JP2001134945A - Optical disc information reproducing apparatus and method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an optical information reproducing apparatus and method capable of compatible reproduction of two types of optical disks with a simple configuration. In an information reproducing apparatus for reproducing an optical disk having a first recording density and an optical disk having a second recording density lower than the first recording density, a light source mainly includes a plurality of adjacent tracks formed on the optical disk. Irradiate the beam and the sub-beam. Here, the main beam has a dimension in the track tangential direction corresponding to the resolution of the optical disk of the first recording density, and has a shape elongated in the track perpendicular direction of the optical disk. The light detecting element detects reflected light of the main beam and the sub-beam from the optical disk surface, respectively, and reproduces information of the optical disk based on the detection signal. Here, the crosstalk component from the adjacent track included in the signal reproduced from the reflected light of the main beam is canceled using the signal reproduced from the reflected light of the sub beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing apparatus capable of reproducing information recorded on an optical recording medium at a high density and having a function compatible with information recorded at a low density. is there.

[0002]

2. Description of the Related Art In recent years, DVDs (digital video discs) for providing high quality digital video and audio and optical disc apparatuses for reproducing the DVDs, so-called players, have been remarkably popularized. However, the recent spread of DVD players is simply D
Not only due to the high quality of VD, but many of them are compatible with conventional media, ie CDs (Compact Discs).
It is a great place that guarantees the reproduction of music. A low-density optical disk (for example, CD) using an upper optical disk device corresponding to an optical disk (for example, DVD) recorded at high density
Playing at first glance seems easy. However, since the pit marks formed on the optical disk are designed to be optimal for the shape of the laser beam spot irradiated on the pit marks, even if the density is low, it is necessary to reproduce those that do not meet the optimal conditions. Various issues arise.

The most typical example is a so-called folding phenomenon that occurs when a low-density recording pit is reproduced with a minute laser beam spot emitted from a high-resolution pickup. Digital video / audio information is preliminarily formed on the optical disc in the form of pits having irregularities, but a film (aluminum, gold, etc.) of the same reflectance is formed on the entire surface of the optical disc (for example, CD) regardless of whether it is a pit or not. )
Has been deposited. The information can be identified even if the reflectance is the same because the diffraction effect by the pit edge is used. That is, the width of the pit is formed to be about half the laser beam spot diameter so that a part of the irradiated laser beam is diffracted and scattered by the edge of the pit and does not enter the photodetector of the optical head. I have. However, when trying to reproduce the pits using a high-resolution pickup corresponding to an optical disk (for example, DVD) with a higher density than this optical disk, most of the laser beam spots are inside the uneven pits because the laser beam spot is very small. Is irradiated. For this reason, sufficient diffraction and scattering by the edge is not performed, and as a result, reflected light increases during pit reproduction. This is a so-called folding phenomenon. Here, it is assumed that the spherical aberration due to the difference in the base material thickness between both disks (for example, CD and DVD) has been solved by some means.

[0004]

Therefore, in order to reproduce two types of optical disks, a method has been proposed in which a laser beam spot is enlarged by providing an aperture at the time of low-density reproduction, for example, as disclosed in Japanese Patent Application Laid-Open No. H8-102079. ing. However, this method requires expensive optical elements such as a nonlinear optical filter. Also, Japanese Patent Application Laid-Open No. 9-1858
As disclosed in Japanese Patent Application Laid-Open No. 33-208 or Japanese Patent Application Laid-Open No. 10-208276, a method of switching lenses having different NAs has been proposed. However, when switching lenses, the structure of the pickup becomes complicated. Further, a method of enlarging a laser beam spot by limiting an aperture using a hologram or the like has been proposed. The utilization efficiency of the laser beam is reduced due to the diffraction loss due to the hologram.

An object of the present invention is to provide an optical information reproducing apparatus and method capable of compatible reproduction of two types of optical disks with a simple configuration.

