JP2009140569A - Optical drive device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical drive device in which variation caused by reflectance caused in a push-pull signal PP can be canceled. <P>SOLUTION: The optical drive device 1 receives the input of a push-pull signal and corrects the received push-pull signal on the basis of a variation amount indication signal indicating the amount of variation caused by reflectance caused in the push-pull signal. Thereby, the variation amount indication signal indicates the amount of variation caused by reflectance, so that variation caused by reflectance caused in the push-pull signal PP can be canceled. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical drive device, and more particularly to an optical drive device suitable for use in reproducing or recording an optical disc having a nonuniform recording surface reflectance.

  An optical drive device for reproducing and recording an optical disk such as a CD (Compact Disc), a DVD, an HD-DVD, and a BD (Blu-ray Disc (registered trademark)) includes an optical pickup. The optical pickup has a forward optical system that generates a light beam and converges it on the recording surface of the optical disk by an objective lens, and a return optical system that includes a photodetector that receives the light beam reflected by the recording surface of the optical disk. ing.

  Since the focal position of the light beam needs to be aligned with the center of the track formed on the recording surface of the optical disk, the optical drive device is a control called tracking servo for adjusting the deviation of the focal position in the radial direction of the optical disk. (For example, control by the differential astigmatic push-pull method described in Patent Document 1). The tracking servo will be briefly described below.

FIG. 10 is a view showing the appearance of the photodetector 1000 as seen from the light beam irradiation direction. As shown in the figure, the photodetector 1000 includes photodiodes PD1 and PD2 arranged one above the other. The light beam reflected by the recording surface of the optical disk forms a spot S on the photodetector 1000. When the focal position on the recording surface is aligned with the center of the track, the intensity of the light beam received by the photodiodes PD1 and PD2 becomes equal, so that the difference between the output signals I1 and I2 of the photodiodes PD1 and PD2 The value of the expressed push-pull signal PP = I1-I2 is 0. On the other hand, when the focal position on the recording surface is shifted in the radial direction of the optical disc, the value of the push-pull signal PP is a value other than zero. The tracking servo uses such a property of the push-pull signal, and the optical drive device controls the position of the objective lens so that the value of the push-pull signal PP becomes 0, so that the focal position in the optical disk radial direction Adjust the deviation.
Japanese Laid-Open Patent Publication No. 4-168631

  By the way, the optical disk recording surface is constituted by a multilayer film, and the film thickness of each layer is not necessarily uniform. For this reason, the reflectance of the recording surface is not necessarily uniform. Since the intensity of the spot S also depends on the reflectance, if the reflectance of the recording surface is not uniform, the push-pull signal PP varies as the light beam moves on the optical disk recording surface. Since such fluctuations (hereinafter referred to as reflectance-induced fluctuations) adversely affect the tracking servo results, a technique for canceling fluctuations in the push-pull signal PP is desired.

  Accordingly, one of the objects of the present invention is to provide an optical drive device capable of canceling the reflectance-induced variation that occurs in the push-pull signal PP due to the non-uniform reflectance of the optical recording medium.

  An optical drive device according to the present invention for solving the above-described problems is received on the basis of a fluctuation amount instruction signal that receives an input of a push-pull signal and indicates an amount of reflectance-induced fluctuation that occurs in the push-pull signal. It is characterized by correcting the signal.

  According to the present invention, since the fluctuation amount instruction signal indicates the amount of fluctuation due to reflectance, it is possible to cancel the reflectance fluctuation due to the push-pull signal PP.

  In the optical drive device, the fluctuation amount instruction signal includes a first envelope signal that envelops the maximum value of the push-pull signal for each first period, and a second envelope signal that is longer than the first period. It is good also as being a difference signal with the 2nd envelope signal formed by enveloping the maximum value of the said push pull signal for every period. In this way, it is possible to appropriately acquire the fluctuation amount instruction signal. The maximum value may be replaced with the minimum value.

  In each of the above optical drive devices, it is preferable that the first period is determined based on the vibration period of the push-pull signal, and the second period is determined based on the fluctuation period of the reflectance-induced fluctuation.

  In the optical drive device, the fluctuation amount instruction signal is a difference signal between the low-frequency component of the push-pull signal and an envelope signal that envelops the maximum value or minimum value of the low-frequency component for each predetermined period. It is good. In this case, it is preferable that the low frequency component includes at least the frequency component of the reflectance-induced variation, and the predetermined period is determined based on the variation period of the reflectance-induced variation.

