JP2778389B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for recording a signal on an optical disk or reproducing a recorded signal on the optical disk by using a light spot focused on a semiconductor laser. The present invention relates to a direction detecting circuit for determining the direction in which a light spot required for tracking pull-in crosses a track.

[0002]

2. Description of the Related Art In recent years, using a small magneto-optical disk,
Optical disk devices for recording digital audio data have been developed. Conventionally, a read-only optical disk called a compact disk, in which pits having irregularities are cut, has been used for recording digital audio data. In a compact disc, pits are formed in a recording area of the optical disc, and when a light spot crosses a track, a track cross component is generated in a reproduced signal. By utilizing this, the direction in which the light spot crosses the track is determined, and the tracking pull-in at the time of access is speeded up.

A configuration of a direction detecting circuit in a conventional compact disk exclusively for reproduction using pits having irregularities will be described with reference to FIG.

In FIG. 7, 1 is an optical disk, 2 is a spindle motor for rotating the optical disk 1, and 3 is an optical head for recording and reproducing signals. A light beam emitted from a semiconductor laser 4 serving as a light source is converted into parallel light by a collimating lens 5 and then reflected by a polarization beam splitter 6. The light beam passes through a λ / 4 plate 7, is converted into circularly polarized light, is narrowed down by an objective lens 8, and is
The light spot on the track.

The light reflected by the optical disk 1 passes through an objective lens 8 and is converted into linearly polarized light by a λ / 4 plate 7.
The light passes through the polarizing beam splitter 6 and enters the photodetector 9.
The photodetector 9 is usually divided into a plurality of parts, and here, a four-part photodetector is shown as an example.

The output of the photodetector 9 is calculated by a calculation circuit 10 to obtain a focus error signal FE and a tracking error signal T.
E. A reproduction signal RF is generated. The reproduction signal RF is obtained by summing the outputs of the photodetector 9 divided into four parts. Reproduction signal RF
The difference between the sum signal AS and the sum signal AS is that the band of the sum signal AS is usually 100
KH or less, and the signal calculation method is the same.

[0007] 11 in the envelope detection circuit detects the envelope V _EN track cross components in the reproduction signal RF that occurs when the light spot crosses a track. 1
A peak detection circuit 2 detects a peak level V _PK of a track cross component in the reproduction signal RF. An attenuator 13 attenuates the peak level V _PK of the track cross component at a predetermined ratio to generate a comparison level V _TH .

Reference numeral 14 denotes a first comparator, which is an envelope V _EN
Is compared with the comparison level V _TH to detect an off-track signal OFTR indicating whether the light spot is on a track or between tracks. Reference numeral 15 denotes a second comparator, which compares the tracking error signal TE with a zero-cross signal to detect a cross signal CROSS indicating that the light spot crosses the track.

Reference numeral 16 denotes direction detecting means for determining the direction in which the light spot crosses the track based on the phase relationship between the off-track signal OFTR and the cross signal CROSS, and is constituted by a flip-flop circuit. The off-track signal OFTR of the data input is latched by the cross signal CROSS of the clock input, and the output Q becomes the direction detection signal DIR indicating the direction.

The direction detection signal DIR is used for clipping one side of the tracking actuator driving stage during tracking pull-in at the time of access, suppressing vibration of the tracking actuator, and speeding up pull-in.

Next, the operation of the conventional direction detection circuit configured as described above will be described with reference to FIG.

FIG. 8 shows a waveform when the light spot moves from the inner circumference to the outer circumference. From the top, (a) shows the state of the track on the optical disk, (b) shows the reproduction signal RF, and (c)
Indicates a track cross component envelope V _EN , a peak level V _PK , and a comparison level V _TH . (D) is an off-track signal OFTR which is an output of the first comparator 14, (e) is a tracking error signal TE, and (f) is a second comparator 15
(G) is the direction detection signal DIR.

Since the light spot crosses the track from the inner circumference to the outer circumference, a track cross component on a sine wave is generated in the reproduced signal RF of FIG. The envelope _VEN and the peak level V _{PK of the} track cross component are detected, and the peak level V _PK is attenuated at a predetermined ratio to obtain the comparison level V _TH.
Is made. As shown in (c), the attenuation ratio is set so that the comparison level _VTH falls substantially at the center of the envelope _VEN . Comparison level V _TH envelope V _EN in the first comparator 14 is compared, the off-track signal OFTR of (d)
Is detected. On the other hand, the tracking error signal TE
The comparator 15 performs zero-cross comparison, and the cross signal CROSS of (f) is detected. Since the light spot is moving in the outer peripheral direction, the cross signal CROSS has a rising edge of the clock as shown in FIG. The data input “low” of the off-track signal OFTR in (d) is latched by the clock of the cross signal CROSS in (f), and the direction detection signal DIR in (g) becomes “low”.

