JP2008059715A - Optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To evaluate jitter by detecting an amplitude of the shortest data length in an optical disk drive. <P>SOLUTION: A preceding RF1 signal from elements A and D in a photodetector 10a of the optical disk drive, is delayed by only 2T at a delay element 15, and is added to a subsequent RF2 signal from elements B and C at an adder 16. A PR class of an HD DVD is PR [1, 2, 2, 2, 1], while the RF1 signal is delayed by only 2T and adding the RF1 signal to the RF2 signal, so that the PR class can be substantially converted to PR [1, 2, 1], and an amplitude of a 2T signal length can be detected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to processing of a reproduction signal output from an optical disc apparatus, and more particularly from a divided photodetector.

  Conventionally, in an optical disk apparatus, a laser beam of reproduction power is irradiated from a laser diode of an optical pickup onto an optical disk, the reflected light is photoelectrically converted by a four-divided photodetector of the optical pickup, and the output signals of the respective photodetectors of the four-divided photodetector are added. Thus, a reproduction RF signal is obtained.

  However, when the reproduction-power laser beam passes through the pits on the optical disk, there may be a phase difference between the output side of the quadrant photodetector obtained from the pit reflected light on the leading side and the trailing side in the pit traveling direction. is there. This phase difference is caused by diffraction due to the pit depth on the optical disk, a pickup optical system, and the like, and varies depending on the optical disk device, the type of the optical disk, the reproduction speed, and the like.

  FIG. 6 shows the configuration of the reproduction system of the optical disk apparatus, and FIG. 7 shows an RF sum signal obtained by adding the signals. In FIG. 6, a pit 6 is formed on a track 5 on an optical disc. The track 5 is irradiated with a laser beam 100 having a reproduction power, and the reflected light is detected by a four-divided photodetector 10a. The four-divided photo detector 10a is divided into four photo detectors, photo detector A to photo detector D. Photo detectors A and B are located on the inner circumference side of the optical disc, and photo detectors C and D are located on the outer circumference side of the optical disc. Photo detectors A and D and photo detectors B and C are photo detectors divided with respect to the track direction of the optical disk. As the optical disk rotates, the pit 6 moves in the arrow direction in the figure. D is a preceding group of photodetectors, and photodetectors B and C are groups of succeeding photodetectors. The signal A from the photo detector A, the signal B from the photo detector B, the signal C from the photo detector C, and the signal D from the photo detector D are supplied to the adder 16, and all the signals are added to output a reproduction RF signal. The reproduced RF signal is supplied to the decoder and demodulated. Signals A and D are signals on the preceding side, signals B and C are signals on the following side, and signals on the following side are signals on the leading side due to diffraction due to the type of optical disk and pit depth. May cause a phase difference. When the phase difference occurs in this way, the resolution of the reproduction RF signal that is the sum signal thereof is lowered.

  The following patent document describes at least a pair of photodetectors for receiving reflected light from an optical disc in the direction of the information track of the optical disc in order to reduce the waveform distortion of a reproduction signal caused by the frequency characteristics of the optical head. And a phase advance means for advancing the phase of the photodetector output at a high frequency at one output stage of the pair of photodetectors, and the output of the phase advance means and the pair of photodetectors Adding the other output is disclosed.

JP 7-98938 A

  On the other hand, in next-generation optical discs such as HD DVD and BD (Blu-ray Disc), the playback signal receives intersymbol interference from the front and back pits due to the relationship between the pits on the disc and the laser spot diameter. It has been proposed that reproduction is performed by PRML (Partial Response Maximum Likelihood) method by actively using interference. Here, PRML is a signal processing method for reading the most probable data from a reproduction signal while suppressing interference between the front and rear pits, and PR detection for recording and reproducing data in a narrow frequency band without suppressing waveform interference. This is a composite technique of ML decoding in which the most probable bit string is decoded from a plurality of reproduced signal strings instead of being discriminated for each bit. The HD DVD PR class is PR [1, 2, 2, 2, 1] due to the transfer characteristics between the media and the pickup, but uses the shortest inversion 2T (T is the reference time length) modulation code. PR [1,2,2,2,1] has a problem that the amplitude of the 2T signal cannot be obtained. Normally, when evaluating a signal, the jitter of the 2T signal is evaluated. However, since the amplitude of the 2T signal cannot be obtained with HD DVD, evaluation cannot be performed. Instead, methods such as PRSNR and sBER are used. For example, PRSNR is an accumulative calculation of SNR (amplitude-to-noise ratio) obtained in consideration of intersymbol interference of a signal obtained by a PR equalizer within a predetermined period, so evaluation for each T is impossible. Therefore, it is difficult to tune the strategy during recording.

