JP5348208B2 - Optical drive device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To mutually complement demerits of a DPP method and a DPD method without switching of a DPD signal and a DPP signal. <P>SOLUTION: An optical drive device includes: an optical system for irradiating a recording surface of an optical disk with a light beam; a photodetector 5 for receiving the light beam which has been reflected on the recording surface and outputting a signal corresponding to a light reception quantity; a signal generating section 30 for generating a DPP signal and a DPD signal from an output signal of the photodetector 5; a tracking error signal generating section 31 for correcting the DPP signal on the basis of a correction value to be acquired from the DPD signal to generate a tracking error signal TE; and a tracking servo section 35 for performing tracking servo on the basis of the tracking error signal TE. <P>COPYRIGHT: (C)2013,JPO&amp;INPIT

Description

  The present invention relates to an optical drive device, and more particularly to an optical drive device that performs tracking servo.

  In an optical drive device that plays back an optical disc, the focus servo that focuses the recording surface by moving the objective lens perpendicular to the recording surface of the optical disc, and the object to be played back by moving the objective lens parallel to the recording surface of the optical disc And a tracking servo for focusing the light beam on the center of the land or groove.

  Specific methods of tracking servo include a differential push-pull method (DPP method) and a phase difference detection method (DPD method). The former uses 0th-order diffracted light and ± 1st-order diffracted light obtained by passing a light beam through a diffraction grating, and is less affected by movement (lens shift) of the objective lens in the recording surface. However, there is a demerit that a large offset is generated by a light beam (stray light) reflected at a place other than the access target layer. This demerit becomes remarkable when recording / reproducing of a multilayered optical disk (multilayer optical disk) is performed. The latter uses the diffraction by the code recorded on the recording layer, and has the advantage that there is almost no influence by lens shift or stray light, but has the disadvantage that it cannot be controlled in the area without the code (unrecorded area). . Because of this demerit, the DPD method is usually used only for ROM disks whose recording area is predetermined.

  In Patent Document 1, the DPP method is used when the irradiation position of the light beam is in the unrecorded area, and the DPD method is used when the light beam is in the recording area. An example in which tracking servo can be performed while complementing is disclosed.

Japanese Patent No. 4527184

  One of the objects of the present invention is to provide an optical drive device capable of mutually complementing the disadvantages of the DPP method and the DPD method without switching as disclosed in Patent Document 1.

In order to achieve the above object, an optical drive device according to the present invention includes an optical system for irradiating a recording surface of an optical disc with a light beam, a light beam reflected by the recording surface, and a signal corresponding to the received light amount. From the DPD signal, a DPP signal generating means for generating a DPP signal from the output signal of the photodetector, a DPD signal generating means for generating a DPD signal from the output signal of the photodetector, and the DPD signal A tracking error signal generating unit that generates a tracking error signal by correcting the DPP signal based on the acquired correction value, and a tracking servo unit that performs tracking servo based on the tracking error signal. To do.

  According to the present invention, since the DPP signal is corrected based on the correction value acquired from the DPD signal, the disadvantages of the DPP method and the DPD method can be complemented without switching between the DPD signal and the DPP signal.

  In the optical drive device, the correction value may be a value indicating an amplitude of the DPD signal obtained when the correction is not performed.

  In the optical drive device, the tracking error signal generation unit may acquire the correction value so that the amplitude of the DPD signal is within a predetermined range.

  Further, in the optical drive device, the tracking error signal generating unit may acquire a correction value based on the amplitude of the DPD signal when the amplitude of the DPD signal changes beyond the predetermined range. It is good also as having.

  In the optical drive device, the correction value acquisition unit further includes a correction value storage unit that stores the correction value, and the correction value acquisition unit is configured such that the amplitude of the DPD signal changes beyond the predetermined range. In addition, a total value of the amplitude of the DPD signal and the correction value stored in the correction value storage unit is acquired as the correction value, and is stored in the correction value storage unit by the acquired correction value. The correction value may be updated.

  In each of the optical drive devices, the tracking error signal generation unit may include a correction unit that generates the tracking error signal by adding a value corresponding to the correction value to the DPP signal.

  In the optical drive device, the value corresponding to the correction value is a value obtained by multiplying the correction value by a given coefficient, and the coefficient is obtained by multiplying the DPD signal by the coefficient. The slope of the obtained signal and the slope of the DPP signal may be determined to be equal to each other in the vicinity of the track center.

  According to the present invention, since the DPP signal is corrected based on the correction value acquired from the DPD signal, the disadvantages of the DPP method and the DPD method can be complemented without switching between the DPD signal and the DPP signal.

1 is a schematic diagram of an optical drive device according to an embodiment of the present invention. It is a top view of the photodetector by embodiment of this invention. It is a figure which shows the functional block of the part in connection with the production | generation of tracking error signal TE and tracking servo among the various functions which the process part by embodiment of this invention has. It is a figure which shows the mode of a change when the focal position of a light beam moves to the radial direction of the optical disk 11 (track jump) about each of a DPP signal and a DPD signal. It is a figure which shows the locus | trajectory of the movement of the spot of the main beam MB on the optical disk surface by embodiment of this invention, and has shown the case where there is no stray light. It is a figure which shows the locus | trajectory of the movement of the spot of the main beam MB on the optical disk surface by embodiment of this invention, and has shown the case where stray light exists. It is a figure which shows the processing flow of the correction value acquisition part by embodiment of this invention. It is explanatory drawing of the coefficient k by embodiment of this invention. It is a figure which shows the specific circuit structure of the correction value acquisition part and correction | amendment part by embodiment of this invention. It is a figure which shows an example of the time change of the signal which flows through each circuit element shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram of an optical drive device 1 according to an embodiment of the present invention.

