JP2004164828A - Optical disk drive - Google Patents

Abstract

A highly accurate tracking control is realized by generating a highly accurate tracking error (TE) signal even when the size of a mark on an optical disk is reduced.
An optical disc apparatus according to the present invention includes: an optical system that irradiates a loaded optical disc with light; and receives reflected light from the optical disc in a plurality of areas and generates a plurality of reproduction signals corresponding to the amount of light received in each area. A photodetector, a filter for receiving a plurality of reproduced signals, and outputting a plurality of processed signals in which frequency components determined according to the length of a mark among frequency components of each signal are reduced; A phase difference detector that detects a phase difference, a signal generator that generates a TE signal indicating a positional relationship between a light irradiation position on an optical disc and a track based on the phase difference, and a control signal based on the TE signal. And a control unit for generating a light, and controls a light irradiation position in a direction crossing a track on the optical disc based on the control signal.
[Selection diagram] FIG.

Description

  The present invention relates to a technique for reproducing and / or recording information on various types of information carriers such as a reproduction-only type and a recording / reproduction type. More specifically, the present invention relates to an optical disc apparatus that controls a beam spot to accurately scan a track of an optical disc when reproducing and / or recording information by irradiating a light beam such as a laser beam to the optical disc. About.

  As an information carrier on which digital information can be recorded, an optical disc such as a digital versatile disc (DVD) has attracted attention. In recent years, since the amount of digital information to be recorded has been increasing, optical disks have been required to have higher densities.

  The optical disc has one or more tracks. In the case of a read-only optical disk, information is recorded by an array of pits and spaces formed along a track. In the case of a recordable optical disk, the information is recorded by an array of recording marks and spaces formed along a track. Recorded by Here, the “pit” is a portion (a concave portion or a convex portion) displaced in a direction perpendicular to the mirror-like recording surface, and is formed in an embossed shape. A “recording mark” is a portion where a phase change or the like of a recording film locally occurs due to irradiation of a laser pulse. "Space" refers to a portion of the track where no pits or recording marks are formed. The pits and spaces have different light beam reflectivities, and the recording marks and spaces have different light beam reflectivities. Hereinafter, in this specification, pits and recording marks having different reflectivity on a track are simply referred to as “marks”.

  An optical disk device that records and / or reproduces information using an optical disk is required to have even higher reliability. The optical disk device performs tracking control for moving a beam spot along a track, thereby reading a mark.

  A tracking control using a phase difference tracking error signal detection method (hereinafter, referred to as a phase difference TE signal detection method) is known as tracking control in a conventional optical disc device. For example, in a phase difference TE signal detection method described in Patent Document 1, a reflected light from an optical disk is received by a plurality of photodetectors, and a tracking error signal is detected using a change in an intensity pattern on the photodetectors. (Hereinafter, referred to as “TE signal” in this specification). The TE signal corresponds to the amount of deviation of the beam spot from the track center (here, the mark center). The optical disk device implements tracking control based on the detected TE signal. According to the phase difference TE signal detection method, since the TE signal is detected using the temporal change of the intensity pattern instead of the intensity change of the reflected light, the detection sensitivity does not depend on the output of the light beam. Further, since the detection can be performed by one beam, there is an advantage that a light source to be used may have a low output. As described above, the phase difference TE signal detection method has various advantages, and has conventionally been used in many reproducing devices such as CD-ROM drives and DVD-ROM drives.

  Hereinafter, a conventional optical disc apparatus using the phase difference TE signal detection method will be described in detail with reference to FIG. FIG. 10 shows a configuration of a conventional optical disk device 500. Such an optical disk device 500 is described in, for example, Patent Document 2.

  The optical disk device 500 generates a TE signal as follows. First, when the light source 101 emits a linearly polarized light beam, the collimator lens 102 converts the light beam into parallel light, and the polarization beam splitter 103 reflects the light beam and directs it to the quarter-wave plate 104. When the quarter-wave plate 104 generates a circularly polarized light beam, the objective lens 105 focuses the light beam on the optical disc 20.

  When the light beam is reflected by the optical disk 20, it passes through the polarization beam splitter 103, passes through the condenser lens 107, and enters the four-divided region of the photodetector 108. When each area of the photodetector 108 outputs an electric signal corresponding to the amount of received light, the preamplifiers 109a to 109d convert the electric signal into a voltage signal. Adder 110a adds the output signals of preamplifiers 109a and 109c, and outputs addition signal A + C. Adder 110b adds the output signals of preamplifiers 109b and 109d, and outputs addition signal B + D. The binarization circuits 111a and 111b convert the added signals A + C and B + D into binary signals a1 and a2 according to a predetermined slice level. FIG. 11 shows the waveforms of the addition signals A + C, B + D and the binarized signals a1, a2.

