JP3550538B2 - Optical disk drive - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical disk device that uses an optical disk having tracks formed by pits, recording marks, grooves, or lands on the entire surface or a part of a recording surface, and more particularly to a technique related to tracking control in the optical disk device.
[0002]
[Prior art]
In a recording / reproducing apparatus for an optical disk represented by a CD or a DVD, a light beam tracks a spirally formed track by using a tracking control method called a DPD (phase difference) method or a push-pull method. When the light beam tracks on the track formed by the pits and marks, the recorded information is reflected on the reflected light, and the information is reproduced. In addition, a mark is recorded by tracking a light beam on a track formed by grooves and lands and modulating the amount of incident light.
[0003]
Currently, optical disks represented by CDs (CD-ROM, CD-R, CD-RW, etc.) and DVDs (DVD-ROM, DVD-R, DVD-RW, etc.) on the market are in the near infrared region. Laser light in the red region is used. For a CD, a laser wavelength of about 780 to 830 nm is used, and for a DVD having a recording density seven times or more that of a CD, a laser wavelength of about 650 nm is used. Then, in an optical disc with further improved recording density, a blue laser is used.
[0004]
Each optical disk is designed according to the laser wavelength used for each optical disk, and in particular, the recording density is designed according to the spot diameter of the light beam that is largely governed by the laser wavelength. Therefore, a DVD having a large spot diameter and a laser having a wavelength of 780 to 830 nm cannot read a DVD or an optical disk for a blue laser, and a laser having a wavelength of 650 nm for a DVD cannot read an optical disk for a blue laser. Conversely, DVD lasers can read CDs and DVDs, and blue lasers can read CDs, DVDs, and optical discs for blue lasers in principle. This is because, as described above, when a laser having a shorter wavelength is used, a smaller light beam spot can be realized, so that a resolution sufficient for reproducing an optical disk having a small recording density can be obtained. In fact, a DVD device uses a laser beam having a wavelength of 650 nm to reproduce a CD-ROM designed for a laser beam having a wavelength of 780 to 830 nm.
[0005]
[Problems to be solved by the invention]
However, when trying to reproduce a CD or DVD using the push-pull method in an optical disk device having a blue laser, it is not possible to trace the track formed on the CD or DVD well, and as a result, the CD or DVD cannot be reproduced with the blue laser. There was a problem that playback was not possible. Particularly, in a CD or DVD (a so-called partial ROM disk) having a ROM area formed by pits and a recordable area formed by grooves and lands, a track error signal is continuously generated between the ROM area and the recordable area. Without this, there is a problem that the track is deviated.
[0006]
The present invention has been made in view of the above points, and an object of the present invention is to accurately track an optical disk designed for a red laser or a near-infrared laser even in an optical disk device using a blue laser and reproduce the optical disk. It is an object of the present invention to provide a technology that enables
[0007]
[Means for Solving the Problems]
The present invention achieves the above-mentioned object,An area where information is recorded by forming pits in advance and an area where information is recorded in the form of a mark in a groove are irradiated with a light beam onto an optical disc which forms one track, and based on the reflected light, In an optical disk device that performs tracking control of a light beam, a region to which a light beam is irradiated is determined based on a tangential push-pull signal obtained from the pits and marks, and the polarity of the tracking control is inverted accordingly, Track pit area and mark area continuously without interruptionIs composed.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described. First, prior to the description of each embodiment of the present invention, a push-pull method for obtaining a tracking servo signal used for tracking control of an optical disc will be described.
[0015]
The push-pull method is a method in which a difference in light amount between an inner peripheral side and an outer peripheral side of a reflected light beam divided in a direction along a track tangential direction is obtained, and this is used as a tracking signal. FIG. 3 shows an example of a block configuration diagram for generating a tracking servo signal. In FIG. 12, 1 is a light beam, 2 is a photodetector, 3-1 and 3-2 are addition circuits, 17 is a difference circuit, and 18 is an LPF (low-pass filter).
