JPH06325397A - Optical disk device - Google Patents

Abstract

PURPOSE:To enhance the precision and the stability in tracking control by suppressing a false signal component in a tracking error signal due to the movement of an objective lens. CONSTITUTION:In an optical disk device reproducing an optical disk with a revolving-shaped information track by an optical head, the outputs of two photodetectors belonging to the same side for one side division line 7Y of quadripartite photodetector 7 photoelectrically converting a reflection beam from the optical disk 1 are multiplied respectively. From the difference of these two multiplication results, a first temporary tracking error signal E1 is detected, and the outputs of two photodetectors belonging to the same side for one side division line 7Y are added respectively, and from the difference of these two addition results, a second temporary tracking error signal E2 is detected. By synthesizing these first, second temporary tracking error signals, the false signal component is suppressed, and the objective lens 6 is controlled by the signal EO with high precision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for reproducing an optical disk having a circular information track formed by concave information pits, and more particularly to a tracking control circuit therefor.

[0002]

2. Description of the Related Art A first example of a conventional optical disk device will be described with reference to FIG. FIG. 2 is a diagram showing a first example of a conventional optical disk device. In the figure, reference numeral 1 denotes an optical disk having a number of information tracks arranged in a circular shape, and a part of the cross section of the optical disk cut in the radial direction is shown. 2 is a light source such as a semiconductor laser, 3 is the light source 2
A collimating lens for collimating the light beam from the light source 2 into a parallel light beam; It is a quarter-wave plate that rotates the polarization direction of the reflected light flux R by 90 °.

P is a light spot condensed by the objective lens 6, and 11 is the objective lens 6 for the optical disk 1.
Tracking actuator for moving the light spot P in a direction (hereinafter, also referred to as a radial direction) X orthogonal to the direction Y of the information track by moving the light spot P in the radial direction of the above. A light-collecting lens 7 is a four-division photodetector for receiving the light beam from the light-collecting lens 15 and performing photoelectric conversion. The photodetector 7 is divided by a dividing line 7Y corresponding to the center line of the information track and a dividing line 7X orthogonal to the dividing line 7Y to form four photodetectors 7a, 7b, 7c and 7d.

Reference numeral 31 is a summing amplifier for amplifying and adding the output signals B and C of the photodetectors 7b and 7c belonging to one side of the dividing line 7Y, and 32 is a photodetector belonging to one side of the dividing line 7Y. A summing amplifier for amplifying and adding the output signals D and A of 7d and 7a, and 35 is an output signal 34 of the summing amplifier 32.
A subtracter 10 for subtracting the output signal 33 of the summing amplifier 31 from is a tracking drive circuit for driving the tracking actuator 11 including a low-pass filter. The light source 2, the collimator lens 3, and the
Polarization beam splitter 4, quarter wavelength plate 5, objective lens 6, tracking actuator 11, condenser lens 1
The 5- or 4-division photodetector 7 is integrally configured as an optical head for reading information pits (hereinafter, also simply referred to as pits) formed on the optical disc.

Information tracks are concentrically or spirally formed on the reflection film surface 12 of the optical disc 1.
There are many information pits (pits) 13 on this information track.
Is carved in a concave shape. FIG. 3 is a diagram showing a part of the information track. In the figure, a large number of information pits are formed on the information track provided on the optical disc.
A pit row is formed by 13, and a land portion 14 is provided between the pits. The four-division photodetector 7 is divided into four photodetectors by the orthogonal division lines 7Y and 7X. The four-division photodetector 7 is placed such that the division line 7Y is the center of the reflected light beam from the beam splitter 4, and the direction of the information track projected on the photodetector 7 (hereinafter, also referred to as the track direction). Note)
Y and the direction of the dividing line 7Y are arranged so as to correspond to each other. Therefore, the dividing line 7X of the photodetector 7 corresponds to the radial direction X of the optical disc 1.

