JPH10334571A - Signal recording medium discriminating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the reliability of discriminating a signal recording medium by canceling unstable factors even when there are such unstable factors as a fluctuation of a light source of an optical head and a change of an intensity level, etc., of light beam emitted from the optical head due to a temp. characteristic and a secular change, etc., and also reducing a variation in an optical characteristic due to deformation, etc., of the signal recording medium. SOLUTION: This discriminating method is performed in such a way that a ratio of amplitude values of focus error signals respectively under the using state of 1st and 2nd light beams suitable for 1st and 2nd signal recording media respectively is calculated (a step h), then, this ratio is compared with a reference value to discriminate which is the 1st or the 2nd signal recording medium (a step i). Thus, by using the ratio to discriminate the signal recording medium, the unstable factor caused by the intensity level of the light beam emitted from the optical head and influence of variance of the optical characteristic of the signal recording medium are absorbed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a signal recording medium discriminating method for discriminating between first and second signal recording media having different thicknesses of a substrate up to a signal recording surface.

[0002]

2. Description of the Related Art CDs (compact discs) have become widespread as optical discs on which signals are optically read using an optical head. A DVD (Digital Versatile Disk) standardized to increase the capacity by recording at a higher density than a CD while ensuring mechanical compatibility has been developed.

[0003] DVDs have a higher signal recording density than CDs. Therefore, as an optical head compatible with DVDs, the wavelength of the laser element of the light source is shortened and the NA of the objective lens is increased to improve the resolution of the optical system. Imaging is required.

By the way, in a DVD player, C
Playback of D is also required. Since the thickness of the transparent substrate up to the signal recording surface differs greatly between DVD and CD, the CD is reproduced using a light beam adapted to DVD. The light beam cannot be properly focused on the signal recording surface of the CD. Therefore, it is necessary to switch the light beam to be used in the reproduction of the DVD and the reproduction of the CD so that the reproduction is performed using the light beam having the optical characteristic suitable for each disk.

In addition, it is necessary to switch a setting state of an internal circuit such as switching a signal processing circuit to be used in accordance with a mounted disk, switching disk rotation control, and the like.

[0006] From these needs, the DVD player needs to determine the mounted disk. Conventionally, such a method of discriminating a disc is disclosed in, for example,
This publication discloses a method for discriminating a disc based on whether a peak value of a focus error signal obtained by moving a focus position of a light beam in a focus direction exceeds a threshold value or not. I have.

[0007]

By the way, the focus error signal level varies with the optical characteristics of the disk due to variations in the material of the signal recording surface of the disk and the substrate, the deformation of the disk, etc., and the variations in the semiconductor laser as the light source. It is not constant due to unstable factors such as changes in the intensity level of the light beam emitted from the optical head due to temperature, temperature characteristics, or changes over time. For this reason, there is a large variation in the focus error signal level for each disk and each optical head, and it is difficult to set a threshold value in the above-described disk determination method, and there is a problem that the reliability of disk determination is reduced.

[0008]

According to the present invention, an amplitude value of a focus error signal for a signal recording medium, which is obtained by moving a focal position of a light beam in a focusing direction, to a first signal recording medium adapted to the first signal recording medium. The measurement is performed in each of the use state of one light beam and the use state of the second light beam compatible with the second signal recording medium, and the ratio of the measured amplitude value of each focus error signal is calculated. The first and second signal recording media are determined by comparing the ratio with a preset reference value.

In this case, by calculating the ratio of the amplitude values of the focus error signal, the difference between the optical characteristics of the signal recording medium and the emission from the optical head when a common light source is used for the first and second signal recording media. An unstable element of the change in the intensity level of the light beam to be canceled is canceled, and the reference value can be set without being affected by these unstable elements.

[0010]

FIG. 1 is a flowchart showing one embodiment of a signal recording medium discrimination method according to the present invention.

The signal recording medium discriminating method shown in FIG.
And CD disc. Hereinafter, a method of discriminating a disc will be described with reference to the flowchart of FIG.

When it is determined that the disk is mounted on the disk device (step a), the setting mode of the optical head is recognized (step b). Here, the optical head is D
The setting mode can be switched between a first mode in which a light beam conforming to VD is obtained and a second mode in which a light beam conforming to CD is obtained.

After the setting mode of the optical head is recognized, it is determined whether or not the mode switching is necessary (step c). If the mode switching is not required, the focal position of the light beam is moved in the focus direction. The process moves to the focus search operation (step d).

At the time of a focus search operation, the voltage level of a focus error signal (FE signal) obtained from the photodetector of the optical head is detected, the amplitude value of the focus error signal is measured from the detected output, and the amplitude value is stored. (Step e).

