JPH05197988A - Optical disk device - Google Patents

Abstract

PURPOSE:To accurately control by detecting with two photodetectors, envelope- detecting the output signal of each photodetector and tracking-controlling by regarding the difference of each detected signal as a tracking control signal. CONSTITUTION:The output of a quadripartite photodetector 1 is added by a specified formula and amplified, and signals TA1, TA2 are outputted. The signal TA1 is envelope-detected by a detector 30 through an HPF 27 and becomes the signal TB1 and the signal TA2 is processed by the HPF 28 and the detector 31 and becomes the signal TB2 similarly. The signal TE2 obtained by subtracting the signal TB2 from the signal TB1 is outputted by a subtractor 25. The result of a comparator 23 is investigated by a system controller 16 and a selector 24 is switched so that the signal TE2 is outputted when the amplitude of the signal TE2 is larger than a prescribed value and the TE1 is outputted when smaller, and a tracking control part 13 is tracking-controlled. Thus, accurate tracking-control is performed regardless of the kind of a track.

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 recording or reproducing information.

[0002]

2. Description of the Related Art In recent years, in addition to conventional read-only optical discs such as compact discs (CD), recordable optical discs are becoming widespread. The difference between these two types of optical discs is that the track of a read-only optical disc is composed of pit rows, whereas the track of a recordable optical disc has a continuous guide groove, and information is stored in or in this guide groove. It is to be recorded between the groove and the guide groove.

A push-pull method is generally known as a tracking control means for an optical disk device. However, even if an optical disk having such different tracks has a groove or pit depth of λ. / 4
(Λ: wavelength of laser light used in optical disk medium) This is a system of tracking control means commonly applied to those shallower than that.

A conventional technique of push-pull type tracking control means for these different types of tracks will be described below. This system can be implemented with a common device configuration for both types of tracks. Figure 3
(A) is a layout diagram of an optical head optical system configured using four-division light receiving elements. In FIG. 3A, 1 is a 4-division light receiving element, 2 is an optical disk, 3 is an objective lens, 4
Is a half mirror, 5 is a condenser lens, 6 is a cylindrical lens, 7
Is a collimator lens, and 8 is a semiconductor laser.

The luminous flux emitted from the semiconductor laser 8 is
The collimator lens 7 makes a parallel light beam, which is reflected by the half mirror 4 arranged at an angle of 45 degrees in the optical path, and is converged on the recording surface of the optical disc 2 by the objective lens 3. The light beam reflected from the recording surface of the optical disk 2 is made into a parallel light beam again by the objective lens 3, passes through the half mirror 4, and is guided to the four-division light receiving element 1 by the condenser lens 5 and the cylindrical lens 6. When the laser light is focused on the recording surface of the optical disc 2, the four-division light receiving element 1 is placed at a position where the light receiving bundle made astigmatic by the cylindrical lens 6 becomes the circle of least confusion, and the axis of the cylindrical lens 6 is It is placed so as to form 45 degrees with the dividing line of each element of the four-division light receiving element 1. As shown in FIG. 3B, the constituent elements of the four-division light receiving element 1 are replaced by S1, S2, S3 and S4.
The photoelectric conversion output is also given the same sign. Further, in the four-division light receiving element 1, the dividing lines of the respective elements, for example, the dividing lines of the elements S1 and S2 and the elements S3 and S4 are arranged in the direction corresponding to the track and the intersections of the dividing lines coincide with the optical axis. It is located in

Next, the structure of a conventional optical disk device using such an optical head will be described with reference to FIG. FIG. 4 is a block diagram of the main part of such an optical disc device. In FIG. 4, 1 is a four-division light receiving element,
9, 10 and 11 are addable amplifiers, 12 is a focusing control unit, 13 is a tracking control unit, and 14 is an LPF.
(Low-pass filter), 15 is an information signal detection unit, 16
Is the system controller. The four-division light receiving element 1 is
It is the same as that shown in FIG.

The output of each component S1 to S4 is an amplifier 9,
It is input to 10, 11 and is operated and amplified according to the reference numerals shown in FIG. Therefore, the output of the amplifier 9 is the signal FE represented by FE = S1-S2 + S3-S4, which is sent to the focusing control unit 12 as the focusing control signal FE.

The output of the amplifier 10 is a signal TE0 represented by TE0 = S1-S2-S3 + S4, the high frequency of which is removed by the LPF 14 and the signal is sent to the tracking controller 13 as the tracking control signal TE1.