When the light spot is moving in the inner circumferential direction contrary to the outer circumferential direction described above, the rising of the clock of the cross signal CROSS in (f) is reversed. At this time, at the rise of the cross signal CROSS at (f),
The off-track signal OFTR in (d) is “high”,
As a result, the direction detection signal DIR becomes “high”.

As described above, the off-track signal OF
The direction in which the light spot crosses the track is determined from the phase relationship between TR and the cross signal CROSS, and is output as a direction detection signal DIR.

[0016]

However, in the above-described conventional direction detection method, the reproduced signal (sum signal AS) to which the output of the photodetector is added contains the RF component of the pit and the modulation of the track cross component. Is assumed to be a sufficiently large read-only optical disk. On the other hand, in an unrecorded track of a magneto-optical disk or a phase change type disk, the track cross component generated in the sum signal AS to which the output of the photodetector is added has a low degree of modulation, and the center of the track cross component is set to the comparison level. It is difficult to slice and detect the direction.

The tracks and pits of a read-only optical disk and a magneto-optical disk using uneven pits will be described with reference to FIG. (A) shows a state of a track of a read-only optical disk using uneven pits. Numeral 100 denotes irregularities of the aluminum reflection film called pits, and the pit depth d1 is approximately λ / (5) with respect to the laser wavelength λ and the substrate refractive index n.
n). The pit depth d1 is determined based on the balance between the efficiency of signal reading by light diffraction and the efficiency of push-pull detection of a tracking error signal. 10
Reference numeral 1 denotes a transparent disk substrate, which is usually made of polycarbonate, and has a thickness of 1.2 mm. The interval between the pits is called a track pitch T _P and is about 1.6 μm.

FIG. 2B shows the state of tracks on the magneto-optical disk. This is the same for the tracks of the phase change type disc except for the change in the pit reflectivity. Assuming that the light beam impinges from above, reference numeral 102 denotes a groove, and a pit 104 is recorded by a recording signal. The land 103 is located between the grooves. The groove depth d2 of the groove is λ / λ with respect to the laser wavelength λ in order to maximize the efficiency of push-pull detection of the tracking error signal.
(8n). The groove depth λ / (8n) is less efficient than a read-only optical disc for reading a signal by light diffraction. This is the reason why the degree of modulation of the track cross component is worse on a magneto-optical disc than on a read-only optical disc. The track pitch T _P is about 1.6 μm as in the case of the reproduction only. Here, on the magneto-optical disk, the pit 104 is magnetically recorded on the perpendicular magnetic recording film on the N pole and the S pole. Therefore, unlike a read-only optical disk, a change in optical reflectivity does not occur in a pit recording state. On the other hand, in a phase-change disk, the reflectance of pits on a recorded disk is different from that on an unrecorded portion.

Next, the manner in which the modulation degree of the track cross component generated in the sum signal AS to which the output of the photodetector is added becomes lower in the magneto-optical disk will be described with reference to FIG.
(A) shows a state of a reproduction signal (sum signal AS) at the time of track cross of a conventional pit-only optical disk for reproduction. (B) shows a state of the sum signal AS at the time of track crossing of the magneto-optical disk.

Here, in the read-only optical disk (a), the modulation degree defined by (A1-A2) / (A1 + A2) is 2
0% or more. On the other hand, the modulation degree of the magneto-optical disk of (b) is as low as about 10%. The modulation factor indicates the ratio of the AC component to the DC component. A low modulation factor indicates that the track cross component is small and is easily affected by the fluctuation of the DC component. A read-only optical disk generally has a high reflectance of 70% or more, while a magneto-optical disk has a low reflectance of about 20%.

From the above conditions, it is difficult to detect the direction by slicing the center of the envelope of the track cross component included in the sum signal in the unrecorded track of the magneto-optical disk or the phase change type disk. Had.

The present invention solves the above-mentioned conventional problem. The center of a track cross component is tracked by a comparison level formed from the average of the peak level and the bottom level of the track cross component detected from the AC-coupled sum signal. It is an object of the present invention to provide an optical disc apparatus provided with a direction detecting means for surely detecting a moving direction of a light spot with respect to a track by slicing.

