JPH0887758A - Optical disk device - Google Patents

Abstract

PURPOSE: To obtain a constant tracking error signal in which an offset is small by receiving the reflected light from an optical disk with necessary quadripartite optical detectors and generating the tracking error signal obtained by processing the detection outputs with BPFs, multipliers and a subtracter. CONSTITUTION: The reflected light from an optical disk 12 irradiated with a spot light irradiation is received with light detectors 1711 and 17<12> , 17r1 and 17r2 quadri-sected in a track direction and the direction perpendicular to the track direction and the detection output of detectors 1711 and 1712 and the detection output of detectors 17r1 and 17r2 are respectively added in adders 271 , 27r to become tracking components-Low frequency components including offset components of these components are eliminated with HPFs 181 , 18r and processed with multipliers 19. 19 performing squaring operations a subtrator 20 and the tracking error signal is generated By this constitution, the stable tracking error signal in which the offset due to the moving of an objective lens and the inclination of the optical disk, etc., is small is obtained and therefore, this device can cope with a high density optical disk.

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,
In particular, it relates to a tracking error signal detection method.

[0002]

2. Description of the Related Art Generally, in an optical disc apparatus which irradiates an optical disc with a light beam as a minute light spot and detects the reflected light to perform reproduction, there is a tracking control in which the light spot accurately follows an information track on the optical disc. This is necessary, and for this purpose, it is necessary to detect a tracking error signal indicating an error in the irradiation position of the light spot on the information track.

A push-pull method (optical disk technology, supervised by Morio Onoue, Radio Technology Co., p.86) is one of typical methods of tracking error signal detection methods used in conventional optical disk devices. This method will be briefly described with reference to FIG. The light generated from the light source 13 such as a semiconductor laser is used by the collimator lens 1
It becomes a parallel light flux via 4 and enters the beam splitter 15. The light transmitted through the beam splitter 15 is condensed by the objective lens 16 and irradiated as a fine light spot on the information recording surface 11 of the optical disc 10. The light applied to the optical disc 10 is reflected by the information recording surface 11,
It passes through the objective lens 16 and enters the beam splitter 15 again. The light reflected by the beam splitter 15 is photoelectrically converted by the photodetector 22, and a tracking error is detected by calculation from this signal.

The photodetector 22 has a light receiving surface divided into two light receiving regions 22l and 22r by a dividing line 22Y.
The dividing line 22Y is arranged parallel to the direction of the information track projected on the photodetector 22 (hereinafter, simply referred to as the track direction on the photodetector surface). If the center of the light spot coincides with the center of the information track 12 (mark row such as pit row or guide groove) formed in a spiral or concentric shape on the information recording surface 11 of the optical disc 10, 2
The magnitudes of the signals obtained from the two light receiving regions 22l and 22r are equal, but when they are deviated, the balance of the signals obtained from the two light receiving regions 22l and 22r is lost depending on the deviating direction and the amount of deviating. . Therefore, the tracking error signal can be detected by taking the difference between the signals obtained from the two light receiving regions 22l and 22r by the differential amplifier 20.

As described above, in the push-pull method, the tracking error signal can be detected by a simple system using a two-divided photodetector, so that it is suitable for reducing the cost of the device. Widely used in.
The problems of the push-pull method have also been analyzed in detail, and if there is an inclination of the optical disc in the radial direction or movement of the objective lens in the optical disc radial direction due to tracking operation, etc. It is known that the tracking error signal does not become zero even if there is a light spot. The signal detected at this time is called an offset of the tracking error signal. If such an offset is included in the tracking error signal, the light spot will be an information track according to the amount of offset when tracking control is applied. You will pass through a position deviated from. In order to reproduce accurate signal reproduction, this track deviation must be suppressed to a certain value or less, and the amount of offset generated needs to be less than a certain value with respect to the amplitude of the tracking error signal.

On the other hand, in order to increase the recording density of the optical disk, it is necessary to narrow the track pitch. For example, if the track pitch is narrowed without changing the size of the light spot, the resolution of the optical system is lowered. Therefore, the amplitude of the tracking error signal is reduced. In short, in the device using the narrow track pitch optical disc,
The conventional problems become more serious problems.

As a method of solving this problem, by improving the control method, the relative angle between the optical disk and the optical pickup caused by the movement of the objective lens (hereinafter referred to as the objective lens shift) or the tilt of the optical disk, which is the cause of the offset. There are two types of methods considered: a method for suppressing the value of a constant value or less, and a method for realizing a tracking error detection method in which an offset does not occur even if there are these factors causing the offset.

The former is mainly the conventional solution. For example, a separate system is used as the optical system of the optical pickup and a two-stage servo is used for tracking control to reduce the amount of movement of the objective lens, or a mechanism for controlling the tilt of the optical pickup is provided to match the tilt of the optical disc. It has been reported that the tilt of the optical pickup is adjusted to reduce the influence of the tilt of the optical disc. However, although these methods have been individually put to practical use, it is difficult to realize both mechanisms at the same time, and even if they can be realized at the same time, they cannot be applied to an optical disc with a narrow track pitch that has severe requirements. difficult.

