JP2009048731A - Optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device which improves reliability in focus servo control by determining a T-F crosstalk characteristic. <P>SOLUTION: The optical disk device comprises an error signal generator. The error signal generator includes an error signal generating circuit and a corrector. The error signal generating circuit calculates an output of a light receiving element in a PU head and outputs a focus error FE and a tracking error TE. A gain variable amplifier 52 in the corrector multiplies TE by a gain (FE amplification L1/TE amplification L1). A phase inverting circuit 55 inverts an output of the gain variable amplifier 52. A selector 56 selects the output of the gain variable amplifier 52 and an output of the phase inverting circuit 55. A differential amplifier 57 substracts an output of the selector 56 from the error FE. A third P-P detecting circuit 58 measures an amplification of an output 131 of the differential amplifier 57, and on the basis of the measured amplification, determines the output of the selector 56. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus having a light receiving element whose detection area is divided into four, and more particularly to an optical disc apparatus that reduces a crosstalk component of a tracking error signal that appears in a focus error signal.

  An optical disc apparatus that reads an optical disc such as a DVD or a CD generally includes a light receiving element having a detection region arranged by dividing a quadrangle into four. Servo that moves the actuator to follow a predetermined track based on the values of the focus error signal that is an error signal in the direction perpendicular to the disk and the tracking error signal that is the error signal in the radial direction of the disk from the calculation of the light receiving element. Take control.

  Here, the mounting position of the light receiving element is often difficult in the manufacturing process, and the error cannot always be set to zero. It is known that when there is this error, a component similar to the tracking error signal is added to the focus error signal when the pickup position of the pickup head on the disk jumps across the track. This phenomenon is called TF crosstalk.

  When TF crosstalk occurs, the following phenomenon is known. That is, at the stage where the tracking direction is not controlled and the focus is set on the surface of the optical disc, tracking control to the track is not performed, so that the irradiation position may cross the track as described above. At this time, the actuator for adjusting the focus is controlled so that the focus error is zero. However, due to such TF crosstalk, a component similar to the tracking error signal is added to the focus error signal. Then, while crossing the track, the target position to be controlled by this focus error deviates from the original position and is shaken by this component. As a result, even if the actuator is caused to follow so that the focus error is set to 0, the focus is shifted from the original position. Therefore, when TF crosstalk occurs, the focus is lost or the focus is hardly turned on.

Therefore, it has been proposed to correct the focus error signal in order to allow such TF crosstalk (see, for example, Patent Documents 1 to 3). In particular, paragraph 34 of Patent Document 1 describes that correction is made to a focus error signal using the ratio of the amplitude of the tracking error signal to the amplitude of the focus error signal.
JP 2004-227694 A JP 05-81687 A

  However, Patent Document 1 does not describe in which direction the addition or subtraction is performed. There is a possibility that the TF crosstalk component in the focus error signal may be out of phase with the tracking error signal or in a normal phase depending on the tendency of the attachment error. As a result, if the TF crosstalk is subtracted uniformly, the TF crosstalk may possibly increase.

  The present invention was devised to solve the above-described problems, and improved the reliability of focus servo control by judging the characteristics of TF crosstalk when correcting TF crosstalk. To provide an optical disk device.

  In order to solve the above problems, the following configuration can be adopted.

(1) a light receiving element that receives a reflected light from an optical disc by dividing a detection region into four regions by two axes, a track direction axis and an axis orthogonal to the track direction axis;
The difference between the addition result of the output of the pair of detection areas located at one diagonal of the four detection areas and the addition result of the pair of detection areas located at the other diagonal is calculated, and the calculation result is focused In an optical disc device comprising an error signal generation circuit that outputs an error signal,
A detection unit for detecting an amplitude ratio K obtained by dividing the amplitude of the focus error signal by the amplitude of the tracking error signal;
A variable gain amplifier that performs adjustment for amplifying or attenuating by inputting the tracking error signal, the variable gain amplifier having an amplification factor set based on the ratio K;
An inverting circuit for inverting the signal of the variable gain amplifier;
A selector for selecting one of the output of the variable gain amplifier and the output of the inverting circuit;
A subtractor that cancels a crosstalk component by calculating a difference between the focus error signal and the output signal of the selector;
Determining means for predetermining a signal output by the selector based on an output of the light receiving element;

  In this configuration, since the deciding means predetermines the positive / negative tendency of the TF crosstalk, the TF crosstalk component can be more reliably reduced and the reliability of the focus servo control can be improved. .

