JP2002197687A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk device such that normal tracking control is performed even when a track error signal is distorted due to the defect such as the scratch on the optical disk. SOLUTION: The reflected light of the optical disk is entered onto the light receiving surface of photodetectors 24a-24d. The amplitude of an output sum signal V1 of the photodetectors 24a and 24c is limited to a specified value by a limiter circuit 33a. The amplitude of an output sum signal V1' of the photodetectors 24b and 24d is limited to the above specified value by a limiter circuit 33b. By binarization circuits 34a and 34b, input signals V2 and V2' are respectively binarized by using thresholds of specified rates with respect to the average of maximum amplitudes of these input signals. Phases of output signals V3 and V3' of the binarization circuits 34a and 34b are compared with each other by a phase comparator circuit 35 to provide a signal V4 showing the phase difference, an the track error signal. The tracking control is carried out by using this track error signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a DPD (Differentia)
The present invention relates to an optical disk device that generates a track error signal by applying a (Phase Detection) method and performs tracking control.

[0002]

2. Description of the Related Art In an optical disk apparatus to which the DPD method is applied, a laser beam reflected from an optical disk is incident on a light receiving element such as a four-division photodiode and changes in light intensity distribution on a light detection area of the four-division photodiode. Is detected. The light detection area is divided into four sections diagonally, and signals from the light detection areas located opposite to each other with respect to the center point of the detection area are added, and two sum signals are obtained from the four areas. The track error signal is obtained by taking the phase difference between the two sum signals. Tracking control is performed based on this track error signal.

In order for the track error signal to accurately reflect the radial position of the laser beam spot with respect to the track on the optical disk, the mounting position and angle of the four-division photodiode are accurately adjusted.

[0004]

If the positional adjustment of the mounting position and angle of the four-division photodiode is insufficient, the waveforms of the sum signal and the track error signal are distorted, and retries are performed during reproduction. I had to play the data. Further, when there is a defect such as a scratch, dust, or fingerprint on the optical disk, the track error signal waveform is distorted, and tracking becomes unstable.

[0005] When the track error signal waveform is distorted in this way, retry increases during reproduction, so that extra processing time is required, and as a result, the reproduction speed of data particularly at defective portions is reduced.

Accordingly, the present invention is applicable to a case where the track error signal is distorted due to low positional accuracy of the light receiving element for receiving the reflected light of the optical disk and a defect on the disk.
It is an object of the present invention to provide an optical disk device capable of performing normal tracking control.

[0007]

In order to achieve the above object, an optical disk apparatus according to the present invention comprises a plurality of light receiving elements for receiving reflected light from an optical disk, and a light receiving element selected from the plurality of light receiving elements. A first adding circuit for adding outputs,
A second adding circuit for adding outputs of other light receiving elements selected from the plurality of light receiving elements, and a first adding circuit for limiting output signal amplitudes of the first and second adding circuits to a constant value, respectively. And the second limiter circuit and the output signals of the first and second limiter circuits are input, and the input is binarized using a threshold at a predetermined ratio with respect to the average of the maximum amplitude of the input signal. Comparing the phases of the output signals of the first and second binarization circuits with the first and second binarization circuits,
A phase comparison circuit for providing a phase difference.

Further, the optical disk device of the present invention is characterized in that the first
And a defect detection circuit for detecting a defective portion on the disk based on an output signal of the second addition circuit, and input to the first and second binarization circuits in accordance with an output of the defect detection circuit. Switching means for switching the output signal to one of the first and second adder circuit outputs and the first and second limiter circuit outputs.

Even when a defect such as a scratch is present on the optical disk and the track error detection signal is distorted, the distortion is removed by the limiter circuit and normal tracking control is performed.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an optical disk device to which the present invention is applied. The optical disk 1 is rotated by a motor 3 at a constant linear velocity, for example. Recording and reproduction of information on and from the optical disc 1 are performed by an optical pickup 5.
Done by The optical pickup 5 is fixed to a drive coil 7 constituting a movable part of a linear motor 6,
This drive coil 7 is controlled by a linear motor control circuit 8.

