JP2007066413A - Wobble signal reproducing apparatus, and wobble signal reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a reliable wobble signal more easily. <P>SOLUTION: A wobble signal reproducing part 16 for reproducing the wobble signal corresponding to wobble formed in tracks of an optical disk comprises: an amplitude change detection part 40 for detecting a change in amplitude of a detection wobble signal detected by scanning wobbling tracks with a light beam; a cross-talk signal estimation part 42 for estimating a cross-talk signal contained in the detected wobble signal based on the detected amplitude change and the detection wobble signal; and a wobble signal producing part 44 for eliminating the estimated cross-talk signal from the detection wobble signal to produce the true wobble signal. Since the amplitude change of the detection wobble signal reflects a phase difference between the wobble signal and the cross-talk signal, the configuration of this wobble signal reproducing part 16 enables estimation of the cross-talk signal based on the detection wobble signal and production of the wobble signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wobble signal reproducing apparatus and a wobble signal reproducing method for reproducing a wobble signal corresponding to a wobble formed on a track of an optical disc.

  Conventionally, optical disks capable of recording a large amount of data have been widely distributed. An optical disc apparatus records and reproduces information by condensing a laser beam on an information recording layer formed on a transparent substrate of the optical disc. On the information recording layer of the optical disc, a track made of a physical concave portion or convex portion is formed, and information is recorded and reproduced along this track.

  Some optical disks have tracks wobbled in the radial direction of the optical disk. In such an optical disc, the wobble waveform (wobble waveform) of this track is acquired as a wobble signal, and the address and recording clock are specified based on the obtained wobble signal.

  Here, the wobble signal is reproduced based on a change in the reflected light obtained by scanning the laser beam along the track. Here, the detected wobble signal detected by the laser beam scanning may include a wobble signal component of an adjacent track, that is, a so-called crosstalk component. In particular, in recent years, there is a strong demand for an increase in storage capacity, and the track pitch tends to be narrower. As the track pitch is reduced, the influence of the crosstalk component is also increased. Such a crosstalk component causes an increase in the jitter value of the wobble signal and a disturbance in the waveform of the address modulation portion, which in turn causes an increase in address error.

  Thus, many techniques have been proposed in the past for removing a crosstalk component from a detected wobble signal and obtaining a highly reliable wobble signal. For example, Patent Documents 1 and 2 propose a technique for removing a crosstalk component included in a detected wobble signal detected by a main beam based on a signal detected by a sub beam. Patent Documents 3 and 4 disclose techniques for removing crosstalk components based on detection signals of adjacent tracks.

JP 2001-034977 A JP 2001-134945 A JP 2002-342938 JP 2003-196840 A

  However, in each of Patent Documents 1 to 4, it is necessary to reproduce a signal different from the wobble signal originally desired to be acquired. Therefore, there is a problem that the signal processing configuration and the mechanical configuration of the apparatus become complicated.

  Accordingly, an object of the present invention is to provide a wobble signal reproducing apparatus and a wobble signal reproducing method that can more easily reproduce a reliable wobble signal.

  The wobble signal reproducing apparatus of the present invention is a wobble signal reproducing apparatus for reproducing a wobble signal corresponding to a wobble formed on a track of an optical disc, and detects a detected wobble signal by scanning a light beam on the wobbled track. Crosstalk signal estimation for estimating a crosstalk signal included in the detected wobble signal based on the detected amplitude change and the detected wobble signal based on the detected amplitude change and the detected amplitude change and the detected wobble signal And wobble signal generation means for generating a true wobble signal by removing the estimated crosstalk signal from the detected wobble signal.

  In a preferred aspect, the crosstalk signal estimation means uses the change in amplitude as a reference for calculating the phase difference between the detected wobble signal and the crosstalk signal. The crosstalk signal estimation means is preferably a PLL circuit that receives the amplitude change and the detected wobble signal.