  The gain of the variable gain amplifier is preferably set to the amplitude ratio K. However, even when the gain is determined based on K, for example, K × (1 ± 10%), the effect of this configuration can occur. .

  (2) When the mirror surface is set in the apparatus instead of the optical disk, the determining unit measures the balance of the reflected light of the four detection regions of the light receiving element based on the reflected light applied to the mirror surface. Based on the result, a signal output from the selector is determined.

  In this configuration, since the determining unit measures the balance of the reflected light of the four detection regions of the light receiving element, it is possible to determine whether the amplitude of the TF crosstalk is positive or negative.

  (3) The determination means includes an amplitude measurement unit that measures the amplitude of the output of the subtractor, and switches the selector to measure the smaller output amplitude of the subtractor as a signal output by the selector. decide.

  In this configuration, since the positive or negative of the TF crosstalk is determined in advance by selecting the one with the smaller output amplitude of the selector, the determination means can automatically determine this positive or negative.

  According to the present invention, since the determination means determines in advance whether the TF crosstalk is positive or negative, the TF crosstalk component can be more reliably reduced, and the reliability of the focus servo control can be improved. it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The optical disk apparatus of this embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an optical disc apparatus according to the present embodiment, and shows a configuration related to operations of pickup focus control and tracking servo control. A well-known technique can be used about the structure of the part which is not shown in figure. In addition, the control signal of the control part 39 is shown with the dotted line.

  The optical disc apparatus 1 includes a pickup head 6 (hereinafter referred to as a PU head 6) that reads data recorded on an optical disc 100 (hereinafter simply referred to as a “disc”), a recording / reproducing circuit 3, and a servo circuit 32. And a driver 33, a thread motor 35, a spindle motor 34 that rotates the optical disc 100, and a control unit 11 that controls the apparatus main body 1.

  The PU head 6 includes a semiconductor laser diode (corresponding to 65 in FIG. 2), a light receiving element (corresponding to 11 in FIG. 2), and an optical system, and the light receiving element detects the reflected light of the disk 100. The PU head 6 is movably attached to an axis provided along the radial direction of the optical disc 100. The thread motor 35 rotates this shaft to move the PU head 6 in the radial direction of the optical disc 100.

  The recording / reproducing circuit 31 fully adds the outputs of the plurality of light receiving elements of the PU head 6 to generate an RF signal, amplifies the RF signal, processes the RF signal, and extracts AV (Audio Visual) data. In addition, a control circuit for controlling a voltage applied to the semiconductor laser diode in the PU head 6 from the encoded data and a driver circuit are provided. Thus, a signal applied to the semiconductor laser diode is generated when data is recorded on the disk 100.

  The servo circuit 32 performs tracking adjustment based on a tracking error signal (hereinafter referred to as “TE”) and a focus error signal (hereinafter referred to as “FE”) given from the error signal generation unit 10, respectively. A tracking servo signal and a focus servo signal for performing focus adjustment are generated.

The servo circuit 32 generates a signal for driving the sled motor 35 based on the seek control signal input from the control unit 11 and outputs the signal to the driver 33.
The driver 33 drives the biaxial actuator (corresponding to 68 and 69 in FIG. 2) and the thread motor 35 in the PU head 6 based on the signal generated by the servo circuit 32.

  Note that controlling the two-axis actuator based on the tracking servo signal and the focus servo signal to apply the servo is called “tracking servo control”.

  The thread motor 7 rotates a shaft passing through the PU head 6 to move in the radial direction of the optical disc 100 (also referred to as a coarse seek or a traverse seek), and changes the position where the optical disc 100 is irradiated with laser light. The spindle motor 8 rotates the optical disc 100.

  The control unit 39 is constituted by a microcomputer or a system IC including the microcomputer, and includes a CPU, a RAM, and a ROM for storing control data. The control unit 9 controls the operation of each unit of the PU head 6, the error signal generation unit 10, the recording / reproduction circuit 31, and the servo circuit 32 based on the input received by the operation unit 8. The ROM of the control unit 9 stores subroutines for executing various processes.