The linear motor control circuit 8 includes a speed detection circuit 9
The speed signal of the optical pickup 5 detected by the speed detection circuit 9 is sent to the linear motor control circuit 8. A permanent magnet (not shown) is provided at a fixed portion of the linear motor 6. When the drive coil 7 is excited by the linear motor control circuit 8, the optical pickup 5 is moved in the radial direction of the optical disc 1.

The optical pickup 5 is provided with an objective lens 10 supported by a wire or a leaf spring (not shown). The objective lens 10 can be moved in the focusing direction (the direction of the optical axis of the lens) by driving the drive coil 11, and can be moved in the tracking direction (the direction orthogonal to the optical axis of the lens) by driving the drive coil 12. Is possible.

A light beam is emitted from the semiconductor laser oscillator 9 by the drive control of the laser control circuit 13. The light beam emitted from the semiconductor laser oscillator 19 is irradiated on the optical disc 1 via the collimator lens 20, the half prism 21, and the objective lens 10. The reflected light from the optical disc 1 is guided to a photodetector 24 via an objective lens 10, a half prism 21, a condenser lens 22, and a cylindrical lens 23.

The photodetector 24 includes a four-divided photodetector cell 24.
a, 24b, 24c and 24d. The output signal of the photodetector cell 24a is supplied to one end of an adder 26a via a current / voltage conversion amplifier 25a. The output signal of the light detection cell 24b is supplied to one end of an adder 26b via an amplifier 25b. The output signal of the light detection cell 24c is supplied to the other end of the adder 26a via the amplifier 25c. The output signal of the light detection cell 24d is
It is supplied to the other end of the adder 26b via d.

The output signal of the adder 26a is
And the non-inverting input terminal of the differential amplifier 14 is supplied with the output signal of the adder 26b. The differential amplifier 14 outputs a signal corresponding to the difference between the two output signals of the adders 26a and 26b as a focus error signal. This output is supplied to the focusing control circuit 27. The output signal of the focusing control circuit 27 is supplied to the focusing drive coil 12. Thus, control is performed such that the laser beam is always just focused on the optical disc 1.

The output signals of the adders 26a and 26b are also supplied to the phase difference detecting circuit 17 according to the present invention. The phase difference detection circuit 17 detects the phase difference between the output signals of the adders 26a and 26b, and supplies this phase difference to the tracking control circuit 28 as a track error signal. The tracking control circuit 28 generates a track drive signal according to the track error signal from the phase difference detection circuit 17.

The track driving signal output from the tracking control circuit 28 is the driving coil 1 in the tracking direction.
1 is supplied. Further, a track difference signal used in the tracking control circuit 28 is supplied to the linear motor control circuit 8.

By performing the above-described focusing control and tracking control, a full addition signal of the output signals of the photodetection cells 24a to 24d of the photodetector 24, that is, an output signal of the adder 26c corresponds to the recording information. Thus, a change in reflectivity from bits formed on tracks of the optical disc 1 is reflected. This signal is supplied to the data reproducing circuit 18. The data reproduction circuit 18 reproduces recorded data based on a reproduction clock signal from the PLL circuit 16.

When the objective lens 10 is moved by the tracking control circuit 28, the linear motor 6, that is, the optical pickup 5 is moved by the linear motor control circuit 8 so that the objective lens 10 is located near the center of the optical pickup 5. Be moved.

The motor control circuit 4, the linear motor control circuit 8, the laser control circuit 15, the PLL circuit 16, the data reproduction circuit 18, the focusing control circuit 27, the tracking control circuit 28, the error correction circuit 32 and the like are connected via a bus 29. It is controlled by the CPU 30. The CPU 30 performs a predetermined operation according to a program recorded in the memory 2.

