JP3500038B2 - Signal recording medium discrimination 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 signal recording medium discriminating method for discriminating first and second signal recording media having different substrate thicknesses up to a signal recording surface.

[0002]

2. Description of the Related Art CD (Compact Disc) is widely used as an optical disc for optically reading signals by using an optical head. A DVD (Digital Versatile Disk) standardized with the aim of increasing the capacity by recording at a higher density than a CD while ensuring mechanical compatibility is being developed.

Since a DVD has a higher signal recording density than a CD, an optical head compatible with a DVD has a high resolution of an optical system by shortening a wavelength of a laser element of a light source and expanding an NA of an objective lens. Imaging is required.

By the way, in a DVD player, C
Reproduction of D is also required. Since the thickness of the transparent substrate up to the signal recording surface is significantly different between DVD and CD, which is approximately 1: 2, when a CD is reproduced using a light beam adapted for DVD, it is affected by spherical aberration and the like. 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 between the reproduction of the DVD and the reproduction of the CD so that the reproduction is performed by using the light beam having the optical characteristic suitable for each disk.

Further, it is necessary to switch the signal processing circuit to be used corresponding to the mounted disc, and to switch the setting state of the internal circuit such as switching the disc rotation control.

Because of these requirements, it is necessary to discriminate the loaded disk in the DVD player. Conventionally, as a method for discriminating such a disc, for example, Japanese Patent Laid-Open No. 9-
Japanese Patent No. 106617 discloses a method for disc discrimination based on whether or not a peak value of a focus error signal obtained by moving a focal position of a light beam in a focus direction exceeds a threshold value. There is.

[0007]

By the way, the focus error signal level is different in the optical characteristics of the disc due to variations in the material of the signal recording surface of the disc, the substrate, etc., and the variations in the semiconductor laser used as the light source. It is not constant due to unstable factors such as changes in intensity level of the light beam emitted from the optical head due to temperature characteristics, changes over time, and the like. Therefore, there is a large variation in the focus error signal level for each disc and for each optical head, which makes it difficult to set the threshold value in the above-described disc discrimination method, and there is a problem that the disc discrimination reliability decreases.

[0008]

According to the present invention, an amplitude value of a focus error signal for a signal recording medium obtained by moving a focal position of a light beam in a focusing direction is adapted to a first signal recording medium. The measurement is performed under the use condition of one light beam and during the use condition of the second light beam suitable for the second signal recording medium, and the ratio of the amplitude values of the respective measured focus error signals is calculated. The first and second signal recording media are discriminated by comparing the ratio with a preset reference value.

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

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flow chart showing an embodiment of a signal recording medium discriminating method according to the present invention.

The signal recording medium discriminating method shown in FIG.
And disc discrimination of CD. A disc discriminating method will be described below with reference to the flowchart of FIG.

When it is determined that the disc is loaded in the disc 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.

When the setting mode of the optical head is recognized, it is then determined whether mode switching is necessary (step c). If mode switching is not necessary, the focal position of the light beam is moved in the focus direction. Then, the focus search operation (step d) is started.

During the focus search operation, the voltage level of the 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 detection output, and the amplitude value is stored. (Step e).

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

When the mode of the optical head is switched, the setting mode of the optical head is recognized (step b),
After it is determined whether 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 the numerical data. And the 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 in this way, the stored ratio of the amplitude values of the focus error signal in each mode is changed. It is calculated (step h).

The ratio of the amplitude value of the focus error signal in each mode is compared with a reference value which is a boundary standard preset for disc division, and the ratio of the amplitude value of the focus error signal in each mode is compared by the comparison. 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).

By the way, the ratio of the amplitude value of the focus error signal in each of the first mode and the second mode of the optical head to the amplitude value of the focus error signal in each mode is set to the first mode and the second mode. When an optical head capable of switching modes was used, measurement with an optical head of 6 samples gave measured values as shown in FIG. 2 for DVD and CD. As the optical head, a single semiconductor laser with a short wavelength (635 nm) is commonly used in each mode, and
A structure corresponding to each mode is used by switching the aperture diameter that limits the light beam entering the objective lens.

In the measured values shown in FIG. 2, when the ratio of the amplitude value of the focus error signal in each mode is shown in the histogram of FIG. 3, the DVD has a range of 20 to 30% and a range of 30 to 30 as indicated by hatched bars. All are in the 40% range, while the CDs are all in the 80-90% range and 90-100% range 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 disc is narrow.
Therefore, it is easy to set the boundary reference for discriminating between DVD and CD, and it is possible to surely discriminate between DVD and CD.

Therefore, in this case, 60% is used as the boundary reference, and the reference value obtained by converting the boundary reference into numerical data is compared with the ratio data calculated as the 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 judged as a DVD, while if the ratio data is larger than the reference value, it can be judged as a CD.

By the way, 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 changes with time, and changes depending on the usage conditions. However, by comparing the ratio of the amplitude value of the focus error signal in each mode with the reference value, the DVD or CD
Since the above is used for discriminating and the above ratio is used for disc discriminating, the unstable element can be canceled.