The output of the amplifier 11 is a signal AS represented by AS = S1 + S2 + S3 + S4, and this signal includes the optical disk 2
Since the information recorded in (1) is included, it is sent to the information signal detecting section 15.

Now, the cause and the nature of the signal TE0 which is the source of the tracking control signal TE1 will be described. The form is different between the signal TE0 obtained from the guide groove and the signal TE0 obtained from the track composed of the pit train. First, the signal TE0 obtained from the continuous guide groove
The response characteristic of the laser spot with respect to the movement in the direction perpendicular to the track is an S-shaped periodic function having the same period as the track pitch. FIG. 5 is a diagram showing the characteristic. The cause is usually explained by the interference between the 0th-order diffracted light and the ± 1st-order diffracted light from the groove.

FIGS. 6A and 6B are schematic diagrams for explaining the state of this interference. The upper part of each figure shows the distribution of each diffracted light on the pupil of the objective lens, and the lower part shows the tracks. It is sectional drawing of the light amount distribution of the perpendicular direction. FIG. 6A shows the case where the laser spot is at the track center.
(B) indicates the time when the track is deviated from the track. The shape of these light quantity distributions changes depending on the manner of interference between the 0th-order diffracted light and the ± 1st-order diffracted light, and the + 1st-order diffracted light and the −1st-order diffracted light have a sign of the phase shift of the light wave caused by the position shift from the track of the laser spot Is reversed, so (a) in FIG.
As shown in the lower diagram of FIG. 6B, the light amount distribution on the pupil is asymmetric with respect to the center line parallel to the track. In the four-divided light receiving element 1, since the predetermined dividing line is placed so as to correspond to the center line as described above, the signal TE0 reflects this asymmetry and exhibits the characteristic shown in FIG.

On the other hand, the signal TE0 obtained from the track composed of the pit train is different from this, and since the reflected light is modulated by the traveling of the pit, a high frequency resulting therefrom is superimposed. FIG. 7 is a diagram showing the response characteristic of the signal TE0 with respect to the movement of the laser spot in the direction perpendicular to the track. However, the high frequency as shown in the figure is not actually superimposed and observed, and when there are laser spots at each position on the horizontal axis, the signal TE0 has the amplitude shown in the figure.
Indicates that is vibrating with time.

The cause of this characteristic can be explained as follows. FIG. 8 is a time response waveform of the signal TE0 generated when the laser spot is tracking-controlled while being deviated from the track center by a certain amount. By analogy with the origin of the light amount distribution on the pupil of the objective lens due to the diffracted light generated from the guide groove, the maximum of the waveform of FIG. 8 occurs when the laser spot is on the pit, and the minimum of the waveform is It can be considered to occur when the laser spot is in a pitless position or in the middle of a pit. It goes without saying that the maximum amplitude of this waveform is equal to the amplitude of the signal TE0 generated from the track in which only the guide groove exists, when the length of the pit is sufficiently long with respect to the size of the laser spot. Therefore, the DC component of this waveform is mainly determined by the magnitude of the maximum value, and the amount of deviation of the laser spot from the track center can be detected by the DC component of the waveform. That is, the signal T
If the high frequency component generated from the modulation by the pits is removed from E0, the response characteristic of the signal TE0 to the movement of the laser spot in the direction perpendicular to the track becomes the characteristic of the shape shown by the dotted line in FIG. The shape is the same as the characteristic shown in FIG. 5 obtained for the guide groove. This corresponds to obtaining the signal TE1 by removing the high frequency from the signal TE0 by the LPF 14 in FIG.

The operation of the conventional optical disk device configured as described above will be described below. Figure 9
[Fig. 4] is a graph of the shape of a light receiving bundle on the four-division light receiving element 1 that changes depending on the focus state of a laser spot and a focusing control signal FE.

First, when the focus point of the laser light emitted from the optical head is brought closer to the rotating optical disk 2, the light receiving flux is caused by the surface deviation of the optical disk 2 on the four-division light receiving element 1 as shown in FIG. ) (1), (2), (3)
It changes as shown in. When the laser light is focused on the optical disc 2, this light flux becomes circular as shown in (2) of FIG. 9A, and when it is defocused in the front and rear direction, (1) or (() of FIG. 9A). It becomes oval like 3). Therefore, since the output of the amplifier 2 in FIG. 3 is the focusing control signal FE defined by the above-mentioned formula FE = S1-S2 + S3-S4, the response as shown in FIG. Will be shown.

