JP2000182257A - Method for reproducing information of optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to detect both signals with high reliability by detecting pits or wobbling by controlling tracking without using a tracking error signal in the neighborhood of a pit position or in a pit detecting window, or controlling to decrease a gain of a tracking control system. SOLUTION: Tracking control is carried out without using a tracking error detection signal at a pit position, and in the position not adjoining the pit, wobbling signal is detected by equalizing each output amplitude of each pair of recording marks in a detection output of a photo-detector which is divided into two straight and opposed to one or more pairs of track tangents of an optical pickup. Otherwise, by detecting a pit by dividing plural groups of photo- detectors into two blocks to the track tangent and controlling a gain, it is possible to reduce deterioration of a signal to noise ratio of a pit signal caused by either meandering of tracking by pit or symmetry of a recording mark in a pit part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reproducing information from an optical recording medium having a land having wobbled grooves and pits with high reliability by reproducing wobbles and pits after data recording in the groove. It is about.

[0002]

2. Description of the Related Art Conventionally, an information reproducing method for an optical recording medium such as a DVD having wobble grooves and having pits formed at predetermined intervals in an area between the grooves (for example, see Japanese Patent Application Laid-Open No. 9-326138). Then
The pits are areas on both sides of the groove (referred to as "lands")
The wobbled signal detected from the groove controls the rotation of the optical recording medium, and attempts to detect the position of the recording signal on the optical recording medium based on the pit signal detected from the pit. However, pits or wobbles on an optical recording medium could not be reproduced with high reliability after recording a mark.

Therefore, a technique for detecting a wobble of an optical recording medium with high reliability even after recording the wobble (for example, Japanese Patent Laid-Open No. 5-12 / 1993).
No. 8564). This technology is
When the tilt between the objective lens and the media occurs, or when there is an error in mounting the photodetector of the pickup, an offset occurs in the difference between the photodetector detection outputs divided into two orthogonally and opposingly in the track tangential direction,
Although the S / N ratio deteriorates due to the leakage due to the recording mark on the wobble detection signal after recording, the gain of the photodetector detection output becomes equal based on the output obtained by the difference signal detection means of the two divided photodetectors. By adjusting the gain as described above, the deterioration of the S / N ratio is prevented.

Further, when the position of the laser beam with respect to the photodetector moves due to factors such as temperature, an offset is generated in the difference between the photodetector detection outputs that are divided into two orthogonally and opposingly in the tangential direction of the track, resulting in a wobble detection signal after recording. Leaked by the recording mark on the S
Although the / N ratio deteriorates, in order to reduce the effect of the recording signal, the effect of the recording signal is reduced by the output Rf obtained by adding each of the two divided photodetector outputs, and each photodetector output is normalized. There is also a technique for preventing the deterioration of the S / N ratio by subtracting the output (for example, see Japanese Patent Application Laid-Open No. 6-290462).

In the above-described technique, no measures are taken against pits formed at predetermined intervals in a region between grooves, a focus error, a tracking error, and an optical axis shift due to continuous reproduction.

In general, an optical disk drive driven by a combination of a rotary motor and a gear, which is a method having low rigidity as a seek mechanism, is designed so that an objective lens accurately tracks tracks on an optical disk during continuous reproduction. The seek system on which the pickup is mounted moves with a delay with respect to the movement of the objective lens. At this time, the optical axis of the objective lens and the center of the photodetector are shifted, and an optical axis shift due to seek occurs.

[0007]

A signal is applied to a wobbled groove on an optical recording medium having wobbled grooves and having pits formed at predetermined intervals in a region (referred to as a "land") between the grooves. Upon recording, a recording mark is recorded in the groove.

Originally, if this recording mark is accurately recorded at the center of the groove, and the recording mark is symmetrical with respect to the track center without being affected by the pit portion on the land,
When detecting pits and wobbles during playback after recording, the focus position is set to the optimum position for detecting the pits, there is no track deviation, and the tangential direction between the optical axis of the objective lens and the track of the pickup / photodetector. If the division centers match, the recording mark signal can be canceled by subtracting the output of the photodetector facing the tangential direction of the track of the photodetector.

That is, since the influence of the recording marks can be eliminated, pits and wobbles can be detected with high reliability.

FIG. 6 is a diagram showing an example of the state of a recording mark at a pit position on an optical recording medium and an example of a diffraction image on a photodetector when there is bleeding and tracking error at the pit position of the recording mark. FIG. 7 is a timing chart showing the occurrence of noise when detecting a pit or wobble. FIG. 8 is a diagram showing the configuration of the four-segment photodetector 1 shown in FIG.

In FIG. 6, for the sake of simplicity, FIG. 6A shows a groove (groove) 50 on the optical disk as a straight line without the wobble, and FIG. 6B shows a groove when there is no tracking error. A light spot (indicated by a circle in the drawing) 51 and a recording mark (a black solid portion in the drawing) 52 are shown on the reference numeral 50. FIG. 4C shows a quadrant photodetector (quadrant photo) corresponding to the light spot. The diffraction image 53 (the portion blacked out in the figure) 53 on the diode 1 is shown, and the diffraction image 53 is exaggerated from the actual one for easy understanding.

The diffraction image 53 differs depending on the type of media or the layer structure. Although a typical example of a four-segment photodetector is shown here, a two-segment photodetector or a photodetector with a larger number of divisions may be used depending on a focusing error or tracking error detection method. So that it can be applied.

In FIG. 6, the recording mark 52 is asymmetric with respect to the tangent of the track since there is no heat wall due to the land 55 where the pit (also referred to as "pre-pit") 54 is present. Therefore, the diffraction image 53 based on the recording mark 52 is symmetrical where there are no pits 54 as shown in FIG.