Further, even if the discs of the same type have variations in optical characteristics due to variations in the material of the signal recording surface and the substrate, deformation of the signal recording medium, etc.,
Even in this case, the influence of the variation appears on both the amplitude values of the focus error signal in each mode.Therefore, by using the ratio of the amplitude value of the focus error signal in each mode for disc discrimination, the variation in the optical characteristics of the disc is detected. 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 with the disc loaded,
The mode switching control circuit 1 allows the optical head 2 to be, for example, a DV.
The first mode is set so that a light beam conforming to D can be obtained. Then, the focus search operation is performed with the optical head 2 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 the FE signal amplitude. The value measurement circuit 4 converts the detected numerical data into numerical data and detects the amplitude value of the focus error signal from the detected output as numerical data. Then, the amplitude value is stored in the memory 5.

After that, it is judged whether or not the amplitude values of the focus error signal in both the first mode and the second mode of the optical head are measured according to the storage condition of the memory 5, and the focus error signal in both modes is detected. 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 FE signal amplitude value measuring circuit 4 measures the amplitude value of the focus error signal when the optical head 2 is set in the second mode as numerical data, and the amplitude value is stored in the memory 5.

In this way, 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, the arithmetic circuit 6 stores the focus error in each of the stored modes. The ratio of the amplitude values of the signals is calculated. The calculated ratio data is compared with a reference value of numerical data serving as a boundary reference set to discriminate between DVD and CD by the disc determination circuit 7, and the disc determination circuit 7 determines that the ratio data is greater than the reference value. If it is smaller, it is judged as DVD and a judgment signal indicating that is output, and if the ratio data is larger than the reference value, it is judged as CD and a judgment signal indicating that is output.

The determination signal output from the disc determination circuit 7 is used as a switching signal for switching the operation setting states of the optical head 2 and the internal circuit, and is applied to the disc on which the operation setting states of the optical head 2 and the internal circuit are mounted. Switch to a suitable state.

In the above-mentioned embodiment, the optical head is achieved by switching the aperture diameter for limiting the light beam incident on the objective lens so as to adapt to the first mode and the second mode. However, as a method of switching this aperture diameter, there are a method of changing the incident light beam diameter of a single objective lens using a filter and a method of switching and using objective lenses having different characteristics. You may use.

Further, in the above-mentioned 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, but each mode of the first mode and the second mode is explained. An independent optical head may be used for a semiconductor laser having a wavelength compatible with the above, or a structure may be provided with dedicated optical heads for reproducing DVDs and CDs. 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 the determination, the effect of canceling the unstable element of the intensity level of the light beam emitted from the optical head, and It can be expected to reduce the variation in the optical characteristics of the disc.

[0032]

As described above, according to the present invention, the amplitude value of each focus error signal when the respective light beams of the first and second light beams which are compatible with the first and second signal recording media are in use. Of the first and second signal recording media is determined by comparing the ratio and the reference value, and the above ratio is used to determine the signal recording medium. Even if there are unstable factors such as variations in the intensity level of the light beam emitted from the optical head due to variations, temperature characteristics, changes over time, etc., those unstable factors can be canceled out, and the material of the signal recording surface or substrate It is possible to reduce variations in optical characteristics that may occur even in the same type of signal recording medium due to variations in the signal recording medium, deformation of the signal recording medium, and the like, and it is possible to improve reliability of signal recording medium discrimination.

Further, 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 is used, and the mode is switched by a single optical head. If the amplitude value of each focus error signal is measured in both the 1st mode and the 2nd mode, the intensity level of the 1st and 2nd light beams changes when the light beams are in use. Since the matching portion of the resulting optical requirements increases, the effect of canceling the unstable element due to the change in the intensity level of the light beam can be enhanced. In particular, by adopting a configuration in which the light beams from the same light source are used in both the first mode and the second mode, it is possible to standardize the part that is most caused by the change in the intensity level of the light beam and cancel the unstable element. The effect can be expected even more.

[Brief description of drawings]

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

FIG. 2 shows DVDs and Cs obtained by using a plurality of optical head samples for measuring values required for the signal recording medium discriminating method according to the present invention.
It is a measurement value data display figure which shows the result measured by D and.

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

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

[Explanation of symbols]

1 Mode switching control circuit 2 Optical head 4 FE signal amplitude value measurement circuit 5 memory 6 arithmetic circuit 7 Disc judgment circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takao Fukumoto               2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture               Sanyo Electric Co., Ltd.                (56) References JP-A-9-106617 (JP, A)

Claims (3)

(57) [Claims] 1. A signal recording medium discrimination method for discriminating first and second signal recording media having different substrate thicknesses up to a signal recording surface, wherein a focal position of a light beam is moved in a focus direction. The obtained amplitude value of the focus error signal with respect to the signal recording medium is set to the use state of the first light beam suitable for the first signal recording medium and the use state of the second light beam suitable for the second signal recording medium. By measuring each time, calculating the ratio of the amplitude values of the respective measured focus error signals, and comparing the ratio with a preset reference value.
And a signal recording medium determination method for determining the second signal recording medium. 2. An optical head that is 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 the mode is switched by using the optical head. 2. The signal recording medium discriminating 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. The optical head having a structure using a light beam from the same light source in both the first mode and the second mode is used as the optical head.
The signal recording medium determination method described.