  In each of the above optical drive devices, the push-pull signal may be corrected by adding a fluctuation amount instruction to the push-pull signal. According to this, since the push-pull signal can be shifted by the variation, it is possible to cancel the reflectance-induced variation that occurs in the push-pull signal PP.

  Each of the optical drive devices further includes an output signal generation unit that generates an output signal based on a difference signal between the push-pull signal and a reverse phase signal of the push-pull signal, and the push-pull that is input to the output signal generation unit One of the first envelope signal and the second envelope signal is added to the signal, and the other of the first envelope signal and the second envelope signal is added to the reverse phase signal input to the output signal generating means. By doing so, it is also possible to add the fluctuation amount instruction signal to the push-pull signal and thereby correct the push-pull signal. According to this, it is possible to add the difference signal to the push-pull signal without performing a subtraction process for generating the difference signal.

  In the optical drive device, the push-pull signal is a sub-push-pull signal generated based on the output signal of the sub-beam light receiving unit, and the tracking error signal may be generated based on the corrected sub-push-pull signal. Good. According to this, since the fluctuation generated in the tracking error signal with the fluctuation of the sub push-pull signal can be canceled, the tracking servo can be performed with high accuracy.

  Further, in the optical drive device, it may be determined whether or not the optical drive device is in a track-on mode. If the optical drive device is in a track-on mode, the tracking error signal may be amplified. This makes it possible to obtain an optimal tracking error signal even in the track-on mode.

  In the case of the track-on mode, the corrected sub push-pull signal includes the maximum value or the minimum value of the sub push-pull signal for each period determined based on the fluctuation period of the reflectance-induced fluctuation. An envelope signal may be used. According to this, the calculation amount of the optical drive device can be reduced.

  According to the present invention, it is possible to cancel the reflectance-induced variation that occurs in the push-pull signal PP.

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

  In this embodiment, first, offset and reflectance-induced fluctuations that occur in a push-pull signal used in tracking servo will be described in detail, and then the configuration and operation of the optical drive device according to this embodiment will be described.

  There are two types of offset that occur in the push-pull signal. One is due to lens shift, and the other is due to stray light. Of these, the offset due to stray light causes reflectivity-induced fluctuations.

  First, offset due to lens shift will be described. The cause of the offset caused by the lens shift is that the optical axis of the light beam is shifted from the center of the objective lens due to the movement of the objective lens for converging the light beam on the recording surface of the optical disc. This offset can be canceled by the differential push-pull method.

  The differential push-pull method will be described with reference to FIG. FIG. 1 is an external view of a photodetector 6 for receiving a return light beam from a recording surface.

  As shown in FIG. 1, the photodetector 6 includes a main beam light receiving unit M, a first sub beam light receiving unit S1, and a second sub beam light receiving unit S2. The light beam is irradiated onto the recording surface in a state of being separated into three beams (0th order diffracted light and ± 1st order diffracted light) by the diffraction grating, and the first sub beam light receiving unit S1, the main beam light receiving unit M, and the second sub beam light receiving unit. S2 receives the return light beam of the + 1st order diffracted light (first sub beam SB1), the return light beam of the 0th order diffracted light (main beam MB), and the return light beam of the −1st order diffracted light (second sub beam SB2), respectively.

  Each light receiving unit is a four-divided light receiving unit in which four light receiving regions each having a square light receiving surface of a predetermined size are arranged in a square shape. Specifically, the main beam light receiving unit M includes light receiving areas a, b, c, and d clockwise from the upper right of the drawing. The first sub-beam light receiving unit S1 includes light receiving regions e1, e2, e3, e4 clockwise from the upper right of the drawing. The second sub-beam light receiving unit S2 includes light receiving regions f1, f2, f3, and f4 clockwise from the upper right of the drawing.

Each light receiving unit that receives the light beam outputs 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 light receiving region. Hereinafter, output signals corresponding to the respective light receiving regions a, b, c, d, e1, e2, e3, e4, f1, f2, f3, and f4 are respectively represented as I _a , I _b , I _c , I _d , I _e1, and _{I e2, I e3, I e4} , I f1, I f2, I f3, I f4.

