay circuit 14- 16: Waveform equalization circuit 17: Tap coefficient calculation circuit 22: Tilt detection circuit

Claims (9)

[Claims] 1. An optical means for simultaneously irradiating a target track on an optical disc and three tracks on both sides thereof with a light beam, and detecting reflected light reflecting information recorded on these three tracks, and said optical means. A reproducing unit that converts information reflected in the reflected light detected by the electric signal into an electric signal and provides the electric signal as a reproduction signal; and a delay unit that delays a reproduction signal of three tracks provided from the reproduction unit by a predetermined time. An equalizing means for respectively correcting the frequency characteristics of the three-track reproduced signal provided from the delay means; a control means for controlling a correction amount of the frequency characteristic by the equalizing means; A tilt calculating means for calculating a tilt amount of the optical disc based on a frequency characteristic correction amount control, wherein the equalizing means comprises a transversal A control unit for controlling a correction amount of a frequency characteristic by the equalization unit by changing a tap coefficient group of the transversal filter; and a signal value reproduced from the three tracks. A sequence as an observed value sequence, and a predetermined signal value sequence corresponding to the signal value sequence reproduced from the target track as an ideal value sequence, a relational expression between the observed value sequence and the tap coefficient group,
A tap coefficient group that satisfies a condition that minimizes the sum of squares of the residual of the measured value series obtained by the relational expression represented by a linear combination of the tap coefficient group and the ideal value series over a plurality of channel bits is obtained by batch processing. An optical disc apparatus, wherein the tilt calculating means obtains a relative inclination between the optical disc and the optical means by calculating between the tap coefficient groups. 2. The method according to claim 1, wherein in deriving the tap coefficient group, a signal value sequence obtained by reproducing a learning data sequence as a known data sequence in the target track over a plurality of channel bits is used. Optical disk device. 3. The control means according to claim 1, wherein said control means retains a value of a tap coefficient group obtained in a previous learning data sequence when said reproducing means reproduces an intermediate portion between said learning data sequence and said learning data sequence. 3. The optical disk device according to claim 2, wherein said equalizing means is controlled. 4. The learning data sequence includes a synchronization code included in user data, an ID included in a header area, an address mark included in a header area, data included in a lead-in area of a disk, and a lead-out of a disk. 4. The optical disk device according to claim 2, wherein the data is any one of data included in the area. 5. The reproduction of the learning data area on the optical disk, wherein predetermined data is recorded only on a target track, and normal user data is recorded on both adjacent tracks. 4. The optical disk device according to claim 2, wherein 6. A tilt calculating means for simultaneously calculating a relative inclination in a disk radial direction and a relative inclination in a track tangential direction between the optical disk and the optical means by calculating between the tap coefficient groups. The optical disk device according to claim 2. 7. A transversal filter tap coefficient group for a reproduction signal of a track adjacent to the target track on the inner circumference side of the disc is represented by α = ｛α _−n ,..., Α ₋₁ , α ₀ , α ₁ ,. α _n } (where n is a positive integer), and the tap coefficient group of the transversal filter for the reproduction signal of the target track is β = {β _−n ,..., β ₋₁ , β ₀ , β ₁ ,. and _n} (where n is a positive integer), the tap coefficient group of the transversal filter for the reproduction signal of the track which is adjacent to the disk outer circumferential side of the target track _{γ = {γ -n, ...,} γ -1, γ 0 , Γ ₁ ,..., Γ _n } (where n is a positive integer), and the tilt calculating means calculates the relative inclination of the optical disc and the optical means in the radial direction of the disc by tap coefficient group α Perform the operation between the elements of and The optical disk apparatus according to claim 2, 3 and 6, characterized. Wherein said tap coefficient group of the transversal filter for the reproduction signal of the track adjacent to the disk inner circumference side of the target track _{α = {α -n, ...,} α -1, α 0, α 1, ..., α _n } (where n is a positive integer), and the tap coefficient group of the transversal filter for the reproduction signal of the target track is β = {β _−n ,..., β ₋₁ , β ₀ , β ₁ ,. and _n} (where n is a positive integer), the tap coefficient group of the transversal filter for the reproduction signal of the track which is adjacent to the disk outer circumferential side of the target track _{γ = {γ -n, ...,} γ -1, γ 0 , Γ ₁ ,..., Γ _n } (where n is a positive integer), and the tilt amount calculation means calculates a relative inclination of the optical disc and the optical means in the track tangential direction by using a tap coefficient Between elements in group α, or Between elements in flops coefficient group beta, or claim 2, characterized in that performing an operation between elements of the tap coefficient group gamma, or 6, wherein the optical disk apparatus. 9. An ideal value sequence generation data area in which the same data sequence as the learning data sequence is recorded on the optical disc in a state where crosstalk is reduced, and the ideal value sequence generation data area is reproduced. 3. The optical disk device according to claim 2, wherein the data obtained by sampling the reproduced signal at the time of performing the conversion is used as the ideal value series.