JP2010086573A - Information recording and reproducing apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To select a proper tracking error signal before tracking control. <P>SOLUTION: An information recording and reproducing apparatus 1 includes: a tracking control part 14 which generates a first tracking error signal by a push-pull method from a read signal based on reflected light; a tracking control part 14 which generates a second tracking error signal by a DPD (Differential Phase Detection) method from the read signal; a CPU 16 which compares the polarities of the first tracking error signal with the second tracking error signal, and selects one of the first and second tracking error signals on the basis of the result of the comparison; and a tracking control part 14 which performs tracking control on the basis of the selected one of the first tracking error signal and the second tracking error signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technical field of an information recording / reproducing apparatus and method including means for generating a tracking signal for performing tracking control, for example.

  In an optical disc such as a CD, DVD, or Blu-ray Disc, a data pattern recorded on the optical disc (for example, a combination of recording marks, recording pits, spaces, etc.) or a recording track on which a data pattern is to be recorded is recorded. Tracking control is performed in order to suitably irradiate the laser beam for reproduction. By this tracking control, the data pattern can be read correctly or the data pattern can be recorded at a suitable position.

  As such tracking control methods, a push-pull method, a DPD (Differential Phase Detection) method, a 3-beam method, and the like are known. Among these methods, in the push-pull method, a read signal (in other words, when a single laser beam is irradiated onto the optical disc surface and the reflected light from the track is received by a light receiving element having a light receiving region divided into two parts (in other words, Each output of the push-pull signal) is compared, and a tracking signal is generated based on the comparison result. In the DPD method, a phase of a read signal (in other words, a DPD signal) when a light receiving element having a plurality of light receiving regions receives reflected light is compared, and a tracking signal is generated based on the comparison result. .

  Patent Document 1 adopts a method of generating tracking signals by the push-pull method and the DPD method, comparing the reproduction quality of both, and performing tracking control based on a higher quality tracking signal. Yes.

JP 2006-59505 A

  By the way, the polarity of the push-pull signal, which is a read signal obtained by the above-described push-pull method, may be reversed depending on the pit depth on the optical disk surface. For example, assuming that the wavelength of the laser light from the optical pickup is λ, the polarity of the push-pull signal is reversed when the pit depth is λ / 4. When tracking control is performed using a push-pull signal whose polarity is reversed in this way, the tracking servo loop does not close and it is difficult to do so, and even if it can be closed, control of the tracking servo will subsequently fail. There is a technical problem.

  The present invention has been made in view of such problems, and before tracking control is performed to determine whether the polarity of a tracking error signal (so-called push-pull signal) generated by the push-pull method is inverted. It is an object to perform tracking control using a suitable tracking error signal.

  In order to solve the above-described problems, an information recording / reproducing apparatus of the present invention irradiates a laser beam on the information recording medium and performs reflection of the laser light in order to perform at least one of recording and reproducing information on the information recording medium. An information recording / reproducing apparatus including an optical pickup for receiving light, wherein the first signal generating unit generates a first tracking error signal by a push-pull method from the read signal based on the reflected light, and DPD (Differential) from the read signal A second signal generating means for generating a second tracking error signal by a phase detection method, and the polarities of the first tracking error signal and the second tracking error signal are compared with each other, and the first tracking error signal is compared based on the comparison result. Signal determination means for selecting one of the first tracking error signal and the second tracking error signal; Tracking control means for performing tracking control based on one of the selected first tracking error signal and second tracking error signal.

  In order to solve the above-described problems, an information recording / reproducing method of the present invention irradiates a laser beam on the information recording medium and performs reflection of the laser light in order to perform at least one of recording and reproducing information on the information recording medium. An information recording / reproducing method in an information recording / reproducing apparatus including an optical pickup for receiving light, the first signal generating step for generating a first tracking error signal by a push-pull method from a read signal based on the reflected light, and the reading A second signal generation step of generating a second tracking error signal from the signal by a DPD (Differential Phase Detection) method, and the respective polarities of the first tracking error signal and the second tracking error signal are compared with each other, and the comparison result One of the first tracking error signal and the second tracking error signal based on A signal determination step for selecting, and a tracking control step for performing tracking control based on one of the selected first tracking error signal and second tracking error signal.

