JP2006147018A - Optical disk drive and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk drive capable of analyzing an RF signal more minutely in adopting a PRML (partial response maximum likelihood)method for a reproduction system and its control method. <P>SOLUTION: This optical disk drive in which an optical disk is irradiated with a laser beam, the light quantity of reflected light of the laser beam that is changed by information recorded in the optical disk is received and a reproduced signal corresponding to the light quantity of the reflected light is obtained has a buffer for sequentially storing quantization levels of the reproduced signal at a prescribed period, a memory in which a plurality of quantization levels stored in the buffer are written, and a memory access control circuit for controlling data transfer between the buffer and the memory. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical disc apparatus and a control method thereof.

  In recent years, with the start of BS / terrestrial digital broadcasting and the widespread use of high-definition and large-screen displays, optical discs capable of recording high-definition video for a long time have been demanded. Therefore, for example, an optical disc compliant with the HDDVD (High Definition DVD) standard and an HDDVD drive device that records and reproduces information on the optical disc have attracted attention.

  HDDVD is a standard for a large-capacity optical disk, which is a successor of DVD, formulated by the DVD Forum. A blue-violet laser with a wavelength of 405 nm is used for reproduction, and it is said that the reproduction-only ROM standard has a storage capacity of 15 GB for a single layer on one side and 30 GB for two layers. The rewritable standard currently under discussion is scheduled to be 40 GB for a single-sided single layer 20 GB and two layers.

  It has been pointed out that with respect to the RF signal reproduced from the HDDVD optical disc, it is difficult to adopt the waveform slicing method of the current DVD standard (DVD ± R / RW, etc.) as the recording density becomes higher. For example, an RF signal obtained from a short mark (2T (2 / 64.8 MHz) or the like) has a small amplitude level, and the waveform is likely to become dull due to causes such as crosstalk between tracks or intersymbol interference.

  As described above, it is difficult to binarize an RF signal with a single slice level in the playback process of the HDDVD drive device. For this reason, it is difficult to measure the pulse width of the binarized signal (commonly referred to as EFM signal) of the RF signal employed in the current DVD standard when evaluating the jitter (bleeding) of the RF signal. (For example, refer to Patent Document 1 shown below).

  Therefore, in HDDVD, adoption of a PRML (Partial Response Maximum Likelihood) method is being considered instead of the waveform slice method. The PRML method is a technique that combines a PR equalizer that equalizes an RF signal into a desired signal waveform and an ML decoder (Viterbi decoder) (for example, Non-Patent Document 1 shown below). reference).

  Also, HDDVD stipulates that a value called “PRSNR” is used as a reference for write strategy adjustment and the like. The PRSNR is a cumulative calculation of SNR (amplitude-to-noise ratio) obtained by taking into account the intersymbol interference of the signal obtained by the PR equalizer within a predetermined period. The PRSNR is generally obtained based on the following (Formula 1) (for example, see Non-Patent Document 2 shown below).

PRSNR = E (SNR (T)) (Formula 1)
However,
SNR (T) = (S (T) squared + N (T) squared) / N (T) squared E (SNR (T)): Obtain the average value of the cumulative sum of SNRs for all sampling periods function.
S (T): The amplitude level of the RF signal (measured waveform) measured at the sampling period T.
N (T): A difference level of an amplitude between an ideal RF signal (ideal waveform) and an actually measured waveform in the sampling period T.

FIG. 9 is a diagram illustrating a process of calculating the PRSNR. The ideal waveform shown in the figure is an ideal waveform of an RF signal with a small bit error, and the actually measured waveform is a waveform of the RF signal actually measured to calculate the PRSNR. As shown in the figure, in the calculation of PRSNR, first, a predetermined adjustment period is spent to remove the unstable factor at the beginning of the calculation. Thereafter, after a cumulative calculation using a large number of sampling data for the amplitude level of the RF signal, the PRSNR converges to a certain stable value.
JP 2000-99997 A JP 2002-32961 A Toshiaki Iwanaga, “PRML Signal Processing Technology”, Trikes, Inc., September 2, 1996, pp 203-216 S. Ohkubo and 4 others, “Signal-to-Noise Ratio in a PRML Detection”, Technical Digest of ISOM2003, 2003

  As shown in FIG. 9, in order for PRSNR to converge to a certain stable value, an adjustment period at the beginning of calculation and a lot of sampling data regarding the amplitude level of the RF signal, that is, a sampling period over a long period of time are required. . Therefore, it is unclear how long the sampling period is required and whether the value of the PRSNR is reliable enough for use in jitter evaluation of RF signals, write strategy adjustment, and the like.