Using these output signals, the main push-pull signal MPP and the sub push-pull signal SPP are defined by the following equations (1) and (2).
MPP = (I _a + I _d ) − (I _b + I _c ) (1)
SPP = (I _e1 + I _f1 ) + (I _e4 + I _f4 ) − (I _e2 + I _f2 ) − (I _e3 + I _f3 ) (2)

  First, assuming that there is no offset due to lens shift, when the focal position of the main beam MB is at a predetermined position in the track (the center of the land or group), the main beam received by each light receiving region of the main beam light receiving unit M. The intensities of MB are equal to each other, and MPP = 0. On the other hand, when the focal position of the main beam MB deviates from the predetermined position in the track in the radial direction of the optical disc, the upper half light receiving areas a and d and the lower half light receiving areas b and c of the main beam light receiving section M are shown in FIG. Light and dark occur between the two, and MPP ≠ 0. Therefore, by moving the objective lens so that the MPP becomes 0, the focal position of the main beam MB can be adjusted to the predetermined position in the track (tracking servo).

  However, in reality, an offset due to lens shift occurs. As a result, the position where the MPP becomes 0 is different from the predetermined position, and it becomes difficult to perform the tracking servo. Therefore, the sub push-pull signal SPP is used to cancel the lens shift. Hereinafter, this point will be described.

  2A and 2B are diagrams showing the relationship between the lens shift amount and MPP and SPP, respectively. FIG. 2C shows the relationship between the lens shift amount and a tracking error signal TE described later.

As shown in FIG. 2A, the MPP offset amount is proportional to the lens shift amount (the distance between the optical axis and the objective lens center). Further, as indicated by SPPoffset0 in FIG. 2B, the SPP offset amount is also proportional to the lens shift amount. Therefore, in the tracking error signal TE shown in the following equation (3), the lens shift is canceled as shown in FIG. Incidentally, k _t is a correction coefficient is predetermined lens shift just as can be canceled.
_{TE = MPP-k t SPP ···} (3)

  Thus, according to the differential push-pull method, offset due to lens shift can be canceled.

  Next, offset due to stray light and the reflectance-induced fluctuation will be described.

  First, the photodetector 6 receives a return light beam reflected from a desired recording surface as well as a return light beam reflected from a desired recording surface such as another layer. This is called stray light, and FIG. 1 also shows an example of stray light (stray light L). Since the stray light L is generally a light beam that is not in focus at all, the spot of the stray light L is larger than the main beam MB or the like as shown in FIG.

  The stray light particularly affects the sub push-pull signal SPP. This is because the intensity of the sub beam is weaker than that of the main beam, so that the SPP is greatly amplified in the calculation of Equation (3). The degree of influence increases with lens shift. This is because the stray light moves on the photodetector 6 with the lens shift, and the symmetry of the stray light received by the sub-beam light receiving portions S1 and S2 is lost. Note that stray light hardly affects the main push-pull signal MPP. This is because the main beam light receiving unit M is sufficiently covered with stray light as a whole even if stray light moves with lens shift.

  SPPoffset1 in FIG. 2B shows an example of an SPP in which an offset occurs due to the influence of stray light. Since an SPP affected by stray light has an offset due to stray light in addition to an offset due to lens shift, as shown in FIG. 2B, the relationship between the SPP offset amount and the lens shift amount is SPPoffset0 (the offset due to stray light is 0). The SPP offset amount). As a result, as indicated by TE1 in FIG. 2C, a similar offset due to stray light appears in the tracking error signal TE.

  In addition, the offset amount of the stray light offset (stray light offset amount) is a value corresponding to the reflectance of the optical disk recording surface. Therefore, if the reflectance of the optical disk recording surface is not uniform, the amount of stray light offset varies depending on the access position of the recording surface (variation due to reflectance).

  In FIG. 2B, SPPoffset1 indicates the SPP offset amount when the reflectance has a certain value, and SPPoffset2 indicates the SPP offset amount when the reflectance has another value. As described above, the stray light offset amount fluctuates because the reflectance of the recording surface is not uniform, and the influence thereof also appears in the tracking error signal TE as indicated by TE1 and TE2 in FIG.

Unless there is a reflectance-induced variation, the effect of the offset due to stray light itself on the tracking servo is limited. For example, it is a pre-correction coefficient k _t if in the lens shift amount of function, since it is possible to cancel the stray light offset from the tracking error signal TE.

  However, if the stray light offset has a reflectance-induced variation as shown in FIG. 2C, the conventional technique cannot cancel the reflectance-induced variation from the tracking error signal TE, and the tracking servo accuracy deteriorates. Therefore, in the present embodiment, in order to cancel the reflectance-induced variation from the tracking error signal TE, the sub-push-pull signal SPP is used by using the variation-amount instruction signal indicating the amount of the reflectance-induced variation that occurs in the sub-push-pull signal SPP. Correct. Hereinafter, the configuration and operation of the optical drive apparatus according to the present embodiment for realizing such correction will be described in detail.

  FIG. 3 is a schematic diagram of the optical drive device 1 for reproducing and recording the optical disc 11.

