JP2005071545A - Optical disk drive and tracking balance adjustment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust tracking balance by using a simple configuration. <P>SOLUTION: A tracking error signal generation means employs a phase difference method to generate a tracking error signal which corresponds to tracking shifting on the basis of a reproduced signal from a disk. Since the phase difference method is employed, the tracking error signal is not affected by the amplitude fluctuation of the reproduced signal. A tracking balance control means controls the DC component of the tracking error signal to control tracking balance. The DC component control can be realized with simple circuitry, and hence a device size can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical disc apparatus that adjusts tracking balance so that a light beam appropriately follows a track on an optical disc. The present invention also relates to a tracking balance adjustment method for adjusting a tracking balance in order to appropriately follow a light beam to a track on an optical disk.

  In recent years, an optical disk has been adopted as a storage medium having a large capacity and excellent random access. An optical disk recording / reproducing apparatus employs a pickup that irradiates a rotating disk with laser light. The pickup collects the laser light and irradiates the disc surface with a focused spot to record information, and also converts the reflected light from the disc into an electric signal for reproduction.

  A track having pits arranged in a spiral shape or concentric circles is formed on the disk surface, and the pickup irradiates a focused spot along the track. However, due to the eccentricity of the center hole of the optical disk, the eccentricity of the track, the axial deflection of the rotating shaft of the turntable, etc., the focal spot position due to the laser beam emitted from the pickup is eccentric. Therefore, an error signal for tracking servo is detected, and tracking control is performed so that the focused spot accurately traces the track by control based on the error signal.

  As a method for detecting a tracking error signal, there are a push-pull method, a three-beam method, a phase difference method (DPD (Differential Phase Ditection)), and the like. The tracking error signal acquired by these methods is given to the actuator. The tracking error signal is a signal that changes above or below a reference potential with a polarity corresponding to the tracking deviation direction. The actuator changes the focus spot position of the laser beam in accordance with the polarity of the tracking error signal, thereby turning the focus spot on-track.

  By the way, the tracking error signal fluctuates up and down with respect to a reference potential with time due to wobble or the like of the track. It is desirable to use a tracking error signal whose amplitude on the positive and negative side is symmetrical with respect to the reference potential. However, the tracking error signal detected due to the distortion of the condensing spot shape, the distortion of the track shape, etc. becomes an asymmetric waveform with respect to the reference potential, and the amplitude on the positive side and the amplitude on the negative side Ratio (tracking balance) may not be appropriate.

  Due to the recent demand for high-density optical disks, the track linear density is increasing and the track pitch is decreasing. As the density of such optical discs increases, the tracking balance shift greatly affects recording and reproduction. If the tracking balance is not appropriate, the recording / reproducing accuracy may decrease.

Therefore, various techniques for adjusting the tracking balance have been proposed. For example, Patent Document 1 discloses a technique for monitoring a tracking error signal and readjusting the tracking balance as necessary.
JP2000-99964

  However, sufficient recording / reproducing accuracy cannot be obtained only by adjusting the tracking balance by the technique disclosed in Patent Document 1. In particular, as the density of the disk increases, the effect of tracking balance deviation increases, which makes it difficult to improve the recording / reproducing accuracy.

  The present invention has been made in view of such problems, and an object thereof is to provide an optical disc apparatus and a tracking balance adjustment method capable of performing tracking balance adjustment that improves recording and reproduction accuracy.

  An optical disc apparatus according to the present invention includes tracking error signal generating means for generating a tracking error signal corresponding to a tracking deviation by a phase difference method based on a reproduction signal from a disc, and tracking by controlling a direct current component of the tracking error signal. Tracking balance control means for controlling the balance is provided.

  In the present invention, the tracking error signal generating means employs a phase difference method to generate a tracking error signal corresponding to the tracking deviation based on the reproduction signal from the disk. Since the phase difference method is adopted, the tracking error signal is not affected by the amplitude variation of the reproduction signal. The tracking balance control means controls the tracking balance with a simple configuration that controls the DC component of the tracking error signal.

