JP3208865B2 - Optical disc reproduction signal equalization apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As storage media for computers and package media for image information, the density of optical disks has been increasing. As one method for responding to the increase in the density of the optical disk, there is a method of improving the resolution by making the numerical aperture of the objective lens larger than that of the conventional optical disk. This is generally referred to as high N.D. A. It is called "ka."

In an optical disk system, the frequency characteristic of an optical pickup is generally called MTF (Modulation Transfer Function). This M
TF is defined by a spatial frequency. here,
Cut-off frequency f _c of the MTF, the wavelength of the laser beam used for the optical pickup λ and an objective lens numerical aperture N.
A. Uniquely,

(Equation 3) It is expressed as Here, for example, λ = 0.532 μm,
N. A. = 0.6, f _c = 2255.6 (book /
mm).

However, the gain characteristics of the MTF is not flat up to the cut-off frequency f _c, the monotonous decrease. Therefore, the reproduced waveform is band-limited. The reproduced waveforms at this time are shown in FIGS. FIG. 22A shows the MTF and line intensity distribution at this time.

[0005] Figure 21 (A), (B) reproduced signals shown in the shortest repetition frequency f _c / 2,1 / T is 5f _c (T is the width of the window), when the density of the line direction information compact discs This is an example in which a reproduced waveform (eye pattern) is observed under a condition twice as large. 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 degrees. Such a state is described as not opening the eye.

Therefore, for example, using an equalizer (3-tap equalizer) using a fixed 3-tap delay circuit (transversal filter) shown in FIG.
Is corrected. FIG. 22B shows the frequency characteristics of the 3-tap equalizer. Further, FIG.
5 shows the MTF corrected by the tap equalizer.

[0007] Reproduced waveforms corrected by the fixed three-tap equalizer are shown in FIGS. 21 (C) and 21 (D).
As shown in FIG. 21C, when the tangential skew of the disk is 0 degrees, 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 disk is 0.3 degrees, the eye pattern is not sufficiently opened even if a fixed 3-tap delay circuit (transversal filter) is applied, and the signal is not sufficiently opened. Extraction is difficult. Such a tangential skew amount is a very common value in a general compact disk device.

[0008]

An optical disk represented 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 inclined with respect to the optical axis of the objective lens, the N.V. A. Coma is generated in proportion to the third power of .theta. And the amount .theta. Of the tilt (skew) of the optical disk. This coma is given by Seidel's aberration coefficient equation when θ is small enough.

(Equation 4) It is expressed as Here, W31 is the third-order coma aberration, t is the disk substrate thickness, n is the disk substrate refractive index, θ is the disk skew amount, and NA is the numerical aperture of the objective lens.

For example, an objective lens having a numerical aperture 1.33 times (numerical aperture NA: 0.6) that of a general compact disk objective lens system (numerical aperture NA: 0.45) In the system, coma aberration occurs 2.37 times at the same disk skew amount as that of the compact disk. Due to such distortion of the wavefront, the image spot on the disk becomes asymmetric, and the inter-symbol interference increases remarkably. Even if the MTF is corrected by the fixed 3-tap equalizer, the waveform distortion is large and the signal There is a problem that it is difficult to extract the

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 can be reduced. As a result, an optical disk reproduction signal equalizer and an optical disk reproduction signal capable of reproducing a high-density optical disk with an inexpensive optical disk device having relatively large tangential skew .
And to obtain the method .

[0011]

In order to achieve the above object, an optical disk reproduction signal equalizing apparatus according to the present invention comprises:
Tilt detecting means for detecting the tilt of the laser and recording on the optical disc
Information changes continuously according to the rotation of the optical disk
Input from the optical pickup, equalize and output
And a filter means for applying pressure.
Connected to a plurality of rows to input and delay the reproduced signal.
A delay unit, connected between the delay unit and the connection point
Coefficient multiplying means for multiplying a signal appearing on a signal by a constant coefficient
And one end of the serially connected delay means,
A signal appearing at the connection point is added to the signal by the inclination detecting means.
Variable multiplied by a variable coefficient that changes according to the detected slope
Coefficient multiplying means, an output of the fixed coefficient multiplying means,
Adds the output of the variable coefficient multiplication means and outputs an equalized playback signal
And delay means for adding the delay amounts of the plurality of delay means.
And the coefficient of the fixed coefficient multiplying means,
The optical pick is defined symmetrically from the center connection point of the step.
It has a value that depends on the up optical constant.