  The optical drive device 1 performs at least one of reproduction and recording of the optical disk 11. Various optical recording media such as CD, DVD, and BD can be used as the optical disc 11, but in this embodiment, a disk-shaped optical disc (multilayer optical disc) having a recording surface that is multilayered by a multilayer film is used. .

  As shown in FIG. 1, the optical drive device 1 includes a laser light source 2, an optical system 3, an objective lens 4, a photodetector 5, and a processing unit 6. Among these, the laser light source 2, the optical system 3, the objective lens 4, and the photodetector 5 constitute an optical pickup.

  The optical system 3 includes a diffraction grating 21, a beam splitter 22, a collimator lens 23, a ¼ wavelength plate 24, and a sensor lens (astigmatism optical element, cylindrical lens) 25. The optical system 3 functions as an outward optical system that guides the light beam generated by the laser light source 2 to the optical disc 11, and also serves as a return optical system that guides the reflected light beam, which is a light beam reflected by the optical disc 11, to the photodetector 5. Function.

  In the forward optical system, the diffraction grating 21 decomposes the light beam emitted from the laser light source 2 into three beams (0th-order diffracted light and ± 1st-order diffracted light) and makes it incident on the beam splitter 22 as S-polarized light. The beam splitter 22 reflects the incident S-polarized light and bends its path in the direction of the optical disk 11. The collimator lens 23 converts the light beam incident from the beam splitter 22 into parallel light. The quarter wavelength plate 24 converts the light beam that has passed through the collimator lens 23 into circularly polarized light. The light beam that has passed through the quarter-wave plate 24 enters the objective lens 4.

  The objective lens 4, together with the collimator lens 23, condenses the light beam generated by the laser light source 2 on the access target layer among the plurality of recording layers of the optical disc 11 and detects the reflected light beam reflected by the optical disc 11. A lens system for condensing light onto the device 5 is constructed. Specifically, the objective lens 4 condenses the light beam incident from the optical system 3 (the light beam that has passed through the collimator lens 23 and becomes parallel light) on the optical disk 11, and is recorded on the recording surface of the optical disk 11. The reflected light beam reflected is returned to parallel light. The reflected light beam returned to the parallel light passes through the collimator lens 23 and is condensed on the photodetector 5.

  Here, the reflected light beam is diffracted by the land group of the recording surface, and is decomposed into 0th order diffracted light and ± 1st order diffracted light. The 0th order diffracted light and the ± 1st order diffracted light are different from the 0th order diffracted light and ± 1st order diffracted light generated by the diffraction grating 21. In this specification, the 0th-order diffracted light, the + 1st-order diffracted light, and the −1st-order diffracted light decomposed by the diffraction grating 21 are referred to as a main beam MB, a subbeam SB1, and a subbeam SB2, respectively. In some cases, it refers to diffracted light generated by diffraction at a land group on the recording surface. The main beam MB, the sub beam SB1, and the sub beam SB2 each independently generate a reflected light beam.

  In the return path optical system, the reflected light beam that has passed through the objective lens 4 and has become P-polarized light by reciprocating the quarter-wave plate 24 is incident on the collimator lens 23. The reflected light beam that has passed through the collimator lens 23 is incident on the beam splitter 22 while being condensed. The beam splitter 22 transmits the incident reflected light beam and makes it incident on the sensor lens 25 (cylindrical lens). The sensor lens 25 gives astigmatism to the reflected light beam incident from the beam splitter 22. The reflected light beam provided with astigmatism enters the photodetector 5.

  FIG. 2 is a top view of the photodetector 5. As shown in the figure, the photodetector 5 has light receiving surfaces 5a to 5c that are all square. As shown in FIG. 2, the light receiving surface 5a is divided into four light receiving regions each having a square shape. On the other hand, each of the light receiving surfaces 5b and 5c is divided into two light receiving regions by a center line in the vertical direction (direction perpendicular to the side facing the light receiving surface 5a). The photodetector 5 is configured to output a signal having an amplitude of a value (amount of received light) obtained by dividing the intensity of the light beam by the area of the light receiving surface for each of the light receiving regions.

  The light receiving surfaces 5a to 5c are provided for the purpose of receiving the main beam MB, the sub beam SB1, and the sub beam SB2, respectively, and are arranged at positions where signal light spots of the corresponding reflected light beams are formed. The four light receiving areas of the light receiving surface 5a are light receiving areas A to D counterclockwise from the upper left. The two light receiving areas on the light receiving surface 5b are light receiving areas E1 and E2 in order from the top. Similarly, the two light receiving areas of the light receiving surface 5c are light receiving areas F1 and F2 in order from the top.