Focusing control section 12 in FIG.
Controls the focusing of the optical head by moving the objective lens in the optical axis direction so that the focusing control signal FE becomes zero. Next, the laser spot tracking control is performed to follow the movement of the track caused by the eccentricity of the optical disc 2. As described above, the tracking control signal TE1 having the same shape is obtained regardless of whether it is the guide groove or the pit row.
1 is sent to the tracking controller 13, and the tracking controller 13 controls the position of the laser spot so that the signal TE1 becomes zero. When the tracking control is performed in this way, the recorded information can be detected from the signal AS shown in FIG.

By the way, in the tracking control of the laser spot, only the objective lens 3 shown in FIG. 3 is moved in the direction perpendicular to the optical axis of the optical system so as to follow the track from the inner circumference to the outer circumference of the optical disk 2. Is common. At this time, since the central axis of the laser emission light beam coincides with the optical axis of the fixed optical system, the light beam emitted from the objective lens 3 is decentered from the optical axis of the optical system due to the track tracking of the objective lens 3. The central axis of the light flux reflected from the optical disk 2 is displaced, and the central axis of the light receiving bundle and the optical axis of the light receiving optical system do not match. This discrepancy also occurs when the optical disk surface is tilted with respect to the optical axis of the optical system. By this, 4
A position shift of the light receiving bundle occurs on the divided light receiving element 1 as shown in FIG. 10, and the balance of the amount of received light on both sides of the dividing line in the track direction is lost. Therefore, the tracking control signal TE1 becomes zero when the laser spot position deviates from the normal track center. FIG. 11 is a diagram showing the response characteristic of the signal TE0 with respect to the movement of the laser spot from the track center when the positional deviation of the light receiving bundle has occurred. The signal TE0 shows the characteristics of the envelope curve indicated by the solid line in the case of a track composed of a continuous guide groove, and becomes a signal in which high frequencies are superimposed in the case of a track composed of a pit string. The illustrated high frequencies are schematic as in FIG. 7. At this time, the tracking control signal TE
The response characteristic of No. 1 shows the characteristic of the envelope curve indicated by the solid line without change in the case of the guide groove and the characteristic indicated by the dotted line in the case of the pit row. These characteristics intersect with the horizontal axis at positions deviated from the origin because the above-mentioned DC component is added. The tracking control unit 13 uses the tracking control signal T
Since the laser spot position is controlled so that E1 becomes zero, the position of the laser spot is always controlled at a position deviated from the track center. Hereinafter, the deviation of the laser spot from the track center thus generated will be referred to as a tracking offset.

As described above, the push-pull type tracking control means has a possibility of causing a tracking offset, but since it is a method realized by a simple device structure, it is particularly suitable for an optical disc having a guide groove. On the other hand, it is a commonly used tracking control method.

[0019]

Such a tracking offset occurs because the light quantity on both sides of the dividing line of the four-division light-receiving element 1 is lost due to the positional deviation of the light-receiving bundle. It is determined by the amount of light near the dividing line. As shown in (a) and (b) of FIG. 6, since the light amount near the center line of the pupil of the objective lens 3 is mainly occupied by the 0th-order diffracted light, in the portion where the groove and the pit exist, the division is performed. It can be considered that the amount of light near the line is determined by the amount of 0th-order diffracted light. On the other hand, since there is no ± 1st-order diffracted light where there is no pit, all the reflected light from the optical disc 2 has the same distribution as the 0th-order diffracted light.
Therefore, in the track formed by the pit row, the amount of light evenly distributed in the vicinity of the division line of the four-divided light receiving element 1 is larger than that in the track formed by the guide groove, and even if the above-mentioned positional deviation amount of the light receiving bundle is equal. , The DC component added to the characteristics of the tracking control signal TE1 shown in FIG.
Further, even when the reflectance of the optical disk 2 is the same and the depths of the guide groove and the pit are the same, the amplitude of the S-shaped tracking control signal TE1 caused by the displacement of the laser spot from the track is compared with each track. Then, as is clear from FIG. 11, the amplitude of the tracking control signal TE1 obtained from the track including the pit train is always smaller. Further, as shown in FIG. 11, when the generated DC components are equal, a smaller amplitude of the tracking control signal TE1 causes more tracking offset.

Therefore, due to the above two causes, even if the above-mentioned positional deviation of the light receiving bundle is the same, the generated tracking offset amount is an optical disk having a pit row rather than an optical disk 2 having a track having a guide groove. There was a problem that 2 was larger.

