JP3760825B2 - Optical disk device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk device, and more particularly to a technique for detecting prepits formed on an optical disk.
[0002]
[Prior art]
Conventionally, in an optical disc such as a DVD-R / RW, prepits having address information of an information recording track are formed on a track adjacent to the information track, for example, an outer land adjacent to the groove. The in-plane position of the optical disk is determined by detecting this pre-pit.
[0003]
In general, pre-pits are detected as follows. That is, the return light of the laser beam irradiated to the center of the information recording track is converted into an electric signal by a quadrant photodetector divided in the radial direction and the circumferential direction, and the difference between the two signals from the photodetector divided in the radial direction is converted. Is calculated. Then, the modulation component of the recording power is removed by the difference calculation, and the pre-pit signal included in the difference signal is extracted and decoded.
[0004]
[Problems to be solved by the invention]
However, when the difference between the two signals from the photo detectors divided in the radial direction is calculated, the modulation component of the recording power cannot be completely removed, and particularly remains at the edge portion immediately after the start of recording and immediately after the completion of recording. , Will remain as noise. Moreover, since the laser power is higher at the recording power than at the playback power and the amount of return light at the recording power is also increased, the noise level at the recording power is increased and is about the same as or higher than the pre-pit level at the playback power. Or more. In this case, the noise at the recording power and the prepit signal at the reproduction power cannot be distinguished on the level, and even if the difference signal is binarized by a predetermined threshold and the prepit signal is extracted, It becomes difficult to extract. That is, if you try to remove the noise at the recording power by increasing the threshold, the prepit signal at the playback power is also removed, and if you try to extract the prepit signal at the reproducing power by reducing the threshold, the recording Power noise is also erroneously extracted as a pre-pit signal. Note that since the period during which the recording power is applied is the mark period and the period during which the reproduction power is applied is the space period, it can be said that the above problem is difficult to extract the prepit signal in the space period.
[0005]
On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 2000-31344, a circuit for detecting a prepit in the mark period and a circuit for detecting a prepit in the space period are provided in parallel, and the prepit is detected in each of the mark period and the space period. Although the above problem can be solved, a circuit for generating a gate signal for signal processing in each of the mark period and the space period is required, which complicates the circuit configuration.
[0006]
The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to reliably detect prepit information even in a space period or a period in which a laser beam having a reproduction power is irradiated with a relatively simple configuration. It is an object of the present invention to provide an optical disc apparatus that can perform the above-described process.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an optical disc apparatus that performs recording while detecting prepit information previously formed on an optical disc, and records data by irradiating the optical disc with a laser beam having a recording power. Of the return light into an electrical signal, at least a photodetector divided into two in the radial direction of the optical disc, a gain adjuster for adjusting the gains of the two signals from the two-divided photodetector, and gain-adjusted 2 a limiter for limiting the maximum level of the one of the signals, that Yusuke a calculator for calculating the difference between two signals from the limiter, and an extraction means for extracting the prepit information contained in the difference signal from the arithmetic unit .
[0008]
Here, it is preferable that the limit level of the limiter is a level smaller than the return light level of the recording power and higher than the return light level of the laser light in the space period .
[0009]
A second computing unit that computes a difference between the two signals that have undergone gain adjustment; a second extracting unit that extracts the pre-pit information included in the difference signal from the second computing unit; the extracting unit; It is preferable to further include a means for calculating a logical sum of the two extracting means.
[0010]
As described above, in the optical disc apparatus according to the present invention, after adjusting the gains of two signals from at least a photo detector divided into two in the radial direction of the optical disc, for example, a quad photo detector, the upper limit level of the two signals is limited by the limiter. To do. Limiting the upper limit level by the limiter means, in other words, replacing the return optical signal level at the time of signal recording power with a constant value. As a result, the noise component contained in the return optical signal at the recording power is removed, and by calculating the difference between the two signals, the pre-pit information at the reproduction power (space period) without being affected by the noise at the recording power. Can be extracted.