  According to the present invention, it is possible to perform tracking balance adjustment that improves recording and reproduction accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an optical disc apparatus according to an embodiment of the present invention.

  In the present embodiment, high-precision tracking is enabled by performing tracking balance adjustment according to the operation mode of the optical disc apparatus. Specifically, the tracking balance adjustment is different between the jump mode in which the optical pickup is moved in the radial direction of the disc and the focused spot is moved (seeked) to the target track, and the following mode in which normal recording / playback is performed. To do.

  Furthermore, in this embodiment, in order to simplify the circuit configuration for tracking balance adjustment, tracking error signal detection by the phase difference method (DPD) is employed, and tracking balance adjustment is performed by adjusting the DC component. Adjustments are made.

  As described above, tracking error signal detection methods include the DPP method, the three-beam method, the push-pull method, and the like in addition to the DPD method. In any of these DPP method, three-beam method, and push-pull method, the amplitude of the tracking error signal changes according to the amplitude of the reproduction signal. The amplitude of the reproduction signal changes for each position in the disk surface in accordance with a change in reflectance due to a scratch on the disk surface, a fingerprint, or the like. At a position where the reflectivity of the disk is high, the level of the reproduction signal becomes high and the amplitude of the tracking error signal also becomes large. On the other hand, the amplitude of the tracking error signal is relatively small at a position where the reflectance of the disk is low. In the DC component adjustment performed on the tracking error signal having a relatively large amplitude, the adjustment level is relatively large. Therefore, assuming that the adjustment level is constant, the amplitude of the tracking error signal at a position where the reflectance is low may be relatively small with respect to the adjustment level, and the tracking servo pull-in range may be exceeded. Is also possible.

  On the other hand, in the DPD method, the amplitude of the tracking error signal is not affected by the amplitude of the reproduction signal. For this reason, in the present embodiment, the DPD method is adopted as a tracking error signal detection method. In the DPD method, there has conventionally been a technique for adjusting the tracking balance by changing the delay amount of two detected phase difference signals. However, this method requires the use of two delay elements, and has the disadvantage that the circuit scale increases.

  1 records information on an optical disk D such as a CD-R, CD-RW, DVD-R, DVD-RW, or DVD-RAM, and reproduces data recorded on the optical disk D, for example. Be able to.

  In FIG. 1, the optical disk apparatus includes an optical pickup 10, a modulation circuit 21, a recording / reproduction control unit 22, a laser control circuit 23, a signal processing circuit 24, a demodulation circuit 25, an actuator 26, a focus tracking control unit 30, a controller 41, and a memory 43. , A jitter detection circuit 44 and an error detection circuit 45. As will be described later, the jitter detection circuit 44 and the error detection circuit 45 can be omitted.

  The disk D is an optical disk that is rotatably supported by a disk motor (not shown). The rotation speed of the disk D is controlled based on a signal included in reproduction data from a demodulation circuit 25 described later.

  The optical pickup 10 emits a laser beam at a position facing the disk D, irradiates a focused spot on the recording surface of the disk D, and photoelectrically converts reflected light from the recording surface of the disk D. That is, the laser 11 of the optical pickup 10 is controlled by the laser control circuit 23 to irradiate the light beam. The collimating lens 12 converts the light beam from the laser 11 into parallel light and emits it to a polarizing beam splitter (hereinafter referred to as PBS) 13. The PBS 13 separates the incident light from the collimating lens 12 and the reflected light from the disk D. The incident light from the collimating lens 12 is transmitted as it is and emitted to the quarter-wave plate 14, and from the disk D. The reflected light is reflected and guided to the condenser lens 16.

