JPH11265508A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk device capable of improving reproducing signals SNR at the time of reproducing a recordable optical disk at a high linear velocity without inviting cost rise and the increase of a circuit scale. SOLUTION: This optical disk device for reproducing signals recorded in the recordable optical disk 10 is provided with a linear velocity detection means 60 for detecting the linear velocity of the optical disk 10 and a laser power control means 61 for increasing the power of a laser beam for irradiating the optical disk 10 corresponding to the height of the linear velocity detected in the linear velocity detection means 60. Reproducing power is increased by the laser power control means 61 within the range of not making a repetitive reproduction possible number of times at the time of a high linear velocity less than the repetitive reproduction possible number of times at the time of a low linear velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for reproducing an optical disk, and more particularly, to improving a reproduction signal SNR (signal-to-noise ratio of a reproduction signal) when reproducing a recordable optical disk at a high linear velocity. Accordingly, the present invention relates to an optical disk in which the error rate at the time of reproducing the optical disk is reduced and the recording density thereof is improved.

[0002]

2. Description of the Related Art In recent years, as data processing technology and signal processing technology typified by advances in computers have become more complicated and faster, data storage devices such as optical disk devices have been required to have larger capacity and higher speed. (Higher transfer rate) is required.

[0003] A higher transfer rate in an optical disk device is achieved by increasing the linear velocity of the optical disk during recording / reproducing (the relative speed between the laser light spot irradiated on the optical disk by the optical head and the optical disk).
The following key technologies are required as main component technologies at that time. (A) Servo control technology having high control characteristics such as stability even at a high linear velocity. (B) High-speed recording technology. (C) Broadband playback technology. Since the present invention relates to the broadband reproduction technique, the broadband reproduction technique will be described below.

[1] Relationship between Linear Velocity and Reproduced Signal SNR Disc noise and system noise are major noises that lower the reproduced signal SNR during reproduction of an optical disk. FIG. 5 shows an example of the relationship between these noises on the frequency axis.

Since the total amount of the disk noise is determined by the resolution of the optical system in the optical head, the total amount of the disk noise within the transmission band (DC to cutoff frequency of the optical system) is constant on the frequency axis. Therefore, as shown in FIG. 5, the noise power density (noise level) is lower at the high linear velocity than at the low linear velocity, but the noise is distributed over a wide band.

On the other hand, system noise is mainly noise of a head amplifier in an optical head. In the optical head,
A photodiode is usually used as a photoelectric conversion element for converting return light from an optical disk into an electric signal, but a transimpedance amplifier is used as a head amplifier because the output of the photodiode is a current. The noise of this transimpedance amplifier does not change depending on the linear velocity, but as shown in FIG. 5, the noise power density tends to increase as the frequency increases.

The total noise in FIG. 5 is obtained by adding (square addition) disk noise and system noise. As described above, the total amount of disk noise in the transmission band is constant, whereas the noise power density of system noise increases as the frequency increases. Noise increases.

On the other hand, the level of the reproduced signal is determined by the resolution of the optical system in the optical head, and does not depend on the linear velocity. As a result, the reproduced signal SNR deteriorates as the linear velocity increases.

[2] Relationship between Reproduction Power and Reproducible Number of Reproductions Recording of a signal on a recordable optical disk utilizes the temperature rise of a recording film due to irradiation of a laser beam. That is, for example, in a phase change type optical disk, recording is performed by a reversible phase change (for example, a change between amorphous and crystalline) of the recording film due to a rise in temperature. The recording is performed by applying an external magnetic field in a state where the temperature is raised above the Curie point.

[0010] On the other hand, reproduction of a recordable optical disk is performed by irradiating a recording film with a laser beam having a power of about 1/10 of the power at the time of recording. However, irradiation of a laser beam having such a power also involves a certain rise in the temperature of the recording film. Therefore, each time reproduction is repeated, the recording signal gradually deteriorates (specifically, the signal level decreases, noise increases, and jitter increases), and the number of times that reproduction can be repeated is limited. Then, as exemplified in FIG. 6, the laser power at the time of reproduction (referred to as reproduction power)
Is higher, the deterioration of the recording signal becomes more remarkable, so that the number of times of repetitive reproduction is reduced.

