JP3941220B2 - Optical disk playback device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc reproducing apparatus for reproducing two optical discs having different substrate thicknesses.
[0002]
[Prior art]
Conventionally, as the interest in multimedia increases, there is an increasing demand for recording large volumes of data such as moving images on an optical disk. As a result, optical discs have been developed in the direction of higher capacity and higher speed.
[0003]
However, since the ease of handling is important for optical discs, as typified by compact discs (CDs), it is very welcome to increase the diameter of the discs to increase capacity, that is, to increase the recording area. Is in a situation that is not. Therefore, in order to realize an increase in the capacity of the optical disc, there is an interest in further increasing the recording density.
[0004]
Against this background, DVD (Digital Versatile Disc) has been put to practical use as a system in which the recording capacity is increased to about 7 times that of a conventional CD. In this system, the recording capacity is increased by shortening the oscillation wavelength of the laser diode from 780 nm to 650 nm and increasing the numerical aperture NA from 0.45 to 0.6 of CD. Since the diameter of the spot focused on the disk is proportional to (wavelength / NA), the spot can be narrowed down further, and the recording density can be increased.
[0005]
DVD and CD are systems of different formats with different recording densities and substrate thicknesses, but the function of being able to reproduce both with the same reproducing device will promote the introduction of the DVD market.
[0006]
However, since the DVD pickup is optimally designed for a DVD substrate thickness of 0.6 mm, the spot after passing through a 1.2 mm substrate equal to the CD format is spherical when nothing is done. Since a kind of optical distortion called aberration is added, the spot condensed on the disk becomes blurred due to the influence. Therefore, it has been difficult to reproduce a good signal from a CD with a DVD pickup.
[0007]
Therefore, for example, Japanese Patent Laid-Open No. 7-311945 proposes a system that realizes compatible reproduction of DVD and CD by focusing the two points for CD and DVD by performing hologram processing on the objective lens. .
[0008]
[Problems to be solved by the invention]
By the way, in the system proposed in the above-mentioned Japanese Patent Application Laid-Open No. 7-31195, since the signal of the disc is always reproduced while two focal points are connected, even if a DVD is reproduced, it is unnecessary for a CD. Spots are created, and even when a CD is played, an unnecessary spot for DVD is created. Therefore, it is necessary to increase the output of the laser diode in order to obtain the amount of light at each spot to a level where good signal detection is possible, and there are problems in terms of power consumption and laser diode life due to poor light utilization efficiency. It was.
[0009]
Although a DVD and CD lens can be mounted on the same pickup and the lens can be switched according to the disc to be played, two objective lenses must be used and a lens switching mechanism is required. Therefore, there are problems in terms of miniaturization and cost. In addition, since a plurality of lenses are mounted on the movable part, there is a problem that power consumption due to servo increases due to an increase in weight of the movable part.
[0010]
Therefore, the present invention prevents the deterioration of the light utilization efficiency, achieves low power consumption and a long laser life, realizes downsizing and cost reduction, and reproduces two types of optical disks having different substrate thicknesses. An object is to provide a playback device.
[0011]
[Means for Solving the Problems]
When an attempt is made to reproduce a CD signal using a DVD pickup, the objective lens is designed so that the optical aberration is reduced when it passes through the substrate thickness specified in each format, that is, on the recording surface. Therefore, the DVD format and the CD format have different substrate thicknesses of 0.6 mm and 1.2 mm, respectively. Therefore, when optically reproducing a CD signal using a DVD pickup, the substrate thickness specified by the format is used. The spot cannot be narrowed down sufficiently due to the influence of wavefront aberration (the main component is spherical aberration) generated by the difference in height.
[0012]
Normally, when there is aberration, the spot focused on the disk becomes blurry, so part of the blurred spot reaches the front and back pits, causing intersymbol interference, and adjacent tracks. Crosstalk is caused by reaching up to. Therefore, the reproduction signal using the optical pickup with the aberration is a signal mixed with noise as compared with the case of using the signal having no wavefront aberration.
[0013]
However, since the recording density differs between the CD and the DVD, it is considered that the influence of the CD spot with a low recording density is small because the spot for the DVD is originally small even with the same wavefront aberration amount. Therefore, it is possible to reproduce a CD signal by using a DVD pickup by properly processing a reproduction signal distorted due to deterioration.
