JPH10334573A - Optical disk reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately discriminate whether an optical disk is the CD(compact disk) or the single layer DVD(digital video disk) or even the double layer DVD. SOLUTION: At the time of reproducing information recorded on an optical disk 10, an objective lens 21 is moved in its separating direction from the optical disk 10 while the optical disk 10 is irradiated with laser light through the objective lens 21. While the objective lens 21 is moved, whether the optical disk 10 is the double layer DVD or not is discriminated based on the number of S-shaped curves generated in a focus error signal generated by a focus error signal generating means 34 based on an output from a photodetector 24. Further, an optical disk 10 is rotated, and while the objective lens 21 is focus-controlled, whether the optical disk 10 is the CD or the single layer DVD is discriminated based on the size of an amplitude of a frequency component generated in a regenerative signal generated by a regenerative signal generating means 33 based on the output of the photodetector 24.

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 used for reproducing information recorded on an optical disk.

[0002]

2. Description of the Related Art Recently, compact disks (CDs) have become widespread as optical disks capable of recording various types of information such as image information and audio information at a high density. FIG. 13A is a cross-sectional view of a main part of the CD. CD11 is a disk substrate 11 having a thickness of 1.2 mm.
a recording layer 11b is provided on the back side of the recording layer 11a, and information recorded on the recording layer 11b is radiated from an optical pickup of the optical disc reproducing apparatus from a surface opposite to the back side on which the recording layer 11b is provided. It is reproduced by a laser beam. In the CD 11, the reflectance of the recording layer 11b irradiated with the laser beam is 70% or more.

Recently, a DVD (digital vi) has been used for such a CD so that information can be recorded at a higher density.
deo desk: digital video disc) has been developed. In DVDs on which information has been recorded at high density, the diameter of the light spot formed by the laser light must be smaller than the diameter of the light spot formed by the laser light used for reproducing information on the CD. There is. The diameter of the light spot of the laser beam can be reduced by using a laser beam having a short wavelength or by increasing the numerical aperture of an objective lens on which the laser beam is irradiated onto the optical disc.

As a DVD, a DVD having only one recording layer and a DVD having two recording layers have been developed.
FIG. 13B shows a single-layer DVD provided with one recording layer.
It is sectional drawing of the principal part of. The single-layer DVD 12 has a recording layer 12b provided on the back surface of a disk substrate 12a having a thickness of 0.6 mm, which is half the thickness of the CD 11. A sub-disk substrate 12c is attached to the back of the disk substrate 12a. In the recording layer 12b of the single-layer DVD 12, the pit spacing and the track spacing are smaller than the pit spacing and the track spacing in the recording layer 11b of the CD 11. The information recorded on the recording layer 12b is reproduced by a laser beam emitted from the surface opposite to the back surface on which the recording layer 12b is provided. The reflectance of the recording layer 12b in such a single-layer DVD 12 is 7 as in the case of the CD 11.
0% or more.

FIG. 13C is an end view of a main part of the dual-layer DVD. This double-layer DVD 13 has a recording layer 13b on the back.
Are provided with a pair of disk substrates 13a each having a thickness of 0.6 mm, and the back surfaces of the disk substrates 13a provided with the respective recording layers 13b are bonded to each other. In such a dual-layer DVD 13, information recorded on each recording layer 13b is reproduced by a laser beam irradiated from one side. Double layer DVD
The reflectance of the recording layer 13b at 13 is smaller than that of the CD 11 and the single-layer DVD 12, and is 25 to 40%.

When reproducing information recorded on the recording layer 11b of the CD 11, a laser beam having a wavelength of 780 nm is normally irradiated through an objective lens having a numerical aperture of 0.45. In contrast, a single-layer DVD 12
When reproducing information recorded on the recording layer 12b of
Normally, laser light having a wavelength of 630 to 650 nm is used. As shown in FIG. 14A, the laser light is passed through an objective lens 14 having a numerical aperture of 0.6 to form a single-layer DVD 1.
The second recording layer 12b is irradiated. Similarly, when reproducing information recorded on each recording layer 13b of the two-layer DVD 13, a laser beam having a wavelength of 630 to 650 nm is irradiated through the objective lens 14 having a numerical aperture of 0.6.

[0007] As described above, when the information recorded on the CD 11 is reproduced, the one-layer DVD 12 and the two-layer DVD 13 are read.
When the information recorded in the DVD is reproduced, laser beams having different wavelengths are used.
And the wavelength used for reproducing the double-layer DVD 13 is 630.
For laser light of 〜650 nm, the numerical aperture is 0.38
The information recorded on the CD 11 can be reproduced by eliminating the aberration of the laser beam by using the objective lens which has become smaller.