FIG. 3D shows a light spot 5 irradiated onto the groove 50 when there is a tracking error.
1 and a recording mark 52, and (e) shows a diffraction image 53 on the four-segment photodetector 1 corresponding to the light spot. The diffraction image 53 is drawn ignoring the effect of the pits 54.

Accordingly, the diffraction image 53 based on the recording mark 52 becomes similarly asymmetric with respect to the tangent of the track when the tracking error increases. Although not shown, if the focus position is shifted, the diffraction image of the recording mark becomes similarly asymmetric.

Further, when continuous playback is performed,
Deviation between the optical axis of the objective lens and the division line in the track tangent direction of the four-divided photodetector 1 (referred to as "optical axis deviation")
When there is, the diffraction image 53 on the four-divided photodetector 1 shifts in a direction perpendicular to the track tangential direction.

When these phenomena occur, the recording mark signal must be canceled when the prepit or wobble is to be detected based on the subtraction of the photodetector output facing the tangential direction of the track of the four-divided photodetector 1. Can not be done. That is, since the influence of the recording mark cannot be eliminated, the reliability of pit and wobble detection cannot be improved.

In the timing chart shown in FIG. 7, even if the output of the photodetector is subtracted due to the asymmetry of the diffraction image of the recording mark when there is a tracking error, the signal of the recording mark leaks and the pit or wobble is detected. This indicates that noise will occur.

When a plurality of sets of photodetectors are divided into two blocks with respect to the track tangent line, and the amplitude of the recording mark signal of the sum output in each of the divided blocks is subtracted to detect a pit or a wobble, for example, as shown in FIG. In each of the photodetectors A, B, C, and D of the four-split photodetector 1 shown in FIG. 8, the gain is set so that the output sum "A + B" of the photodetectors A and B and the output sum "C + D" of the photodetectors C and D are equal. When the control is performed, the gain of the photodetector facing the tangent to the track is not equal as shown in FIG. 8, and the diffraction image of the recording mark is perpendicular to the tangent to the track as shown by arrow 60 in FIG. When the diffraction images on A and B or C and D are not axisymmetric with respect to the An output amplitude difference is generated between each pair of the recording mark signals (the pair of A and C and the pair of B and D) in the detection output of the photodetector which is divided into two parts orthogonal to and tangent to the tangent line of the set of tracks. Of the output of the photodetectors B and D or "BD" of the output of the photodetectors B and D, the recording mark leaks, and as a result, is recorded in "(A + B)-(C + D)". This causes a mark leakage signal.

Therefore, it is necessary to pay attention to each detection output of one or a plurality of photodetectors which are divided into two orthogonally and opposingly in the track tangential direction. That is, the amplitude is A +
When the gain is controlled so that B = C + D, the gain may vary. In this case, FIG.
When there is a detection light as indicated by 0, an amplitude difference occurs.

Now, regarding noise generated by an asymmetric diffraction image from a recording mark where a pre-pit is present, a certain difference between the gain of A + B = C + D in order to improve the S / N ratio at the moment of detection of the pre-pit. Attach

Further, if the tracking error is large, the asymmetry of the diffraction image from the recording mark becomes large, so it is important to reduce the tracking error. Then, after reducing the tracking error, an AGC circuit may be used to offset the diffraction image generated due to the axial deviation between the optical axis of the objective lens and the division line in the tracking direction on the photodetector due to the movement in the direction perpendicular to the track tangent to the track. . At this time, in the example shown in FIG. 8, not the AGC circuits corresponding to A + B and C + D, but the 4G corresponding to each photodetector.
AGC circuits are required.

Further, once detection is possible, a detection window is provided to reduce erroneous detection. Also, among the three pre-pits 54,
To detect which is the first, first, if a pit is detected, a pre-pit always comes to the next window when indicating the head position of the address information, so if it does not come, judge that it is not the first I do. (This is the pit SYN
C code). Once detection is possible, a detection window is provided to increase reliability. Even if there is a focus error, since the detected light diffraction image has considerable asymmetry, it is necessary to control the focus error so as to be considerably small.

An object of the present invention is to make it possible to detect a pit and a wobble signal with high reliability even when a recording mark exists on a groove.

[0025]

According to the present invention, there is provided an information reproducing apparatus for reproducing information on an optical recording medium having grooves and pits formed at predetermined intervals in a region between the grooves. Provided is a method of detecting a pit or a wobble by performing tracking control without using a tracking error detection signal near a pit position or in a pit detection window, or performing tracking control so as to reduce the gain of a tracking control system.

Also, by accessing a target position on an optical recording medium having a wobbled groove or an optical recording medium having a wobbled groove and having pits formed at predetermined intervals in an area between the grooves. In the information reproducing method for reproducing information, the pits or wobbles may be detected while reproducing the area where the recording mark is recorded, based on a method of detecting a tracking error detection signal from the recording mark.

Further, in the above information reproducing method for an optical recording medium, the tracking error detection signal is
It may be detected by a phase difference method.

Also, by accessing a target position on an optical recording medium having a wobbled groove or an optical recording medium having a wobbled groove and having pits formed at predetermined intervals in an area between the grooves. In the information reproducing method for reproducing information, when the pit or wobble is detected while reproducing the area where the recording mark is recorded based on the method of detecting the offset correction signal of the tracking error signal obtained by the push-pull method from the recording mark. Good.

Further, in the information reproducing method for an optical recording medium as described above, the offset correction may be performed by a phase difference method.

In the above-described information reproducing method for an optical recording medium, the tracking control is performed without using the tracking error detection signal near the pit position or in the pit detection window, or the tracking control is performed so as to reduce the gain of the tracking control system. To detect pits or wobbles.

