JPH08255360A - Optical disk device - Google Patents

Abstract

PURPOSE: To effectively remove the DC offset component of a tracking error signal owing to the inclination of an optical axis and the movement of an objective lens by inputting signals from two light receiving surfaces to a 1st subtractor and generating a push-pull signal, etc. CONSTITUTION: A photodetector 21 has the two light receiving surfaces 21A and 21B divided into two in the direction along a track of a disk. A light spot S reaching the photodetector 21 after reflecting from the disk is incident upon approximately the middle of the photodetector 21, and the output signals of the light receiving surfaces 21A and 21B are amplified by amplifiers 22A and 23B, where the output of the amplifier 22A is inputted to a subtractor 23 and an envelope detecting circuit 24A, while the output of the amplifier 22B is inputted to the subtractor 23 and an envelope detecting circuit 24B. The output of the subtractor 23 is inputted to a subtractor 28 via a low pass filter 27. Outputs of the envelope detecting circuits 22A and 24B are inputted via low pass filters 25A and 25B to a subtractor 26, and its output is inputted via the subtractor 28, a phase compensation circuit 29 and a driving circuit 30 to a tracking actuator 31, so that an objective lens is driven, and tracking servo control is carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error detection system for an optical disk device for recording / reproducing information signals by using an optical information recording medium.

[0002]

2. Description of the Related Art In an optical disc apparatus for reproducing a digital audio signal or a video signal recorded on a disc-shaped optical information recording medium, an optical spot is focused on the recording surface of the disc and An optical head and a servo control system are used as a means for scanning along the track of the disk. Among these, some methods are known as methods for detecting a tracking error signal for scanning a light spot along a track.

As one of the tracking error signal detecting methods, a tracking error signal detecting method disclosed in Japanese Patent Laid-Open No. 4-23234 will be described below with reference to FIG.

FIG. 6 is a circuit diagram showing both the light receiving surface of the photodetector and the light spot on the photodetector, and the configuration of the signal processing circuit. In FIG. 6, reference numeral 11 denotes a photodetector including two light receiving surfaces 11A and 11B divided corresponding to the track direction of the optical disc. The reflected light spot S of the light beam applied to the optical disc is incident on the photodetector 11. The differential component of the signals detected by the two light receiving surfaces 11A and 11B is a tracking error signal by the so-called push-pull method.

In the optical disk device, when the optical axis is tilted due to the warp of the disk or the objective lens is moved for tracking control, the position of the light spot S moves on the photodetector 11 and the two light receiving surfaces 11A. , 11B signal levels are unbalanced. Therefore, with the simple push-pull method, the center value of the tracking error signal fluctuates, and normal tracking control cannot be performed.

On the other hand, in the method shown in FIG. 6, after the output of the light receiving surface 11A is amplified by the amplifier 12A, the peak level of the signal is detected by the peak detector 13A and is input to the low pass filter 14A to be DC unbalanced. The component is detected. This signal and the output of the amplifier 12A are input to the subtractor 15A to remove the DC unbalanced component from the output signal of the amplifier 12A. Similar processing is performed on the output of the light-receiving surface 11B, and a signal from which the DC unbalanced component is removed is obtained as the output of the subtractor 15B. Thereafter, these two signals are input to the subtractor 16 to generate a differential component, and the tracking error signal TE is obtained via the low pass filter 17.

[0007]

However, in an actual optical disk device, since the light intensity distribution in the light spot S, the position adjustment error of the photodetector 11 and the like are different for each optical head, the two light receiving surfaces 11A and 11B. The output signal waveform of is not completely symmetrical. Therefore, in general, the center of the waveform of the tracking error signal and the center of operation of the tracking servo do not always match without adjustment, and balance adjustment is required to match them.

However, in the conventional tracking error detecting method, the DC components are removed from the output signals of the two light receiving surfaces 11A and 11B, respectively, and then the subtracter 17 generates the differential components of the signals from the two light receiving surfaces. Therefore, there is a problem that balance adjustment is impossible.