In this case, for example, the numerical aperture used for reproducing information of the single-layer DVD 12 and the double-layer DVD 13 is 0.6.
And an objective lens having a numerical aperture of 0.38 used for reproducing information from the CD 11 are prepared, and each objective lens is switched according to the type of the optical disk.

Further, as shown in FIG.
In the optical disc reproducing apparatus using the objective lens 14 for reproducing information of the VD 12 and the dual-layer DVD 13, when the optical disc is a CD, an opening 15a for shielding the outer peripheral portion of the laser beam irradiated on the objective lens 14 is provided. A method has also been proposed in which the numerical aperture changer 15 is inserted into the laser light irradiation area to reduce the apparent numerical aperture of the objective lens 14.

[0010]

However, in any of the optical disk reproducing apparatuses, it is necessary to determine whether the optical disk on which information to be reproduced is recorded is a CD or a DVD. However, CDs and DVDs are not housed in dedicated cartridge cases like floppy disks and MDs (mini disks), and their diameters are equal to 12 cm, and their thicknesses are further reduced. Since it is 1.2 mm, it is not easy for a user to distinguish between a CD and a DVD. Moreover, it is troublesome for the user to switch the objective lens or to move the numerical aperture converter 15. There is a problem that it is troublesome.

For this purpose, an optical disk reproducing apparatus capable of discriminating whether an optical disk on which information is recorded is a CD or a DVD is disclosed in, for example, JP-A-6-162648,
JP-A-8-221766, JP-A-6-26718
No. 1 publication. In these publications, CD
A disc is distinguished from a CD based on the difference between the reflectance of the recording layer irradiated with the laser beam and the DVD. However, as described above, one layer D
In the case of VD and CD, since the reflectance of the recording layer irradiated with the laser beam is equal, there is a problem that the method disclosed in these publications cannot discriminate between CD and single-layer DVD. .

Japanese Patent Application Laid-Open No. 8-263867 discloses that an optical disk is irradiated with a laser beam while oscillating an objective lens toward and away from the optical disk, and a light detector which receives reflected light from the optical disk. There is disclosed a method for determining whether an optical disk is a CD or a DVD based on an output high-frequency signal.

In the method disclosed in this publication, as described above, the recording layer is located on the back surface of the CD, whereas the recording layer is located at the center in the thickness direction of the single-layer DVD. Therefore, based on the fact that the DVD recording layer is arranged closer to the objective lens than the CD recording layer, C
D and DVD are determined. However, with such a method, it is possible to distinguish between a CD and a DVD, but there is a problem that it is not possible to distinguish between a single-layer DVD and a double-layer DVD in which the recording layer is located at the center in the thickness direction. is there.

Further, in this method, when the objective lens is vibrated with respect to the optical disk, focus control and tracking control of the laser beam are not performed. Therefore, only when the track of the optical disk is focused, the high-frequency signal is not transmitted. Since the amplitude becomes maximum and the amplitude becomes smaller in other cases, there is a possibility that the CD and the DVD cannot be accurately distinguished.

The present invention has been made to solve such a problem, and has as its object not only CD and DVD having the same reflectance in the recording layer but also the recording layer at the same position in the thickness direction. It is an object of the present invention to provide an optical disk reproducing apparatus that can accurately determine whether a single-layer DVD or a double-layer DVD is arranged.

[0016]

According to a first aspect of the present invention, an optical disk reproducing apparatus irradiates a laser beam to an optical disk through an objective lens, and receives the laser beam reflected by the optical disk by a photodetector. The reproduction signal, the focus error signal, and the tracking error signal are respectively generated based on the output of the photodetector, and the objective lens performs the focus control and the focus error based on the focus error signal and the tracking error signal, respectively. An optical disk reproducing device that is controlled to be tracked, wherein the objective lens is moved along the optical axis direction with respect to the optical disk while the laser light is irradiated on the optical disk through the objective lens, and the objective lens is moved. Focus error signal generated while moving Based on the number of shaped curve, characterized in that is adapted to determine the type of the optical disc.

An optical disk reproducing apparatus according to a second aspect of the present invention
A configuration for determining the type of the optical disk based on the magnitude of the amplitude of the frequency component generated in the reproduction signal while performing focus control on the objective lens with respect to the rotating optical disk based on the focus error signal. Have.