As for the latter method, a tracking error detection method (hereinafter referred to as a multiplication method) which is a combination of the push-pull method and the heterodyne method has been proposed. (The 54th Annual Meeting of the Applied Physics Society of Japan: 28a-
SF-16) This multiplication method uses a 4-division photodetector,
One of the dividing lines on the light receiving surface is aligned with the track direction, and two regions on one side are defined as regions A and D, and the other two regions on the other side are defined as regions B and C with the dividing line as a boundary.
When the output signals from B, C and D are signals A, B, C and D, the tracking error signal (T
ES) is generated.

TES = A × D−B × C (1) According to a report of the Japan Society of Applied Physics, if the tracking error signal is obtained by this calculation, the track pitch is 0.72 μm.
m, laser wavelength 670 nm, numerical aperture of objective lens 0.6
It has been shown that the 0 system produces almost no offset for a 400 μm objective shift. However, in reality, it is not possible to remove the effects described below among the effects of the objective lens shift by simply performing the calculation of the expression (1). That is, the deviation of the light intensity caused by the shift of the objective lens in the radial direction of the optical disc occurs with respect to the direction perpendicular to the direction of the information track on the photodetector, and for example, a division line parallel to the direction of the information track is formed. If the A and D sides become stronger with the sandwich, B and C
It becomes weaker on the side, weaker on the A and D sides, and stronger on the B and C sides. This effect is emphasized by multiplication in the course of the calculation shown in the equation (1), and an offset occurs in the tracking error signal.

[0011]

As described above, in the push-pull method, which is one of the conventional tracking error signal detection methods, when the tilt of the optical disk in the radial direction of the optical disk or the objective lens shift due to the tracking operation causes an error signal to be offset. Occurs, and there is a problem in that the track following accuracy decreases. Several methods have been proposed for suppressing the cause of offset, but a method that can realize stable tracking control even for an optical disc with a narrow track pitch has not yet been known. On the other hand, a method of detecting an error in which an offset hardly occurs is also proposed,
There is an offset generation factor whose influence cannot be removed even by this method, and an offset depending on this factor remains.

The present invention provides an optical disc apparatus capable of detecting a tracking error signal which enables a stable tracking control with a small offset due to the movement of the objective lens or the inclination of the optical disc even for an optical disc having a narrow track pitch. The purpose is to provide.

[0013]

In order to solve the above-mentioned problems, the present invention relates to a plurality of output signals of a 4-division photodetector or 2-division photodetector for tracking error detection,
The essence is to generate a tracking error signal by performing a calculation process including a high-pass filter process for removing a signal component in a low frequency region including an offset component.

That is, according to the first aspect of the invention, the light from the light source is focused on the information recording surface of the optical disc having the information track to irradiate a light spot on the information track, and the reflected light from the optical disc is detected by a photodetector. Then, in the optical disc device that detects the tracking error from the output signal,
As a photodetector, the light receiving surface has a light receiving region divided into four by a first dividing line along a direction corresponding to the information track direction of the optical disc and a second dividing line substantially orthogonal to the first dividing line. A split photodetector is used, and a set of signals with the first and second light receiving regions on one side with the first split line of the photodetector as a boundary and the third and fourth sets on the other side. Then, the difference between the two signals, which have been subjected to addition processing, high-pass filtering processing, and squaring processing processing for each set of output signals in the light receiving area, is generated as a tracking error signal indicating an error in the irradiation position of the light spot with respect to the information track. It is characterized by

According to a second aspect of the invention, the same four-division photodetector as that of the first aspect is used as the photodetector, and the first division line on one side of the first division line of the photodetector is a boundary. The difference between two signals obtained by high-pass filtering and multiplying the pair of signals from the two light-receiving areas and the pair of output signals from the third and fourth light-receiving areas on the other side is used as a tracking error. It is characterized in that it is generated as a signal.

According to a third invention, the same four-division photodetector as that of the first invention is used as the photodetector, and the first and the first ones on one side with the first division line of the photodetector as a boundary. The high-pass filtering process and the phase of each highest repetition frequency component are respectively added to the pair of signals of the two light-receiving areas and the pair of output signals of the third and fourth light-receiving areas on the other side, and the phases are multiplied. It is characterized in that the difference between the two signals subjected to the multiplication processing is generated as a tracking error signal.

According to a fourth aspect of the invention, the same four-division photodetector as that of the first aspect is used as the photodetector, and the first division line on one side is the first division line of the photodetector as a boundary. The signal set of the two light-receiving regions and the signal set of the output signals of the third and fourth light-receiving regions on the other side are binarized and then subjected to an exclusive OR operation to obtain two signals. The difference is generated as a tracking error signal.

A fifth aspect of the present invention is a photodetector which is a two-divided photodetector having first and second photodetection regions whose light-receiving surface is divided by dividing lines along a direction corresponding to the information track direction of the optical disc. It is characterized in that a difference is generated as a tracking error signal between two signals obtained by subjecting the output signals of the first and second light receiving regions of this photodetector to high pass filter processing and square calculation processing, respectively. .