Further, in the conventional method, the DC component is effectively removed by setting the ratio of the resistors R1 and R2 to R1 / R2 = 0.5 to 0.8. Although described, the ratio of the resistance values, that is, the optimum value of the coefficient in the subtraction process is different for each disk, and therefore it is desirable to set the optimum value every time the disk is replaced. However, in the conventional method, there are two adjustment points, that is, the subtracter 15A side and the subtractor 15B side, and there is a problem that the configuration is complicated and the operation becomes complicated.

[0010]

[Means for Solving the Problems] In order to solve the problems,
In the optical disk device of the present invention, the signals from the two light receiving surfaces are input to the first subtractor to generate a so-called push-pull signal, and after detecting the envelopes of the signals from the two light receiving surfaces, the second Input to the subtractor of D
The differential component of the C component is detected. And the first and second
A third subtractor for subtracting the output of the subtractor is provided to obtain the tracking error signal.

Further, in the optical disk device of the present invention, the first
Alternatively, there is provided balance adjusting means for matching the center of the waveform of the tracking error signal with the center of operation of the tracking servo by the coefficient of the subtraction process of the second subtractor,
The coefficient of the third subtractor is provided with the offset removal adjusting means for minimizing the fluctuation of the center value of the tracking error signal with respect to the inclination of the optical axis and the movement of the objective lens.

Further, in order to automatically perform the balance adjustment and the offset removal adjustment, the objective lens movement signal generating means and the system control means for controlling them are provided.

[0013]

In the optical disk device of the present invention, the signals from the two light receiving surfaces of the photodetector are input to the first subtractor to generate the push-pull signal. On the other hand, the signals from these two light receiving surfaces are respectively input to the first and second envelope detection circuits to detect the upper envelope of each signal, and these signals are respectively passed to the second subtractor via the low pass filter. Input and detect the differential component of DC offset. Next, the outputs of the first and second subtractors are input to the third subtractor to remove the DC offset component from the push-pull signal.

At this time, the DC offset component is removed by adjusting the gain for the output signal of the second subtractor. Further, balance adjustment is performed by finely adjusting the gain on the input side of the first or second subtractor.

Further, the system control means is used to turn on the focus servo control prior to the tracking servo control, and in this state, the DC offset component removal adjustment and the balance adjustment are automatically performed while monitoring the tracking error signal.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical disk device which is an embodiment of the present invention will be described below with reference to the drawings.

First, the configuration of the optical disk device as the first embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a circuit diagram showing a light receiving surface of a photodetector and a light spot on the photodetector and a configuration of a signal processing circuit of an optical disk device.

In FIG. 1, the photodetector 21 has two light receiving surfaces 21A and 21B which are divided into two in the direction along the track of the disk. The light spot S that has been reflected from the disk and reached the photodetector 21 enters the photodetector 21 at substantially the center thereof. The output signals of the light receiving surfaces 21A and 21B are amplified by the amplifiers 22A and 22B, respectively. Amplifier 2
The output of 2A is the subtractor 23 and the envelope detection circuit 2
4A, and the output of the amplifier 22B is input to the subtractor 23 and the envelope detection circuit 24B. Subtractor 2
The output of 3 is input to the subtractor 28 via the low pass filter 27.

Envelope detector circuits 24A and 24B
Outputs of low-pass filters 25A and 25B, respectively.
Is input to the subtractor 26 via. The output of the subtractor 26 is input to the subtractor 28, and the output of the subtractor 28 is supplied to the tracking actuator 31 via the phase compensation circuit 29 and the drive circuit 30. Tracking actuator 3
The objective lens is driven by 1 to perform tracking servo control.

Next, the operation of this embodiment will be described with reference to FIG.

In FIG. 2, (a) is a plan view showing the relationship between the photodetector 21 and the light spot S when the objective lens is in the neutral position and (b) is moved from the neutral position. is there. Further, (c) to (g) respectively show the amplifier 22A, the amplifier 22B, the low-pass filter 27, the subtracter 26, and the subtracter when only the focus servo control is on and the light spot on the disk scans across the track. FIG. 4 is a diagram showing a signal waveform of the container 28, where the waveform on the left side of each figure shows the state where the light spot S is (a), and the waveform on the right side is (b)
Indicates the state of. Further, (h) is an enlarged view of the signal waveform of the subtractor 28. In the figure, REF indicates a reference voltage for circuit operation, that is, a voltage when there is no signal.