  An object of the present invention is to provide an optical disc apparatus capable of reliably evaluating the signal quality of an optical disc having an extremely short minimum pit length of, for example, 2T, such as HD DVD and BD, that is, a high density optical disc.

  The present invention is divided into a plurality of parts in the track direction of the optical disc, and light receiving means for photoelectrically converting reflected light from the optical disc by each divided element and outputting an RF signal; And a delay means for delaying the RF signal of each element preceding by a predetermined delay amount according to the number of divisions and the degree of the preceding time, and an adding means for adding the delayed RF signals of each element .

  In the present invention, the light receiving means is divided into two in the track direction, and the delay means delays the RF signal of the preceding element among the divided RF signals of the elements by 2T (T is a reference time length). You may let them.

  Further, in the present invention, the light receiving means is divided into four in the track direction, and the delay means converts the RF signals of the preceding three elements out of the four divided RF signals into 3T, 2T, T, respectively. You may delay by (T is reference time length).

  Further, in the present invention, the light receiving means is divided into three in the track direction, and the delaying means outputs the RF signals of the preceding two elements among the divided RF signals of the elements to 2T and T (T May be delayed by a reference time length).

  The present invention also relates to an optical disk apparatus that reproduces data recorded on an optical disk using the PRML method, and is divided into a plurality of pieces in the track direction of the optical disk, and the reflected light from the optical disk is photoelectrically converted by the divided elements. Light receiving means for converting and outputting an RF signal, and delay means for delaying the RF signal of each element preceding in time among the RF signals of each element by a predetermined delay amount according to the number of divisions and the degree of the preceding time Adding means for adding the RF signals of the delayed elements, demodulating means for demodulating by PRML method using the output of the adding means, and evaluating means for evaluating the jitter of the reproduction signal using the output of the adding means It is characterized by having.

According to the present invention, a short signal such as a 2T signal is used to substantially convert (convert to a lower class) the PR class by appropriately delaying and adding the RF signal from each element obtained by division. Can be easily detected.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Basic principle>
First, the basic principle of this embodiment will be described. The reproduction RF signal is obtained by adding all the signals A to D of the respective elements (photodetectors A to D) of the four-divided photodetector when a four-divided photodetector is used. That is,
Reproduction RF signal = signal A + signal B + signal C + signal D
It is. Photodetector A and photodetector D are temporally preceding elements, signal A + signal D is a leading signal, and signal B + signal C is a trailing signal. The reproduction RF signal is decoded by the PRML method. In the PRML system, the reproduced signal at the N times in succession and the target signal are compared and binarized into the most probable bit string. The direct slice method is generally used as an optical disc reproduction method. However, when the pit length is 2T, the signal amplitude is small, and it is difficult to extract a 2T signal by the direct slice method. In the PRML method, a target signal having a time transition closest to a reproduction signal is selected, and a bit string for generating the target signal is output as a decoding result. The target signal is calculated by convolution of a designated impulse response (PR class) and a bit string. Therefore, an appropriate PR class corresponding to the recording density of the optical disc is selected. Assuming that the PR class is expressed by PR [a, b], PR [1, 1] indicates a characteristic that appears at a ratio of 1: 1 at two discrimination points where impulse responses are continuous. Accordingly, the response output for the input {0... 1} is {0. PR [1,2,1] indicates a characteristic that appears at a ratio of 1: 2: 1 at three identification points where impulse responses are continuous. Therefore, the response characteristic for the input {0 ·····} is {0 ········}. In the case of HD DVD, the PR class is PR [1, 2, 2, 2, 1], which appears at a ratio of 1: 2: 2: 2: 1 at five identification points where impulse responses are continuous. It shows that. Now, when the reflected light of the HD DVD is received by a four-divided photodetector and divided into a signal A + signal D and a signal B + signal C, the PR class of the signal A + signal D is PR [1,2,1], the signal B + signal The PR class of C can be regarded as PR [1,2,1] delayed by 2T from the signal A + signal D. That is, the signal A + signal D preceding in time is PR [1, 2, 1, 0, 0], and the signal B + signal C following in time is PR [0, 0, 1, 2, 1]. .., PR [1,2,1,0,0] + PR [0,0,1,2,1] = PR [1,2,2,2,1].