Further, in an information reproducing method for reproducing information on an optical recording medium having grooves and having pits formed at predetermined intervals in a region between the grooves, when reproducing a region having a recording mark already, One set or a plurality of sets of optical pickups, each detection output amplitude of the photodetector divided into two orthogonally and opposingly in the track tangential direction, or the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent, and each block is divided into two blocks. It is preferable to detect the pits by controlling the gain of the opposing recording mark signal amplitudes of the sum output in the above so as to improve the reliability of the pit detection near the pit detection position.

Also, in an information reproducing method for reproducing information on an optical recording medium having grooves and having pits formed at predetermined intervals in an area between the grooves, an area in which recording marks are already recorded is reproduced. When a pit is detected, only one or a plurality of sets of optical pickups are orthogonally and opposingly divided into two parts in a detection window provided in the vicinity including a pit detection position or a position where pit detection is predicted. Each detection output amplitude,
Alternatively, the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent line, and the opposing recording mark signal amplitudes of the sum output in each block are gained so as to improve the reliability of pit detection near the pit detection position. Is controlled to detect pits.

Furthermore, in an information reproducing method for reproducing information by accessing a target position on an optical recording medium having wobbled grooves and having pits formed at predetermined intervals in an area between the grooves, an information recording method has been described. When reproducing the area where the mark is recorded, except for a pit detection position or a detection window provided in the vicinity including a position where pit detection is predicted, one or more sets of optical pickups are perpendicular to the track tangential direction. The detected output amplitude of the photodetector divided into two opposing portions or the plurality of sets of photodetectors is divided into two blocks with respect to the track tangent line, and the gain is adjusted so that the amplitude of the recording mark signal of the sum output in each block becomes equal. It is preferable to detect the wobble by controlling the setting.

In the information reproducing method for an optical recording medium as described above, one or more sets of optical pickups each have a detection output amplitude of a photodetector which is divided into two parts orthogonally and opposingly in a track tangential direction, or When a set of photodetectors is divided into two blocks with respect to the track tangent line, and the sum of the recording mark signal amplitudes in each block is compared, it is preferable that only one of the comparison targets is gain-controlled to detect pits or wobbles.

Further, in an information reproducing method for reproducing information on an optical recording medium having grooves and having pits formed at predetermined intervals in a region between the grooves, when reproducing the pits, It is preferable to set the upper spot focal position to a position where an optimum pit signal can be obtained.

In the information reproducing method for reproducing information on the optical recording medium as described above, the position where the optimum pit signal is obtained may be obtained based on the relationship between the tracking signal amplitude and the spot focal position. .

Further, by accessing a target position on an optical recording medium having a wobbled groove or an optical recording medium having a wobbled groove and having pits formed at predetermined intervals in an area between the grooves. In the information reproducing method for reproducing information, when the optical axis shift between the objective lens and the photodetector position shifts by a predetermined value or more during continuous reproduction or continuous recording, the seek axis is corrected by driving the seek mechanism. In such a case, the seek mechanism may be driven so as to add an offset in a direction opposite to a direction in which the optical axis deviation during continuous playback becomes larger than when the optical axis shift is zero, thereby performing continuous playback.

According to a first aspect of the present invention, there is provided a method for reproducing information on an optical recording medium, comprising the steps of: reproducing information on an optical recording medium having grooves and having pits formed at predetermined intervals in an area between the grooves; Use a pit detection window that detects the vicinity of the pit position so that the light spot on the groove does not meander due to the offset of the tracking error signal due to the pit that exists asymmetrically to the groove, or a pit detection window that predicts that there is a pit in advance. Tracking control so as not to use the tracking error detection signal in the pit detection window, or tracking control so as to reduce the gain of the tracking control system, so that the diffraction image on the photodetector caused by the tracking error does not become asymmetric. Pits or wobbles can be detected with high reliability. Ukoto can. Further, the present invention is effective not only at the time of reproduction at a place where a recording mark is present, but also at the time of recording or at the time of reproduction of a place without a recording mark.

According to a second aspect of the present invention, there is provided an information reproducing method for an optical recording medium, comprising: an optical recording medium having wobbled grooves; or wobbled grooves, and pits formed at predetermined intervals in a region between the grooves. When detecting pits or wobbles while reproducing information recorded on an optical recording medium, the tracking error is detected by a radial tilt between the objective lens and the optical recording medium in a well-known tracking error detection method, a push-pull method. Since a tracking error occurs due to an offset on the signal and a wobble or pit detection error increases, a push-pull method is not used as the tracking error detection signal to reduce the tracking error, and the tracking error detection signal is directly detected from the recording mark. Method to reduce tracking deviation And detects the pits or wobble Te, can be increased strongly reliability pits or wobble detection in the radial tilt.

In other words, correcting the tracking deviation of the recording mark finally detected on the photodetector is the optimal method for most hindering the influence of the noise caused by the recording mark. In addition, when recording on an optical recording medium, it is determined whether or not an area in which information is recorded (an area where a recording mark is present) is being reproduced, based on a rule of a modulation code in outputting an information reproduction signal (Rf signal). The determination can be made based on whether or not the generated pulse width is equal to or larger than the determined number.

According to a third aspect of the present invention, there is provided a method of reproducing information from an optical recording medium, comprising a phase difference method (DPD) which is strong against radial tilt.
Method) to detect the tracking error detection signal.
For example, a DV that stores information in an array of pits on an optical recording medium
The DPD method is adopted as a tracking detection method when reproducing a D-ROM medium. Since a DVD-type recording / reproducing apparatus often has a DVD-ROM reproducing function, a DPD detecting circuit is usually provided, and if the DPD detecting circuit is also used, cost is reduced. No need to upload.

According to a fourth aspect of the present invention, there is provided a method for reproducing information from an optical recording medium, comprising: reproducing an information-recorded area based on a method of detecting, from a recording mark, an offset correction signal of a tracking error signal obtained by a push-pull method. Since pits or wobbles are detected inside, pits or wobbles that are strong in radial tilt and highly reliable can be detected.