Also, in the present invention, the plurality of delay means are
A first variable variable for multiplying the signal before delay by the variable coefficient
Number multiplying means, and the signal delayed by the plurality of delaying means
Second coefficient multiplying means for multiplying the variable coefficient by the variable coefficient.
The first variable coefficient according to the inclination detected by the detecting means.
The output of the multiplication means and the output of the second variable coefficient multiplication means
And selecting means for selecting one of the two and outputting the result to the adding means.
Including.

Preferably, the delay amount τ ₂ before or after the center connection point is 1.22λ / (2NA · v) ≦ τ ₂ ≤2.23λ / (2NA · v), where λ is the optical pickup. It is defined that the wavelength of the light source, NA is the numerical aperture of the objective lens of the optical pickup, and v is the linear velocity of the rotating optical disk.

According to the present invention, there is provided
The optical disc reproduction signal equalization method is a
Information changes continuously according to the rotation of the optical disk
An optical disc that receives a reproduction signal from an optical pickup and equalizes it
A method for equalizing a disk playback signal, wherein the tilt of the optical disk is
And depended on the optical constants of the optical pickup
The playback signal is delayed by a delay amount, and the
Depends on the optical constants of the optical pickup
The first signal is generated by multiplying the first signal by
According to the tilt of the optical disk
Multiplying the variable variable coefficient to generate a second signal;
1 and the second signal are added to generate an equalized reproduction signal.
I do.

In the present invention, the second signal is used to generate the second signal.
The signal to be delayed before or after the delay
Is selected based on the tilt of the optical disk.

Preferably, the delay amount τ ₂ before or after the intermediate point of the delay is 1.22λ / (2NA · v) ≦ τ ₂ ≦ 2.23λ / (2NA · v), where λ is an optical pickup. , NA is the numerical aperture of the objective lens of the optical pickup, and v is the linear velocity of the rotating optical disk.

Further, the filter coefficient of the arithmetic circuit having a variable filter coefficient is proportional to the amount of tilt of the optical disk.

According to the optical disk reproduction signal equalizing apparatus described above,
If one end of a plurality of delay means connected in series is
The playback signal from the up is input. Fixed coefficient multiplication means
Multiplies the signal from between the delay means by a certain coefficient. That
The output signal depends on the optical constants of the optical pickup.
It becomes On the other hand, before a plurality of delay means connected in series,
Or from the variable coefficient multiplying means connected later,
The signal multiplied by the coefficient that changes according to the slope of the
It is. The adding means includes an output of the fixed coefficient multiplying means and a variable coefficient.
The output of the multiplication means is added to output an equalized reproduction signal.
The waveform of the equalized reproduction signal is
To minimize the effect of number-dependent corrections,
Only the edge near one side is additionally corrected according to the inclination of the
You. The variable coefficient multiplying means multiplies the signal before delay by a variable coefficient.
First variable coefficient multiplying means for calculating
Second variable coefficient multiplying means for multiplying the coefficients,
Force selection means, the tilt of the disc
For example, adding a playback signal according to the positive or negative polarity of the slope
The edge to be corrected is switched.

As described above, the optical constant of the optical pickup is
Disk with little loss of the effect of the dependent correction.
The reproduction signal waveform due to the coma generated by the cue
Asymmetric distortion is corrected electrically.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment will be described below. As described above, in the optical disk device, the optical pickup M
The cutoff frequency f _C of the TF is determined by the wavelength λ and the numerical aperture of the objective lens N. A. Is uniquely expressed as (Equation 3). Here, for example, λ = 0.532 μm; A. = 0.6
In the case of, f _c = 2255.6 (lines / mm). Hereinafter, the frequency without special mention is the above-mentioned frequency f _C = 2255.6.
(Book / mm).