[0023]

In order to achieve this object, an optical disk apparatus according to the present invention comprises an AC amplifier for removing a DC signal and a sum signal obtained by adding outputs of a photodetector, and a light spot crossing a track. A peak detection circuit that detects a peak level of a track cross component generated in the sum signal from an output of the AC amplifier; and a bottom detection circuit that detects a bottom level of the track cross component from an output of the AC amplifier. A first comparator for comparing a comparison level formed by applying a predetermined offset to an average level of the peak level and the bottom level, and a track cross component of the output of the AC amplifier; A second comparator for detecting a zero crossing of the error signal, and a light spot is formed based on a phase relationship between an output of the first comparator and an output of the second comparator. And a direction detecting means for determining a direction transverse to the rack.

[0024]

According to the present invention, when a light spot crosses a track, a track cross component having a low degree of modulation is generated in the sum signal. The AC amplifier removes the fluctuation of the DC component from the sum signal and amplifies only the track cross component. The peak level and the bottom level of the amplified track cross component are detected, and a comparison level is generated by adding an offset to the average. The comparison level and the amplified track cross component are compared by a first comparator, and an off-track signal is detected.
Since the comparison level is made based on the average of the peak and bottom of the track cross component, the comparison level stably slices around the center with respect to the amplitude fluctuation of the track cross component , and
An off-track signal free from noise is obtained. The second comparator performs a zero-cross comparison of the tracking error signal and detects a cross signal. The off-track signal is latched by the direction detection means at the clock of the cross signal, and becomes a direction detection signal indicating the moving direction of the light spot with respect to the track.

[0025]

An embodiment of the present invention will be described below with reference to the drawings. First, the underlying technology of the present invention
Then, the first and second embodiments will be described, and the first and second embodiments will be described.
The features of the present invention with respect to the examples will be described as third and fourth embodiments.
I will tell.

FIG. 1 is a diagram showing a configuration of a direction detecting circuit of an optical disk device according to a first embodiment of the present invention.
A description will be given of newly added and changed portions in FIG. 7 which is a configuration diagram of the conventional example described above. In FIG. 1, 2 enclosed by a broken line
Reference numeral 0 denotes an AC amplifier, which includes a capacitor 21, a resistor 22, and an amplifier 23. The AC amplifier 20 removes the DC component from the sum signal AS and outputs an amplified sum signal AS2. 2
Reference numeral 4 denotes a peak detection circuit which detects a peak level V _PK of a track cross component generated in the sum signal AS2 when the light spot crosses the track. 25 is a bottom detection circuit.
Detecting a bottom level V _BT of track cross component generated sum signal AS2. The comparison level V _TH is created by averaging the peak level V _PK and the bottom level V _BT .

The operation of detecting the direction of the optical disk device of the present embodiment configured as described above will be described with reference to FIG. The optical disk is a magneto-optical disk, and the sum signal AS
Does not generate a reproduction signal component.

In FIG. 2, the detection of the cross signal CROSS is the same as the conventional one and is omitted for simplicity. FIG. 2 shows, in order from the top, (a) a sum signal AS, (b) a sum signal AS with a DC component removed and amplified, peak level V _PK , bottom level V _BT , comparison level V _TH , and (c) 1 off-track signal OFTR output from the comparator 14
Is shown. Up to time t1, the light spot follows the track, traverses the track from time t1 to t2, and at time t2
From the track again. During the time from t1 to t2 when the vehicle crosses the track, a track cross component is generated in the sum signal AS as shown in FIG. The sum signal AS2 obtained by removing and amplifying the DC component is represented by (b)
As shown in (2), the signal moves upward with time due to the time constant of the AC coupling. Sum signal AS with DC component removed and amplified
The peak level V _PK of 2 is detected by following the sum signal AS2 as shown by the two-dot chain line. Further, the bottom level V _BT of the sum signal AS2 is detected as shown by a one-dot chain line. As indicated by a broken line from the average of the peak level V _PK and the bottom level V _BT , a comparison level V _TH that slices substantially following the center of the sum signal AS2 is created. The comparison level V _TH is compared with the sum signal AS2, and the off-track signal O
The FTR is reliably detected as shown in FIG.

The off-track signal OFTR is a cross signal C detected by zero-crossing the tracking error signal TE.
The direction detection signal D is latched by using ROSS as a clock.
An IR is created.