[3] Relationship between Linear Velocity and Number of Reproducible Reproductions The higher the linear velocity at the time of reproduction, the shorter the time for irradiating the recording film with a laser beam spot, and the higher the recording film per reproduction. Since the temperature is lowered, the number of times of reproducible reproduction is increased.

[4] Relationship among Reproduction Power, Linear Velocity, Reproduction Signal SNR, and Number of Reproducible Reproductions in Conventional Optical Disk Apparatus In a conventional optical disk apparatus, reproduction of a recordable optical disk is performed as shown in FIG. Regardless of the linear velocity, the reproduction is performed at a constant reproduction power p (reproduction power capable of securing a constant number m of repeatable reproductions guaranteed by the apparatus even when the linear velocity is the minimum velocity Lv1). Therefore, from the relations of [1] and [3], in the conventional optical disk device, as shown in FIG. 3, as the linear velocity becomes higher, the number of repetitive reproductions increases (more than m), but the reproduction signal becomes higher. The SNR will deteriorate.

[0013]

As described above, in the conventional optical disk device, as the linear velocity increases, the reproduced signal S becomes higher.
As the NR deteriorates, the error rate increases. As described above, in recent years, demands for higher transfer rates (that is, higher linear velocities) for optical disc apparatuses have been further increased, and thus, the deterioration of the reproduction signal SNR has become an increasingly serious problem.

As one method of solving this problem, system noise has been reduced by reducing the noise of a head amplifier (transimpedance amplifier). However, this method has a new problem such as an increase in cost and an increase in circuit scale.

Accordingly, an object of the present invention is to provide a reproduction signal SNR for reproducing a recordable optical disc at a high linear velocity.
It is an object of the present invention to provide an optical disk device that can be improved without increasing cost and circuit scale.

[0016]

SUMMARY OF THE INVENTION An optical disk apparatus according to the present invention is an optical disk apparatus for reproducing a signal recorded on a recordable optical disk. Laser power control means for increasing the power of the laser beam in accordance with the level of the linear velocity detected by the linear velocity detection means.

According to this optical disk device, the reproduction power is increased by the laser power control means in accordance with the level of the linear velocity detected by the linear velocity detection means. When the reproduction power increases, the level of the reproduction signal increases,
The effect of system noise is reduced. Thereby, deterioration of the reproduction signal SNR at the time of reproduction at a high linear velocity is suppressed.

The linear velocity detecting means performs an operation based on, for example, position information from a position sensor of an existing optical head and information on the number of revolutions of an existing spindle motor, or as another example, from an optical disk. By converting the reproduced address data into the position information of the optical head and performing an operation based on this position information and the rotation speed information of the spindle motor, it is possible to reduce the noise of the head amplifier as compared with the conventional method. It can be realized at a low cost with a much smaller circuit. Also, changing the reproducing power in accordance with the linear velocity detected in this way can be realized at a low cost with a much smaller circuit than in reducing the noise of the head amplifier.

Therefore, according to this optical disk device, the deterioration of the reproduction signal SNR at the time of reproduction at a high linear velocity is suppressed without increasing the cost and the circuit scale.

As an example, it is preferable that the laser power control means increase the power of the laser beam within a range where the number of repetitive reproductions of the optical disk is not less at high linear velocity than at low linear velocity. is there.

By doing so, at the time of reproduction at a high linear velocity, deterioration of the reproduction signal SNR is suppressed while maintaining a constant number of reproducible reproductions guaranteed by the apparatus.