According to a fifth aspect of the present invention, there is provided a method for reproducing information from an optical recording medium, wherein a tracking error signal of both a push-pull signal and a signal obtained by a phase difference method (DPD method) which is strong against radial tilt are directly compared (difference). Pits or wobbles are detected by performing offset correction based on the offset correction signals, and pits or wobbles that are strong in radial tilt and highly reliable can be detected.

According to a sixth aspect of the present invention, there is provided a method for reproducing information from an optical recording medium, wherein tracking control is performed without using a tracking error detection signal near a pit position or in a pit detection window.
Alternatively, since pits or wobbles are detected by performing tracking control so as to reduce the gain of the tracking control system, meandering on the groove can be avoided, and the reliability of pit or wobble detection can be improved.

According to a seventh aspect of the present invention, there is provided a method for reproducing information from an optical recording medium, the method comprising the steps of: forming a groove on the optical recording medium having pits formed at predetermined intervals in a region between the grooves; When reproducing, the detection output amplitude of each of two or more photodetectors orthogonal and opposite to one set or a plurality of sets of track tangents of the optical pickup, or the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent, By detecting the pits by controlling the gain so that the reliability of the pit detection is improved near the pit detection position, the amplitude of the recording mark signal facing each of the sum outputs in each block is detected. The noise can be maximized, and the difference between the amplitudes of the opposing recording mark signals approaches zero. Can be detected Tsu bets, it is possible to prevent the signal-to-noise degradation of the pit signal under the influence of bleeding of the recording mark in the pit positions on the land.

According to the information reproducing method of an optical recording medium of the present invention, when reproducing an area in which a recording mark is already recorded, it is provided near a pit detection position or a position including a position where pit detection is predicted. Only within the detection window
One set or a plurality of sets of optical pickups have respective detection output amplitudes of photodetectors which are orthogonally and opposingly divided into two in the track tangential direction, or the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent, and the sum of each block is calculated. The pits are detected by controlling the gain of the output recording mark signal amplitudes in the vicinity of the pit detection position so as to improve the reliability of the pit detection. The optimum pit detection can be performed in a detection window provided in the vicinity including the position to be detected, and the reliability of the pit detection can be further improved.

According to a ninth aspect of the present invention, there is provided a method for reproducing information from an optical recording medium, wherein the recording marks on the optical recording medium have wobbled grooves and pits are formed at predetermined intervals in an area between the grooves. When reproducing an area in which a pit is detected, except for a detection window provided near a pit detection position or a position including a position where pit detection is predicted, one set or a plurality of sets of optical pickups are orthogonal and opposite to the track tangential direction. Then, the detected output amplitude of the photodetector divided into two or the plurality of sets of photodetectors is divided into two blocks with respect to the track tangent, and the gain is set and controlled so that the recording mark signal amplitude of the sum output in each block becomes equal ( That is, it differs from the detection window provided near the pit detection position or the vicinity including the position where the pit detection is predicted. Since detecting the wobble setting control) and in-can detect pits and the wobble, respectively optimum conditions.

According to a tenth aspect of the present invention, there is provided a method for reproducing information from an optical recording medium, wherein one or a plurality of sets of optical pickups each have a detection output amplitude of a photodetector divided into two parts which are orthogonal to each other in a tangential direction of a track and are divided into two parts. When a set of photodetectors is divided into two blocks with respect to the track tangent and the sum output recording mark signal amplitude in each block is compared, only one of the comparison targets is gain-controlled to detect a pit or wobble. Alternatively, wobble detection reliability can be improved, and the number of circuits for gain control can be reduced, so that cost can be reduced.

According to a method of reproducing information on an optical recording medium according to the present invention, when reproducing pits on an optical recording medium having grooves and pits formed at predetermined intervals in a region between the grooves. Then, the spot focal position on the optical recording medium is set to a position where an optimum pit signal can be obtained.

This is because there is a point where the pit signal amplitude becomes maximum depending on the focal position of the light spot on the optical recording medium,
Since this maximum point is often different from the position where the jitter of the recording mark is minimized or the position where the push-pull tracking error signal is maximized, when reproducing pits, the spot focal position on the optical recording medium must be changed. It is set at the position where the maximum pit signal can be obtained.

Further, since the diffraction image of the recording mark on the photodetector changes depending on the focal position, the quality of the pit signal is better when there is no recording mark than when there is a recording mark, and the detection becomes easier. It is better to adjust the focal position where there is.

For the setting of the focal position, for example, in the case of an optical disk drive, inspection is performed at the time of factory shipment, the setting data is stored in a flash ROM in the apparatus, and the fixed setting data is read and used. .

In the optical disk drive, a recording mark is written in a predetermined area on the medium for adjustment once, pit amplitude data is collected by changing the focal position for the recording mark, and set based on the pit amplitude data. If the data is determined and rewritten, the setting data can be adjusted to the optimum setting data according to the medium actually used.

In the information reproducing method for an optical recording medium according to the twelfth aspect of the present invention, the position where the optimum pit signal is obtained is obtained based on the relationship between the tracking signal amplitude and the spot focal position. The focus position can be quickly obtained. In other words, it takes a lot of time to record many times, and it takes time to find the focal position where the maximum pit amplitude can be obtained without recording. Since the relationship between the focus position where the amplitude of the tracking signal becomes maximum and the focus position where the pit signal becomes maximum is known in advance, if only the maximum position of the amplitude of the tracking error signal is obtained, the pit detection can be performed. The focus position can be determined faster.

Since the relationship between the tracking signal amplitude and the pit signal versus the spot focal position generally has a practical level of correlation, the above-described method is effective. Also,
The tracking error signal is obtained by moving the optical pickup including the objective lens in the seek direction (radial direction).

