JP2000173163A - Signal recording medium discrimination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of discrimination by discriminating two signal recording media having different substrate thicknesses employing the comparison output obtained by comparing the maximum value of the amount of the changes in focus error signals per unit time with a reference value and the setting condition of an optical head while executing a focus search. SOLUTION: A maximum value detecting circuit 8 compares the amount of voltage changes successively detected by a change amount detecting circuit 7. Then, a larger voltage change amount is stored based on the comparision and the circuit 8 detects the amount of the voltage change finally stored as the maximum value of the amount of the voltage changes obtained in a focus search operation. Then, confirmation is made to determine whether the setting condition of an optical head 1 is in a first setting condition, in which light beams optirnully fit to a DVD are generated, or not. Then, a disk discriminating circuit 9 compares the maximum value of the amount of voltage changes detected by the circuit 8 and the reference value of the voltage data that becomes a boundary reference that is set to classify a DVD and a CD.

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. DVDs (digital versatile discs) have been commercialized in order to increase the capacity by recording at higher density than CDs while ensuring mechanical compatibility.

[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, Japanese Patent Application Laid-Open No. 9-106617, which discloses a focus obtained by moving a focal position of a light beam in a focus direction. A method for discriminating a disk based on whether the peak value of an error signal exceeds a threshold is disclosed.

[0008]

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.

[0009]

SUMMARY OF THE INVENTION The present invention focuses on the amount of change per unit time of a focus error signal on a signal recording medium obtained by executing a focus search operation for moving a focal position of a light beam in a focus direction. The measurement is sequentially performed along with the search operation, and the maximum value of the change is detected. This maximum value indicates the amount of change in the steepest area of the focus error signal. When the light beam generated from the optical head conforms to the optical characteristics of the signal recording medium, the maximum value becomes a sufficiently large change amount because the aberration is suppressed, while exceeding the reference value. When the light beam generated from the head does not conform to the optical characteristics of the signal recording medium, the amount of change in the maximum value becomes small due to an increase in aberration. Therefore, when the light beam generated from the optical head does not conform to the optical characteristics of the signal recording medium, the maximum value of the change amount when the optical beam does not conform to the optical characteristics of the signal recording medium is By setting a reference value between the maximum value of the non-conforming variation and the maximum value of the conforming variation, it is sufficiently smaller than the maximum value of the It is determined whether the setting state of the optical head at the time of executing the focus search operation is suitable or incompatible with the signal recording medium depending on whether the maximum value of the optical head is above or below the reference value. Then, the first and second signal recording media are recognized by recognizing whether the setting state of the optical head at the time of executing the focus search operation has been set to the state of generating the first light beam or the second light beam. Is determined.

In addition, the amount of change per unit time of the focus error signal is detected during the focus search operation, the amount of reflected light from the signal recording medium is detected, and the maximum value of the amount of change is determined by the maximum value of the amount of reflected light. The division is performed, and the operation value obtained by the division is compared with a preset reference value. Thereby, the difference in the optical characteristics of the signal recording medium and the unstable element of the change in the intensity level of the light beam emitted from the optical head when the common light source is used for the first and second signal recording media are canceled out. , The reliability of discrimination between the first and second signal recording media is improved.

[0011]

FIG. 1 is a flowchart showing an embodiment of a signal recording medium discriminating method according to the present invention, and FIG. 2 is a circuit block diagram showing an example of a disc discriminating apparatus provided with the signal recording medium discriminating method of FIG. is there.

FIG. 1 shows a signal recording medium discriminating method and FIG.
The disc discriminating device shown in FIG. 1 is adapted to discriminate a disc from a DVD and a CD.

The disc discriminating operation will be described below with reference to FIGS.

The optical head 1 includes a setting state switching control circuit 2
Thus, the setting state is controlled to be switched to the first setting state or the second setting state so that a light beam suitable for DVD or CD is generated.

The optical head 1 is set to a first setting state in which a light beam conforming to, for example, a DVD is generated in an initial state at the time of power-on. The setting state is held until the next disk determination is performed.

When the disk is loaded (step a),
A focus search signal is generated from the focus search signal generation circuit 3, and the optical head 1 executes a focus search operation according to the focus search signal (step b).

During the focus search operation, the light detector 4
The focus error signal (FE signal) is generated by the FE signal generation circuit 5 by arithmetically processing the light reception output obtained from the predetermined light receiving element. The voltage level of the FE signal generated by the FE signal generation circuit 5 is subjected to analog-to-digital conversion (A / D conversion) by the analog-to-digital conversion circuit 6 at regular intervals, and is sequentially taken into the change amount detection circuit 7 as voltage data. It is.