When the objective lens is in the neutral position,
As shown in (a), the light spot S is incident on the center of the photodetector 21. However, when the objective lens moves due to the operation of the tracking actuator, the light spot S moves from the center of the photodetector 21 as shown in (b). The same phenomenon occurs even if the optical axis is tilted due to the tilt of the disk.

2C and 2D show output waveforms of the amplifier 22A and the amplifier 22B, respectively. Further, since the outputs of the amplifier 22A and the amplifier 22B are envelope-detected by the envelope detection circuits 24A and 24B, respectively,
The outputs of the low pass filters 25A and 25B are
The upper envelope of the waveform shown in FIGS. 2 (c) and 2 (d) is obtained.

As shown in (c) and (d) of FIG. 2, when the light spot S is in (a), that is, when the objective lens is in the neutral position, the signal levels of the outputs of the amplifiers 22A and 22B are almost the same. equal. However, in the state where the light spot S is (b), the amount of light incident on the light receiving surfaces 21A and 21B becomes unbalanced, so that the signal level of the output of the amplifier 22A becomes small and becomes large in the amplifier 22B.

The output of the low-pass filter 27 is (e)
As shown in, a differential component of the outputs of the amplifiers 22A and 22B, that is, a tracking error signal by the push-pull method is obtained. Further, as shown in (f), the differential component of the upper envelope of the waveforms (c) and (d) is obtained at the output of the subtractor 26.

Here, in the states (a) and (b) of the light spot S, the push-pull signal (e) corresponds to the signal level changes shown in (c) and (d). Of the center level of V and the differential signal of the envelope of (f) are V
It varies by o and Ve. For Vo and Ve, Vo =
Since there is a relationship of (0.7 to 0.85) × Ve, by setting the ratio of the gains G3 and G4 of the inverting and non-inverting inputs of the subtractor 28 to G4 / G3 = 0.7 to 0.85. At the output of the subtractor 28, a push-pull signal with the DC offset component removed is obtained as shown in (g). As a result, a tracking error signal having no DC offset component can be obtained even if the position of the light spot S on the photodetector 21 moves.

By the way, in an actual optical disk device, the light intensity distribution in the light spot S, the position adjustment error of the photodetector, etc. differ from device to device, so the output signal waveforms of the two light receiving surfaces are not completely symmetrical. . Therefore, the values of A and B shown in (h) of FIG. 2 do not necessarily match. Therefore, it is necessary to adjust the balance so that the values of A and B in FIG. 2 (h) match and the center of the waveform of the tracking error signal and the center of operation of the tracking servo match. This adjustment is
Gain G1 of the inverting and non-inverting inputs of the subtractor 26 of FIG.
By adjusting at least one of G2 and G2, the output of the subtractor 26, that is, the DC offset component shown in FIG. Further, the balance adjustment can be similarly performed by adjusting the gain of the subtractor 23 instead of the subtractor 26. Since the balance adjustment is performed by finely adjusting the gain of the subtractor 26 or the subtractor 23, this adjustment does not impair the DC offset component removal performance of the push-pull signal.

According to the present embodiment, the tracking error signal detection method by the push-pull method of the optical disk device effectively removes the DC offset component of the tracking error signal due to the tilt of the optical axis or the movement of the objective lens, and at the same time DC
1 for offset component removal adjustment and 1 for balance adjustment
It can be performed with a simple structure by adjusting the location.

Next, the structure of the optical disk device as the second embodiment of the present invention will be described with reference to FIG.

FIG. 3 is a circuit diagram showing both the light-receiving surface of the photodetector and the light spot on the photodetector and the configuration of the signal processing circuit in the optical disk device. In FIG. 3, the photodetector 2
Reference numeral 1 denotes four light-receiving surfaces 21A, 21B, 2 which are divided into four in the direction along the track of the disc and in the direction perpendicular to the direction.
It has 1C and 21D. The light spot S that has been reflected from the disk and reached the photodetector 21 is
It is incident on approximately the center of 1. Light-receiving surface 21A, 21B, 21C
And the output signals of 21D are amplifiers 22A and 22D, respectively.
Amplified at B, 22C and 22D. Amplifier 22A ~
The outputs of 22D are the adders 32A with the connections shown in the figure.
~ 32D. Adders 32A, 32B, 32
The outputs of C and 32D are amplifiers 22A and 22C,
The sum signals of the amplifiers 22B and 22D, the amplifiers 22A and 22B, and the amplifiers 22C and 22D are obtained. Furthermore, the amplifier 2
The outputs of 2A, 22B, 22C and 22D are adders 37
Is added and input to the signal reproduction circuit 38.