  Returning to FIG. The processing unit 6 is configured by a DSP (Digital Signal Processor) having an A / D conversion function that converts analog signals for multiple channels into digital data as an example, and receives an output signal from the photodetector 5, A focus error signal FE, a full addition signal (pull-in signal PI, RF signal RF), and a tracking error signal TE are generated.

Of these, it is the tracking error signal TE that directly receives the effects of the present invention. As will be described in detail later, when the focus error signal FE and the full addition signal are described first, the processing unit 6 converts the focus error signal FE into the following equation (2) according to the following equation (1). Thus, it is preferable to generate the full addition signals respectively. Here, I _X indicates the amount of light received by the light receiving region (or correction light receiving surface) X. The same applies to the following description.

  The CPU 7 is a processing device built in a computer, a DVD recorder, or the like, and instructs the processing unit 6 to perform either reproduction or writing and specifies an access position on the optical disc 11 via an interface (not shown). An instruction signal is transmitted. The processing unit 6 that has received this instruction signal performs focus servo and tracking servo. The focus servo is a process of focusing on the surface of the access target layer by moving the objective lens 4 perpendicularly to the surface of the optical disc 11 until the focus error signal FE becomes zero. The tracking servo is a process for realizing a track-on state by moving the objective lens 4 in parallel with the surface of the optical disc 11 to a position where the tracking error signal TE becomes zero (this movement is called “lens shift”). The tracking servo is executed in a state where the focus servo is on (a state where the surface of the access target layer is focused and the focus error signal is zero). When the track is turned on, the CPU 7 acquires the RF signal RF generated by the processing unit 6 as a data signal.

  Now, the tracking error signal TE will be described. FIG. 3 is a diagram illustrating functional blocks of a part related to generation of the tracking error signal TE and tracking servo among various functions of the processing unit 6. As shown in the figure, the processing unit 6 includes a signal generation unit 30 (DPP signal generation unit, DPD signal generation unit), a tracking error signal generation unit 31 (tracking error signal generation unit), and a tracking servo unit 35 (tracking servo). Means). The tracking error signal generation unit 31 includes a correction value acquisition unit 32 (correction value acquisition unit) and a correction unit 33 (correction unit).

  The signal generator 30 generates a differential push-pull (DPP) signal DPP (hereinafter referred to as “DPP signal”) by a differential push-pull method, and a phase difference (DPD) signal DPD ( (Hereinafter referred to as “DPD signal”). More specifically, for the DPP signal, first, the signal generator 30 generates a main push-pull (MPP) signal MPP according to the expression (3) based on the output signals of the light receiving areas A to D, and also receives the light receiving area E1. , E2, F1, and F2 are used to generate a sub push-pull (SPP) signal SPP by Equation (4). Then, as shown in Equation (5), a DPP signal is generated by subtracting a signal obtained by multiplying the SPP signal SPP by m (m is a constant) from the MPP signal MPP.

  For the DPD signal, the signal generation unit 30 outputs a signal indicating the phase difference between the output signal of the light receiving region A and the output signal of the light receiving region B, and the output signal of the light receiving region C, as shown in the following equation (6). The DPD signal is generated by adding the signal indicating the phase difference of the output signal of the light receiving region D. P (X, Y) is a function indicating the phase difference between the signal X and the signal Y.

  FIG. 4 is a diagram showing a change state when the focal position of the light beam moves in the radial direction of the optical disc 11 (track jump) for each of the DPP signal and the DPD signal. In the figure, the horizontal direction corresponds to the radial direction of the optical disk 11. In the lower part of the drawing, lands and grooves, and a symbol C formed on the land surface are shown. In this embodiment, the code C is formed on the land surface, but the code C may be formed on the groove bottom surface, or may be formed on both the land surface and the groove bottom surface. Good. In FIG. 4, it is assumed that the DPP signal and the DPD signal have the same amplitude.

  As shown in FIG. 4, the DPP signal has a predetermined value Vref (intermediate value) when it is at the land center (center of the land in the optical disk radial direction = track center) and the groove center (center of the groove in the optical disk radial direction). The maximum value (or the minimum value) is obtained when the focal position of the light beam is near the boundary between the land and the groove. On the other hand, the DPD signal is the same as the DPP signal in that it has a predetermined value Vref (intermediate value) when it is at the center of the land and the groove, but the slope near the track center (the amplitude of the DPP signal and that of the DPD signal are the same). Is slightly different from the DPP signal. This is a phenomenon that occurs because the DPP signal and the DPD signal use different light beam diffractions (the boundary between land and groove in the DPP signal and the outer edge of the code C in the DPD signal).

  As described above, the DPP signal has a characteristic that a large offset is generated by a light beam (stray light) reflected at a place other than the access target layer (in the case of a multilayer optical disc, particularly a recording layer other than the access target layer). Such an offset hardly occurs in the DPD signal. The effect of this will be described in detail with reference to FIGS.

  FIGS. 5 and 6 are both diagrams showing the locus of movement of the spot of the main beam MB on the surface of the optical disk 11, and are drawn on the assumption that tracking servo is performed using the DPP signal as the tracking error signal TE. . Here, the sub beams SB1 and SB2 are omitted, but can be considered in the same manner as the main beam MB.