The change amount detection circuit 7 calculates the difference between the newly fetched voltage data and the voltage data fetched immediately before, and detects the voltage change amount per unit time of the FE signal (step c). ).

The voltage change amounts sequentially detected by the change amount detection circuit 7 are compared by a maximum value detection circuit 8, and the larger voltage change amount is stored in the comparison, and the maximum value detection circuit 8 finally The stored voltage change amount is detected as the maximum value of the voltage change amount obtained during the focus search operation (step d).

Thereafter, the optical head 1 is set to the DVD
(Step e), and the maximum value of the voltage change detected by the maximum value detection circuit 8 by the disk determination circuit 9 is set to DVD. Is compared with a reference value of voltage data serving as a boundary reference set for distinguishing between and CD (steps f and g).

When the setting state of the optical head 1 is in the first setting state, when it is determined that the maximum value of the voltage change amount detected by the maximum value detection circuit 8 is larger than the reference value, the disk determination circuit 9 DVD is determined and a determination signal indicating the determination is output (step h).
When it is determined that the maximum value of the voltage change detected by the above is not more than the reference value, the disk determination circuit 9 determines that the disk is a CD and outputs a determination signal indicating that (step i).

If the setting state of the optical head 1 is CD
If the maximum value of the voltage change detected by the maximum value detection circuit 8 is determined to be larger than the reference value in the second setting state in which a light beam conforming to 9 outputs a determination signal indicating that the disc is a CD (step i). On the other hand, if the maximum value of the voltage change detected by the maximum value detection circuit 8 is determined to be equal to or less than the reference value, the disc is discarded. The determination circuit 9 determines that the DVD is a DVD, and outputs a determination signal indicating that (step h).

The discrimination signal output from the disc discrimination circuit 9 is used to switch the operation setting state of the optical head 1 and the internal circuit, and is adapted to the disc on which the operation setting state of the optical head 1 and the internal circuit is mounted. Switch to the state in which

If the setting state of the optical head 1 is not suitable for the disk, a light beam not suitable for the optical characteristics of the disk will be irradiated on the signal recording surface of the disk, and the signal from the disk surface will be emitted. The aberration generated in the light beam by the substrate up to the recording surface becomes larger than when a light beam that is adapted to the optical characteristics of the disc is irradiated on the signal recording surface.

Due to this aberration, the manner in which the focus error signal changes during the focus search operation changes, and a light beam whose characteristics match the optical characteristics of the disc irradiates the signal recording surface during the focus search operation. In this case, the level change of the focus error signal becomes steep. On the other hand, when a light beam that does not conform to the optical characteristics of the disc is irradiated on the signal recording surface, the level change of the focus error signal becomes gentle.

FIG. 3 shows the setting state of the optical head 1 on a DVD.
FIGS. 4A and 4B are diagrams showing the principle of disc discrimination in a case where the state is adapted to FIG. 3A, wherein FIG. 4A is a waveform diagram showing characteristics of a focus error signal in the case of a CD and a DVD, and FIG. FIG. 7C is a diagram illustrating a change amount of a signal per unit time, and FIG. 7C is a diagram illustrating a transition of a maximum value of a change amount of a focus error signal per unit time in the case of a CD and a DVD.

When the focus search operation is performed with the setting state of the optical head 1 being adapted to the DVD, the characteristics of the focus error signal are as shown in FIGS. 3A and 3B for the CD and DVD, respectively. ).

When the amount of change of the focus error signal per unit time is detected for each sampling period T of the A / D conversion circuit 6, the amount of change is determined for both CD and DVD in FIG. And (B) are time charts.

The transition of the maximum value of the change amount per unit time in the focus error signal is shown in a time chart as shown in FIGS. 3A and 3B. The maximum value of the change amount is the farcus search. It becomes the value held at the end of the operation.

Here, the maximum value of the amount of change per unit time in the focus error signal is represented by (B) in FIG.
(A) when the light beam generated from the optical head 1 conforms to the optical characteristics of the disk, and when the light beam generated from the optical head 1 There is a sufficiently large difference between the case where the optical property is not matched and the case where the optical property is not matched.

The level difference between the conforming time and the non-conforming time at the maximum value of the amount of change per unit time of the focus error signal is sufficient even if the disc has variations.
This also occurs in DVDs and CDs.

Therefore, the level difference between the conforming time and the non-conforming time at the maximum value of the amount of change per unit time of the focus error signal is averaged in a plurality of samples of each disk, and the level substantially at the center of the average is determined as the disk. Circuit 9
By setting to the reference value Vr used as a determination criterion, it is possible to determine whether the setting state of the optical head 1 is appropriate or incompatible with the disc.