  The quarter-wave plate 14 converts linearly polarized light and circularly polarized light, converts the linearly polarized light from the PBS 13 into circularly polarized light, and outputs the circularly polarized light to the objective lens 15. The objective lens 15 irradiates the disc D with the light emitted from the quarter-wave plate 14 as a focused spot having a predetermined diameter, and guides the reflected light from the disc D to the quarter-wave plate 14. The quarter-wave plate 14 receives reflected light from the disk D via the objective lens 15, converts circularly polarized light into linearly polarized light, and emits the light to the PBS 13.

  The objective lens 15 is moved by an actuator 26, which will be described later, so that the focused spot can be moved in the focusing direction (direction perpendicular to the disk surface) and the tracking direction (radial direction). . Further, the optical pickup 10 can be moved in the radial direction of the disk D by a coarse motion motor (not shown), and the focused spot can be moved (seek) to the target track.

  The condenser lens 16 collects the reflected light from the PBS 13 and guides it to the photodetector 17. The photodetector 17 is a four-divided light receiving element that receives the reflected light from the disk D. That is, the light detector 17 has a light receiving surface that is divided into four parts in the vertical and horizontal directions, and outputs four electric signals corresponding to the incident light of the divided light receiving parts 17a to 17d. FIG. 2 is an explanatory diagram showing the relationship between the reflected light from the disk D and the four output signals from the four-divided light receiving element.

  FIG. 2 shows the recording surface of the disk D. FIG. 2 shows three tracks formed on the recording surface, and pits shown by oblique lines are formed on each track. The circular area indicates the irradiation area of the focused spot, and the reflected light of this irradiation area enters the light receiving surface of the photodetector 17. Reflected light of the four portions A to D in the irradiation region of FIG. 2 is incident on the four divided light receiving portions 17 a to 17 d of the photodetector 17. Outputs of the divided light receiving units 17 a to 17 d are output to the focus tracking control unit 30.

  The focus tracking control unit 30 includes a focus error signal generation circuit 31, a focus control circuit 32, a tracking error signal generation circuit 33, a tracking control circuit 34, and a balance control circuit 42. The focus tracking control unit 30 receives a recording / playback instruction from a host (not shown) via the controller 41, and achieves a focus servo and tracking servo function.

  In other words, the focus error signal generation circuit 31 generates a focus error signal for focus servo using the output from the photodetector 17 and outputs the focus error signal to the focus control circuit 32. The focus control circuit 32 drives the actuator 26 so that the focus error signal becomes zero.

  On the other hand, the tracking error signal generation circuit 33 uses the output from the photodetector 17 to generate a tracking error signal for tracking servo. This tracking error signal is given to the balance control circuit 42. The balance control circuit 42 outputs a tracking error signal to the tracking control circuit 34 after adjusting the tracking balance by controlling the direct current as will be described later. The tracking control circuit 34 drives the actuator 26 so that the tracking error signal becomes zero.

  The actuator 26 is controlled by the focus control circuit 32 to move the focused spot in the focusing direction to obtain a good focus. The actuator 26 is controlled by the tracking control circuit 34 to move the focused spot in the tracking direction so as to obtain good tracking. Further, the actuator 26 is controlled by the recording / reproducing control unit 22 (not shown), and drives the optical pickup 10 so that the light beam is appropriately condensed at a target recording position.

  The signal from the photodetector 17 is also given to the signal processing circuit 24. The signal processing circuit 24 equalizes the input signal and then binarizes it. The binarized signal from the signal processing circuit 24 is output to the demodulation circuit 25. The demodulating circuit 25 performs a demodulation process corresponding to the modulation method at the time of recording on the input binarized signal and outputs reproduced data.

  The modulation circuit 21 modulates recording information (data symbols) provided from a host (not shown) into a channel bit sequence according to a predetermined modulation method. The channel bit sequence corresponding to the recording information from the modulation circuit 21 is input to the recording / reproducing control unit 22. A recording / playback instruction from the host is input to the recording / playback control unit 22 via the controller 41.