  In another preferred aspect, it is also desirable that the crosstalk signal estimating means determines the amplitude of the crosstalk signal based on a difference between the maximum amplitude value and the minimum amplitude value of the detected wobble signal. More specifically, it is desirable that the crosstalk signal estimating means estimate the crosstalk signal by setting the half of the difference between the maximum amplitude value and the minimum amplitude value of the detected wobble signal as the amplitude of the crosstalk signal.

  In another preferred aspect, the crosstalk signal estimating means estimates a crosstalk signal included in the detected wobble signal and generates an antiphase signal having an opposite phase to the crosstalk signal, and the wobble signal generating means generates A true wobble signal is generated by adding the detected antiphase signal and the detected wobble signal.

  Another wobble signal reproduction method according to the present invention is a wobble signal reproduction method for reproducing a wobble signal corresponding to a wobble formed on a track of an optical disc, wherein the wobble signal is scanned on the wobbled track to detect the wobble signal. A reproduction step for detecting an amplitude change, an amplitude change detection step for detecting an amplitude change of the detected wobble signal, and a crosstalk signal for estimating a crosstalk signal included in the detected wobble signal based on the detected amplitude change and the detected wobble signal. And a wobble signal generation step of generating a true wobble signal by removing the estimated crosstalk signal from the detected wobble signal.

  According to the present invention, a crosstalk signal is estimated based on a detected wobble signal obtained by scanning a light beam on a wobbled track. For this reason, it is not necessary to provide a light source or scanning step dedicated to detecting the crosstalk signal, and a reliable wobble signal can be reproduced more easily.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an optical disc drive 12 according to an embodiment of the present invention. The optical disk 10 having a wobble formed on a track is driven to rotate by a spindle motor (not shown). The pickup 13 (PU) includes a single laser diode (LD) that is disposed to face the optical disc 10 and that irradiates the surface of the optical disc 10 with laser light. The laser diode is driven by a laser diode drive circuit 22 (LDD), and irradiates a laser beam with a recording power when recording data and a laser beam with a reproduction power when reproducing data. The pickup 13 has a photodetector that converts the laser light reflected from the optical disk 10 into an electrical signal, and outputs the converted signal to the signal processing unit 14. Note that the light receiving region of the photodetector is divided into a plurality of parts as will be described later.

  The signal processing unit 14 is provided with an RF signal reproduction unit 18 and a wobble signal reproduction unit 16. The RF signal reproduction unit 18 generates a reproduction RF signal based on the signal from the pickup 13. The reproduced RF signal is binarized and then output to the decoder 20. The decoder 20 demodulates the input binarized signal and outputs it to the controller 21. Demodulation is performed by generating a synchronous clock signal from the binarized signal by a PLL circuit (not shown). The demodulated data output to the controller 21 is output to a host device such as a computer (not shown).

  The wobble signal reproduction unit 16 reproduces the wobble signal based on the signal from the pickup 13. The flow of wobble signal reproduction will be described in detail later. The reproduced wobble signal is binarized and then output to the decoder 20. Based on the wobble signal, the decoder 20 demodulates address information indicating a position on the optical disc 10 and specifies a recording clock.

  The controller 21 controls the operation of each unit such as the RF signal reproducing unit 18 and the wobble signal reproducing unit 16. At the time of data recording, the recording data supplied from the host device is encoded and the LDD is driven, and the power is modulated with the set recording strategy to record the data.

  The servo controller 24 performs rotation control of the spindle motor, movement control of the pickup 13 in the radial direction of the optical disk 10, control of the objective lens provided in the pickup 13 in the tracking direction and focus direction, and the like. These controls are performed according to a tracking error, a focusing error, etc. calculated by the signal processing unit 14.