  FIG. 5 shows a case where there is no stray light. In this case, no offset occurs in the DPP signal, and the spot of the main beam MB moves around the track center.

FIG. 6 shows a case where stray light is present. In this case, an offset occurs in the DPP signal. If the DPP signal when there is no stray light is DPP ₀ , and the amount of offset due to stray light is a, the DPP signal in this case is expressed by the following equation (7).

The tracking servo is a process for controlling the position of the objective lens 4 so that the tracking error signal TE (in this case, the DPP signal) becomes zero. Therefore, when the DPP signal is expressed by Expression (7), the processing unit 6 controls the position of the objective lens 4 so that DPP ₀ = a. In this case, the spot of the main beam MB does not come to the center of the track, but moves on the surface of the optical disk 11 at a position shifted by the offset a as shown in FIG. The processing unit 6 has a function of correcting the DPP signal with the DPD signal in order to prevent such a positional shift that occurs when tracking servo is performed using the DPP signal as the tracking error signal TE. Hereinafter, processing for realizing this function will be described in detail in the order of the correction value acquisition unit 32, the correction unit 33, and the tracking servo unit 35.

  FIG. 7 is a diagram illustrating a processing flow of the correction value acquisition unit 32. The processing of the correction value acquisition unit 32 will be described with reference to FIGS.

  As illustrated in FIG. 3, the correction value acquisition unit 32 includes a correction value storage unit 34 (correction value storage unit) that stores the correction value DIS. Here, the correction value DIS is a value indicating the amplitude (displacement from the intermediate value Vref) of the DPD signal obtained when correction by the correction unit 33 is not performed. The correction value DIS stored in the correction value storage unit 34 in the initial state is 0 as shown in FIG. 7 (step S1).

  As shown in FIG. 3, the correction value acquisition unit 32 receives a track-on signal Ton from a tracking servo unit 35 described later. As will be described in detail later, the track-on signal Ton is a signal that is activated when the value of the tracking error signal TE is kept equal to the predetermined value Vref for a predetermined time (track-on state). The correction value acquisition unit 32 does not perform special processing while the track-on signal Ton is inactive (not in the track-on state) (No determination in step S2).

  When the track-on signal Ton is activated in the track-on state (Yes determination in step S2), the correction value acquisition unit 32 starts monitoring the DPD signal generated by the signal generation unit 30 (step S3). . Then, when the amplitude of the DPD signal changes beyond a predetermined range, the correction value DIS is acquired based on the amplitude of the DPD signal. The predetermined range here may be a range of the predetermined value α up and down from the predetermined value Vref which is an intermediate value of the amplitude of the DPD signal. That is, the correction value acquisition unit 32 acquires the correction value DIS based on the amplitude of the DPD signal when the amplitude of the DPD signal is equal to or lower than Vref−α or equal to or higher than Vref + α.

  The acquisition of the correction value DIS will be described in detail. First, as shown in FIG. 7, the correction value acquisition unit 32 acquires the total value of the amplitude of the DPD signal and the held correction value DIS (step S4). . The total value is acquired and output as a new correction value DIS, and the correction value DIS stored in the correction value storage unit 34 is updated with the new correction value DIS (step S5).

  Next, the processing of the correction unit 33 (FIG. 3) will be described. The correction unit 33 has a function of generating a tracking error signal TE by correcting the DPP signal based on the correction value DIS acquired by the correction value acquisition unit 32. Specifically, the tracking error signal TE is generated by adding a value corresponding to the correction value DIS to the DPP signal.

  Here, the “value according to the correction value DIS” is a value kDIS obtained by multiplying the correction value DIS by a given coefficient k. The coefficient k is determined such that the slope of the signal obtained by multiplying the DPD signal by the coefficient k and the slope of the DPP signal are equal to each other in the vicinity of the track center.

  FIG. 8 is an explanatory diagram of the coefficient k. The DPD signal and DPP signal shown in the figure are the same as those shown in FIG. As shown in the figure, by appropriately determining the coefficient k, the slope of the signal (kDPP) obtained by multiplying the DPD signal by the coefficient k and the slope of the DPP signal are aligned near the track center. Is possible. The coefficient k is determined in this way.

  The tracking error signal TE generated by the correcting unit 33 is expressed by the following equation (8). The correction unit 33 outputs the generated tracking error signal TE to the tracking servo unit 35.

  Next, the processing of the tracking servo unit 35 (FIG. 3) will be described. The tracking servo unit 35 performs tracking servo based on the tracking error signal TE input from the correction unit 33. Specifically, the objective lens 4 is moved in parallel with the surface of the optical disk 11 to a position where the tracking error signal TE becomes zero. In this tracking servo, unlike the example of FIG. 6, it is possible to bring the spot of the main beam MB to the center of the track even if there is stray light. This will be described in detail below.

  When the spot of the main beam MB is deviated from the track center as shown in FIG. 6, the amplitude of the DPD signal is Vref + b. However, b = a / k. If the predetermined value α described above is equal to b, the correction value acquisition unit 32 acquires b as the correction value DIS when the amplitude of the DPD signal becomes Vref + b. Therefore, the tracking error signal TE generated thereafter is expressed by the following equation (9).

  Substituting Equation (7) and b = a / k into Equation (9) yields the following Equation (10).