Then, the first mode and the second mode of the optical head
It is determined whether the amplitude values of the focus error signals in both modes are measured (step f). If the amplitude values of the focus error signals in both modes are not measured, the mode switching of the optical head is performed. Is performed (step g).

When the mode switching of the optical head is performed, the setting mode of the optical head is recognized (step b).
After it is determined whether or not the mode switching is necessary (step c), the focus search operation (step d) is performed again, and the amplitude value of the focus error signal in the state where the mode switching of the optical head is performed is represented by numerical data. And its amplitude value is stored (step e).

When the measurement of the amplitude value of the focus error signal in both the first mode and the second mode of the optical head is completed as described above, the ratio of the amplitude value of the focus error signal in each of the stored modes is reduced. An operation is performed (step h).

The ratio of the amplitude value of the focus error signal in each mode is compared with a reference value serving as a boundary reference set in advance for disc classification, and the comparison results in the ratio of the amplitude value of the focus error signal in each mode. It is determined whether the disc is a DVD or a CD depending on whether the disc is smaller or larger than the reference value (step i).

The ratio between the amplitude value of the focus error signal in each of the first mode and the second mode of the optical head and the amplitude value of the focus error signal in each mode is set between the first mode and the second mode. When an optical head capable of switching modes was used, measurement was performed with six optical heads, and measurement values as shown in FIG. 2 were obtained for DVD and CD. As an optical head, a single semiconductor laser having a short wavelength (635 nm) is commonly used in each mode.
The configuration is adapted to correspond to each mode by switching the aperture diameter for limiting the light beam incident on the objective lens.

When the ratio of the amplitude value of the focus error signal in each mode in the measured values shown in FIG. 2 is represented by a histogram in FIG. 3, the DVD has a range of 20% to 30% and a range of 30% to 30% as indicated by hatched bars. The CDs are all in the range of 40%, while the CDs are all in the range of 80-90% and 90-100% as shown by the filled bars.

As described above, the ratio of the amplitude value of the focus error signal in each mode is greatly different between the DVD and the CD, and the distribution range of each disk is narrow.
Therefore, it is easy to set a boundary reference for distinguishing between DVD and CD, and it is possible to reliably distinguish between DVD and CD.

Therefore, in this case, 60% is set as a boundary reference, and a reference value obtained by converting the boundary reference into numerical data is compared with ratio data calculated as a ratio of the amplitude value of the focus error signal in each mode. If the ratio data is smaller than the reference value, it can be determined to be DVD, while if the ratio data is larger than the reference value, it can be determined to be CD.

Incidentally, the intensity level of the light beam emitted from the optical head varies from one optical head to another due to variations and temperature characteristics of the semiconductor laser serving as a light source, or unstable factors such as aging, and changes depending on the use condition. Compares the ratio of the amplitude value of the focus error signal in each mode with the reference value to determine whether the DVD or CD
Since the discrimination is made and the ratio is used for disc discrimination, the unstable element can be canceled.

Further, even if the discs are of the same type due to variations in the material of the signal recording surface or the substrate, deformation of the signal recording medium, etc., the optical characteristics vary from disk to disk.
Even in this case, since the influence of the variation appears in both the amplitude values of the focus error signal in each mode, the variation in the optical characteristics of the disk is determined by using the ratio of the amplitude value of the focus error signal in each mode for disc determination. Can be reduced.

FIG. 4 is a circuit block diagram showing an example of a disc discriminating apparatus provided with the signal recording medium discriminating method of FIG. The disc discriminating operation will be described below with reference to FIG.

In the initial state where the disc is mounted,
The mode switching control circuit 1 causes the optical head 2 to, for example,
The first mode is set so that a light beam conforming to D is obtained. Then, a focus search operation is performed in a state where the optical head 2 is set to the first mode, and the voltage level of the focus error signal (FE signal) obtained from the photodetector 3 during the focus search operation is equal to the FE signal amplitude. The value measurement circuit 4 converts the value into numerical data and detects it, and the amplitude value of the focus error signal is measured as numerical data from the detection output. Then, the amplitude value is stored in the memory 5.

Thereafter, it is determined whether or not the amplitude value of the focus error signal in both the first mode and the second mode of the optical head is measured based on the storage state of the memory 5, and the focus error signal in both modes is measured. When the amplitude value is not measured, the mode switching control circuit 1 switches the mode of the optical head 2 so that the amplitude value not stored in the memory 5 is measured.
In this case, the focus search operation is performed with the optical head 2 set to the second mode. Then, the amplitude value of the focus error signal in a state where the optical head 2 is set to the second mode is measured as numerical data by the FE signal amplitude value measuring circuit 4, and the amplitude value is stored in the memory 5.