  FIG. 2 is a diagram illustrating the types of signals output from the pickup 13. In the present embodiment, the light receiving region of the photodetector 26 provided in the pickup 13 is divided into two in the radial direction. Then, a sum signal is generated by adding the signal obtained by amplifying the output from one light receiving region 26 a by the amplifier circuit 28 and the signal obtained by amplifying the output from the other light receiving region 26 b by the amplifier circuit 28. Is done. This sum signal is output to the RF signal reproducing unit 18. The RF signal reproduction unit 18 generates a reproduction RF signal based on this sum signal.

  Also, a difference signal is generated by subtracting a signal obtained by amplifying the output from the other light receiving region 26b by the amplifier circuit 28 from a signal obtained by amplifying the output from one light receiving region 26a by the subtracting circuit 32. The This difference signal is output to the wobble signal reproducing unit 16. The wobble signal reproducing unit 16 reproduces the wobble signal based on the difference signal. It should be noted that the manner of dividing the light receiving area of the photodetector 26 described here is merely an example, and of course, it may be divided into a larger number.

  Here, the wobble signal reproduced by the wobble signal reproducing unit 16 will be described in detail. FIG. 3 shows a state where the track is viewed from above. The track of the optical disk 10 is slightly meandering in the radial direction, and this is called wobble. When the focused beam spot 34 is scanned along the wobbled track 35a, the wobble frequency is higher than the bandwidth of the tracking servo signal. Go straight through the center.

  At this time, the sum signal hardly changes, and only the difference signal changes in accordance with the wobble. Hereinafter, this changing difference signal is referred to as a detected wobble signal. This detected wobble signal is originally used for detection of physical address information, recording clock reference, adjustment of the rotation frequency of the spindle motor, and the like. However, in recent years, with an increase in the storage capacity of the optical disc 10, the track pitch is narrowed, and there is a problem that the wobble signal component of the adjacent track 35b, that is, a so-called crosstalk component is included in the detected wobble signal.

  4 and 5 are diagrams for explaining the influence of the crosstalk signal on the wobble detection signal. In FIG. 4, a solid line indicates a wobble signal corresponding to a wobble formed on a track to be scanned, in other words, a wobble signal in a state where no crosstalk component is mixed. A broken line indicates a crosstalk signal mixed in the wobble signal. The frequency of the wobble formed on each track is slightly different. Therefore, as shown in FIG. 4, the crosstalk signal and the wobble signal have different frequencies, and the phase difference between the two signals gradually changes. The detected wobble signal obtained as a difference signal from the pickup 13 is a combination of both signals and has a waveform as shown in FIG. As apparent from FIG. 5, the waveform of the detected wobble signal is greatly changed compared to the original wobble signal, and accurate address information and clock signal cannot be reproduced from the detected wobble signal.

  Therefore, conventionally, many techniques for removing the crosstalk component from the detected wobble signal have been proposed. For example, in addition to the main beam that scans the center of the track, there is a technique that provides sub-beams that scan the inside and outside of the track in the radial direction. This is to generate a crosstalk signal generated based on the signal detected by the sub-beam, and to remove the crosstalk signal generated from the detected wobble signal detected by the main beam. According to this technique, it is possible to detect both the detected wobble signal and the crosstalk signal in one scan. However, in the case of this technique, it is necessary to provide a photodetector for detecting a sub beam and a signal processing circuit for processing a signal output from the photodetector to generate a crosstalk signal, and one-beam control is adopted. It cannot be easily applied to the device.

  As another technique, there is a technique for generating a crosstalk signal based on a signal obtained by scanning an adjacent track, and removing this from the detected wobble signal. According to such a technique, it is not necessary to provide a photodetector for detecting a sub beam and a signal processing circuit for processing a signal output from the photodetector. However, on the other hand, it is necessary to scan a plurality of tracks in order to reproduce the wobble signal of one track, which causes problems such as an increase in signal processing time and a complicated signal processing configuration.

  Therefore, in this embodiment, the wobble signal reproducing unit 16 is configured to be able to reproduce a reliable wobble signal more easily. This will be described with reference to FIG. FIG. 6 is a block diagram showing a more detailed configuration of the wobble signal reproducing unit 16.

