JP2007280483A - Optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device capable of eliminating the effect of crosstalk between tracks, improving an address detection error rate, and improving recording timing generation efficiency. <P>SOLUTION: This device is provided with a detector 127 for detecting the size of cross talk between the tracks of an optical disk 101, a multiplier 501 for multiplying the demodulated signal of MSK modulation by a constant, and a multiplier 502 for multiplying the demodulated signal of STW modulation by a constant. By adjusting a ration of constants between the multipliers 501 and 502 according to crosstalk between tracks detected by the detector 127 to eliminate the effect of the crosstalk between the tracks, an address detection error rate is improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus for recording information on an optical disc having a meandering recording track called wobble or reproducing the recorded information, and more particularly to a technique for reproducing wobble applied to an information track of an optical disc.

  Conventionally, typical optical information recording media for recording data (for example, high-density recording) include, for example, CD (Compact-Disc), DVD (Digital-Video-Disc), and BD (Blue-ray). Disc) and the like.

  FIG. 3 shows these optical information recording media. FIG. 3A is a diagram showing an outline of a recording medium, and FIG. 3B is a diagram showing an enlarged part thereof. Each of these recording media has a disk shape, and a spiral guide groove (information track) 201 is provided in advance from the inner periphery to the outer periphery of the disk plane or from the outer periphery to the inner periphery in the manufacturing stage.

  The guide groove basically has a small undulation (meandering, swinging) with a predetermined amplitude and a single period, and this is called a wobble.

  In the disk recording / reproducing apparatus, this wobble signal is detected by a push-pull signal, and physical position information detection, servo rotation speed control or recording clock generation is performed based on the signal component obtained therefrom. Further, as shown in FIG. 3B, the recording mark 202 is generated by irradiating the laser beam 203 on the wobble, and data is recorded.

  In order to recognize the physical position information on the disc, the wobble is modulated based on the address information, and the address information can be recognized by demodulating the detected wobble signal. For example, in BD, MSK (Minimum Shift Keying) and STW (Saw Tooth Wobble) are used as modulation schemes.

  In the case of BD, it is a means for indicating address information 1 bit by 56 wobble signals. By combining the basic wobble signal and the wobble signal subjected to the above two MSK and STW modulation, Realized.

  Here, the basic wobble signal, MSK, and STW can be mathematically expressed by the following models.

Basic wobble: COS (ωt)
MSK: COS (ωt + π)
STW: COS (ωt) ± a × SIN (2ωt) (for example, a = 0.25)
In general, heterodyne detection is used as means for detecting a signal subjected to MSK modulation and STW modulation. That is, detection is performed by multiplying a signal synchronized with each modulation signal and removing unnecessary high frequencies by the LPF.

  In addition, in address read by BD wobble, address information bits “0” and “1” are expressed by 56 wobbles, so that both MSK and STW are used in an complementary manner by having both in ADIP-Unit. Although the C / N is good as a feature of MSK, the signal is modulated to a narrow area of 3 wobble, so if wobble cannot be detected over a certain range due to scratches or dust, MSK It is difficult to detect.

  On the other hand, as a feature of the STW, the signal level to be detected is small because, for example, the wobble which is the basic carrier is added at an amplitude ratio of 0.25 times. For this reason, the C / N of STW equivalent to 1 wobble is lower than that of MSK. However, since it exists over a wide range, even if the wobble cannot be detected over a certain range due to scratches or dust, the address can be detected from the remaining detectable wobble signals.

By the way, since the address can be detected by two signals such as the MSK and STW signals, it becomes a problem which one is used as the address information bit. In that case,
Address bit = αMSK + βSTW
As shown in the calculation formula, the address information bit is detected by adding and using both the MSK and STW signals at an appropriate ratio.

  In recent optical discs, the track pitch, which is the distance between adjacent grooves, tends to be narrowed with an increase in recording density, for example, 0.74 μm for DVD and 0.37 μm for BD. For this reason, the influence of crosstalk from adjacent tracks tends to increase.

  Further, since the track itself is wobbled, if adjacent grooves exist in the same phase as shown in FIG. 4A, the influence of crosstalk from the adjacent track is small. On the other hand, as shown in FIG. 4B, the influence of the crosstalk from the adjacent track becomes large at the location where the adjacent wobbles are in opposite phases.