  In addition, the final value of the PRSNR that is regarded as converged appears as an accumulated error of the past sampling period. Here, since the final value of PRSNR is obtained as a result of cumulative calculation, the progress of the calculation process cannot be confirmed. Therefore, it is not easy to analyze what causes the error component included in the PRSNR only by the final value.

  In this way, in an HDDVD drive apparatus that employs PRML playback processing, only the PRSNR value defined in the HDDVD standard is used to perform more detailed RF signal analysis in jitter evaluation and write strategy adjustment. There was a limit to going.

  The main present invention for solving the above-mentioned problems is that an optical disk is irradiated with laser light, the amount of reflected light of the laser light that is changed by information recorded on the optical disk is received, and the amount of reflected light is reduced. In an optical disk apparatus for obtaining a corresponding reproduction signal, a buffer for sequentially storing quantization levels of the reproduction signal in a predetermined cycle, a memory to which a plurality of quantization levels stored in the buffer are written, the buffer and the memory And a memory access control circuit for controlling data transfer between the first and second terminals.

  According to the present invention, it is possible to provide an optical disc apparatus and a control method thereof that enable more detailed analysis of an RF signal obtained from an optical disc when the PRML system is adopted in a reproduction system.

=== Configuration of optical disc apparatus ===
Based on FIG. 1, the structure of the optical disk apparatus 100 which concerns on one Embodiment of this invention is demonstrated. The optical disc apparatus 100 is an apparatus that reproduces information recorded on the optical disc 10 by irradiating the optical disc 10 compliant with HDDVD or the like with laser light. That is, the PRML method is adopted in the reproduction system. Of course, an apparatus for recording information on the optical disc 10 may also be used.

  Further, the optical disc apparatus 100 analyzes an RF signal obtained as a result of irradiating the optical disc 10 with laser light. Then, the optical disc apparatus 100 performs a quantitative evaluation of the degree of bleeding of a reproduction signal obtained from the optical disc 10 called “jitter” and a write pulse modulation pattern suitable for the optical disc 10 by analyzing the RF signal. Strategy adjustment will be performed.

  The optical pickup 11 is an LD (Laser Diode) that emits blue laser light in a 400 nm band (for example, 405 nm), PD that receives reflected light of the blue laser light from the optical disc 10 and detects the intensity of the light amount as a change in voltage value. (Photo Detector), an LD driving circuit for driving the LD, an objective lens having a predetermined numerical aperture (for example, 0.65), various servo mechanisms, and the like.

  The preamplifier 12 amplifies the voltage signal detected in the PD of the optical pickup 11 with a predetermined amplification factor, and generates an analog RF signal. The preamplifier 12 has an AGC (Automatic Gain Control) function for automatically adjusting its own amplification factor and a function for generating various servo control signals.

  The A / D converter 13 samples and holds the analog RF signal generated in the preamplifier 12 at a predetermined sampling period, and further performs quantization with a predetermined binary number (quantization number). Thus, the digital signal is converted into an RF signal.

  The PR equalizer 14 equalizes the RF signal after A / D conversion into a desired signal waveform in consideration of intersymbol interference. For example, the PR (1, 1) characteristic is a characteristic in which an impulse response appears at a ratio of 1: 1 at two consecutive identification points, and a response output for an input of {0 ·· 010 ·· 0}. Becomes {0 ·· 0110 ·· 0}.

  Further, using the delay operator D, the transfer function H (D) of the PR (1,1) characteristic is expressed as “1 + D”. Therefore, in the PR (1, 1) characteristic, the response output for the input {00} is {0}, the response output for the input {01} and the input {10} is {1}, and the response output for the input {11} is {2}. }. That is, the PR {1, 1} characteristic takes three values {0, 1, 2} as the response output.