  The recording / reproducing control unit 22 is controlled by the controller 41 to supply the channel bit sequence to the laser control circuit 23. The laser control circuit 23 converts the channel bit sequence into a laser drive waveform and applies it to the laser 11 to drive the laser 11 in pulses. As a result, the laser 11 can emit a recording light beam corresponding to a desired bit sequence.

  In the present embodiment, the output of the photodetector 17 is also supplied to the jitter detection circuit 44. The output (reproduction signal) of the photodetector 17 has a frequency envelope according to the regularity of the pits. The jitter detection circuit 44 detects, for example, jitter generated in the reproduction signal from the deviation of the frequency envelope of the reproduction signal from the photodetector 17 and outputs it to the controller 41. The output of the demodulation circuit 25 is given to the error detection circuit 45. The error detection circuit 45 detects an error included in the reproduction data and outputs a detection result to the controller 41.

  The controller 41 calculates an optimum tracking balance value by using at least one information of the jitter detection result from the jitter detection circuit 44 and the error detection result of the error detection circuit 45. The controller 41 gives the calculated tracking balance value to the memory 43 for storage, and generates a DC offset control signal for controlling the balance control circuit 42 using the tracking balance value read from the memory 43. Yes.

  For example, the controller 41 controls the tracking control circuit 34 to turn off tracking. Then, the controller 41 detects the peak and bottom values of the output of the tracking error signal generation circuit 33 at the time of tracking off. The controller 41 calculates a reference potential to be set based on the detected potential between the peak and the bottom and the tracking balance value to be set. This potential is supplied to the balance control circuit 42 as a DC offset control signal.

  Note that the jitter generated in the reproduction signal and the error rate of the reproduction data have a close relationship, and the controller 41 performs tracking balance control that minimizes the generation of jitter, thereby minimizing the error rate. Can be considered.

  For example, the controller 41 calculates the tracking balance value based on the detection result of jitter or the like and stores it in the memory 43 when the disk D is inserted or when the power of the apparatus is turned on. The controller 41 may calculate a tracking balance value at an arbitrary timing using jitter detected at an arbitrary timing and store the tracking balance value in the memory 43.

  Note that the jitter corresponds to the environment such as the optical pickup, circuit system, disk, and device temperature. Therefore, jitter can be predicted to some extent at the time of factory shipment. Therefore, the memory 43 may be constituted by a ROM, and the tracking balance value calculated according to the predicted jitter may be stored in the memory 43 at the factory shipment stage. In this case, the jitter detection circuit 44 and the error detection circuit 45 can be omitted.

  FIG. 3 is a block diagram showing a part of the tracking servo system of FIG. FIG. 3 shows the detection of the tracking error signal by the DPD method.

  The outputs of the divided light receiving portions 17a and 17c of the photodetector 17 are given to the amplifier 51, and the outputs of the divided light receiving portions 17b and 17d are given to the amplifier 52. The amplifiers 51 and 52 amplify the input signal. The output terminal of the amplifier 51 is given to the comparator 55 through a high-pass filter 53 composed of a capacitor and a resistor. The output terminal of the amplifier 52 is given to a comparator 56 through a high-pass filter 54 composed of a capacitor and a resistor.

  The sum signal of the divided light receiving portions 17 a and 17 c is amplified by the amplifier 51, and only the modulation component is extracted by the high pass filter 53. The sum signal of the divided light receiving portions 17b and 17d is amplified by the amplifier 52, and only the modulation component is taken out by the high pass filter 54. The comparators 55 and 56 binarize the sum signal of the divided light receiving units 17a and 17c and the sum signal of the divided light receiving units 17b and 17d, respectively, and apply the binarized signal to the phase comparator 57 as a phase difference signal.

  Now, assuming that the focused spot moves in the direction of the arrow in FIG. 2, the reflected light from the pits is incident on the divided light receiving portions 17a and 17b first, and the reflected light from the pits is not incident last. It is the part 17c, 17d side. Thus, two phase difference signals that rise, for example, based on signals from the divided light receiving units 17a, 17b and fall, for example, based on signals from the divided light receiving units 17c, 17d, are input to the phase comparator 57.