  Various optical recording media such as CD, DVD, HD-DVD, and BD can be used for the optical disc 11. In this embodiment, a disc-shaped optical disc having a recording surface that is multilayered by a multilayer film is used. . The film thickness of each layer is preferably uniform originally, but in reality, the film thickness near the center of the disk is often larger than the film thickness near the periphery. Also, the film thickness may be non-uniform even within the same circumference.

  As shown in FIG. 3, the optical drive device 1 includes a laser light source 2, an optical system 3, an objective lens 4, a lens driving unit 5, a photodetector 6, and a processing unit 7.

  The optical system 3 includes a diffraction grating 21, a beam splitter 22, a collimator lens 23, a quarter wavelength plate 24, and a sensor lens (cylindrical lens) 25. The optical system 3 functions as an outward optical system that guides the light beam emitted from the laser light source 2 to the optical disc 11, and also functions as a return optical system that guides the return beam from the optical disc 11 to the photodetector 6.

  First, 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 enters the beam splitter 22 as P-polarized light. The beam splitter 22 reflects the incident P-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.

  Next, in the return optical system, the beam splitter 22 transmits 100% of the light beam reflected by the recording surface and further passing through the quarter wavelength plate 24 to become S-polarized light and traveling backward through the return optical system. The light enters the sensor lens 25. The sensor lens 25 gives astigmatism to the light beam incident from the beam splitter 22. The light beam provided with astigmatism enters the photodetector 6.

  The objective lens 4 has a function of condensing a light beam incident from the optical system 3 (a light beam in a parallel light state) on the optical disk 11 and returning a return light beam from the optical disk 11 to parallel light.

  The lens driving unit 5 moves the objective lens 4 in the radial direction of the optical disk 11 based on the tracking error signal TE output from the processing unit 7, thereby positioning the spot formed on the recording surface by the light beam on the optical disk 11. Move in the radial direction (tracking servo). Further, the lens driving unit 5 moves the objective lens 4 in a direction perpendicular to the recording surface of the optical disk 11 based on the focus error signal FE output from the processing unit 7, thereby forming a light beam on the recording surface. The position of the spot to be moved is moved toward and away from the recording surface (focus servo).

  The photodetector 6 is installed on a plane that intersects the optical path of the return light beam emitted from the optical system 3 as shown in FIG. The detailed configuration is as shown in FIG.

As an example, the processing unit 7 is configured by a DSP (Digital Signal Processor) having an A / D conversion function for converting analog signals for multiple channels into digital data, and the output signals I _a and I of the photodetector 6. _b , I _c , I _d , I _e1 , I _e2 , I _e3 , I _e4 , I _f1 , I _f2 , I _f3 , and I _f4 are received, and three types of signals, that is, a reproduction signal RF and a focus error signal are received. FE and tracking error signal TE are generated.

The reproduction signal RF is a signal indicating the data recorded on the recording surface, and is represented by the equation (4). The processing unit 7 outputs the generated reproduction signal RF to a CPU (not shown).
RF = I _a + I _b + I _c + I _d (4)

The focus error signal FE is a signal used for focus servo. For example, in the focus servo of the differential astigmatism method, the focus error signal FE is expressed as in Expression (5). Note that k _f in the equation is a correction coefficient. The processing unit 7 outputs the generated focus error signal FE to the lens driving unit 5.
FE = (I _a + I _c ) − (I _b + I _d ) + k _f {(I _e1 + I _f1 ) + (I _e3 + I _f3 ) − (I _e2 + I _f2 ) − (I _e4 + I _f4 )} 5)

The tracking error signal TE is as described above. Hereinafter, a specific configuration for canceling the reflectance-induced variation that occurs in the tracking error signal TE will be described with reference to a functional block diagram of the processing unit 7. In the following description, the optical drive apparatus 1 or the like will be described taking the case of learning the correction coefficient k _t when a new optical disc is inserted.

  FIG. 4 is a functional block diagram of the processing unit 7.

  As shown in FIG. 4, the processing unit 7 functionally includes an MPP generation unit 71, an MPP processing unit 72, an SPP generation unit 73, an SPP processing unit 74, and a TE generation unit 75.

  The MPP generation unit 71 calculates the main push-pull signal MPP according to Equation (1), and outputs the MPP normal phase signal MPPp and the reverse phase signal (a signal obtained by inverting the phase of the normal phase signal) MPPn. The MPP processing unit 72 performs processing for removing noise components from the main push-pull signal MPP calculated by the MPP generation unit 71. Details of the processing of the MPP processing unit 72 will be described later.