  On the other hand, in the case of the PR {1, 2, 1} characteristic, it is a characteristic in which an impulse response appears at a ratio of 1: 2: 1 at three consecutive identification points, and the input {0 ·· 010 ·· 0}. The response output for is {0 ·· 01210 ·· 0}. The transfer function H (D) is expressed as “(1 + D) squared”, and takes five values {0, 1, 2, 3, 4} as its response output.

  Thus, in the PR characteristic, the RF signal is equalized to a multi-value waveform. An explanation of the PR system including the PR equalizer 14 is disclosed in, for example, “Toshiaki Iwanaga,“ PRML Signal Processing Technology ”, Trikes, Inc., September 2, 1996, pp 192-195”.

  The Viterbi decoder 15 performs Viterbi decoding, which is one of maximum likelihood decoding, on the RF signal after waveform equalization in the PR equalizer 14. Viterbi decoding is the selection of the code sequence having the smallest error from the sample sequence of the RF signal equalized by the PR equalizer 14, that is, the code sequence having the maximum likelihood, among all code sequences satisfying a predetermined PR characteristic. Then, decoding according to the selected code sequence is performed.

  A detailed description of the ML system including the Viterbi decoder 15 is disclosed in, for example, “Toshiaki Iwanaga,“ PRML Signal Processing Technology ”, Trikes, Inc., September 2, 1996, pp 185-191”. .

  The decoder circuit 16 performs a predetermined demodulation process on the Viterbi-decoded RF signal. Further, predetermined error correction processing (for example, ECC processing) is performed on the demodulated signal. The reproduction data as a result of these decoding processes is output to the outside via an A / D converter (not shown).

  The PRSNR calculation circuit 17 calculates a PRSNR used as a reference in the write strategy adjustment or the like based on the quantization level of the RF signal after waveform equalization in the PR equalizer 14. Intermediate data during the cumulative calculation of PRSNR and the finally obtained PRSNR value are stored in the buffer 18.

  The buffer 19 sequentially stores the quantization level of the RF signal after A / D conversion every predetermined sampling period. The quantization level of the RF signal after A / D conversion stored sequentially in the buffer 19 is the quantization level of the RF signal after A / D conversion output from the A / D converter 13 or PR. One of the quantization levels of the RF signal after waveform equalization output from the equalizer 14 is employed.

  The memory access control circuit 20 controls access (write / read) to the memory 21. The memory 21 is a main storage device such as a DRAM or SDRAM that can be directly accessed by the microcomputer 30. For example, the memory access control circuit 20 performs data transfer control for collectively writing a plurality of quantization levels of the RF signal stored in the buffer 19 into a predetermined storage area of the memory 21.

  The histogram generation circuit 25 generates an appearance frequency histogram for the quantization level read from the memory 21 via the memory access control circuit 20. The processing in the histogram generation circuit 25 may be performed by the microcomputer 30. However, in order to reduce the processing load on the microcomputer 30, a histogram generation circuit 22 is provided separately from the microcomputer 30 as shown in FIG. Is preferred.

  The statistical calculation circuit 22 performs predetermined statistical calculation processing for obtaining various statistics (average, variance, appearance frequency, etc.) for the quantization level read from the memory 21 via the memory access control circuit 20. The processing result is written again into the memory 21. That is, the statistical calculation circuit 22 is provided to make the analysis of the RF signal by the microcomputer 30 easy and detailed. The processing in the statistical calculation circuit 22 may be performed by the microcomputer 30. However, to reduce the processing load on the microcomputer 30, the statistical calculation circuit 22 is independent of the microcomputer 30 as shown in FIG. It is preferable to provide it.

  The encoder circuit 23 performs predetermined modulation processing according to the standard of the optical disc 10 on the recording data to the optical disc 10 supplied from an external device (such as a personal computer). For example, an RLL (Run Length Limited) code is employed in the modulation process. The RLL code, when expressed by RLL (x, y), is such that “0” appearing continuously between “1” and “1” is set to the minimum x and the maximum y.

  The write strategy circuit 24 performs a predetermined modulation process on the recording data by the encoder circuit 23 to control the drive (write strategy) of the LD of the optical pickup 11. A recording pulse of a predetermined pattern is output from the LD of the optical pickup 11 based on the recording data subjected to this modulation process.