  In this case, if the focused spot deviates from the track, the rising timings of the two phase difference signals (binarized signals) based on the signals from the divided light receiving portions 17a and 17b are shifted, and the light from the divided light receiving portions 17c and 17d is lost. The fall timings of the two phase difference signals based on the signals are shifted. The phase comparator 57 generates a pulse signal generated by the difference between the rising timing and the falling timing. The pulse signal from the phase comparator 57 is given to the D / A converter 58. The D / A converter 58 converts the pulse signal from the phase comparator 57 into an analog signal and outputs it as a tracking error signal.

  FIG. 4 is a waveform diagram showing a tracking error signal from the D / A converter 58. The tracking error signal has a predetermined amplitude on each of the positive polarity side and the negative polarity side with respect to a reference voltage. The tracking balance value is (peak voltage of tracking error signal−reference voltage) / (reference voltage−bottom voltage of tracking error signal). It is assumed that the electrical offset received from each circuit in the signal output from the photodetector 17 has been canceled.

  In the present embodiment, the tracking error signal from the phase comparator 57 is supplied to the comparator 60 of the balance control circuit 42. The balance control circuit 42 includes a comparator 60 and a D / A converter 61. The D / A converter 61 is supplied with a DC offset control signal from the controller 41. The D / A converter 61 converts the digital DC offset control signal into an analog signal and supplies it to the comparator 60. The comparator 60 adjusts the direct current component of the tracking error signal by obtaining the difference between the tracking error signal from the phase comparator 57 and the DC offset control signal. For example, as shown in FIG. 4, the DC component of the tracking error signal is changed from a solid line to a broken line based on the DC offset control signal. The broken line in FIG. 4 indicates the direct current component when the tracking balance value is 1. The tracking error signal whose DC offset has been adjusted is given to the tracking control circuit 34.

  Next, the operation of the embodiment configured as described above will be described.

  First, recording of information on the optical disc D will be described. The modulation circuit 21 modulates recording information (data symbol) provided from the host into a channel bit sequence according to a predetermined modulation method. The channel bit sequence corresponding to the recording information is input to the recording / playback control unit 22. Further, a recording / reproducing instruction (in this case, a recording instruction) from the host is input to the recording / reproducing control unit 22. The recording / reproducing control unit 22 outputs a control signal to the actuator 26 and drives the optical pickup so that the light beam is appropriately focused at the target recording position. Further, the recording / reproducing control unit 22 supplies the channel bit sequence to the laser control circuit 23. The laser control circuit 23 converts the channel bit series into a laser driving waveform and drives the laser 11. That is, the laser control circuit 23 drives the laser 11 in pulses. Accordingly, the laser 11 emits a recording light beam corresponding to a desired bit sequence. The recording light beam emitted from the laser 11 is converted into parallel light by the collimating lens 12, enters the PBS 13, and is transmitted therethrough. The beam that has passed through the PBS 13 passes through the quarter-wave plate 14 and is focused on the information recording surface of the optical disc D by the objective lens 15. The focused light beam for recording is maintained in a state where the best minute spot can be obtained on the recording surface by the focus control by the focus control circuit 32 and the actuator 26 and the tracking control by the tracking control circuit 34 and the actuator 26. Is done. The tracking control method will be described later.

  Next, reproduction of data from the optical disc D by the optical disc apparatus will be described.