  As the influence of the crosstalk, the MSK signal of the adjacent track leaks to cause erroneous detection, and the amplitude and phase of the MSK signal and STW signal are modulated. In the case of a 23 GB BD, this modulation period is known to be approximately the period of rotation of the disk 27, and in particular, fluctuation in the amplitude direction due to crosstalk between tracks is sometimes called a wobble beat.

In addition, the technique regarding the modulation | alteration etc. of the above wobbles is described in Unexamined-Japanese-Patent No. 2003-123267, for example (patent document 1).
JP 2003-123267 A

  In recent years, the track pitch of optical discs has become narrower, and the influence of crosstalk between adjacent tracks tends to increase. As a result, the C / N of the detected wobble signal deteriorates, leading to deterioration of characteristics in a system that performs address detection and recording timing generation based on the detected wobble information. For this reason, it is necessary to take measures to improve the address detection error rate and improve the recording timing generation capability with respect to crosstalk between tracks.

  An object of the present invention is to provide an optical disc apparatus that can eliminate the influence of crosstalk between tracks, improve the error rate of address detection, or improve the recording timing generation capability.

  Usually, a signal such as address information is embedded in the wobble of the optical disk by two modulation methods, MSK modulation and STW modulation, and the address information is detected by adding the detection results of both. The present invention detects the magnitude of crosstalk between tracks on an optical disc, and adjusts the ratio of the demodulated signal when adding the demodulated signal of MSK modulation and the demodulated signal of STW modulation according to the detection result. Further, the magnitude of the inter-track crosstalk is detected by detecting the phase modulation amount based on the inter-track cross talk of the STW modulation signal.

  According to the present invention, the influence of crosstalk between adjacent tracks can be removed, and the error rate of address detection due to wobble of an information track can be improved. Further, it is possible to prevent a decrease in recording timing generation capability.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of an optical disc apparatus according to the present invention. The optical disk apparatus according to the present embodiment records or reproduces information by irradiating an optical disk with a recording or reproducing light beam from an optical pickup.

  In the figure, reference numeral 101 denotes an optical disc as an information recording medium, which has the same configuration as that in FIG. That is, a spiral guide groove (information track) is provided in advance from the inner circumference to the outer circumference of the disk plane or from the outer circumference to the inner circumference. As described above, the guide groove is slightly undulating (meandering, swinging), and information such as address information is added to the wobble. The optical disc 101 includes CD, DVD, BD, and the like.

  Laser light from an internal semiconductor laser (not shown) is condensed on the optical disk 101 by an optical pickup (OPU) 102, and the reflected light is detected by a photodetector (not shown). A wobble signal is extracted and amplified (for example, AGC) in the analog front end (AFE) 103 from the reflected light detected by the photodetector, and A / D conversion is performed.

  The PLL circuit 125 is a circuit that generates a signal having the same frequency and phase as the basic wobble signal. The PLL circuit 125 includes a multiplier 104, an LPF 105, a loop filter 106, a VCO (voltage controlled oscillator) 107, a 69 counter 108, a waveform generation table 109, and the like.

  Since the PLL circuit 125 is well-known and will be described briefly, the wobble signal (COS wave) is multiplied by the SIN wave 110 generated internally by the multiplier 104 to detect the phase error. Further, an unnecessary high frequency component of the output of the multiplier 104 is removed by the LPF 105, signal processing is performed by the loop filter 106 having an appropriate band, and a VCO (voltage controlled oscillator) 107 is operated.

  The VCO 107 generates a clock multiplied by 69 with respect to the wobble signal. The 69 counter 108 is operated by this clock, and the waveform generation table 109 generates a SIN wave 110 and a COS wave 111 according to the output value of the counter 108.

  Further, the waveform generation table 118 generates a double frequency SIN wave 119 and a double frequency COS wave 120 according to the output value of the counter 108. The SIN wave 119 has a double frequency with respect to the SIN wave 110, and the COS wave 120 has a double frequency with respect to the COS wave 111.