[0014]
In order to solve the above-described problem, an optical disc playback apparatus according to the present invention is an optical disc playback apparatus that plays back information recorded on at least two types of optical discs having different thicknesses. An optical pickup designed for a type of optical disc, and information reproducing means for performing different waveform equalization processing on the pickup signal from the optical pickup according to one or the other type of the at least two types of optical discs, When information is reproduced from the other type of optical disc, the information reproducing means is caused to perform waveform equalization processing by estimation calculation using class classification adaptive processing on the information for the other optical disc.
[0016]
The class classification adaptive processing divides a pickup signal from the other type of optical disc, detects a signal level pattern for each divided signal, classifies the class based on the detected pattern, This is a process for calculating the optimum estimated value based on the prediction coefficient value obtained by learning in advance.
[0017]
In the class classification adaptation process, classes are classified by adaptive dynamic range coding.
[0018]
The substrate thickness of the one type of optical disk is smaller than the substrate thickness of the other type of optical disk. For example, a DVD with a substrate thickness of 0.6 mm and an optical disk with a substrate thickness of 1.2 mm are targeted.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an optical disk reproducing apparatus according to the present invention will be described below with reference to the drawings. This embodiment is an optical disk reproducing apparatus shown in FIG. 1 that reproduces a plurality of optical disks having different recording densities and substrate thicknesses using a single pickup. This optical disk playback device is intended for playback of DVDs with a high recording density and a substrate thickness of 0.6 mm, and CDs with a normal recording density and a substrate thickness of 1.2 mm. Play the signal.
[0020]
An objective lens with a numerical aperture NA of 0.6 is used as a DVD pickup, but an objective lens with a numerical aperture NA of 0.45 is generally used as a CD pickup. The conditions are different and as a result, spherical aberration occurs.
[0021]
However, since the recording density differs between the CD and the DVD, it is considered that the influence of the CD spot with a low recording density is small because the spot for the DVD is originally small even with the same wavefront aberration amount. Therefore, it is possible to reproduce a CD signal by using a DVD pickup by properly processing a reproduction signal distorted due to deterioration.
[0022]
Therefore, the optical disk reproducing apparatus 10 includes an optical pickup 11 designed for DVD, and an RF amplifier 12 that performs different waveform equalization processing on the pickup signal from the optical pickup 11 according to DVD or CD, When information is reproduced from the CD, a waveform equalization process is performed to cause the RF amplifier 12 to estimate and calculate information for the CD.
[0023]
Specifically, as shown in FIG. 1, the optical disk reproducing apparatus 10 reads information recorded on an optical disk (DVD or CD) 1 and outputs a pickup signal, and data from the pickup signal of the optical pickup 11. An RF amplifier 12 that obtains an RF signal, a focus error signal (FE), and a tracking error signal (TE) that are reproduction signals, and an RF signal from the RF amplifier 12 is subjected to processing such as demodulation and error detection / correction to obtain data. A digital signal processing circuit 13 to be reproduced, a D / A converter 14 that converts data from the digital signal processing circuit 13 into an analog signal and supplies the analog signal to the output terminal 15, a focus error signal, a tracking error signal, and the like from the RF amplifier 12 Based on the focus servo and tracking server of the pickup 11 And a servo processing circuit 16 for controlling the rotation of the optical disk 1, a spindle motor 17 for rotating the optical disk 1, and the above-described respective parts, and two waveform equalizers described later in the RF amplifier 12. And a system controller 18 for controlling supply of a pickup signal to the system.
[0024]
The RF amplifier 12 adds all four detection signals from, for example, a four-divided photodetector of the pickup 11, and switches between an arithmetic unit 20 that generates an RF signal and an RF signal from the arithmetic unit 20 under the control of the system controller 18. The switch 21, the DVD waveform equalizer 22 that modifies the signal waveform of the DVD RF signal supplied by switching the switch 21 to reduce waveform interference, and the CD RF signal supplied by switching the switch 21 Presence / absence of signal by shaping CD waveform equalizer 23 for estimating and calculating signal waveform by class classification application processing described later, and RF signal from DVD waveform equalizer 22 or CD waveform equalizer 23 The focus error signal FE is detected by using a shaper 24 that converts the signal into a pulse signal that represents a predetermined value and a predetermined detection signal from the quadrant photodetector A focus error detection circuit 25, and a tracking error detection circuit 26 for detecting a tracking error signal TE using a predetermined detection signal as well.