It is a block diagram which shows notionally the basic structural example of the information recording / reproducing apparatus based on a present Example. It is a flowchart which shows the flow of the tracking error signal selection operation example of the information recording / reproducing apparatus based on a present Example. It is a graph which shows notionally the comparison of the polarity of the tracking error signal concerning this example. It is a flowchart which shows the flow of the example of polarity comparison operation | movement of the tracking error signal of the information recording / reproducing apparatus based on a present Example. It is a graph which shows notionally the relation between the signal level of a tracking error signal concerning this example, and a threshold.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Information recording / reproducing apparatus 10 Disk drive 12 Optical pick-up 121 Laser diode 122 Photo detector 13 Signal recording / reproducing part 14 Tracking control part 15 Memory 16 CPU
17 Input / output control unit 18 Bus 20 Host computer

<1>
In an embodiment of the information recording / reproducing apparatus of the present invention, the information recording medium is irradiated with a laser beam and the reflected light of the laser beam is received in order to perform at least one of recording and reproducing information with respect to the information recording medium. An information recording / reproducing apparatus including an optical pickup, wherein a first signal generation unit generates a first tracking error signal by a push-pull method from a read signal based on the reflected light, and a DPD (Differential Phase Detection) method from the read signal And second signal generating means for generating a second tracking error signal according to the above, the polarities of the first tracking error signal and the second tracking error signal are compared with each other, and the first tracking error signal is based on the comparison result. And a signal determination means for selecting one of the second tracking error signals, Tracking control means for performing tracking control based on one of the first tracking error signal and the second tracking error signal.

  According to the embodiment of the information recording / reproducing apparatus of the present invention, the first tracking error signal generated from the read signal using the DPD method and the second tracking error generated from the read signal using the push-pull method are used. By comparing the polarity with the signal, either one is selected as a tracking error signal used for tracking control.

  According to the first signal generating means of the present embodiment, the first tracking error signal is generated using the push-pull method. Typically, the push-pull signal has a property that the signal level = 0 at the center of the track, that is, the tracking center, and the relative movement direction of the irradiating laser light with respect to the information recording medium is determined. Thus, the land and groove on the recording surface of the information recording medium are discriminated depending on whether the polarity of the push-pull signal changes from positive to negative or from negative to positive with such a track center as a boundary. Note that such polarity (that is, a mode of positive and negative fluctuations with the track center as a boundary) varies depending on the pit depth on the recording surface of the information recording medium. In other words, when the wavelength of the laser beam is λ, the relationship between the polarity of the push-pull signal and the land and groove is inverted depending on whether the pit depth is less than or equal to λ / 4. Therefore, there is a technical problem that the tracking servo control fails or fails when it is used for tracking control without considering the inversion of the polarity of the first tracking error signal.

  According to the second signal generation means of the present embodiment, the second tracking error signal is generated using the DPD method. That is, the tracking signal is generated based on the phase comparison result of the read signal (that is, the result of the phase comparison process). The DPD signal generated in this way is referred to as a second tracking error signal. In general, the second tracking error signal takes a sawtooth shape.

  In such a second tracking error signal generated using the DPD method, polarity inversion does not occur due to the pit depth of the information recording medium. Therefore, there is no possibility that the tracking control as described above may fail or the tracking servo control may fail. On the other hand, the second tracking error signal also has a technical problem that a lot of noise is mixed when an information recording medium, which is typically an optical disk, has a low rotation speed. In order to perform reproduction, a further configuration that can eliminate the influence of such noise is required. From such a background, it is preferable that tracking control using the first tracking error signal generated by the push-pull method can be performed as much as possible.

  According to the signal determination unit of the present embodiment, the polarities of the first tracking error signal and the second tracking error signal generated as described above are compared. Based on the comparison result, it is typically determined whether or not the polarity of the first tracking error signal is inverted. Specifically, for example, after detecting each tracking error signal, the polarity of each signal at a predetermined timing is acquired and compared with each other. Then, one of the first tracking error signal and the second tracking error signal is selected based on the comparison result.

  Typically, when the polarities of the tracking error signals do not match, it is determined that the polarity of the first tracking error signal is inverted. As described above, the inversion of the polarity of the first tracking error signal is caused by the pit depth on the recording surface of the information recording medium. For the information recording medium thus determined, The tracking control using the first tracking error signal may cause the technical problem described above. Therefore, the second tracking error signal is preferably selected and used for tracking control by the tracking control means. A method of selecting a tracking error signal based on the result of such comparison will be described in detail later.

