JPH0676299A - Method and device for reproducing optical disk data - Google Patents

Abstract

PURPOSE:To reproduce an optical disk with high density with an inexpensive optical disk device by reducing an occurring amt. in waveform distortion and jitters in a regenerative signal from an optical diskeven under a condition when the occurring amt. in a disk skew is increased. CONSTITUTION:A first tap 12 and a second tap 13 are provided further on front and back of three taps equalizer constituted of a transversal filter and correcting the waveform distortion in the regenerative signal from the optical disk 40. Further, a skew amt. in the disk 40 is detected by a skew sensor 30 detecting the disk skew amt. Weighing coefficients (gain of variable amplifier 121, 131) to the first tap 12 and the second tap 13 are adjusted based on the skew amt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and more particularly to a method and apparatus for reproducing data stored in a high density optical disk.

[0002]

2. Description of the Related Art As a storage device for computers and a package medium for image information, optical discs are becoming higher in density. As one method for dealing with the high density of the optical disc, there is a method of increasing the numerical aperture of the objective lens to be larger than that of the conventional optical disc to improve the resolution. This is generally referred to as the high N.V. A. Is called

In an optical disc system, the frequency characteristic of an optical pickup is generally called MTF (modulation transfer function). This M
TF is defined by spatial frequency. here,
The cut-off frequency f _c of the MTF is the wavelength λ of the laser light used in the optical pickup and the numerical aperture N.V. of the objective lens.
A. Uniquely by

[Equation 3] Is expressed as Here, for example, λ = 0.532 μm,
N. A. = 0.6, f _c = 2255.6 (books /
mm).

However, the gain characteristic of the MTF is not flat up to the cutoff frequency f _c , but decreases monotonically. Therefore, the reproduced waveform is band-limited. The reproduced waveforms at this time are shown in FIGS. 21 (A) and 21 (B). The MTF and line intensity distribution at this time are shown in FIG.

In the reproduction signal shown in FIGS. 21A and 21B, the shortest repetition frequency is f _c / 2, 1 / T is 5 f _c (T is the width of the window), and the density of information in the linear direction is a compact disc. This is an example of observing the reproduced waveform (eye pattern) under the condition of twice the above. As shown in FIG. 21A, under the above conditions, it is difficult to extract a signal even when the tangential skew (skew amount) of the disk is 0 degree. Such a state is expressed as the eye does not open.

Therefore, for example, an MTF using a fixed 3-tap delay circuit (transversal filter) shown in FIG. 23 (3-tap equalizer) is used.
To correct. FIG. 22B shows the frequency characteristic of this 3-tap equalizer. In addition, in FIG.
The MTF after being corrected by the taps equalizer is shown.

The reproduced waveforms corrected by the fixed 3-tap equalizer are shown in FIGS. 21 (C) and 21 (D).
As shown in FIG. 21C, when the tangential skew of the disc is 0 degree, the eye pattern is open, and the signal can be sufficiently extracted (detected). However, as shown in FIG. 21D, when the tangential skew of the disc is 0.3 degrees, the eye pattern is not sufficiently opened even if a fixed 3-tap delay circuit (transversal filter) is applied, and Is difficult to extract. This tangential skew amount is a very general value in a general compact disk device.

[0008]

An optical disk typified by a compact disk has a structure in which a reflective surface on which data is stored is covered with a transparent substrate having a thickness of about 1.2 mm. Therefore, when the disc is tilted with respect to the optical axis of the objective lens, N. A. Coma occurs in proportion to about the third power of the above and the amount θ of inclination (skew) of the optical disc. When θ is sufficiently small, this coma aberration is given by the Seidel aberration coefficient formula

[Equation 4] Is expressed as Here, W31 is the third-order coma aberration, t is the disc substrate thickness, n is the disc substrate refractive index, θ is the disc skew amount, and NA is the numerical aperture of the objective lens.

For example, an objective lens having a numerical aperture (numerical aperture NA of 0.6) 1.33 times that of a general compact disc objective lens system (numerical aperture NA of 0.45). In the system, with the same disc skew amount as the compact disc, a coma aberration of 2.37 times occurs. Due to such wavefront distortion, the image forming spot on the disk becomes asymmetrical, so that the intersymbol interference increases remarkably, and even if the MTF is corrected by the fixed 3-tap equalizer, the waveform distortion is large and a sufficient signal is obtained. There was a problem in that it would be difficult to extract.

The present invention has been made in view of the above-mentioned problems of the prior art. Even under the condition that the amount of tangential skew is large, the amount of distortion and jitter of the reproduced signal waveform of the optical disk is reduced. It is an object of the present invention to provide an optical disk data reproducing method and apparatus capable of reproducing a high density optical disk with an inexpensive optical disk device in which tangential skew is relatively large as a result.

[0011]

In order to achieve the above object, an optical disk data reproducing method and apparatus according to the present invention convert reflected light from an optical disk into an electric signal by at least a two-division system to determine the tilt of the optical disk. The amount of the electric signal is detected, the electric signal is filtered based on a filter coefficient defined according to the amount of tilt of the optical disc, the result is output, and the data stored in the optical disc is reproduced from the output. .