[0006]

An optical information reproducing apparatus according to the present invention is an information reproducing apparatus for reproducing an optical disk having a first recording density and an optical disk having a second recording density lower than the first recording density. A light source for irradiating a plurality of adjacent tracks formed on the optical disk with a main beam and a sub beam, and a photodetector for detecting reflected light of the main beam and the sub beam from the optical disk surface irradiated by the light source, respectively. And a reproducing unit for reproducing information on the optical disk based on a signal from the photodetector. Here, the main beam generated by the light source has a dimension in the track tangent direction corresponding to the resolution of the optical disk of the first recording density, and has a shape elongated in the track perpendicular direction of the optical disk. Further, the reproducing unit includes a first canceling unit that cancels a crosstalk component from an adjacent track included in a signal reproduced from the reflected light of the main beam using a signal reproduced from the reflected light of the sub beam. . In this optical information reproducing apparatus, for example, the ratio of the major axis to the minor axis of the main beam is 1.2 or more and 2.0 or less. In this optical information reproducing apparatus, for example, the reproducing section reproduces information recorded on the optical disk having the first recording density by using the first canceling means using a main beam and a sub beam, The information recorded on the optical disk of the second recording density is reproduced using only the main beam. In this optical information reproducing apparatus, for example, the ratio of the width of a pit forming information on an optical disk of a first recording density to the width of a pit forming information on an optical disk of a second recording density is 1.5 to 2.0. It is.

The optical information reproducing apparatus further includes a tracking control section for controlling the tracking of the optical head having the light source by using a tracking error signal generated based on an output signal from the light detecting element. The light source irradiates a main beam and two sub-beams to the optical disc, and the tracking control unit divides the reflected light of the main beam when reproducing information recorded on the optical disc having the first recording density. A tracking error signal is generated from the mutual phase difference between the signals received by the photodetector and the reflected light of the sub-beam is received by the photodetector when reproducing information recorded on the optical disc of the second recording density. Tracking error signal generating means for generating a tracking error signal from the signal obtained as a result. The optical information reproducing apparatus further includes a tracking control unit that controls the tracking of the light source by a tracking error signal generated based on an output signal from the photodetector. Here, the light source irradiates a main beam and two sub-beams to a plurality of tracks adjacent to each other on an optical disk surface having a track groove, and the tracking control unit generates a main beam and a reflected beam of the main beam. A push-pull tracking error signal generating means for generating a push-pull tracking error signal; and a crosstalk component from an adjacent track included in the push-pull tracking error signal obtained by the push-pull tracking error signal generating means, And a second canceling means for canceling by using.

In this optical information reproducing apparatus, preferably, in the optical information reproduction of an optical disk having identification marks formed at predetermined intervals on a track, the first canceling means includes a first light source irradiated by the light source. Delay means for giving a relative time difference between the reproduced signal by the beam and the reproduced signal by the second beam, and the second light emitted by the light source after the first identification mark is detected by the first beam in an arbitrary track. To jump to the above track,
A time measuring means for measuring a time until the second identification mark is detected by the second beam; and a difference between the time measurement value and a time interval determined from the first and second identification mark intervals. And delay amount determining means for determining the delay amount of the delay means accordingly. Note that this delay amount is determined by
Generally, it can be adopted in a three-beam crosstalk canceller. In this optical information reproducing apparatus, for example, the delay means sets the delay amount with the clock cycle as one unit. In this optical information reproducing apparatus, for example, the delay means has a function of sequentially transmitting a signal in accordance with a clock, and the clock is generated at least in synchronization with a reproduced signal obtained by the main beam.