  FIG. 2 shows the PU head 6 of the optical disc apparatus 1 according to the present invention. As shown in FIG. 2, the PU head 6 includes an objective lens 62, a polarization beam splitter 63, a collimator lens 64, a semiconductor laser diode 65, a detection lens 66, and a cylindrical lens 67. The semiconductor laser diode 65 emits a laser beam. The collimator lens 64 converts the emitted laser beam into a parallel laser beam. The polarization beam splitter 63 passes a part of the laser beam and reflects a part thereof. The objective lens 62 condenses the laser beam transmitted through the polarization beam splitter 63 toward the disk 100. Thereby, a light spot is formed on the pit row on the surface of the disk 100.

  The objective lens 62 converts the reflected light from the disk 100 into parallel light. The polarization beam splitter 63 reflects part of the light returned from the objective lens 62 to the detection lens 66. The laser beam condensed by the detection lens 66 passes through a cylindrical lens 67 (cylindrical lens) that is an astigmatism generation element, and forms a spot near the center of the light receiving element 11. Therefore, the spot formed on the light receiving element 11 becomes a perfect circle when the objective lens 62 is in an appropriate position, that is, when the focal point is on the surface of the disk 100, and becomes an ellipse when it is off. In addition, when the focal point is near and far, the direction of the major axis of the ellipse is shifted by 90 degrees. Therefore, the optical disc apparatus 1 uses this property to detect a focus error signal to be described later.

  FIG. 3 is a block diagram illustrating an electrical configuration of the error signal generation unit 10 of the embodiment. The error signal generation unit 10 includes an error signal generation circuit 12 and a correction processing unit 13. The error signal generation circuit 12 includes four adders 21, 22, 24, 25 and two subtractors 23, 26.

  The light receiving element 11 is composed of, for example, a photodiode. The detection region of the light receiving element 11 is divided into four detection regions A to D by two axes of a track direction axis 111 and an axis 112 orthogonal to the track direction axis 111. The adder 21 adds the outputs of the pair of detection areas A and C located at one diagonal of the four detection areas A to D. The adder 22 adds the outputs of the pair of detection areas B and D located at the other diagonal of the four detection areas A to D. Then, the subtracter 23 subtracts the output of the adder 22 from the output of the adder 21 and outputs the subtraction result as the focus error signal FE. That is, the focus error signal FE is a difference in the amount of light received by adding diagonals, and can be calculated by A + C− (B + D).

  The adder 24 adds the outputs of the two detection areas A and D located on one side with respect to the track direction axis 111 among the four detection areas A to D. The adder 25 adds the outputs of the two detection areas B and C located on the other side of the track direction axis 111 among the four detection areas A to D. The subtractor 26 subtracts the output of the adder 25 from the output of the adder 24, and outputs the subtraction result as a push-pull tracking error signal TE.

  That is, the tracking error signal can be detected by the difference in the amount of received light in the radial direction, and the result calculated by A + D− (B + C) can be used as the detection result. Here, when A, B, C, and D are represented by mathematical expressions, the received light amount voltage is represented. The same applies to the following.

  The correction processing unit 13 uses the signals of the four detection areas A to D to perform correction so as to reduce TF crosstalk. Details will be described later.

  Next, the influence on the focus error signal FE when there is an attachment error in the light receiving element 11 will be described with reference to FIGS. A, B, C, and D in FIGS. 4A and 5A correspond to A, B, C, and D in FIG. 3, and the direction of D → A or C → B is the track direction. It shall be.

Here, in preparation for the following description, FE and TE are analyzed using the above-described mathematical expressions. As described above, TE is a difference in received light amount voltage in the radial direction,
TE = (A + D) − (B + C). Transform this,
TE = A-B + D-C
It can be. On the other hand, the focus error FE is obtained by subtracting the sum of the light receiving voltages of the light receiving elements in the diagonal direction.
FE = A + C- (B + D)
It becomes. Transform this,
FE = A-B- (DC)
It can be. Therefore, it can be seen that the difference between the focus error FE and the tracking error TE is a difference in whether (D−C) is positive or negative.