The optical disc device shown in FIG. 2 employs a so-called push-pull method as its tracking control method. The operation related to the tracking control will be described below. In FIG. 2, the light beam generated from the light source 2 is converted into a parallel light beam by the collimator lens 3, passes through the polarization beam splitter 4, and reaches the quarter wavelength plate 5. In the quarter-wave plate 5, linearly polarized light is converted into circularly polarized light, which is condensed in a spot shape by the objective lens 6 and focused on the reflection film surface 12 of the optical disc 1.

Since a pit 13 is formed on the reflecting film surface 12, when the light spot P is on the pit 13, the light beam is diffracted and scattered, and the objective lens 6
The amount of light collected at is smaller than when the light spot P is on the land portion 14. Further, the circularly polarized light beam is reflected with the same rotation, and the turning direction is reversed with respect to the traveling direction. This inverted light beam is 1/4
Polarization beam splitter 4 converted into linearly polarized light by wave plate 5
Is reflected by the condenser lens 15 and condensed by the condenser lens 15.
It is incident on the split photodetector 7.

In this type of optical disk device, the deviation between the center of the track and the center of the beam spot (hereinafter, the deviation between the center of the light spot and the center of the information track is referred to as a tracking error) is detected. The light beam reflected and diffracted by the pits is received by at least a pair of photodetectors symmetrically arranged on the dividing line of the photodetector corresponding to the track center, and the output difference between the pair of photodetectors is extracted. Is the basis. That is, when the center of the light spot P is on the center line of the pit 13 in the track direction, a reflected diffracted light distribution symmetrical to the dividing line corresponding to the track direction is obtained, and otherwise, asymmetric. Light distribution.

As described above, when the center of the light beam spot is deviated from the center of the track, the center of the pit row is deviated with respect to one dividing line Y of the photodetector.
The difference in the amount of light received by the detectors 7a and 7b or the difference in the amount of light received by 7c and 7d of the four-division photodetector 7 depends on the deviation of the pits with respect to the beam spot.
In FIG. 2, in the summing amplifier 31, two photodetectors 7 on the same side of the dividing line 7Y of the photodetector 7 are included.
Output signals B and C corresponding to the respective received light amounts of b and 7c
Are amplified and added.

Similarly, in the summing amplifier 32, two photodetectors d and 7 on the same side of the dividing line 7Y of the photodetector 7 are provided.
The respective output signals D and A corresponding to the respective light receiving amounts of a are amplified and added. In the subtractor 35, the summing amplifier 31
Output signal 33 from the output signal 34 of the summing amplifier 32
Is subtracted. The output of the subtractor 35 is taken out as a tracking error signal E2 indicating a tracking error and supplied to the tracking drive circuit 10. In this tracking drive circuit 10, high frequency components are removed by a low pass filter, and the tracking actuator 1
1 is controlled so that the center of the light spot P always illuminates the center of the track.

Next, a second example of the conventional optical disk device will be described with reference to FIG. FIG. 4 is a diagram showing a second example of a conventional optical disk device, which is disclosed in Japanese Patent Application No.
The apparatus proposed by No. 40356 is shown. In FIG. 4, the same components and the same signals as those in FIG. 2 and the same signals are designated by the same reference numerals, and the description thereof will be omitted. The optical head and the optical disc 1 shown in FIG. 4 are the same as those shown in FIG. 2, and the positional relationship between the four-division photodetector 7 and the optical disc 1 is also the same. In FIG. 4, signals B, C, D, and A are output signals of the four photodetectors 7b, 7c, 7d, and 7a of the four-division photodetector 7, and their AC components are b and c, respectively. , D, a.

The signals B, C, D and A are applied to and amplified by the AC amplifiers 21, 22, 23 and 24, respectively. The outputs of the AC amplifiers 21 and 22 are applied to a multiplier 25 and multiplied, and the outputs of the AC amplifiers 23 and 24 are multiplied by the multiplier 2.
6 is applied and multiplied. The subtractor 29 outputs the output signal 28 of the multiplier 25 from the output signal 28 of the multiplier 26.
7 is subtracted. The output of the subtractor 29 is taken out as a tracking error signal E1 indicating a tracking error and applied to the tracking drive circuit 10.