FIG. 1 shows the configuration of a first high-density optical disk apparatus 1 according to the present invention. The first high-density optical disc device 1
A variable equalizer 10 with two taps added before and after a three-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 3
This is a 5-tap equalizer provided with a first tap 12 and a second tap 13 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, 114 and an addition circuit 115. Here, the delay circuits 110 and 111 are delay circuits that give a unit delay amount τ ₁ to the input signal and output the same. The amplifiers 112 and 114 are amplification circuits that multiply the input signal by the weighting coefficient (a) and output the result. The amplifier 113 is an amplifier circuit that multiplies an input signal by one and outputs it. The adder 115 includes the amplifiers 112 to 1
14 is an addition circuit that adds the output of the variable gain amplifier 14 and the output signal of one of the variable gain amplifier 121 and the variable gain 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.

Here, the variable gain amplifier 121 is an amplifier circuit that multiplies each input signal by a weighting coefficient (b) and outputs the result. Here, this weighting factor is variable,
Adjusted based on the 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
These are delay circuits that delay input signals by a delay amount τ ₀ and output the delayed signals.

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 disc device 1. In the first embodiment, when the output of the comparator 22 has a logical value of 1, the connection shown in FIG. Is a logical value 0, the connection is opposite to that shown in FIG.

The inverting amplifier 21 is an amplifying circuit for inverting the input signal (multiplying it by -1) and outputting the inverted signal. The comparator 22 compares the output of the skew sensor 30 with a reference voltage, and sends a switch signal to the switch 20 as a logical value (0 or 1).
As a comparison circuit. 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 the output signal 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 the inclination (skew) of the optical disk 40. The optical disk 40 is a high-density optical disk. The connection of each part of the first high-density optical disk device 1 described above is as shown in FIG. Other parts of the first high-density optical disk device 1 not described above are omitted in FIG.

Hereinafter, the operation of the first high-density optical disk device 1 will be described. First, a method of obtaining the delay amount will be described. Τ ₂ shown in FIG. 1 is a 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 is an amount that does not depend on the type of the reproduced signal (the shortest repeated pit length) but only on the optical constant of the optical pickup.

The numerical aperture of the objective lens (not shown) is NA,
Assuming that the wavelength of a laser beam (not shown) (light source) used in the first high-density optical disc device 1 is λ, the delay amount τ ₂
The center value of

(Equation 5) It is expressed as

Here, a sufficient effect on waveform shaping can be obtained without setting the delay amount τ ₂ to a strict value. That is, it is only necessary to satisfy the relationship of (Equation 1). Therefore, for example, the wavelength λ = 0.532 μm, A. =
In the case of 0.6, the central value of the delay amount τ ₂ is τ ₂ = 0.73 μ
m, and may satisfy 0.54 μm ≦ τ ₂ ≦ 0.99 μm (unit: length; m).

Here, in an actual electric circuit, the unit of the delay amount is given by time. The coefficient for replacing 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 center of

(Equation 6) Satisfies (Equation 2). For example, v = 6
m / sec, λ = 0.532 μm, N.P. A. In the case of = 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, the center value may be deviated.

Next, the weighting coefficient will be described. FIG.
, The weighting coefficient for the delay amount τ ₂ is h (t +
τ ₂ ) and c for h (t−τ ₂ ). However, h (t + τ ₂ ) and h (t−τ ₂ ) are not used at once, but 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.

The magnitudes of the weighting coefficients b and c of h (t + τ ₂ ) and h (t−τ ₂ ) are
0 is adjusted to a value proportional to the absolute value of the signal, and h (
The weighting coefficients b and c of t + τ ₂ ) and h (t−τ ₂ ) are set to be negatively weighted with respect to the source signal h (t).

The operation of the skew sensor 30 will be described below. FIG. 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-split photodetector 301
Is composed of two light receiving elements 301a and 301b,
This element detects 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 included in the two-segment photodetector 301. The lens 303 is a lens that collects light emitted from the LED 300 and reflected by the disk 40. The spot 304 is emitted from the LED 300 and
The light reflected at 0 is an imaging spot formed on the two-segment photodetector 301.

As described above, the skew sensor 30 generally includes the LED 300, the two-part photodetector 301, and the lens. Also, the lens 30
As shown in FIG. 2B, the LED 3 may be one in which the LED 300 and the two-part photodetector 301 are molded.

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

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

Next, the operation principle of the first high-density optical disc apparatus 1 of the present invention will be described. As shown in FIG. 4A, the intensity distribution of the diffraction image by the circular aperture having no uniform aberration and having no aberration is shown in FIG.