An optical disk reproducing apparatus according to claim 3 is
The output gain of the photodetector is changed based on the type of the optical disc to be determined.

An optical disk reproducing apparatus according to claim 4 is
The outer peripheral edge of the laser light passing through the objective lens is shielded so that the apparent numerical aperture of the objective lens is changed based on the type of the determined optical disc.

An optical disk reproducing apparatus according to claim 5 is
Irradiate the optical disc with laser light through the objective lens,
The laser beam reflected by the optical disk is received by a photodetector. Based on the output of the photodetector, a reproduction signal, a focus error signal, and a tracking error signal are generated, and a focus error signal is generated. An optical disc reproducing apparatus wherein focus control and tracking control of an objective lens are performed based on a signal and a tracking error signal, respectively. The type of optical disc is determined based on the magnitude of the amplitude of the frequency component generated in the signal.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an example of an embodiment of an optical disk reproducing apparatus according to the present invention. This optical disk reproducing apparatus has a spindle motor 4
Optical pickup 20 for irradiating an optical disk 10 rotated by 6 with a semiconductor laser beam to form a light spot
have.

FIG. 2 is a schematic structural view of the optical pickup 20. In the optical pickup 20, the laser light oscillated from the semiconductor laser element 25 is collimated by a collimating lens 26, the traveling direction is bent by a half mirror 27 at right angles, and Is to be irradiated.
The laser light reflected by the optical disk 10 is applied to the half mirror 27 through the objective lens 21, travels straight through the half mirror 27, and is provided on the photodetector 24 by the condenser lens 28.

The objective lens 21 arranged opposite to the optical disk 10 is moved in the optical axis direction (focus direction) perpendicular to the optical disk 10 by a focus actuator 22 formed by a coil, and is formed by a coil. The tracking actuator 23 moves the optical disk 10 in a direction perpendicular to the optical axis along the surface of the optical disk 10. The focus actuator 22 moves the objective lens 21 in a direction perpendicular to the optical disc 10 so that the light spot of the laser beam irradiated on the optical disc 10 is focused on the recording surface 10b of the optical disc 10. Perform focus control. In addition, the tracking actuator 23
Controls the tracking of moving the objective lens 21 along the optical disc 10 so that the light spot of the laser beam irradiated on the optical disc 10 follows a track formed on the recording surface 10b of the optical disc 10.

The semiconductor laser element 25 has 630 to 65
A laser beam having a wavelength of 0 nm is oscillated, and the numerical aperture of the objective lens 21 is
It is as large as 0.6 so that the light is focused on the recording layer 10b of the DVD (Digital Video Disk) without aberration.

A numerical aperture converter 29 is provided between the objective lens 21 and the half mirror 27. FIG. 3 is a plan view of the numerical aperture converter 29. Numerical aperture converter 29
Is configured such that a base end portion of a numerical aperture converter 29b provided with a circular opening portion 29a at a distal end portion is rotated along the optical disk 10 about a rotation axis 29c, The opening 29a of the conversion body 29b is rotated between a numerical aperture change position facing the objective lens 21 and a retracted position outside the laser light irradiation area within the irradiation area of the laser light irradiated on the optical disk 10. You. When the opening 29a of the numerical aperture converter 29b is at the numerical aperture change position facing the objective lens 21, the outer peripheral edge portion of the light beam of the laser light emitted from the half mirror 27 to the objective lens 21 is changed by the periphery of the opening 29a. The light is shielded, and the numerical aperture of the objective lens 21 is reduced. Therefore, when the optical disc 10 is a CD, the aperture 29a of the numerical aperture converter 29b faces the objective lens 21, and the objective lens 21
Is reduced to about 0.38.

The numerical aperture converter 29b includes a permanent magnet 29d attached to the end face at the base end thereof, and a numerical aperture converter 29 formed by a pair of coils.
The rotation is controlled by g. The numerical aperture converting actuator 29g is provided with a numerical aperture converting body 29.
b at the numerical aperture conversion position where the aperture 29a of the numerical aperture b faces the objective lens 21 and at the retracted position where the aperture 29a of the numerical aperture converter 29b does not face the objective lens 21.
A pair of coils are arranged so as to oppose 9d, and the energization of each coil is controlled so that the permanent magnet 29d is repelled by the other coil when attracted by one of the coils. It is supposed to be.

