JP3011230B2 - Optical disc playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus on which information is optically recorded.

[0002]

2. Description of the Related Art High density optical discs have been widely studied as package media and storage devices for image information. In an optical disk reproducing apparatus, a beam spot obtained by condensing a laser beam through an objective lens is irradiated onto an optical disk surface, the reflected light is detected by a light receiving element, and a reproduced signal is obtained as a light receiving signal converted into an electric signal.

[0003] Generally, the light receiving element is often formed by being divided into two or more parts. In this case, the reproduced signal is obtained by simply adding a light receiving signal detected on each light receiving surface by an adder. Has been used as

[0004] The reproduction signal of this optical disk is particularly effective when information is recorded at high density, even if there is no inclination (tangential skew) (0 degree) in the signal reading progress direction of the optical disk. Because the impact is large,
The opening of the eye is so small that errors tend to occur during signal identification. However, in this case, the eyes can be opened to reduce identification errors by waveform equalization using a simple equalizer (such as a 3-tap transversal filter).

On the other hand, when the inclination (tangential skew) of the signal reading progress direction of the optical disk is large,
The amount of coma aberration increases, and the reproduction signal deteriorates due to the increase in intersymbol interference.

In such a case, a simple equalizer such as a three-tap transversal filter cannot open the eye sufficiently, and the signal cannot be correctly identified as it is.

As a method of electrically compensating for such a deterioration of the reproduced signal in accordance with the skew, Japanese Patent Laid-Open No. 1-171 is disclosed.
As shown in No. 159, by changing the transfer function of the noise reduction circuit according to the skew,
There is a method for reducing deterioration of a reproduced signal mainly due to crosstalk.

Further, as disclosed in Japanese Patent Application Laid-Open No. 6-76299, there is known a method of adjusting the weighting coefficient of a transversal filter based on the amount of skew to reduce distortion of a reproduced signal.

[0009]

In the prior art described above, the method of changing the transfer function of noise reduction in accordance with the skew does not directly reduce the deterioration of the reproduced signal due to the occurrence of coma aberration. It is difficult to sufficiently reduce the influence of coma when skew occurs.

In the case of the method of adjusting the weighting coefficient of the transversal filter based on the skew, a large number of taps (at least 5 taps) is required to obtain a sufficient effect, and the number of elements is increased to increase the circuit number. Problems such as an increase in scale arise.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to reduce the deterioration of a reproduced signal which occurs when the tangential skew of an optical disk is large, by using a relatively simple circuit. It is assumed that.

[0012]

According to a first aspect of the present invention, there is provided an optical disk reproducing apparatus for irradiating an optical disk with a laser spot, detecting reflected light of the laser spot with a light receiving means, and reproducing information. The light receiving means 1 is divided into at least two parts before and after corresponding to a signal reading progress direction of the laser spot, and receives a light receiving signal from a front light receiving surface A and a light receiving signal from a rear light receiving surface B of the light receiving means 1. Adding means 4 for adding the signals at a predetermined ratio, and skew detecting means 6 for detecting the amount of tilt of the optical disk.
And a control means 7 for changing the addition ratio of the addition means 4 in accordance with the amount of tilt of the optical disk detected by the skew detection means 6.

According to a second aspect of the present invention, there is provided the optical disk reproducing apparatus according to the first aspect, wherein the addition ratio is determined by an amplification factor variable means provided between the light receiving means and the adding means. The amplification ratio of No. 3 was changed to change the addition ratio.

According to a third aspect of the present invention, there is provided the optical disk reproducing apparatus according to the second aspect, wherein the amplification factor varying means includes one of the front light receiving surface A and the rear light receiving surface B. And the adding means 4.

In order to achieve the above object, the present invention provides an optical disk reproducing apparatus for irradiating an optical disk 5 with a laser spot, detecting reflected light of the laser spot by light receiving means 1 and reproducing information, and The means 1 is divided into at least two parts before and after corresponding to the signal reading advancing direction of the laser spot, and converts a light receiving signal from a front light receiving surface A and a light receiving signal from a rear light receiving surface B of the light receiving means 1. Adding means 4 for adding at a predetermined ratio, skew detecting means 6 for detecting the amount of tilt of the optical disk, and control means for changing the adding ratio of the adding means according to the amount of tilt of the optical disk detected by the skew detecting means 7, a light receiving signal from the front light receiving surface and a light receiving signal from the rear light receiving surface of the light receiving means divided into at least two parts in front and back corresponding to the signal reading progress direction. It is obtained by configured to add at a ratio corresponding to the signal to tangential skew amount.