(Equation 7) It is known that it is represented by the following first-order Bessel function: FIG. 4B shows a point spread function (point spread function) in this case.

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

(Equation 8) It is represented by Therefore,

(Equation 9) Is a bright point, and

(Equation 10) The point represented by is a dark point.

The point spread function shown in FIG. 4 (B) is projected onto one axis and weighted to obtain a line intensity distribution (line spread function) shown in FIG. 4 (C). It is. In a system in which a spot moves along one axis (track in the optical disk 40) and reads a signal like the optical disk 40, 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 spots and dark spots shown in FIG. 4A directly appear as distribution characteristics. As shown in FIG. 4C, I = 0 does not occur even at the dark point, but takes a minimum value. Characteristic diagrams when the disk 40 is tilted from 0 to 0.3 degrees by displaying the line spread function in logarithm and pairing it with a point spread function (point spread function) are shown in FIGS. .

FIGS. 5 (A), 6 (A), 7 (A) and 8 (A) show the case where the disc 40 is at 0 degree (deg),
The line spread function when tilted by 0.1 degrees, 0.2 degrees, and 0.3 degrees (disc skew is 0 degrees, 0.1 degrees, 0.2 degrees, and 0.3 degrees) is shown. FIG. 5 (B),
FIGS. 6 (B), 7 (B), and 8 (B) show the disk 40 at 0 degree (deg), 0.1 degree, 0.2 degree, and 0 degree, respectively.
Tilt 3 degrees (disk skew 0 degrees, 0.1 degrees, 0.2 degrees
Shows the point spread function (degrees, 0.3 degrees).

As described in the prior art, the disk 4
When 0 is inclined with respect to the objective lens optical axis (not shown),
N. A. Coma occurs in proportion to the third power of and the skew amount θ. When represented by Seidel's aberration coefficient equation, when θ is sufficiently small, Equation 4 is obtained. Here, W31 is the third-order coma aberration, t is the substrate thickness of the disk 40, and n is the disk 4
0 substrate refractive index, θ is the amount of disk skew, NA is the numerical aperture of the objective lens N. A. It is.

It can be seen that the image spot on the disk 40 becomes asymmetric due to such distortion of the wavefront, and that the intensity of the side significantly increases as the skew amount θ increases. Here, the line spread function shown in FIGS. 5B to 8B is λ = 0.532 μm, A.
This is an example when = 0.6. This increase in the intensity of the side significantly increases intersymbol interference. Even when the MTF is corrected by the equalizer shown in FIG. 23, the waveform distortion is large as shown in FIG. Becomes difficult.

Next, regarding the MTF correction using the equalizer (three-tap equalizer) 11 using the three-tap delay circuit (transversal filter) described in the prior art, the line intensity distribution (line spread function) will be described. This will be described with reference to FIG. FIG. 22 shows the operation principle of the 3-tap equalizer 11 using the line spread function.

First, in FIG. 22, when considered on the frequency axis, the original MTF of the optical system is as shown in FIG. The MTF is corrected using the three-tap equalizer 11 shown in FIG.

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

Thus, comparing (F) and (H) in FIG. 22, it can be seen that the gain is increased near (1/2) of the cutoff frequency. FIG. 22B illustrates this phenomenon as a superposition of the intensity distribution (line spread function). The signal delayed by the 3-tap equalizer 11 is superimposed by weighting a spatially separated line spread function. FIGS. 22A and 22C show states before and after the 3-tap equalizer 11, and the width of the distribution is narrowed as a result. This is equivalent to an improvement in frequency characteristics.

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

In FIG. 9, (A) shows the line spread before the equalization by the 3-tap equalizer 11.
This 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
This is a linear display of the line spread function after equalization by.

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

As can be seen from FIG. 9, there is not much effect on the asymmetric distortion of the line spread function due to the disk skew. So 3
The tap equalizer 11 increases the number of taps by one so as to remove an asymmetric portion near the delay amount τ _{2 that} cannot be removed. Center value of this asymmetric part it goes without saying that the tau _2. This is the technical point of the high-density optical disk device of the present invention. Generally the amount of delay tau _2, represented by formula (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 disk 40 is not a completely uniform distribution but a Gaussian distribution.