  The SPP generation unit 73 calculates the sub push-pull signal SPP by Expression (2), and outputs the SPP normal phase signal SPPp and the negative phase signal SPPn. The SPP processing unit 74 performs processing (sub-push pull signal SPP correction processing) for removing noise components and reflectance-induced fluctuations from the sub push-pull signal SPP calculated by the SPP generation unit 73. Details of the processing of the SPP processing unit 74 will be described later.

  The TE generation unit 75 substitutes MPP (MPPo) processed by the MPP processing unit 72 and SPP (SPPo) processed by the SPP processing unit 74 into Expression (3) to generate a tracking error signal. It outputs to the drive part 5 (FIG. 3).

  FIG. 5 is a diagram illustrating an internal configuration of the MPP processing unit 72.

  As shown in FIG. 5, the MPP processing unit 72 includes an operational amplifier 720.

  MPPp and MPPn output from the MPP generation unit 71 are input to the non-inverting input terminal (+) and the inverting input terminal (−) of the operational amplifier 720, respectively.

The non-inverting input terminal (+) of the operational amplifier 720 is connected to the reference voltage Vref via the resistor R. The output terminal of the operational amplifier 720 is connected to the inverting input terminal (−) via the feedback resistor R. As a result of such a configuration, the operational amplifier 720 generates an output signal MPPo represented by the following equation (6) based on the difference signal between MPPp and MPPn.
MPPo = MPPp−MPPn + Vref = 2 × MPP + Vref (6)

  Even if there are noise components in MPPp and MPPn, MPPo cancels them as is apparent from equation (6). The MPP processing unit 72 outputs MPPo from which the noise component has been removed in this way. This series of processing is called differential-single conversion processing because the differential signals (MPPp and MPPn) are converted into one output signal MPPo.

  Next, in addition to the differential-single conversion process, the SPP processing unit 74 also performs a process for removing the reflectance-induced variation for the sub push-pull signal SPP calculated by the SPP generation unit 73. Since the configuration for performing the differential-single conversion process is the same as that of the MPP processing unit 72, description thereof will be omitted, and the configuration for removing the reflectance-induced variation will be described below. In the description, first, the principle of processing will be described with reference to FIG. 6, and then a specific configuration for realizing the processing will be described.

  FIG. 6 shows the waveform of the sub push-pull signal SPP.

Although the output signal of the photodetector 6 is a direct current signal, track jumps frequently occur during learning of the correction coefficient k _t , so that the value vibrates as if it were alternating current. The fine waveform of the SPP shown in FIG. 6 is caused by such oscillation of the output signal of the photodetector 6. The fact that the SPP in FIG. 6 rises to the right as a whole is the effect of offset due to lens shift. Variations in the amount of stray light offset due to non-uniform reflectivity of the recording surface appear on the SPP waveform as low-frequency pulsations (reflectance-induced variations) as shown in FIG. FIG. 6 shows the range of the lens shift amount limited to a range in which the lens shift amount and the SPP offset amount are in a proportional relationship.

  The SPP processing unit 74 (FIG. 4) generates a top envelope signal (first envelope signal) SPPte that envelops the maximum value of the SPP for each first period, and the second longer than the first period. A top hold signal (second envelope signal) SPPth that envelops the maximum value of the SPP for each period is generated. The first period is preferably determined based on the vibration period of the sub push-pull signal SPP so that the first envelope signal envelopes the maximum point of vibration of the sub push-pull signal SPP. On the other hand, it is preferable that the second period is determined based on the fluctuation period of the reflectance-induced variation so as to envelop the maximum point of the reflectance-induced variation.

  The difference signal (= SPPth−SPPte) between the top hold signal SPPth and the top envelope signal SPPte generated in this way is a variation amount instruction signal indicating the amount of variation caused by reflectance. Therefore, the SPP processing unit 74 corrects the sub push-pull signal SPP by adding the difference signals. Thereby, it is possible to remove the reflectance-induced variation from the sub push-pull signal SPP.

  The above is the principle of the process for removing the reflectance-induced variation from the sub push-pull signal SPP. In practice, because of the differential-single conversion process, an addition process using an operational amplifier is performed instead of simply adding a differential signal to the sub push-pull signal SPP. This will be described in detail below.

  FIG. 7 is a diagram illustrating an internal configuration of the SPP processing unit 74.

  As shown in FIG. 7, the SPP processing unit 74 includes a top hold signal generation unit 740, a top envelope signal generation unit 741, and an operational amplifier 742 (output signal generation means).