  In the example of FIG. 4, as shown in FIG. 4A, it is assumed that the center of the beam spot is attached closer to the A and B sides due to the attachment error.

  In both the examples of FIGS. 4 and 5, the locus of the center (hereinafter referred to as “bright part”) at which the light beam hits relatively strongly compared to other detection regions is represented by the following locus (1 ) The state of TE and the state of FE detected when passing through (2) are shown. Here, the trajectories (1) and (2) indicate that the central axis in the track direction (between A and B or between D and C) is the track direction axis 111, and the bright portion is the outer periphery from the TR (A Or, after moving in the direction of C), the trajectory returns to TR, moves in the direction of the inner circumference (B or C), and then returns to the axis 111.

  FIG. 4B shows a change in TE over time when there is an attachment error in FIG. At this time, in the case of (1), since the bright part moves to the outer periphery, TE is positive, and in the case of (2), TE is negative.

  Here, in the attached state of FIG. 4A, the received light amount voltages of A and B are smaller than the received light amount voltages of C and D. If there is no error in the radial direction, TE will not be affected by the mounting error. This is because TE detects an error component in the radial direction.

  Further, from the above formula, if the bright portion is 115 in the attachment state of FIG. 4A, even if there is a component Δ of attachment error, (A + Δ) − (B + Δ), (D + Δ) − (C + Δ ) Is offset and does not appear to appear in FE. However, in practice, when the beam spot crosses the track, the bright part is shifted from the track direction axis 111, and the light is unbalanced. For example, along the trajectory (1), the received light amount of A becomes relatively large due to an attachment error. At this time, an error of FE> 0 appears in the FE that should be 0. Further, each time the beam spot crosses the track, the state of the left side is a bright part, the right side is a dark part, the right side is a dark part, and the left side is a bright part with respect to the axis 111 alternately. As a result, a periodic error occurs in the FE. It can be said that the trajectories of (1) and (2) above simulate the light-dark imbalance of light.

  In the following, the influence on the FE when the center of the bright part of the beam spot moves along the trajectories (1) and (2) will be considered using FIG. At this time, for the sake of simplicity, it is assumed that the distance between the optical disc 100 and the lens is constant. In the case of the locus (1), AB and DC are positive values. At this time, since the bright part moves to A, AB becomes larger than DC. Therefore, FE ≧ 0. In the case of the locus (2), AB and DC are positive values. At this time, since the center of the beam spot moves to B, AB becomes smaller than DC. Therefore, FE ≦ 0. As described above, when the bright portion moves along the trajectories (1) and (2), the FE becomes as shown in FIG.

  As shown in FIG. 4D, a signal similar to TE appears in FE. In the example of FIG. 4, FE and TE have the same phase.

  Next, the example of FIG. 5 will be described. In the example of FIG. 5, as shown in FIG. 5 (A), they are attached to the C and D sides with an attachment error. Also in this case, the center of the beam spot is moved along the same trajectory as (1) and (2) in FIG. At this time, the time change of TE is as shown in FIG. 5B, as in FIG. As shown in FIG. 5B, even in this case, the influence of the mounting error does not appear in TE. This is because TE detects an error component in the radial direction.

  Hereinafter, the influence on the FE when the center of the bright part of the beam spot moves along the trajectories (1) and (2) will be considered with reference to FIG. Also here, it is assumed that the distance between the optical disc 100 and the lens is constant. In the case of locus (1), AB and DC are negative values. At this time, since the bright part moves to C, DC becomes smaller than AB. Therefore, FE ≦ 0. In the case of the locus (2), AB and DC are negative values. At this time, since the center of the bright part of the beam spot moves to C, AB becomes smaller than DC. Therefore, FE ≧ 0. From the above consideration, when the bright part moves along the trajectories (1) and (2), the FE becomes as shown in FIG.

  As shown in FIG. 5D, a signal similar to TE appears in FE. In the example of FIG. 5, these FE and TE are in opposite phases.

  As described above with reference to FIGS. 4 and 5, even if the focus distance between the lens and the disk 100 is constant, a component similar to TE is carried on the FE. The riding direction of this component is reversed depending on which side has an attachment error with respect to the axis 112 orthogonal to the track direction axis.