Further, means for converting the reflected light from the optical disk into an electric signal by at least a two-division method, means for detecting the amount of tilt of the optical disk, and means for detecting the tilt of the optical disk for the electric signal are detected. A means for filtering and outputting based on a filter coefficient defined according to the amount of tilt of the recorded optical disc, and means for reproducing the data stored on the optical disc from the output signal of the filtering means. Characterize.

Further, the filtering means is composed of a multi-stage transversal filter.

Further, the transversal filter is
It is characterized by including an arithmetic circuit having a constant filter coefficient and an arithmetic circuit having a variable filter coefficient.

Further, the delay amount τ ₂ of the delay circuit of the transversal filter is defined by (Equation 1).

Further, the delay amount τ ₂ of the delay circuit of the transversal filter is defined by (Equation 2).

Further, the filter coefficient of the arithmetic circuit in which the filter coefficient is variable is proportional to the amount of inclination of the optical disk.

Further, the transversal filter includes a plurality of arithmetic circuits having different filter coefficients and constant filter coefficients, and the arithmetic circuits having a plurality of constant filter coefficients of different filter coefficients are set to the amount of inclination of the optical disc. It is characterized in that it has means for selecting according to it.

[0019]

The skew sensor detects the amount of inclination (disc skew) of the optical disc. The variable transversal filter (variable equalizer) adjusts the weighting coefficient (filter coefficient) to be used in accordance with the disk skew amount detected by the skew sensor, and performs waveform shaping (filtering) processing based on this weighting coefficient. . Thereby, the distortion of the reproduced waveform due to the coma aberration caused by the disc skew is electrically corrected.

[0020]

EXAMPLE A first example will be described below. As described above, in the optical disc device, the M of the optical pickup is
The cutoff frequency f _C of the TF has a wavelength λ and an objective lens numerical aperture N. A. Is uniquely expressed as (Equation 3). Here, for example, λ = 0.532 μm, N.V. A. = 0.6
In the case of, f _c = 2255.6 (lines / mm). Hereinafter, the frequency unless otherwise specified is the above frequency f _C = 2255.6.
(Book / mm) is shown.

FIG. 1 shows the configuration of the first high density optical disk device 1 of the present invention. The first high-density optical disc device 1 is
The variable equalizer 10 in which 2 taps are further added before and after the 3-tap equalizer (transversal filter) 11 shown in FIG. 23 is applied to a high-density optical disk device.

In FIG. 1, the variable equalizer 10 has three
It is a 5-tap equalizer in which a first tap 12 and a second tap 13 are provided before and after the tap equalizer 11. The 3-tap equalizer 11 includes a delay circuit 110,
This is a transversal filter composed of 111, fixed gain amplifiers 112, 113 and 114, and an addition circuit 115. Here, the delay circuits 110 and 111 are delay circuits that give and output a unit delay amount τ ₁ for each input signal. Each of the amplifiers 112 and 114 is an amplifier circuit that multiplies an input signal by a weighting coefficient (a) and outputs the result. The amplifier 113 is an amplifier circuit that multiplies an input signal by one and outputs the multiplied signal. The adder 115 includes amplifiers 112 to 1
14 is an addition circuit for adding the output of 14 and the output signal of any one of the gain variable amplifier 121 and the gain variable amplifier 131.

The first tap 12 is a tap circuit composed of a delay circuit 120 and a variable gain amplifier 121. The second tap 13 is a tap circuit including a delay circuit 130 and a variable gain amplifier 131.

The variable gain amplifier 121 is an amplifier circuit that multiplies each input signal by a weighting coefficient (b) and outputs the result. Where this weighting factor is variable,
Adjusted based on gain control signal. Also,
The variable gain amplifier 131 is an amplifier circuit that multiplies each input signal by a weighting coefficient (c) and outputs the result. here,
This weighting factor is variable and is adjusted based on the gain control signal. The delay circuits 120 and 130 are
Each of the delay circuits delays the input signal by the delay amount τ ₀ and outputs the delayed signal.

The switch 20 is a switch circuit for selecting one of the output of the variable gain amplifier 121 and the output of the variable gain amplifier 131 as the input of the adder 115 based on the output signal of the comparator 22. The connection of the switch 20 differs depending on the configuration of the first high density optical disk device 1, but in the first embodiment, when the output of the comparator 22 is a logical value 1, the connection shown in FIG. Has a logical value of 0, the connection is the opposite of that shown in FIG.

The inverting amplifier 21 is an amplifier circuit which inverts (-1 times) the input signal and outputs it. The comparator 22 compares the output of the skew sensor 30 with a reference voltage and sends a switching signal to the switch 20 as a logical value (0 or 1).
Is a comparison circuit that outputs as. For example, the comparator 22 outputs a logical value 1 when the output signal of the skew sensor 30 is a positive value, and outputs a logical value 0 when it is a negative value.