When the amplitude value of the focus error signal in both the first mode and the second mode of the optical head 2 is stored in the memory 5 in this way, the arithmetic circuit 6 stores the focus error signal in each mode. The ratio of the amplitude values of the signal is calculated. The calculated ratio data is compared with a reference value of numerical data serving as a boundary reference set for discriminating between DVD and CD by the disk determination circuit 7, and the disk determination circuit 7 compares the ratio data with the reference value. When the ratio is smaller, the DVD is determined and a determination signal indicating the fact is output. On the other hand, when the ratio data is larger than the reference value, the determination is made as the CD and a determination signal indicating the fact is output.

The determination signal output from the disk determination circuit 7 is used as a switching signal for switching the operation setting state of the optical head 2 and the internal circuit, and is used for a disk mounted with the operation setting state of the optical head 2 and the internal circuit. Switch to a suitable state.

In the above-described embodiment, the optical head is achieved by switching the aperture diameter for limiting the light beam incident on the objective lens so as to conform to the first mode and the second mode. However, there are two methods to switch the aperture diameter: a method of changing the incident light beam diameter of a single objective lens using a filter, and a method of switching and using an objective lens with different characteristics. May be used.

In the above-described embodiment, the case where a single semiconductor laser having a short wavelength (635 nm) is commonly used in each mode as the optical head has been described. However, each mode of the first mode and the second mode is used. An independent optical head may be used for a semiconductor laser having a wavelength suitable for the optical disk, or a dedicated optical head may be provided for reproducing a DVD and a CD. By using the ratio of the amplitude value of the focus error signal in the use state of each of the first and second light beams for discrimination, the effect of canceling out the unstable element of the intensity level of the light beam emitted from the optical head, and The effect of reducing the variation in the optical characteristics of the disc can be expected.

[0032]

As described above, according to the present invention, the amplitude value of each focus error signal in the use state of each of the first and second light beams adapted to the first and second signal recording media, respectively. By comparing the ratio of the optical recording medium with the reference value, it is determined whether the signal recording medium is the first signal recording medium or the second signal recording medium. Even if there are unstable elements such as variations in the intensity level of the light beam emitted from the optical head due to variations, temperature characteristics, and changes over time, the unstable elements can be canceled out, and the material of the signal recording surface and the substrate Thus, even if the signal recording media are of the same type, variations in the optical characteristics caused by the variations of the signal recording media and the like can be reduced, and the reliability of discriminating the signal recording media can be improved.

Further, an optical head capable of switching between a first mode in which a first light beam is obtained and a second mode in which a second light beam is obtained is used. If the amplitude value of each focus error signal is measured in both the first mode and the second mode, a change in the intensity level of the light beam in the use state of each of the first and second light beams can be obtained. Since the number of coincidences of the optical requirements caused by the change increases, the effect of canceling out the unstable element caused by the change in the intensity level of the light beam can be enhanced. In particular, by employing a configuration in which the light beam from the same light source is used in both the first mode and the second mode, the portion most caused by the change in the intensity level of the light beam can be shared, and the unstable element is canceled. The effect can be expected even more.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of a signal recording medium discrimination method according to the present invention.

FIG. 2 is a diagram illustrating a DVD and a C using a plurality of optical head samples for each measurement value required for the signal recording medium discrimination method according to the present invention.
FIG. 9 is a measured value data display diagram showing the results of actual measurement with D.

FIG. 3 is a histogram displayed based on the measured values shown in FIG.

FIG. 4 is a circuit block diagram showing an example of a disc discriminating apparatus provided with the signal recording medium discriminating method of FIG.

[Explanation of symbols]

 Reference Signs List 1 mode switching control circuit 2 optical head 4 FE signal amplitude value measuring circuit 5 memory 6 arithmetic circuit 7 disk discriminating circuit

Claims (3)

[Claims] 1. A signal recording medium discriminating method for discriminating first and second signal recording media having different thicknesses of a substrate up to a signal recording surface, wherein a focus position of a light beam is moved in a focus direction. The amplitude value of the focus error signal for the obtained signal recording medium is determined by using the first light beam suitable for the first signal recording medium and the second light beam suitable for the second signal recording medium. By measuring each time, calculating the ratio of the measured amplitude value of each focus error signal, and comparing the ratio with a preset reference value, the first
And a signal recording medium discriminating method for discriminating a second signal recording medium. 2. An optical head capable of mode switching between a first mode in which the first light beam is obtained and a second mode in which the second light beam is obtained, and a mode switching of the optical head is performed. 2. The signal recording medium discrimination method according to claim 1, wherein the amplitude value of each focus error signal is measured in both the first mode and the second mode. 3. An optical head having a configuration using light beams from the same light source in both of a first mode and a second mode is used as the optical head.
The signal recording medium discriminating method described in the above.