[0016]
When a light beam is irradiated onto the pit row, the reflected light is diffracted by the pits due to the positional relationship between the two, but in the push-pull method, the reflected light is divided into two in each of the inner and outer peripheral sides of the optical disk. And a tracking servo signal is generated based on the average intensity.
[0017]
The adders 3-1 and 3-2 add the output signals of the elements located on the inner circumference side and the outer circumference side of the photodetector 2, and output the addition result to the difference circuit 17. The difference circuit 17 outputs the difference result of the two signals from the adders 3-1 and 3-2 to the LPF 18, and removes the high-frequency components of the individual pits from the difference result to produce a low-frequency component, in other words. For example, the principle of the push-pull method is to extract a signal component corresponding to a slight average shift between the light beam and the pit row as a tracking servo signal.
[0018]
The above is the principle of generating the tracking servo signal by the push-pull method. The push-pull signal is, as shown in FIG. 13, the output of the elements a and d located in front of the beam traveling direction. It can also be obtained from the difference. Although not shown in the drawing, similarly, it can be obtained from the output difference between the elements b and c located behind the beam traveling direction. When the push-pull signal is obtained from the two elements, the addition circuits (addition amplifiers) 3-1 and 3-2 can be omitted, and the cost can be reduced.
[0019]
<First embodiment>
FIG. 1 is a block diagram showing a circuit configuration for generating a tracking servo signal in the optical disc device according to the first embodiment of the present invention. In FIG. 1, 1 is a light beam, 2 is a photodetector, 3-1 and 3-2 are addition circuits, 16 is a switch, 17 is a difference circuit, and 18 is an LPF.
[0020]
In each embodiment of the present invention including this embodiment, the tracking servo signal is generated by the above-described push-pull method, and the polarity of the tracking control (push-pull tracking) is switched according to the type of the optical disc to be reproduced. ing.
[0021]
A controller (not shown) inputs to the switch 16 whether or not to reverse the polarity of the tracking control. When reproducing the disk "1" designed for a wavelength of 410 nm, "Normal" is output from the controller, and the switch falls to the R side. The polarity of the tracking control at this time is the same as that of the device of the conventional example shown in FIG. 12, so that the tracking of the disk "1" can be accurately performed. When reproducing the disk "2" designed for the wavelength of 650 nm, "Inv" is output from the controller, and the switch 16 falls to the L side. The polarity of the tracking control at this time is opposite to that of the conventional apparatus shown in FIG. 12, so that the tracking of the disk "2" can be accurately performed.
[0022]
In order to determine whether a signal of “Normal” or “Inv” is input from the controller, the controller needs to know the type of the disk (disk “1” or disk “2”). For this purpose, a disc type selection switch may be provided in the apparatus so that the user can input the disc type to the controller, or the disc itself may be used before disc playback by utilizing the characteristics of each disc. May automatically determine the disc type.
[0023]
An example of a method in which the apparatus itself automatically discriminates the disc “1” and the disc “2” will be described with reference to FIG.
[0024]
First, when a disk (optical disk) is inserted into the optical disk device of the present embodiment, the device outputs "Norm" from the controller to perform tracking (step S1) and determine whether or not the RF signal can be reproduced. (Step S2). If the RF signal can be reproduced (YES in step S2), the inserted disc is determined to be a disc “1” designed for 410 nm (step S3). Various methods can be considered for determining whether or not the RF signal can be reproduced. Here, the determination is made based on whether or not an RF signal amplitude larger than a certain reference level can be obtained.
[0025]
If the RF signal could not be reproduced (NO in step S2), "Inv" is output from the controller, the tracking is switched by switching the polarity of the tracking control (step S4), and it is determined whether the RF signal can be reproduced. A determination is made (step S5). Here, if the RF signal can be reproduced (YES in step S5), the inserted disc is determined to be the disc “2” designed for 650 nm (step S6). If the RF signal cannot be reproduced (NO in step S5), it is determined that the inserted disk is a third disk that is neither disk "1" nor disk "2" (step S7). If it is determined that the disk is “1” or “2”, tracking may be performed with an appropriate polarity. If it is determined that the disk is a third disk, the disk may be ejected from the apparatus as necessary. The user may be notified of the fact that the disc cannot be reproduced by displaying it on a display provided in the apparatus or by issuing a warning sound.