The amplifier 23 is an amplifier circuit for amplifying the output signal of the skew sensor 30. Skew sensor 30
Is a circuit for detecting the amount θ of inclination (skew) of the optical disc 40. The optical disc 40 is a high density optical disc. The connection of each part of the first high-density optical disk device 1 described above is as shown in FIG. Further, other parts of the first high-density optical disk device 1 which are not described above are omitted in FIG.

The operation of the first high density optical disk device 1 will be described below. First, how to obtain the delay amount will be described. Τ ₂ shown in FIG. 1 is the delay amount of the variable equalizer 10 of the present invention with respect to the source signal (t = 0). Here, the relationship of τ ₂ = τ ₁ + τ ₀ holds for the delay amount τ ₂ . This delay amount τ ₂ does not depend on the type of reproduction signal (shortest repeating pit length), but only on the optical constant of the optical pickup.

The numerical aperture of the objective lens (not shown) is NA,
If the wavelength of the laser light (not shown) (light source) used in the first high-density optical disk device 1 is λ, the delay amount τ ₂
Is the median of

[Equation 5] Is expressed as

Here, it is possible to obtain a sufficient effect for waveform shaping without setting the delay amount τ ₂ to a strict value. That is, it suffices to satisfy the relationship of (Expression 1). Therefore, for example, the wavelength λ = 0.532 μm, N.V. A. =
In the case of 0.6, the central value of the delay amount τ ₂ is τ ₂ = 0.73μ
m, and may satisfy 0.54 μm ≦ τ ₂ ≦ 0.99 μm (unit is length; m).

Here, in an actual electric circuit, the unit of the delay amount is given by time. The coefficient that replaces the delay amount represented by the above length with time is the linear velocity v of the disk. Therefore, when the linear velocity is v, the delay amount τ ₂
The heart of

[Equation 6] It is sufficient to satisfy (Equation 2) given by For example v = 6
m / sec, λ = 0.532 μm, N.M. A. = 0.6, the central value of the delay amount τ ₂ is τ ₂ = 122 nsec. However, as described above, 90 nsec ≦ τ ₂ ≦ 165
If nsec is satisfied, it may deviate from the central value.

Next, the weighting coefficient will be described. Figure 1
, The weighting factor for the delay amount τ ₂ is h (t +
τ ₂ ) is represented by b, and h (t−τ ₂ ) is represented by c. However, both h (t + τ ₂ ) and h (t−τ ₂ ) are not used at the same time and are selected by the switch 20. The signal of the skew sensor is a signal having positive and negative polarities, and one of the two is uniquely selected depending on the polarity.

Further, the weighting coefficients b and c of h (t + τ ₂ ) and h (t−τ ₂ ) are different in magnitude from the skew sensor 3.
It is adjusted to a value proportional to the absolute value of the signal of 0, and h (
The weighting factors b and c of t + τ ₂ ) and h (t−τ ₂ ) are set so as to be negatively weighted with respect to the source signal h (t).

The operation of the skew sensor 30 will be described below. 2A shows a configuration diagram of the skew sensor 30, and FIG. 2B shows a side view. In FIG. 2A, LE
D300 is a light emitting diode used as a light source of the skew sensor 30. 2-part photo detector 301
Is composed of two light receiving elements 301a and 301b,
It is an element that detects the light emitted from the LED 300 and reflected by the disk 40. The arithmetic circuit 302 is a differential arithmetic circuit that subtracts the output of the light receiving element 301b from the output of the light receiving element 301 that constitutes the two-divided photodetector 301. The lens 303 is a lens that collects the light emitted from the LED 300 and reflected by the disk 40. The spot 304 is emitted from the LED 300, and the disc 4
The light reflected by 0 is an image spot formed on the two-divided photodetector 301.

As described above, the skew sensor 30 is generally composed of the LED 300, the two-divided photodetector 301 and the lens. Also, the lens 30
As shown in FIG. 2 (B), 3 may be a molded LED 300 and a two-divided photodetector 301.

As shown in FIG. 2B, the image of the LED 300 is reflected by the disk 40 and the two-divided photodetector 30.
Image on 1. When the disk 40 tilts, LED300
Image moves on the two-division photodetector 301 in the division direction. The skew sensor 30 utilizes that the differential amount of the two-divided photodetector 301 (the difference between the light amounts detected by the light receiving elements 301a and 301b of the two-divided photodetector 301) is approximately proportional to the tilt amount of the disc 40. The skew amount θ is detected.

FIG. 3 shows an output signal of the skew sensor 30 shown in FIG. The range where the slope is linear is the range where there is linearity, and this range is used as the skew error signal.

Next, the operation principle of the first high density optical disk device 1 of the present invention will be described. As shown in FIG. 4A, the intensity distribution of the diffracted image with a circular aperture with a uniform light amount and no aberration is

[Equation 7] It is known to be expressed by the following first-order Bessel function. The point spread distribution (point spread function) in this case is shown in FIG.