FIG. 2 is a block diagram showing a configuration of the phase difference detection circuit 17 according to the first embodiment of the present invention. DPD
In tracking control by the method, the light detection cell 24
a, 24c, ie, the output V1 of the adder 26a, and the sum signal of the outputs of the photodetector cells 24b, 24d, ie, the track error signal V4 corresponding to the phase difference between the output V1 ′ of the adder 26b. Tracking control is performed based on this.

As shown in FIG. 2, the phase difference detecting circuit 17 of the present invention includes a limiter 3 for limiting the amplitudes of the output signals V1 and V1 'of the adders 26a and 26b at a constant level.
3a and 33b, binarization circuits 34a and 34b for binarizing the output signals V2 and V2 'of the limiters 33a and 33b, respectively, outputs V3 of the binarization circuits 34a and 34b,
A phase comparison / LPF circuit 35 for detecting and smoothing the phase difference of V3 'and outputting a track error signal V4 is included.

FIG. 3 is a waveform chart for explaining the basic operation of the phase difference detecting circuit 17. FIG. 3A shows an input signal waveform V1 of the limiter circuit 33a. This waveform shows a waveform when a laser beam generated from the pickup 5 accurately traces a track on the optical disk and receives reflected light at a location where a defect such as a flaw, dust, or fingerprint exists. If there are no such defects on the disc,
Although the amplitudes of the inputs V1 and V 'are substantially constant, when there is a defect, the amplitude of the defective portion becomes small as shown in FIG.

The limiter circuit 33a adjusts the level of the input signal V1 to a level VL that is approximately 1/2 of the average maximum amplitude Vp of the input signal V1.
Limit one. As a result, the limiter circuit 33 a
A signal V2 having substantially the same amplitude as shown in FIG. The binarization circuit 34a is configured to output the amplitude VL of the input signal V2 substantially equal to one.
At the level VSL of / 2, the input signal V2 is binarized.
The operation of the limiter circuits 33a and 33b is the same,
The operation of the binarization circuits 34a and 34b is the same.

FIG. 4 is a block diagram showing the configuration of the limiter circuit 33a. The peak detection circuit 36
The peak value (average maximum amplitude) VP of the output V1 is detected. The level generation circuit 37 generates a voltage level VL that is approximately の of the peak value VP detected by the peak detection circuit 36. The LPF (low-pass filter) is a level generation circuit 37
Smoothes the voltage level VL generated by. The limiter 39 limits the amplitude of the input signal V1 to the voltage level VL, and outputs a signal V2 shown in FIG. If the input amplitude fluctuates depending on the disk, the peak detection of the signal is performed sufficiently slower than the speed at which the defect occurs, and the level generation circuit 37 determines the amplitude at which the limiter works from the peak amplitude.

FIG. 5 shows a configuration example of the limiter 39. 3
9a and 39b are resistors, 39c is a diode 39d, and an operational amplifier. Note that the signal waveform shown in FIG. 3B shows the output of the limiter 39 inverted for convenience of explanation. The operation of the limiter circuit 33b is the same as that of the limiter circuit 33a.

FIG. 6 is a waveform diagram for explaining the operation of the binarization circuits 34a and 34b and the phase comparison / LPF 35. FIG. 6A is a waveform diagram when the laser beam generated from the pickup 5 accurately traces a track on the optical disk. In this case, the phase difference detection circuit 1
7, there is no phase difference between the inputs V1 and V1 ', and the rising and falling edges of the binarized signals V3 and V3' almost coincide. Therefore, the phase difference signal VD after the phase comparison hardly occurs.

FIG. 6B is a waveform diagram when the laser beam generated from the pickup 5 is slightly deviated from the center of the track on the optical disk. In such a case, a phase difference occurs between the input V1 and the input V1 'of the phase difference detection circuit 17. Here, a case is shown in which the input V1 'has a leading phase with respect to the input V1 of the phase difference detection circuit 17. As shown in FIG. 6B, the timings of the rising and falling edges of the binarized signals V3 and V3 'are shifted, that is, a phase difference occurs.