[0022]

FIG. 4 shows an example of the configuration of an optical disk device (existing optical disk device) to which the present invention is applied. In this optical disk device, the phase-change optical disk 10 is mounted on a shaft of a spindle motor 20 and rotates. For example, the spindle servo circuit 21 controls the motor 2 based on the rotation speed information obtained based on the FG signal output from the spindle motor 20.
Control is performed so that 0 becomes a predetermined rotation speed.

Recording and reproduction of signals on the optical disk 10 are performed by an optical head 30. In the optical head 30, laser light is emitted from an LD (laser diode) 31 driven by a laser drive current from a laser drive circuit 32. This laser beam is partially polarized prism 39.
The light is reflected by a and enters a monitor-PD (monitoring photodetector using a photodiode) 33, but most of the light passes through a polarizing prism 39 a and is collected in a spot state by an objective lens 39 b supported by an actuator 36. The light is emitted and irradiates the recording film of the optical disk 10.

The laser light reflected by the optical disk 10 passes through an objective lens 39b, and is reflected by a polarizing prism 39a, and then a PD (photodetector using a photodiode) 34
Incident on. The output of the PD 34 is amplified by a head amplifier (transimpedance amplifier) 35. The entire optical head 30 can be moved in the radial direction of the optical disk 10 by the feed mechanism 37. The position sensor 38 detects the position of the optical head 30 in the disk radial direction.

Focus / Tracking Servo Circuit 4
0 indicates an objective lens 39 based on the focus / tracking servo error signal output from the head amplifier 35.
b. The actuator 36 is controlled to adjust the position of the objective lens 39b so that the distance between the optical disk 10 falls within the depth of focus of the objective lens 39b and the laser beam spot accurately scans the track on the recording surface.

The address decoder 41 includes a head amplifier 3
By decoding the address signal output from 5, the optical head 30 generates address data indicating the physical address on the optical disk 10 of the sector currently irradiating the laser light spot.

The reproduction signal processing circuit 42 generates reproduction data by performing EFM demodulation, error correction, decoding of a compressed signal, and the like on the RF signal output from the head amplifier 35 during reproduction.

The laser power control circuit 50 includes a monitor P
By controlling the laser drive circuit 32 so that the output (signal representing the power of the laser light incident on the monitor-PD 33) level of D33 becomes equal to a predetermined reference level,
The power of the laser beam from the LD 31 is controlled. here,
Since the power of the laser beam is different between the time of reproduction and the time of recording, there are two levels of reference levels: a read power reference voltage 51 and a recording power reference voltage 52. In addition, a laser beam having a plurality of types of power is often used at the time of recording. In this case, there are a plurality of levels of the recording power reference voltage.

The recording signal processing circuit 53 sends a recording pulse generated based on data to be recorded to the laser driving circuit 32 during recording. The laser drive circuit 32 switches the laser drive current according to the recording pulse.

Next, an example in which the present invention is applied to the optical disk device shown in FIG. 4 will be described. FIG. 1 shows a first example, in which a linear velocity detection circuit 60 and a reproduction power control circuit 61 are added to the optical disk apparatus of FIG. The other parts in FIG. 1 may be the same as those in FIG. 4, and thus the same reference numerals are given and the duplicated description will be omitted.

The linear velocity detecting circuit 60 obtains the linear velocity Lv by performing the following calculation based on the position information from the position sensor 38 and the information on the number of revolutions from the spindle servo circuit 21 (where r and f are , The distance in the disk radial direction from the center of the optical disk 10 to the current position of the optical head 30, and the rotation speed of the spindle motor 20). Lv = 2πrf

The higher the linear velocity Lv detected by the linear velocity detecting circuit 60 is, the higher the linear power Lv detected by the linear power detecting circuit 60 is. As the track to be read becomes closer to the outer periphery of the optical disk 10), the reproduction power reference voltage 51 is controlled to increase the reference level. Thus, the power of the laser beam from the LD 31 during reproduction increases as the linear velocity Lv increases.