This is a so-called Airy ring or Air
It is called y disk. Airy dis
k is ν = 0, 1.64π, 2.69π, 3.51
π ,. ． ． ． It becomes a bright point at ν = 1.22π, 2.23
π, 3.23π ,. ． ． ． It becomes a dark spot (I = 0). Here, the objective lens numerical aperture N. A. To N
A, the wavelength of the light source is λ, and the length x on the disc 40 is x, the light intensity distribution on the disc 40 is
The relationship between ν and x

[Equation 8] It is represented by. Therefore,

[Equation 9] The point represented by becomes a bright point,

[Equation 10] The point represented by is the dark spot.

The line spread function (line spread function) shown in FIG. 4C is obtained by projecting one point spread function shown in FIG. 4B onto the axis and weighting it. Is. In a system such as the optical disc 40 in which a spot moves on one axis (track in the optical disc 40) to read a signal, the phenomenon can be relatively easily captured by using such a line spread function.

In the line spread function shown in FIG. 4C, the bright points and dark points shown in FIG. 4A appear as the characteristics of the distribution as they are. As shown in FIG. 4C, even at a dark spot, I = 0 is not obtained, but a minimum value is obtained. FIG. 8 shows a characteristic diagram when the line spread function is logarithmically displayed, paired with a point spread function (point spread function), and the disk 40 is tilted from 0 to 0.3 degrees.

5 (A), 6 (A), 7 (A), and 8 (A), the disk 40 is 0 degrees (deg),
The line spread function when tilted by 0.1 degree, 0.2 degree and 0.3 degree (disk skew 0 degree, 0.1 degree, 0.2 degree and 0.3 degree) is shown. FIG. 5 (B),
6 (B), 7 (B), and 8 (B), the disk 40 is 0 degree (deg), 0.1 degree, 0.2 degree, 0.
Tilt 3 degrees (disk skew 0 degree, 0.1 degree, 0.2
Point spread function in the case of 0.3 degrees).

As described in the prior art, the disk 4
When 0 is tilted with respect to the optical axis of the objective lens (not shown),
N. A. A coma aberration is generated in proportion to the cube of 3 and the skew amount θ. According to Seidel's aberration coefficient formula, when θ is sufficiently small, it becomes (Formula 4). Here, W31 is the third-order coma aberration, t is the substrate thickness of the disc 40, and n is the disc 4
0 substrate refractive index, θ is disc skew amount, NA is objective lens numerical aperture N.V. A. Is.

It can be seen that due to such distortion of the wavefront, the image spot on the disk 40 becomes asymmetric, and the side intensity remarkably increases as the skew amount θ increases. Here, the line spread function shown in FIGS. 5 (B) to 8 (B) has λ = 0.532 μm, N.V. A.
This is an example in the case of = 0.6. The increase in the intensity on this side significantly increases the intersymbol interference, and even if the MTF is corrected by the equalizer as shown in FIG. 23, the waveform distortion is large as shown in FIG. 21D, and it is necessary to sufficiently extract the signal. Becomes difficult.

Next, regarding the MTF correction using the equalizer (3 taps equalizer) 11 using the 3-tap delay circuit (transversal filter) described in the prior art, the line intensity distribution (line spread function) Will be explained. FIG. 22 shows the operation principle of the 3-tap equalizer 11 using the line spread function.

First, considering the frequency axis in FIG. 22, the original MTF of the optical system is as shown in FIG. 22 (F). Then, the MTF is corrected by using the 3-tap equalizer 11 shown in FIG.

In FIG. 22, (A) shows the line spread function before equalization. (B)
FIG. 3 is a diagram showing the principle of the 3-tap equalizer 11.
(C) shows the line spread function after being equalized by the 3-tap equalizer 11.
(D) is a logarithmic display of (A). (E)
Is a logarithmic representation of (C). (G) is a frequency characteristic of the 3-tap equalizer 11. (H) is
This is the MTF after being equalized by the 3-tap equalizer 11.

As described above, by comparing (F) and (H) of FIG. 22, it can be seen that the gain is increased in the vicinity of (1/2) of the cutoff frequency. FIG. 22B shows this phenomenon as a superposition of intensity distributions (line spread functions). The signals delayed by the 3-tap equalizer 11 are weighted on the spatially separated line spread functions and superimposed. 22A and 22C show the states before and after the 3-tap equalizer 11, and the width of the distribution is narrowed as a result. This is equivalent to the improved frequency characteristics.

Next, consider the case where there is disk skew. FIGS. 9A to 9C show the correction by the 3-tap equalizer 11 which is regarded as the superposition of the line spread function when there is a disk skew.

In FIG. 9, (A) shows the line spread before equalization by the 3-tap equalizer 11.
It is a linear display of the function. (B)
FIG. 3 is a diagram showing the principle of equalization by the 3-tap equalizer 11. (C) is a 3-tap equalizer 11
It is a linear display of the line spread function after equalization by.

(D) is a logarithmic representation of (A). (E) is a logarithmic display of (C).
(F) is a diagram showing the principle of equalization by the variable equalizer (variable 5-tap equalizer) 10.
(G) is a linear display of the line spread function after equalization by the variable equalizer 10. (H) is a logarithmic display of (G).