According to the information reproducing method of an optical recording medium of the present invention, first, an optical recording medium having a wobble groove or a wobble groove, and pits are formed at predetermined intervals in a region between the grooves. When the optical axis shifts due to a seek with respect to the optical recording medium, the diffraction image on the photodetector shifts in a direction perpendicular to the tangential direction of the track.

When such a shift occurs, the recording mark signal cannot be canceled when the prepit or the wobble is detected by subtracting the output from the photodetector facing the tangential direction of the track of the photodetector.

When pits or wobbles are detected as described above, noise due to recording marks is reduced.
Other noise is amplified by the optical axis shift, and eventually the error rate of pit or wobble detection increases in proportion to the axis shift amount.

That is, when there is an axis deviation, the asymmetry on the photodetector increases, and the imbalance of the recording mark signal of the photodetector output is adjusted by controlling the gain. However, the irradiation of the spotlight on the photodetector decreases. The output of the photodetector on the opposite side amplifies the recording mark signal and also amplifies other noise components.

Accordingly, continuous reproduction or continuous reproduction is performed on an optical recording medium having wobbled grooves or an optical recording medium having wobbled grooves and having pits formed at predetermined intervals in an area between the grooves. At the time of reproduction before recording, when the optical axis deviation between the objective lens and the photodetector position is deviated by a predetermined value or more, the optical axis deviation is corrected by driving the seek mechanism. By driving the drive so that an offset is added in the direction opposite to the direction in which it becomes greater than zero and performing continuous reproduction, the signal-to-noise degradation of the wobble signal and the pit signal can be reduced, and the allowable light When the amount of axis deviation is constant, the allowable amount can be increased on both sides from the position where there is no optical axis deviation, and the pit or wobble is theoretically twice as large as the allowable amount. Detection can be performed.

[0061]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a pit and wobble detecting device of an optical disk drive employing the information reproducing method for an optical recording medium according to the present invention.

FIG. 2 is a block diagram showing a configuration of each AGC circuit of FIG. FIG. 3 is a timing chart for explaining a tracking method which is not affected by pits in the pit and wobble detection device shown in FIG.

This pit and wobble detection device is shown in FIG.
As shown in FIG. 1, an optical pickup is provided with a four-division photodetector 1 using a four-division diode, and a laser is emitted from a laser diode (not shown) of an optical disk drive (not shown) to an optical disk (not shown). By irradiating the beam, the reflected light is received by the four-divided photodetector 1.

The optical disk is, for example, a DVD-
R, DVD-RW or the like. On the recording surface of the optical disk, a fixed period of time is provided for controlling the rotation of the optical disk or for generating a writing reference clock, as shown in FIG. Groove with wobble
A pit (also referred to as “pre-pit”) 54 is formed on the land 55 between the grooves 50 to indicate address information and the like.

First, the outputs Ia to Id from the photodetectors (photodiodes) 1a to 1d of the four-split photodetector 1 are supplied to amplifiers (amplifiers A1) 2a and 2a, respectively.
Amplifier (Amplifier B1) 2b, Amplifier (Amplifier C1) 2
c and an amplifier (amplifier D1) 2d.

Thereafter, the outputs from the amplifiers 2a to 2d are respectively supplied to the AGC circuits (AGC circuit-A) 3a, AG
C circuit (AGC circuit-B) 3b, AGC circuit (AGC circuit-C) 3c, and AGC circuit (AGC circuit-D) 3d
Are supplied to a first addition circuit (addition circuit 1) 4a and a second addition circuit (addition circuit 2) 4b.

The difference between the outputs of the AGC circuit 2d and the AGC circuit 2a is obtained by the subtraction circuit (subtraction circuit DA) 5a, and the difference between the outputs of the AGC circuit 2c and the AGC circuit 2b is obtained by the subtraction circuit (subtraction circuit CB) 5b. , A subtraction circuit 5a and a subtraction circuit 5 by an addition circuit (addition circuit LPP) 4c.
Take the sum of the outputs of b.

That is, the light spot on the four-divided photodetector 1 is divided into the photodetectors 1a to 1a facing each other in the tangential track direction on the optical disk.
1d to separately detect the difference "Id-Ia" between the outputs of the photodetectors 1d and 1a facing each other and the difference "Ic-Ib" between the outputs of the photodetectors 1c and 1b, and sum them ("Id + Ic)-( Ia + Id) ", a tracking error signal is obtained. This method is a well-known push-pull method.

The operation of the outputs from the amplifiers 2a to 2d is pushed by a first addition circuit (addition circuit 1) 4a, a second addition circuit (addition circuit 2) 4b, and a first subtraction circuit (subtraction circuit 1) 5c. A signal is obtained.

On the other hand, the detection of pits and wobbles in the area where the recording mark is present is preferably set so that the pit detection is optimum near the pits, and the wobble detection is optimized otherwise. .

However, in the method of inserting information such as an address into the wobble, a sufficiently high signal-to-noise is required for the wobble signal. However, the information such as the address is inserted into the pit, and the wobble is simply written for controlling the optical disc rotation motor. In the method used for clock generation, there is no problem even if the signal-to-noise of the wobble is slightly deteriorated, and rather, high reliability is required for pit detection.

Therefore, the pit and wobble detection device detects pits and wobbles so that pit detection is optimized. The phase shift of the clock is corrected by the pit.

In this pit and wobble detecting device, the photo detectors 1d and 1c are located on the inner circumference of the optical disk (ie, the center of the optical disk), and the pit located on the inner circumference of the optical disk is the address of the groove on the optical disk. Etc. have information.

First, as shown in FIG. 6, there is no tracking error, the light spot 51 runs in the center of the groove 50, and the wobble detection is performed so that the influence of the recording mark 52 on the groove 50 without pits is reduced. For this purpose, each of the AC (AC) AGC circuits 3a to 3c shown in FIG.
When the gain setting control of 3d is performed, a blur 56 occurs in the recording mark 52 in the pit 54. Therefore, in the pit 54, noise based on the recording mark 52 is added to the output from the addition circuit LPP.