FIG. 2 shows an example of the relationship among the linear velocity, the reproduction power, the reproduction signal SNR, and the number of times of repetitive reproduction by the optical disk device of FIG. 1, and FIG. It is shown in comparison with. The reproduction power control circuit 61 determines that the linear velocity is the minimum velocity L
v1 (in the case of the CAV method, the optical disk 10
(When the innermost track is scanned), the reproducing power reference voltage 51 is controlled so that the reproducing power matches the reproducing power p in FIG. Therefore, the number of times of repetitive reproduction at this time matches the number m in FIG. When the linear velocity is higher than the minimum velocity Lv1 (when scanning a track other than the innermost circumference of the optical disk 10 in the case of the CAV method), the reproduction power control circuit 61 can repeatedly reproduce. The reproduction power reference voltage 51 is controlled such that the reproduction power increases at such a degree that the number of times maintains this m.

Therefore, in the case of the relationship shown in FIG.
Since the influence of system noise is reduced by increasing the reproduction power as the linear velocity increases, deterioration of the reproduction signal SNR during reproduction at a high linear velocity is suppressed. (Note that FIG. 2
For convenience, the reproduction signal SNR is drawn as being constant regardless of the linear velocity. In practice, the reproduction signal SNR is not always constant as described above, but the increase in the reproduction power does not change the deterioration of the reproduction signal SNR. )

Further, in the case of the relationship shown in FIG. 2, even at the time of reproduction at a high linear velocity, the constant number m of reproducible reproductions guaranteed by the apparatus is maintained.

Since the linear velocity detecting circuit 60 merely performs a simple calculation based on the position information from the existing position sensor 38 and the rotational speed information from the spindle servo circuit 21, the linear amplifier detecting circuit 60 controls the head amplifier 35. It can be realized at a much smaller scale and at a lower cost as compared with the case where the noise is reduced. Also, since the reproducing power control circuit 61 only controls the reproducing power reference voltage 51 so that the reference level changes in accordance with the linear velocity, the reproducing power control circuit 61 is much smaller than the noise reduction of the head amplifier 35. It can be realized on a scale and at low cost. Therefore, there is no increase in cost and circuit size as in the case where the noise of the head amplifier 35 is reduced.

FIG. 3 shows a second example in which the present invention is applied to the optical disk device of FIG. In this example, the address / radius conversion table 6 is based on the address data from the address decoder 41 and the rotation speed information from the spindle servo circuit 21 instead of the linear velocity detection circuit 60 in FIG.
2, a linear velocity detection circuit 63 for determining the linear velocity Lv is provided. The other parts in FIG. 3 may be the same as those in FIG. 1, and thus the same reference numerals are given and the duplicated description will be omitted.

Since the address data indicates the physical address on the optical disc 10 of the sector to which the optical head 30 is currently irradiating the laser light spot, the address data value and the center of the optical disc 10 The distance r in the disk radial direction to the current position corresponds one-to-one. The address / radius conversion table 62 is a table in which the value of the address data and the distance r are recorded correspondingly for each sector on the optical disk 10. The linear velocity detection circuit 63 uses the address / radius conversion table 62
After obtaining the information of the distance r by referring to FIG. 1, the same Lv = 2πrf as performed by the linear velocity detecting circuit 60 in the example of FIG.
Is calculated to obtain the linear velocity Lv.

The processing performed by the reproduction power control circuit 61 may be the same as in the above-described example of FIG. Therefore, in the example of FIG. 3 as well, the deterioration of the reproduction signal SNR at the time of reproduction at a high linear velocity is suppressed, and the constant number of times m of repeated reproduction that is guaranteed by the apparatus at the time of reproduction at a high linear velocity is also Will be maintained.

Also in the example of FIG. 3, the address / radius conversion table 62 and the linear velocity detecting circuit 63 can be realized at a much smaller scale and at a lower cost as compared with the case where the noise of the head amplifier 35 is also reduced. is there. Therefore, the cost and the circuit scale do not increase as in the case where the noise of the head amplifier 35 is reduced.