As shown in Equation (10), the tracking error signal TE that is the corrected DPP signal is equal to the signal DPP ₀ that is the DPP signal when there is no stray light. As a result, the optical drive apparatus 1 can bring the spot of the main beam MB to the center of the track even if there is stray light.

  In addition, the tracking servo unit 35 performs processing for generating the above-described track-on signal Ton. Specifically, the value of the tracking error signal TE supplied from the tracking error signal generation unit 31 is monitored, and the state equal to the predetermined value Vref, which is an intermediate value of the amplitude, continues for a predetermined time (track on state). The track on signal Ton is activated. When the value of the tracking error signal TE does not become equal to the predetermined value Vref, the track-on signal Ton is deactivated. However, a predetermined hysteresis is set in the tracking error signal generation unit 31 and the tracking error signal TE is within a predetermined time. For example, even if the value of the tracking error signal TE deviates from the predetermined value Vref, the state where the track-on signal Ton is activated is maintained. As a result, frequent switching of the state of the track-on signal Ton is prevented.

  The processing of the correction value acquisition unit 32, the correction unit 33, and the tracking servo unit 35 has been described in detail above. Next, a specific circuit configuration for realizing the correction value acquisition unit 32 and the correction unit 33 will be described.

FIG. 9 is a diagram illustrating specific circuit configurations of the correction value acquisition unit 32 and the correction unit 33. FIG. 10 is a diagram showing an example of a time change of a signal flowing through each circuit element shown in FIG. In this example, it is assumed that the offset of the DPP signal continues to increase at a constant rate due to the influence of stray light. Reference numeral O _X shown in FIG. 10 shows an output signal components denoted by reference numeral X in Fig.

  First, the correction value acquisition unit 32 will be described. As shown in FIG. 9, the correction value acquisition unit 32 includes comparators 50 and 51, an OR circuit 52, an AND circuit 53, delay circuits 54 to 58, switches 59 to 63, 71, 72, 75, 76, 79, 82, 84, a subtractor 69, an adder 70, buffers 74, 78, 81, and capacitors 73, 77, 80, 83.

  The DPD signal is supplied from the signal generation unit 30 to the non-inverting input terminal of the comparator 50 and the inverting input terminal of the comparator 51. A voltage Vref + α is supplied to the inverting input terminal of the comparator 50 from a constant voltage circuit (not shown). A voltage Vref-α is supplied to a non-inverting input terminal of the comparator 51 from a constant voltage circuit (not shown). Each output signal of the comparators 50 and 51 is supplied to the OR circuit 52.

  The AND circuit 53 is supplied with the track-on signal Ton from the tracking servo section 35 and the output signal of the OR circuit 52. The output signal Vo1 of the AND circuit 53 is supplied to the delay circuit 54 which is the first stage of the delay circuit array including the delay circuits 54 to 58.

  FIG. 4 shows an example of the output signal Vo1. As shown in the figure, the output signal Vo1 is a binary signal that goes low when the amplitude of the DPD signal is between the voltage Vref−α and the voltage Vref + α, and goes high otherwise.

Returning to FIG. Each of the delay circuits 54 to 58 is a circuit that delays an input signal by a predetermined time and outputs it. As shown in FIG. 9, the delay circuit 54 has an output signal Vo1, the delay circuit 55 has an output signal from the delay circuit 54, the delay circuit 56 has an output signal from the delay circuit 55, and the delay circuit 57 has an output from the delay circuit 56. The signal / delay circuit 58 is supplied with the output signal of the delay circuit 57. With this configuration, the output signals O54 to O58 of the delay circuits _{54 to 58} are signals obtained by sequentially delaying the output signal Vo1 by a predetermined time as shown in FIG.

The switches 59 to 63 are 1-circuit 2-contact type switches that switch the input source in accordance with the value of the output signal Vo1. More specifically, the switch 59 outputs the output signal of the delay circuit 55 when the output signal Vo1 is high, and outputs the output signal Vo1 when it is low. As a result, the output signal O ₅₉ of the switch 59 in the example of FIG. 10 becomes a signal that rises at the rising edge of the output signal O ₅₅ and falls at the falling edge of the output signal Vo 1 as shown in FIG.

The switch 60 outputs the output signal of the delay circuit 54 when the output signal Vo1 is high, and outputs the output signal of the delay circuit 55 when the output signal Vo1 is low. As a result, the output signal O ₆₀ of the switch 60 according to the example of FIG. 10 becomes a signal that rises when the output signal O ₅₄ rises and falls when the output signal O ₅₅ falls, as shown in FIG.

The switch 61 outputs the output signal Vo1 when the output signal Vo1 is high, and outputs the output signal of the delay circuit 54 when the output signal Vo1 is low. Thus, the output signal O ₆₁ of the switch 61 according to the example of FIG. 10, as shown in the drawing, rises at the rising edge of the output signal Vo1, the falls at the fall of the output signal O _54.

The switch 62 outputs the output signal of the delay circuit 57 when the output signal Vo1 is high, and outputs the output signal of the delay circuit 56 when it is low. As a result, the output signal O ₆₂ of the switch 62 according to the example of FIG. 10 becomes a signal that rises when the output signal O ₅₇ rises and falls when the output signal O ₅₆ falls, as shown in FIG.