In the tracking drive circuit 10, after the high frequency component of the tracking error signal E1 is removed by the low pass filter, the tracking actuator 11 is controlled by this signal. By the way,
Alternatively, in the conventional optical disk device as shown in FIG. 4, since the optical disk 1 has an inclination caused by surface wobbling or warpage, the surface of the optical disk is not perpendicular to the optical axis of the light beam, which is a tracking error. There is a problem that a false signal is generated in the signal, the accuracy and stability of the tracking control are reduced, and the allowable tilt value of the optical disc in the tracking control is reduced.

When the objective lens 6 is driven in the radial direction of the optical disc 1 during tracking control,
There is also a problem that the center position of the reflected light R shifts and the light amount of the laser light incident on the photodetector 7 becomes unbalanced, and a false signal due to this is detected by being superimposed on the tracking difference signal. Further, during the tracking operation, the objective lens 6 is moved in the radial direction of the optical disc 1 via the tracking actuator 11 so that the light spot is always scanned on the center line of the information track of the optical disc 1. In this case, the center position of the reflected light R shifts, the light amount of the laser light incident on the photodetector 7 becomes unbalanced, and a false signal due to lens shift is superimposed on the tracking error signals E2 and E1. .

The amplitude and characteristics of the false signal due to the lens shift depend on the depth of the information pit formed on the optical disc and the detection method of the tracking error signal. The relationship between the depth of the information pit, the tracking error detection method, and the tracking error signal will be described below with reference to FIGS.
It will be explained based on. FIG. 5 is a diagram showing an example of the tracking error signal when the pit depth is 60 nm, and FIG. 6 is a diagram showing an example of the tracking error signal when the pit depth is 110 nm. In each case, the wavelength λ of the reproducing laser light is 670 nm, the transparent substrate of the optical disc is polycarbonate having a refractive index of 1.59, and the horizontal axis indicates time.

The tracking error signal E2 shown in FIG.
Pit depth is 60 nm (60n when converted to optical depth)
m × 1.59) optical disc 1 was prepared and measured using the optical disc device shown in FIG. 2. The optical disc 1 having a pit depth of 60 nm was subjected to tracking control while rotating at a predetermined speed. This is a case where the state of the tracking error signal E2 is observed while the objective lens 6 that is turned off and controls the position of the laser light spot is moved in the radial direction of the optical disc 1 at a constant speed. Here, the wavelength λ of the laser light is 670 nm, and the objective lens 6 is measured at about 1 HZ while moving within a range of about ± 200 μm from the center. As shown in the figure, the amplitude of the true tracking error signal indicating the tracking error is S2, and the amplitude of the false signal component is N2. Here, the point where the false signal reaches a peak coincides with the point where the objective lens 6 has moved the most from the center.

Similarly, the tracking error signal E1 shown in FIG. 5 is measured by using the optical disc device shown in FIG. 4 after the optical disc 1 having a pit depth of 60 nm is prepared. While rotating the 60 nm optical disc 1 at a predetermined speed, the tracking control is turned off, and the objective lens 6 for controlling the position of the laser beam spot is moved at a constant velocity in the radial direction of the optical disc 1,
This is a case where the state of the tracking error signal E1 is observed. Here again, the wavelength λ of the laser light is 670 nm, and the objective lens 6 is about 1 HZ and about ± 200 μm from the center.
It is measured while moving in the range. In this case, the amplitude of the true tracking error signal indicating the tracking error is S1, and the amplitude of the false signal component is N1.

Here, S1 / N1 corresponding to the signal-to-noise ratio (hereinafter, also referred to as S / N) was 1 / 0.08.
This S / N is S / N of the signal E2 as is clear from FIG.
It is a much better value than N. However, when the tracking error signal as described above is measured by changing the pit depth of the optical disc 1 without changing the optical head,
It can be seen that the state of the tracking error signal E1 changes according to the pit depth. That is, the depth of the information pit was changed from 60 nm to 110 nm by changing the thickness of the transparent substrate of the optical disc 1. As a result, the S / N of the tracking error signal E2 does not change significantly depending on the pit depth, but the S / N of the tracking error signal E1 does not change.
Varies greatly depending on the pit depth.