[Equation 11] This is because it is represented by

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

Next, the weighting factor will be considered. FIG.
0 degree, 0.1 degree, 0.2 degree, 0,3
Shows the logarithmic representation of the line spread function against degrees. FIG. 10A shows an optical system only (without an equalizer). (B) shows the result after correction by the 3-tap equalizer (fixed 3-tap equalizer) 11. As can be seen from (A) and (B), the ratio of the side lobe value raised by the disk skew to the central peak value and the disk skew amount are substantially proportional.

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

Next, as a specific example, actual numerical values 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.P. 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

Here, in the case of τ ₂ = 0.73 μm and a linear velocity of 6 m / sec, when the above-mentioned delay amount is expressed in time, τ ₁ = 33 nsec and τ ₂ = 122 nsec. Here, the weighting coefficient to be changed according to the disk skew amount is b = c = −0.2 × | θ |: θ (degrees) .

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

The eye pattern and the jitter histogram with respect to the disk skew amount of -0.3 degrees to +0.3 degrees at the constants described above are compared with the conventional 3-tap equalizer 11.
FIGS. 11 to 12 and FIG. 1 show a comparison between the case where only the variable transversal filter 10 is used and the case where the variable transversal filter 10 is used.
3 to 14. FIGS. 11 and 12 are comparisons of eye patterns with respect to the disc 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 conventional technique is used.

FIGS. 13 and 14 are comparisons of the 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 related art is used.

[0061] FIG. 15, the end to the horizontal axis tangential disk
FIG. 10 is a graph showing a skew amount (degree) and a variance (standard deviation) of jitter normalized by a window T on a vertical axis. That is, it is a graph in which the tangential skew dependence of the jitter shown in FIG. 9 is summarized.

FIG. 15A 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 reduces the jitter with respect to the disk skew and makes it easier to detect a signal. The output signal of the variable equalizer 10 obtained by the operation described above is input to a data reproducing circuit (not shown) of the first high-density optical disk device 1, and the data stored and formed on the disk 40 is reproduced. .

The effects obtained by the first high-density optical disk device 1 will be described with reference to FIGS.
FIG. 16 shows a reproduced waveform (eye pattern) when the tangential skew is 0.3 degrees. FIG.
2A shows an eye pattern without an equalizer, FIG. 2B shows an eye pattern using a conventional three-tap equalizer 11, and FIG. 2C shows a variable equalizer 10 of the first high-density optical disk device 1. This is an eye pattern in the case of using. The eye pattern shown in (C) is
Compared with the eye patterns shown in (A) and (B), it is clear that the waveform distortion is clearly small and the signal can be easily extracted.

As can be seen with reference to FIG. 15, obviously, the optical disk data reproducing method and apparatus of the present invention reduce the dependency of jitter due to tangential skew, and reduce the amount of jitter even if the tangential skew increases. Is small.

Therefore, the following effects are obtained. (1) Numerical aperture of objective lens A. , The distortion of the reproduced waveform due to the coma caused by the disk skew can be electrically corrected. Therefore, a very inexpensive high-density optical disk system can be supplied by applying the first high-density optical disk device 1 of the present invention. (2) Objective lens numerical aperture N.P. A. Is large, it is possible to electrically correct the distortion of the reproduced waveform due to the coma caused by the disk 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.

Hereinafter, a second embodiment will be described. FIG.
FIG. 7 is a diagram showing a configuration of the second high-density optical disk device 2. In FIG. 17, each part of the second high-density optical disc device 2 is the same as the first high-density optical disc device 1 shown in FIG.
Are the same as the parts with the same reference numerals.

As in the second high-density optical disk apparatus 2 shown in FIG. 17, the 3-tap equalizer 11 shown in FIG.
For example, in a compact disk device, signal detection is generally performed without an equalizer. When the second high-density optical disk device 2 is applied to such a system, an effect similar to that of the first high-density optical disk device 1 can be obtained with a simpler circuit configuration.

Hereinafter, a third embodiment will be described. FIG.
FIG. 8 is a diagram showing a configuration of the third high-density optical disk device 3. In FIG. 18, each part of the third high-density optical disc device 3 is the same as the first high-density optical disc device 1 shown in FIG.
Are the same as those of 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 obtained by further increasing the order of the 3-tap equalizer 11 in the first high-density optical disk device 1 of FIG. In the third high-density optical disk device 3 shown in FIG. 18, an example is shown in which a fixed 5-tap equalizer is used. However, the number of taps is not limited to 5 and may be 7, for example. As described above, by increasing the number of stages of the equalizer, 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.