As can be seen by referring to FIG. 9, there is little effect on the asymmetrical distortion of the line spread function due to disk skew. There 3
The tap equalizer 11 increases by one tap so as to remove an asymmetric portion near the delay amount τ _{2 that} cannot be removed. Needless to say, the central value of this asymmetric portion is τ ₂ . This is the technical point of the high-density optical disk device of the present invention. The delay amount τ ₂ is generally represented by (Equation 5). The reason is that the intensity distribution on the pupil plane of the objective lens (not shown) of the pickup (not shown) for the optical disc 40 is not a completely uniform distribution, but a Gaussian distribution.

[Equation 11] This is because

The track direction of the optical disk 40 is the x direction,
Assuming that the radius of the objective lens pupil is r, the index r / ωx, which indicates the uniformity of the intensity distribution, takes a value of about 0.2 to 0.8, which is similar to diffraction by a circular aperture having a substantially uniform intensity distribution. Can be treated to.

Next, the weighting coefficient will be considered. Figure 10
Disk skew 0 degree, 0.1 degree, 0.2 degree, 0,3
A logarithmic representation of the line spread function against degrees is shown. FIG. 10A shows an optical system only (without an equalizer). (B) is after correction by the 3-tap equalizer (fixed 3-tap equalizer) 11. As can be seen with reference to (A) and (B), the ratio of the side lobe value that rises due to the disk skew to the central peak value is substantially proportional to the disk skew amount.

Therefore, for example, if a coefficient that minimizes the side lobe at a disk skew of 0.3 degrees is determined, then that coefficient may be set to a value proportional to the disk skew amount. For example, the coefficient is 0 when the disk skew is 0 degree. Further, only one of + τ ₂ and −τ ₂ may be weighted. The choice depends on the direction of the disc skew, which is the sidelobe side. Figure 1
In this way, the line after the weighting coefficient is corrected in proportion to the disc skew amount (using the variable equalizer 10 (variable 5-tap equalizer)) to 0 (C)
Shows the logarithmic display of the spread function. The amount of side lobe is small regardless of the disc skew.

Next, as a concrete example, an actual numerical value will be described. The constants of the optical pickup of the first high density optical disc device 1 are as follows. λ = 0.532 μm N.V. A. = 0.6 r / ωx = 0.7 r / ωy = 0.7 The constants of the 3-tap equalizer 11 are as follows. τ ₁ = 0.2 μm a = −0.2

Here, τ ₂ = 0.73 μm, linear velocity 6 m /
In the case of sec, when the delay amount is expressed by time, τ ₁ = 33nsec τ ₂ = 122nsec. Here, the weighting coefficient changed by the disc skew amount is b = c = −2 | θ |: θ (degrees).

For example, when | θ | = 0.1 degrees, b = c
= -0.02. When | θ | = 0.2 degrees, b = c = −0.04. Also, | θ | = 0.3
In the case of degrees, b = c = -0.06.

The eye pattern and the jitter histogram for the disk skew amount of −0.3 degrees to +0.3 degrees with the constants described above are shown in the conventional 3-tap equalizer 11 as an example.
Comparison between the case where only the variable transversal filter 10 is used and the case where the variable transversal filter 10 is used is shown in FIGS.
3 to FIG. FIG. 11 and FIG. 12 are comparisons of eye patterns for the disk skew amount of −0.3 degrees (deg) to +0.3 degrees (deg). FIG. 11 shows a case where the variable transversal filter 10 is used. FIG. 12 shows a case where only the 3-tap equalizer 11 described as the prior art is used.

FIGS. 13 and 14 are comparisons of jitter histograms with respect to the disk skew amount of −0.3 degrees (deg) to +0.3 degrees (deg). FIG. 13 is a jitter histogram when the variable transversal filter 10 is used. FIG. 14 is a jitter histogram when only the 3-tap equalizer 11 described as the prior art is used.

FIG. 15 is a graph showing the tangential skew amount on the horizontal axis and the variance value (standard deviation) of the jitter standardized by the window T on the vertical axis. That is, it corresponds to a graph in which the tangential skew dependence of jitter shown in FIG. 9 is summarized.

In FIG. 15, (A) shows a graph without an equalizer. (B) shows a graph when the 3-tap equalizer 11 is used. (C) shows a graph when the variable equalizer 10 is used.

It is apparent that the present invention makes it easier to detect a signal because the jitter is reduced with respect to the disk skew. The output signal of the variable equalizer 10 obtained by the above-described operation is input to the data reproducing circuit (not shown) of the first high density optical disk device 1, and the data stored in the disk 40 is reproduced. .

The effects obtained by the first high-density optical disk device 1 will be described with reference to FIGS. 15 and 16.
FIG. 16 shows a reproduced waveform (eye pattern) when the tangential skew is 0.3 degree. FIG.
2A is an eye pattern without an equalizer, FIG. 3B is an eye pattern with a conventional 3-tap equalizer 11, and FIG. 3C is a variable equalizer 10 of the first high-density optical disc device 1. It is an eye pattern when using. The eye pattern shown in (C) is
As compared with the eye patterns shown in (A) and (B), it is obvious that the waveform distortion is small and the signal extraction is easy.