For example, when the pit depth is 75 nm, the S / N of the tracking error signal E1 is 1 / 0.29, and when the pit depth is 90 nm and 110 nm, the S / N of the tracking error signal E1 is 1. It was /0.46. By the way, the pit depth of music compact discs currently on the market is about 110 nm, and the wavelength λ of the reproduction laser light is about 780 nm. The reproduction is performed by setting the height to 60 nm and shortening the wavelength λ of the reproduction laser light to 670 nm.

[0020]

As described above, in the conventional optical disk device, a false signal resulting from the movement of the objective lens is superimposed on the tracking error signal, and the signal-to-noise ratio of the tracking error signal is poor. However, there has been a problem that the accuracy and stability of tracking control in the optical disk device deteriorates. The present invention has been made in view of the above problems, and provides an optical disc device that suppresses a false signal component of a tracking error signal due to movement of an objective lens and improves accuracy and stability in tracking control. The purpose is to do.

[0021]

In the optical disk device of the present invention, the reflected light from the optical disk having concave information pits provided in a circular shape is divided into four divisions in which one division line corresponds to the center line of the information track. An optical disc device configured to receive light by a photodetector, wherein outputs of two photodetectors belonging to the same side with respect to the one division line are multiplied by each other among outputs of the four-division photodetector. Then, the first tracking error detecting means for detecting a tracking error from the difference between the two multiplication results and the two of the outputs of the four-division photodetector belonging to the same side with respect to the one division line. The second tracking error detecting means for adding the outputs of the photodetectors and detecting the tracking error from the difference between the two addition results, and the first and second tracking error detecting means. A synthesizing means for synthesizing force,
This is an optical disk device in which the tracking actuator is driven according to the output of the combining means to control the objective lens.

[0022]

Out of the outputs of the four-division photodetector in which one of the division lines corresponds to the center line of the information track, the outputs of two photodetectors belonging to the same side with respect to the one division line are respectively output. The first provisional tracking error signal is obtained from the difference between the two multiplication results, and two light detections belonging to the same side with respect to the one division line among the outputs of the four-division photodetector are obtained. The outputs of the devices are added together, and a second provisional tracking error signal is obtained from the difference between the two addition results. A false signal resulting from the movement of the objective lens is superimposed on the first and second provisional tracking error signals. In this case, assuming that the true signal components in the two provisional tracking error signals have the same polarity, the false signal has the opposite polarity, so that the first and second provisional tracking error signals are combined. In the tracking error signal obtained as described above, since the false signal components are canceled and suppressed, the signal-to-noise ratio of the tracking error signal is improved as compared with the first or second tentative tracking error signal, The tracking control in the optical disk device becomes extremely stable and highly accurate.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical disk device of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing a main part of an embodiment of an optical disk device of the present invention. In FIG. 1, the same components and the same signals as those in FIG. 2 or FIG. 4 and the same signals are designated by the same reference numerals and the description thereof will be omitted. The optical head shown in FIG. 1 and the optical disc 1 are the same as those shown in FIGS. 2 and 4, and the positional relationship between the four-division photodetector 7 and the optical disc 1 is also the same.

In the embodiment of the optical disc apparatus of the present invention shown in FIG. 1, the reflected light from the optical disc 1 on which the information pits are formed is received by the four-division photodetector 7 to detect the first tracking error. The first provisional tracking error signal E1 is detected by the means T1, and the second provisional tracking error signal E2 is detected by the second tracking error detection means T2.
Is detected. Then, the first temporary tracking error signal E1 and the second temporary tracking error signal E2 are combined by the combiner 36, and the tracking error signal E0 in which the false signal is suppressed is detected.

In FIG. 1, four photodetectors divided by a division line 7Y corresponding to the track direction Y of the four-division photodetector 7 and a division line 7X corresponding to the radial direction X, Signals B, C, 7b, 7c, 7d, 7a
D and A are output respectively. The detection of the first provisional tracking error signal E1 is performed by the first tracking error detection means T1 by calculating the AC components b, c, d, a of the signals B, C, D, A. The detection of the two temporary tracking error signals E2 is performed by detecting the signals B, C, D,
The calculation of A is performed by the second tracking error detection means T2.