  The top hold signal generation unit 740 generates the top hold signal SPPth and outputs a signal obtained by amplifying the amplitude twice. The top envelope signal generation unit 741 generates the top envelope signal (second envelope signal) SPPte and outputs a signal obtained by amplifying the amplitude twice.

SPPp added with 2 × SPPth is input to the non-inverting input terminal (+) of the operational amplifier 742. Further, SPPn to which 2 × SPPte is added is input to the inverting input terminal (−). As a result, the output signal SPPo represented by the following equation (7) is output to the output terminal of the operational amplifier 742.
SPPo = SPPp−SPPn + Vref + 2 × (SPPth−SPPte) = 2 × (SPP + SPPth−SPPte) + Vref (7)

  As shown in Expression (7), in the SPPo, the reflectance-induced variation (= SPPth−SPPte) generated in the sub push-pull signal SPP is removed.

  Although FIG. 7 illustrates an example in which 2 × SPPth is added to SPPp and 2 × SPPte is added to SPPn, a differential signal may be added to the output signal SPPo after differential-single conversion. In the output signal SPPo after the single conversion, it is not necessary to double the differential signal as in the above example. Moreover, it is good also as adding a difference signal to SPPn.

  As described above, according to the optical drive device 1, since the fluctuation amount instruction signal is added to the sub push-pull signal SPP, the sub push-pull signal SPP can be shifted by the fluctuation amount of the reflectance-induced fluctuation. it can. Therefore, since the reflectance of the recording surface is not uniform, it is possible to cancel the reflectance-induced variation that occurs in the sub push-pull signal SPP.

  Further, by performing the addition process in combination with the differential-single conversion process, it is possible to add the fluctuation amount instruction signal to the sub push-pull signal SPP without performing the subtraction process for generating the fluctuation amount instruction signal. It is possible.

Further, at the time of learning of the correction coefficient k _t using the low tracking error signal blurring after canceling the reflectance caused variation, it is possible to obtain the stable correction coefficient k _t.

  Note that the above processing can also be used when an optical disc is being reproduced or recorded (in a track-on mode). In this case, a track jump does not occur unless a track shift occurs, so that the SPP does not exhibit a high-frequency behavior as shown in FIG. When the SPP changes due to the track deviation, the change becomes a relatively low frequency and is reflected in the SPPte. Accordingly, the track shift information is not included in the SPPo obtained by the equation (7). That is, in this case, since 2 × (SPPth-SPPte) cancels the variation of SPPp-SPPn, SPPo is a top hold signal that envelops the maximum value of SPPp-SPPn for each second period. It becomes. For this reason, the information component of the track deviation included in the tracking error signal TE is only the amount included in the main push-pull signal MPP, and is about half that in the case where the present invention is not used.

  Therefore, the TE generation unit 75 determines whether or not the optical drive device 1 is in the track-on mode. If the optical drive device 1 is in the track-on mode, the TE generation unit 75 performs an amplification process on the generated tracking error signal TE to obtain about twice. It is preferable to output to the lens driving unit 5 after amplification.

  In this case, it is also possible to obtain SPPo without calculating Equation (7) in the first place. Specifically, using the top hold signal SPPpth enveloping the maximum value of SPPp for each second period and the bottom hold signal SPPPnbh enveloping the minimum value of SPPn for each second period, SPPo = SPPpth-SPPnbh + Vref. Also, using the bottom hold signal SPPpbh enveloping the minimum value of SPPp for each second period and the top hold signal SPPnth enveloping the maximum value of SPPn for each second period, SPPo = SPPppbh− SPPnth + Vref may be set, or SPPo = SPP1th (SPP1bh) may be set by using a top hold signal SPP1th (SPP1bh) enveloping the maximum value (minimum value) of SPPp-SPPn for each second period. By doing so, the calculation of Expression (7) becomes unnecessary, so that the processing amount of the optical drive device 1 is reduced.

  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, the difference signal between the top hold signal and the top envelope signal is used as the fluctuation amount instruction signal, but other signals shown below can also be used.

For example, a bottom hold signal SPPbh that envelops the minimum value of the sub push-pull signal SPP for each first period and a bottom envelope signal that envelops the minimum value of the sub push-pull signal SPP for each second period. SPPbe can also be used as the fluctuation amount instruction signal. FIG. 6 also shows each of these signals. In this case, equation (7) is changed to equation (8).
SPPo = SPPp−SPPn + Vref + 2 × (SPPbh−SPPbe) = 2 × (SPP + SPPbh−SPPbe) + Vref (8)

Even in this case, it is possible to cancel the reflectance-induced variation that similarly occurs in the sub push-pull signal SPP. As for which of the difference signal between the top hold signal and the top envelope signal and the difference signal between the bottom hold signal and the bottom envelope signal to be used as the fluctuation amount instruction signal, select a signal whose change with respect to the offset amount is more linear. It is desirable. Further, it is desirable that in the correction coefficient k _t during learning and tracking servo at the time of selecting the same.