At the time of adding the light receiving signal from the front light receiving surface and the light receiving signal from the rear light receiving surface of the light receiving element divided at least back and forth in accordance with the signal reading progress direction, the reproduced signal by tangential skew is added. By changing the addition ratio in a direction to reduce the deterioration, it is possible to reduce the deterioration of the reproduction signal when the tangential skew amount is large.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical disk reproducing apparatus according to the present invention will be described below with reference to the accompanying drawings. FIG.
FIG. 1 is a block diagram of an embodiment of an optical disk reproducing apparatus according to the present invention.

First, the reflected light from the optical disk is detected by a light receiving element (light receiving means) 1 divided into front and rear portions corresponding to the signal reading traveling direction. The light receiving signals detected by the front light receiving surface A and the rear light receiving surface B of the light receiving element 1 are supplied to variable amplifier circuits (amplification ratio varying means) 2 and 3, respectively.

On the other hand, the tangential skew amount of the optical disk 5 is detected by a skew sensor (skew detecting means) 6, and a signal corresponding to the skew amount is supplied to a control circuit (control means) 7.

The control circuit (control means) 7 controls the variable amplifier circuit 2 according to the skew amount based on a signal from the skew sensor.
And a gain control signal is sent so as to set the gain values of (3) and (3) to predetermined values.

Variable amplification circuits (amplification rate varying means) 2 and 3
Amplifies the received light signal supplied thereto with a gain corresponding to the gain control signal, and supplies the amplified signal to the adder 4. Then, finally, the two light receiving signals amplified by the gain value according to the skew amount are added to be output as a reproduction signal added at a predetermined ratio.

The case where the gain control signal is sent so that the gain values of the two variable amplifier circuits 2 and 3 are set to a predetermined value has been described above. However, the present invention is not limited to this, and one variable amplifier circuit is used. Similar results can be achieved with a simpler configuration using 2 or 3.

The principle of operation of the optical disk reproducing apparatus according to the present invention will be described below with reference to the drawings. When there is no tangential skew (0 degree) on the optical disk, the beam spot has an intensity distribution symmetrical on the optical disk surface, as shown in FIG.

In an optical disc, intersymbol interference occurs due to the relationship between the spot size and the code (pit) size. In general, the higher the information recording density, the greater the effect of the intersymbol interference. Opening becomes smaller.

If the eye opening is small, an error is likely to occur in signal identification. However, if there is no skew, the effect of intersymbol interference is reduced by a simple equalizer to sufficiently open the eye. Can be sized.

However, when there is a tangential skew, coma aberration occurs in the spot, and as shown in FIG. 2B, the intensity distribution becomes asymmetrical before and after, thereby increasing intersymbol interference. This increase in intersymbol interference degrades the reproduced signal, and the eye opening becomes smaller than in a state without skew, thereby increasing identification errors.

When the beam spot is irradiated on the pits in the positional relationship shown in FIG. 3, the intensity distribution of the reflected light on the light receiving element in a state where there is no skew is as shown in FIG. Due to the light diffraction phenomenon at the pits, the intensity distribution becomes asymmetrical between the front and the back, whereby the information of the pits can be reproduced.

On the other hand, when tangential skew occurs, the intensity distribution of the reflected light is as shown in FIG. 4B, and a difference appears in the intensity distribution as compared with the case where there is no skew. This difference is an increase in intersymbol interference due to the occurrence of coma aberration, which is a factor of deteriorating a reproduced signal.

This change in the intensity distribution appears largely on either the front light receiving surface or the rear light receiving surface in accordance with the direction of the tangential skew, and the amount of change in the intensity distribution corresponds to the skew amount. I have.

When the change in the intensity distribution is large on the front light receiving surface, the change in the amount of light on the front light receiving surface is large, so that it appears as a change in the front light receiving signal. Appears as a change in the received light signal.

FIG. 5 shows a front light receiving signal and a rear light receiving signal when a certain pit row is read. The horizontal axis in FIG. 5 represents the progress in the signal reading direction.

FIG. 5A shows a case where there is no tangential skew, and FIG. 5B shows a case where there is tangential skew. As shown in FIG. 5B, when the skew occurs, the amplitude of the front or rear light receiving signal corresponding to the direction of the skew decreases.

When the reproduction signal is the total light reception signal on the light receiving surface, that is, the simple addition of the front light reception signal and the rear light reception signal, the decrease in the amplitude of one of the light reception signals causes the deterioration of the reproduction signal, and The opening becomes smaller.