  The wobble signal reproduction unit 16 detects an amplitude change of the detected wobble signal, an amplitude change detection unit 40, and a crosstalk signal estimation unit 42 that estimates a crosstalk signal and generates an antiphase signal having a phase opposite to that of the crosstalk signal. And a wobble signal generation unit 44 that generates an original wobble signal based on the detected wobble signal and the generated crosstalk signal.

  The amplitude change detection unit 40 receives a detected wobble signal obtained by synthesizing the wobble signal and the crosstalk signal. The input detection wobble signal is input to the peak detection circuit 46 and the bottom detection circuit 48. The peak detection circuit 46 sequentially detects the peak value of the detected wobble signal, and the bottom detection circuit 48 sequentially detects the bottom value of the detected wobble signal. The detected peak value and bottom value are sequentially output to the amplitude change signal generation unit 50. The amplitude change signal generation unit 50 generates a top envelope signal composed of a peak value and a bottom envelope signal composed of a bottom value based on the sequentially input peak value and bottom value. Further, an amplitude change signal indicating an amplitude change of the detected wobble signal is generated from the difference between the two generated envelope signals. FIG. 7 is a diagram showing an envelope signal and an amplitude change signal generated by the amplitude change detection unit 40. In FIG. 7, the upper part shows the detected wobble signal and the envelope signal, and the lower part shows the amplitude change signal. Also, the numbers shown below the amplitude change signal indicate the phase difference between the wobble signal and the crosstalk signal.

  Here, the generated amplitude change signal indicates not only the amplitude of the detected wobble signal but also the change in the phase difference between the original wobble signal and the crosstalk signal included in the detected wobble signal. That is, as described above, the frequencies of the wobble signal and the crosstalk signal are different, and the phase difference between the two signals changes sequentially. This change in phase difference appears as a change in the amplitude of the detected wobble signal obtained by combining both signals. More specifically, when the wobble signal and the crosstalk signal have the same phase, the amplitude of the detected wobble signal takes a maximum value. On the other hand, when the wobble signal and the crosstalk signal are in opposite phases, the crosstalk signal and the wobble signal weaken each other, and the amplitude of the detected wobble signal becomes the minimum value. That is, the amplitude change signal indicating the amplitude change of the detected wobble signal can be said to be a signal indicating a change in the phase difference between the wobble signal and the crosstalk signal. The amplitude change signal indicating the change in phase difference is generated by the amplitude change signal generator 50 and then output to the crosstalk signal estimator 42.

  Based on the detected wobble signal and the amplitude change signal, the crosstalk signal estimating unit 42 generates an antiphase signal of the crosstalk signal included in the detected wobble signal. The detected wobble signal input to the crosstalk signal estimating unit 42 is binarized by the binarizing unit 52. The binarized binarized signal is output to the PLL circuit and the frequency is detected. The PLL circuit includes a phase comparison circuit 54, a voltage control transmission circuit 58 (VCO), and an addition circuit 56 for adding an amplitude change signal to the output signal from the phase comparison circuit 54. By adding the amplitude change signal to the output signal of the phase comparison circuit 54, the PLL output signal has a waveform whose phase changes in accordance with the amplitude change signal. Specifically, the PLL output signal has an opposite phase to the detected wobble signal at the peak of the amplitude change signal, and thereafter, as the amplitude change signal approaches the bottom, the phase difference with respect to the wobble signal decreases, and the bottom of the amplitude change signal. Sometimes it is in phase with the detected wobble signal.

  FIG. 8 is a diagram illustrating the relationship between the amplitude change signal, the detected wobble signal, and the PLL output signal. In FIG. 8, the upper stage shows the amplitude change signal, the interruption shows the detected wobble signal, and the lower stage shows the PLL output signal.