As shown in FIG. 1, the focus actuator 22 and the tracking actuator 23 of the optical pickup 20 are driven by a focus driving means 44 and a tracking driving means 43, respectively. The driving means 43 is controlled by the control means 31. Further, the numerical aperture conversion actuator 29g is driven by a numerical aperture conversion drive unit 42, and the numerical aperture conversion drive unit 42 is also controlled by the control unit 31. Further, the oscillation of the semiconductor laser element 25 is controlled by a laser driving unit 41, and the laser driving unit 41 is also controlled by the control unit 31. Further, the control unit 31 controls a spindle motor rotation drive unit 45 that controls a spindle motor 46 that drives the optical disk 10 to rotate.

Light detector 24 in optical pickup 20
Is supplied to a gain conversion means 32 constituted by, for example, an amplifier. The gain conversion means 32 converts the output of the photodetector 24 into a predetermined gain by the control means 31, and outputs the output of the gain conversion means 32 to the reproduction signal generation means 33 and the focus error signal generation means 34. Tracking error signal generating means 35
Are given respectively.

The reproduced signal generating means 33 generates an output signal corresponding to the amount of light received by the photodetector 24 as a reproduced signal R. The generated reproduced signal R is binarized by the binarizing means 36. Then, the information is output as a reproduction digital signal FD, and information recorded on the optical disc 10 is reproduced based on the reproduction digital signal FD. The reproduction signal R generated by the reproduction signal generation means 33 is
It is provided to the control means 31 via the amplitude detection means 37 for discriminating the type of 0.

The focus error signal generation means 34 generates a focus error signal based on the amount of light received by the photodetector 24, and outputs the generated focus error signal F directly to the control means 31. Then, it is used for focus control and is given to the control means 31 via the S-shaped number detection means 38 for determining the type of the optical disc 10.

The tracking error signal generating means 35
A tracking error signal is generated based on the amount of light received by the photodetector 24, and the generated tracking error signal F is directly given to the control means 31 so as to be used for tracking control. .

As shown in FIG. 4, the photodetector 24 has four areas 24a for receiving the reflected light from the optical disc 10,
24b, 24c, and 24d.
An electric signal corresponding to the amount of light received at 24d is output from each of the regions 24a to 24d. Output signals from the respective regions 24 a to 24 d of the photodetector 24 are output to four operational amplifiers 32 a
32b, 32c, and 32d. Each of the operational amplifiers 32 a to 32 d is controlled by the control unit 31.
The amplifier gain is changed so that the gain is in accordance with the type of the optical disk 10.
The signals output from the four regions 24a to 24d are set to predetermined gains set by the control means 31 by the operational amplifiers 32a to 32d.

The focus error signal generating means 34 to which the output of the gain converting means 32 is provided includes a pair of adders 34
a and 34b, and a subtractor 34c for subtracting the output of each of the adders 34a and 34b. One of the adders 34a of the focus error signal generating means 34 has an operational amplifier 3 in the gain converting means 32.
The outputs of 2a and 32c are provided, respectively, and the outputs of the operational amplifiers 32a and 32c are added and output to the subtractor 34c. The other adder 34
b is an operational amplifier 32b in the gain conversion means 32
And 32d are provided, and the outputs of these operational amplifiers 32b and 32d are added,
It is output to the subtractor 34c. The subtractor 34c subtracts the output of the adder 32a and the output of the adder 32b, and outputs the result of the subtraction as the focus error signal F to the control means 31 and the S-shaped number detecting means 38.

Assuming that the outputs of the operational amplifiers 32a, 32b, 32c, and 32d in the gain converting means 32 are A, B, C, and D, respectively, the output of the adder 34a of the focus error signal generating means 34 is (A + C). The output of the adder 34b is (B + D). Therefore,
The output of the subtractor 34c is (A + C)-(B + D), and this (A + C)-(B + D) is obtained as the focus error signal F obtained by the astigmatism method.
And output to the S-number detecting means 38.

The control circuit 31 controls the focus driving means 44 based on the focus error signal F output from the focus error signal generating means 34,
The objective lens 21 is driven by the focus actuator 22 so that the light spot of the laser beam irradiated on the optical disc 10 is focused on the recording layer 10b of the optical disc 10.

As shown in FIG. 5, the S-shaped number detecting means 38 to which the focus error signal F output from the focus error signal generating means 34 is input is provided to the comparator 3 as shown in FIG.
8a and a counter 38b.
The focus error signal F output from the focus error signal generation means 34 is input to the minus input terminal of the comparator 38. A predetermined voltage Vh is applied to a positive input terminal of the comparator 38a.
The comparator 38a outputs a high-level signal to the counter 38b when the focus error signal F becomes equal to or higher than a predetermined voltage Vh. The counter 38b counts the number of high-level signals output from the comparator 38a, and outputs the counted value to the control means 31.