  The microcomputer 30 is a processor that controls the entire optical disc apparatus 100. For example, the microcomputer 30 determines a recording pulse pattern set in the write strategy circuit 24 based on the PRSNR value stored in the buffer 18. Further, the microcomputer 30 displays the statistics of the quantization level of the RF signal stored in the memory 21 on a predetermined display device 40.

  In the present invention, the optical disc apparatus 100 (HDDVD drive apparatus or the like) adopting the PRML system as a reproduction system is targeted. In view of this, regarding the RF signal after A / D conversion obtained from the optical disc 10, the transition of the quantization level for each predetermined period is written into the memory 21 via the buffer 19. Therefore, the statistical calculation circuit 22 or the microcomputer 30 can grasp the transition of the quantization level of the RF signal written in the memory 21, and as a result, analyze the RF signal obtained from the optical disc 10 in more detail. Is possible.

=== Analysis of RF signal ===
<Histogram generation>
As an example of the analysis of the RF signal in the optical disc apparatus 100, generation of a histogram of appearance frequency for each quantization level of the measured RF signal will be described.

  FIG. 2 is a flowchart showing a flow of a series of processing of the optical disc apparatus 100 from the sequential storage of the sample value S (T + n: n = integer) to the buffer 19 to the generation of the histogram.

  First, the measured quantization level of the RF signal that is the output of the A / D converter 13 or the output of the PR equalizer 14, that is, the sample value S (T + n) is sequentially stored in the buffer 19 (S200). Then, batch data transfer is performed in units of a plurality of sample values S (T + n) from the buffer 19 to the memory 21 via the memory access control circuit 20 (S201).

  At this time, the sample values S (T + n) are stored in the memory 21 in a state of being arranged in time series. For example, as shown in FIG. 3, sample value S (T) at address N, sample value S (T + 1) after one cycle at address N + 1,..., Sample value S after four cycles at address N + 4 (T + 4) is stored.

  Then, the histogram generation circuit 25 counts the number of sample values S (T + n) belonging to each quantization level A based on the sample values S (T + n) written in the memory 21 (S202). This count value C is written in the memory 21 in association with the quantization level A (S203).

  At this time, in the memory 21, for example, as shown in FIG. 3, the quantization level A (0) and the count value C (0) related thereto at the address M address, and the quantization level A (1) at the address M + 1 address. , And a count value C (1),..., And a count level C (3) related to the quantization level A (3) are stored at address M + 3.

  The quantization level A (k) indicating the histogram data and the count value C (k) related thereto are used as coordinate data by the count value C for each quantization level A in the microcomputer 30 and displayed on the display device 40 as a histogram. Image processing can be performed.

  FIG. 4 is a diagram showing the contents of histograms of the ideal waveform and the actually measured waveform of the RF signal. First, the mark ◯ shown on the ideal waveform (solid line) of the RF signal is the ideal value of the sample value S (T + n). The appearance frequency (ideal histogram) for each level related to the ideal value of the sample value S (T + n) is shown as a solid line graph of sample data versus appearance frequency shown on the right side in FIG.

  On the other hand, the ▲ mark shown on the measured waveform (dotted line) of the RF signal is the measured value of the sample value S (T + n). The appearance frequency (measurement histogram) for each level relating to the actual measurement value of the sample value S (T + n) is shown as a dotted line graph of sample data versus appearance frequency shown on the right side in FIG.

  As described above, the optical disc apparatus 100 can confirm the distribution of the quantization level of the RF signal obtained from the optical disc 10 by generating the histogram of the appearance frequency for each quantization level of the RF signal obtained from the optical disc 10. It becomes. Therefore, for example, a threshold value such as an upper limit / lower limit of the distribution of the quantization level of the RF signal in a predetermined range can be set.

  As described above, the quantization level (sample value) of the RF signal stored in the buffer 19 and the memory 21 is the quantization level of the RF signal output from the A / D converter 13 or PR equalization. One of the quantization levels of the RF signal output from the device 14.

  In the former case, the analysis of the RF signal obtained from the optical disc 10 is performed using the quantization level of the RF signal immediately after the A / D conversion, and therefore, for example, the process (PR equalization) subsequent to the A / D converter 13 is performed. Compared with the case where the quantization level of the RF signal on which the signal has been subjected to (such as or Viterbi decoding) is used, the RF signal can be analyzed more accurately. An example of the histogram display in this case is shown in FIG.