[0011]
The prepit information at the time of recording power can be calculated by calculating the difference between two signals without limiting the upper limit level as in the conventional case, and detecting the prepit information included in the difference signal. By calculating the logical sum of the prepit information in the space period, the prepit information can be detected in both the mark period and the space period.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings, taking a DVD-R as an optical disk as an example.
[0013]
FIG. 1 is a block diagram showing the configuration of the optical disc apparatus according to this embodiment. The optical disk (DVD-R) 10 is driven to rotate by CAV (or CLV) by a spindle motor 12. Prepits (land prepits: LPP) are formed at predetermined intervals in an area (land) between grooves, which are information recording tracks of the optical disc 10, and the in-plane position of the optical disc 10 is determined by detecting these prepits. Can be identified.
[0014]
The optical pickup 14 is disposed opposite to the optical disc 10 and records data by irradiating the optical disc 10 with a recording power laser beam, and reproduces recorded data by irradiating a laser beam with reproduction power. At the time of recording, the recording data from the controller 20 is modulated by the encoder 18 and further converted into a drive signal by the LD drive unit 16 to drive the laser diode (LD) of the optical pickup 14. More specifically, in the mark period for forming pits, 3T is recorded with a single recording power pulse, and 4T to 14T is recorded with a plurality of recording power pulses (multi-pulse or pulse train). During the space period, laser light of reproduction power (bias power) is irradiated and no pit is formed. At the time of reproduction, the return light amount converted into an electric signal by the four-divided photodetector in the optical pickup 14 is supplied to the RF signal processing unit 22, demodulated by the decoder 24, and then supplied to the controller 20 as reproduction data.
[0015]
The RF signal processing unit 22 includes an amplifier, an equalizer, a binarization unit, a PLL unit, etc., boosts the RF signal, binarizes it, generates a synchronous clock, and outputs it to the decoder 24. The reproduction RF signal is also supplied to the pre-pit detection unit 26.
[0016]
The prepit detection unit 26 detects a signal component of a prepit formed in a land adjacent to the groove (a land adjacent to the outer peripheral side of the groove) included in the reproduction RF signal, and supplies the signal component to the controller 20. The configuration of the prepit detection unit 26 will be further described later.
[0017]
The controller 20 is constituted by a microcomputer or the like, and supplies recording data to the encoder 18 and supplies detected prepit information to the encoder 18. The encoder 18 modulates the recording data and periodically inserts synchronization information based on the pre-pit detection information to supply a data signal to the LD driving unit 16.
[0018]
In addition, there is a servo system that generates a focus error signal and a tracking error signal, and controls focus and tracking by focus servo and tracking servo. However, since this is the same as the conventional one, description thereof is omitted.
[0019]
FIG. 2 schematically shows a recording method of the optical disc 10 in the present embodiment. As described above, the optical disk 10 has prepits 100 formed on the land at predetermined intervals. On the other hand, the data recorded in the groove is divided in advance for each SYNC frame which is an information unit, and one sector is composed of 26 SYNC frames, and one ECC block is composed of 16 sectors. Then, synchronization information (SYNC) 200 for synchronizing each SYNC frame is inserted at the head of each SYNC frame. As the synchronization information SYNC, 14T that is sufficiently longer than the longest 11T that appears in the data modulation portion is used so that the SYNC frame synchronization can be surely obtained. In the DVD-R standard, either a mark or a space can be selected as the 14T SYNC pulse.
[0020]
In FIG. 2, the groove is wobbled (meandered) at a predetermined frequency, which is to detect the rotation speed of the optical disc 10 by detecting the wobble frequency.