[0026]
<Comparative Example 1>
The optical disk reproducing apparatus used in this comparative example uses an optical pickup using an optical system including a laser beam having a wavelength of 410 nm and an objective lens having an NA of 0.6, and reproduction is performed at a linear velocity of 3.5 m / sec. I have. An actuator that drives the objective lens and performs tracking has a response speed of about 5 kHz. For the tracking, a push-pull signal subjected to the processing described in FIG. 12 is used. Normally, the band required for tracking is lower than the band of pits and marks, and if a signal of an unnecessarily high frequency is sent to an actuator that performs tracking, the actuator driver and the actuator coil generate heat, leading to damage to the device. This is why the LPF 18 is used.
[0027]
Two types of disks, a ROM disk designed for a red laser and a ROM disk designed for a blue laser, were prepared.
[0028]
The blue laser disk (disk “1”) has a track pitch of 0.47 μm and a shortest pit length of 0.27 μm, and pits on which 8/16 modulated recording is performed are formed on a 0.6 mm thick substrate. Have been.
[0029]
The red laser disk (disk “2”) has a track pitch of 0.74 μm and a minimum pit length of 0.4 μm, and 8/16 modulated pits are formed on a 0.6 mm thick substrate. It is a so-called DVD.
[0030]
When the apparatus used in this comparative example generates a tracking servo signal by the push-pull method and reproduces the disk "1", accurate tracking can be performed, and the RF signal is reproduced with 7.5% jitter. We were able to. On the other hand, an attempt was made to reproduce the disk "2" with the same device, but the tracking could not be performed accurately and the data could not be reproduced.
[0031]
This phenomenon occurs for the following reason. FIG. 5 shows the relationship between the pit depth or groove depth and the push-pull signal amplitude measured with laser wavelengths of 410 nm light and 650 nm light. The vertical axis in FIG. 5 is normalized by the maximum value of the push-pull signal amplitude measured at each wavelength. The polarity of the push-pull signal is inverted when the pit depth or groove depth is λ / 4n. Here, λ is the wavelength of the laser beam, and n is the refractive index of the disk substrate. Now, since polycarbonate having n = 1.55 is used for the disk substrate, when measured at a wavelength of 650 nm, the polarity of the push-pull signal amplitude is reversed at a pit depth of 105 nm. When measured at a wavelength of 410 nm, the polarity of the push-pull signal is inverted at a pit depth of 66 nm.
[0032]
FIG. 6 shows the relationship between the pit depth and the RF signal amplitude. The largest RF signal amplitude is obtained at the pit depth λ / 4n. The vertical axis in FIG. 6 is normalized by the maximum value of the RF signal amplitude measured at each wavelength. The pit depth of each disk is adjusted for each wavelength, and as shown in FIGS. 5 and 6, the disk “1” is about 50 nm, and the disk “2” is about 85 nm. This is a result of designing each disk so as to obtain a good balance between the push-pull signal and the RF signal.
[0033]
Since the apparatus of this comparative example uses 410 nm light, the polarity of the tracking signal obtained on the disk “1” designed for 410 nm and the polarity of the tracking signal obtained on the disk “2” designed for 650 nm Is upside down. This is the reason that the disk of the comparative example could not track the disk “2”. That is, even if the disk "2" is to be reproduced by the apparatus of the comparative example, the beam spot does not scan on the track composed of the pit rows, but scans between the pit rows, that is, between tracks. become. In this case, the RF signal is not output, and therefore, cannot be reproduced.
[0034]
<Second embodiment>
The circuit configuration for generating the tracking servo signal in the optical disc device according to the present embodiment is the same as that of the first embodiment shown in FIG.