The control means 31 determines whether the optical disk 10 is a two-layer DVD or a one-layer D based on the number of high levels of the comparator 38a counted by the counter 38b.
Whether it is VD or CD, the numerical aperture conversion driving means 42
And outputs a predetermined signal to drive the numerical aperture conversion actuator 29g such that the aperture 29a of the numerical aperture converter 29b faces the objective lens 21 when the optical disk 10 is a single-layer DVD or CD. I have.

The outputs of the operational amplifiers 32a, 32b, 32c and 32d in the gain converting means 32 are given to one adder 33a constituting the reproduction signal generating means 33. The outputs of all the operational amplifiers 32a to 32d are added, and the addition result is output to the amplitude detection means 37 for determining the type of the optical disk 10 as a reproduction signal R corresponding to the total amount of light received by the photodetector 24. And the binarizing means 36
Is output to The binarizing means 36 includes the reproduction signal generating means 3
The reproduction signal R generated in 3 is binarized into a high level and a low level with respect to a predetermined reference voltage, and is output as a digital reproduction signal RD. Then, based on the digital reproduction signal RD, information recorded on the optical disk 10 is reproduced.

As shown in FIG. 6, the amplitude detecting means 37 for determining the type of the optical disk 10 has a peak hold circuit 37a and a bottom hold circuit 37b to which the reproduction signal R is inputted, respectively.
a and the bottom hold circuit 37b detect the peak value and the bottom value of the reproduction signal R, respectively. Peak hold circuit 37a and bottom hold circuit 37
The output of b is given to the subtractor 37c, respectively.
The subtractor 37c outputs the difference between the two outputs, that is, the envelope amplitude voltage of the reproduced signal R. The output of the subtracter 37c is digitally converted by the comparator 37d and is provided to the control means 31.

The tracking error signal generating means 3
5 generates a tracking error signal T by a DPD method (phase difference method), and the generated tracking error signal T is given to the control device 31.

The operation of the optical disk reproducing apparatus having such a configuration will be described with reference to the flowchart shown in FIG.
When reproducing information from the optical disk 10, the control unit 3
First, the numerical aperture conversion driving means 42 is controlled so that the numerical aperture conversion actuator 29g is operated so that the apparent numerical aperture of the objective lens 21 does not become small.
Thereby, the numerical aperture converter 29b of the numerical aperture converter 29 is rotated, and the opening 29a of the numerical aperture converter 29b is set to the retracted position not facing the objective lens 21 (see step S1 in FIG. 7). Hereinafter the same). Next, the control means 31
Outputs a predetermined signal to the gain conversion means 32 and controls the gain by the gain conversion means 32 to be the amplifier gain G1 corresponding to the single-layer DVD (step S).
2).

In such a state, the control means 31
Controls the laser driving means 41 so that the laser light is oscillated from the semiconductor laser element 25 (step S3). Further, the control means 31 controls the focus driving means 44 so that the objective lens 21 moves in the optical axis direction (from top to bottom) away from the optical disc 10 (step S4).

As a result, the laser light oscillated from the semiconductor laser element 25 is irradiated on the optical disc 10,
Light reflected from the recording layer 10b of the optical disk 10 is received by the photodetector 24. At this time, the objective lens 21
Is moved in a direction away from the optical disc 10, when the objective lens 21 moves from a position closer to a position farther than a focus position for focusing on one recording layer 10 b, a signal output from the focus error signal generator 34 is output. The focus error signal F outputs one S-shaped curve. Therefore, the focus error signal F is
The number of S-shaped curves corresponding to the number of zero recording layers 10b is output. That is, in the case of a CD or a single-layer DVD having one recording layer, the number of S-shaped curves of the focus error signal F is one, whereas a two-layer having two recording layers is used.
In the case of a layer DVD, the number of S-shaped curves of the focus error signal F is two.