According to a sixth aspect of the invention, the same two-divided photodetector as that of the fourth aspect is used as the photodetector, and high-pass filters are respectively applied to the output signals of the first and second light receiving regions of the photodetector. The difference between the two signals subjected to the processing and the absolute value calculation processing is generated as a tracking error signal.

In the present invention, as the high-pass filter processing applied to the output signal of each light receiving region of the photodetector,
It is desirable to use a high-pass filter having a characteristic of sufficiently attenuating a signal within the tracking control band, or a high-pass filter having a characteristic of sufficiently attenuating at least the frequency component of the rotational speed of the optical disc at a cutoff frequency substantially equal to or less than the tracking control band.

[0021]

As described above, according to the present invention, a signal in a frequency band containing a component that causes a track offset is attenuated or removed by a high-pass filter process with respect to each output signal of a plurality of light receiving regions of a photodetector. By doing so, a tracking error signal with a small offset is generated.

The reason why a tracking error signal with a small offset can be generated by using the high-pass filter processing will be described with reference to FIG. 2 (a) (b)
FIG. 4 shows an example of the spectrum of the information reproduction signal and the spectrum of the amount of movement of the objective lens in the optical disc radial direction.

The offset of the tracking error signal due to the shift of the objective lens has a frequency band at the same level as the tracking control band (0 to f _CH (Hz)) at most. This is because the shift of the objective lens occurs due to the tracking control for following the track shake due to the eccentricity of the optical disk or the shaft shake of the spindle motor. In addition, the offset of the tracking error signal due to the inclination of the optical disc in the radial direction is the number of rotations of the optical disc (f ₀ (H
z)) in the frequency band of several times to several tens of times at most. This is because the inclination of the optical disc in the radial direction is caused by the distortion of the optical disc such as warpage and the shaft runout of the spindle motor, and the frequency component above a certain level can hardly occur.

In the present invention, in the calculation for obtaining the tracking error signal, the signal in the band including these offsets is attenuated or removed by the high pass filter. In this case, if the cutoff frequency (f _C ) of the high pass filter is set so as to cut the signal within the tracking control band (f _CH <f _C <f _SL ), almost all the frequency components of the offset that may exist are removed. be able to.

If the cause of the offset is directly removed in this way, the tracking error signal is not affected by the objective lens shift or the radial tilt of the optical disk. The frequency component of the offset is mainly a fundamental frequency component (a component of the same frequency as the optical disk rotation speed f ₀ (Hz)), so if the cutoff frequency of the high-pass filter is determined so as to remove this frequency component at least. (F ₀ <f _C
<F _SL ), an offset reducing effect can be obtained.

The method using the high-pass filter according to the present invention is very effective in reducing or eliminating the influence of offset, but cannot be applied to the conventional push-pull method. This is because, in the push-pull method, the band of the tracking error signal overlaps the band of the offset, so that the push-pull signal necessary for tracking error detection is also removed by the high-pass filter, and the tracking error signal cannot be obtained.

Therefore, in the present invention, the tracking error signal is a mark (pit) on the optical disk included in the output signal of each light receiving area of the photodetector of two or four divisions having a division line parallel to the information track direction. It is generated from the corresponding information reproduction signal component. Since this information reproduction signal component is in a frequency range (f _{SL to} f _SH (Hz): f _CH <f _SL ) higher than the control band (0 to f _CH (Hz)) for normal tracking, the high pass filter is attenuated. Without passing, it is guided to the arithmetic circuit.

In the arithmetic circuit, when the photodetector is a four-division photodetector, basically, a set of output signals (P) of two light-receiving regions on the same side with respect to a dividing line parallel to the track direction (P).
111, Pl2 pair and Pr1, Pr2 pair) are respectively subjected to high-pass filter processing and square calculation processing (addition and multiplication) or absolute value calculation processing, and then the difference between them is calculated to obtain a tracking error. Generate a signal. In the case of a two-division photodetector, a tracking error signal is generated by performing a high-pass filter process and a square calculation process or an absolute value calculation process on the output signals of the two light receiving regions, and then taking the difference between them. The calculation formulas of these tracking error signals are: TES = (Pl1 + Pl2) ² − (Pr1 + Pr2) ² (2) TES = | Pl1 + Pl2 | − | Pr1 + Pr2 | (3) TES = Pl1 × Pl2 when a four-division photodetector is used. -Pr1 * Pr2 (4) Pl1, Pl2, Pr1, Pr2: a signal obtained by performing high-pass filtering on the four outputs of the photodetector. When using the two-division photodetector, TES = Pl ² −Pr ² (5) TES = | Pl | − | Pr | (6) Pl, Pr: a signal obtained by performing high-pass filtering on two outputs of the photodetector. By performing such a calculation, it is possible to generate a tracking error signal by using a component proportional to the signal amplitude of the information reproduction signal while avoiding the occurrence of an offset due to the inclination of the optical disc in the radial direction by the high-pass filtering process. And stable tracking operation can be realized.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows the configuration of a tracking error detection system according to the first embodiment. This figure shows only the part relating to the tracking error detection of the optical disc, and the other focusing error detection system, the actuator for moving the objective lens, the control circuit, the signal processing circuit, etc. are omitted. In addition, except for the photodetector and the tracking error detection portion after that, it is the same as FIG. 21 described in the related art.