  The binarized signals a1 and a2 are compared by the phase comparator 112 for the phase of the edge. The phase comparator 112 outputs a pulse signal having a time width corresponding to the amount of phase advance as the phase advance signal b1, and outputs a pulse signal having a time width corresponding to the amount of phase delay as the phase delay signal b2. FIG. 11 shows the waveforms of the phase advance signal b1 and the phase delay signal b2. The LPFs 113a and 113b smooth the phase advance signal b1 and the phase delay signal b2 and convert them into voltage signals having a level corresponding to the pulse width. The voltage signals output from the LPFs 113a and 113b are subtracted by the subtractor 114 to become a phase difference TE signal Δte according to the beam spot track deviation. The optical disk device 500 generates a phase difference TE signal by the above processing.

The control circuit 117 has a phase compensating circuit and a low-frequency compensating circuit composed of, for example, a digital filter by a digital signal processor (hereinafter, referred to as “DSP”). To process. As a result, the control circuit 117 generates a tracking drive signal. The drive circuit 50 amplifies the tracking drive signal and outputs the signal to the tracking actuator 115. As a result, the tracking actuator 115 changes the position of the objective lens 105 in the radial direction of the optical disc 20, and the beam spot scans on a desired track of the optical disc 20.
JP-A-10-149550 (page 5, FIG. 11) JP-A-2000-315327 (pages 9-10, FIG. 9)

  As the density of optical disks further increases in the future, accurate TE signals cannot be obtained with conventional optical disk devices, and as a result, accurate tracking control may not be possible. The reason is as follows. When the size of the mark becomes smaller than the size of the beam spot with the increase in the density of the optical disk, the amplitude of the intensity change of the reflected light when passing through the mark becomes smaller. In extreme cases, the amplitude can be as low as the noise level. Since the quality of a signal obtained based on such an amplitude is low, if the TE signal is generated based on this signal, the quality of the TE signal will also be low.

  Further, a signal having a small amplitude is more susceptible to a minute change in a slice level at the time of binarization in a binarization circuit than a signal having a large amplitude, and an error occurs in the TE signal due to the influence. . Since the binarization circuit is an electric circuit, and the electrical characteristics of elements in the circuit vary, it is difficult to match the slice level between the two binarization circuits. Therefore, there is a large possibility that the slice level slightly changes, and the possibility that an error occurs in the TE signal increases. Note that it is possible to amplify a signal having a small amplitude, but this is not appropriate because it amplifies unnecessary noise components.

  The effect of a small change in the slice level will be described with reference to FIG. FIG. 12 shows waveforms of various output signals in a case where there is no small deviation Δv in the slice level and in a case where it is present. FIG. 12A shows the waveforms of the output signals A + C and B + D of the adders 110a and 110b when the beam spot has a certain deviation from the track (when the beam spot is off-track). When there is no shift in the slice levels in the binarization circuits 111a and 111b, each slice level becomes S1, and when there is a shift by Δv, each slice level becomes S1 and S2. Since the beam spot is off-track, A + C and B + D have a certain shift in the time axis direction.

  Part (b) of FIG. 12 shows the waveforms of the output signals a1, a2, b1, and b2 when there is no shift in the slice level. From this figure, it is understood that there is a constant phase advance in the signals A + C and B + D from the phase advance signal b1. It is further understood from the phase delay signal b2 that there is no phase delay in the signals A + C and B + D.

  On the other hand, FIG. 12C shows the waveforms of the output signals a1, a2, b1, and b2 when the slice level is shifted by Δv. When comparing b1 and b2 of the part (b) with b1 and b2 of the part (c), there is a difference in the waveform due to the difference in the slice level. This difference is a detection error. The detection error is particularly large in a portion where the signal amplitude of the reproduced signals A + C and B + D when passing through the shortest mark is small, and relatively small in other portions. In a high-density optical disk, the shortest mark length is much shorter than the shortest length of a conventional mark, so that the signal amplitude obtained from the shortest mark is extremely small as shown in FIG. As a result, when reproducing a high-density optical disk, the detection error due to the small deviation Δv of the slice level increases and cannot be ignored.

  In the conventional optical disk device, a portion where the amplitudes of the reproduced signals A + C and B + D are small causes a detection error of the TE signal to be large, thereby deteriorating the quality of the TE signal.

  An object of the present invention is to generate a high-accuracy TE signal even when the size of a mark on an information carrier is reduced, and realize highly accurate tracking control.