As can be seen from FIG. 15, the optical disc data reproducing method and the apparatus thereof according to the present invention clearly reduce the dependency of jitter due to tangential skew, and the amount of jitter is increased even if the tangential skew is increased. Is small.

Therefore, the following effects are obtained. (1) Objective lens numerical aperture N.V. A. Even if is large, the distortion of the reproduced waveform due to the coma aberration caused by the disk skew can be electrically corrected. Therefore, by applying the first high density optical disk device 1 of the present invention, a very inexpensive high density optical disk system can be supplied. (2) Objective lens numerical aperture N.V. A. Even if is large, it is possible to electrically correct the distortion of the reproduced waveform due to the coma aberration generated by the disc skew. Therefore, by applying the first high density optical disk device 1 of the present invention, a very reliable high density optical disk system can be supplied. (3) As described above, since the allowable value of the disk skew can be increased, it is possible to supply a high density optical disk system using an optical disk which is a high density disk but is inexpensive to manufacture.

The second embodiment will be described below. Figure 1
7 is a diagram showing the configuration of the second high-density optical disk device 2. 17, each part of the second high density optical disk device 2 is the same as the first high density optical disk device 1 shown in FIG.
Is the same as the part with the same reference numeral.

Like the second high-density optical disk device 2 shown in FIG. 17, the 3-tap equalizer 11 shown in FIG. 1 is used.
In general, in a compact disc device, signal detection is performed without an equalizer. When the second high-density optical disk device 2 is applied to such a system, the same effect as that of the first high-density optical disk device 1 can be obtained with a simpler circuit configuration.

The third embodiment will be described below. Figure 1
8 is a diagram showing the configuration of the third high-density optical disk device 3. 18, parts of the third high-density optical disk device 3 are the same as those of the first high-density optical disk device 1 shown in FIG.
Are the same as those indicated by the same reference numerals. Here, τa ₁ and τa ₂ shown in the delay circuits 110a, 110b, 111a, and 111b in FIG. 18 indicate the delay amounts of the respective delay circuits.

The third high density optical disk device 3 is a device in which the order of the 3-tap equalizer 11 in the first high density optical disk device 1 of FIG. 1 is further increased. In the third high-density optical disk device 3 shown in FIG. 18, an example using a fixed 5-tap equalizer is shown, but the number of taps is not limited to 5, and may be 7, for example. In this way, by increasing the number of equalizer stages, it is possible to further improve the accuracy of signal detection as compared with the variable equalizer 10 of the first high-density optical disc device 1.

The fourth embodiment will be described below. FIG. 19 is a diagram showing the configuration of the fourth high-density optical disk device 4. 19, fixed gain amplifiers 121a to 121a
21c and 131a to 131c are variable gain amplifiers 121 of the first high-density optical disk device 1, respectively.
131 is replaced. In addition, b _{1 to} b ₃ and c _{1 to} c ₃ shown in the fixed gain amplifiers 121a to 121c and 131a to 131c in FIG. 19 represent the gains of the fixed gain amplifiers. The other parts are the same as those of the first high-density optical disk device 1 shown in FIG.

The switches 122 and 132 are controlled by a gain switching signal corresponding to the gain control signal in the first high density optical disk device 1, and fixed gain amplifiers 121a to 121c and 131a to 131, respectively.
This is a switch for selecting the output of c.

A variable gain amplifier 12 capable of continuously setting the gain of the amplifier of the first high density optical disk device 1.
Even when the fixed gain amplifiers 121a to 121c and 131a to 131c having different gains are used to switch the gains discretely and the skew amount is corrected instead of 1, 131, it is almost the first high level. It is possible to obtain substantially the same effect as that of the density optical disk device 1.

The fifth embodiment will be described below. FIG. 20 is a diagram showing the configuration of the fifth high-density optical disk device 5. Each part of the fifth high-density optical disk device 5 is shown in FIG.
The same applies to each part of the first high density optical disk device 1 shown in FIG. 9 and the fourth high density optical disk device 4 shown in FIG. The fifth high-density optical disk device 5 is a combination of the 3-tap equalizer 11 and the skew amount correction by the fixed gain amplifiers 121a to 121c shown in the fourth embodiment.

Even if the transversal filter has such a structure, the same effect as that of the fourth high-density optical disk device 4 can be obtained. In addition, in the fourth and fifth embodiments, an example in which the number of steps is changed to four levels including 0 (no switch is connected) is shown. This stage may be any number of stages including 0 as long as it is 2 or more.

The optical disk data reproducing method and apparatus of the present invention described above can have various configurations other than those described above. The embodiments described above are merely examples. In particular, each delay circuit and each amplifier circuit forming the variable equalizer used in the high-density optical disk device of the present invention does not matter whether digital signal processing or analog signal processing is performed.

[0077]

As described above, according to the optical disk data reproducing method and apparatus of the present invention, the objective lens numerical aperture N. A. Even if is large, the distortion of the reproduced waveform due to the coma aberration caused by the disk skew can be electrically corrected. Therefore, a very inexpensive high density optical disc system can be provided.