[0021]
FIG. 3 schematically shows the relationship between the SYNC frame, the synchronization information (SY), and the prepit. The SYNC frame is roughly divided into an even frame (EVEN frame) and an odd frame (ODD frame), and the pre-pit is usually formed corresponding to the even frame. However, if prepits are arranged at approximately the same position on both lands adjacent to the groove to be recorded, two prepit components will be mixed in the return light. Therefore, shift to odd frames to avoid such interference. Arranged. The wobble frequency is 8 times the SYNC frame frequency, and the pre-pits are arranged so as to be positioned at the vertices of the first three wobbles in one SYNC frame, and the first pre-pit among them is the SYNC indicating the synchronization position. It becomes a pre-pit. The optical disk apparatus can detect the synchronization position by detecting this SYNC pre-pit from the reproduction signal, and records data by assigning 14T of synchronization information (SYNC data) to this synchronization position.
[0022]
FIG. 4 shows the arrangement of the four-divided photodetectors in the optical pickup 14 in relation to the laser spot. The quadrant photodetector is divided into two in the radial direction of the optical disc 10 and into two in the circumferential direction. The photodetectors divided into two in the radial direction are (A and D) and (B and C), and the photodetectors divided in the circumferential direction are (A and B) and (C and D). The photodetectors located on the land side where the land pre-pits (LPP) 100 are formed are (A and D).
[0023]
FIG. 5 shows a block diagram of the pre-pit detector 26 in FIG. The pre-pit detector 26 includes adders 26a and 26b, auto gain controls (AGC) 26c and 26d, limiter amplifiers 26g and 26h, differential amplifiers 26e and 26i, binarizers 26f and 26j, and an OR calculator 26k. Configured.
[0024]
The signals from the detectors A and D of the quadrant photodetector are supplied to the adder 26a. The adder 26a calculates the sum of the two signals and supplies the (A + D) signal to the AGC 26c.
[0025]
On the other hand, the signals from the photodetectors B and C are supplied to the adder 26b. The adder 26b calculates the sum of the two signals and supplies the (B + C) signal to 26d.
[0026]
The AGCs 26c and 26d adjust the gain so that the levels of the (A + D) signal and the (B + C) signal substantially match, and output the result to the differential amplifier 26e. That is, the (A + D) signal is output to the non-inverting input terminal (+), and the (B + C) signal is output to the inverting input terminal (−).
[0027]
The differential amplifier 26e functions as a second arithmetic unit, calculates a difference between the two signals, and outputs an (A + D)-(B + C) signal to the binarizer 26f.
[0028]
The binarizer 26f functions as a second extraction unit, binarizes the (A + D)-(B + C) signal from the differential amplifier 26e with a predetermined threshold, extracts prepit information, and performs an OR operation unit To 26k. The configurations of the adders 26a, 26b, AGCs 26c, 26d, the differential amplifier 26e, and the binarizer 26f are the conventional ones for calculating pre-pit information by calculating a difference between signals from two photodetectors divided in the radial direction. Although it is the same as the circuit, the prepit signal in the mark period can be extracted by adjusting the threshold appropriately (threshold that can remove noise in the mark period), but the prepit signal in the space period can be extracted. It becomes difficult. The reason for this is that, as described above, the laser light is the recording power in the mark period, and the noise level included in the return light quantity is large, which is equal to or higher than the prepit signal level in the space period.
[0029]
Therefore, in addition to the conventional circuit configuration described above, the prepit detection unit 26 in the present embodiment is provided with limiter amplifiers 26g and 26h, a differential amplifier 26i, and a binarizer 26j, which detect prepit information in the space period. . The prepit information in both the mark and space periods is detected by performing a logical OR operation with the prepit information in the mark period from the binarizer 26f.
[0030]
That is, the gain-adjusted (A + D) signal from the AGC 26c is supplied to the differential amplifier 26e and also to the limiter amplifier 26h. The limiter amplifier 26h is an amplifier that limits the upper limit level of the input signal. In other words, when the upper limit value of the input signal exceeds a predetermined upper limit value, the limiter amplifier 26h is replaced with the upper limit value and output. The (A + D) signal whose upper limit level is limited from the limiter amplifier 26h is supplied to the differential amplifier 26i.