  In addition, a difference signal between the low frequency component of the sub push-pull signal SPP and an envelope signal that envelops the maximum value or minimum value of the low frequency component for each predetermined period can be used as the variation instruction signal. The low frequency component preferably includes at least a fluctuation frequency component of reflectance-induced fluctuation. Further, it is preferable that the predetermined period is determined based on a fluctuation period of the reflectance-induced variation so that the envelope signal envelopes the maximum point of the reflectance-induced variation.

FIG. 8 shows an example of a low-frequency component SPP _LPF1 obtained by passing the sub push-pull signal SPP through a low-pass filter and an envelope signal SPP _LPFth1 enveloping the maximum value. Since the difference signal between these signals is the same as the difference signal between the top hold signal and the top envelope signal, similarly to the above, it can be used to cancel the reflectivity-induced variation occurring in the sub push-pull signal SPP.

In the sub push-pull signal SPP, a noise component called confocal crosstalk (amplitude and offset fluctuation) may appear. Such a noise component is preferably removed by a low-pass filter. However, since the confocal crosstalk frequency is intermediate between the SPP frequency and the SPP _LPF1 , the cutoff of the low-pass filter is used to remove this noise component. It is necessary to lower the frequency. Since the cut-off frequency is inversely proportional to the product of capacitance and resistance, it is necessary to use a large-capacitance capacitor or a high-resistance resistor to lower the cut-off frequency, and confocal crosstalk is removed from the sub push-pull signal SPP. There are cases where it is not possible.

FIG. 9 shows an example of the low frequency component SPP _{LPF2 in} which confocal crosstalk remains in such a case. As shown in the figure, the low frequency component SPP _LPF2 includes a confocal crosstalk component in addition to the low frequency component SPP _LPF1 .

As shown in FIG. 9, the envelope signal SPP _LPFth2 that _envelops the maximum value of the low frequency component SPP _LPF2 for each predetermined period is larger than the envelope signal SPP _LPFth1 by the confocal crosstalk amplitude. Will have. In such a case, the difference signal may be calculated using the envelope signal SPP _LPFth2 .

  8 and 9, only the envelope signal formed by enveloping the maximum value of the low frequency component is shown, but it is needless to say that the envelope signal formed by enveloping the minimum value may be used.

  In the above-described embodiment, the reflectance-induced variation (the reflectance-induced variation of the offset due to stray light) that causes a significant effect when there is an offset due to the lens shift has been described as an example. It is possible to apply the present invention. For example, the reflectivity differs at the boundary of the unrecorded / recorded area of the optical disk, for example, and the push-pull signal may vary accordingly. The present invention can also be used to cancel such fluctuations.

  In the above embodiment, the example in which the present invention is applied to the differential push-pull method using the main push-pull signal MPP and the sub push-pull signal SPP has been described. However, for example, the one-beam method using only the main push-pull signal MPP In addition, the present invention is applicable. In the above embodiment, only the reflectivity-induced variation that occurs in stray light is considered as a problem. However, the reflectivity-induced variation also occurs in the reflected light in the focused layer. In the differential push-pull method, even if the reflection-induced fluctuation occurs in the reflected light in the focused layer, the main push-pull signal MPP and the sub push-pull signal SPP cancel each other, so this fluctuation is included in the tracking error signal. No effect remains. On the other hand, in the one-beam method, the reflectance-induced fluctuation that occurs in the reflected light from the focused layer is reflected in the main push-pull signal MPP, that is, the tracking error signal TE. By applying the present invention to the main push-pull signal MPP of the one-beam method, it is possible to cancel the reflectance-induced variation that has occurred in the main push-pull signal MPP, so that the reflectance-induced variation is reflected in the tracking error signal TE. Can be prevented.