The objective lens numerical aperture N.V. A. Even if is large, it is possible to electrically correct the distortion of the reproduced waveform due to the coma aberration generated by the disc skew. Therefore, it is possible to provide a highly reliable high density optical disc system.

Further, since the allowable value of the disc skew can be increased, it is possible to provide a high density optical disc system using an optical disc which is a high density disc but is inexpensive to manufacture.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first high-density optical disk device.

FIG. 2 is a diagram showing a configuration and a side view of a skew sensor.

FIG. 3 is a diagram showing an output signal of a skew sensor.

FIG. 4 is a diagram showing an intensity distribution of a diffraction image by a circular aperture having a uniform light amount distribution and having no aberration.

FIG. 5: The line spread function is displayed logarithmically and paired with the point spread function (point spread function), and the inclination of the disk is 0 degree (deg).
It is a figure which shows the line spread function in the case of (disk skew 0 degree).

FIG. 6 shows a line spread function logarithmically displayed, paired with a point spread function (point spread function), and tilted the disk by 0.1 degree (deg) (disk skew 0.1 degree). It is a figure which shows the line spread function in a case.

FIG. 7 shows a line spread function logarithmically displayed, paired with a point spread function (point spread function), and tilted the disk by 0.2 degree (deg) (disk skew 0.2 degree). It is a figure which shows the line spread function in a case.

FIG. 8 shows a line spread function logarithmically displayed, paired with a point spread function (point spread function), and tilted the disk by 0.3 degree (deg) (disk skew 0.3 degree). It is a figure which shows the line spread function in a case.

FIG. 9 is a diagram showing correction by a 3-tap equalizer, which is captured as a superposition of line spread functions when there is disk skew.

FIG. 10 is a diagram showing logarithmic display of a line spread function with respect to disk skew.

FIG. 11 is a diagram showing a comparison of eye patterns for a disk skew amount of −0.3 degrees to +0.3 degrees when a variable transversal filter is used.

FIG. 12 is a diagram showing a comparison of eye patterns with respect to a disk skew amount of −0.3 degrees to +0.3 degrees when only a conventional 3-tap equalizer is used.

FIG. 13 is a diagram showing a comparison of jitter histograms with respect to a disk skew amount of −0.3 degrees to +0.3 degrees when a variable transversal filter is used.

FIG. 14 is a diagram showing a comparison of a jitter histogram with respect to a disk skew amount of −0.3 degrees to +0.3 degrees when only a conventional 3-tap equalizer is used.

FIG. 15 is a diagram showing a graph in which a horizontal axis represents a tangential skew amount and a vertical axis represents a dispersion value (standard deviation) of jitter standardized by a window T in the first high-density optical disk device.

FIG. 16 is a diagram showing a reproduced waveform (eye pattern) when the tangential skew is 0.3 degrees in the first high density optical disk device.

FIG. 17 is a diagram showing a configuration of a second high density optical disc device.

FIG. 18 is a diagram showing a configuration of a third high density optical disc device.

FIG. 19 is a diagram showing a configuration of a fourth high density optical disc device.

FIG. 20 is a diagram showing a configuration of a fifth high density optical disc device.

FIG. 21 is a gain characteristic of MTF showing a cutoff frequency f _c.
It is a figure which shows the reproduction | regeneration waveform with which the band limitation was carried out when it is not flat until it decreases monotonously.

FIG. 22 is a gain characteristic of MTF showing a cutoff frequency f _c.
It is a figure which shows MTF and line intensity distribution at the time of not being flat but monotonically decreasing.

FIG. 23 is a diagram showing a configuration of an equalizer using a fixed 3-tap delay circuit (transversal filter).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st high density optical disk apparatus 2 ... 2nd high density optical disk apparatus 3 ... 3rd high density optical disk apparatus 4 ... 4th high density optical disk apparatus 5 ... 5th High-density optical disk device 10 ... Variable equalizer 11 ... 3-tap equalizer 110, 111 ... Delay circuit 112-114 ... Amplifier 115 ... Adder circuit 12 ... First tap 120 ... Delay circuit 121 ... Variable amplifiers 121a to 121c ... Fixed gain amplifier 122 ... Switch 13 ... Second tap 130 ... Delay circuit 131 ... Variable amplifiers 131a to 131c ... Fixed Gain amplifier 132 ... Switch 20 ... Switch 21 ... Inversion amplifier 22 ... Comparator 23 ... Amplifier 30 ... Skew sensor 30 300 ... LED 300 301 ... Two-divided photodetector 302 ... Calculation circuit 303 ... Lens 304 ... Spot 40 ... Disc

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[Procedure amendment]

[Submission date] November 18, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction content]

This is a so-called Airy ring or Air
It is called y disk. Airy dis
k is ν = 0, 1.64π, 2.69π, 3.51
π ,. ． ． ． It becomes a bright point at ν = 1.22π, 2.23
π, 3.23π ,. ． ． ． It becomes a dark spot (I = 0). Here, the objective lens numerical aperture N. A. To N
A, the wavelength of the light source is λ, and the length x on the disc 40 is x, the light intensity distribution on the disc 40 is
The relationship between ν and x