  The optical disk device according to the present invention is loaded with an optical disk having a track on which a plurality of marks are formed. The optical disc device is an optical system that irradiates the loaded optical disc with light, a photodetector that receives reflected light from the optical disc in a plurality of areas, and generates a plurality of reproduction signals according to the amount of light received in each area, A filter for receiving the plurality of reproduced signals and outputting a plurality of processed signals in which frequency components determined according to the length of the mark among frequency components of each reproduced signal are reduced; A phase difference detection unit that detects a phase difference, a signal generation unit that generates a tracking error signal indicating a positional relationship between the light irradiation position and the track on the optical disc based on the phase difference, and the tracking error signal And a control unit for generating a control signal based on the control signal. The optical disk device controls an irradiation position of the light in a direction crossing the track on the optical disk based on the control signal.

  In a preferred embodiment, the optical system includes a light source, a lens that focuses light from the light source, and an actuator that moves a position of the lens, and drives the actuator based on the control signal. The position of the lens is controlled so that the light irradiation position coincides with the center of the track.

  In a preferred embodiment, the filter removes the frequency component.

  In a preferred embodiment, the filter removes a frequency component of a specific frequency determined based on a shortest length of the mark.

  In a preferred embodiment, the filter removes a frequency component equal to or higher than the specific frequency.

  In a preferred embodiment, the filter further removes a frequency component corresponding to a mark next to the shortest mark of the mark.

  In a preferred embodiment, the optical disc determines a frequency according to a linear velocity of the track at the irradiation position of the light and a length of the mark, and the filter determines a frequency component corresponding to the determined frequency. Reduce.

  A tracking control method according to the present invention includes the steps of irradiating an optical disc having tracks on which a plurality of marks are formed with light, receiving reflected light from the optical disc in a plurality of areas, Generating a plurality of reproduction signals; receiving the plurality of reproduction signals; and outputting a plurality of processing signals in which, of the frequency components of each reproduction signal, frequency components determined according to the length of the mark are reduced. Detecting a phase difference between the plurality of processing signals; and generating a tracking error signal indicating a positional relationship between the light irradiation position and the track on the optical disc based on the phase difference. Generating a control signal based on the tracking error signal; and controlling the light based on the control signal. Comprising a step of controlling the irradiation position of the light in a direction transverse to the tracks on the disk.

  The tracking control program according to the present invention can be executed in an optical disc apparatus loaded with an optical disc having a track on which a plurality of marks are formed, and irradiating the loaded optical disc with light, Receiving reflected light from a plurality of regions; generating a plurality of reproduction signals according to the amount of light received in each region; receiving the plurality of reproduction signals; A signal for outputting a plurality of processing signals with reduced frequency components determined according to the length of the signal, detecting a phase difference between the plurality of processing signals, and, based on the phase difference, Generating a tracking error signal indicating a positional relationship between the light irradiation position and the track; Generating a control signal based on the tracking error signal, based on said control signal, and a step of controlling the irradiation position of the light in a direction transverse to the track on the optical disc.

  A chip circuit according to the present invention includes: an optical system that irradiates an optical disk having a track on which a plurality of marks are formed with light; A light detector that generates a reproduction signal, and is mounted on an optical disc device that controls the irradiation position of the light in a direction crossing the track on the optical disc based on the control signal. A chip circuit that receives the plurality of reproduction signals, and among the frequency components of each reproduction signal, outputs a plurality of processed signals in which frequency components determined according to the length of the mark are reduced; A phase difference detection circuit that detects a phase difference between the processing signals, and a signal generation circuit that generates a tracking error signal indicating a positional relationship between the light irradiation position and the track on the optical disc based on the phase difference, A control circuit for generating the control signal based on the tracking error signal.

  According to the present invention, since the frequency component determined according to the length of the mark by the filter is reduced, for example, the large amplitude component is used by removing the influence of the small amplitude component which is a cause of the detection error. A phase difference TE signal can be generated. Therefore, even when an optical disk of high density is loaded, the optical disk device can obtain a high-quality TE signal, realize accurate tracking control, and realize highly reliable recording and reproduction.

  Hereinafter, an embodiment of an optical disk device according to the present invention will be described with reference to the accompanying drawings.

  First, before describing an embodiment of the optical disk device according to the present invention, an optical disk loaded in the optical disk device will be described. FIG. 1A shows the structure of the optical disc 20. The optical disc 20 is, for example, a rewritable, write-once, or read-only Blu-ray disc (hereinafter referred to as “BD”), and has a base material 21, a protective layer 23, and an information surface 24. The optical disc 20 has a protective layer 23, an information surface 24, and a substrate 21 laminated in this order from the side irradiated with the light beam 30. The base material 21 is a substrate having a thickness of about 1 mm and supports the information surface 24. The information surface 24 is a layer on which information is recorded. For example, in the case of a rewritable disc, a phase change film is formed, and in the case of a write-once disc, an organic dye is applied. The protective layer 23 is a transparent medium having a thickness of about 0.1 mm, and transmits the light beam 30 while protecting the information surface 24 from scratches, dirt, and the like. For reference, FIG. 1A shows a state in which the optical disc 20 is irradiated with the light beam 30.