The switch 63 outputs the output signal of the delay circuit 56 when the output signal Vo1 is high, and outputs the output signal of the delay circuit 57 when it is low. As a result, the output signal O ₆₃ of the switch 63 according to the example of FIG. 10 becomes a signal that rises when the output signal O ₅₆ rises and falls when the output signal O ₅₇ falls, as shown in FIG.

  The output signals of the switches 59 to 63 are supplied to a switch 75, a switch 72, a switch 71, a switch 79, and a switch 82, as shown in FIG.

  The subtracter 69 is supplied with the DPD signal from the signal generator 30 and the voltage Vref from a constant voltage circuit (not shown). The subtracter 69 shifts the potential of the DPD signal to the minus side by the voltage Vref, and outputs a signal DPD-Vref obtained as a result.

  The adder 70 is supplied with the signal DPD-Vref from the subtractor 69 and the output signal of the switch 84. The adder 70 adds these signals, and outputs a resultant addition signal to the switch 71.

The switch 71 connects its own input terminal to the output terminal of the adder 70 when the output signal O ₆₁ of the switch 61 is high, and to one circuit and two contacts that connect to the output terminal of the switch 75 when it is low. It is an expression switch.

The switch 72 is a one-circuit, one-contact type switch that is inserted between the output end of the switch 71 and the input end of the buffer 74. When the output signal O60 of the switch ₆₀ is high, the switch 72 becomes non-conductive. When it is, it becomes conductive.

  The capacitor 73 is inserted between a signal line connecting the output terminal of the switch 72 and the input terminal of the buffer 74 and a power supply wiring (hereinafter referred to as “ground wiring”) to which a ground potential is supplied. Hereinafter, a signal indicated by the voltage between the electrodes of the capacitor 73 is referred to as a signal S1.

  The buffer 74 is a circuit that buffers the signal S1. Since the buffer 74 is provided, the potential of the signal S1 is maintained even when a current flows through the output terminal of the buffer 74. The same applies to the buffers 78 and 81, which are circuits for buffering the signals S2 and S3, respectively. Even if a current flows through the output terminals of the buffers 78 and 81, the potential of the corresponding signal is maintained.

The switch 75 is a one-circuit / one-contact switch inserted between the output end of the buffer 74 and one input end of the switch 76. The switch 75 is turned on when the output signal O59 of the switch ₅₉ is high, and is low. When it is, it becomes non-conductive.

The switch 76 is supplied with the track-on signal Ton from the tracking servo section 35 and the output signal O ₅₈ of the delay circuit 58. Switch 76, the input terminal of itself, when the track-on signal Ton is high, and connected to the output terminal of the switch 75 at the timing when the output signal O ₅₈ rises, the ground wire when the track-on signal Ton is low Is a one-circuit, two-contact switch connected to Even after the track-on signal Ton transitions from low to high, until the timing at which the output signal O ₅₈ rises, the input terminal of the switch 76 is connected to the ground wiring.

  The capacitor 77 is inserted between the signal line connecting the output terminal of the switch 76 and the input terminal of the buffer 78 and the ground wiring. Hereinafter, a signal indicated by the voltage between the electrodes of the capacitor 77 is referred to as a signal S2. When the track-on signal Ton is low, since the output terminal of the switch 76 is connected to the ground wiring, the potential of the signal S2 becomes 0 as illustrated in FIG. The signal S2 is supplied to the correction unit 33 through the buffer 78 as a correction value DIS.

The switch 79 is a one-circuit, one-contact type switch that is inserted between the output end of the buffer 78 and the input end of the buffer 81. The switch 79 is conductive when the output signal O62 of the switch ₆₂ is high, and is low. In some cases, it becomes non-conductive.

  The capacitor 80 is inserted between the signal line connecting the output terminal of the switch 79 and the input terminal of the buffer 81 and the ground wiring. Hereinafter, a signal indicated by the voltage between the electrodes of the capacitor 80 is referred to as a signal S3.

The switch 82 is a one-circuit / one-contact switch inserted between the output terminal of the buffer 81 and one input terminal of the switch 84, and becomes non-conductive when the output signal O63 of the switch ₆₃ is high, Conduction when low.

  Capacitor 83 is inserted between a signal line connecting the output terminal of switch 82 and one input terminal of switch 84 and the ground wiring. Hereinafter, a signal indicated by the voltage between the electrodes of the capacitor 83 is referred to as a signal S4. The capacitor 83 corresponds to the correction value storage unit 34 shown in FIG.

A track-on signal Ton is supplied to the switch 84 from the tracking servo section 35. Switch 84, when the track-on signal Ton is high, and starts to output the signal S4 at the timing when the output signal O ₅₈ rises to an input end connected to the ground wiring when the track-on signal Ton is low 1 This is a circuit 2-contact type switch. Even after the track-on signal Ton transitions from low to high, until the timing at which the output signal O ₅₈ rises, the input terminal of the switch 84 is connected to the ground wiring. Therefore, the output signal O ₇₀ of the adder 70 when the track-on signal Ton is low is the same signal as the signal obtained by subtracting Vref from the DPD signal, as illustrated in FIG.