[0035]
In the present embodiment, in addition to the operation of the first embodiment, it is further determined that the disk is a partial ROM disk for red laser (disk "3"). The polarity of the tracking control (push-pull tracking) is switched between the and the pit area.
[0036]
A controller (not shown) inputs to the switch 16 whether or not to reverse the polarity of the tracking control. When reproducing the mark area of the disk "3", "Normal" is output from the controller, and the switch 16 falls to the R side. The polarity of the tracking control at this time is the same as that of the conventional apparatus shown in FIG. 12, so that the tracking of the mark area of the disk "3" can be accurately performed. When reproducing the pit area of the disk "3", "Inv" is output from the controller, and the switch 16 falls to the L side. The polarity of the tracking control at this time is opposite to that of the conventional apparatus shown in FIG. 12, so that the pit area of the disk "3" can be accurately tracked.
[0037]
The timing for switching the switch 16 is obtained from the address information written in the RF signal. For example, consider a case where a mark area is reproduced and a pit area appears subsequently. Since the format of the disc is known in advance, the addresses of the mark area and the pit area are known from the viewpoint of the apparatus. Therefore, if the address during the reproduction of the mark area is always checked, the timing at which the pit area appears can be completely grasped. At this timing, the switch 16 is switched to switch the polarity of the tracking control. The timing of shifting from the pit area to the mark area can also be obtained from the address information in the same manner.
[0038]
If the type of the disc can be determined, the format is known in advance, so the addresses of the pit area and the mark area can be known. Conversely, to obtain the timing for switching the tracking control polarity from the address information as described above, it is necessary to know the type of the disc in advance.
[0039]
In order for the controller to know the type of the disk (disk "1" or disk "2" or disk "3"), a disk type selection switch must be provided on the device so that the user himself can input the disk type to the controller. Alternatively, the apparatus itself may automatically determine the disc type before reproducing the disc by utilizing the characteristics of each disc.
[0040]
An example of a method in which the apparatus itself automatically discriminates the disk “1”, the disk “2”, and the disk “3” will be described with reference to FIG.
[0041]
First, when a disk (optical disk) is inserted into the optical disk apparatus of the present embodiment, the apparatus moves its pickup to a radial position where all of the disks "1", "2" and "3" are known to be pit areas. Move to (Step S21). Next, tracking is performed by outputting "Normal" from the controller (step S22), and it is determined whether or not the RF signal can be reproduced (step S23). If the RF signal can be reproduced (YES in step S23), it is determined that the inserted disc is the disc “1” designed for 410 nm (step S24).
[0042]
If the RF signal could not be reproduced (NO in step S23), the apparatus moves to a radial position that is known to be a pit area on disk "2" and a mark area on disk "3". The pickup is moved (Step S25). Next, tracking is performed by outputting "Normal" from the controller (step S26), and it is determined whether or not the RF signal can be reproduced (step S27). If the RF signal can be reproduced (YES in step S27), it is determined that the inserted disk is the disk “3” designed for 650 nm (step S28).
[0043]
If the RF signal could not be reproduced here (NO in step S27), the pickup outputs "Inv" from the controller in that position, and performs tracking by switching the polarity of tracking control (step S29). It is determined whether or not the RF signal can be reproduced (step S30). Here, if the RF signal can be reproduced (if YES in step S30), it is determined that the inserted disk is the disk “2” designed for 650 nm (step S31). If the RF signal cannot be reproduced (NO in step S30), it is determined that the inserted disk is neither the disk "1" nor the disk "2" or the disk "3" and is the fourth disk ( Step S32).
[0044]
If it is determined that the disk is “1”, “2” or “3”, tracking may be performed with the appropriate polarity. In particular, if the disk is determined to be “3”, tracking is performed based on the address information. What is necessary is just to obtain the timing of switching the polarity. If it is determined that the disc is a fourth disc other than the discs "1", "2", and "3", the disc is ejected from the apparatus as necessary, or the fact that the disc cannot be reproduced is notified to the apparatus. It can be communicated to the user by displaying it on a provided display or emitting a warning sound.