  Hereinafter, the correction processing unit 13 will be described with reference to FIGS. 6 and 7. The correction processing unit 13 subtracts such a TE component from the FE and performs correction for canceling.

  FIG. 6 shows a part of the correction processing unit 13. The correction processing unit 13 includes a PP (peak to peak) detection circuit 41, a second PP detection circuit 42, and a ratio detection unit 43. The first P-P detection circuits 41 and 42 detect the peaks of the FE and TE waveforms (in the following description, these are referred to as L1 and L2, respectively), measure the amplitude, and use the detection results as the ratio detection unit 43. Output to. The ratio detection unit 43 obtains the ratio K determined as (K = L2 / L1), and outputs the ratio K to the crosstalk correction unit 13.

  The reason why the correction processing unit 13 calculates this ratio is as follows. That is, the correction processing unit 13 performs calculation to remove the TE component from the FE later. However, the TE and TE components appearing in FE have different amplitudes. Therefore, the ratio detector 43 calculates this ratio in order to match this amplitude.

  FIG. 7 is a block diagram showing a configuration for performing post-processing of the ratio K shown in FIG. 6 among the configurations of the correction processing unit 13. A control signal of the correction control unit 54 is indicated by a dotted line.

  The variable gain amplifier 52 amplifies the tracking error signal TE in accordance with an instruction from the correction control unit 54. The correction control unit 54 includes a microcomputer or a system IC including the microcomputer, and includes a CPU, a RAM, and a ROM. The correction control unit 54 controls the gain of the variable gain amplifier 52 and selects a signal in the selector 56 by a subroutine stored in the ROM. The correction control unit 54 sets the ratio 151 (the output of the ratio detection unit 43 shown in FIG. 6) to the gain of the variable gain amplifier 52.

  The inverting circuit 55 can be configured by an amplifier circuit having a gain of 1 using an operational amplifier or the like. The inverting circuit 55 inverts the phase of the output of the variable gain amplifier 52 by 180 degrees. The selector 56 can be constituted by a multiplexer, for example, and selects either the output signal of the variable gain amplifier 52 as it is or the output signal of the inverting circuit 55. The selection is performed based on an instruction from the correction control unit 54 as described above.

  The differential amplifier 57 subtracts a signal (a signal output from the switch 53) from the focus error signal FE, and outputs an output 131 of the differential amplifier 57 to the servo circuit 32. Thereby, the correction | amendment which removes TE component from FE can be performed. Further, the third PP detection circuit 58 measures the amplitude of the output 131. It can be said that the correction is adapted to the individual PU head 6 when the selector 53 is switched and the amplitude is measured and the amplitude is smaller.

Next, a flow for automatically setting the selector 53 will be described with reference to FIG. This processing is executed by the correction control unit 54 by starting the subprogram recorded in the ROM.
In ST11, the correction control unit 54 sets the output of the selector to the side that directly outputs from the variable gain amplifier 52 (referred to as “amplifier direct side” in the drawing).
In ST12, the driver 33 drives the actuator 69 to perform focus control.
In ST13, the driver 33 drives the tracking actuator 68 to intentionally move the irradiation position so as to cross the track.
In ST14, the third P-P detection circuit 58 measures the amplitude of the output 131 of the differential amplifier 57. Let this amplitude be L3.

In ST 21, the correction control unit 54 sets the output of the selector to the output side of the phase inverting circuit 55.
In ST22 to ST24, exactly the same operation as ST12 to ST24 is performed. However, the amplitude measured in ST24 is L4.

  In ST31, it is determined whether L3 exceeds L4. When L3> L4 (YES in ST31), the selector 56 is set to the output side of the phase inverting circuit 55. If L3 ≦ L4 (NO in ST31), the selector is set to the gain variable amplifier 52 direct side. After ST32 and ST33, the flow ends.

  In ST31, it may be determined whether L3 is L4 or more. What is necessary is just to be able to judge based on the comparison of L3 and L4. Further, any of the measurement orders of ST11 to ST14 and ST21 to ST24 may be first.

  It supplements about the above embodiment.