[Equation 8] It is represented by. Therefore,

[Equation 9] The point represented by becomes a bright point,

[Equation 10] The point represented by is the dark spot.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction content]

As can be seen by referring to FIG. 9, there is little effect on the asymmetrical distortion of the line spread function due to disk skew. There 3
The tap equalizer 11 increases by one tap so as to remove an asymmetric portion near the delay amount τ _{2 that} cannot be removed. Needless to say, the central value of this asymmetric portion is τ ₂ . This is the technical point of the high-density optical disk device of the present invention. The delay amount τ ₂ is generally represented by (Equation 5). The reason is that the intensity distribution on the pupil plane of the objective lens (not shown) of the pickup (not shown) for the optical disc 40 is not a completely uniform distribution, but a Gaussian distribution.

[Equation 11] This is because

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction content]

The track direction of the optical disk 40 is the x direction,
Assuming that the radius of the objective lens pupil is r, the index r / ω _x , which indicates the uniformity of the intensity distribution, takes a value of about 0.2 to 0.8, and diffraction by a circular aperture having a substantially uniform intensity distribution Can be treated similarly. ω _x and ω _y are in the x direction and y direction
1 / e ² , which is the so-called beam diameter.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0056

[Correction method] Change

[Correction content]

Next, as a concrete example, an actual numerical value will be described. The constants of the optical pickup of the first high density optical disc device 1 are as follows. λ = 0.532 μm N.V. A. = 0.6 r / ω _x = 0.7 r / ω _y = 0.7 Further, the constants of the 3-tap equalizer 11 are as follows. τ ₁ = 0.2 μm a = −0.2

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0057

[Correction method] Change

[Correction content]

Here, τ ₂ = 0.73 μm, linear velocity 6 m /
In the case of sec, when the delay amount is expressed by time, τ ₁ = 33 nsec τ ₂ = 122 nsec. Here, the weighting coefficient changed by the disc skew amount is b = c = −0.2 × | θ |: θ (degrees) .

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0061

[Correction method] Change

[Correction content]

FIG. 15 shows the tangential disc on the horizontal axis.
FIG. 9 is a diagram showing a graph in which a cusk amount (degree) and a vertical axis represent a variance value (standard deviation) of jitter standardized by a window T. That is, it corresponds to a graph in which the tangential skew dependence of jitter shown in FIG. 9 is summarized.

[Procedure Amendment 7]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 4

[Correction method] Change

[Correction content]

[Figure 4]

[Procedure Amendment 8]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

[Procedure Amendment 9]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

[Procedure Amendment 10]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

[Figure 7]

[Procedure Amendment 11]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

[Procedure Amendment 12]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 11

[Correction method] Change

[Correction content]

FIG. 11

[Procedure Amendment 13]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 12

[Correction method] Change

[Correction content]

[Fig. 12]

[Procedure Amendment 14]

[Document name to be corrected] Drawing

[Correction target item name] Fig. 16

[Correction method] Change

[Correction content]

FIG. 16

[Procedure Amendment 15]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 21

[Correction method] Change

[Correction content]

FIG. 21

Claims (8)

[Claims] 1. A filter coefficient that converts reflected light from an optical disc into an electric signal by at least a two-division method, detects the amount of inclination of the optical disc, and regulates the electric signal according to the amount of inclination of the optical disc. An optical disk data reproducing method for filtering data based on the above, outputting the result, and reproducing the data stored in the optical disk from the output. 2. A means for converting the reflected light from the optical disk into an electric signal by at least two division method, a means for detecting the amount of tilt of the optical disk, and a means for detecting the tilt of the optical disk for the electric signal. Optical disk data having means for filtering and outputting based on a filter coefficient defined according to the amount of tilt of the optical disk that has been recorded, and means for reproducing the data stored in the optical disk from the output signal of the filtering means. Playback device. 3. The optical disc data reproducing apparatus according to claim 2, wherein the filtering means is composed of a multi-stage transversal filter. 4. The optical disc data reproducing apparatus according to claim 3, wherein the transversal filter includes an arithmetic circuit having a constant filter coefficient and an arithmetic circuit having a variable filter coefficient. . 5. The optical disc data reproducing apparatus according to claim 4, wherein the delay amount of the delay circuit of the transversal filter is τ _2.
Is the following An optical disk data reproducing device characterized by: 6. The optical disc data reproducing apparatus according to claim 4, wherein the delay amount τ ₂ of the delay circuit of the transversal filter.
Is given by An optical disk data reproducing device characterized by: 7. The optical disk data reproducing apparatus according to claim 4, 5, or 6, wherein the filter coefficient of the arithmetic circuit having a variable filter coefficient is proportional to the amount of tilt of the optical disk. Optical disk data reproducing device for. 8. The optical disc data reproducing apparatus according to claim 4, 5, or 6, wherein the transversal filter includes a plurality of arithmetic circuits having different filter coefficients and constant filter coefficients.
An optical disk data reproducing apparatus having means for selecting a plurality of arithmetic circuits each having a constant filter coefficient having different filter coefficients according to the amount of inclination of the optical disk.