  A recording / reproduction instruction (in this case, a reproduction instruction) is input from the host to the recording / reproduction control unit 22. The recording / reproduction control unit 22 outputs a reproduction control signal to the laser control circuit 23 in accordance with a reproduction instruction from the host. The laser control circuit 23 drives the laser 11 based on the reproduction control signal. Accordingly, the laser 11 irradiates a reproduction light beam. The reproduction light beam emitted from the laser 11 is converted into parallel light by the collimator lens 12 and is incident on the PBS 13 and transmitted therethrough. The light beam that has passed through the PBS 13 passes through the quarter-wave plate 14 and is focused on the information recording surface of the optical disc D by the objective lens 15. The condensed light beam for reproduction is maintained in a state where the best minute spot can be obtained on the recording surface by the focus control by the focus control circuit 32 and the actuator 26 and the tracking control by the tracking control circuit 34 and the actuator 26. The The details of the tracking control will be described later in detail. At this time, the reproducing light beam irradiated on the optical disk D is reflected by the reflective film or the reflective recording film in the information recording surface. The reflected light passes through the objective lens 15 in the reverse direction and becomes parallel light again. The reflected light passes through the quarter-wave plate 14, has a polarization perpendicular to the incident light, and is reflected by the PBS 13. The beam reflected by the PBS 13 becomes convergent light by the condenser lens 16 and enters the photodetector 17. Light incident on the photodetector 17 is photoelectrically converted into an electric signal and amplified. The amplified signal is equalized and binarized by the signal processing circuit 24 and sent to the demodulation circuit 25. The demodulation circuit 25 performs a demodulation operation corresponding to a predetermined modulation method and outputs reproduction data.

  Further, a focus error signal is generated by the focus error signal generation circuit 31 based on a part of the electric signal output from the photodetector 17. Similarly, the tracking error signal generation circuit 33 generates a tracking error signal based on a part of the electrical signal output from the photodetector 17. The focus control circuit 32 controls the actuator 26 based on the focus error signal to control the focus of the beam spot. The tracking control circuit 34 controls the actuator 26 based on the tracking error signal and controls tracking of the beam spot.

  In the conventional method, electrical correction is performed on the signal output from the photodetector so that the tracking balance value becomes 1 with emphasis on the symmetry of the tracking balance. This is for improving the stability of the tracking servo. However, since such correction is an adjustment method limited to servo performance, it is not always a means to improve the quality of reproduction / recording.

  Here, the cause of the tracking balance deviation is considered. The tracking balance deviation includes the following factors.

・ Factor 1: Photosensor sensitivity balance shift ・ Factor 2: Optical offset due to lens shift, etc. ・ Factor 3: Focus spot quality In the case of factor 1, if the ball pattern on the photodetector 17 is uniform, Originally, the sum signal of the signals detected by the divided light receiving units 17a and 17c and the sum signal of the signals detected by the divided light receiving units 17b and 17d should be the same signal. However, even if the ball pattern on the photodetector 17 is uniform, the sum signal of the signals detected by the divided light receiving portions 17a and 17c due to the difference in sensitivity (sensitivity error) between the divided light receiving portions 17a to 17d. And the sum signal of the signals detected by the divided light receiving portions 17b and 17d may not be the same signal. In such an example, even if the tracking balance is deviated, the objective lens actually traces the track correctly, so that the conventional electrical correction is effective.

  In the case of factor 2, the focused spot itself imaged on the disk cannot correctly trace the track due to a lens shift or the like. In such a case, the track cannot be correctly traced only by electrically correcting the tracking error signal. A bias must be applied to the tracking actuator and the objective lens 15 must be moved to the correct position before monitoring the tracking error signal.

  Factor 1 and factor 2 described above are the ideal spots where there is no aberration in the focused spot. However, there are actually focused spots that are not ideal. Factor 3 assumes such a case. When there is aberration in the optical system, the spot shape is not stable, so the ball patterns formed on the photodetector 17 are various. It is difficult to find an ideal servo point for tracking based on the tracking error signal obtained thereby. Further, even if all of them are ideal condensing spots, it is extremely difficult to isolate the cause of tracking balance deviation under the current situation where there is no means for knowing the absolute position of the objective lens 15. For this reason, a new index is required to replace the conventional method in which adjustment is performed only with the servo error signal.