  The optical disc 20 is provided with one or a plurality of tracks 25. The track pitch (track interval) of each track 25 is, for example, 0.32 μm. FIG. 1B shows a track 25 provided on the optical disc 20. Along each track 25, a mark 26 and a space 27 in a region between marks are provided. The optical disk device described later controls the light beam irradiation position 31 in a direction (radial direction) crossing the track 25 so that the light beam irradiation position 31 is placed on the track 25 (for example, the center of the light beam is Center line). Such control is called tracking control. By the tracking control, the optical disc device 100 can read information from a desired track position or record information at the track position.

  In the following, the length L of the mark 26 is defined along the circumferential direction along the track 25 as shown. The shortest length Lmin of the mark is uniquely determined according to the amount of data that can be recorded on the optical disc 20 and the modulation method according to various optical disc standards. For example, it is 0.16 μm for a 23.3 GB BD, Is 0.4 μm.

  FIG. 2 shows the configuration of the optical disc device 100 according to the present embodiment. The optical disk device 100 includes an optical head 35, an optical disk controller (hereinafter, referred to as “ODC”) 40, a drive circuit 50, and a disk type determination unit 60. Further, the optical disk device 100 has a disk motor (not shown) for rotating the optical disk 20, and controls the rotation speed so that the linear velocity of a track on which information is reproduced and / or recorded is adjusted. Keep constant. Although the illustrated optical disk 20 is not a component of the optical disk device 100, it is illustrated for convenience of description.

  Hereinafter, each component of the optical disc device 100 will be specifically described. The optical head 35 includes a light source 101, a collimator lens 102, a polarization beam splitter 103, a quarter-wave plate 104, an objective lens 105, a condenser lens 107, a photodetector 108, and preamplifiers 109a to 109d. Having. In this specification, the preamplifiers 109a to 109d are described as components of the optical head 35, but they may be provided outside the optical head 35.

  The light source 101 of the optical head 35 is, for example, a semiconductor laser element that generates a blue-violet laser (light beam) having a wavelength of 405 nm, and outputs a light beam to the information surface 24 of the optical disc 20. The collimator lens 102 is a lens that converts divergent light emitted from the light source 101 into parallel light. The polarization beam splitter 103 is an optical element that totally reflects linearly polarized light emitted from the light source 101 and completely transmits linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light source 101. The 波長 wavelength plate 104 is an optical element that converts the polarization of transmitted light from circularly polarized light to linearly polarized light, or from linearly polarized light to circularly polarized light. The objective lens 105 is a lens that focuses a light beam on the information surface of the optical disc 20. The condensing lens 107 is a lens that condenses the light beam transmitted through the polarization beam splitter 103 on the photodetector 108. The photodetector 108 is an element that has four divided detection areas A to D and converts received light into a current signal. The preamplifiers 109a to 109d are electric elements that convert current signals output from the four-divided detection areas A to D of the photodetector 108 into voltage signals. The tracking actuator 115 is an actuator that moves the objective lens 105 in the radial direction of the optical disc 20.

  Next, the ODC 40 will be described. The ODC 40 includes adders 110a and 110b, filters 118a and 118b, binarization circuits 111a and 111b, a phase comparator 112, low-pass filters (LPF) 113a and 113b, a subtractor 114, and a control circuit 117. Having. These are all realized as electric circuits.

  The adder 110a of the ODC 40 adds and outputs two output signals of the preamplifiers 109a and 109c. The adder 110b adds the two output signals of the preamplifiers 109b and 109d and outputs the result. The binarization circuits 111a and 111b binarize the output signals of the filters 118a and 118b and output. The phase comparator 112 compares the binarized signals output from the binarization circuits 111a and 111b, and outputs a pulse having a time width corresponding to the phase advance and phase delay of the edge. Low-pass filters (LPF) 113 a and 113 b smooth the pulse signal output from phase comparator 112. The subtractor 114 outputs a difference between the smoothed signals from the LPFs 113a and 113b. The control circuit 117 outputs a tracking control signal based on the output signal from the subtractor 114.