Therefore, the gain of each of the AGC circuits 3a to 3d may be changed in advance so that the influence of the bleed 56 generated on the recording mark 52 in the pit 54 is reduced.

As shown in FIG. 6, alternating current (AC) AGC is performed on a groove 50 having no pits 54 in order to detect the wobble without being affected by the recording mark 52.
If the gains of the circuits 3a to 3d are set, the recording marks 52 at the pits 54 are affected by bleeding (portions shaded in the drawing) 56. Therefore, at the pits 54, the recording marks 52 are added to the output from the addition circuit 4c. Noise due to noise.

Therefore, each AG should be preliminarily reduced in the pit 54 so that the influence of the bleed 56 of the recording mark 52 is reduced.
What is necessary is just to change the gain of the C circuits 3a to 3d. That is, as shown in FIG. 2, although the embodiment of the well-known AGC circuit is shown here, each reference voltage Vref in FIG.
May be set in accordance with the above conditions.

This setting may be made either by the optical disk drive by checking the pit detection error and by itself or by fixing it in advance.

First, as shown in FIG. 6, in the pit 54 on the inner peripheral side with respect to the groove, the output from the amplifier 2d is larger than the output from the amplifier 2a with respect to the recording mark amplitude of the recording mark 52. Similarly, the output from the amplifier 2c becomes larger than the output from the amplifier 2b.

Therefore, the gain setting of the AGC circuit is
AGC circuit 3d or AGC circuit
The gain of the circuit 3c may be reduced, or the gain of the AGC circuit 3a or 3b may be increased. This may be performed by setting the reference voltage Vref of the AGC circuit.

In practice, in order to obtain an optimum pit signal-to-noise ratio, the reference voltage Vref is set by the optical disk drive by checking the pit detection error and the signal quality of the wobble, or fixed in advance. It is good to adopt such a method.

As described above, the output from the adder circuit 4c is a signal having a good signal-to-noise pattern for the pits on the inner circumference side with respect to the groove. On the other hand, a pit and a wobble signal on the outer peripheral side are included.

In order to separate the pit and wobble signal, the wobble signal is detected by a band-pass filter 6 which passes only the vicinity of the reproduction frequency band of the wobble signal. Further, only the pit signal is passed by the high-pass filter 7. This output example is shown as a high-pass filter output in FIG.

Further, the pits on the inner circumference side with respect to the groove are signals on the plus side in FIG. That is, it is a pit signal on the inner circumference side of the disc including the above-mentioned groove address information. Therefore, in order to detect only the pit signal including the address information on the inner circumference side with respect to the groove, the first binarization circuit (binarization circuit 1) 8 in FIG.
through a.

In FIG. 1, the pits on both sides of the groove being tracked are output from the high-pass filter 7, so that the spots meander unless this effect is taken into account. Therefore, the high-pass filter 7
Is passed through a full-wave rectifier circuit 9 and input to a second binarization circuit (binarization circuit 2) 8b. Then, the monostable multivibrator 10 is hit based on the signal from the second binarization circuit 8b.

FIG. 3 shows how the signals of the respective parts change in this case.
It was shown to. As shown in FIG. 3 (e), a method of taking a pit component from the push-pull output signal by a low-pass filter is also conceivable. However, a pit signal that is an impulse-like (non-sinusoidal) signal and whose period is not constant is considered as this low-pass signal. It cannot be removed by the filter, and a DC component is inevitably generated. Therefore, when the track pitch becomes narrow in high-density recording, the value becomes a value that cannot be ignored.

In the pit and wobble detecting device, the push-pull output signal is delayed through the delay circuit 11 in FIG. 1, and the output from the delay circuit 11 is supplied to the sample and hold circuit 1.
2 always holds the output from the second binarization circuit 8b.

When there is a pit in the output from the monostable multivibrator 10 indicating the vicinity of the pit,
When the output from the monostable multivibrator 10 is positive, the output from the sample hold circuit 12 is selected, and when the output is negative, the output from the delay circuit 11 is selected to obtain a pit removal signal. FIG. 3 shows how the signal of each part changes in this case.

FIG. 4 is a circuit diagram of a tracking error detection system employed in a DVD-ROM drive.
FIG. 5 is a timing chart of output signals from each unit of the circuit of FIG.

As shown in FIG. 4, this circuit is a circuit known as a phase difference method (DPD method).
The split photodetector 1 and the four amplifiers 2a to 2d are the same as those in FIG. In the timing chart of FIG. 5, the signals A1, B1, C1, and D1 from the amplifier have the recording mark output at a fixed period and the influence of the distortion of the diffraction image due to tracking deviation and the like, for the sake of easy explanation. It is drawn ignoring.

This phase difference method is known as a method in which an offset hardly appears on a tracking error signal due to a disc tilt or the like. In general, this circuit is inserted into a DVD recording / reproducing drive in order to read DVD-ROM media. Therefore, the cost increase by using this circuit is small.

First, as shown in FIG. 1, the DPD signal TV on which the offset due to the disc tilt is hardly applied.
E and the pit removal signal are compared, and an offset on the push-pull signal is detected through a first low-pass filter (low-pass filter 1) 13a which is much lower than the tracking control band but can pass low-frequency components such as disc tilt, and The offset of the pit removal signal S2 in the figure is removed by the addition circuit (addition circuit 3) 4d.

In order to remove signals outside the band required for tracking control, there is no meandering due to the influence of pits through the second low-pass filter (low-pass filter 2) 13b, and there is little tracking error due to the tilt of the disk or the like. The signal S1 is obtained.