  The SIN wave 110 is used for phase error detection of the PLL circuit 125 as described above. The COS wave 111 is used for MSK detection by being multiplied by the wobble signal by the multiplier 112. The output of the multiplier 112 is input to the MSK detector 114 after the high-frequency component is removed by the LPF 113, and the MSK detector 114 performs MSK detection (MSK demodulation).

  The double frequency SIN wave 119 is multiplied by the wobble signal by the multiplier 115 and used for STW detection. The output of the multiplier 115 is input to the STW detector 117 after the high-frequency component is removed by the LPF 116, and STW detection (STW demodulation) is performed by the STW detector 117.

  By the way, in the case of MSK detection using a COS wave having the same frequency as that of the basic wobble, the PLL circuit 125 follows the influence of the phase modulation due to the crosstalk between the tracks, so that it is not affected by the crosstalk between the tracks.

  FIG. 2 shows signals of various parts of the apparatus shown in FIG. 2A is the basic wobble signal, FIG. 2B is the MSK signal embedded in the basic wobble, FIG. 2C is the COS wave 111, FIG. 2D is the output of the multiplier 112, FIG. 2E shows the output of the LPF 113.

  As can be seen from FIG. 2A and FIG. 2C, the basic wobble and the COS wave 111 have the same frequency. With respect to MSK detection, phase modulation is performed by the cross-talk between tracks of the optical disc 101 by the phase tracking operation of the PLL circuit 125. It is not affected.

  2F shows the STW signal, FIG. 2G shows the double SIN wave 119, FIG. 2H shows the output signal of the multiplier 115, and FIG. 2I shows the output signal of the LPF 116.

  On the other hand, in the case of STW detection, the PLL circuit 125 cannot cancel the influence of the phase modulation due to the crosstalk between tracks, so that the detection result of the STW detector 117 is strongly influenced by the crosstalk between tracks. Note that the double SIN wave 119 shown in FIG. 2 (g) is output from the waveform generation table 118 and multiplied by the multiplier 115. The double SIN wave 119 corresponds to the STW signal in FIG. 2 (f). The phase is finely adjusted.

  Next, the PLL circuit 126 will be described. The PLL circuit 126 includes a waveform generation table 118, a multiplier 121, an LPF 122, an integrator 123, a phase conversion unit 124, and the like. The PLL circuit 126 outputs the double SIN wave 119 and the double COS wave 120 from the waveform generation table 118. Further, as will be described later, the STW signal (modulation signal portion), the double SIN wave 119, and the double SIN wave 119 in FIG. A phase error with the double COS wave 120 is detected.

  Next, a circuit loop of the PLL circuit 126 will be described. The PLL circuit 126 multiplies the wobble signal by the multiplier 121 by the COS wave 120 having the double frequency that is orthogonal to the STW signal (modulation signal) shown in FIG. 2F, and the multiplication result is unnecessary by the LPF 122. The high frequency component is removed. The result shows a level proportional to the phase error signal between the STW signal (modulation signal portion) and the carriers 119 and 120 generated inside.

  In this embodiment, for this reason, the output of the LPF 122 is integrated by the integrator 123, and appropriate level conversion is performed by the phase converter 124 so that the output becomes a phase difference. Further, by giving the output (phase difference) of the phase converter 124 to the waveform generation table 118, the influence of phase modulation due to crosstalk between tracks can be canceled out.

  Here, when the loop of the PLL circuit 126 is broken as described above (when the feedback of the PLL circuit 126 is not applied), the phase error canceling operation by the PLL circuit 126 does not work, so the output of the LPF 122 is The level is proportional to the phase error signal.

  On the other hand, when the loop circuit of the PLL circuit 126 is operating (when the feedback of the PLL circuit 126 is applied), the output of the phase converter 124 indicates a level proportional to the phase error signal. These phase error signals indicate the strength of crosstalk caused by adjacent tracks.

  Therefore, by monitoring the output of the LPF 122 or the output of the phase conversion unit 124, the strength of the influence of crosstalk between tracks can be detected. In FIG. 1, the output of the phase converter 124 is detected by a detector 127 which is a means for detecting crosstalk between tracks.

  Here, as described above, signals are embedded in wobbles by two modulation schemes, MSK and STW, and both can detect addresses. Actually, the detection results of both are added at a certain ratio and binarized to detect the address bits.