  The operation of each component of the correction value acquisition unit 32 described above will be described in detail with reference to FIGS. Since the operations of the comparators 50 and 51, the OR circuit 52, the AND circuit 53, the delay circuits 54 to 58, and the switches 59 to 63 are as described above, they are omitted.

  When tracking control is started, the track-on signal Ton becomes high soon. At this time, the potential of the DPD signal is usually between the voltage Vref−α and the voltage Vref + α, and the output signal Vo1 is low. The input ends of the switches 76 and 84 are connected to the ground wiring, and therefore the potential of the signal S2 and the potential of one input end of the adder 70 are both zero.

Next, the potential of the DPD signal increases (because the stray light increases and the offset of the DPP signal increases, which increases the tracking servo misalignment) and exceeds Vref + α, thereby activating the output signal Vo1. First, the output signal O _{61 of the} switch ₆₁ is activated. Thereby, the output signal _{O 70} of the adder 70 as the output signal _{O 71} of the switch 71 is outputted. At this point, the input end of the switch 84 is still connected to the ground wiring. Therefore, the output signal O ₇₀ becomes the signal DPD-Vref generated by the subtractor 69 described above. If the potential of the DPD signal is equal to Vref + α, the potential of the output signal O ₇₀ is α.

On the other hand, the output signal O ₆₀ in at this point still switch 60 is a wax, the switch 72 is conductive. Therefore, the capacitor 73 is charged by the output signal O ₇₁ (= output signal O ₇₀ ), and after a while, the potential of the signal S 1 reaches the potential of the output signal O ₇₀ as shown in FIG. In FIG. 10, this reached potential is α, but strictly speaking, the DPD signal changes during charging, so it is not always equal to α. However, since it may be approximately equal to α, FIG. 10 shows that the ultimate potential is equal to α for the sake of simplicity. The same applies to the other signals S2 to S4.

When the output signal O ₆₁ is activated and a predetermined time elapses, the output signal O ₆₀ is activated next. Then, the switch 72 becomes non-conductive and the charging of the capacitor 73 is finished. Thereafter, the potential of the signal S1 is held at α.

Next, when the output signals O ₅₉ , O ₆₃ , and O ₆₂ sequentially become high as shown in FIG. 10 while the output signals O ₆₁ and O ₆₀ are both kept high, the switches 75, 82, and 79 are sequentially turned on. The state changes from the non-conductive state to the conductive state, from the conductive state to the non-conductive state, and from the non-conductive state to the conductive state. Thereafter, in response to the output signal O ₅₈ becoming high, the connection destination of the input end of the switch 76 is switched from the ground wiring to the output end of the switch 75, and the capacitor 77 of the signal S1 is passed through the switch 75 in the conductive state. Charging starts. At the same time, charging of the capacitor 80 is also started. After some time, as shown in FIG. 10, the potential of the signal S2 and the signal S3 reaches the potential of the output signal O _70. As shown in FIG. 9, the signal S <b> 2 is supplied as a correction value DIS to the correction unit 33 via the buffer 78. Thereafter, the correction unit 33 performs correction by adding the potential α to the DPP signal, and the amplitude of the DPD signal temporarily returns to near Vref as shown in FIG.

In FIG. 10, it is assumed that there is a slight time lag between the charging start timing of the capacitors 77 and 80 and the timing at which the amplitude change of the DPD signal starts. Potential of the signal S2, S3 reaches the potential of the output signal _{O 70} during this time lag. If there is no time lag, the signal Vo1 is frequently switched and the potential of the DPD signal is controlled in the vicinity of Vref + α. Even in such a case, the effect of the present invention can be obtained. is there.

When the amplitude of the DPD signal returns within the range from the voltage Vref−α to the voltage Vref + α, the output signal Vo1 returns to low as shown in FIG. Then, first, the output signal O ₅₉ returns to low, and the switch 75 becomes non-conductive. Subsequently, the output signals O ₆₁ and O ₆₀ are sequentially low. After the output signal O ₆₀ becomes low, the input end of the switch 71 is connected to the output end of the switch 75 and the switch 72 is turned on, so that the capacitor 73 and the capacitor 77 are connected to the signal line and the ground wiring. It is in a state of being connected in parallel. However, since the voltage between the electrodes is equal to each other at this point, no charge transfer occurs. That is, at this time, the potentials of the signals S1 and S2 are held.

Next, the output signal O ₆₂ returns to low and the switch 79 becomes non-conductive. Since the charge does not move through the buffer 81, the charge in the capacitor 80 loses its escape field, and the potential of the signal S3 is held. When the output signal O ₆₃ returns to low next in this state, the switch 82 becomes conductive and the signal S 3 starts to be supplied to the capacitor 83. As a result, the capacitor 83 is charged, and after a while, the potential of the signal S4 reaches the potential of the correction value DIS (signal S2) as shown in FIG. Thereafter, the switch 82 is kept in a conductive state and the input terminal of the switch 84 is kept connected to the capacitor 83 side, but the charge of the capacitor 83 does not flow out through the buffer 81 and the adder 70. Thereafter, the potential of the signal S4 is held at the potential of the correction value DIS. As a result, the correction value DIS is stored in the capacitor 83 as the correction value storage unit 34. The correction value DIS at this point is approximately equal to α.