  The filters 118a and 118b of the ODC 40 receive the reproduction signals from the adders 110a and 110b, and reduce the frequency components of the respective reproduction signals that are determined according to the length L of the mark 26 on the optical disc 20. Output the processed signal. The frequency characteristics of the filters 118a and 118b are as shown in FIGS. 5 and 7, for example. Details will be described later.

  The drive circuit 50 outputs a tracking actuator drive signal to the tracking actuator 115 based on the tracking control signal output from the control circuit 117.

  The disc type discriminating unit 60 discriminates the type of the optical disc 20 loaded in the optical disc device 100, and outputs a discrimination signal indicating a discrimination result. The “type” includes not only the type of a disc such as a CD, a DVD, and a BD, but also a rewritable type, a write-once type, or a read-only type. The disc type discrimination unit 60 can discriminate the type of the optical disc 20 based on, for example, the amount of spherical aberration of the loaded optical disc 20.

  Note that the disk type determination unit 60 may be provided in the ODC 40. The adders 110a and 110b of the ODC 40 may be provided in the optical head 35.

  As will be described in detail below, the optical disc device 100 detects a track shift by using a track shift detecting unit including the phase difference detecting unit, the subtractor 114, and the LPF 113. The “phase difference detection unit” here includes adders 110 a and 110 b, binarization circuits 111 a and 111 b, and a phase comparator 112. The optical disc device 100 includes the track shift detecting unit, the phase difference detecting unit, the optical head 35, the filters 118a and 118, and the tracking control unit. The tracking control unit includes a tracking actuator 115, a drive circuit 50, and a control circuit 117.

  Although the optical disc device 100 according to the present embodiment detects the phase difference using the edge of the binarized signal, this is an example, and the phase difference can be detected by another method.

  Hereinafter, a tracking control process performed by the optical disc device 100 will be described with reference to FIGS. FIG. 3 shows a procedure of the tracking control process of the optical disc device 100. In step S301, the optical disk device 100 irradiates the optical disk 20 with the light beam 30 from the light source 101. Next, in step S302, the photodetector 108 receives the reflected light from the optical disc 20 in the plurality of areas A to D, and outputs a reproduction signal according to the amount of light received in each area. Thereafter, the adder 110a adds the output signals of the preamplifiers 109a and 109c and outputs a reproduced signal A + C. The adder 110b adds the output signals of the preamplifiers 109b and 109d and outputs a reproduction signal B + D. The processing up to step S302 is the same as that of the conventional optical disk apparatus 500.

  FIG. 4 shows an example of the frequency characteristics of the reproduced signal. In the figure, the horizontal axis represents frequency, and the vertical axis represents amplitude. Since various lengths are given to the marks 26 on the optical disc 20, the frequency characteristics of the reproduced signal are represented by frequencies f [0], f [1],..., F [max- 1] and f [max]. The minimum frequency f [0] corresponds to the signal frequency obtained when reproducing the mark having the maximum mark length Lmax, and the maximum frequency f [max] corresponds to the signal frequency obtained when reproducing the mark having the minimum mark length Lmin. I do. It is understood that the signal amplitude at the maximum frequency f [max] is much smaller than the signal amplitude at other frequencies.

  For example, in a 23.3 GB BD, when the linear velocity of the track 25 is 5.28 m / s, the maximum frequency f [max] for the shortest mark length of 0.16 μm is 16.5 MHz. In the present embodiment, since the optical disc 20 is rotated so that the linear velocity becomes constant, the frequency f [max] is a fixed value and can be calculated in advance. Since the linear velocity changes depending on the rotation method of the optical disk and the speed of the recording / reproducing operation (double speed, quadruple speed, etc.), the frequency (including the maximum frequency f [max]) corresponding to each mark length is the rotation speed and the mark speed. Varies based on length.

  Next, in step S303 in FIG. 3, the frequency components corresponding to the shortest length Lmin of the mark among the frequency components of the reproduced signals A + C and B + D are reduced by the filters 118a and 118b. As a result, filter output signals A1 and A2 are obtained.

  The processing in step S303 will be described more specifically with reference to FIG. FIG. 5 shows frequency characteristics of the filters 118a and 118b. The horizontal axis represents frequency, and the vertical axis represents gain. As illustrated, each of the filters 118a and 118b has a characteristic of attenuating the component of the frequency f [max]. The frequency f [max] is a frequency determined by the linear velocity of the track when the beam spot passes through the mark and the shortest length of the mark, and is the same as the frequency band f [max] of the small amplitude signal shown in FIG. It is. Since the linear velocity changes as described above, the controller of the optical disk device 100 or the ODC 40 can dynamically change the frequency characteristic (cutoff frequency f [max]) of the filter by changing the set value or the like. Specifically, if the linear velocity is v and the mark length is L, the frequency can be expressed as f = v / (2L). The filters 118a and 118b have a gain of 0 dB up to the frequency f [max-1] and pass the input signal as it is. However, the frequency characteristics of both filters are changed from the frequency f [0] to f [max]. ], And a band-pass characteristic that removes signal components at frequencies lower than the frequency f [0] and higher than the frequency f [max] may be used.