  In the description of FIG. 1 described above, the blocks have been separated for each function. However, on implementation, any of these functions may be configured by a system IC in which a plurality of functions are integrated. One block may be divided into a plurality of blocks.

In FIG. 7, a correction control unit 54 and a selector 56 are provided. However, if the analog circuit is configured such that the ratio 151 is input to the gain of the variable gain amplifier 52, the correction control unit 54 does not need to control the variable gain amplifier 52. Further, it is confirmed in advance whether any of the patterns shown in FIGS. 4 and 5 is attached, and if it is determined in advance whether or not to pass through the inverting circuit, the correction control unit 54, the selector 56, the third PP detection circuit. 58 is not necessarily required.
Alternatively, the selector 56 may be manually switched by a dip switch or the like, and the selector 56 may be adjusted after the device 1 is manufactured. Further, as a method of confirming whether the attachment error is the pattern of FIG. 4 or FIG. 5, a mirror that totally reflects is placed instead of the disk 100 and the ratio of the received light amount voltage is measured. it can. Further, the error signal generator 10 may be configured by the correction controller 54 and the controller 39.

It is a figure showing the front end of embodiment of the optical disk device based on this invention. It is a block diagram which shows the electric constitution of this embodiment. It is a block diagram which shows the detailed structure of the error signal generation part of this embodiment. It is a figure explaining T / F crosstalk. It is a figure explaining T / F crosstalk. 3 is a diagram illustrating a part of the configuration of a correction processing unit 13. FIG. 3 is a diagram illustrating a part of the configuration of a correction processing unit 13. FIG. 3 is a diagram illustrating a part of the configuration of a correction processing unit 13. FIG.

Explanation of symbols

1-optical disk device, 10-error signal generator, 11-light receiving element,
12-error signal generation circuit, 13-correction processing unit, 15-change width ratio detection unit,
31-recording / reproducing circuit, 32-servo circuit, 33-driver,
34-spindle motor, 35-thread motor, 39-control unit,
41-first PP detection circuit, 42-second PP detection circuit, 43-ratio detection unit,
151-output, 52-gain variable amplifier, 54-correction control unit,
55-phase inverting circuit, 56-selector, 57-differential amplifier,
58-third PP detection circuit, 6-PU head, 61-optical disc,
62-objective lens, 63-polarizing beam splitter, 64-collimator lens,
65-semiconductor laser diode, 66-detection lens, 67-cylindrical lens,
68-actuator, 69-actuator, 100-optical disc,
111-track direction axis, 112-axis orthogonal to the track direction axis, A to D-detection region,
FE-focus error signal, TE-tracking error signal

Claims (3)

A detection region is divided into four regions by two axes, a track direction axis and an axis orthogonal to the track direction axis, and a light receiving element that receives reflected light from the optical disc;
The difference between the addition result of the output of the pair of detection areas located at one diagonal of the four detection areas and the addition result of the pair of detection areas located at the other diagonal is calculated, and the calculation result is focused In an optical disc device comprising an error signal generation circuit that outputs an error signal,
A detection unit for detecting a ratio K obtained by dividing the amplitude of the focus error signal by the amplitude of the tracking error signal;
A variable gain amplifier that performs adjustment for amplifying or attenuating by inputting the tracking error signal, the variable gain amplifier having an amplification factor set based on the ratio K;
An inverting circuit for inverting the signal of the variable gain amplifier;
A selector for selecting either the output of the variable gain amplifier or the output of the inverting circuit;
A subtractor that cancels a crosstalk component by calculating a difference between the focus error signal and the output signal of the selector;
An optical disc apparatus comprising: a determining unit that predetermines a signal output from the selector based on an output of the light receiving element.   The determination means measures the balance of the reflected light of the four detection areas of the light receiving element based on the reflected light applied to the mirror surface when a mirror surface is set in the apparatus instead of the optical disk, The optical disk apparatus according to claim 1, wherein a signal output from the selector is determined based on the signal.   The determining means includes an amplitude measuring unit that measures the amplitude of the output of the subtractor, and determines a signal output by the selector based on a comparison of the amplitudes of the output of the subtractor measured by switching the selector. The optical disc apparatus according to claim 1.

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