In this embodiment, the accuracy is further improved by removing the influence of the pit meandering from the DPD signal TVE in the same manner as described above.

Further, when pits or wobbles are reproduced in an area having a recording mark, only the DPD signal TVE may be used, and a tracking error signal may be formed by removing the influence of meandering in the same manner as described above.

This method uses a push-pull output when reproducing a place where there is no recording mark at the time of recording, and a DPD only at a place where there is a recording mark when actually recording.
Use signals. The method for detecting the presence or absence of a recording mark is preferably performed by the method described above.

In this embodiment, a plurality of functions (corresponding to the invention described in each claim) for solving the above-mentioned problems are provided, but they are trade-offs (necessary functions, It may be arbitrarily selected according to cost or the like. Further, in this embodiment, the tracking signal is delayed, but the phase delay of the control system due to this delay is slight and is at a level that can be sufficiently corrected.

In this way, tracking control is performed without using the tracking error detection signal at the pit position, and at a place where no pits are adjacent, the optical pickup directly or opposes the tangent of one or more sets of tracks. The output amplitude of each set of recording mark signals in the detection output of the photodetector divided into two is equalized, all the output amplitudes are equalized, or the plurality of sets of photodetectors are two blocks with respect to the track tangent. The sum of each of the divided blocks is taken, and the sum is detected so as to make each sum equal, and a wobble signal is detected. Output of each set of recording mark signals in the photodetector detection output divided into two parts. Or the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent, and the sum of the divided blocks is gain-controlled so that pit detection is optimized to detect pits. In addition, it is possible to reduce the deterioration of the signal-to-noise of the pit signal due to the meandering of the tracking by the pit and the deviation of the symmetry of the recording mark in the pit portion.

Further, by performing focusing control at a position where pit detection is optimal based on the line symmetry of the diffraction image on the photodetector and the pit amplitude, the signal-to-noise degradation of the wobble signal and pit signal due to the focusing position is reduced. Can be prevented.

Further, at the time of continuous reproduction or reproduction until continuous recording, the optical axis deviation between the objective lens and the photodetector position gradually increases. When the deviation exceeds a certain value, the seek mechanism is driven to reduce the axis deviation. When correcting, the wobble signal and the pit signal are driven by driving the seek mechanism so that the offset is added in the direction opposite to the direction in which the optical axis deviation during continuous playback becomes larger than when it is zero, and performing continuous playback. Signal to noise degradation can be reduced.

The tracking error signal is delayed in order to avoid the influence on the docking error signal in the vicinity of the pit, and a signal before a certain time is used as the tracking error signal in the vicinity of the pit position. The effects can be avoided.

Further, at the time of recording mark reproduction, the occurrence of tracking offset can be reduced by using a phase difference method that is strong against the tilt between the objective lens and the medium.

Further, by determining the gain of each AGC circuit so that the signal-to-noise ratio of the pit signal in the vicinity of the pit position is optimized, the reliability of pit detection can be improved. Further, when a pit is detected, the reliability of the pit detection can be increased by setting the focus position on the optical recording medium at a position where the error rate of the pit detection is minimized.

In the above-described embodiment, description of a part related to focus and seek, which is a known technique, is omitted.

The pit and wobble detection device performs tracking control without using the tracking error detection signal at the pit position to eliminate the influence of tracking wobbles due to pits and to cause a tracking error due to tilt. In addition, a tracking error signal or an offset correction signal is generated from a recording mark to reduce its influence.

In a group in which pits are not adjacent to each other, the respective output amplitudes of the respective sets of recording mark signals in the detection output of the photodetector divided into two parts which are orthogonal to and opposite to one or more sets of track tangents of the optical pickup are equal. Or equalize all the output amplitudes, or divide the plurality of sets of photodetectors into two blocks with respect to the track tangent line, take the sum of the divided blocks, and make them equal. Detects the wobble signal with high reliability without detecting the influence of the recording mark, and detects the photodetector in which the pit is divided into two parts in the adjacent groove, which are orthogonal to and opposite to one or more sets of track tangents of the optical pickup. The magnitude of each output of each set of record mark signals at the output,
Alternatively, the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent, and the sum of the divided blocks is gain-controlled so that pit detection is optimized to eliminate the influence of recording marks.

Therefore, it is possible to reduce the deterioration of the signal-to-noise of the pit signal due to the deviation of the symmetry of the recording mark in the pit portion for pit detection.

Further, focusing control is performed at a position where pit detection is optimal based on the line symmetry of the diffraction image on the photodetector and the pit amplitude, thereby improving the signal-to-noise ratio of the wobble signal and the pit signal.

Then, in a mode other than the recording mode of continuous recording, or in continuous reproduction, when the optical axis deviation is corrected by the seek mechanism in order to reduce the signal-to-noise deterioration of the wobble signal and the pit signal, continuous reproduction is performed. The wobble signal and the pit signal are generated by driving the seek mechanism so that the offset is applied in the direction opposite to the direction in which the optical axis deviation becomes larger than when the optical axis deviation is zero. It reduces noise degradation.

[0110]

As described above, according to the information reproducing method for an optical recording medium according to the present invention, the signal-to-noise can be increased by increasing the pit signal. In addition, pits and wobble signals can always be detected with high reliability regardless of whether or not there is a recording mark on the groove.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a pit and wobble detection device of an optical disk drive employing a method for reproducing information from an optical recording medium according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of each AGC circuit of FIG. 1;

FIG. 3 is a timing chart for explaining a tracking method that is not affected by pits in the pit and wobble detection device shown in FIG.

FIG. 4 is a circuit diagram of a tracking error detection method employed in a DVD-ROM drive.

FIG. 5 is a timing chart of output signals from each section of the circuit of FIG. 4;

FIG. 6 is a diagram showing an example of a state of a recording mark at a pit position on an optical recording medium, and an example of a diffraction image on a photodetector when there is bleeding and a tracking error at the pit position of the recording mark.