The present invention is intended to solve the above-mentioned problems, and for an optical disc having a track composed of pit rows,
It is an object of the present invention to provide an optical disk device in which tracking offset is unlikely to occur.

[0022]

In order to solve the above problems, the first means of the present invention is to provide at least two photodetectors for detecting the reflected light from the information track of the optical disc composed of pit rows. Detection means for detecting the envelope by removing the DC component from each output signal of these photodetectors, tracking control signal detection means for detecting the difference between the respective signals subjected to the envelope detection, and a laser based on the tracking control signal. And a tracking control means for performing spot tracking control.

The second means of the present invention is to provide at least two photodetectors for detecting the reflected light from the tracks of the optical disc formed by the guide grooves or pit rows, and the output signals of these photodetectors. Detecting means for removing the DC component from the envelope to detect the envelope, and first tracking control signal detecting means for detecting the difference between the output signals subjected to the envelope detection,
Second tracking control signal detecting means for detecting a difference between output signals of the photodetector, and tracking for selectively switching the two tracking control signals detected by the first and second tracking control signal detecting means. The control signal switching means and the tracking control means for performing tracking control of the laser spot based on the signal output from the tracking control signal switching means are provided.

The third means of the present invention compares the tracking control signal switching means in the second means with the amplitude magnitude of the signal obtained by the first tracking control signal detecting means and a predetermined value. The configuration is such that switching is performed according to the result obtained.

[0025]

In the first means, the DC component of each output signal of the photodetector is different in magnitude when the light receiving bundle is displaced, but the DC component is removed and the envelope detection is performed. Since each output signal is a high-frequency envelope that oscillates with time, it is not affected by the magnitude of the DC component. Further, when the tilt of the optical disc or the amount of movement of the objective lens is not so large, the vignetting of the light beam is slight, and thus the amplitude of the high frequency hardly changes. That is,
Each output signal whose envelope has been detected by removing the DC component is unlikely to be affected by the optical axis shift of the light receiving bundle. Further, the differential signal of each signal subjected to envelope detection has the same shape as that of a normal push-pull tracking control signal. Therefore, by performing tracking control using the differential signal, it is possible to reduce the tracking offset, which has been a problem in the conventional push-pull type tracking control means, caused by the inclination of the optical disc surface or the movement of the objective lens due to the track following. It becomes possible.

In the second means, the two tracking control signals are selectively switched by the tracking control signal switching means, so that not only the optical disk formed by the guide grooves or the pit rows but also the guide grooves are formed. Accurate tracking control is possible even for optical discs.

Further, since the type of the track of the optical disk can be automatically discriminated by the third means,
Accurate tracking control is possible regardless of the type of track on the optical disc.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the main part of the optical disk device in this embodiment. It should be noted that those having the same functions as those of the conventional one are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 1, the optical disc device includes
Addition is possible in addition to the four-division light receiving element 1, the amplifiers 9 and 11, the focusing control unit 12, the tracking control unit 13, the LPF (low pass filter) 14, the information signal detection unit 15 and the system controller 16 which have been provided conventionally. Amplifiers 21 and 22, a comparator 23, and a selector 2 as a tracking control signal switching means.
4, a subtracter 25 as a first tracking control signal detecting means, a subtractor 26 as a second tracking control signal detecting means, and an HPF (high pass filter) 2.
7, 28 and detectors 30, 31 are provided. It should be noted that the optical head optical system of the present embodiment is constructed similarly to the optical system shown in FIG. 3, and in the optical system, the four-division light receiving element 1 is arranged in the same manner as described in the conventional example.

The amplifiers 41 and 42 add the outputs of the four-division light receiving element 1 as shown in the following equation and amplify them to obtain the signal TA.
1 and TA2 are output. TA1 = S1 + S4 TA2 = S2 + S3 The signal TA1 has a DC component removed by the HPF 27, and is envelope-detected by the detector 30 to become a signal TB1. The signal TA2 is similarly supplied to the HPF 28 and the detector 3
As a result, the signal TB2 is obtained. The subtractor 25 outputs a signal TE2 obtained by subtracting the signal TB2 from the signal TB1.

Here, the reason why tracking control using the signal TE2 can reduce the tracking offset caused by the optical axis shift of the light receiving bundle described in the description of the conventional example will be described.