Therefore, by determining whether the setting state of the optical head 1 is suitable or incompatible with the disc and recognizing the current setting state of the optical head 1, the DV is determined.
Disc distinction between D and CD can be performed.

That is, the optical head 1 is
If the current setting state of the optical head 1 is determined to be appropriate, it is determined that the optical head 1 is a DVD if the current setting state of the optical head 1 is the first setting state suitable for DVD. If the setting state is the second setting state suitable for a CD, it is determined that the CD is a CD.

On the other hand, when it is determined that the setting state of the optical head 1 with respect to the disc is incompatible, if the current setting state of the optical head 1 is the first setting state suitable for DVD, it is determined that the disc is a CD. If the current setting state of the optical head 1 is the second setting state suitable for CD, it is determined that the optical head 1 is a DVD.

In the optical head 1, the switching between the first setting state suitable for DVD and the second setting state suitable for CD is performed by switching the aperture diameter for limiting the light beam incident on the objective lens. This is achieved by switching the laser light source used.

FIG. 4 is a circuit block diagram showing an embodiment of a signal recording medium discriminating method according to the present invention which employs a method different from that of FIG. 4, the same circuits as those in FIG. 2 are denoted by the same reference numerals.

The circuit shown in FIG. 4 includes a reflected light amount signal generating circuit 10 for generating a reflected light amount signal indicating the amount of reflected light of the light beam reflected by the disk from the light receiving level received by the photodetector 4, The voltage level of the reflected light amount signal generated by the light amount signal generation circuit 10 is changed to the A / D conversion circuit 6.
The reflected light amount detection circuit 11 detects the maximum value of the reflected light amount by sequentially comparing the received voltage data, and the voltage change amount of the focus error signal detected by the maximum value detection circuit 8. An arithmetic circuit 12 for dividing the maximum value by the maximum value of the reflected light amount detected by the reflected light amount detection circuit 11 is provided.

The operation value calculated by the operation circuit 12 is compared with a reference value set in advance by the disk discrimination circuit 9, and the disc type is determined based on the comparison result and the setting state of the optical head 1.

The intensity level of the light beam emitted from the optical head 1 varies depending on the use conditions due to unstable characteristics such as temperature characteristics and aging of the semiconductor laser as a light source. Since the voltage depends on the voltage level of the reflected light amount, the unstable element can be canceled by dividing the maximum value of the change amount of the focus error signal by the maximum value of the reflected light amount, thereby reducing erroneous disc type determination. Can be achieved.

Also, there is a variation in optical characteristics even if the disks are of the same type due to the variations and types of the material of the signal recording surface and the substrate, or the distortion of the disk shape. Since the difference is canceled by dividing the maximum value of the change amount of the focus error signal by the maximum value of the reflected light amount, erroneous determination of the disc type can be reduced.

The reflected light quantity signal from the reflected light quantity signal generation circuit 10 is A / D-converted by the A / D conversion circuit 6 with the focus error signal from the FE signal generation circuit 5 by time division. A configuration may be adopted in which the reflected light amount signal and the focus error signal are independently A / D converted by separate A / D conversion circuits.

In the above-described embodiment, the reflected light amount detection circuit 11 detects the maximum value of the reflected light amount by sequentially comparing the voltage data of the reflected light amount signal to detect the maximum value of the reflected light amount. However, when the focus is on the signal recording surface where the focus error signal becomes "0", the amount of change per unit time of the focus error signal becomes maximum, and at this time the amount of reflected light also becomes maximum. The maximum value of the change amount per unit time of the signal may be divided by the reflected light amount at the time when the maximum value of the change amount is obtained.

In this case, the focus error signal from the FE signal generating circuit 5 and the reflected light amount signal from the reflected light amount signal generating circuit 10 are A / D converted by the A / D conversion circuit 6 in an A / D manner.
With the / D conversion configuration, the focus error signal and the reflected light amount signal cannot be captured at the same time, but
The time difference due to time division can be almost ignored.

FIG. 5 is a flowchart showing a method executed when confirming disc discrimination.

Confirmation of the disc discrimination is executed after disc discrimination described with reference to FIGS. 1 and 2 or disc discrimination described with reference to FIG. 4 is performed. Is switched (step j).

Thereafter, a disk discriminating operation similar to any one of the disk discriminating operations shown in the above-described two embodiments is performed (step k), and the disc type determined by the disc discriminating operation is the previous disk discriminating operation. It is determined whether or not the result matches the determination (step l).