Hereinafter, a fourth embodiment will be described. FIG. 19 is a diagram showing the configuration of the fourth high-density optical disk device 4. In FIG. 19, fixed gain amplifiers 121a to 121a
Reference numerals 21c and 131a to 131c denote corresponding gain variable amplifiers 121 of the first high-density optical disc device 1,
131 is substituted. Further, b _{1 to} b ₃ and c _{1 to} c ₃ shown in the fixed gain amplifiers 121 a to 121 c and 131 a to 131 c in FIG. 19 indicate the gains of the fixed gain amplifiers. The other parts are the same as the parts of the first high-density optical disk device 1 shown in FIG.

The switches 122 and 132 are controlled by gain switching signals corresponding to gain control signals 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.

The gain variable amplifier 12 of the first high-density optical disk device 1 capable of continuously setting the gain of the amplifier
1 and 131, the gains are discretely switched by fixed gain amplifiers 121a to 121c and 131a to 131c having different gains to correct the skew amount. Almost the same effects as in the high-density optical disc device 1 can be obtained.

Hereinafter, a fifth embodiment will be described. 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.
19 and the fourth high-density optical disk device 4 shown in FIG. The fifth high-density optical disk device 5 combines the 3-tap equalizer 11 with the skew correction by the fixed gain amplifiers 121a to 121c shown in the fourth embodiment.

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

The optical disk data reproducing method and apparatus of the present invention described above can have various configurations in addition to the above. The embodiments described above are examples. In particular, it does not matter whether each delay circuit and each amplifier circuit constituting the variable equalizer used in the high-density optical disk device of the present invention perform digital signal processing or analog signal processing.

[0077]

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

Further, the numerical aperture of the objective lens N.P. A. Is large, it is possible to electrically correct the distortion of the reproduced waveform due to the coma caused by the disk skew. Therefore, a very reliable high-density optical disk system can be provided.

Further, since the allowable value of the disk skew can be increased, it is possible to provide a high-density optical disk system using an optical disk which is a high-density disk and whose production cost is low.

[Brief description of the 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 illustrating 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 no aberration and having a uniform light amount distribution.

FIG. 5 shows a logarithmic representation of a line spread function, pairs it with a point spread function (point spread function), and has a disk inclination of 0 degree (deg).
It is a figure showing a line spread function in case of (disk skew 0 degrees).

FIG. 6 shows a logarithmic representation of the line spread function, paired with a point spread function (point spread function), and tilted the disc by 0.1 degree (deg) (disc skew: 0.1 degree). It is a figure showing a line spread function in the case.

FIG. 7 shows a logarithmic representation of a line spread function, paired with a point spread function (point spread function), and tilted the disc 0.2 degrees (deg) (disc skew 0.2 degrees). It is a figure showing a line spread function in the case.

FIG. 8 shows a logarithmic representation of a line spread function, which is paired with a point spread function (point spread function), in which the disk is tilted by 0.3 degree (deg) (disk skew: 0.3 degree). It is a figure showing a line spread function in the case.

FIG. 9 is a diagram illustrating correction by a three-tap equalizer that is regarded as superposition of a line spread function when there is disk skew;

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

FIG. 11 is a diagram showing a comparison of an eye pattern with respect to a disc 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 an eye pattern with respect to a disc skew amount of −0.3 degrees to +0.3 degrees when only the conventional 3-tap equalizer is used.

FIG. 13 is a diagram illustrating a comparison of a jitter histogram with respect to a disc 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 the conventional 3-tap equalizer is used.

FIG. 15 is a graph showing the tangential skew amount on the horizontal axis and the variance (standard deviation) of the jitter normalized by the window T on the vertical axis 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 illustrating a configuration of a second high-density optical disk device.

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

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

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

FIG. 21 shows that the gain characteristic of the MTF is the cutoff frequency _fc.
FIG. 10 is a diagram showing a reproduction waveform in which the band is limited in a case where the waveform is not flat but monotonically decreased.