FIG. 2 shows a signal TA generated at a position of a track composed of a pit row, in which the positional deviation of the laser spot from the track is associated with the groove of the pit.
It represents the size of 1, TA2, TB1, TB2 and TE2. Regarding the signals TA1 and TA2, FIG.
The high frequencies shown in FIG. 7 are schematic similar to those shown in FIGS. 7 and 11, and indicate that each signal oscillates temporally with the illustrated amplitude due to the modulation generated during the traveling of the pit. (E) and (d) of FIG. 2 show that it is possible to obtain either of the two envelopes represented by the solid line and the dotted line by envelope detection by removing the DC component from the signal TA1 and the signal TA2. ing. The signal TE2 is
The envelope obtained by adopting the envelope represented by the solid line from among the envelopes is shown. However, the vertical scales of the signals TA1 and TA2 are different from those of other signals.

Now, the DC component DC of the signals TA1 and TA2
When the position deviation of the light receiving bundle occurs as described above, the DC1 and the DC2 have different sizes as illustrated. This was the cause of the tracking offset in the configuration of the conventional example. However, since the signals TB1 and TB2 are high-frequency envelopes that oscillate with time, the DC component DC1
And is not affected by the size of DC2. Further, when the tilt of the optical disc 2 or the above-mentioned movement amount of the objective lens 3 is not so large, the vignetting of the light beam is slight,
The amplitude of the high frequency hardly changes. That is, the signals TB1 and TB2 are unlikely to be affected by the above-mentioned optical axis shift of the light receiving bundle. Further, the signal TE2 has the same shape as the normal push-pull tracking control signal (FIG. 4) described in the conventional example, as shown in the figure. Therefore, it is possible to perform the tracking control using the signal TE2, and the signal TE2 is generated from the signals TB1 and TB2 which are hardly affected by the optical axis shift of the light receiving bundle described above. If TE2 is used as the tracking control signal, it is possible to reduce the tracking offset, which has been a problem in the past.

Next, the structure of this embodiment will be described with reference to FIG. The tracking control signal TE2 obtained as described above is compared by the comparator 23 with the amplitude of the signal TE2 and a predetermined value. In addition, the signal TA sent to the subtractor 26
1 and TA2 are calculated, pass through the LPF 14, and become a signal TE1 used as a tracking control signal in the conventional example. The selector 24 sends either the signal TE1 or the signal TE2 to the tracking controller 13 based on an instruction from the system controller 16.

The operation of this embodiment configured as described above will be described. The operations relating to the focusing control unit 12 and the information signal detection unit 15 are the same as those in the conventional example, and the description thereof will be omitted.

First, the system controller 16 performs focusing control so that the laser light is focused on the optical disk 2. Next, the system controller 16 controls the tracking controller 13 to forcibly move the laser spot in the direction perpendicular to the track to cause the laser spot to traverse the track, and the comparator 23 compares the amplitude of the vibration of the signal TE2 with it. Check in. As described above, the signal TE2
Is obtained by processing a high-frequency signal generated by the presence of pits, so that at this time, when the optical disc 2 having a track composed of pit rows is inserted in the apparatus, the amplitude of the signal TE2 is When the optical disc 1 having the track having the guide groove is inserted, the amplitude of the signal TE2 becomes smaller than the predetermined value.

The system controller 16 includes a comparator 23.
The selector 24 is switched so as to output the signal TE2 when the amplitude of the signal TE2 is larger than a predetermined value and outputs the signal TE1 when the amplitude of the signal TE2 is smaller than the predetermined value, and the tracking control unit 13 is tracked. Control. In this way, the type of the inserted optical disc 2 is discriminated, and the tracking control with a reduced tracking offset is applied to the optical disc 2 having the track formed of the pit row in which the conventional tracking offset is likely to occur.

As described above, according to the present embodiment, the high frequency generated by the existence of pits is high in the optical disc having the track composed of the pit row in which the tracking control means of the conventional push-pull system is likely to cause the tracking offset. By performing tracking control using the signal TE2 generated from the amplitude of the component as a tracking control signal, it is possible to reduce the tracking offset that occurs due to the inclination of the optical disc 2 or the movement of the objective lens 3 due to track following. Further, the comparator 23 compares the magnitude of the amplitude of the signal TE2 generated by the laser spot crossing the track with a predetermined value to determine the type of the track of the optical disk 2, and the selector 24 performs the tracking suitable for the optical disk 2. By performing the tracking control by switching to the control signal, it is possible to configure an optical disc device that performs accurate tracking control regardless of the type of track on the optical disc 2.