As a result, when the optical disc 10 is a single-layer DVD having one recording layer and a high reflectivity, FIG.
As shown in FIG. 8A, while the objective lens 21 is moving, as shown in FIG.
, One S-shaped curve appears. Also, the optical disk 10
However, in the case of a CD having a large reflectance having one recording layer 10b, as shown in FIG. 9A, while the objective lens 21 is moving, as shown in FIG. In the focus error signal F, one S-shaped curve appears. On the other hand, when the optical disc 10 is a two-layer DVD having two recording layers 10b and having a small reflectance, FIG.
As shown in FIG. 10, while the objective lens 21 is moving, as shown in FIG. 10B, two S-shaped curves appear in the focus error signal F.

The focus error signal F output from the focus error signal generating means 34 is supplied to a predetermined voltage value Vh by the comparator 38a of the S-shaped number detecting means 38.
And when the voltage value becomes lower than the voltage value Vh, the comparator 38a outputs a pulse signal. Where 2
Each of the S-shaped curves of the layer DVD, the layer DVD, and the CD is Vth
Vth is set in advance so as to be compared. Therefore, as shown in FIG. 8B and FIG. 9B, when the focus error signal F has one S-shaped curve, FIG.
As shown in (c) and FIG. 9 (c), one pulse signal is output from the comparator 38a, and FIG. 10 (b)
As shown in the figure, the S-shaped curve of the focus error signal F is 2
In this case, as shown in FIG. 10C, two pulse signals are output from the comparator 38a. The number of pulses output from the comparator 38a is
The signal is counted by the counter 38b and a predetermined signal corresponding to the pulse number is output.

The control means 31 determines the type of the optical disk 10 based on the number of pulses counted by the counter 38b (step S5). That is, the counter 38
If the number of pulses counted by b is 2, it is determined that the optical disk 10 is a two-layer DVD, and the amplifier gain by the gain conversion means 32 is converted to an amplifier gain G2 corresponding to the two-layer DVD. (Step S6). Then, the spindle motor rotation drive unit 45 is controlled so that the spindle motor 46 is rotated (step S7).

When the optical disk 10 of the dual-layer DVD is rotated by the spindle motor 46, the information recorded on the optical disk 10 is reproduced by the optical pickup 20. In this case, the objective lens 21 remains at a large numerical aperture (0.6) because the laser light emitted by the numerical aperture converter 29 is not shielded.
The laser light is transmitted through the objective lens 21 to the optical disc 1.
It is irradiated to 0.

Then, as in the conventional case, the focus control and the tracking control of the objective lens 21 are performed based on the reflected light from the optical disk 10. The control means 31 controls the focus driving means 4 based on the focus error signal F obtained by the focus error signal generation means 34.
4 is driven, and the focus actuator 22 controls the focus of the objective lens 21 so that the light spot by the laser beam is focused on the recording layer of the optical disk 10 (step S8). The control means 31
Drives the tracking drive unit 43 based on the tracking error signal T generated by the tracking error signal generation unit 35, and controls the tracking actuator 22 so that the light spot of the laser beam follows the track of the rotating optical disk 10. To control the tracking of the objective lens 21 (step S
9).

On the other hand, when the number of pulses counted by the counter 38b is 1, the control means 31
It is determined that the optical disc 10 is a single-layer DVD or CD having one recording layer,
Control for determining whether the layer is a DVD or a CD is performed.
In this case, first, the spindle motor rotation driving unit 45 is controlled so that the spindle motor 46 is rotated (step S10). When the optical disk 10 is rotated, the control unit 31 drives the focus driving unit 44 based on the focus error signal F obtained by the focus error signal generation unit 34, and the light spot by the laser beam is Focus actuator 22 so as to be in focus on the recording layer of
Focus control of the objective lens 21 (step S11).

In such a state, the control means 31 reads an output corresponding to the amplitude of the reproduction signal R detected by the amplitude detection means 37, and determines whether the optical disk 10 is a single-layer DVD or a CD based on the output. Determine (Step S1
2). A reproduction signal R corresponding to the total amount of light received by the photodetector 24 is generated by the reproduction signal generation unit 33 and input to the amplitude detection unit 37.

In this case, for example, when the optical disk 10 is a single-layer DVD, the light spot of the laser beam applied to the rotating single-layer DVD is in a focused state by the focus control. When the optical spot is located on the track, the amplitude of the high-frequency signal output from the photodetector 24 is maximized, as shown in FIG.
The amplitude of the high-frequency signal output from is minimized. Since the tracking of the light spot is not controlled on the rotating single-layer DVD, the high-frequency signal as the reproduction signal R alternates between a state with a small amplitude and a state with a large amplitude.