As described above, according to this embodiment, the AC amplifier (20) for removing the DC component of the sum signal obtained by adding the outputs of the photodetectors, and the sum signal when the light spot crosses the track. A peak detection circuit (24) for detecting the peak level of the generated track cross component from the output of the AC amplifier; and a bottom detection circuit (2) for detecting the bottom level of the track cross component from the output of the AC amplifier.
5) a first comparator (14) for comparing a comparison level formed from an average of the peak level and the bottom level with a track cross component of the output of the AC amplifier; and detecting a zero cross of the tracking error signal. A second comparator (15), and direction detecting means (16) for determining a direction in which the light spot crosses the track based on a phase relationship between an output of the first comparator and an output of the second comparator. When a light spot crosses a track of a magneto-optical disc or an unrecorded track of a phase-change optical disc, the center of the track cross component included in the sum signal is sliced at a comparative level to reliably detect the direction. Can be.

Next, a second embodiment of the present invention will be described.
The second embodiment adds an envelope detection circuit for detecting an envelope V _EN sum signal AS2 is removed by amplifying the DC component in the first embodiment, so that corresponding to the reproduction only optical disk with pit It was made. This is because a reproduction signal is not generated in the sum signal AS on a magneto-optical disc, but on a reproduction-only optical disc having pits, since a reproduction signal exists in the sum signal AS, the influence is removed by an envelope detection circuit, and the direction detection circuit malfunctions. Is prevented from doing so.

FIG. 3 shows the configuration of the second embodiment. 1. Configuration of the First Embodiment An additional 30 envelope detection circuits have been added to FIG.

The direction detecting operation of the second embodiment configured as described above will be described with reference to FIG. The optical disk is a read-only optical disk having pits, and the sum signal AS
Has a reproduction signal component. In FIG. 4, detection of the cross signal CROSS is the same as in the conventional example, and is omitted for simplicity.

FIG. 4 shows, in order from the top, FIG.
The existing sum signal AS, (b) is amplified by removing the DC component
The sum signal AS2, (c) is the envelope V of the sum signal AS2.
_EN, Peak level V_PK, Bottom level V_BT, Comparison level
V_TH, (D) the envelope V _ENOff-track signal using
The signal OFTR, (e) is the sum signal AS as in the first embodiment.
2 is an off-track signal OFTR.

When the light spot crosses the track,
As shown in (a), a track cross component occurs in the sum signal AS. A reproduction signal exists in the sum signal AS. The sum signal AS2 obtained by removing and amplifying the DC component moves upward with time due to the time constant of the AC coupling as shown in (b). As shown by the solid line (c), the by envelope detection circuit 30, the envelope V _EN of the sum signal AS2 the reproduced signal components present in the sum signal AS2 is reliably removed is detected. The peak level V _PK of the sum signal AS2 is detected as shown by a two-dot chain line. Further, the bottom level V _BT of the sum signal AS2 is detected as shown by a one-dot chain line. As indicated by a broken line from the average of the peak level V _PK and the bottom level V _BT , the comparison level V that slices by following substantially the center of the track cross component of the envelope V _EN.
TH is made. The comparison level V _TH is compared with the envelope V _EN from which the reproduction signal component has been removed, and the off-track signal O
The FTR is reliably detected as shown in (d).

On the other hand, as in the first embodiment, the comparison level V
_{When TH} is compared with the sum signal AS2, since the sum signal AS2 has a reproduced signal component, the off-track signal OFTR generates a lot of noise as shown in FIG. The noise of the off-track signal OFTR occurs not only when the light spot is following the track, but also when it crosses the track.

As described above, according to the present embodiment, the envelope detection circuit (30) for detecting the envelope of the track cross component generated when the light spot crosses the track from the sum signal from which the DC component has been removed is provided. The first comparator compares the envelope with the comparison level formed from the average of the peak level and the bottom level, thereby detecting the direction without generating noise even when the reproduced signal is present in the sum signal. Can be. For this reason, the moving direction of the light spot with respect to the track can be reliably detected in all the tracks of the optical disk, the magneto-optical disk, and the phase change disk in which the pit exists.

Next, a third embodiment of the present invention will be described.
The third embodiment is different from the first embodiment in that the comparison level V _TH
And a predetermined offset is added to the sum, and the track cross component of the sum signal AS2 is sliced at the comparison level obtained by adding the offset to generate an off-track detection signal OFTR. This is because during reproduction of the magneto-optical disk, the sum signal A
This is to prevent S2 and the comparison level _VTH from almost overlapping and generating noise in the off-track signal OFTR.