FIG. 22 shows that the gain characteristic of the MTF is the cutoff frequency _fc.
FIG. 7 is a diagram showing an MTF and a line intensity distribution in a case where a monotonous decrease is not performed until the measurement is flat.

FIG. 23 is a diagram illustrating 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 device 2 ... 2nd high-density optical disk device 3 ... 3rd high-density optical disk device 4 ... 4th high-density optical disk device 5 ... 5th High-density optical disk device 10 ... variable equalizer 11 ... 3-tap equalizer 110,111 ... delay circuit 112-114 ... amplifier 115 ... addition circuit 12 ... first tap 120 ... Delay circuit 121 Variable amplifier 121a to 121c Fixed gain amplifier 122 Switch 13 Second tap 130 Delay circuit 131 Variable amplifier 131a to 131c Fixed Gain amplifier 132 Switch 20 Switch 21 Inverting amplifier 22 Comparator 23 Amplifier 30 Skew sensor 30 300 ... LED 300 301 ... two-segment photo detector 302 ... arithmetic circuit 303 ... lens 304 ... spot 40 ... disk

Claims (6)

(57) [Claims] 1. An inclination detecting means for detecting an inclination of an optical disk, and a filter for inputting, from an optical pickup, a reproduced signal in which information recorded on the optical disk changes continuously according to the rotation of the optical disk, and for equalizing and outputting the same. Means, wherein the filter means are connected in series, a plurality of delay means for inputting and delaying the reproduced signal, and a plurality of delay means connected between the delay means and having a constant value for a signal appearing at the connection point. Fixed coefficient multiplying means for multiplying a coefficient, connected to one end of the delay means connected in series, and a signal appearing at the connection point, a variable coefficient which changes according to the inclination detected by the inclination detecting means, Multiplying variable coefficient multiplying means, and adding means for adding an output of the fixed coefficient multiplying means and an output of the variable coefficient multiplying means and outputting an equalized reproduction signal; An optical disc reproduction signal equalizing apparatus, wherein a delay amount and a coefficient of the fixed coefficient multiplying means are defined symmetrically with respect to a center connection point of the plurality of delay means and have a value dependent on an optical constant of the optical pickup. 2. A variable coefficient multiplying means for multiplying a signal before delay by the plurality of delay means by the variable coefficient, and a second coefficient for multiplying a signal after delay by the plurality of delay means by the variable coefficient. Multiplying means; selecting one of the output of the first variable coefficient multiplying means and the output of the second variable coefficient multiplying means according to the inclination detected by the inclination detecting means, and selecting the output to the adding means 2. An optical disk reproduction signal equalizing apparatus according to claim 1, further comprising: 3. The delay τ before or after the center connection point.
₂ is 1.22λ / (2NA · v) ≦ τ ₂ ≦ 2.23λ / (2NA · v), where λ is the wavelength of the light source of the optical pickup, NA is the numerical aperture of the objective lens of the optical pickup, and v is the rotation. The optical disk reproduction signal equalizer according to claim 1, wherein the optical disk reproduction signal equalization speed is defined as: 4. An optical disk reproduction signal equalization method for receiving a reproduction signal in which information recorded on an optical disk changes continuously according to the rotation of the optical disk from an optical pickup and equalizing the information, comprising: Is detected, with a delay amount depending on an optical constant of the optical pickup,
The reproduction signal is delayed, and a signal obtained from the middle of the delay is multiplied by a constant coefficient depending on an optical constant of the optical pickup to generate a first signal, and a signal before or after the delay is generated. An optical disk reproduction signal equalizing method for generating a second signal by multiplying a variable coefficient that varies according to the tilt of the optical disk, adding the first signal and the second signal, and generating an equalized reproduction signal . 5. The reproduction signal of an optical disk according to claim 4, wherein a signal used for generating the second signal is selected as a signal before delay or a signal after delay based on the inclination of the optical disk. Equalization method. 6. The delay amount τ ₂ before or after the intermediate point of the delay is 1.22λ / (2NA · v) ≦ τ ₂ ≦ 2.23λ / (2NA · v), where λ is the optical pickup. 5. The method according to claim 4, wherein the wavelength of the light source, NA is the numerical aperture of the objective lens of the optical pickup, and v is the linear velocity of the rotating optical disk.