A false signal generated by the movement of the objective lens 6 during tracking control is superimposed on the true signal component indicating the tracking error on the first and second temporary tracking error signals E1 and E2. It The first
Of the false signal included in the temporary tracking error signal E1 and the false signal included in the second temporary tracking error signal E2 have opposite polarities.
By canceling the two false signals at 6, a tracking error signal E0 having a good signal-to-noise ratio is obtained,
The tracking error signal E0 is applied to the tracking drive circuit 10 that drives the tracking actuator 11.

In the tracking drive circuit 10, the tracking error signal E0 has its ripple removed and amplified by a low pass filter, and its output is supplied to the tracking actuator 11. The objective lens 6
Are moved in the radial direction of the optical disc 1 according to the output of the tracking drive circuit 10 via the tracking actuator 11 during tracking control.

The first and second temporary tracking error detecting means T1 and T2 will be described below. The first,
The second tracking error detecting means is configured as shown by the chain line in FIG. 1, and will be described in detail below. Figure 1
In this case, the signals B, C, D, and A are the four-division photodetector 7
Of the four photodetectors 7b, 7c, 7d, and 7a, whose AC components are (not shown) b and
c, d and a.

The first tracking error detecting means T1
Then, among the outputs of the four photodetectors of the photodetector 7,
Photodetector 7 belonging to the same side with respect to the dividing line 7Y
The outputs B and C of b and 7c are amplified by the AC amplifiers 21 and 22, respectively, and the outputs D and A of the photodetectors 7d and 7a belonging to the same side with respect to the dividing line 7Y are respectively amplified by the AC amplifiers 23 and 24. Is amplified. The outputs of the AC amplifiers 21 and 22 are applied to and multiplied by a multiplier 25, respectively.
The outputs of 3 and 24 are applied to the multiplier 26 and multiplied, respectively.

The subtractor 29 subtracts the output signal 27 of the multiplier 25 from the output signal 28 of the multiplier 26. The output of the subtractor 29 is applied to the combiner 36 as the first provisional tracking error signal E1. In the second tracking error detecting means T2, among the outputs of the four photodetectors of the photodetector 7, the outputs B and C of the photodetectors 7b and 7c belonging to the same side with respect to the dividing line 7Y. Is amplified and added by the addition amplifier 31, and a signal corresponding to B + C is output to the subtractor 35.

The outputs D and A of the photodetectors 7d and 7a belonging to the same side with respect to the dividing line 7Y are summing amplifier 32.
Then, a signal corresponding to D + A is amplified and added in and input to the subtractor 35. Here, the connection between the summing amplifiers 31 and 32 and the quadrant photodetector 7 is not shown. The subtractor 35 subtracts the output signal 34 of the adding amplifier 32 from the output signal 33 of the adding amplifier 31. The output signal of the subtractor 35 is the second provisional tracking error signal E.
2 and is output to the combiner 36. The output of the synthesizer 36 is supplied to the tracking drive circuit 10 as a tracking error signal E0. In this tracking drive circuit 10, the high frequency component of the tracking error signal E0 is removed by a low pass filter, and the tracking actuator 11 is driven by its output,
The center of the light spot P is controlled so as to always illuminate the center of the track.

In the above-mentioned first provisional tracking signal E1, when the reproduction signal intensity is maximized, that is, when the optical depth of the pit is λ / 4 (λ is the wavelength of the laser light source),
The amplitude S1 of the true signal component of the temporary tracking signal E1 is maximized, and in the above-described second temporary tracking signal E2, the true signal component of the temporary tracking signal E2 is obtained when the optical depth of the pit is λ / 8. Has the maximum amplitude S2. On the other hand, the amplitudes N1 and N2 and the polarities of the false signal components change in relation to the modulation degree of the pits of the optical disc and the optical depth of the pits.