[0045]
Subsequently, a method for obtaining the timing of polarity switching without discriminating the disk will be described below.
[0046]
FIG. 7 shows the relationship between the pit depth and the tangential push-pull signal amplitude measured with light having a wavelength of 410 nm. The tangential push-pull (TPP) signal amplitude becomes maximum around 33 nm where the pit depth is λ / 8n, and the vertical axis in FIG.
[0047]
The polarity of the TPP signal is inverted around a pit depth of λ / 4n near 65 nm, but in order to indicate the polarity, in FIG. 7, the TPP signal is negative in a region having a pit depth of 65 nm or more. I have.
[0048]
Next, the TPP signal will be described with reference to FIGS. FIG. 8 shows a state in which the reflected light is guided to a detector 2 composed of four divided light receiving elements a, b, c, and d. The TPP signal is obtained by using the outputs of the four-divided light receiving elements a, b, c, and d by an arithmetic expression represented by TPP = (a + d)-(b + c). In the present embodiment, when the mark area and the pit area are automatically identified, an addition circuit and a difference circuit shown in FIG. 8 are added.
[0049]
FIG. 9 shows a TPP signal when a pit having a depth of 50 nm is reproduced by the apparatus of the present embodiment having the configuration of FIG. A pulse signal is obtained at the leading edge and the trailing edge of the pit. At the leading edge, a pulse occurs in the positive direction (upward), and at the trailing edge, a pulse occurs in the negative direction (downward).
[0050]
Here, it can be seen from FIG. 7 that when the pits of the disk "3" are reproduced by the apparatus of the present embodiment having the configuration of FIG. 8, a TPP signal having a negative polarity is obtained. Negative polarity means that a pulse occurs in the negative direction at the leading edge of the pit and a pulse occurs in the positive direction at the trailing edge.
[0051]
On the other hand, a mark also has a TPP signal at its leading edge and trailing edge. However, since the mark has no depth, its polarity is always positive and constant regardless of the wavelength.
[0052]
FIG. 10A shows a disk “3” including a mark area and a pit area, and FIG. 10B shows an apparatus of the present embodiment having the configuration of FIG. 3 ”shows a TPP signal obtained when tracking“ 3 ”. The polarity of the TPP signal is different between the mark area and the pit area. By utilizing this, the mark area and the pit area are determined, and the polarity of the tracking control is switched.
[0053]
An example of determining the polarity of the TPP signal will be described with reference to FIG. FIG. 11A shows a case where a pit area comes after a mark area. FIG. 11B shows the obtained TPP signal. Here, a certain positive reference value and a negative reference value are provided. As shown in FIGS. 11C and 11D, when a pulse exceeding the positive reference value is observed, +1 is added. If a pulse exceeding a negative reference value is observed, -1 is output. FIG. 11E shows the result of sequentially adding +1 and −1 outputted here. In the mark portion, +1 is obtained, and in the pit portion, -1 is obtained. By utilizing this, it becomes possible to determine the mark area and the pit area, and the result of the determination is sent to the controller in FIG. The controller switches the polarity of the tracking control in response to the determination result. This makes it possible to obtain the timing for switching the polarity of tracking control without discrimination of the disk.
[0054]
In the first and second embodiments described above, a device that generates a tracking signal from a push-pull signal obtained from four elements has been described. However, as shown in FIG. By performing the same control on a device that generates a tracking signal, it becomes possible to reproduce a disk designed for a red laser by an optical disk device equipped with a blue laser.
[0055]
<Comparative Example 2>
The optical disk reproducing device used in this comparative example is the same as the device used in comparative example 1. The disk to be used is a partial ROM disk (disk "3") designed for a wavelength of 650 nm, which is composed of a ROM area composed of pits and a groove, and allows a user to record information with marks. And a possible area. This disk "3" has already been recorded by another recording device equipped with a 650 nm laser, and the recording area is composed of a pit area and a mark area. The pits provided on the disk "3" have the same depth as the pits on the disk "2".