That is, the light emitted from the light source 13 such as a semiconductor laser becomes a parallel light flux through the collimator lens 14 and enters the beam splitter 15. The light transmitted through the beam splitter 15 is focused on the information recording surface 11 of the optical disc 10 by the objective lens 16 and is irradiated onto the information track 12 as a fine light spot. The light applied to the optical disk 10 is reflected by the information recording surface 11, passes through the objective lens 16, and is again reflected by the beam splitter 15
Incident on. The light reflected by the beam splitter 15 is photoelectrically converted by a photodetector 17 placed in the far field,
A tracking error, that is, an error in the irradiation position of the light spot with respect to the information track 12 is detected from this signal as follows, and a tracking error signal is generated.

In this embodiment, the tracking error signal is generated by the calculation shown in equation (2). That is, in the present embodiment, a four-division photodetector is used as the photodetector 17, and four light receiving regions 17l1,1 of this photodetector 17 are used.
7l2, 17r1, 17r2 output signals Pl1 ', Pl
Of 2 ', Pr1', Pr2 ', Pl1' and Pl2 '
Is added by the adder 27l, and Pr1 'and Pr2' are added by the adder 27r.

Then, the output signals of the adders 27l and 27r are passed through high-pass filters 18l and 18r, respectively, to remove frequency components including the radial tilt of the optical disc 10 and the offset due to the movement of the objective lens 16 in the radial direction of the optical disc.

Next, the output signals P1 and Pr of the high-pass filters 18l and 18r are squared by the multipliers 191 and 19r, respectively, to generate a signal component proportional to the signal amplitude, and the subtracter 2
At 0, the difference between the output signals of the multipliers 191 and 19r is calculated. At this stage, since the output signal of the subtractor 20 contains the component of the information reproduction signal, the low-pass filter 21 removes this component to obtain the tracking error signal.

Next, the method of generating the tracking error signal in this embodiment will be described in more detail with reference to FIGS. In FIG. 1, the information recording surface 1 of the optical disk 10
Consider a case in which the light spot on 1 moves over the mark row with time, while diagonally crossing over the mark row. In FIG. 3, 12a to 12c are a plurality of marks 40.
, Tp is an information track interval, 41 and 42 are light spots, and 43 is a locus thereof. The light spot 41 represents the light spot position at time t = 0 in FIGS. 4 to 9 simultaneously showing the signal waveform of each part in FIG. 1, and similarly the light spot 42 represents the light spot position at time t = −5. ing.

In FIG. 1, the light receiving areas 17l1 and 17l2 on one side of the dividing line 17Y parallel to the direction corresponding to the direction of the information track on the photodetector 17 (hereinafter, simply referred to as the track direction). To the first and second regions L1,
L2, the regions 17r1 and 17r2 on the other side are defined as third and fourth regions R1 and R2, and these regions L1 and R2
1, R2, L2 output signals are Pl1 ', Pr1', Pr
2 ′ and Pl2 ′, and signals obtained by passing these signals through filters having the same bandpass characteristics as the high-pass filters 18l and 18r are designated as Pl1, Pr1, Pr2 and Pl2, these are as shown in FIG. 4 and FIG. It has a nice waveform.

In FIG. 1, the high-pass filters 18l and 18r are passed after being added by the adders 27l and 27r, but here, for the sake of explanation, a model in which they are processed by the high-pass filter and then added is used. . It is clear that the result does not change even if the processing order is changed in this way.

From FIG. 5, the dividing line 1 parallel to the track direction
7Y, the output signals (Pl1
And Pl2 or Pr1 and Pr2) are out of phase but the signal amplitudes are almost equal. On the other hand, the output signals (Pl1 and Pr1 or Pr2 and Pl2) of the two areas facing each other with respect to the dividing line 17Y have almost the same phase, but the balance of the signal amplitude depends on the change in the positional relationship between the light spot and the information track. Change. Therefore,
In order to obtain the tracking error signal, it suffices to detect the difference between the signal amplitudes of the output signals of the two regions facing each other with respect to the dividing line 17Y parallel to the track direction.

FIG. 6 shows an example of the signal waveform after addition is performed based on the signals of FIG. Here, Pl = Pl1 + Pl
2, Pr = Pr1 + Pr2. The signal amplitude of the added signal waveform changes in both Pl and Pr due to the change in the positional relationship between the light spot and the information track as before the addition. Therefore, each of them is squared by the multipliers 19l and 19r to form a signal component proportional to the signal amplitude, and then the subtractor 20 takes the difference between the two, and the low-pass filter 21 extracts the signal component. A tracking error signal as shown in FIG. 7 can be obtained.