Therefore, the combiner 36 calculates E1 + k × E2 with respect to the first temporary tracking error signal E1 and the second temporary tracking error signal E2. Here, k is set to N1 / N2 so that the false signal superimposed on the first temporary tracking error signal E1 and the false signal superimposed on the second temporary tracking error signal E2 are exactly canceled. In practical terms,
The value of k is set in the range of 0.05 to 2. The output of the synthesizer 36 is input to the tracking drive circuit 10 as a true tracking error signal E0.

As described in the conventional example, the circuit is constructed such that the first temporary tracking signal E1 and the second temporary tracking signal E2 have the same polarity in the signal component indicating the true tracking error. If the objective lens 6
Since the polarities of the false signals superimposed with the movement of S are opposite, as shown in FIGS. 5 and 6, the output of the synthesizer 36 suppresses the false signals due to the movement of the objective lens, and S A tracking error signal with a good / N is obtained.

That is, the false signal caused by the shift of the objective lens 6 is detected by the first tracking error signal E1 detected by the first tracking error detection means T1 and the second tracking error detection means T2. The second tracking error signal E2 is
1, the polarities of the false signals included in E2 are opposite to each other. Therefore, when the combiner 36 adds the signals E1 and E2 at an appropriate ratio, for example, a true tracking as shown in FIG. 6 is performed. Since the signal components S1 and S2 indicating an error are added to increase the amplitude and the false signal components N1 and N2 cancel each other out, the tracking error signal EO in which the false signal components are suppressed
Is obtained.

By using the tracking error signal EO, good tracking control can be performed even when reproducing an optical disc recorded at high density.
Further, even when reproducing the currently popular compact disc for music with deep pits using an optical head for reproduction of a high-density optical disc having a small information pit depth, extremely good tracking control can be performed. As is clear from the above description, in the disk device of the present invention, since the false signal superimposed on the two provisional tracking error signals due to the shift of the objective lens is suppressed, the tracking error with a high signal-to-noise ratio is suppressed. A signal can be obtained, and accuracy and stability in tracking control can be improved.

[0037]

As described above in detail, according to the optical disc apparatus of the present invention, two tentative tracking error signals are respectively detected, and when these two signals are combined, the false signal component is canceled. Since they are suppressed together, a highly accurate tracking error signal can be obtained, and an optical disk device with greatly improved accuracy and stability in tracking control can be obtained. Further, by using the reproducing optical head for the high density optical disk, it is possible to reproduce the general compact disk for music very stably.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of an embodiment of an optical disk device of the present invention.

FIG. 2 is a diagram showing a first example of a conventional optical disc device.

FIG. 3 is a diagram showing a part of an information track.

FIG. 4 is a diagram showing a second example of a conventional optical disc device.

FIG. 5 is a diagram showing a tracking error signal when the pit depth is 60 nm.

FIG. 6 is a diagram showing a tracking error signal when the pit depth is 110 nm.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 optical disk, 2 laser light source 6 objective lens, 7 4 division | segmentation photodetector 11 tracking actuator 21-24 AC amplifier, 25, 26 multiplier 31, 32 adder (adding amplifier) 29, 35 subtractor, 36 combining means (composite) E0 tracking error signal E1 first temporary tracking error signal E2 second temporary tracking error signal T1 first tracking error detecting means T2 second tracking error detecting means

Claims (1)

[Claims] 1. An optical disk device for reproducing an optical disk having a circular information track by using an optical head, and a tracking actuator for moving a laser beam spot on the optical disk in a radial direction of the optical disk, A four-division photodetector for photoelectrically converting the reflected light from the optical disc by making one division line correspond to the center line of the information track, and one of the division lines of the output of the four-division photodetector Of the outputs of the four-division photodetector, a first tracking error detection unit that multiplies the outputs of two photodetectors belonging to the same side, and detects a tracking error from the difference between the two multiplication results. , The outputs of two photodetectors belonging to the same side with respect to the one dividing line are respectively added, and from the difference between the two addition results, A second tracking error detecting means for detecting a tracking error and a synthesizing means for synthesizing the outputs of the first and second tracking error detecting means are provided, and the tracking actuator is controlled according to the output of the synthesizing means. An optical disk device characterized by the above.