The phase comparison / LPF circuit 35 generates a phase difference signal VD corresponding to the phase difference. The phase difference signal VD is smoothed by the LPF, and the phase comparison / LPF 35 outputs a track error signal V4 as shown in FIG. This error signal V4 is output from the tracking control circuit 28.
Supplied to The tracking control circuit 28 controls the current flowing through the drive coil 11 in the tracking direction so that the error signal V4 becomes 0.

If there is a defect such as a flaw on the optical disk, the added output waveform of the light detecting element, that is, the input signal waveform of the phase difference detecting circuit 17 is distorted as shown in FIG. At this time,
Generally, the input signals V1 and V1 'are distorted differently. The phase difference detection circuit 17 according to the present invention has limiter circuits 33a and 33b added as compared with the conventional phase difference detection circuit. When the laser beam accurately traces a track on the optical disk, the input signals V1 and V1 'having different distortions from each other due to defects on the disk are directly converted into binary signals as in the prior art. When supplied to the binarization circuit, a phase difference occurs between outputs V3 and V3 'of the binarization circuit. As a result, the phase comparison / LPF circuit 35 outputs an erroneous track error signal. Therefore, the tracking control circuit 28 cannot correctly control the lens driving coil, and normal tracking control becomes impossible.

In the case of the present invention, since the limiter circuits 33a and 33b are provided, it is possible to minimize the influence of distortion of the input signals V1 and V1 'due to a defect on the disk. That is, the distortion portions can be removed by providing the limiter circuits 33a and 33b. Therefore, an accurate track error signal can be generated. FIG. 3C shows the track error signal V4 output without being affected by the waveform distortion due to the defect on the disk.
Show. FIG. 3D shows a track error signal by a conventional phase difference detection circuit affected by waveform distortion due to a defect on the disk.

FIG. 7 is a block diagram showing the configuration of the phase difference detection circuit 17 according to the second embodiment of the present invention. The phase difference detection circuit 17 of the present embodiment is designed to improve the S / N ratio.
Normally, the limiter is not applied, but is applied only when a defect is detected.

Outputs V1 and V of adders 26a and 26b
1 'is further added by the adder 26d, and the adder 26d
Is output to the defect detection circuit 41. The defect detection circuit 41 detects a defective portion on the disk based on the signal V5.

FIG. 8 is a block diagram showing the structure of the defect detection circuit 41. The defect detection circuit 41 is a peak detection circuit 4
2, a level generation circuit 43, a binarization circuit 44, a mono-multi 45, and an envelope potential detection circuit 46. FIG. 9 is a waveform chart showing the operation of the defect detection circuit 41. The peak detection circuit 42 detects the average peak value VP2 of the output signal V5 of the adder 26d as shown in FIG. The level generation circuit 43 generates a slice level VL2 used in the binarization circuit from the average peak value VP2. The envelope potential detection circuit 46 detects the envelope potential VP3 of the signal V5.

The binarization circuit 44 binarizes the envelope potential VP3 using the slice level VL2, and outputs a binarized signal VB shown in FIG. 9B. For convenience of explanation, the signal VB shown in FIG. 9B is obtained by inverting the level of the output of the binarization circuit 44. The mono multi 45 is triggered by the rise of the binarized signal VB and outputs a high level signal for a predetermined time. As a result, the mono multi 45 is shown in FIG.
A signal VM indicating a defective portion is output as shown in FIG.

SW1 and SW2 are binarizing circuits 34a and 34 according to the level of the output signal VM of the defect detecting circuit 41.
The signal input to b is switched. When the output signal VM of the defect detection circuit 41 is at a low level, that is, when there is no defect on the disk, the switches SW1 and SW2 are connected to the adder 26.
When the signal VM is at a high level, that is, when a defect on the disk is detected, the signal VM is connected to the limiter circuits 33a and 33b. As a result,
Only when a defective portion on the disk is detected, the adder 26a
And 26b output signals V1 and V1 'are subjected to a limiter. An error signal V4 is generated based on the signals V2 and V2 'subjected to the limiter.