Since the present invention improves the performance of the tracking control means for a read-only optical disc having a track composed of pit rows, it can be applied to a read-only optical disc device such as a compact disc (CD). It goes without saying that it is also effective. Further, the optical disk has a special data area in which information regarding the data area of the optical disk and the characteristics of its track is written, such as the distinction between the recording area of image data and audio data or the distinction between the read-only area and the recordable area. There is something.
For such an optical disc, by distinguishing the type of the track of the optical disc based on the information,
It is possible to switch the tracking control signal of the present invention.

[0040]

As described above, according to the present invention, at least two photodetectors detect the reflected light from the optical disc with respect to the optical disc having a track composed of a pit row, and the photodetector of each photodetector is detected. By performing envelope detection of the output signal and performing tracking control by using the difference between the detected signals as a tracking control signal, it is possible to reduce the tracking offset that occurs due to the tilt of the optical disc or the movement of the objective lens due to track following. .. Also,
In addition to the tracking control signal thus obtained,
The difference between the output signals of one photodetector is detected as another tracking control signal, and the tracking control signal is switched between the two tracking control signals based on the result of comparing the amplitude of the former tracking control signal with a predetermined value. By performing the control, it is possible to provide an optical disc device capable of performing accurate tracking control regardless of the type of track on the optical disc.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an optical disc device according to an embodiment of the present invention.

FIG. 2 is a diagram showing signals TA1, TA2, TB1 and TB with respect to a positional deviation of a laser spot from a track in a track composed of a pit row in the optical disk device.
It is a figure showing the response characteristic of 2 and TE2.

FIG. 3 is a configuration diagram of an optical system of an optical head in an optical disk device of a conventional example and an example of the present invention.

FIG. 4 is a block diagram of a main part of a conventional optical disc device.

FIG. 5 is a diagram showing a response characteristic of a signal TE0 with respect to a position shift of a laser spot from a track in a track formed of a guide groove.

FIG. 6 is a diagram showing a distribution of diffracted light of each order from a track formed of a guide groove and a light amount distribution on an objective lens.

FIG. 7 is a diagram showing a signal T with respect to a positional deviation of a laser spot from a track in a track composed of a pit row.
It is a schematic diagram which shows the response characteristic of E0.

FIG. 8 is a diagram showing a temporal change of a signal TE0 when a laser spot is track-controlled with a certain amount of positional deviation from the track for a track constituted by a pit row.

9A and 9B are diagrams showing the shape of a light receiving bundle on a four-divided light receiving element with respect to defocus, and the response characteristic of a focusing control signal with respect to defocus.

FIG. 10 is a diagram showing a positional shift of a light receiving bundle on a four-division light receiving element caused by movement of an objective lens due to track following.

FIG. 11 is a diagram showing a response characteristic of a signal TE0 with respect to a position shift of a laser spot from a track when a tracking offset occurs in the track formed of a pit row.

[Explanation of symbols]

1 4-division light receiving element (photodetector) 9, 11, 12, 22 Amplifier 12 Focusing control section 13 Tracking control section 14 LPF (low-pass filter) 15 Information signal detection section 16 System controller 23 Comparator 24 Selector (tracking control signal switching) Means) 25, 26 Subtractor (tracking control signal detection means) 27, 28 HPF (high-pass filter) 30, 31 Detector

Claims (3)

[Claims] 1. At least two photodetectors for detecting reflected light from an information track of an optical disc composed of a pit train, and detection for envelope detection by removing a DC component from each output signal of these photodetectors. An optical disk device comprising: means, a tracking control signal detecting means for detecting a difference between envelope-detected signals, and a tracking control means for performing tracking control of a laser spot based on the tracking control signal. 2. At least 2 for detecting reflected light from a track of an optical disk constituted by guide grooves or pit rows
Two photodetectors, detection means for removing the DC component from the output signals of these photodetectors and envelope detection, and first tracking control signal detection means for detecting the difference between the output signals subjected to the envelope detection. A second tracking control signal detecting means for detecting a difference between output signals of the photodetector, and two tracking control signals detected by the first and second tracking control signal detecting means. An optical disk device comprising: a tracking control signal switching means for switching; and a tracking control means for performing tracking control of a laser spot based on a signal output by the tracking control signal switching means. 3. The tracking control signal switching means,
3. The optical disk device according to claim 2, wherein switching is performed according to a result obtained by comparing the magnitude of the amplitude of the signal obtained by the first tracking control signal detecting means with a predetermined value.