[0025]
The servo processing circuit 16 includes a focus control circuit 30, a tracking control circuit 31, and a slide control circuit 32. Based on a focus error signal, a tracking error signal, and the like from the RF amplifier 12, the focus servo and tracking of the pickup 11 are performed. Servo signals for performing servo and slide servo are sent to the focus driver 34, tracking driver 35 and slide driver 36. The servo processing circuit 16 also has a spindle control circuit 33 and sends a spindle servo signal to the spindle driver 37.
[0026]
The focus driver 34 and the tracking driver 35 move the objective lens of the pickup 11 in the focus direction and the tracking direction according to each servo signal from the servo processing circuit 16. Further, the slide driver 36 slides the pickup 11 via the slide motor 38 in accordance with the slide servo signal. The spindle driver 37 controls the rotation of the spindle motor according to the spindle servo signal.
[0027]
In the optical disk reproducing apparatus 10 having such a configuration, when the system controller 18 determines whether the mounted optical disk 1 is a DVD or a CD after being set to the reproduction mode, the movable piece c of the switch 21 is covered. Connected to either the selection terminal a or b, the RF signal for DVD or CD from the computing unit 20 is sent to the waveform equalizer 22 for DVD or the waveform equalizer 23 for CD. Here, the system controller 18 may determine the CD or the DVD by measuring the substrate thickness of the optical disk 1 when the optical disk 1 is mounted, or the CD or the DVD by some detection signal input from the terminal 19. May be judged.
[0028]
For example, when the optical disk 1 is a DVD (hereinafter, the optical disk 1 is referred to as a DVD unless otherwise noted), the system controller 18 connects the movable piece c of the switch 21 to the selected terminal a. Thereafter, the DVD is rotated by the spindle control circuit 33, the spindle driver 37, and the spindle motor 17.
[0029]
The pickup 11 generates laser light for reproduction from a light source (not shown) and condenses it on the recording surface of the DVD by an optical system including an objective lens. The laser beam reflected by the recording surface enters the quadrant photodetector via an optical system including an objective lens.
[0030]
The four-divided photodetector in the pickup 11 supplies a pickup signal corresponding to the intensity of the incident reflected light to the calculator 20, the focus error detection circuit 25, and the tracking error detection circuit 26 in the RF amplifier 12.
[0031]
The computing unit 20 adds all four detection signals from the four-divided photodetectors to generate an RF signal and supplies it to the switch 21. Since the switch 21 connects the movable piece c to the selected terminal a under the control of the system controller 18, the switch 21 supplies the DVD RF signal to the DVD waveform equalizer 22.
[0032]
The DVD waveform equalizer 22 corrects the signal waveform of the DVD RF signal so as to reduce waveform interference and supplies it to the shaper 24. The shaper 24 shapes the DVD RF signal from the DVD waveform equalizer 22, converts it into a pulse signal, and supplies it to the signal processing circuit 13.
[0033]
Since the RF signal from the RF amplifier 12 is, for example, an EFM signal that remains EFM-modulated, the signal processing circuit 13 performs processing such as clock recovery, synchronization detection, data demodulation, error detection / error correction on the EFM signal. To output data. This data is converted into an analog signal by the D / A converter 14 and output through the output terminal 15.
[0034]
Further, the focus error detection circuit 25 of the RF amplifier 12 detects the focus error signal FE using a predetermined detection signal from the quadrant photodetector. The focus error signal FE is supplied to the servo processing circuit 16. Further, the tracking error detection circuit 26 of the RF amplifier 12 detects the tracking error signal TE using a predetermined detection signal from the quadrant photodetector. Since the servo processing in the servo processing circuit 16 using the focus error signal FE and the tracking error signal TE has already been described, it is omitted here.
[0035]
Next, when the optical disk 1 is a CD (hereinafter, the optical disk 1 is referred to as a CD unless otherwise noted), the system controller 18 connects the movable piece c of the switch 21 to the selected terminal b. Thereafter, the CD is rotationally driven by the spindle control circuit 33, the spindle driver 37, and the spindle motor 17.
[0036]
The pickup 11 generates a reproduction laser beam from a light source (not shown) and collects it on the recording surface of the CD by an optical system including an objective lens. The laser beam reflected by the recording surface enters the quadrant photodetector via an optical system including an objective lens.