The outputs of the adders 32A and 32B are input to the subtractor 33 and become the focus error signal. The output of the subtractor 33 is input to the focus actuator 36 via the phase compensation circuit 34 and the drive circuit 35.

The outputs of the adders 32C and 32D are input to the envelope detection circuit 24A and the subtractor 23, and to the envelope detection circuit 24B and the subtractor 23, respectively. The connections and operations of the envelope detection circuits 24A and 24B and the subtractor 23 and subsequent elements are the same as in the first embodiment.

According to the present embodiment, the tracking error signal detection by the push-pull method effectively removes the DC offset component of the tracking error signal due to the tilt of the optical axis or the movement of the objective lens, and the DC offset component removal adjustment and balance. The adjustment and the adjustment can be performed at one position, respectively, with a simple structure. Further, the focus error signal and the tracking error signal can be collectively detected by one photodetector.

Next, the configuration of the optical disk device as the third embodiment of the present invention will be described with reference to FIGS. 4 and 5.

FIG. 4 is a circuit diagram showing both the light receiving surface of the photodetector and the light spot on the photodetector of the optical disk device, and the configurations of the signal processing circuit and the automatic adjustment circuit. The tracking error signal detection principle in this embodiment is similar to that in the first and second embodiments. The automatic adjustment, which is a feature of this embodiment, will be described below.

In FIG. 4, the subtracter 26 and the subtractor 28 respectively include gain control means 40 and 41 controlled by a signal from the system control circuit 45. Also,
The output of the subtractor 28 is input to the system control circuit 45 via the signal monitor means 42. Reference numeral 43 is a loop switch for opening and closing the tracking control loop, 44 is a signal changeover switch for changing over the input signal of the drive circuit 30, and 46 is a drive signal generation circuit for generating a signal for adjustment. The loop switch 43, the signal changeover switch 44, and the drive signal generation circuit 46 are controlled by signals from the system control circuit 45, respectively.

FIG. 5 is a diagram showing the output waveform of the subtractor 28 when only the focus servo control is performed and the light spot on the disk is scanning across the track, with the horizontal axis representing the objective lens position. Is. In the figure, REF indicates the reference voltage of the circuit, that is, the voltage at the center of operation. FIG. 5 (a)
Is a tracking error signal before adjustment, and the center of the waveform deviates from the reference voltage of the circuit as the objective lens moves.

Here, the signal monitoring means 42 of FIG. 4 is means for detecting the center of the waveform. For example, a low-pass filter is used to suppress the track crossing component of the output waveform of the subtractor 28 and detect the center of the waveform. To do. Alternatively, the subtractor 2
The output waveform of 8 may be converted from analog to digital, and the center of the waveform may be obtained by calculation processing.

At the time of adjustment, the loop switch 43 is opened while the focus servo control is on, and the signal changeover switch 44 is changed over to the drive signal generation circuit 46 side. The tracking actuator 31 is forcibly driven by applying a signal for driving the objective lens from the drive signal generation circuit 46. While the tracking actuator 31 is driven to move the objective lens, the signal monitor means 42 detects the center of the waveform, and the gain control means 41 is adjusted so that the variation of the center of the waveform with respect to the objective lens position is minimized. FIG. 5B shows the output waveform of the subtractor 28 after the above adjustment.

Since the offset of the tracking error signal caused by the movement of the objective lens is removed by the above adjustment,
Next, the gain of the gain control means 40 is adjusted to perform balance adjustment so that the center of the waveform and the center of operation of the circuit coincide with each other. FIG. 5C shows the waveform after this adjustment is executed. In this adjustment, a signal for vibrating the objective lens around the neutral position of the tracking actuator 31 with the focus servo only turned on is used as the drive signal generation circuit 4.
6 is applied. Alternatively, by rotating the disk with only the focus servo turned on, the light spot irradiated on the disk crosses the track of the disk due to the eccentricity of the disk, and therefore the adjustment may be performed in this state.