  By passing the reproduction signals A + C and B + D having the frequency characteristics shown in FIG. 4 through the filters 118a and 118b having the frequency characteristics shown in FIG. 5, the amplitude of the frequency f [max] of the reproduction signal is reduced or eliminated. As a result, signals A1 and A2 having frequency components of frequencies f [0], f [1],..., F [max-1] are obtained. In addition, as shown in FIG. 6, together with the frequency component of the frequency f [max], filters 118a and 118b having frequency characteristics as shown in FIG. 7 are used to filter other frequency components (f [max-1] in the figure). Frequency component). Note that the frequency f [max-1] means a frequency corresponding to a mark that is shortest next to the shortest length of the mark. Removing the frequency f [max] and other frequency components is effective when the amplitude of each frequency component is as small as the noise level.

  FIG. 8 shows waveforms of various signals obtained in the optical disc device 100. When the waveforms of the addition signals A + C and B + D are compared with the waveforms of the filter output signals A1 and A2, the signal waveform (the component of the frequency f [max]) caused by the shortest mark is substantially removed.

  Next, in step S304 in FIG. 3, the phase difference between the filter output signals A1 and A2 is obtained, and a TE signal indicating the positional relationship between the irradiation position of the light beam and the track is generated. This will be described more specifically with reference to FIG. First, the binarization circuits 111a and 111b convert the filter output signals A1 and A2 into binarized signals B1 and B2 according to the "slice level" shown in the graph of the filter output signals A1 and A2. That is, the binarization circuits 111a and 111b respectively generate high-level voltage signals B1 and B2 when the filter output signals A1 and A2 are higher than the slice level and low-level voltages when the filter output signals A1 and A2 are lower than the slice level.

  Subsequently, the phase comparator 112 compares the phases of the edges of the binary signals B1 and B2, outputs a pulse signal having a time width corresponding to the amount of phase advance as the phase advance signal C1, and corresponds to the amount of phase delay. A pulse signal having a time width is output as a phase delay signal C2. These correspond to determining the phase difference between the filter output signals A1 and A2, respectively. FIG. 8 shows a phase lead signal C1 and a phase delay signal C2 where the pulse amplitude is Vpc. Thereafter, the LPFs 113a and 113b respectively smooth the phase advance signal C1 and the phase delay signal C2 and convert them into voltage signals having a level corresponding to the pulse width. When the subtractor 114 subtracts these voltage signals, a phase difference TE signal ΔTE corresponding to the beam spot track deviation is output. Even if the signal obtained from the shortest mark is of the order of the noise level, its signal component is removed, so that the quality of the obtained phase difference TE signal is lower than the quality of the phase difference TE signal obtained in the conventional optical disc apparatus 500. Get higher.

  Next, in step S305 in FIG. 3, the control circuit 117 executes a filter operation for performing phase compensation and low-frequency compensation on the phase difference TE signal, and performs control via a built-in DA converter (not shown). Output a signal. In step S <b> 306, the drive circuit 50 amplifies the control signal with a current and passes a current to the tracking actuator 115. Thus, in step S307, the irradiation position of the light moves in the radial direction of the optical disc 20 by moving the objective lens 105 in the radial direction, and the center of the beam spot can be made to coincide with the center of the track.

  Through the above processing, the optical disc device 100 can obtain a high-quality phase difference TE signal and perform tracking control based on the signal.

  Further, according to the above-described processing, even when the slice level slightly changes during binarization in the binarization circuits 111a and 111b, the influence on the phase difference TE signal can be reduced.

  FIG. 9 shows waveforms of various output signals when there is no minute deviation Δv in the slice level and when there is a case. FIG. 9A shows the waveforms of the output signals A + C and B + D of the adders 110a and 110b when the beam spot has a certain deviation from the track (when the beam spot is off-track). On the other hand, FIG. 9B shows the waveforms of the output signals A1 and A2 of the filters 118a and 118b. As is apparent from this waveform, it is understood that the frequency components caused by the shortest mark are attenuated by the filters 118a and 118b. When there is no shift in the slice levels in the binarization circuits 111a and 111b, each slice level becomes S1, and when there is a shift (shift amount: Δv), each slice level becomes S1 and S2.