FIG. 10 is a block diagram showing the configuration of the phase difference detection circuit 17 according to the third embodiment of the present invention. In the present embodiment, the output signal VM of the defect detection circuit 41 is supplied to the binarization circuits 47 and 48. Binarization circuit 47
And 48, when the output signal VM of the defect detection circuit 41 is at the low level, that is, when there is no defect on the disk, the relatively high slice level V as shown in FIG.
The signals V1 and V1 'are binarized using L, and when the signal VM is at a high level, that is, when a defect on the disk is detected, a relatively low slice level VSL as shown in FIG. To binarize the signals V1 and V1 '. This embodiment has the same effect as the second embodiment shown in FIG.

[0039]

As described above, according to the present invention, disturbance of an error signal when passing through a defective portion on a disk is prevented, and stable tracking can be performed. As a result, the number of retries for reproduction is reduced, and the data reproduction speed at the defective portion is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical disk device to which the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a phase difference detection circuit according to the first embodiment of the present invention.

FIG. 3 is a waveform chart for explaining a basic operation of the phase difference detection circuit.

FIG. 4 is a block diagram illustrating a configuration of a limiter circuit.

FIG. 5 is a diagram illustrating an example of a circuit configuration of a limiter.

FIG. 6 is a waveform chart for explaining the operation of the binarization circuit and the phase comparison / LPF.

FIG. 7 is a block diagram showing a configuration of a phase difference detection circuit according to a second embodiment of the present invention.

FIG. 8 is a block diagram illustrating a configuration of a defect detection circuit.

FIG. 9 is a waveform chart showing the operation of the defect detection circuit.

FIG. 10 is a block diagram showing a configuration of a phase difference detection circuit according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical disk, 3 ... Motor, 10 ... Objective lens, 1
1, 12: lens drive coil, 20: collimator lens, 21: half prism, 22: condenser lens, 23 ...
Cylindrical lenses, 24a to 24d ... photodetection cells,
25a to 25d: current / voltage conversion amplifiers, 26a to 26
c: adder, 33a, 33b: limiter circuit, 34
a, 34b... binarization circuits.

Claims (4)

[Claims] A plurality of light receiving elements for receiving reflected light from an optical disk; a first adding circuit for adding outputs of light receiving elements selected from the plurality of light receiving elements; A second adder circuit for adding the outputs of the other light receiving elements selected in the above, a first and a second limiter circuit for limiting the output signal amplitudes of the first and the second adder circuits to constant values, respectively. An output signal of the first and second limiter circuits is input, and a first and a second input signal are respectively binarized using a threshold at a predetermined ratio with respect to the average of the maximum amplitude of the input signal.
An optical disc device, comprising: a binarization circuit of (1), and a phase comparison circuit that compares phases of output signals of the first and second binarization circuits and provides a phase difference. 2. A defect detecting circuit for detecting a defective portion on a disk based on output signals of the first and second adder circuits, and a first and a second signal detecting means for detecting a defective portion on a disk according to an output of the defect detecting circuit. And a switching unit for switching a signal input to the binarizing circuit to one of the first and second adding circuit outputs and the first and second limiter circuit outputs. An optical disk device as described in the above. 3. The constant value in the first and second limiter circuits is a voltage level having a ratio of about 1/2 of the average of the maximum amplitudes of the outputs of the first and second adder circuits. 3. The optical disk device according to claim 1, wherein: 4. A plurality of light receiving elements for receiving reflected light from an optical disk; a first adding circuit for adding outputs of light receiving elements selected among the plurality of light receiving elements; A second addition circuit that adds the outputs of the other light-receiving elements selected in step (a), a defect detection circuit that detects a defective portion on the disk based on output signals of the first and second addition circuits, First and second binarization circuits for binarizing output signals of the first and second adder circuits using threshold values changed according to the output of the defect detection circuit; and the first and second binarization circuits. An optical disc device comprising: a phase comparison circuit that compares the phases of output signals of a binary binarization circuit and provides a phase difference.