  The comparison of the polarities of the first tracking error signal and the second tracking error signal in the present embodiment is based on, for example, the ratio of the number of times that the polarity inversion has occurred in the total number of comparisons after performing a plurality of comparisons. Or may be performed based on the number of times polarity inversion is detected in a plurality of comparisons. On the other hand, it may be performed based on the result of one-time comparison. Such a comparison condition is preferably set so that it is possible to determine a state in which the polarities of the first tracking error signal and the second tracking error signal do not match (that is, a state in which the polarity of the first tracking error signal is inverted). However, the conditions are not limited to these conditions, and may be set as appropriate by, for example, experiments or simulations.

  As described above, according to the embodiment of the information recording / reproducing apparatus of the present invention, whether or not the polarity of the first tracking error signal generated by the push-pull method is inverted before the tracking control is performed. The tracking control can be performed by selecting an appropriate tracking error signal.

<2>
One aspect of the embodiment of the information recording / reproducing apparatus of the present invention is that the signal determination means is configured such that when the polarities of the first tracking error signal and the second tracking error signal are equal to each other, When a tracking error signal is selected and the polarities of the first tracking error signal and the second tracking error signal are different from each other, the second tracking error signal is selected.

  According to this aspect, the polarities of the first tracking error signal generated from the read signal using the push-pull method and the second tracking error signal generated from the read signal using the DPD method are compared, and When the first and second polarities are equal, typically, it can be determined that the polarity of the first tracking error signal is not inverted. Therefore, the first tracking error signal is selected as the tracking error signal used for tracking control. With this configuration, when it is determined that the polarity of the first tracking error signal is not inverted as described above, suitable tracking control using the first tracking error signal can be performed.

  On the other hand, when the polarities of the first tracking error signal and the second tracking error signal are different from each other, typically, it can be determined that the polarity of the first tracking error signal is inverted. The second tracking error signal is selected as the tracking error signal. With this configuration, it is possible to suitably prevent tracking control from being performed using the first tracking error signal whose polarity is inverted, and tracking control using the second tracking error signal by the DPD method. Can be carried out.

  From the above, before closing the tracking servo loop in tracking control, tracking control failure or tracking servo control failure caused by performing tracking control using the first tracking error signal with reversed polarity, etc. It is possible to prevent the occurrence of technical problems.

<3>
In another aspect of the embodiment of the information recording / reproducing apparatus of the present invention, the signal determination means includes: (i) an absolute value of a signal level of the first tracking error signal is not less than a predetermined first threshold, and the If the absolute value of the signal level of the second tracking error signal is greater than or equal to a predetermined second threshold, the polarities of the first tracking error signal and the second tracking error signal are compared with each other; When the absolute value of the signal level of the first tracking error signal is lower than the first threshold and the absolute value of the signal level of the second tracking error signal is lower than the second threshold, or one of them The polarities of the first tracking error signal and the second tracking error signal are not compared with each other.

  According to this aspect, when the absolute values of the signal levels of the first tracking error signal and the second tracking error signal are both equal to or higher than the predetermined threshold values, the first tracking error signal and the second tracking error signal are set. A comparison of the polarity of the error signal is performed. On the other hand, if the absolute value of the signal level of at least one of the tracking error signals is below the corresponding threshold value, the polarity comparison of the tracking error signals is not performed.

  With this configuration, the polarity comparison is performed when the absolute values of the signal levels of the first tracking error signal and the second tracking error signal are so small that it is difficult to determine the polarity. It is possible to suitably prevent an erroneous determination of the polarity that is caused.

  As an example of such a signal level threshold, it may be set as a predetermined ratio in the amplitude of each tracking error signal, and at least the polarities of the first tracking error signal and the second tracking error signal are accurately determined. When the predetermined first threshold value and the second threshold value that can be calculated are calculated by some method such as experiment or simulation, these threshold values may be used.

<4>
In another aspect of the embodiment of the information recording / reproducing apparatus of the present invention, the signal determining means is (i) when the absolute value of the signal level of the first tracking error signal is lower than a predetermined third threshold value. When the polarities of the first tracking error signal and the second tracking error signal are compared with each other, and (ii) the absolute value of the signal level of the first tracking error signal is not less than the third threshold, The first tracking error signal is selected without comparing the polarities of the first tracking error signal and the second tracking error signal with each other.