Therefore, a case is assumed in which the signal A + signal D, which is the preceding signal, is delayed by 2T in the delay circuit. In this case, since the PR class of the signal A + signal D is PR [0, 0, 1, 2, 1], the reproduction RF signal obtained by adding all the signals is
PR [0,0,1,2,1] + PR [0,0,1,2,1] = PR [0,0,2,4,2,] = PR [0,0,1,2,1,1] ]
And substantially equal to PR [1,2,1]. In PR [1,2,2,2,1], the signal amplitude of 2T becomes small and difficult to detect due to intersymbol interference. However, if PR [1,2,1] and the class are low, there are three discrimination points. Since it only appears at a ratio of 1: 2: 1, there is little intersymbol interference and a signal amplitude of 2T pit length is detected sufficiently large.

  In this embodiment, the PR class is substantially converted by delaying the preceding signal by a predetermined amount as described above, and the signal amplitude of the 2T pit length which is the shortest pit length can be detected. Although the delay is applied to the preceding signal, the amount of delay is set according to the number of divisions and the degree of the preceding time. In the case of being divided into two in the track direction, it is assumed that the preceding side is advanced by 2T, or the succeeding side is delayed by 2T, and the signal on the preceding side is delayed by 2T. The succeeding signal is output as it is without delay, and the delayed preceding signal is added to the delayed signal without delay. The leading side signal may be output as it is, and the trailing side signal may be advanced by 2T and added. The delay circuit can be composed of an arbitrary delay calculation element. When the RF signal is converted into a digital signal, it may be delayed by a digital delay element.

  This embodiment can be similarly applied not only to HD DVD but also to BD. In the BD, for each recording density, the first generation (23.3 GB compatible): PR [1, 2, 1], the second generation (25 GB compatible): PR [1, 2, 2, 1], the third generation ( 27GB): PR [1,2,2,2,1] etc., for example, the third generation may be processed in the same way as HD DVD, and the dividing method of the photodetector 10a is also applied to the second generation. You can respond by changing.

<First Embodiment>
FIG. 1 shows a configuration block diagram of the reproduction system of the present embodiment. This is a case where an HD DVD having a PR class of PR [1, 2, 2, 2, 1] is reproduced. The pit 6 formed on the track of the optical disk 5 is irradiated with the laser beam 100, and the reflected light is detected by the four-divided photodetector 10a of the optical pickup. The quadrant photodetector 10a includes four photodetectors A to D. The photodetectors A and D are arranged on the leading side in the moving direction of the track 5 (arrow direction in the figure), and the photodetectors B and C are arranged on the trailing side in the moving direction. . When the photodetectors B and C are set as the reference position, the photodetectors A and D are relatively disposed on the leading side. The signals from the photodetectors A and D are added and supplied as an RF1 signal to the amplifier 10b, and the signals from the detectors B and C are added and supplied as an RF2 signal to the amplifier 10b.

  The amplifier 10b amplifies both signals with a gain A, and supplies the amplified signals to a low-pass filter (LPF) and equalizers (EQ) 10c and 10d, respectively.

  The LPF / EQ 10c and the LPF / EQ 10d remove high-frequency noise from the RF1 signal and the RF2 signal, respectively, or slightly boost a specific frequency band to supply them to the A / D 12 and A / D 14, respectively. The LPF / EQ 10c and the LPF / EQ 10d preferably have the same characteristics, and may be a simple LPF or a slight boost characteristic near the highest frequency.

  The A / D 12 and A / D 14 convert the RF1 signal and the RF2 signal into digital signals, respectively. The conversion timing in the A / D 12 and A / D 14 is determined by the clock signal CLK, and the RF1 signal and the RF2 signal are sampled and converted into digital signals at the rising timing of CLK. CLK is generated by the PLL 22 and supplied to the A / D 12 and A / D 14.

  The delay element (digital delay element) 15 delays the digital RF1 signal by 2T and outputs the delayed signal to the adder 16. The delay is performed in synchronization with the clock signal CLK, and CLK is supplied from the PLL 22. On the other hand, the digital RF2 signal is supplied to the adder 16 as it is without being delayed by the delay element 15.