  Specifically, a constant α is weighted by the multiplier 501 for the result of the MSK detector 114, and a constant β is weighted by the multiplier 502 for the result of the STW detector 117. The multiplication results of the multipliers 501 and 502 are added by an adder 503, binarized by a binarizer 504, and an address bit is detected by an address bit detector 505.

  Here, the phase modulation caused by the influence of crosstalk can be canceled by the loop of the PLL circuit 125 and the PLL circuit 126 as described above. However, the influence of leakage of MSK (MSK mark) existing in the adjacent track still remains.

  In the present embodiment, when the influence of crosstalk from adjacent tracks is strong, there is a high possibility that the MSK signal is erroneously detected. Therefore, the address is detected with emphasis on the STW detection result.

  Specifically, when the influence of the crosstalk from the adjacent track is strong, the output value of the detector 127 increases, so the value of the constant α of the multiplier 501 is decreased and the value of the constant β of the multiplier 502 is decreased. Adjust to increase. At this time, the larger the output value of the detector 127, the smaller the value of the constant α and the larger the value of the constant β. As a relationship between α and β, for example, a method is conceivable in which α + β = 1 and a ratio of constants α and β is adjusted.

  On the other hand, when the influence of the crosstalk from the adjacent track is small, the possibility of erroneous detection due to leakage of the MSK existing in the adjacent track is low, so address detection is performed with emphasis on the MSK detection result.

  Specifically, when the influence of the crosstalk from the adjacent track is small, the output value of the detector 127 is small. Therefore, the value of the constant α of the multiplier 501 is increased, and the value of the constant β of the multiplier 502 is increased. Adjust so that the value is smaller. At this time, the smaller the output value of the detector 127, the larger the value of the constant α and the smaller the value of the constant β.

  In this way, the intensity of the influence of the crosstalk from the adjacent track is monitored by the detector 127, and the constants α and β of the multipliers 501 and 502 are adjusted based on the detection result of the detector 127, thereby providing a comprehensive result. The address detection error rate can be lowered. At the same time, the recording timing capability can be improved. That is, since the MSK can be accurately demodulated, it is possible to improve both address detection and recording timing capability.

It is a block diagram which shows one Embodiment of this invention. It is a figure which shows an optical disk. It is a figure which shows the signal waveform of each part of FIG. It is a figure explaining the influence of crosstalk in the case where the adjacent groove | channels of an optical disk are in-phase, and a reverse phase.

Explanation of symbols

101 Optical disc 102 Optical pickup (OPU)
103 Analog Front End (AFE)
104 multiplier 105 LPF
106 Loop filter 107 VCO
108 69 counter 109 waveform generation table 110 SIN wave 111 COS wave 112 multiplier 113 LPF
114 MSK detector 115 Multiplier 116 LPF
117 STW detector 118 Waveform generation table 119 Double SIN wave 120 Double COS wave 121 Multiplier 122 LPF
123 accumulator 124 phase converter 125 PLL circuit 126 PLL circuit 127 detector 501 multiplier 502 multiplier 503 adder 504 binarizer 505 address bit detector

Claims (3)

A wobble is formed on an information track of the optical disc, and a signal based on the wobble is embedded by MSK modulation and STW modulation. The demodulated signal of the MSK modulation and the demodulated signal of the STW modulation are added, and the wobble is obtained from the addition result. In the optical disk apparatus for reproducing the signal according to the above, a means for detecting the magnitude of crosstalk between tracks of the optical disk, and the MSK-modulated demodulated signal and the STW-modulated demodulated signal are added according to the detection result of the detecting means Means for adjusting the ratio of the demodulated signal in the case of the optical disc apparatus. 2. The optical disc apparatus according to claim 1, wherein the detecting unit detects the magnitude of the inter-track crosstalk by detecting a phase modulation amount based on the inter-track cross talk of the STW modulation signal. A first multiplier that multiplies the MSK-modulated demodulated signal by a constant; and a second multiplier that multiplies the STW-modulated demodulated signal by a constant. 3. The optical disc apparatus according to claim 1, wherein a ratio of constants of the first and second multiplication means is adjusted accordingly.