[0037]
The four-divided photodetector in the pickup 11 supplies a pickup signal corresponding to the intensity of the incident reflected light to the calculator 20, the focus error detection circuit 25, and the tracking error detection circuit 26 in the RF amplifier 12.
[0038]
The computing unit 20 adds all four detection signals from the four-divided photodetectors to generate an RF signal and supplies it to the switch 21. Since the switch 21 connects the movable piece c to the selected terminal b under the control of the system controller 18, the switch 21 supplies the CD RF signal to the CD waveform equalizer 23.
[0039]
The pickup 11 is designed for a DVD. Optically, when reproducing a CD signal using a DVD pickup, wavefront aberration generated due to a difference in substrate thickness defined by the format. The spot cannot be narrowed down sufficiently due to the influence of.
[0040]
Usually, when there is aberration, the spot focused on the CD becomes blurry, so that part of the spot that has reached the front and rear pits causes intersymbol interference, Crosstalk is caused by reaching the track. Therefore, the reproduction signal using the pickup with the aberration is a signal mixed with noise as compared with the case where the signal having no wavefront aberration is used.
[0041]
However, since the recording density differs between the CD and the DVD, it is considered that the influence of the CD spot with a low recording density is small because the spot for the DVD is originally small even with the same wavefront aberration amount. Therefore, the CD signal can be reproduced using the DVD pickup by successfully performing waveform equalization processing by the CD waveform equalizer 23 on the reproduction signal distorted due to deterioration. Therefore, the CD waveform equalizer 23 estimates and calculates the CD RF signal by the class classification application process.
[0042]
As shown in FIG. 2, the CD waveform equalizer 23 includes a blocking circuit 40, an adaptive dynamic range coding (hereinafter referred to as ADRC) circuit 41, a class code generation circuit 42, a prediction coefficient, The memory 43 and the prediction calculation circuit 44 are provided.
[0043]
The CD RF signal supplied via the selected terminal b of the switch 21 is divided by the block forming circuit 40 for every predetermined number of samples, and ADRC circuit 41 applies ADRC to the block unit data from the block forming circuit 40. A class code corresponding to the class determined by the ADRC circuit 41 is generated by the class code generation circuit 42. The prediction coefficient memory 43 uses the class code from the class code generation circuit 42 as an address, and stores a prediction coefficient of a class corresponding to the class code. Then, the prediction calculation circuit 44 performs a calculation based on the prediction formula using the block unit data supplied from the blocking circuit 40 and the prediction coefficient from the prediction coefficient memory 44, and removes the deteriorated RF signal from the deterioration. The output signal is supplied to the output terminal 45 in place of the RF signal.
[0044]
In the prediction coefficient memory 43, a prediction coefficient for accurately predicting a correct reproduction signal is calculated and stored in advance. There, a set of learning is performed for a reproduction signal when a CD signal is reproduced using an optical pickup for DVD and a reproduction signal when a CD signal is reproduced using a CD pickup which is the original value. It is data.
[0045]
In addition, when forming such learning data, a large number of learning data can be formed by using a plurality of disks instead of using only one data, in order to obtain a more accurate prediction coefficient. Learning data can be obtained.
[0046]
Then, in the prediction calculation circuit 44, the RF signal for CD from which the degradation is removed by calculation using a linear linear combination formula using the block unit data supplied from the blocking circuit 40 and the prediction coefficient from the prediction coefficient memory 44. Is supplied to the shaper 24 from the output terminal 45.
[0047]
Here, the reason why ADRC is used to determine the class will be described. The simplest method of class classification is a method in which a bit sequence of learning data in a divided block is used as a class number as it is. However, this method requires a huge amount of memory. For this reason, the input signal is compressed using ADRC, and effective class division is performed by preserving the characteristics of the signal pattern based on the compressed data pattern. This method enables class classification while adaptively removing redundancy in the dynamic range direction.
[0048]
FIG. 3 shows a detailed configuration of the ADRC circuit 41 that performs 1-bit ADRC. In FIG. 3, regarding the data converted into the block order from the input terminal 51, the detector 52 detects the maximum value MAX and the minimum value MIN for each block. MAX and MIN are supplied to the subtractor 53, and a dynamic range DR is generated at the output thereof. The input data and MIN are supplied to the subtractor 54, and the minimum value MIN is removed from the subtractor 54, thereby generating normalized pixel data.