The direction detecting operation of this embodiment will be described with reference to FIG. The optical disk shown in FIG. 5 is a magneto-optical disk or a phase-change disk and has unrecorded tracks. In FIG. 5, the detection of the cross signal CROSS is the same as in the conventional example and is omitted.

FIG. 5 shows, in order from the top, (a) a sum signal AS having no reproduced signal, (b) a sum signal AS2 from which a DC component has been removed, a comparison level V _TH , and an offset V to the comparison level.
By adding _{OF V TH + V OF, (} c) to compare the level V _TH +
An off-track signal OFTR using V _OF , and (d) is an off-track signal OFTR using V _TH for the comparison level.

When the light spot crosses the track,
As shown in (a), the track cross component is included in the sum signal AS.
Occur. Sum signal amplified by removing DC component of sum signal AS
The signal AS2 has a time constant of AC coupling as shown in (b).
More signals move up. Peak level of sum signal AS2
V_PKAnd bottom level V_BTOf the sum signal AS2
Comparison level V that follows the heart_THIs made. Comparison level V
_THHas a predetermined offset V _OFIs added. offset
V_OFIs compared with the sum signal AS2.
And the off-track signal OFTR is detected as shown in FIG.
It is. Even if the light spot is following the track,
Comparison level V_THOffset V_OFV to which is added_TH
+ V_OFIs an off-track signal that does not overlap with the sum signal AS2.
No noise is generated in the OFTR.

On the other hand, as in the first embodiment, the offset V
Comparing the comparison level V _TH without adding _OF with the sum signal AS2, when the light spot follows the track, the comparison level V _TH and the sum signal AS2 almost overlap,
As shown in (d), noise occurs in the off-track signal OFTR.

As described above, according to this embodiment, by adding a predetermined offset to the comparison level formed from the average of the peak level and the bottom level, the light spot follows the track of the magneto-optical disk. In addition, noise generated in the off-track signal can be eliminated.

Next, a fourth embodiment of the present invention will be described.
The fourth embodiment differs from the first, second and third embodiments in that the first comparator and the second comparator each have a predetermined hysteresis characteristic.

The direction detecting operation of this embodiment will be described with reference to FIG. The optical disk shown in FIG. 6 is a magneto-optical disk or a phase-change disk and has unrecorded tracks. In FIG. 6, the detection of the cross signal CROSS is the same as in the conventional example, and is omitted.

FIG. 6 shows, in order from the top, (a) a sum signal AS having no reproduced signal, (b) a sum signal AS2 from which a DC component has been removed, a comparison level V _TH , a comparison level V _TH1 including hysteresis. V _TH2 , (c) is an off-track signal OFT using V _TH1 and V _TH2 including hysteresis in the comparison level
R.

When the light spot crosses the track,
As shown in (a), a track cross component occurs in the sum signal AS. The sum signal AS2 obtained by removing the DC component of the sum signal AS and amplifying the signal moves upward due to the time constant of the AC coupling as shown in (b). From the average of the peak level V _PK and the bottom level V _BT of the sum signal AS2, a comparison level V _TH that follows the center of the sum signal AS2 is created. Comparison level V
_The sum signal AS2 is compared with V _TH1 and V _{TH2 in} which _TH has a predetermined hysteresis, and the off-track signal OFTR is detected as shown in (c). Even when the light spot is following the track, the comparison level V having hysteresis
_TH1 and _VTH2 do not overlap with the sum signal AS2, and no noise occurs in the off-track signal OFTR.

The second comparator performs a zero-cross comparison of the tracking error signal. Information called ADIP is engraved on the track of the magneto-optical disk in a meandering manner, and the information of the ADIP signal is added to the tracking error signal, which generates noise when performing a zero-cross comparison. For this reason, the noise of the ADIP signal can be reduced by giving the hysteresis characteristic also to the second comparator.

As described above, according to this embodiment, the influence of noise included in the sum signal and the tracking error signal is reduced by providing the first comparator and the second comparator with predetermined hysteresis characteristics. The moving direction of the light spot with respect to the track can be reliably detected.

In the description of the embodiments, an optical disk or a magneto-optical disk having pits is assumed, but it is needless to say that the present invention can be applied to a phase change type disk and other optical disks.