The reflectance of the recording layer of a single-layer DVD is C
Although it is equal to D, the thickness from the surface of the CD to the recording layer is larger than the thickness from the surface of the single-layer DVD to the recording layer. For this reason, when the recording layer of the CD is irradiated with laser light through the objective lens 21 having a large numerical aperture,
An aberration occurs in the laser light. As a result, the reproduction signal R based on the amount of light reflected by the CD and received by the photodetector 24 has substantially the same voltage level as that of a single-layer DVD as shown in FIG. The amplitude is smaller than that of a single-layer DVD.

The reproduced signal R generated from the reproduced signal generating means 33 is input to the amplitude detecting means 37, and the peak value is detected by the peak hold circuit 37a and the bottom value is detected by the bottom hold circuit 37b. . When the optical disc 10 is a single-layer DVD, FIG.
As shown by the solid line in FIG. 1 (b), the peak value of the reproduction signal R is detected, and the bottom value of the reproduction signal R is detected as shown by the broken line in FIG. 11 (b). When the optical disc 10 is a CD, the peak value of the reproduction signal R is detected as shown by the solid line in FIG.
As shown by the broken line in FIG. 12B, the bottom value of the reproduction signal R is detected.

The outputs of the peak hold circuit 37a and the bottom hold circuit 37b are input to an operational amplifier 37c, and the operational amplifier 37c calculates the peak value detected by the peak hold circuit 37a and the bottom value detected by the bottom hold circuit 37b. Subtraction processing is performed. As a result, the difference between the two, that is, the envelope amplitude voltage of the reproduction signal R is output from the operational amplifier 37c as shown in FIG.
(C) and output as shown in FIG. The envelope amplitude voltage output from the operational amplifier 37c is compared with a preset voltage Ve by the comparator 37d, and is digitally converted into a high level and a low level based on the voltage Ve. Therefore, when the optical disk 10 is a single-layer DVD,
While the high level signal is output intermittently from the comparator 37d, when the optical disc 10 is a CD, only the low level signal is output from the comparator 37d.

The output of the comparator 37d of the amplitude detecting means 37 is input to the control means 31. When the output from the reproduction signal amplitude detecting means 37 is at a low level, the optical disc 10 Is determined, the numerical aperture conversion driving means 42 is controlled, and the numerical aperture conversion actuator 29g controls the numerical aperture conversion body 29b.
The numerical aperture converter 29b is rotated so that the opening 29a of the numerical aperture faces the objective lens 21 (step S1 in FIG. 7).
3). Thereby, the laser light oscillated from the semiconductor laser element 25 is transmitted to the aperture 29a of the numerical aperture converter 29b.
Irradiating the objective lens 21 with the laser beam, the apparent numerical aperture of the objective lens becomes small, and the laser beam
The recording layer D is irradiated without aberration.

Further, the control means 31 determines that the optical disk 10 is a CD, so that the amplifier gain of the output of the photodetector 24 by the gain conversion means 32 becomes C
The gain conversion means 32 is controlled so as to be G3 corresponding to D (step S14). After that, the output of the photodetector 24 is set to the amplifier gain G3 by the gain converting means 32, and based on the output, the objective lens 21 of the optical pickup 20 converts the focus error signal F obtained by the focus error signal generating means 34 into the focus error signal F. The optical pickup 20 is controlled based on the tracking error signal generated by the tracking error signal generating means 35 (step S9), and the optical pickup 20 is recorded on the recording layer of the CD. The information is reproduced.

On the other hand, the reproduced signal amplitude detecting means 37
In the case where a high level signal is present in the output of the comparator 37d, the optical disc 10 is
The control means 31 determines that the numerical aperture converter 29
Of the numerical aperture converter 29b without driving the
9a is held at a retracted position not facing the objective lens 21, and the gain of the gain
The focus control is continued while the state of the amplifier gain G1 corresponding to is maintained (step S11), and the tracking control is performed based on the output of the photodetector 24 which has been set to the amplifier gain G1 by the gain conversion means 32 (step S11). S9). As a result, information recorded on the recording layer of the single-layer DVD is reproduced.

[0058]

As described above, according to the optical disk reproducing apparatus of the present invention, the optical disk has two layers based on the number of S-shaped curves of the focus error signal generated while moving the objective lens with respect to the optical disk. Since it is determined that a DVD is a DVD, a double-layer DVD and a single-layer DVD and a CD can be accurately determined. Further, since the CD and the single-layer DVD are distinguished based on the amplitude of the reproduction signal generated in a state where the focus of the objective lens is controlled, the CD and the single-layer DVD are accurately distinguished. be able to.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram of an optical pickup used in the optical disk reproducing device.