Thereafter, as shown in FIG. 10, when the stray light further increases and the DPD signal increases again and exceeds Vref + α again, the output signals O ₇₆ and O ₈₄ are fixed to the output signal O ₇₅ and the signal S4 from the beginning, respectively. Except for this point, the same operation as described above is repeated. In this case, since the correction value DIS≈α is stored in the capacitor 83 as an initial state, the signals S1 to S4 and the correction value DIS that are finally obtained are all equal to 2α as shown in FIG. Become. As a result, the DPD signal can be returned to Vref again, that is, the spot of the main beam MB can be returned to the center of the track, as shown in FIG. 10, despite the further increase in stray light.

  Next, the correction unit 33 will be described. The correction unit 33 includes a multiplier 90 and an adder 91 as shown in FIG.

  The multiplier 90 is a circuit that generates the value kDIS described above by multiplying the correction value DIS output from the correction value acquisition unit 32 by the coefficient k described above. The adder 91 is a circuit that adds the value kDIS to the DPP signal and outputs it as a tracking error signal TE. Specifically, the calculation of the above formula (8) is performed.

  As described above, according to the optical drive device 1 according to the present embodiment, the DPP signal is corrected based on the correction value acquired from the DPD signal, so that the DPP signal and the DPP signal can be switched without switching the DPP signal. The disadvantages of the law and the DPD law can be complemented each other. More specifically, it becomes possible to cancel the offset generated in the DPP signal due to stray light by the correction value.

  In order to perform appropriate correction in the present invention, a configuration in which correction is performed using the correction value DIS is essential. That is, for example, as shown in the following equation (11), even if the DPP signal is corrected using the DPD signal (a signal obtained by multiplying k), an appropriate correction result cannot be obtained. Performing the tracking servo so that the tracking error signal TE shown in Expression (11) becomes zero is nothing but performing the tracking servo so that kDPD = −DPP. If there is stray light, this equation is expressed at the center of the track. It is clear that it does not hold. In other words, in the present invention, it is possible to perform appropriate correction by adopting a configuration in which correction is performed using the correction value DIS.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to such embodiment at all, and this invention can be implemented in various aspects in the range which does not deviate from the summary. Of course.

  For example, in the above embodiment, as the “predetermined range” that determines the acquisition timing of the correction value DIS, the range of the predetermined value α from the predetermined value Vref that is the intermediate value of the amplitude of the DPD signal is used. The range of the predetermined value α may be used as the “predetermined range” from either the upper side or the lower side.

DESCRIPTION OF SYMBOLS 1 Optical drive device 2 Laser light source 3 Optical system 4 Objective lens 5 Photo detector 5a-5c Light-receiving surface 6 Processing part 11 Optical disk 21 Diffraction grating 22 Beam splitter 23 Collimator lens 24 Wavelength plate 25 Sensor lens 30 Signal generation part 31 Tracking error signal Generation unit 32 Correction value acquisition unit 33 Correction unit 34 Correction value storage unit 35 Tracking servo unit 50, 51 Comparator 52 OR circuit 53 AND circuit 54-58 Delay circuits 59-63, 71, 72, 75, 76, 79, 82, 84 Switch 69 Subtractor 70, 91 Adder 73, 77, 80, 83 Capacitor 74, 78, 81 Buffer 90 Multiplier AD, E1, E2, F1, F2 Light receiving area

Claims (7)

An optical system for irradiating a recording surface of an optical disc with a light beam;
A light detector that receives the light beam reflected by the recording surface and outputs a signal corresponding to the amount of light received;
DPP signal generation means for generating a DPP signal from the output signal of the photodetector;
DPD signal generation means for generating a DPD signal from the output signal of the photodetector;
Tracking error signal generating means for generating a tracking error signal by correcting the DPP signal based on a correction value acquired from the DPD signal;
An optical drive device comprising: tracking servo means for performing tracking servo based on the tracking error signal. The optical drive apparatus according to claim 1, wherein the correction value is a value indicating an amplitude of the DPD signal obtained when the correction is not performed. The optical drive device according to claim 2, wherein the tracking error signal generation unit acquires the correction value so that an amplitude of the DPD signal is within a predetermined range. The tracking error signal generation means includes correction value acquisition means for acquiring the correction value based on the amplitude of the DPD signal when the amplitude of the DPD signal changes beyond the predetermined range. The optical drive device according to claim 3. The correction value acquisition means includes correction value storage means for storing the correction value,
The correction value acquisition means corrects the total value of the amplitude of the DPD signal and the correction value stored in the correction value storage means when the amplitude of the DPD signal changes beyond the predetermined range. The optical drive device according to claim 4, wherein the optical drive device is acquired as a value, and the correction value stored in the correction value storage unit is updated with the acquired correction value. 6. The tracking error signal generation means includes correction means for generating the tracking error signal by adding a value corresponding to the correction value to the DPP signal. The optical drive device described in 1. The value according to the correction value is a value obtained by multiplying the correction value by a given coefficient,
The coefficient is determined so that a slope of a signal obtained by multiplying the DPD signal by the coefficient and a slope of the DPP signal are equal to each other in the vicinity of a track center. The optical drive device described in 1.

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