In the third embodiment, the offset is added to the comparison level to change the comparison level of the first comparator. This can also be realized by adding the peak level and the bottom level at a predetermined ratio. it can.

[0052]

As described above, in this embodiment, when the light spot traverses the track, the comparison level (offset or hysteresis characteristic) formed from the average of the peak level and the bottom level of the sum signal from which the DC component has been removed. ) Slicing by tracking the vicinity of the center of the track cross component, the noise included in the sum signal and tracking error signal
Thus, the moving direction of the light spot with respect to the track can be reliably detected without being affected by noise .

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a direction detection circuit of an optical disc device according to a first embodiment of the present invention.

FIG. 2 is a waveform chart showing an operation of the direction detection circuit in the first embodiment.

FIG. 3 is a block diagram showing a configuration of a direction detection circuit of the optical disc device according to a second embodiment of the present invention.

FIG. 4 is a waveform chart showing the operation of the direction detection circuit in the second embodiment.

FIG. 5 is a waveform chart showing the operation of the direction detection circuit according to the third embodiment of the present invention.

FIG. 6 is a waveform chart showing the operation of the direction detection circuit according to the fourth embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a direction detection circuit of a conventional optical disk device.

FIG. 8 is a waveform chart showing the operation of the conventional direction detection circuit.

FIG. 9 is a perspective view showing a track on a conventional read-only optical disk having concavo-convex pits and a magneto-optical disk.

FIG. 10 is a waveform diagram showing a sum signal obtained from a conventional read-only optical disk having uneven pits and a magneto-optical disk.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical disk 2 Spindle motor 3 Optical head 4 Semiconductor laser 8 Objective lens 9 Photodetector 14 First comparator 15 Second comparator 20 AC amplifier 24 Peak detection circuit 25 Bottom detection circuit 30 Envelope detection circuit

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) G11B 7/08-7/095 G11B 21/08-21/10

Claims (4)

(57) [Claims] An optical head for recording and reproducing a signal by causing a light spot to follow a track of an optical disk; a divided photodetector for receiving reflected light from the optical disk; and a difference between outputs of the divided photodetectors. An arithmetic circuit that generates a focus error signal and a tracking error signal from the motion, and generates a sum signal from the addition; an AC amplifier that AC-couples the sum signal to remove a DC component; and when the light spot crosses a track. A peak detection circuit that detects a peak level of a track cross component generated in the sum signal from an output of the AC amplifier; a bottom detection circuit that detects a bottom level of the track cross component from an output of the AC amplifier; To the average level of the peak level and the bottom level
A first level for comparing a comparison level formed by applying a predetermined offset with a track cross component of the output of the AC amplifier;
A second comparator for zero-cross detection of the tracking error signal; and a light spot crossing the track based on a phase relationship between an output of the first comparator and an output of the second comparator. An optical disk device comprising: a direction detecting unit that determines a direction. 2. The optical disk device according to claim 1, further comprising: an envelope detection circuit that detects an envelope of a track cross component generated in a sum signal when the light spot crosses the track from an output of the AC amplifier. An optical disc device , wherein the comparator compares a comparison level with an envelope of the envelope detection circuit. 3. A light spot on a track of an optical disk.
An optical head for recording and reproducing signals to be followed, and a divided light detection for receiving reflected light from the optical disk
Vessels and a focus error from the differential outputs of the divided optical detector
Signal, tracking error signal, sum signal from addition
And an AC amplifier for AC coupling the sum signal to remove a DC component.
And when the light spot traverses the track, the sum signal
The peak level of the track cross component occurring at
A peak detection circuit for detecting from the output of the AC amplifier, and a bottom level of the track cross component to the AC amplifier.
A bottom detection circuit for detecting from the output of the loop, and an average level of the peak level and the bottom level.
The track of the AC amplifier output and the comparison level
A first comparator for comparing a cross component and a second comparator for zero-cross detecting the tracking error signal.
A comparator, and an output of the first comparator and an output of the second comparator.
The direction in which the light spot crosses the track from the phase relationship
Direction detection means for determining whether the first and second comparators are respectively provided with predetermined directions.
Optical disc device having a hysteresis. 4. An optical disk device according to claim 3, wherein
The light signal is generated when the light spot crosses the track
Track cross component envelope
An envelope detection circuit for detecting from an output, the first comparator includes a comparison level and the envelope detection circuit.
An optical disc device that compares with a road envelope.