  On the other hand, part (c) of FIG. 9 shows the waveforms of the output signals B1, B2, C1, and C2 when there is no shift in the slice level, and part (d) shows the output signal when the slice level is shifted by Δv. The waveforms of B1, B2, C1, and C2 are shown. Comparing the C1 and C2 of the (c) portion with the C1 and C2 of the (d) portion, respectively, there is a difference in the waveform of the phase lead signal C1 due to the slight shift Δv of the slice level. Is very small. Further, there is no difference regarding the phase delay signal C2. This is sufficiently smaller than the difference between the waveforms b1 and b2 in the portion (b) of FIG. 12 and the waveforms b1 and b2 in the portion (c) of FIG. 12 related to the conventional optical disk device 500 (FIG. 10).

  From the above, it can be said that by detecting the phase difference using only the portion where the signal amplitudes of the signals A + C and B + D are large, the detection error caused by the small deviation Δv of the slice level can be extremely reduced. Therefore, in the optical disc device 100, the detection error of the TE signal due to the change in the slice level can be suppressed low.

  Each operation of the optical disk device 100 described above is performed based on one or more computer programs. A part of the computer program is usually stored in a memory (not shown) built in the optical disc device or a microcomputer memory (not shown). Such a computer program is executed by a central processing unit (not shown) that controls the operation of the entire optical disc device.

  The ODC 40 can be configured by one or more semiconductor chip circuits. In such a configuration, each component included in the ODC 40 can be regarded as an individual function of the semiconductor chip circuit. The above-mentioned computer program is recorded in a storage area of the semiconductor chip circuit, and a microcomputer (not shown) in the ODC 40 executes processing based on the computer program. After performing the tracking control described above, the ODC 40 also has a reproducing function of reading information recorded on the information surface and performing processing such as error correction and decoding.

  The above-described computer program can be recorded on a recording medium such as an optical recording medium represented by an optical disk, an SD memory card, a semiconductor recording medium represented by an EEPROM, and a magnetic recording medium represented by a flexible disk. The optical disk device 100 can acquire a computer program not only through a recording medium but also through an electric communication line such as the Internet.

  In the present embodiment, the optical disc 20 is described as a BD, but the same effect can be obtained by performing the same processing on a DVD. In recent years, DVD drives have been rotated at higher speeds, and high-accuracy tracking control has been required. Accordingly, the processing according to the present invention is useful. When both types of media, BD and DVD, can be loaded into the optical disc apparatus 100, the disc type discrimination unit 60 shown in FIG. 2 determines the type of the loaded optical disc, and according to the type, filters 118a and 118b. May be switched. For example, a frequency characteristic for BD for attenuating the frequency f [max] and a frequency characteristic for DVD for outputting without reducing all frequencies are provided in advance, and based on the discrimination signal output by the disc type discrimination unit 60. Thus, the frequency characteristics for BD and the frequency characteristics for DVD may be switched. When the frequency characteristics for DVD are used, the signal passed through the filter may be amplified by an equalizer (not shown).

  In the present embodiment, an example in which the output signal of the preamplifier 109 is processed using an analog circuit has been described, but the same effect can be obtained by using a digital circuit. When a digital circuit is used, for example, the output signals of the preamplifiers 109a to 109d may be converted into digital signals by an AD converter, and the subsequent processing may be sequentially performed.

  Further, in the present embodiment, the optical disc device 100 reduces the frequency f [max] component of the reproduction signal corresponding to the shortest mark, but this frequency may be determined according to other conditions. For example, f [max] may be determined according to the type or rotation speed of the optical disk, or the frequency characteristic of the reflected light may be detected, and the frequency corresponding to f [max] may be determined based on the result. Good.

  According to the present invention, a high-quality tracking error signal can be generated to realize high-accuracy tracking control, so that the reliability can be extremely improved even when recording and / or reproducing information using a high-density optical disk. .

2A is a diagram illustrating a structure of the optical disc 20, and FIG. 2B is a diagram illustrating a track 25 provided on the optical disc 20. FIG. 1 is a block diagram illustrating a configuration of an optical disc device 100 according to the present invention. 6 is a flowchart illustrating a procedure of a tracking control process of the optical disc device 100. FIG. 4 is a diagram illustrating an example of a frequency characteristic of a reproduction signal. FIG. 9 is a diagram illustrating an example of frequency characteristics of filters 118a and 118b. FIG. 4 is a diagram illustrating an example of a frequency characteristic of a reproduction signal. FIG. 9 is a diagram illustrating an example of frequency characteristics of filters 118a and 118b. FIG. 4 is a waveform diagram of various signals obtained in the optical disc device 100. FIG. 7 is a waveform diagram of various output signals when a slice level has no small deviation Δv and when there is a slice level. FIG. 11 is a block diagram illustrating a configuration of a conventional optical disc device 500. It is a waveform diagram of addition signals A + C, B + D, binarized signals a1, a2, a phase advance signal b1, and a phase delay signal b2. FIG. 7 is a waveform diagram of various output signals when a slice level has no small deviation Δv and when there is a slice level.