[0031]
On the other hand, the gain-adjusted (B + C) signal from the AGC 26d is supplied to the differential amplifier 26e and also to the limiter amplifier 26g. Similarly to the limiter amplifier 26h, the limiter amplifier 26g is an amplifier that limits the upper limit level of the input signal, and the (B + C) signal from which the upper limit level is limited is supplied from the limiter amplifier 26g to the differential amplifier 26i.
[0032]
Note that the upper limit values in the limiter amplifiers 26h and 26g are, for example, a level that is a certain amount larger than the return light level in the space period and lower than the return light level in the recording power. That is, the return light level of the recording power (return light level B after the pit is formed)> the upper limit value> the return light level of the reproduction power. The upper limit values of the two limiter amplifiers 26g and 26h may be the same.
[0033]
The differential amplifier 26i functions as an arithmetic unit, calculates a difference between two signals whose upper limit levels are limited, and outputs an (A + D)-(B + C) signal to the binarizer 26j. Noise and pre-pit signals in the mark period are removed by the limiter amplifiers 26g and 26h. However, since the pre-pit signal in the space period is not limited by the limiter amplifiers 26g and 26h, the modulation component and noise of the recording power are removed by the difference calculation. Thus, only the pre-pit signal remains, and the binarizer 26j can reliably extract the pre-pit signal in the space period without being affected by the noise component in the mark period.
[0034]
The logical sum calculator 26k calculates the logical sum of the two signals and outputs the logical sum to the controller 20. Since the binarizer 26f outputs a prepit signal in the mark period and the binarizer 26j outputs a prepit signal in the space period, the prepits in the mark period and the space period are calculated by calculating the logical sum of the two. Both signals will be detected.
[0035]
The above processing will be described in more detail using a timing chart.
[0036]
FIG. 6 shows signals of the photodetectors A to D. 6A shows a signal from the photo detector A, FIG. 6B shows a signal from the photo detector B, FIG. 6C shows a signal from the photo detector C, and FIG. 6D shows a signal from the photo detector D. During the mark period, the power of the laser light increases to the recording power, so that the signal level of the return light also increases. Since the recording pulse is a multi-pulse, the return optical signal also has a multi-pulse shape. However, for convenience of explanation, the envelope of the actual return optical signal is shown in the figure. Immediately after the recording power irradiation, since the pit is not formed yet, the signal level of the return light also becomes the maximum (level A), and the return light signal level decreases due to diffraction by the pit along with the pit formation, and eventually becomes a constant value (level B). On the other hand, in the space period, since the laser beam with the reproduction power is irradiated, the signal level of the return light becomes a constant value. If the pre-pit signal LPP is present in the mark period, the LPP signal is included in the return optical signal, and the signal level is reduced by the amount of diffraction by the LPP. The same applies to the space period. In the figure, LPPw indicates the LPP component in the mark period, and LPPr indicates the LPP in the space period. The LPP appears arbitrarily in either the mark period or the space period.
[0037]
Since the photodetectors A and D are located on the land side where the pre-pits LPP are formed, LPPw or LPPr appears as a signal whose level decreases, but the signals from the photodetectors B and C are leveled due to the light diffraction phenomenon. Appears as an increasing signal (a signal whose phase is inverted).
[0038]
FIGS. 7A and 7B show the (A + D) signal and the (B + C) signal that have been gain-adjusted by the AGCs 26c and 26d, respectively. Further, (C) shows an output (A + D)-(B + C) signal of the differential amplifier 26e. It will be understood that the noise level in the mark period and the level of the prepit LPPr in the space period are approximately the same, and the prepit LPPw in the mark period can be detected, but it is difficult to detect LPPr.
[0039]
8A and 8B show a signal from the limiter 26h and a signal from the limiter 26g, respectively. In the drawing, the broken line portion indicates that the upper limit level is limited to a constant value by the limiter amplifiers 26h and 26g, and is missing. Noise in the mark period is removed, and LPPr in the space period remains as it is. LPPw in the mark period is also removed in the same manner as noise, but there is no problem because LPPw is detected by the binarizer 26f.