[0049]
The dynamic range DR is supplied to the divider 55, the normalized data is divided by the dynamic range DR, and the output data of the divider 55 is supplied to the comparator 56. The comparator 56 determines whether it is larger or smaller with reference to a predetermined threshold value. Depending on this result, data DT of “0” or “1” is generated. The comparison output DT is taken out to the output terminal 57. Class division may be performed using the 1-bit ADRC.
[0050]
In the prediction calculation circuit 44 of FIG. 2, the correct RF value is obtained by calculation based on the linear linear combination formula, but the correct RF value may be obtained by calculation based on the non-linear combination formula.
[0051]
Returning to FIG. 1, the shaper 24 shapes the CD RF signal estimated by the CD waveform equalizer 23, converts it into a pulse signal, and supplies the pulse signal to the signal processing circuit 13. The signal processing circuit 13 performs processing such as clock recovery, synchronization detection, data demodulation, error detection / error correction on the CD RF signal (EFM signal) and outputs data. This data is converted into an analog signal by the D / A converter 14 and output through the output terminal 15.
[0052]
As described above, the optical disk reproducing apparatus 10 can reproduce a signal of a CD by using a pickup designed for DVD, so that the optical pickup can be simplified, downsized, and reduced in cost.
[0053]
Further, by adopting a configuration in which a CD waveform equalization process is performed when a CD signal having a large margin is formatted using a DVD pickup, even if a compatible playback function for CD and DVD is added, it is formatted. There is no adverse effect on severe DVD.
[0054]
In addition, according to the present embodiment, only one beam is focused at the time of reproducing the disk, so that the light use efficiency can be increased, power consumption can be reduced, and for example, a laser diode serving as a light source can be realized. Therefore, the life of the laser diode can be extended.
[0055]
In addition, the number of objective lenses required for compatible playback of optical disks of multiple formats can be reduced, and there is no need for a mechanism for switching lenses, thus solving the problem of increased weight of moving parts and reducing unnecessary power consumption. Moreover, since the number of parts of the pickup can be reduced, it can be advantageous in terms of cost.
[0056]
Further, in the prediction calculation circuit 44 of the CD waveform equalizer 23, the prediction equation is switched in accordance with the property of the signal for every predetermined time, so that the processing better than the conventional signal processing by one waveform equalizer. A waveform can be obtained.
[0057]
Needless to say, the present invention is not limited to DVD and CD compatible playback.
[0058]
【The invention's effect】
When reproducing information from the other type of optical disk, the optical disk reproducing apparatus according to the present invention performs waveform equalization processing by estimation calculation using class classification adaptive processing on the information for the other optical disk in the information reproducing means. Therefore, when reproducing at least two types of optical disks having different substrate thicknesses, it is possible to prevent deterioration of light utilization efficiency, to reduce power consumption and extend the life of the laser, and to achieve downsizing and cost reduction.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical disc reproducing apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a detailed configuration of a main part of the optical disc playback apparatus.
FIG. 3 is a block diagram used to describe an ADRC circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical disk (DVD or CD), 10 Optical disk reproducing | regenerating apparatus, 11 Pickup, 12 RF amplifier, 18 System controller, 22 Waveform equalizer for DVD, 23 Waveform equalizer for CD

Claims (4)

In an optical disc reproducing apparatus for reproducing information recorded on at least two types of optical discs having different thicknesses,
An optical pickup designed for one of the at least two types of optical discs;
Information reproducing means for performing different waveform equalization processing on the pickup signal from the optical pickup according to one or the other of the at least two types of optical discs,
When reproducing information from the other type of optical disc, the information reproducing means causes the information for the other optical disc to be subjected to waveform equalization processing by estimation calculation using class classification adaptive processing. Playback device. The class classification adaptive processing divides a pickup signal from the other type of optical disc, detects a signal level pattern for each divided signal, classifies the class based on the detected pattern, in advance based on the obtained prediction coefficients by learning, an optical disk reproducing apparatus according to claim 1, wherein the calculating the optimum estimated values. 3. The optical disk reproducing apparatus according to claim 2 , wherein the class classification adaptive processing classifies the class by adaptive dynamic range encoding.   2. The optical disc reproducing apparatus according to claim 1, wherein the substrate thickness of the one type of optical disc is smaller than the substrate thickness of the other type of optical disc.

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