  According to this aspect, before comparing the polarities of the first tracking error signal and the second tracking error signal, it is determined whether or not the absolute value of the signal level of the first tracking error signal is greater than or equal to the third threshold value. Is done. As a result of the determination, if the absolute value of the signal level of the first tracking error signal is equal to or greater than the third threshold value, the first tracking error signal is selected without performing the above-described polarity comparison. When the absolute value of the signal level is lower than the third threshold value, the polarity is compared.

  In general, it is known that when the polarity of the first tracking error signal is inverted, the signal level decreases. Therefore, by setting the third threshold value so that the signal level reduction based on the inversion of the polarity can be detected, the first tracking error signal and the second tracking error signal can be compared without comparing the respective polarities. It can be determined whether or not the polarity of one tracking error signal is inverted. Therefore, it is possible to determine that the polarity of the first tracking error signal has not been reversed without requiring extra processing or time when it is determined that the polarity comparison is unnecessary, and the first tracking error signal can be determined. Tracking control can be performed by selecting.

<5>
In an embodiment of the information recording / reproducing method of the present invention, the information recording medium is irradiated with laser light and reflected light of the laser light is received in order to perform at least one of recording and reproduction of information on the information recording medium. An information recording / reproducing method in an information recording / reproducing apparatus including an optical pickup, wherein a first tracking error signal is generated from a read signal based on the reflected light by a push-pull method, and a DPD ( A second signal generating step for generating a second tracking error signal by the Differential Phase Detection method, and the polarities of the first tracking error signal and the second tracking error signal are compared with each other, and the above-mentioned results are used to A signal for selecting one of the first tracking error signal and the second tracking error signal A determination step, and a tracking control step for performing tracking control based on one of the selected first tracking error signal and second tracking error signal.

  According to the embodiment of the information recording / reproducing method of the present invention, suitable tracking control is performed while enjoying the same effects as the various effects that can be enjoyed by the above-described embodiment of the information recording / reproducing apparatus of the present invention. Can be implemented.

  Incidentally, in response to the various aspects of the embodiment of the information recording / reproducing apparatus of the present invention described above, the embodiment of the information recording / reproducing method of the present invention can also adopt various aspects.

  As described above, according to the embodiment of the information recording / reproducing apparatus of the present invention, the first signal generating means, the second signal generating means, the signal determining means, and the tracking control means are provided. According to the embodiment of the information recording / reproducing method of the present invention, the information recording / reproducing method includes a first signal generation step, a second signal generation step, a signal determination step, and a tracking control step. Therefore, it is possible to suitably determine whether or not the polarity of the first tracking error signal generated by the push-pull method is inverted before performing the tracking control, and to perform tracking control using a suitable tracking error signal. Can be implemented.

The best mode for carrying out the present invention will be described below with reference to the drawings.
(1) Basic Configuration First, the basic configuration of the information recording / reproducing apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram conceptually showing the basic structure of the information recording / reproducing apparatus 1 in the example. The information recording / reproducing apparatus 1 has a function of recording data on the optical disc 100 and a function of reproducing data recorded on the optical disc 100.

  As shown in FIG. 1, the information recording / reproducing apparatus 1 controls a disk drive 10 on which an optical disk 100 is actually loaded and data is recorded and reproduced, and data recording and reproduction on the disk drive 10. And a host computer 20 such as a personal computer.

  The disc drive 10 includes an optical disc 100, a spindle motor 11, an optical pickup (PU) 12, a signal recording / reproducing unit 13, a tracking control unit 14, a CPU 15, a memory 16, an input / output control unit 17, and a bus 18. Has been. The host computer 20 includes an operation / display control unit, an operation button, a display panel, a CPU, a memory, an input / output control unit, a bus, and the like (not shown).

  The spindle motor 11 rotates and stops the optical disc 100 and operates when accessing the optical disc 100. More specifically, the spindle motor 11 is configured to rotate and stop the optical disc 100 at a predetermined speed while receiving spindle servo from a servo unit or the like (not shown).

  The optical pickup 12 includes, for example, a laser diode (LD) 121, a photo detector (PD) 122, and a collimator lens and an objective lens (not shown) in order to perform recording and reproduction on the optical disc 100. Is done. More specifically, at the time of data recording, the laser diode 121 irradiates the optical disc 100 with the laser beam LB with a predetermined recording power and modulation. As a result, a data pattern corresponding to the data is formed on the recording surface of the optical disc 100. On the other hand, at the time of data reproduction, the laser diode 121 irradiates the optical disc 100 with the laser beam LB with a predetermined reproduction power. The irradiated laser beam LB is reflected on the recording surface of the optical disc 100. The reflected light is received by the photodetector 122 so that data is reproduced.