Therefore, in the present invention, the correction is made by changing the addition ratio when adding the deterioration of the reproduction signal due to the decrease in the amplitude of the front light reception signal or the rear light reception signal caused by the amount and direction of the skew.

FIG. 6 is a diagram showing the appearance of a reproduced signal whose skew has been corrected according to the present invention. In FIG. 6, the horizontal axis represents the progress in the signal reading direction. FIG. 7 is a diagram showing the relationship between the skew amount and the addition ratio.

As shown in FIG. 6, when skew occurs, FIG.
By correcting the reproduction signal according to the relationship between the skew amount and the addition ratio as shown in (1), it is possible to prevent the amplitude from deteriorating, and to approach the reproduction signal when there is no skew. That is, it is possible to reduce the deterioration of the reproduction signal due to the coma when the skew occurs.

In the above description, the light receiving means of the optical disk reproducing apparatus is divided into at least two parts before and after corresponding to the signal reading progress direction of the laser spot, and the light receiving signal from the front light receiving surface of the light receiving means and the rear part The case where the light receiving signal from the light receiving surface is added at a predetermined ratio has been described. However, the present invention is not limited to this. The same idea can be applied to the case where the light receiving signal from the partial light receiving surface and the light receiving signal from the left light receiving surface are added at a predetermined ratio.

[0038]

The optical disk reproducing apparatus according to the present invention converts a light receiving signal from a front light receiving surface and a light receiving signal from a rear light receiving surface of a light receiving element divided into at least two parts before and after corresponding to a signal reading progress direction. Signal addition means for adding at a predetermined ratio, skew detection means for detecting the amount of tilt of the optical disk, and means for changing the addition ratio of the addition means according to the amount of tilt of the optical disk detected by the skew detection means; With this arrangement, it is possible to reduce the deterioration of the reproduction signal due to an increase in intersymbol interference when a skew occurs with a simple device.

Further, the optical disk reproducing apparatus of the present invention
Errors during signal identification can be greatly reduced, and a relatively inexpensive and highly reliable optical disc reproducing apparatus can be realized.

Further, the optical disk reproducing apparatus of the present invention may be a simple apparatus in which the amplification rate varying means is constituted by one system, and a relatively inexpensive and highly reliable optical disk reproducing apparatus can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of an optical disk reproducing apparatus according to the present invention.

FIG. 2 is a diagram showing an intensity distribution of a beam spot on an optical disk surface.

FIG. 3 is a diagram showing a positional relationship between a beam spot and a pit.

FIG. 4 is a perspective view schematically showing an intensity distribution of reflected light on a light receiving element in a state shown in FIG. 3 (a diagram showing a positional relationship between a beam spot and a pit).

FIG. 5 is a diagram showing a relationship between a front light receiving signal and a rear light receiving signal corresponding to the presence / absence of tangential skew.

FIG. 6 is a diagram showing a reproduced signal corrected by the optical disk reproducing device of the present invention.

FIG. 7 is a diagram showing a relationship between a tangential skew and an addition ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light receiving element (light receiving means) 2, 3 Variable amplification circuit (gain variable means) 4 Adder (addition means) 5 Optical disk 6 Skew sensor (skew detecting means) 7 Control circuit (control means) A Front light receiving surface B Rear part Light receiving surface

Claims (3)

(57) [Claims] 1. An optical disk reproducing apparatus for irradiating an optical disk with a laser spot, detecting reflected light of the laser spot with a light receiving means, and reproducing information, wherein the light receiving means is provided in a signal reading progress direction of the laser spot. Correspondingly divided into at least two parts before and after, adding means for adding a light receiving signal from the front light receiving surface and a light receiving signal from the rear light receiving surface of the light receiving means at a predetermined ratio; An optical disc reproducing apparatus comprising: a skew detecting unit for detecting; and a control unit for changing an addition ratio of the adding unit in accordance with an inclination amount of the optical disc detected by the skew detecting unit. 2. The optical disc reproducing apparatus according to claim 1, wherein the addition ratio is changed by changing an amplification ratio of an amplification factor variable unit provided between the light receiving unit and the addition unit. An optical disc reproducing apparatus characterized in that it is configured as described above. 3. The optical disc reproducing apparatus according to claim 2, wherein the amplification factor variable means is provided between one of the front light receiving surface and the rear light receiving surface and the adding means. An optical disc reproducing apparatus characterized in that it is configured as described above.