The cutoff frequencies of the high-pass filters 18l and 18r may be determined so that there is no signal attenuation in the band of the information signal recorded on the optical disk 10 and a large attenuation in the tracking control band. For example, the case where the modulation system of the recorded information signal is the 4/9 modulation system ((3,17) RLL: Run-Length-Limited) and the channel clock (basic clock) is 28.6 (MHz) is taken as an example. Then, the fundamental frequency of the coarsest pattern of the information signal is 0.8 (MHz). In this case, in order to secure 3 kHz as the tracking control band, the cutoff frequency of the high-pass filters 18l and 18r may be about 50 (kHz). The cutoff frequency of the low-pass filter 21 is
On the contrary, there is no signal attenuation in the tracking control band, and the attenuation is determined to be large in the information signal band. In this example, it may be about 50 (kHz), which is the same as that of the high pass filter. The setting of the cutoff frequencies of the high-pass filter and the low-pass filter may be the same in other embodiments described below.

(Second Embodiment) FIG. 10 shows the arrangements of a tracking error detection system and a focus error detection system according to the second embodiment. In this embodiment, an astigmatic optical system 26 is added in front of the photodetector 17, and an adder 27 is further added.
This embodiment differs from the embodiment shown in FIG. 1 in that a focus error detection system including f, 27g, a subtractor 28 and a low pass filter 29 is added. As described above, according to the present embodiment, it becomes possible to detect the focus error by the astigmatism method at the same time by using the photodetector 17 of the tracking error detection system, and the optical system of the entire optical pickup can be made compact and at low cost. It will be possible.

Also in this embodiment, the order of addition and high-pass filtering may be reversed, as in the embodiment shown in FIG. (Third Embodiment) FIG. 11 shows the configuration of a tracking error detection system according to the third embodiment. The optical system and the photodetector 17 are the same as those in the embodiment shown in FIG. In this embodiment,
High-pass filters 18l1, 18l2, 18r1, 18
When the output signals Pl1, Pl2, Pr1, Pr2 of r2 are regarded as a function of time, the calculation corresponding to the following equation is performed to obtain the tracking error signal.

TES = Pl1 (t-d1) × Pl2 (t) -Pr1 (t-dr) × Pr2 (t) (7) d1, dr: time delay amount for phase matching High-pass filters 18l1, 18l2, 18r1 , 18
Of the output signals Pl1, Pl2, Pr1, Pr2 of r2, the phase of the phase advance signal of the phase relationship between Pl1 and Pl2 and Pr1 and Pr2 (here, it is assumed that Pl1 and Pr1) is phase delayed. The elements 24l and 24r are delayed to match. The signals whose phases are matched in this way are multiplied by the multipliers 191 and 19r, and the subtracter 20,
An error signal is obtained through the low pass filter 21. In addition,
At the time of phase alignment, align the phases of Pl1 and Pl2, and
The phases of r1 and Pr2 are matched, but P after phase matching
The phases of l1 and Pr1 do not have to match. Also,
Phase delay elements 24l and 24r and high-pass filter 18l
The order of 1,18l2,18r1,18r2 may be reversed. As the phase delay elements 24l and 24r,
A delay element or a phase shift filter having a low-pass characteristic can be used.

In the embodiment shown in FIG. 1, the adders 27l,
If the phase difference of the signals before addition at 27r is large, the signal amplitude decreases at the stage of addition, so the amplitude of the tracking error signal may decrease and the SN ratio may not be sufficient. According to the example, this point is improved.

That is, in this embodiment, the four-division photodetector 1
The phase of the highest repetition frequency component of the output signals of the two regions on the same side with respect to the dividing line 17Y parallel to the track direction of 7 is matched by the phase delay elements 24l, 24r, and then multiplied by the multipliers 19l, 19r. There is. By performing the multiplication while matching the phases in this way, it is possible to perform an operation that is substantially equivalent to the square operation and to detect the tracking error signal.

In FIG. 8, the product obtained by combining the phases of Pl1 and Pl2 is defined as Pl ₂ , and the product obtained by combining the phases of Pr1 and Pr2 is defined as Pr _2, and the tracking is obtained by taking the difference between the two. An example of an error signal waveform is shown. in this case,
Since no addition is performed as compared with the first embodiment, the multiplier 1
Although the amplitudes of the signals input to 9l and 19r are small, the phase difference matching is performed. Therefore, unlike the first embodiment, the tracking error can be reliably detected even when the phase difference is large.

(Fourth Embodiment) FIG. 12 shows the configuration of a tracking error detection system according to the fourth embodiment. The optical system and the photodetector 17 are the same as those in the embodiment shown in FIG. In this embodiment, the output signals Pl1 'and P1 of the four-division photodetector 17 are used.
The l2 ', Pr1' and Pr2 'signals are respectively passed through high-pass filters 18l1, 18l2, 18r1 and 18r2, and among the output signals Pl1, Pl2, Pr1 and Pr2, Pl1 and Pl2 and Pr1 and Pr2 are directly used as a multiplier 1
The signals 91 and 19r are multiplied, and a tracking error signal is obtained through the subtractor 20 and the low-pass filter 21.