  In the latter case, the RF signal obtained from the optical disc 10 is analyzed using the quantization level of the RF signal after PR equalization. For example, the quantization level of the RF signal immediately after A / D conversion is used. Compared with the case where the noise component is present, the influence of the noise component can be reduced in the analysis of the RF signal. An example of the histogram display in this case is shown in FIG.

<Calculation of average value of each quantization level of RF signal satisfying predetermined condition>
FIG. 7 is a diagram for explaining the average value calculation of each quantization level of the RF signal satisfying the predetermined condition. In addition, the ◯ mark shown on the ideal waveform (solid line) of the RF signal is the ideal value of the sample value S (T + n). On the other hand, the ▲ mark shown on the measured waveform (dotted line) of the RF signal is the measured value of the sample value S (T + n).

  First, in FIG. 7, a plurality of predetermined sections are set with respect to the amplitude of the RF signal, that is, the quantization level of the RF signal. For example, in the example shown in FIG. 7, the quantization level of the RF signal is divided by “25, 15, 5, -5, −15, −25”, and as a result, the sections A, B, C, D, E will be set. In addition, for the setting of this section, for example, the minimum value of the histogram shown in FIG. 6 can be determined as the boundary of each section.

Next, for example, for each sample value S (C) belonging to the interval C of the quantization level “5 to −5”, distribution data for each group based on the following constraint conditions is generated.
<Group (1)>
Condition 1: The quantization level of two sample values immediately before the sample value S (C) changes state from section A to section B.
Condition 2: The quantization level of two sample values immediately following the sample value S (C) in time series changes from the section D to the section E.
Distribution data: Sample value S (T + 1), etc. <Group (2)>
Condition 1: The quantization level of two sample values immediately before the sample value S (C) changes state from section C to section D.
Condition 2: The quantization level of two sample values immediately following the sample value S (C) in time series changes state from section A to section B.
Distribution data: Sample value S (T-2), etc.

  FIG. 8 is a diagram showing the distribution data belonging to the groups (1) and (2) as described above in a graph as quantization level versus appearance frequency. Here, with respect to the distributions of the groups (1) and (2), the average value of the quantization level is calculated based on the appearance frequency. As a result, in the case of the group (1), for example, the average value is “−2.4”. In the case of group (2), for example, the average value is “1.6”.

  As described above, the sample values belonging to the predetermined interval of the same quantization level are grouped based on the interval to which the two previous and subsequent sample values belong, and the average value of the quantization level is obtained for the distribution of each group. It was decided. In addition to the average value, various statistics such as variance may be obtained. As a result, the optical disc apparatus 100 can analyze the RF signal in more detail based on a statistic such as the average value of the quantization level distribution for each group.

Further, as the above-described constraint condition, for example, it can be set as follows.
First, upper limit threshold values set for the sample values S (N−2), S (N−1), S (N + 1), and S (N + 2) for two periods before and after the sample value S (N), respectively. And the sample value S (N) are subject to the average value calculation.

  Note that the upper threshold set for the sample value S (N-2) is TH (N-2), and the lower threshold is TL (N-2). Similarly, the upper / lower threshold values set for the sample values S (N−1), S (N + 1), and S (N + 2) are TH (N−1) / TL (N−1), TH ( N + 1) / TL (N + 1) and TH (N + 2) / TL (N + 2).

  In other words, two upper limit threshold values and two lower limit threshold values are set for each of the total of four sample values for two periods before and after the sample value S (N). The sample value to be used is the target of the average value calculation.

  For example, in the example shown in FIG. 7, when the sample values S (T−2) and S (T + 4) of the measured waveform of the RF signal indicated by ▲ satisfy the above-described constraints, that is, the sample value S (T− 2) and S (T + 4) are the cases where the sample values for two periods before and after that fall within the range of each upper limit / lower limit threshold. At this time, the statistical calculation circuit 22 calculates the average value for the sample values S (T−2) and S (T + 4) that satisfy the constraint condition and other sample values.

  In the above-described embodiment, the sample values S (A), S (B), S (D), and S (E) belonging to other sections A, B, D, and E other than the section C are also described above. Such grouping and average calculation may be performed. Furthermore, in the embodiment described above, the accuracy of the analysis of the RF signal can be improved by performing grouping based on the sample values before and after two.