If the newly determined disk type matches the previous disk determination, the disk determination is determined to be accurate and the disk determination result is determined to be valid (step m), and the newly determined disk type is determined. If the type does not match the previous disk determination, the disk determination is recognized as incorrect and the disk determination result is determined to be invalid (step n).

When the disc discrimination result is judged to be invalid, the disc type is disregarded and the setting state of the optical head 1 is set to either, and the disc is read for the time being, whereby the signal can be correctly reproduced. The setting state of the optical head 1 is switched depending on whether or not.

[0050]

As described above, according to the present invention, during the focus search operation, the comparison output in which the maximum change amount per unit time of the focus error signal is compared with the reference value, and the focus search operation is executed. The first and second signal recording media having different thicknesses of the substrate up to the signal recording surface can be determined depending on the setting state of the optical head at that time.

Also, by dividing the maximum value of the change amount of the focus error signal by the maximum value of the reflected light amount,
Even if there are unstable elements such as the temperature characteristics of the light source of the optical head and changes over time, such unstable elements can be canceled out, and variations and types of the material of the signal recording surface and the substrate, or deformation of the signal recording medium, etc. Thereby, even if the signal recording mediums are of the same type, variations in optical characteristics that occur can be reduced, and erroneous determination of signal recording medium determination can be reduced.

Further, since the setting state of the optical head is switched to confirm the discrimination of the signal recording medium, the validity / invalidity of discrimination of the signal recording medium can be determined, and the reliability of discrimination of the signal recording medium is improved. Can be achieved.

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

3A and 3B are diagrams illustrating the principle of disc discrimination when the setting state of the optical head is set to a state adapted to DVD, and FIG. 3A is a waveform diagram illustrating characteristics of a focus error signal in the case of CD and DVD. B) CD and DV
FIG. 7C is a diagram illustrating a change amount of the focus error signal per unit time in the case of D, and FIG. 7C is a diagram illustrating a transition of a maximum value of a change amount of the focus error signal per unit time in the case of CD and DVD.

FIG. 4 is a circuit block diagram showing an embodiment in which a signal recording medium discriminating method according to the present invention employs a method different from that of FIG. 1;

FIG. 5 is a flowchart showing a method executed when disc discrimination is confirmed.

[Explanation of symbols]

 Reference Signs List 1 optical head 2 setting state switching control circuit 5 FE signal generation circuit 7 change amount detection circuit 8 maximum value detection circuit 9 disk determination circuit 11 reflected light amount detection circuit 12 arithmetic circuit

Claims (3)

[Claims] 1. A first light beam and a second light beam having different optical characteristics suitable for first and second signal recording media having different thicknesses of a substrate up to a signal recording surface can be selectively generated. A signal recording medium discriminating method for discriminating between the first and second signal recording media using a light receiving output received by an optical head, wherein a focus search operation for moving a focal position of a light beam in a focus direction is performed. The amount of change per unit time of the focus error signal with respect to the signal recording medium obtained by performing the focus search operation is sequentially measured, the maximum value of the change amount is detected, and the maximum value is compared with a preset reference value. Compare,
The discrimination between the first and second signal recording media is made based on the comparison output and the setting state of the optical head at the time of executing the focus search operation, which of the first light beam and the second light beam is set. Recording medium discriminating method for performing 2. A first light beam and a second light beam having different optical characteristics suitable for first and second signal recording media having different substrate thicknesses up to a signal recording surface can be selectively generated. A signal recording medium discriminating method for discriminating between the first and second signal recording media using a light receiving output received by an optical head, wherein a focus search operation for moving a focal position of a light beam in a focus direction is performed. The amount of change per unit time of the focus error signal with respect to the signal recording medium obtained by performing the focus search operation is sequentially measured, the maximum value of the change amount is detected, and the signal from the signal recording medium during the focus search operation is detected. At the same time, the maximum value of the reflected light amount is detected, and the calculated value obtained by dividing the maximum value of the change amount by the maximum value of the reflected light amount is obtained. The optical head is compared with a reference value set in advance, and the comparison output and the setting state of the optical head when the focus search operation is executed, which one of the first light beam and the second light beam is set, are determined. 1
And a signal recording medium discriminating method for discriminating a second signal recording medium. 3. A first and a second signal recording medium in both a first setting state in which a setting state of the optical head is switched to generate a first light beam and a second setting state in which a second light beam is generated. 3. The signal recording medium discriminating method according to claim 1, wherein the discrimination is performed by performing the discrimination.