In this embodiment, the tracking signal is generated by the calculation shown in the equation (4) similar to the equation (1). Also in this embodiment, basically, similar to the first embodiment, a multiplication process is performed to generate a signal component proportional to the signal amplitude of the information reproduction signal, and a subtraction is performed to generate a tracking error signal. FIG. 9 shows an example of the tracking error signal generated in this embodiment based on the signal of FIG.

In this embodiment, since the signals having the shifted phases are multiplied, the signal amplitude of the obtained tracking error signal is smaller than that in the third embodiment in which the phases are matched or the first embodiment in which the phase is squared. It becomes smaller, but on the other hand Pl1 and Pl
The difference between the phase shift amount of 2 and the phase shift amount of Pr1 and Pr2 is
Since the light beam becomes larger as it goes away from the track center (that is, the amount of phase shift between Pl1 and Pl2 and the amount of phase shift between Pr1 and Pr2 become unequal), this effect can be used to increase the gain of tracking error detection. There is an advantage that you can.

(Fifth Embodiment) FIG. 13 shows the configuration of a tracking error detection system according to the sixth embodiment. In this embodiment, a digital logic circuit is used for the arithmetic processing for detecting the tracking error. That is, output signals 511, 512, and 4 from the four regions of the photodetector 17
513 and 514 are high-pass filters 515, 516 and 5
17 and 518, and outputs the output signal to the binarization circuit 51.
Digitize at 9,520,521,522. Exclusive OR 523 of the output signals of the binarization circuits 519 and 520
To the analog output by the low pass filter 525.

Similarly, the output signals of the binarization circuits 521 and 522 are input to the exclusive OR 524, and the operation output is converted into an analog amount by the low pass filter 526. The output signal of the low-pass filter 525 and the output signal of the low-pass filter 526 are input to the subtractor 527, and the difference between them is calculated to obtain a tracking error signal 528.

FIG. 14 shows an example of the signal waveform of each part when the light beam deviates from the read track center in the configuration of FIG. The phase difference between the output signal 511 of the light receiving area 17l1 and the output signal 512 of the light receiving area 17l2 of the photodetector 17 is the output signal 513 of the light receiving area 17r1 and the output signal 514 of the light receiving area 17r2 because the light beam deviates from the track center. It is larger than the phase difference with. The output signals of the binarization circuits 519 and 520 are exclusive OR 523.
Is input to. The phase difference is detected as the pulse length (duty ratio) of the output signal of the exclusive OR 523, and converted into an analog amount by the low pass filter 525. Then, the subtracter 527 calculates the difference between the output signals of the low pass filters 525 and 526 to obtain the tracking error signal 528.

According to the present embodiment, the tracking error is detected by more positively utilizing the effect of the high tracking error detection gain described in the fourth embodiment.
That is, after binarizing the output signals of the light receiving regions 17l1 and 17l2 respectively, inputting them to the exclusive OR circuit, performing digital calculation, and then passing them through a low-pass filter, they are proportional to the phase difference between them (analog). Detect the signal. The same calculation is performed for the output signals of the light receiving regions 17r1 and 17r2, and a signal proportional to the phase difference between the two is detected. By taking the difference between these two, the light receiving area 17l
1 and 17l2 output signal phase shift amount and light receiving region 17r
The tracking error signal is obtained by detecting the difference in the amount of phase shift between the output signals 1 and 17r2. By doing this,
Similar to the fourth embodiment, a high tracking error detection gain can be obtained.

(Sixth Embodiment) FIG. 15 shows the configuration of a tracking error detection system according to the sixth embodiment. In the present embodiment, the tracking error is detected by the calculation shown in the equation (5). That is, in this embodiment, a two-divided photodetector is used as the photodetector 22, and the photodetector 22
Output signals P1 ', P of the two light receiving regions 22l, 22r of
First, r ′ is passed through the high-pass filters 18l and 18r to remove frequency components including an offset due to the radial inclination of the optical disc 10 and the movement of the objective lens 16 in the radial direction of the optical disc. Next, the high pass filters 18l and 18r
Output signals Pl and Pr of the multipliers 191 and 19r, respectively.
Squared to produce a signal component proportional to the signal amplitude, and the subtractor 20 takes the difference between the output signals of the two multipliers 191 and 19r. At this stage, since the output signal of the subtractor 20 includes the component of the information reproduction signal, this component is removed by the low pass filter 21 to obtain the tracking error signal.

This embodiment is substantially equivalent to the first embodiment shown in FIG. That is, the output signals of the light receiving regions 22l and 22r of the two-divided photodetector 22 in FIG.
It is equivalent to the output signals of the adders 27l and 27r in FIG.

As described above, according to this embodiment, the structure of the optical system is the same as that of the conventional example, and the circuit structure of the tracking error detecting portion can be realized simply and at low cost. Note that the subtraction and the low-pass filter processing in the calculation for obtaining the tracking error signal may be performed after the square calculation, and the mutual order may be reversed. However, if the order shown in this embodiment is adopted, only one low-pass filter is required, and therefore the circuit configuration can be simplified.