Explanation of reference numerals

Reference Signs List 20 optical disk 30 light beam 35 optical head 40 optical disk controller (ODC)
Reference Signs List 50 drive circuit 60 disc type discriminating unit 100 optical disc device 101 light source 105 objective lens 108 photodetector 110a, 110b adder 111a, 111b binarization circuit 112 phase comparator 113a, 113b low-pass filter 114 subtractor 115 tracking actuator 117 control circuit 118a, 118b Filter

Claims (10)

An optical disc device loaded with an optical disc having a track on which a plurality of marks are formed,
An optical system for irradiating the loaded optical disk with light,
A photodetector that receives reflected light from the optical disc in a plurality of regions and generates a plurality of reproduction signals according to the amount of light received in each region;
A filter that receives the plurality of reproduced signals and outputs a plurality of processed signals in which frequency components determined according to the length of the mark among frequency components of each reproduced signal are reduced;
A phase difference detection unit that detects a phase difference between the plurality of processing signals,
Based on the phase difference, a signal generation unit that generates a tracking error signal indicating a positional relationship between the light irradiation position and the track on the optical disc,
A control unit that generates a control signal based on the tracking error signal, and controls an irradiation position of the light in a direction crossing the track on the optical disc based on the control signal. The optical system has a light source, a lens that focuses light from the light source, and an actuator that moves the position of the lens,
2. The optical disk device according to claim 1, wherein the actuator is driven based on the control signal to control a position of the lens so that an irradiation position of the light coincides with a center of the track. 3.   The optical disk device according to claim 2, wherein the filter removes the frequency component.   3. The optical disc device according to claim 2, wherein the filter removes a frequency component of a specific frequency determined based on a shortest length of the mark.   The optical disc device according to claim 4, wherein the filter removes a frequency component equal to or higher than the specific frequency.   5. The optical disc device according to claim 4, wherein the filter further removes a frequency component corresponding to a mark next to the shortest mark.   The optical disc device determines a frequency according to a linear velocity of the track at the irradiation position of the light and a length of the mark, and the filter reduces a frequency component corresponding to the determined frequency. 2. The optical disc device according to 1. Irradiating light to an optical disc having tracks on which a plurality of marks are formed;
Receiving reflected light from the optical disc in a plurality of areas;
Generating a plurality of reproduction signals according to the amount of light received in each area;
Receiving the plurality of reproduction signals and outputting a plurality of processing signals in which frequency components determined according to the length of the mark are reduced among frequency components of each reproduction signal;
Detecting a phase difference between the plurality of processing signals;
Based on the phase difference, generating a tracking error signal indicating a positional relationship between the track and the irradiation position of the light on the optical disc,
Generating a control signal based on the tracking error signal;
Controlling the irradiation position of the light in a direction crossing the track on the optical disc based on the control signal. A tracking control computer program executable in an optical disk device loaded with an optical disk having tracks on which a plurality of marks are formed, wherein the optical disk device includes:
Irradiating the loaded optical disk with light;
Receiving reflected light from the optical disc in a plurality of areas;
Generating a plurality of reproduction signals according to the amount of light received in each area;
A signal that receives the plurality of reproduction signals and outputs a plurality of processing signals in which frequency components determined according to the length of the mark are reduced among the frequency components of each reproduction signal;
Detecting a phase difference between the plurality of processing signals;
Based on the phase difference, generating a tracking error signal indicating a positional relationship between the track and the irradiation position of the light on the optical disc,
Generating a control signal based on the tracking error signal;
Controlling the irradiation position of the light in a direction crossing the track on the optical disc based on the control signal. An optical system for irradiating light to an optical disc having tracks on which a plurality of marks are formed;
And a photodetector that receives reflected light from the optical disc in a plurality of areas and generates a plurality of reproduction signals according to the amount of light received in each area, and traverses the track on the optical disc based on a control signal. A chip circuit mounted on an optical disc device that controls the irradiation position of the light in a direction,
A filter that receives the plurality of reproduced signals and outputs a plurality of processed signals in which frequency components determined according to the length of the mark among frequency components of each reproduced signal are reduced;
A phase difference detection unit that detects a phase difference between the plurality of processing signals,
Based on the phase difference, a signal generation unit that generates a tracking error signal indicating a positional relationship between the light irradiation position and the track on the optical disc,
A control unit that generates the control signal based on the tracking error signal.

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