  The adder 16 adds the digital RF1 signal delayed by 2T and the digital RF2 signal not delayed to obtain a reproduction signal. The reproduction signal is adjusted in gain by the AGC 18 and then supplied to the PRML processing unit 48 via the equalizer 46. The PRML processing unit 48 includes a PR equalizer and a Viterbi decoder, and performs Viterbi decoding on the reproduced signal waveform-equalized by the PR equalizer. Here, Viterbi decoding is a code sequence having the smallest error from a sample sequence of a signal equalized by a PR equalizer among all code sequences satisfying a predetermined PR characteristic, that is, a code sequence having the maximum likelihood. It selects and performs decoding according to the selected code sequence. In HD DVD, the PR equalizer assumes PR [1, 2, 2, 2, 1] as the PR characteristic. In this embodiment, the delay side 15 delays the preceding signal by the delay element 15 and then performs the subsequent processing. Therefore, the PR equalizer becomes a low class of PR [1,2,1], so that the PR equalizer performs equalization processing as PR [1,2,1]. The signal from the AGC 18 is supplied to the jitter evaluation circuit 44 via the equalizer 40 and the binarization circuit 42, and the jitter is evaluated. Deviations may be evaluated in addition to jitter. The binarized signal is also supplied to the PLL 22, and a clock CLK is generated. The PLL 22 includes a zero-cross detector 22a that detects a zero-cross point of the reproduction signal from the AGC 18, a phase comparator 22b, a charge pump 22c, a current-voltage converter (IV) 22d, a voltage-controlled oscillator (VCO) 22e, and a 1 / N frequency divider. The clock signal CLK from the VCO 22e is supplied to the A / Ds 12 and 14.

  FIG. 2 shows an eye pattern of PR [1,2,2,2,1], and FIG. 3 shows an eye pattern of PR [1,2,1]. In FIG. 2, the amplitude of the 2T signal is almost 0, but in FIG. 3, the 2T signal amplitude is large and can be easily decoded. In addition, since the jitter of the 2T pit length signal can be evaluated by the jitter evaluation circuit 44, strategy tuning is facilitated.

<Second Embodiment>
FIG. 4 shows a configuration block diagram of the present embodiment. This is a case where HD DVD is played back as in the first embodiment. Photodetector 10a is divided into four in the track direction to form photodetectors E, F, G, and H. When the photo detector H is used as a reference, the photo detectors E, F, and G are relatively arranged on the leading side. The photodetector E is arranged on the most leading side. The RF1 signal from the photodetector E is amplified by the amplifier 10b, noise is removed by the LPF / EQ 10c, converted into a digital signal by the A / D 12a, and then delayed by the delay element 15a. The delay amount is 3T. The RF2 signal from the photodetector F is amplified by the amplifier 10b, noise is removed by the LPF / EQ 10d, converted into a digital signal by the A / D 12b, and then delayed by the delay element 15b. The delay amount is 2T. The RF3 signal from the photodetector G is amplified by the amplifier 10b, denoised by the LPF / EQ 10e, converted into a digital signal by the A / D 12c, and then delayed by the delay element 15c. The amount of delay is T. The RF4 signal from the photodetector H is amplified by the amplifier 10b, noise is removed by the LPF / EQ 10f, converted into a digital signal by the A / D 12d, and then output without delay. Each of the A / D 12a to A / D 12d converts the input RF signal into a digital signal in accordance with the clock signal CLK generated by the PLL 22. The adder 16 adds these four signals and outputs them as a reproduction signal.

  The RF1 signal can be expressed as PR [1, 1, 0, 0, 0] in the PR class. The RF2 signal can be expressed as PR [0, 1, 1, 0, 0]. The RF3 signal can be expressed as PR [0, 0, 1, 1, 0], and the RF4 signal can be expressed as PR [0, 0, 0, 1, 1]. If these are simply added, PR [1,2,2,2,1] is obtained. However, in this embodiment, the RF1 signal is delayed by 3T, the RF2 signal is delayed by 2T, and the RF3 signal is delayed by T. When the RF1 signal is delayed by 3T, PR [0, 0, 0, 1, 1] is obtained, and the RF2 signal is When delayed by 2T, PR [0,0,0,1,1] is obtained, and when the RF3 signal is delayed by T, PR [0,0,0,1,1] is obtained. Becomes PR [0,0,0,4,4], which is substantially equal to PR [1,1]. Therefore, a 2T pit length signal is also detected and decoded with a sufficiently large amplitude.

<Third Embodiment>
The configuration of FIG. 1 can be applied when reproducing a BD of PR [1, 2, 2, 1]. In this case, since the RF1 signal can be regarded as PR [1, 2, 0, 0] and the RF2 signal can be regarded as PR [0, 0, 2, 1], the delay element 15 delays the RF1 signal by 2T. The PR class of the delayed RF1 signal is PR [0, 0, 1, 2], and the signal obtained by adding these by the adder 16 is PR [0, 0, 0, 3, 3], which is substantially PR [1, 1]. Therefore, a 2T pit length signal is also detected and decoded with a sufficiently large amplitude.