FIG. 3 is a plan view of a numerical aperture converter provided in the optical pickup.

FIG. 4 is a circuit diagram of a main part in the optical disc reproducing apparatus of the present invention.

FIG. 5 is a circuit diagram of another main part of the optical disc reproducing apparatus of the present invention.

FIG. 6 is a circuit diagram of still another main part of the optical disk reproducing apparatus of the present invention.

FIG. 7 is a flowchart showing an operation of the optical disk reproducing device of the present invention.

8 (a) to 8 (c) each show one optical disk.
6 is a time chart for explaining the operation of an S-shaped number detecting means provided in the optical disc reproducing apparatus of the present invention in the case of a layer DVD.

FIGS. 9A to 9C respectively show that the optical disk is C
5 is a time chart for explaining the operation of the S-shaped number detecting means provided in the optical disc reproducing apparatus of the present invention in the case of D.

FIGS. 10A to 10C are time charts for explaining the operation of the S-number detecting means provided in the optical disk reproducing apparatus of the present invention when the optical disk is a two-layer DVD.

FIG. 11A is a graph showing a reproduction signal generated by reproduction signal generation means provided in the optical disk reproducing apparatus of the present invention when the optical disk is a single-layer DVD, and FIG.
7A is a graph showing the output of the peak hold circuit and the bottom hold circuit of the amplitude detector to which the reproduced signal is input, and FIG. 7C is a graph showing the output of the operational amplifier of the amplitude detector to which the output is given.

FIG. 12A is a graph showing a reproduction signal generated by reproduction signal generation means provided in the optical disk reproducing apparatus of the present invention when the optical disk is a single-layer CD, and FIG.
7A is a graph showing the output of the peak hold circuit and the bottom hold circuit of the amplitude detector to which the reproduced signal is input, and FIG. 7C is a graph showing the output of the operational amplifier of the amplitude detector to which the output is given.

13A is a sectional view of a main part of a CD, and FIG.
FIG. 3C is a cross-sectional view of a main part of the single-layer DVD, and FIG.

14A is a schematic diagram for explaining a reproduction state of information recorded on a single-layer DVD, and FIG. 14B is a schematic diagram for explaining a reproduction state of information recorded on a CD; is there.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical disk 20 Optical pickup 21 Objective lens 22 Focus actuator 23 Tracking actuator 24 Photodetector 25 Semiconductor laser element 29 Numerical aperture converter 29a Opening 29b Numerical aperture converter 29g Numerical aperture conversion actuator 37 Amplitude detecting means 38 S-shaped curve detecting means

Claims (5)

[Claims] 1. An optical disc is irradiated with laser light through an objective lens, and the laser light reflected by the optical disc is received by a photodetector. Based on the output of the photodetector, a reproduction signal, An optical disc reproducing apparatus in which a focus error signal and a tracking error signal are respectively generated, and a focus control and a tracking control of an objective lens are performed based on the focus error signal and the tracking error signal, respectively. An S-shaped curve generated in a focus error signal generated while the objective lens is moving by moving the objective lens along the optical axis direction with respect to the optical disc while the optical disc is being irradiated through the objective lens. The type of optical disc is determined based on the number of And an optical disk reproducing apparatus, characterized in that are. 2. A method for controlling the type of an optical disc based on the magnitude of the amplitude of a frequency component generated in the reproduction signal while performing focus control of an objective lens on a rotating optical disc based on the focus error signal. The optical disk reproducing device according to claim 1, further comprising a configuration for determining. 3. The optical disc reproducing apparatus according to claim 1, wherein a gain of an output of the photodetector is changed based on a type of the optical disc to be determined. 4. An outer peripheral edge of a laser beam passing through the objective lens is shielded so that an apparent numerical aperture of the objective lens is changed based on the type of the optical disc to be determined. The optical disk reproducing device according to claim 1. 5. An optical disc is irradiated with laser light through an objective lens, and the laser light reflected by the optical disc is received by a photodetector. Based on the output of the photodetector, a reproduction signal, An optical disc reproducing apparatus in which a focus error signal and a tracking error signal are respectively generated, and an objective lens is subjected to focus control and tracking control based on the focus error signal and the tracking error signal, respectively. An optical disc reproducing apparatus characterized in that the type of the optical disc is determined based on the magnitude of the amplitude of the frequency component generated in the reproduction signal while performing focus control on the objective lens with respect to the optical disc.