  As is clear from FIG. 8, the PLL output signal is in an opposite phase to the detected wobble signal at the peak of the amplitude change signal. Further, as the amplitude change signal approaches the bottom, the phase difference of the PLL output signal with respect to the detected wobble signal becomes smaller. At the bottom of the amplitude change signal, the PLL output signal is in phase with the detected wobble signal. Strictly speaking, the detected wobble signal and the original wobble signal have a slight phase difference due to the influence of the crosstalk signal, but the phase difference is negligible. Therefore, it can be said that the phase difference between the PLL output signal and the wobble signal increases as the amplitude change signal increases, and conversely, the phase difference between the PLL output signal and the wobble signal decreases as the amplitude change signal decreases.

  On the other hand, the phase difference change of the crosstalk signal with respect to the wobble signal is completely opposite to that of the PLL output signal. That is, as the phase difference of the crosstalk signal relative to the wobble signal decreases, the amplitude change signal increases. Conversely, as the phase difference of the crosstalk signal relative to the wobble signal increases, the amplitude change signal decreases. That is, the phase difference change of the crosstalk signal with respect to the wobble signal is completely opposite to the phase difference change of the PLL output signal with respect to the wobble signal. The PLL output signal can be said to be a rectangular wave signal having an opposite phase to the crosstalk signal.

  The rectangular wave PLL output signal is converted into a sine wave by a low-pass filter 60 (LPF). Further, the signal is amplified to the same amplitude as the crosstalk signal by the amplifier circuit 62 and is output to the wobble signal generation unit 44 as an antiphase signal. Here, the amount of amplification in the amplifier circuit 62 may be determined based on the amplitude change signal, or may be determined based on the decoding result of the wobble signal. When determining the amplification amount based on the amplitude change signal, the amplification amount is determined so that the amplitude value of the antiphase signal becomes half Epp / 2 of the difference Epp between the maximum value and the minimum value of the amplitude change signal. The amplitude of the wobble signal output from the adder circuit 64 described later is set to be approximately an intermediate amplitude value between the maximum amplitude value and the minimum amplitude value of the amplitude change signal. Note that the amplitude of the actual crosstalk signal is not always constant and fluctuates slightly, but this fluctuation amount is small enough to be ignored. Therefore, there is no problem even if the amplitude value of the antiphase signal is uniformly determined based on the amplitude change signal.

  Specifically, the wobble signal generation unit 44 includes an addition circuit 64. The adder circuit 64 receives the detected wobble signal and the antiphase signal generated by the crosstalk signal estimation unit 42. The adder circuit 64 outputs a signal obtained by adding the two signals as a wobble signal. That is, the antiphase signal is a signal having an antiphase with the crosstalk signal. By adding such an antiphase signal to the detected wobble signal, the crosstalk signal mixed in the detected wobble signal is canceled and the original wobble signal can be generated. The generated wobble signal is binarized by the binarizing unit 66 and then output to the decoder 20 unit to be used for detecting address information or for recording clock detection.

  As is clear from the above description, according to the present embodiment, the crosstalk signal is estimated based on the detected wobble signal (difference signal) detected by the pickup 13, and the crosstalk signal included in the detected wobble signal is removed. is doing. Therefore, it is not necessary to provide a photo detector (sub beam photo detector) dedicated to crosstalk signal detection and a sub beam signal processing circuit, and it is not necessary to perform scanning dedicated to crosstalk signal detection. As a result, an original wobble signal that does not include a crosstalk component can be easily obtained, and as a result, recording / reproduction quality can be easily improved.

  The configuration of the wobble signal reproduction unit 16 described above is an example, and may be changed as appropriate. For example, in this embodiment, the amplitude change signal is generated from the difference between the top envelope signal and the bottom envelope signal, but the amplitude change signal is not generated, and the top envelope signal or the bottom envelope signal is used as it is as the amplitude change signal. May be. In addition, instead of generating a signal having a phase opposite to that of the crosstalk signal and adding it to the detected wobble signal, a crosstalk signal is generated based on the detected wobble signal and the amplitude change signal and subtracted from the wobble signal. It may be configured.