[0056]
This recorded disk "3" has a track pitch of 0.74 µm, the shortest pit length and the shortest mark length are both 0.4 µm, and both pits and marks are 8/16 modulated. These are formed. For the recording layer, InAgSbTe which is a phase change material is used. Since the reflectivity of this material is different between the crystalline state and the amorphous state, a mark is formed by using this and information is recorded.
[0057]
In the apparatus used in this comparative example, as shown in FIG. 12, tracking was performed by a push-pull signal, and when the disk "3" was reproduced, accurate tracking could be performed in the mark area, and the RF signal was reduced to 7 in the mark area. % Could be reproduced. On the other hand, in the pit area, accurate tracking could not be performed, and data recorded in the pit could not be reproduced.
[0058]
The reason why tracking cannot be performed in the pit area is the same as the reason described in Comparative Example 1 described above. On the other hand, the mark area is composed of a groove, and the groove depth is adjusted for a 650 nm laser. Its depth is about 30 nm as shown in FIG. At this depth, a push-pull signal having the same polarity is obtained at a wavelength of 410 nm and at a wavelength of 650 nm. For this reason, in the device used in this comparative example, the mark area could be tracked.
[0059]
【The invention's effect】
According to the present invention, an area in which information is recorded by forming pits in advance and an area in which information is recorded in the form of a mark in a groove are formed by irradiating an optical disk having one track with a light beam. In a configuration in which tracking control of a light beam is performed based on the reflected light, an area irradiated with the light beam is determined based on a tangential push-pull signal obtained from a pit and a mark, and the polarity of the tracking control is determined accordingly. The pit area and the mark area are continuously and continuously tracked without interruption. Therefore, by automatically discriminating the disc and automatically detecting the timing of the polarity reversal of the tracking control, an optical disc having a recording area such as a partial ROM disc can be appropriately and continuously reproduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a circuit configuration for generating a tracking servo signal in an optical disc device according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating an example of a flow of a disk discrimination process according to the embodiment of the present invention.
FIG. 3 is a flowchart showing another example of the flow of the disk discrimination process according to the embodiment of the present invention.
FIG. 4 is a block diagram showing another circuit configuration for generating a tracking servo signal in the optical disc device according to the embodiment of the present invention.
FIG. 5 is an explanatory diagram illustrating a relationship between a pit depth, a groove depth, and a push-pull signal amplitude.
FIG. 6 is an explanatory diagram showing a relationship between a pit depth and an RF signal amplitude.
FIG. 7 is an explanatory diagram illustrating a relationship between a pit depth and a tangential push-pull signal amplitude.
FIG. 8 is a block diagram showing a circuit configuration for obtaining a tangential push-pull signal in the optical disc device according to the embodiment of the present invention.
FIG. 9 is an explanatory diagram showing a tangential push-pull signal when a pit train is reproduced.
FIG. 10 is an explanatory diagram showing a tangential push-pull signal when a disc having a mark area and a pit area is reproduced.
FIG. 11 is an explanatory diagram showing a method of determining a mark area and a pit area from a tangential push-pull signal in the optical disc device according to the embodiment of the present invention.
FIG. 12 is a block diagram of a tracking servo signal generation circuit using a conventional push-pull method using four elements.
FIG. 13 is a block diagram of a tracking servo signal generation circuit using a conventional push-pull method using two elements.
[Explanation of symbols]
1 light beam
2 Photo detector
3-1 and 3-2 adder circuits
16 switches
17 Difference circuit
18 LPF (Low Pass Filter)

Claims (1)

An area where information is recorded by forming pits in advance and an area where information is recorded in the form of a mark in a groove are irradiated with a light beam onto an optical disc which forms one track, and based on the reflected light, An optical disc device that performs tracking control of a light beam,
Based on the tangential push-pull signal obtained from the pits and marks, the area irradiated with the light beam is determined, and the polarity of the tracking control is inverted accordingly, so that the pit area and the mark area are continuously connected without interruption. An optical disk device characterized in that tracking is performed .

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