  Therefore, in the present embodiment, the tracking balance adjustment method is changed according to the mode. That is, in the jump mode, the tracking balance is adjusted so that the tracking error signal is symmetric with respect to the reference voltage, that is, the tracking balance value is 1. In the following mode, the tracking balance is adjusted so that the jitter of the reproduction signal and the error of the reproduction data are minimized.

  FIG. 5 is a graph showing the relationship between the tracking balance value and the jitter amount or error rate, with the tracking balance value on the horizontal axis and the jitter amount of the reproduced signal or the error rate of the reproduced data on the vertical axis. FIG. 6 is a flowchart showing a tracking balance adjustment method.

  Assume that the device is turned on. When the recorded disk D is inserted (step S1), the controller 41 first obtains tracking balance values to be set in the jump mode and the following mode. That is, the controller 41 gives a reproduction instruction to the recording / reproduction control unit 22 in step S2.

  A signal from the photodetector 17 is given to the tracking error signal generation circuit 33. It is assumed that the focused spot from the optical pickup 10 is just focused on the disk D by the action of the focus servo. The tracking error signal generation circuit 33 generates a tracking error signal by the DPD method and gives it to the balance control circuit 42. In step S3, the controller 41 calculates a DC offset control signal for setting the tracking balance value to 1 (TB1).

  Next, the controller 41 outputs the initial value of the DC offset control signal to the balance control circuit 42 to set the DC offset of the tracking error signal as the initial value. The tracking error signal with the tracking balance adjusted to the initial value is given to the tracking control circuit 34, and the tracking control circuit 34 controls the actuator 26 based on the tracking error signal. Thereby, the objective lens 15 moves in the tracking direction, and the on-track is maintained.

  The reproduction signal from the photodetector 17 is also given to the jitter detection circuit 44. The jitter detection circuit 44 detects the jitter of the reproduction signal (step S5) and outputs the detection result to the controller 41. Further, the controller 41 changes the DC offset control signal within a predetermined range to sequentially shift the tracking balance value, and obtains a jitter detection result corresponding to each tracking balance value. When jitter is detected for the entire range in step S6, the controller 41 calculates a tracking balance value TBm that minimizes the occurrence of jitter (step S7).

  As shown in FIG. 5, the tracking balance value that minimizes the occurrence of jitter is different from TB1 in which the positive and negative polarities are symmetrical. The controller 41 stores the obtained tracking balance value in the memory 43 (step S8). Thereby, the calculation of the tracking balance value in each mode is completed.

  Thereafter, the controller 41 sets a tracking balance value in accordance with the mode (from step S9). For example, it is assumed that a target track is searched in response to a recording / playback instruction from the host. In this case, the controller 41 sets a jump mode in step S9. That is, the controller 41 generates a DC offset control signal for setting the tracking balance value to 1 and outputs it to the balance control circuit 42 (step S10). The balance control circuit 42 adjusts the DC component of the input tracking error signal to make the tracking balance symmetrical with respect to the positive polarity and the negative polarity (step S12). The tracking control circuit 34 controls the actuator 26 based on a tracking error signal having a tracking balance value of 1 to achieve on-track. In the jump mode, since the optical pickup 10 seeks at a high speed from a relatively distant position and approaches the target track, the focused spot is difficult to converge on the target track. In this case, since the tracking balance is set to symmetry, the focused spot is on-tracked to the target track in a relatively short time.

  Next, when the following mode is entered during normal recording / reproduction (step S9), the controller 41 reads the tracking balance value held in the memory 43 in step S11, and performs DC offset control for obtaining this tracking balance value. Generate a signal. The balance control circuit 42 controls the direct current component of the tracking error signal based on the DC offset control signal from the controller 41 (step S12). As a result, the tracking error signal becomes a tracking balance value held in the memory 43 by changing the DC component. Tracking servo is applied using this tracking error signal. As a result, the reproduced signal from the optical pickup 10 has the smallest jitter.

  As described above, in this embodiment, the tracking balance of the tracking error signal detected by the DPD method is controlled by adjusting the DC component of the tracking error signal, and effective tracking control is possible with a simple configuration. is there.