  As mentioned above, although embodiment of this invention was described, embodiment mentioned above is for making an understanding of this invention easy, and is not for limiting and interpreting this invention. The present invention can be changed / improved without departing from the gist thereof, and equivalents thereof are also included.

1 is a diagram illustrating a configuration of an optical disc device according to an embodiment of the present invention. It is a flowchart which shows the flow of a series of processes of the optical disk apparatus until it produces | generates the histogram data based on embodiment of this invention. It is a figure which shows an example of the content memorize | stored in the memory which concerns on embodiment of this invention. It is a figure which shows an example of the histogram display of each of the ideal waveform and measured waveform of RF signal which concern on embodiment of this invention. It is a figure which shows an example of the histogram display which concerns on embodiment of this invention. It is a figure which shows an example of the histogram display which concerns on embodiment of this invention. It is a figure for demonstrating calculation of the average value which concerns on embodiment of this invention. It is a figure which shows the dispersion | variation in the measurement result of RF signal which concerns on embodiment of this invention. It is a figure which shows the calculation process of PRSNR defined by HDDVD.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical disk 11 Optical pick-up 12 Preamplifier 13 A / D converter 14 PR equalizer 15 Viterbi decoder 16 Decoder circuit 17 PRSNR calculation circuit 18, 19 Buffer 20 Memory access control circuit 21 Memory 22 Statistical calculation circuit 23 Encoder circuit 24 Write strategy Circuit 25 Histogram generation circuit 30 Microcomputer 40 Display device 100 Optical disk device

Claims (11)

In an optical disc apparatus that irradiates an optical disc with laser light, receives the amount of reflected light of the laser light that is changed by information recorded on the optical disc, and obtains a reproduction signal according to the amount of reflected light.
A buffer for sequentially storing the quantization level of the reproduction signal in a predetermined cycle;
A memory in which a plurality of quantization levels stored in the buffer are written;
A memory access control circuit for controlling data transfer between the buffer and the memory;
An optical disc apparatus comprising:   2. The optical disc apparatus according to claim 1, further comprising a histogram generation circuit that generates a histogram indicating an appearance frequency of each quantization level based on the quantization level read from the memory.   The optical disc apparatus according to claim 2, further comprising a statistical calculation circuit that performs predetermined statistical calculation processing on the quantization level read from the memory.   4. The optical disc apparatus according to claim 3, wherein the statistical calculation circuit performs the predetermined statistical calculation processing based on the histogram. An equalizer for performing waveform equalization on the reproduced signal;
The optical disk apparatus according to claim 1, wherein the buffer sequentially stores a quantization level of an output signal of the equalizer at a predetermined period.   For each of the quantization levels written in the memory, the statistical calculation circuit sets a constraint condition that the quantization levels for a predetermined period before and after the quantization level belong within a predetermined range, and then stores the quantization level in the memory. 4. The optical disk apparatus according to claim 3, wherein a statistical calculation process is performed on a written quantization level that satisfies the constraint condition. A method of controlling an optical disc apparatus that irradiates an optical disc with laser light, receives the amount of reflected light of the laser light that is changed by information recorded on the optical disc, and obtains a reproduction signal according to the amount of reflected light. Sequentially storing the quantization level of the reproduction signal in a predetermined buffer at a predetermined period;
Writing a plurality of quantization levels stored in the buffer to a predetermined memory;
A method for controlling an optical disc apparatus, comprising:   8. The method of controlling an optical disc apparatus according to claim 7, further comprising a step of generating a histogram indicating an appearance frequency of each quantization level based on the quantization level read from the memory.   9. The method of controlling an optical disc device according to claim 8, further comprising a step of performing a predetermined statistical calculation process on the quantization level read from the memory.   10. The method of controlling an optical disk device according to claim 9, wherein the step of performing the predetermined statistical calculation process is a step of performing the predetermined statistical calculation process based on the histogram. Further comprising a step of performing waveform equalization on the reproduction signal,
11. The optical disk apparatus according to claim 7, wherein the step of sequentially storing in the buffer stores the quantization level of the output signal of the equalizer sequentially at a predetermined period. Control method.

Images