The gain of the gain control means 40 is first adjusted so that the center of the waveform coincides with the operation center of the circuit, and then the gain control means 41 is adjusted to adjust the tracking error signal caused by the movement of the objective lens. The offset may be removed. Further, since these adjustments are automatically performed through the system control circuit 45, they can be easily performed, for example, each time the power of the optical disk device is turned on or each time the disk is replaced. Therefore, it absorbs changes over time in the device and variations in tracking signals from disc to disc,
Always stable tracking servo control can be realized.

According to this embodiment, the DC offset component removal adjustment and the balance adjustment of the tracking error signal due to the inclination of the optical axis and the movement of the objective lens can be automatically performed with a simple structure. Further, this eliminates the influence of the change with time of the apparatus and the variation of the disk, and a stable operation can be obtained.

[0043]

According to the present invention, it is possible to effectively remove the DC offset component of the tracking error signal due to the tilt of the optical axis or the movement of the objective lens by the tracking error signal detection method by the push-pull method of the optical disk device.
Further, the DC offset component removal adjustment and the balance adjustment can be performed with a simple configuration by adjusting each at one location. Further, the DC offset component removal adjustment and the balance adjustment can be automatically performed, and stable tracking servo control can be performed without the influence of the change with time of the device and the disc variation.

[Brief description of drawings]

FIG. 1 shows an optical disc device according to a first embodiment of the present invention,
FIG. 3 is a circuit diagram showing both the light receiving surface of the photodetector, the light spot on the photodetector, and the configuration of the signal processing circuit.

FIG. 2 is a waveform diagram illustrating the operation of the optical disc device according to the first embodiment.

FIG. 3 is a second circuit diagram showing the light receiving surface of the photodetector of the optical disc device of the second embodiment, the light spot on the photodetector, and the configuration of the signal processing circuit.

FIG. 4 is a third circuit diagram showing the light receiving surface of the photodetector of the optical disk device of the third embodiment, the light spot on the photodetector, and the configuration of the signal processing circuit.

FIG. 5 is a waveform diagram for explaining the operation of the optical disc device of the third embodiment.

FIG. 6 is an explanatory diagram of a photodetector and a signal processing circuit as an example of a tracking error detecting method of a conventional optical disc device.

[Explanation of symbols]

21 ... Photodetector, 23 ... Subtractor, 24A ... Envelope detection circuit, 24B ... Envelope detection circuit, 26 ... Subtractor, 28 ... Subtractor, 31 ... Tracking actuator, 40 ... Gain control means, 41 ... Gain control means, 42 ...
Signal monitor means, 45 ... System control circuit, 46 ... Drive signal generation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Inoue Masayuki Inoue, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock Company, Hitachi Media Visual Media Research Institute (72) Yoshio Suzuki Suzuki, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Hitachi Media Media Research Laboratories

Claims (5)

[Claims] 1. An optical disk apparatus having an optical head for reproducing an information signal from an optical information recording medium, and servo control means for performing tracking control of the optical head based on an error signal from the optical head. In the above, a plurality of photodetector elements for dividing the reflected light flux from the optical disc into a plurality of pieces along the track direction of the optical disc and detecting them independently, and a difference signal of two signals from the photodetector element are A first subtractor for generating, first and second detecting means for detecting envelopes of two signals from the photodetector, respectively, and first and second
A second subtractor for generating a difference signal of the signals of the detection means of
An optical disc device, comprising: a third subtractor for generating a difference signal between outputs of the first and second subtractors, and performing tracking control by the output signal of the third subtractor. 2. The optical disk device according to claim 1, further comprising first gain adjusting means for adjusting an output signal voltage of the second subtractor which is input to the third subtractor. 3. The optical disk device according to claim 1, further comprising second gain adjusting means for adjusting an output signal voltage of the first or second detecting means which is input to the second subtractor. 4. The optical disk device according to claim 1 or 2, further comprising a second gain adjusting means for adjusting an output signal voltage of the photodetection element input to the first subtractor. 5. A system control means for controlling the first gain adjusting means and the second gain adjusting means, an objective lens driving means controlled by the system controlling means, and An optical disk device having a signal detecting means for detecting the output of the third subtractor and inputting the result to the system control means.