  Note that the photodetector 122 has a light receiving region in the traveling direction of the laser light LB (in other words, the rotational direction of the optical disc 100) and the direction substantially orthogonal to the traveling direction of the laser light LB (in other words, the radial direction of the optical disc 100). The four-division photodetector is divided along each of the tracking methods).

  The signal recording / reproducing unit 13 performs recording / reproduction with respect to the optical disc 100 by controlling the spindle motor 11 and the optical pickup 12 under the control of the CPU 15. More specifically, the signal recording / reproducing unit 13 includes, for example, a laser diode driver (LD driver) and a head amplifier. The laser diode driver generates a drive signal, for example, and drives the laser diode 121 provided in the optical pickup 12. The head amplifier amplifies the output signal of the photodetector 122 provided in the optical pickup 12 (that is, a signal indicating the reflected light of the laser beam and is a read signal), and outputs the amplified signal.

  The tracking control unit 14 performs tracking control of the optical pickup 12. More specifically, the tracking control unit 14 generates a tracking signal (in other words, a tracking error signal) based on the output signal of the photodetector 122. The “first generation unit” and the “second generation unit” of the present invention. Is a specific example. Further, the tracking control unit 14 outputs a tracking signal to an actuator (not shown) for realizing movement of the optical pickup 12 in the tracking direction under the control of the CPU 16 described later. As a result, an actuator (not shown) moves the optical pickup 12 along the tracking direction based on the tracking signal output from the tracking control unit 14. In this embodiment, the tracking control unit 14 generates a tracking signal using a push-pull method and a DPD (Differential Phase Detection) method. Any one of these generated tracking signals (that is, push-pull signal and DPD signal) is selected by a CPU 16 to be described later, and the selected tracking signal is output to an actuator and used for movement of the optical pickup. It is done.

  The CPU 16 is connected to the signal recording / reproducing unit 13, the tracking control unit 14, the memory 15 and the input / output control unit 17 via the bus 18, and the signal recording / reproducing unit 13, the tracking control unit 14, the memory 15 and the input / output control unit. By instructing 17, the entire disk drive 10 is controlled. Usually, software or firmware for operating the CPU 16 is stored in the memory 15.

  In addition, the CPU 16 according to the present embodiment has a function as a specific example of the “signal determination unit” in the present invention, and sets the polarities of the push-pull signal and the DPD signal output from the tracking control unit 14. Compare. Then, based on the comparison result, a tracking signal that is actually used by the tracking control unit 14 is selected and notified to the tracking control unit 14.

  The memory 15 is a buffer area for data used for recording and reproducing operations, an area used as an intermediate buffer when data is converted to data that can be used by the signal recording / reproducing unit 13, and the like. Used in. The memory 15 stores a ROM area in which a program (that is, firmware) for operating the information recording / reproducing apparatus 1 is stored, data temporarily used for recording and reproducing operations, firmware, etc. It is composed of a RAM area or the like in which variables necessary for operation are stored.

  The input / output control unit 17 controls data input / output from the outside to the disk drive 10. A drive control command issued from an external host computer 20 connected to the disk drive 10 via an interface such as SCSI or ATAPI is transmitted to the CPU 16 via the input / output control unit 17. Similarly, data used for the recording operation and the reproduction operation is exchanged with the host computer 20 via the input / output control unit 17.

  A specific example of the disk drive information recording / reproducing apparatus 1 described above is a household device such as a player device that reproduces video. This player device is a device that outputs a video signal reproduced from a disc to an external display device such as a television. In another specific example, the disk drive 10 is a disk drive that records or reproduces data under the control of a host computer 20 such as a known personal computer or workstation.

(2) Operation Example Next, a basic operation example of the information recording / reproducing apparatus 1 according to the present embodiment will be described with reference to FIGS. Here, the selection operation of the tracking signal used for recording or reproducing operation in the tracking control unit 14 by the CPU 16 will be described.

  In this embodiment, the CPU 16 compares the polarity of the push-pull signal and the DPD signal generated by the tracking control unit 14 based on the read signal output from the photodetector 122 so that the CPU 16 determines the push-pull signal and the DPD signal. Either one of the signals is selected and controlled to be used for a so-called tracking control operation in the tracking control unit 14. FIG. 2 is a flowchart schematically showing the flow of such a basic operation of the information recording / reproducing apparatus 1 according to the present embodiment. Here, the basic operation of the tracking control according to the present embodiment will be described first with reference to FIG.