FIG. 7 is a timing chart showing the occurrence of noise when a pit or wobble is detected.

FIG. 8 is a diagram showing a configuration of a four-segment photodetector 1 shown in FIG.

[Explanation of symbols]

 1: 4-split photodetector 2: Amplifier 3: AGC circuit 4: Adder circuit 5: Subtractor circuit 6: Band pass filter 7: High pass filter 8: Binarization circuit 9: Full-wave rectifier circuit 10: Monostable multivibrator 11: Delay Circuit 12: Sample hold circuit 13: Low pass filter 14: Inverter 50: Groove (groove) 51: Light spot 52: Recording mark 53: Diffraction image 54: Pit 55: Land 56: Bleed

Claims (13)

[Claims] 1. An information reproducing method for reproducing information on an optical recording medium having grooves and having pits formed at predetermined intervals in a region between the grooves, wherein a tracking error near a pit position or a pit detection window is provided. An information reproducing method for an optical recording medium, wherein a pit or a wobble is detected by performing tracking control without using a detection signal or performing tracking control so as to reduce a gain of the tracking control system. 2. Accessing a target position on an optical recording medium having a wobbled groove or an optical recording medium having a wobbled groove and having pits formed at predetermined intervals in a region between the grooves. An information reproducing method for reproducing information, wherein the pit or the wobble is detected while reproducing the area where the recording mark is recorded based on a method of detecting a tracking error detection signal from a recording mark. Information reproduction method. 3. The information reproducing method for an optical recording medium according to claim 2, wherein the tracking error detection signal is detected by a phase difference method. 4. Accessing a target position on an optical recording medium having a wobbled groove or an optical recording medium having a wobbled groove and having pits formed at predetermined intervals in an area between the grooves. In the information reproducing method for reproducing information, the pit or wobble is detected while reproducing the area where the recording mark is recorded based on a method of detecting an offset correction signal of a tracking error signal obtained by a push-pull method from the recording mark. An information reproducing method for an optical recording medium, comprising: 5. The information reproducing method for an optical recording medium according to claim 4, wherein the offset correction is performed by a phase difference method. 6. The information reproducing method for an optical recording medium according to claim 2, wherein the tracking control is performed without using a tracking error detection signal near a pit position or in a pit detection window. An information reproducing method for an optical recording medium, wherein a pit or a wobble is detected by performing tracking control so as to reduce a system gain. 7. An information reproducing method for reproducing information on an optical recording medium having grooves and having pits formed at predetermined intervals in a region between the grooves. One set or a plurality of sets of optical pickups, each detection output amplitude of a photodetector which is orthogonally and opposingly divided into two in a track tangential direction, or the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent, and each block is divided into two blocks. The method according to claim 1, wherein the pits are detected by controlling the gains of the mutually opposite recording mark signal amplitudes in the vicinity of the pit detection position so as to improve the reliability of the pit detection. 8. An information reproducing method for reproducing information on an optical recording medium having grooves and having pits formed at predetermined intervals in an area between the grooves, wherein an area in which a recording mark is already recorded is reproduced. When a pit is detected, only one or a plurality of sets of optical pickups are orthogonally and opposingly divided into two parts in a detection window provided in the vicinity including a pit detection position or a position where pit detection is predicted. , Or the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent, and the opposed recording mark signal amplitudes of the sum output in each block are determined by the reliability of pit detection near the pit detection position. Pit detection by controlling gain so as to improve readability of optical recording medium . 9. An information reproducing method for reproducing information by accessing a target position on an optical recording medium having wobbled grooves and having pits formed at predetermined intervals in an area between the grooves, wherein the information has been recorded. When reproducing the area where the mark is recorded, except for a pit detection position or a detection window provided in the vicinity including a position where pit detection is predicted, one or more sets of optical pickups are perpendicular to the track tangential direction. Each detection output amplitude of the photodetector divided into two opposing parts,
Alternatively, the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent line, and a wobble is detected by setting and controlling a gain so that the amplitude of a recording mark signal of a sum output in each block becomes equal. A method for reproducing information from a recording medium. 10. The method for reproducing information from an optical recording medium according to claim 7, wherein one or a plurality of sets of optical pickups are divided into two sections which are orthogonal to and traverse in a track tangential direction. Each of the detected output amplitudes or the plurality of sets of photodetectors are divided into two blocks with respect to the track tangent line, and when comparing the amplitude of the recording mark signal of the sum output in each block, gain control is performed on only one of the comparison targets. Pits or wobbles for detecting information on an optical recording medium. 11. An information reproducing method for reproducing information on an optical recording medium having grooves and having pits formed at predetermined intervals in a region between the grooves, wherein the pits are reproduced when the pits are reproduced. An information reproducing method for an optical recording medium, wherein an upper spot focal position is set to a position where an optimum pit signal is obtained. 12. The information reproducing method for reproducing information on an optical recording medium according to claim 11, wherein a position where the optimum pit signal is obtained is obtained based on a relationship between a tracking signal amplitude and a spot focal position. An information reproducing method for an optical recording medium, comprising: 13. An optical recording medium having a wobbled groove, or an optical recording medium having a wobbled groove,
In an information reproducing method for reproducing information by accessing a target position on an optical recording medium in which pits are formed at predetermined intervals in an area between the grooves, an objective lens and a photodetector are used during continuous reproduction or until continuous recording. When correcting the optical axis shift by driving the seek mechanism when the optical axis shift of the position is shifted by a predetermined value or more, the seek mechanism becomes larger than when the optical axis shift during continuous reproduction is zero. A method for reproducing information on an optical recording medium, wherein the information is reproduced continuously by driving so as to add an offset in a direction opposite to the direction.