<Fourth embodiment>
FIG. 5 shows a configuration block diagram of the present embodiment. This is a case of reproducing the BD of PR [1, 2, 2, 1]. The photo detector 10a is divided into three in the track direction to be photo detectors E, F, and G. When the photo detector G is used as a reference, the photo detectors E and F are relatively disposed on the preceding side. The photodetector E is arranged on the most leading side. The RF1 signal from the photodetector E is amplified by the amplifier 10b, noise is removed by the LPF / EQ 10c, converted into a digital signal by the A / D 12a, and then delayed by the delay element 15a. The delay amount is 2T. The RF2 signal from the photodetector F is amplified by the amplifier 10b, noise is removed by the LPF / EQ 10d, converted into a digital signal by the A / D 12b, and then delayed by the delay element 15b. The amount of delay is T. The RF3 signal from the photodetector G is amplified by the amplifier 10b, denoised by the LPF / EQ 10e, converted into a digital signal by the A / D 12c, and then output without delay. Each of the A / D 12a to A / D 12c converts the input RF signal into a digital signal in accordance with the clock signal CLK generated by the PLL 22. The adder 16 adds these three signals and outputs them as a reproduction signal.

  The RF1 signal can be expressed as PR [1, 1, 0, 0] in the PR class. The RF2 signal can be expressed as PR [0, 1, 1, 0]. The RF3 signal can be expressed as PR [0, 0, 1, 1]. If these are simply added, PR [1,2,2,1] is obtained. However, in this embodiment, the RF1 signal is delayed by 2T and the RF2 signal is delayed by T. When the RF1 signal is delayed by 2T, PR [0, 0, 1, 1] is obtained, and when the RF2 signal is delayed by T, PR [0 , 0, 1, 1], the signal obtained by adding them by the adder 16 becomes PR [0, 0, 3, 3], which is substantially equal to PR [1, 1]. Therefore, a 2T pit length signal is also detected and decoded with a sufficiently large amplitude.

1 is a block diagram showing the configuration of a reproduction system of an optical disc apparatus according to an embodiment. It is an eye pattern figure of PR [1, 2, 2, 2, 1]. It is an eye pattern figure of PR [1, 2, 1]. It is a block diagram of a playback system according to another embodiment. It is a block diagram of a playback system according to another embodiment. It is a block diagram of a photodetector. It is a wave form diagram of a preceding side signal, a succeeding side signal, and a reproduction RF signal.

Explanation of symbols

  5 tracks, 6 pits, 10a photodetector, 15 delay elements.

Claims (5)

A light receiving means that is divided into a plurality of parts in the track direction of the optical disk, photoelectrically converts reflected light from the optical disk by each divided element, and outputs an RF signal;
Delay means for delaying the RF signal of each element preceding in time among the RF signals of each element by a predetermined delay amount corresponding to the number of divisions and the degree of the preceding time;
Adding means for adding the delayed RF signal of each element;
An optical disc apparatus comprising: The apparatus of claim 1.
The light receiving means is divided into two in the track direction,
The delay means delays the RF signal of the preceding element among the RF signals of the elements divided into two by 2T (T is a reference time length). The apparatus of claim 1.
The light receiving means is divided into four in the track direction,
The delay means delays the RF signals of the preceding three elements among the RF signals of the elements divided into four by 3T, 2T, and T (T is a reference time length), respectively. The apparatus of claim 1.
The light receiving means is divided into three in the track direction,
The optical disc apparatus characterized in that the delay means delays the RF signals of the two preceding elements among the RF signals of the elements divided into three by 2T and T (T is a reference time length), respectively. An optical disc apparatus for reproducing data recorded on an optical disc using a PRML method,
A light receiving means that is divided into a plurality of parts in the track direction of the optical disk, photoelectrically converts reflected light from the optical disk by each divided element, and outputs an RF signal;
Delay means for delaying the RF signal of each element preceding in time among the RF signals of each element by a predetermined delay amount corresponding to the number of divisions and the degree of the preceding time;
Adding means for adding the delayed RF signal of each element;
Demodulating means for demodulating by the PRML method using the output of the adding means;
Evaluation means for evaluating the jitter of the reproduction signal using the output of the addition means;
An optical disc apparatus comprising:

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