  First, as shown in FIG. 2, the optical disc 100 is mounted on the disc drive 10 of the information recording / reproducing apparatus 1 (step S100), and the operation is started. Next, the optical disc 100 is rotated by the spindle motor 11, the laser diode 121 is irradiated with laser light, and the focus control signal is generated from the reflected light from the recording surface of the optical disc 100 received by the photodetector 122. After that, the focus control operation of the optical pickup 12 by an actuator (not shown) is performed (step S110). Typically, the series of operations may be performed in a manner similar to that performed by a known information recording / reproducing apparatus or a disk drive. For example, an unillustrated configuration such as an actuator is also known. It may be the composition of.

  Subsequently, a push-pull signal is generated based on the read signal by the tracking control unit 14, and the signal level of the push-pull signal is measured by the CPU 16 (step S120). At this time, when the signal level of the push-pull signal falls below a predetermined threshold (step S120: Yes), subsequently, the CPU 16 determines the polarity of the push-pull signal (step S130).

  Typically, the polarity of the push-pull signal may be reversed according to the pit depth on the recording surface of the optical disc 100. On the other hand, such inversion does not occur in the DPD signal. With reference to FIG. 3, the inversion of the polarity of the push-pull signal will be described in comparison with the DPD signal. FIG. 3 is a graph schematically showing the relationship between the polarity inversion of the push-pull signal and the DPD signal.

  Typically, the polarity of the push-pull signal (that is, the manner of positive and negative fluctuations with the track center as a boundary) varies depending on the pit depth on the recording surface of the optical disc 100. Specifically, the polarity of the push-pull signal is reversed using the wavelength λ of the recording / reproducing laser beam LB when the pit depth = λ / 4. On the other hand, the pit depth does not affect the polarity of the DPD signal.

  Therefore, for example, the push-pull signal in FIG. 3A in which the pit depth = λ / 3 and the push-pull signal in FIG. 3B in which the pit depth = λ / 6, for example, are shown in the drawing. The polarity reversal is observed. Therefore, in this embodiment, whether or not the polarity of the push-pull signal is inverted by comparing the polarity of the push-pull signal with the polarity of the DPD signal in FIG. Determine.

  Next, with reference to FIG. 4, the operation of determining the polarity of the push-pull signal according to the present embodiment (that is, the above-described step S130) will be described in detail. FIG. 4 is a flowchart schematically showing the flow of the operation.

  First, when the polarity determination operation of the push-pull signal is started, the push-pull signal amplitude is measured by the operation of the tracking control unit 14 (step S200). Based on the obtained push-pull signal amplitude and, for example, a predetermined coefficient stored in the memory 15, the CPU 16 calculates a threshold A that is a threshold of the signal level of the push-pull signal for performing polarity determination. (Step S210). Next, similarly, the amplitude of the DPD signal is measured by the operation of the tracking control unit 14 (step S220), and the CPU 16 calculates a threshold value B that is a threshold value of the signal level of the DPD signal for performing the polarity determination ( Step S230). Then, a variable i = 0, which is a counter for trying to compare the polarities of the push-pull signal and the DPD signal a predetermined number of times, and a counter pp_pd = 0 that counts the number of times that the polarities do not coincide with each other are set. (Step S240). Note that these operations are not limited to the order of the flowcharts, and may be performed in succession or simultaneously.

  Subsequently, first, the signal level of the DPD signal is measured by the operation of the tracking control unit 14 (step S250).

  Then, the CPU 16 compares the signal level of the obtained DPD signal with the threshold value B (step S260). At this time, when the signal level of the DPD signal exceeds the threshold B (step S260: Yes), it is determined that the polarity of the DPD signal is + (step S270).

  On the other hand, when the signal level of the DPD signal is equal to or lower than the threshold value B (step S260: No), it is next determined whether or not the signal level of the DPD signal is lower than the threshold value -B (step S280). Therefore, when the signal level of the DPD signal is lower than the threshold −B (step S280: Yes), it is determined that the polarity of the DPD signal is − (step S290).

  Further, when the signal level of the DPD signal is equal to or lower than the threshold value B and equal to or higher than the threshold value −B (step S260: No and step S280: No), the signal level detection operation of the DPD signal is started again (step S260). S250).