[0040]
9A and 9B show a signal from the differential amplifier 26i and a signal from the binarizer 26j, respectively. By calculating the difference between the two signals, the components and noise accompanying the recording power modulation in the mark period are removed, and only the LPPr in the space period exists. If such a signal is binarized using a predetermined threshold indicated by a one-dot chain line in the figure, only LPPr in the space period can be reliably extracted.
[0041]
FIG. 10 shows signals supplied to the controller 20 from the logical sum calculator 26k. Since the logical sum calculator 26k outputs a logical sum of the mark period LPPw from the binarizer 26f and the space period LPPr from the binarizer 26j, a signal in which LPPw and LPPr are mixed as shown in the figure. Is output. Therefore, even if the LPP exists in either the mark period or the space period, the LPP can be reliably detected.
[0042]
In this embodiment, the LPP in the space period is simply detected by limiting the upper limit level of the signal instead of detecting the LPP by sample-holding the return optical signal in the mark period and the space period, as in the prior art. Therefore, the configuration can be simplified.
[0043]
As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various change is possible.
[0044]
For example, in the present embodiment, the DVD-R has been described as an example, but the present invention can be similarly applied to an arbitrary optical disc (DVD-RW or the like) on which prepits are formed.
[0045]
In this embodiment, a low-pass filter can be provided after the differential amplifier 26i to remove noise, and then binarized by the binarizer 26j.
[0046]
Further, as shown in FIG. 3, since the LPP is located at the top of the wobble, that is, exists in synchronization with the wobble signal, the gate is set using the wobble signal detected to control the rotation speed, and 2 It is also possible to extract the LPPr only in the vicinity of the wobble vertex by the valueizer 26j. The binarizer 26f can also extract the LPPw by setting the gate using the wobble signal.
[0047]
【The invention's effect】
As described above, according to the present invention, the prepit information in the space period can be reliably extracted, and the prepit information can be detected in both the mark and space periods together with the prepit information in the mark period.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical disc apparatus according to an embodiment.
FIG. 2 is an explanatory diagram showing a relationship between a groove, a land, a land pre-pit LPP, and synchronization information.
FIG. 3 is an explanatory diagram showing a relationship between a sync frame and synchronization information.
FIG. 4 is a diagram illustrating the arrangement of a four-divided photo detector.
5 is a configuration block diagram of a pre-pit detection unit in FIG. 1. FIG.
FIG. 6 is a first timing chart according to the embodiment.
FIG. 7 is a timing chart (part 2) in the embodiment.
FIG. 8 is a timing chart (part 3) in the embodiment.
FIG. 9 is a timing chart (part 4) in the embodiment.
FIG. 10 is an explanatory diagram of an output signal from a logical sum calculator in the embodiment.
[Explanation of symbols]
10 optical disk, 12 spindle motor, 14 optical pickup, 16 LD drive unit, 18 encoder, 20 controller, 22 RF signal processing unit, 24 decoder, 26 pre-pit detection unit.

Claims (2)

An optical disc apparatus that performs recording while detecting pre-pit information formed in advance on an optical disc,
A photodetector divided into at least two in the radial direction of the optical disc for converting return light into an electrical signal when data is recorded by irradiating the optical disc with a laser beam of recording power;
A gain adjuster for respectively adjusting the gains of the two signals from the two-divided photodetectors;
A limiter for limiting the upper limit level of the two signals whose gains have been adjusted;
An arithmetic unit for calculating a difference between two signals from the limiter;
Extracting means for extracting the pre-pit information included in the difference signal from the computing unit;
Have a restriction level of the limiter, an optical disk apparatus which is a higher level than the laser light of the return light level less space period than the recording power of the return light level. The apparatus of claim 1, further comprising:
A second computing unit for computing a difference between the two signals whose gains have been adjusted;
Second extraction means for extracting the pre-pit information included in the difference signal from the second computing unit;
Means for calculating a logical sum of the extraction means and the second extraction means;
An optical disc apparatus comprising:

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