In the above example, the reproduction power at the high linear velocity is increased within a range where the number of repetitive reproductions of the optical disk 10 at the high linear velocity does not become smaller than that at the low linear velocity. However, for example, when it is desired that the improvement of the reproduction signal SNR at the time of the high linear velocity is prioritized over the maintenance of the number of reproducible times, the reproducing power at the high linear velocity is set to be smaller than the number of reproducible times at the low linear velocity. Alternatively, the number of repetitive reproductions at a high linear velocity may be increased to such an extent that the number becomes smaller.

In the above example, the present invention is applied to an optical disk apparatus for recording / reproducing on / from a phase change optical disk. However, the present invention is applied to other recordable optical disks (for example, magneto-optical disks). The present invention may be applied to an optical disk device that performs reproduction.

Further, the present invention is not limited to the above-described example, and may take various other configurations without departing from the gist of the present invention.

[0044]

As described above, according to the optical disk device of the present invention, the reproduction signal SNR at the time of reproducing a recordable optical disk at a high linear velocity can be improved without increasing the cost and the circuit size. can do.

As a result of the improvement in the reproduction signal SNR at the time of reproduction at a high linear velocity, the error rate at the time of reproduction at a high linear velocity is reduced, and the recording density in an area of the optical disk where the linear velocity is high is obtained. Can also be increased.

When the reproducing power is increased within a range where the number of times of repetitive reproduction of the optical disk is not reduced at a high linear velocity than at a low linear velocity, the apparatus guarantees the reproduction at a high linear velocity. It is possible to improve the reproduction signal SNR while maintaining a certain number of times of reproducible reproduction.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example in which the present invention is applied to the optical disk device of FIG.

FIG. 2 is a diagram showing an example of characteristics of the optical disk device of FIG.

FIG. 3 is a diagram showing another example in which the present invention is applied to the optical disc device of FIG. 4;

FIG. 4 is a diagram showing an example of the configuration of an optical disk device to which the present invention is applied.

FIG. 5 is a diagram illustrating an example of noise during reproduction of an optical disk.

FIG. 6 is a diagram showing an example of a relationship between reproduction power and the number of times of reproducible reproduction.

FIG. 7 is a diagram illustrating an example of characteristics of a conventional optical disc device.

[Explanation of symbols]

10 ‥‥ optical disk, 20 ‥‥ spindle motor, 2
1 ‥‥ spindle servo circuit, 30 ‥‥ optical head, 3
5 head amplifier, 38 position sensor, 41 address decoder, 50 laser power control circuit, 51
{Reproduction power reference voltage, 60, 63} linear velocity detection circuit, 61 {reproduction power control circuit, 62} address /
Radius conversion table

Claims (4)

[Claims] 1. An optical disc apparatus for reproducing a signal recorded on a recordable optical disc, comprising: a linear velocity detecting means for detecting a linear velocity of the optical disc; An optical disk device comprising: laser power control means for increasing the linear velocity in accordance with the level of the linear velocity detected in (1). 2. The optical disk device according to claim 1, wherein said linear velocity detecting means includes: position information from a position sensor for detecting a position in a disk radial direction of an optical head for irradiating the optical disk with laser light; An optical disk device for detecting a linear velocity based on information on the number of rotations of a spindle motor for rotating the optical disk. 3. The optical disk device according to claim 1, wherein the linear velocity detecting unit is configured to detect a position of an optical head that irradiates a laser beam on the optical disk with address data reproduced from the optical disk in a radial direction of the disk. An optical disk device, wherein the linear velocity is converted into information, and a linear velocity is detected based on the position information and rotation speed information of a spindle motor for rotating the optical disk. 4. The optical disk device according to claim 1, wherein the laser power control means sets the number of times that the optical disk can be repeatedly reproduced at a high linear velocity within a range not less than at a low linear velocity. An optical disk device, wherein the power of the laser light is increased.