  In the above embodiment, the DC offset control signal is generated so as to minimize the jitter in the following mode, but the DC offset control signal is generated so that the error occurring in the reproduction data is minimized. Also good.

  In this embodiment, the DC offset control signal from the controller is converted into an analog signal by the D / A converter 61 and applied to the comparator 60 to control the DC component of the tracking error signal. Various methods can be adopted as a method for controlling the DC component of the error signal.

  In addition, this invention is not limited to the said embodiment, In the implementation stage, it can change variously in the range which does not deviate from the summary. The above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and is described in the column of the effect of the invention. When an effect is obtained, a configuration in which this configuration requirement is deleted can be extracted as an invention.

  As described above, the optical disk device and the tracking balance adjustment method according to the present invention are useful for a disk device capable of recording and reproduction, and are suitable for tracking control of a DVD standard optical disk device, for example.

1 is a block diagram showing a schematic configuration of an optical disc apparatus according to an embodiment of the present invention. FIG. 3 is an explanatory diagram showing a relationship between reflected light from a disk D and four output signals from a four-divided light receiving element. The block diagram which shows the tracking servo system of FIG. The wave form diagram which shows the tracking error signal from a D / A converter. The graph which shows the relationship between a tracking balance value and a jitter amount or an error rate. The flowchart which shows the adjustment method of tracking balance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical pick-up, 11 ... Laser, 12 ... Collimating lens, 13 ... Polarizing beam splitter (PBS), 14 ... Quarter wavelength plate, 15 ... Objective lens, 16 ... Condensing lens, 17 ... Photodetector, 21 DESCRIPTION OF SYMBOLS ... Modulation circuit, 22 ... Recording / reproduction control part, 23 ... Laser control circuit, 24 ... Signal processing circuit, 25 ... Demodulation circuit, 26 ... Actuator, 30 ... Focus tracking control part, 31 ... Focus error signal generation circuit, 32 ... Focus Control circuit 33 ... Tracking error signal generation circuit 34 ... Tracking control circuit 41 ... Controller 42 ... Balance control circuit 43 ... Memory 44 ... Jitter detection circuit 45 ... Error detection circuit
Agent Patent Attorney Susumu Ito

Claims (8)

Tracking error signal generating means for generating a tracking error signal according to a tracking error based on a reproduction signal from a disc by a phase difference method;
An optical disc apparatus comprising tracking balance control means for controlling a tracking balance by controlling a direct current component of the tracking error signal. And a controller for controlling the tracking balance control means to set the tracking balance value to 1 in the jump mode and to set the tracking balance value to the lowest error rate for the reproduction signal in the following mode. An optical disc device characterized. The optical disc apparatus, wherein the controller detects jitter of the reproduction signal, and sets the tracking balance value that minimizes the detected jitter in the following mode. 2. The optical disc apparatus according to claim 1, further comprising storage means for storing information for controlling the tracking balance control means in the following mode. 5. The optical disc apparatus according to claim 4, wherein the storage means is preset with information for controlling the tracking balance control means in the following mode. 5. The optical disk apparatus according to claim 4, wherein the controller obtains information for controlling the tracking balance control means in the following mode when power is turned on or when the disk is inserted, and stores the information in the storage means. A procedure for generating a tracking error signal according to a tracking deviation based on a reproduction signal from a disc by a phase difference method
And a tracking balance adjustment method comprising: controlling a tracking balance by controlling a direct current component of the tracking error signal. A light detecting means for photoelectrically converting the reflected light from the disk by a light receiving element divided into four;
A phase shift of a signal from each light receiving element of the light detection means is detected to generate two phase difference signals having a phase difference corresponding to the tracking shift, and an amplitude corresponding to the phase shift of the two phase difference signals. And tracking error signal generating means for generating a tracking error signal of polarity,
An optical disc apparatus comprising tracking balance control means for controlling a tracking balance by controlling a direct current component of the tracking error signal.

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