It is an external view at the time of seeing the photodetector by embodiment of this invention from the irradiation direction of a light beam. (A) (b) (c) is a figure which shows the relationship between a lens shift amount, a main push pull signal, a sub push pull signal, and a tracking error signal, respectively. 1 is a schematic diagram of an optical drive device according to an embodiment of the present invention. It is a functional block diagram of the process part by embodiment of this invention. It is a figure which shows the internal structure of the MPP process part by embodiment of this invention. It is a figure which shows the sub push pull signal, top hold signal, bottom hold signal, top envelope signal, and bottom envelope signal by embodiment of this invention. It is a figure which shows the internal structure of the SPP process part of embodiment of this invention. It is a figure which shows the low frequency component obtained by letting a sub push pull signal and a sub push pull signal pass a low pass filter by the modification of embodiment of this invention, and its envelope signal. It is a figure which shows the low frequency component obtained by letting the sub push pull signal by the modification of embodiment of this invention pass a low-pass filter, the low frequency component on which the confocal crosstalk was superimposed, and its envelope signal. It is an external view at the time of seeing the photodetector by the background art of this invention from the irradiation direction of a light beam.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical drive apparatus 2 Laser light source 3 Optical system 4 Objective lens 5 Lens drive part 6 Photodetector 7 Processing part 11 Optical disk 21 Diffraction grating 22 Beam splitter 23 Collimator lens 24 1/4 wavelength plate 25 Sensor lens 71 MPP generation part 72 MPP Processing unit 73 SPP generation unit 74 SPP processing unit 75 TE generation unit 720, 742 Operational amplifier 740 Top hold signal generation unit 741 Top envelope signal generation unit a, b, c, d, e1, e2, e3, e4, f1, f2, f3, f4 light receiving region L stray light M main beam light receiving unit MB main beam S1 first sub beam light receiving unit S2 second sub beam light receiving unit SB1 first sub beam SB2 second sub beam SPP sub push pull signal SPPbe bottom envelope signal SPPbh bottom hold signal SPP _LPF1 , SPP _PF2 low frequency components _{SPP LPFth1, SPP LPFth2} envelope signal SPPte top Embedded signal SPPth top hold signal TE Tracking error signal

Claims (11)

  The push-pull signal received is received, and the received push-pull signal is received based on a fluctuation amount instruction signal indicating the amount of fluctuation caused by the reflectance generated in the push-pull signal due to non-uniform reflectance of the optical recording medium. An optical drive device characterized by correcting.   The fluctuation amount instruction signal includes a first envelope signal enveloping a maximum value of the push-pull signal for each first period, and a push-pull signal for each second period longer than the first period. The optical drive device according to claim 1, wherein the optical drive device is a difference signal with respect to a second envelope signal formed by enveloping the maximum value.   The fluctuation amount instruction signal includes a first envelope signal enveloping a minimum value of the push-pull signal for each first period, and a push-pull signal for each second period longer than the first period. 2. The optical drive device according to claim 1, wherein the optical drive device is a difference signal from a second envelope signal formed by enveloping the minimum value.   4. The method according to claim 2, wherein the first period is determined based on a vibration period of the push-pull signal, and the second period is determined based on a fluctuation period of the reflectance-induced fluctuation. The optical drive device described.   The variation instruction signal is a difference signal between a low-frequency component of the push-pull signal and an envelope signal that envelops a maximum value or a minimum value of the low-frequency component for each predetermined period. The optical drive device according to claim 1.   6. The optical drive device according to claim 5, wherein the low frequency component includes at least a fluctuation frequency component of the reflectance-induced variation, and the predetermined period is determined based on a variation period of the reflectance-induced variation. .   The optical drive apparatus according to claim 1, wherein the push-pull signal is corrected by adding the fluctuation amount instruction signal to the push-pull signal. An output signal generating means for generating an output signal based on a differential signal between the push-pull signal and a reverse-phase signal of the push-pull signal;
One of the first envelope signal and the second envelope signal is added to the push-pull signal input to the output signal generation unit, and the reverse phase signal input to the output signal generation unit The fluctuation amount instruction signal is added to the push-pull signal by adding the other one of the first envelope signal and the second envelope signal, thereby correcting the push-pull signal. The optical drive apparatus as described in any one of Claims 2 thru | or 4. The push-pull signal is a sub push-pull signal generated based on the output signal of the sub-beam light receiving unit,
9. The optical drive device according to claim 1, wherein a tracking error signal is generated based on the corrected sub push-pull signal.   10. The optical drive device according to claim 9, wherein it is determined whether or not the optical drive device is in a track-on mode, and if the tracking drive signal is in the track-on mode, an amplification process is performed on the tracking error signal.   In the case of the track-on mode, the corrected sub push-pull signal envelops the maximum value or the minimum value of the sub push-pull signal for each period determined based on the fluctuation period of the reflectance-induced variation. The optical drive device according to claim 10, wherein an envelope signal is used.

Images