(Seventh Embodiment) FIG. 16 shows the arrangement of a tracking error detection system according to the seventh embodiment. The configuration of the optical system is similar to that of the embodiment shown in FIG. In this embodiment, the tracking error is detected by the calculation shown in the equation (6). That is, in this embodiment, FIG.
The absolute value calculation circuits 401 and 402 are used instead of the multipliers 19l and 19r in FIG.
A subtracter 20 takes the difference between the output signals of 1,402 and passes it through a low pass filter 21 to obtain a tracking error signal.

FIG. 17 shows an example of the configuration of the absolute value operation circuit 401, which has a known configuration in which the absolute value of the input voltage is detected by a circuit in which two operational amplifiers 411 and 412 are combined with resistors and diodes. is there.

(Eighth Embodiment) FIG. 18 shows the configuration of a tracking error detection system according to the eighth embodiment. Since the optical system is the same as that of the embodiment shown in FIG. 15, it is omitted in this figure, and only the photodetector 22 and the signal detection system after it are shown. In this embodiment, the high pass filters 18l, 18r
After the output signals P1 and Pr of P1 are added by the adder 30, the signal Ps binarized by the binarization circuit 31 is multiplied by P1 and Pr by the multipliers 191 and 19r, respectively.
An absolute value calculation is performed on each of 1 and Pr. An example of signal waveforms input to the multipliers 191, 19r is shown in FIG.
9, shown in FIG. Here, the output signal Ps of the binarization circuit 31 is a binary signal having a positive value and a negative value centered on zero, but it may be a binary value of a positive value and zero.

[0059]

As described above, according to the present invention, it is possible to obtain a stable tracking error signal with a small offset due to the shift of the objective lens in the radial direction of the optical disc, the inclination of the optical disc in the radial direction, and the like. Therefore, if tracking control is performed using this tracking error signal, sufficiently stable tracking control can be realized even for an optical disc having a narrow track pitch and a high linear recording density.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a tracking error detection system in an optical disc device according to a first embodiment.

FIG. 2 is a diagram showing an example of a spectrum of an information reproduction signal and a spectrum of an amount of movement of an objective lens.

FIG. 3 is a diagram showing a model of a positional relationship between a light spot and an information mark for explaining a tracking error detection principle according to the present invention.

FIG. 4 is a diagram showing an output signal waveform of the 4-division photodetector in FIG.

5 is a diagram showing a signal waveform obtained by performing high-pass filtering on the signal of FIG.

FIG. 6 is a diagram showing a signal waveform obtained by adding, squaring, and low-pass filtering the signal of FIG.

FIG. 7 is a diagram showing a tracking error signal waveform in the first embodiment.

FIG. 8 is a diagram showing a tracking error signal waveform in the third embodiment.

FIG. 9 is a diagram showing a tracking error signal waveform according to the fourth embodiment.

FIG. 10 is a diagram showing a configuration of a tracking error detection system and a focus error detection system in the optical disc device according to the second embodiment.

FIG. 11 is a diagram showing a configuration of a tracking error detection system in an optical disc device according to a third embodiment.

FIG. 12 is a diagram showing a configuration of a tracking error detection system in an optical disc device according to a fourth embodiment.

FIG. 13 is a diagram showing a configuration of a tracking error detection system in an optical disc device according to a fifth embodiment.

FIG. 14 is a diagram for explaining the principle of tracking error detection in the fifth embodiment.

FIG. 15 is a diagram showing a configuration of a tracking error detection system in an optical disc device according to a sixth embodiment.

FIG. 16 is a diagram showing a configuration of a tracking error detection system in an optical disc device according to a seventh embodiment.

17 is a diagram showing a configuration of an absolute value detection circuit in FIG.

FIG. 18 is a diagram showing the configuration of a tracking error detection system in an optical disc device according to an eighth embodiment.

19 is a diagram showing an output signal waveform of the first multiplier in FIG.

20 is a diagram showing an output signal waveform of the second multiplier in FIG.

FIG. 21 is a diagram for explaining an example of a conventional tracking error detection method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Optical disc 11 ... Information recording surface 12 ... Information track 13 ... Light source 16 ... Objective lens 17 ... 4-division photodetector 17l1 ... 1st light receiving area L1 17l2 ... 2nd light receiving area L2 17r1 ... 3rd light receiving area R1 17r2 ... Fourth light-receiving region R2 17Y ... Dividing line of light-receiving region 18l1, 18l2, 18r1, 18r2 ... High-pass filter 19l, 19r ... Multiplier 22 ... 2-division photodetector 22Y ... Dividing line of light-receiving region 21l ... First Light receiving region L 22r ... Second light receiving region R 241, 24r ... Delay element for phase matching or phase shift filter having low pass characteristic 401, 402 ... Absolute value calculation circuit 515, 516, 517, 518 ... High pass Filters 519, 520, 521, 522 ... Binarization circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sadaya Fujimoto 70 Yanagi-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Yanagimachi Co., Ltd. (72) Inventor, Hisanobu Sugaya Komukai Toshiba-cho, Kawasaki-shi, Kanagawa Prefecture 1-share Inside the Toshiba Research and Development Center