  Following the determination of the DPD signal polarity, the signal level of the push-pull signal is similarly measured by the operation of the tracking control unit 14 (step S300).

  Then, the CPU 16 compares the signal level of the obtained push-pull signal with the threshold value A (step S310). At this time, when the signal level of the push-pull signal exceeds the threshold A (step S310: Yes), it is determined that the polarity of the push-pull signal is + (step S320).

  On the other hand, when the signal level of the push-pull signal is equal to or lower than the threshold value A (step S310: No), it is next determined whether or not the signal level of the push-pull signal is lower than the threshold value -A (step S330). . Therefore, when the signal level of the push-pull signal is lower than the threshold −A (step S330: Yes), it is determined that the polarity of the push-pull signal is − (step S340).

  When the signal level of the push-pull signal is equal to or lower than the threshold value A and equal to or higher than the threshold value -A (step S310: No and step S330: No), the operation starts again from the detection of the signal level of the push-pull signal. (Step S250).

  That is, in this embodiment, the polarity of the push-pull signal and the DPD signal is determined by comparing with the threshold A and the threshold B. With reference to FIG. 5, the aspect of such comparison will be specifically described. FIG. 5 is a graph showing the relationship between the signal levels of the push-pull signal and the DPD signal used for the operation and the threshold value of the signal level for each polarity determination.

  In this embodiment, the case where the signal level exceeds a predetermined threshold value is determined as polarity +, and the case where the signal level falls below a negative value of the threshold value is determined as polarity-(see FIG. 5). On the other hand, if the absolute value of the signal level is lower than the absolute value of the threshold value (for example, in the case of a push-pull signal, the signal level is A or less, -A or more), the polarity may not be accurately determined. In view of this, the polarity determination operation of the present embodiment is controlled so as to shift to the next trial without performing the polarity determination in the current trial.

  As an example of such a threshold A and threshold B, a predetermined ratio in the amplitude of each tracking error signal may be set. As an example, the threshold A is set to 12.5% of the amplitude of the push-pull signal, and the threshold B is set to 25% of the amplitude of the DPD. However, the threshold value is not limited to such a numerical value, and may be, for example, 50% of the amplitude, one third, or another ratio or a threshold acquired by another method. Such threshold A and threshold B are set so that at least the polarities of the push-pull signal and the DPD signal described above can be accurately determined, and may be calculated as appropriate through experiments, simulations, and the like. .

  Returning to FIG. 4 again, next, the CPU 16 compares the push-pull signal polarity with the DPD signal polarity (step S350). Here, if the polarities do not match (that is, push-pull signal polarity + and DPD signal polarity-or push-pull signal polarity-and DPD signal polarity +), the counter pp_pd is added (step S360). ). Further, the trial number counter i is added (step S370).

  After such a trial is repeated a predetermined number of times (N times in this embodiment) (step S380: Yes), in this embodiment, the number of times that the push-pull signal polarity does not match the DPD signal polarity by the CPU 16 A comparison is made between (that is, the value of the counter pp_pd) and a predetermined threshold value X (step S390). As a result, when a polarity mismatch of the threshold value X times or more is detected, it is determined that the polarity of the push-pull signal is determined (in other words, a flag is set) (step S400). Note that the numerical values of N and X are set as threshold values for the number of times a mismatch in polarity within the number of trials is detected, for example, 15 mismatches in 50 trials. It may be set appropriately.

  Here, returning to FIG. 2 again, the flow of selecting the tracking error signal using the result of the comparison between the push-pull signal polarity and the DPD signal polarity will be described.

  When it is determined whether or not the polarity of the push-pull signal is inverted by a series of operations in step S160 (that is, steps S200 to S400) (step S140: Yes, ie, FIG. 4 (Step S390: Yes), the DPD signal is selected as the tracking error signal (Step S150). On the other hand, when it is determined that the polarity of the push-pull signal is not inverted (step S140: No, ie, step S390: No in FIG. 4), the push-pull signal is selected as the tracking error signal (step S160).

  Further, when the signal level of the push-pull signal measured in step S120 exceeds a predetermined threshold different from the above-described threshold A (step S120: Yes), the push-pull signal and the DPD signal described above are operated by the operation of the CPU 16. The push-pull signal is selected as a tracking error without performing the operation of determining the polarity of the push-pull signal by comparing the polarities.