  Some optical discs 10 are formed with wobbles whose phases are reversed in the middle. Even with such a phase inversion type wobble, the method of this embodiment can be used as it is. That is, even in the case of the phase inversion type wobble, the phase difference between the wobble signal and the crosstalk signal appears as a change in the amplitude of the detected wobble signal. By estimating the phase of the wobble signal from the amplitude change and the detected wobble signal, a crosstalk signal or a signal having a phase opposite to that of the crosstalk signal can be generated even for a phase inversion type wobble.

It is a block diagram which shows the structure of the optical disk drive which is embodiment of this invention. It is a figure which shows the kind of signal output from a pick-up. It is the schematic which looked at the track of the optical disk from the upper surface. It is a figure which shows a wobble signal and a crosstalk signal. It is a figure which shows a detection wobble signal. It is a block diagram which shows the structure of a wobble signal reproduction | regeneration part. It is a figure which shows an envelope signal and an amplitude change signal. It is a figure which shows the relationship between an amplitude change signal, a detection wobble signal, and a PLL output signal.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Optical disk, 12 Optical disk drive, 13 Pickup, 14 Signal processing part, 16 Wobble signal reproduction | regeneration part, 18 RF signal reproduction | regeneration part, 20 Decoder, 21 Controller, 22 Laser diode drive circuit, 24 Servo control part, 26 Photo detector, 34 Beam spot , 35 tracks, 40 amplitude change detector, 42 crosstalk signal estimator, 44 wobble signal generator.

Claims (7)

A wobble signal reproducing device for reproducing a wobble signal corresponding to a wobble formed on a track of an optical disc,
Detecting means for detecting a detected wobble signal by scanning a light beam on the wobbled track;
An amplitude change detecting means for detecting an amplitude change of the detected wobble signal;
Crosstalk signal estimating means for estimating a crosstalk signal included in the detected wobble signal based on the detected amplitude change and the detected wobble signal;
Wobble signal generation means for generating a true wobble signal by removing the estimated crosstalk signal from the detected wobble signal;
A wobble signal reproducing device comprising: The wobble signal reproducing device according to claim 1,
The wobble signal reproducing apparatus characterized in that the crosstalk signal estimating means uses the amplitude change as a reference for calculating a phase difference between the detected wobble signal and the crosstalk signal. The wobble signal reproducing device according to claim 2,
The wobble signal reproducing apparatus, wherein the crosstalk signal estimating means is a PLL circuit that receives an amplitude change and a detected wobble signal. The wobble signal reproduction device according to any one of claims 1 to 3,
The crosstalk signal estimating means determines the amplitude of the crosstalk signal based on the difference between the maximum amplitude value and the minimum amplitude value of the detected wobble signal. The wobble signal reproducing device according to claim 4,
The wobble signal reproducing device, wherein the crosstalk signal estimating means estimates the crosstalk signal by using a half of the difference between the maximum amplitude value and the minimum amplitude value of the detected wobble signal as the amplitude of the crosstalk signal. The wobble signal reproducing device according to any one of claims 1 to 5,
The crosstalk signal estimation means estimates a crosstalk signal included in the detected wobble signal and generates an antiphase signal having an antiphase with the crosstalk signal,
A wobble signal reproducing device, wherein the wobble signal generating means generates a true wobble signal by adding the generated antiphase signal and the detected wobble signal. A wobble signal reproduction method for reproducing a wobble signal corresponding to a wobble formed on a track of an optical disc,
A reproduction step of detecting a detected wobble signal by scanning a light beam on a wobbled track;
An amplitude change detecting step for detecting an amplitude change of the detected wobble signal;
A crosstalk signal estimation step for estimating a crosstalk signal included in the detected wobble signal based on the detected amplitude change and the detected wobble signal;
A wobble signal generation step of generating a true wobble signal by removing the estimated crosstalk signal from the detected wobble signal;
A wobble signal reproduction method comprising:

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