Claims (7)

[Claims] 1. An optical system for focusing light from a light source on a recording surface of an optical disk having an information track and irradiating the information track as a light spot, and a light receiving surface along a direction corresponding to the information track direction of the optical disk. And a photodetector having a light-receiving region divided into four by a first dividing line and a second dividing line which is substantially orthogonal to the first dividing line, and a photodetector for detecting reflected light from the optical disc, and the photodetector. A pair of signals with the first and second light receiving areas on one side of the first dividing line of the container and a pair of output signals of the third and fourth light receiving areas on the other side. On the other hand, there is provided a means for generating a difference between the two signals, which are respectively subjected to addition processing, high-pass filtering processing and multiplication processing, as a tracking error signal indicating an error in the irradiation position of the light spot with respect to the information track. Optical disc apparatus according to claim and. 2. An optical system for focusing light from a light source on a recording surface of an optical disc having an information track and irradiating the information track as a light spot, and a light receiving surface along a direction corresponding to the information track direction of the optical disc. And a photodetector having a light-receiving region divided into four by a first dividing line and a second dividing line which is substantially orthogonal to the first dividing line, and a photodetector for detecting reflected light from the optical disc, and the photodetector. A pair of signals with the first and second light receiving areas on one side of the first dividing line of the container and a pair of output signals of the third and fourth light receiving areas on the other side. 2 which has been subjected to high-pass filter processing and multiplication processing, respectively.
And a means for generating a difference between two signals as a tracking error signal indicating an error in the irradiation position of the light spot with respect to the information track. 3. An optical system for focusing light from a light source on a recording surface of an optical disc having an information track and irradiating the information track as a light spot, and a light receiving surface along a direction corresponding to the information track direction of the optical disc. And a photodetector having a light-receiving region divided into four by a first dividing line and a second dividing line which is substantially orthogonal to the first dividing line, and a photodetector for detecting reflected light from the optical disc, and the photodetector. A pair of signals with the first and second light receiving areas on one side of the first dividing line of the container and a pair of output signals of the third and fourth light receiving areas on the other side. Tracking indicating the error in the irradiation position of the light spot with respect to the information track, on the other hand, the difference between the two signals that has been subjected to high-pass filter processing and multiplication processing for matching and multiplying the phases of the respective highest repetition frequency components. Optical disk apparatus characterized by comprising a means for generating an error signal. 4. An optical system for focusing light from a light source on a recording surface of an optical disc having an information track and irradiating the information track as a light spot, and a light-receiving surface along a direction corresponding to the information track direction of the optical disc. And a photodetector having a light-receiving region divided into four by a first dividing line and a second dividing line which is substantially orthogonal to the first dividing line, and a photodetector for detecting reflected light from the optical disc, and the photodetector. Of the output signals of the first and second light receiving areas on one side of the first dividing line of the container and the output signals of the third and fourth light receiving areas on the other side. On the other hand, means for generating a difference between two signals obtained by performing an exclusive OR after the high pass filter processing and the binarization processing as a tracking error signal indicating an error in the irradiation position of the light spot with respect to the information track. Optical disk apparatus characterized by comprising. 5. An optical system for focusing light from a light source on a recording surface of an optical disk having an information track and irradiating the information track as a light spot, and an optical spot for irradiating the information recording surface of the optical disk having the information track. Light detection means for detecting reflected light from the optical disk, which has a light irradiation means and first and second light receiving areas whose light receiving surface is divided by a dividing line along a direction corresponding to the information track direction of the optical disk. And a difference between two signals obtained by subjecting the output signals of the first and second light receiving regions of the photodetector to high pass filter processing and square calculation processing, respectively, to irradiate the information track with the light spot. An optical disk device, comprising: a means for generating a tracking error signal indicating a position error. 6. An optical system for focusing light from a light source on a recording surface of an optical disc having an information track and irradiating the information track as a light spot, and an optical spot for irradiating the information recording surface of the optical disc having the information track. Light detection means for detecting reflected light from the optical disk, which has a light irradiation means and first and second light receiving areas whose light receiving surface is divided by a dividing line along a direction corresponding to the information track direction of the optical disk. And a difference between two signals obtained by performing high-pass filter processing and absolute value calculation processing on the output signals of the first and second light receiving regions of the photodetector, and irradiating the information spot with the light spot. An optical disk device, comprising: a means for generating a tracking error signal indicating a position error. 7. A high-pass filter having a characteristic of sufficiently attenuating a signal within a tracking control band for the high-pass filter processing, or attenuating at least a frequency component of the number of revolutions of the optical disc whose cutoff frequency is substantially below the tracking control band. 7. The optical disk device according to claim 1, wherein a high-pass filter having a characteristic that enables the optical disk device is used.