  In general, when the polarity of the push-pull signal is inverted, the signal level is decreased, and thus such a decrease in the signal level is not detected (in other words, the signal level is sufficiently high). Therefore, it can be determined that polarity reversal has not occurred. Therefore, the push-pull signal polarity determination operation described above is performed by determining the signal level of the push-pull signal using a threshold value calculated so as to detect the signal level reduction based on the polarity inversion. Without implementation, at least a state in which the polarity of the push-pull signal is not inverted can be detected. An example of such a threshold value is a numerical value set from a range such as 30% to 50% of the signal level of a push-pull signal in a normal optical disc. However, as long as it is a numerical value set so that at least the state in which the polarity of the push-pull signal is not determined can be suitably detected, it may be calculated as appropriate by experiments or simulations.

  According to the operation described above, it is preferable to determine whether or not the polarity of the push-pull signal is inverted before performing the tracking control, and if the push-pull signal is inverted, the DPD signal is It is possible to perform control so that the tracking control used is performed. Even if the polarity of the push-pull signal is inverted, if the signal level is high to some extent, it is possible to perform control so as to perform tracking control using the push-pull signal whose polarity is inverted. Therefore, it is possible to suitably prevent a situation in which a tracking servo control failure or failure occurs due to the polarity of the push-pull signal used for tracking control being inverted.

  As an example, the tracking error signal selection operation described in this embodiment is preferably performed in a series of operations when the optical disc 100 is mounted on the disc drive 10, for example. Prior to the actual recording / reproducing operation, an appropriate tracking error signal used for tracking control for the optical disc 100 can be selected.

  The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification, and information recording / reproduction with such changes is possible. The apparatus and the information recording / reproducing method are also included in the technical scope of the present invention.

Claims (5)

An information recording / reproducing apparatus including an optical pickup that irradiates the information recording medium with laser light and receives reflected light of the laser light in order to perform at least one of information recording and reproduction on the information recording medium,
First signal generating means for generating a first tracking error signal by a push-pull method from a read signal based on the reflected light;
Second signal generating means for generating a second tracking error signal by a DPD (Differential Phase Detection) method from the read signal;
Signal determination for comparing the polarities of the first tracking error signal and the second tracking error signal with each other and selecting either the first tracking error signal or the second tracking error signal based on the comparison result Means,
Tracking information means for performing tracking control based on one of the selected first tracking error signal and second tracking error signal.   The signal determination unit selects the first tracking error signal when the polarities of the first tracking error signal and the second tracking error signal are equal to each other, and selects the first tracking error signal and the second tracking error signal. 2. The information recording / reproducing apparatus according to claim 1, wherein when the polarities of the tracking error signals are different from each other, the second tracking error signal is selected.   (I) the absolute value of the signal level of the first tracking error signal is greater than or equal to a predetermined first threshold value, and the absolute value of the signal level of the second tracking error signal is a predetermined second threshold value; In the case of the above, the polarities of the first tracking error signal and the second tracking error signal are compared with each other, and (ii) the absolute value of the signal level of the first tracking error signal is equal to the first threshold value. And the absolute value of the signal level of the second tracking error signal is lower than the second threshold value or one of them, the first tracking error signal and the second tracking error signal respectively. 3. The information recording / reproducing apparatus according to claim 1, wherein the polarities are not compared with each other.   The signal determining means is (i) the polarities of the first tracking error signal and the second tracking error signal when the absolute value of the signal level of the first tracking error signal is below a predetermined third threshold value. And (ii) the polarities of the first tracking error signal and the second tracking error signal when the absolute value of the signal level of the first tracking error signal is greater than or equal to the third threshold value. The information recording / reproducing apparatus according to any one of claims 1 to 3, wherein the first tracking error signal is selected without comparing each other. Information recording / reproducing method in an information recording / reproducing apparatus comprising an optical pickup for irradiating the information recording medium with laser light and receiving reflected light of the laser light to perform at least one of recording and reproducing information on the information recording medium Because
A first signal generation step of generating a first tracking error signal by a push-pull method from a read signal based on the reflected light;
A second signal generation step of generating a second tracking error signal by a DPD (Differential Phase Detection) method from the read signal;
Signal determination for comparing the polarities of the first tracking error signal and the second tracking error signal with each other and selecting either the first tracking error signal or the second tracking error signal based on the comparison result Process,
And a tracking control step for performing tracking control based on one of the selected first tracking error signal and second tracking error signal.

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