According to the optical information reproducing method of the present invention, in the optical information reproducing of an optical disk in which identification marks are formed at predetermined intervals on a track, a main beam and a sub-beam are provided on a plurality of adjacent tracks formed on the optical disk. To correct the time difference between the reproduction signal by the main beam and the reproduction signal by the sub-beam to cancel the crosstalk between tracks mixed in the main beam by using the sub-beam to obtain the reproduction signal by the main beam. This is an optical information reproducing method. here,
The crosstalk between tracks is performed by irradiating a first beam on a first identification mark formed on an arbitrary track, and after a track jump, on the track at a predetermined interval with respect to the first identification mark. The second mark provided is irradiated with a second beam, and a difference between a time interval at which the first and second identification marks are detected by the respective beams and a time interval determined from the predetermined interval is determined. The time difference is corrected and canceled accordingly. In this optical information reproducing method, for example, the time interval is measured using a clock generated in synchronization with a signal obtained by reproducing a group of information recorded in advance on an optical disk. In this optical information reproducing method,
For example, the time difference is corrected using one cycle of a clock generated in synchronization with a signal obtained by reproducing a group of information recorded in advance on an optical disk as one correction unit.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference symbols indicate the same or equivalent ones. (Embodiment 1) FIG. 1 is a block diagram of an optical disk device according to Embodiment 1 of the present invention. This optical disk apparatus reproduces two types of optical disks of high density and low density (for example, DVD and CD). In FIG. 1, an optical disc 100 is rotated by a spindle motor (not shown). The laser light source 1, the diffraction grating 2, the half mirror 3, the objective lens 4, the photodetector 5 and the actuator 24 constitute an optical head that is moved on the optical disc 100 by the tracking control unit 25. A laser beam emitted from a laser light source 1 is split into three beams by a diffraction grating 2 and then passed through a half mirror 3 into an objective lens 4.
To generate three beam spots L0 (main spot), L1 and L2 (sub-spots) on the optical disc 100. The reflected light of these beams from the optical disk 100 again enters the photodetector 5 via the objective lens 4 and the half mirror 3. The main spot L0 is a photo element 5a, 5b, 5c,
It is divided into four by 5d, and each is output as an electric signal. These output signals are combined by the adder 10, become a reproduction signal HF through the switch 15, and are supplied to the reproduction unit 28 that reproduces optical information.

Here, the characteristic feature is that the optical disc 100
Is formed in an elliptical shape that is long in the direction perpendicular to the track. The dimension of the beam spot in the track tangential direction is set according to the resolution of a high-density optical disk. The reason for this shape will be described with reference to FIG. Generally, the shape of a beam spot applied to an optical disk is substantially circular as shown in FIG.
Since both sides of the beam are diffracted and scattered at the edge of the pit P1, a part of the reflected light does not reach the photodetector, so that a reproduced signal HFA as shown is obtained. However, when trying to reproduce the pit mark P2 recorded at a low density by using this, since the beam spot irradiates the inside of the pit P2 as shown in FIG. No effect is obtained and the reproduction signal H
In the FB, a so-called turn-back occurs as shown. Therefore, as shown in FIG. 2C, if the shape of the beam spot is set to be an ellipse long in the direction perpendicular to the track, the edge of the low-density pit P2 can be sufficiently diffracted, so that the folded back of the reproduction signal HF is improved. You.

As a means for forming the beam into an elliptical shape, for example, as shown in FIG. 3, a laser diode is used for the laser emission source 1, and the elliptical beam is used as it is, or not particularly shown. However, there is a method using an elliptical correction optical system having a weak angular magnification that weakens the ellipticity somewhat. Assuming that the ratio of the width of the high density pit P1 to the width of the low density pit P2 is about 1.5 to 2.0,
It is desirable that the ratio of the length (Lrad) of the beam spot on the recording surface of the optical disc 100 in the direction perpendicular to the track to the length (Ltan) in the tangential direction is 1.2 ≦ Lrad / Ltan ≦ 1.5 (1). The basis of the lower limit of 1.2 in the equation (1) is a beam width at which a minimum amount of diffracted light can be obtained so as not to cause significant folding, and the basis of the upper limit of 1.5 is that the influence of crosstalk from an adjacent track is allowable. The maximum beam width possible.

The reason why the elliptical shape is long only in the direction perpendicular to the track is to prevent the resolution in the direction tangential to the track from being lowered. Therefore, even if information recorded at a high density is reproduced by an elliptical beam, the degree of deterioration of the reproduced signal due to code interference from an adjacent pit mark is almost the same as in the related art. However, even if the elliptical shape is within the range of the expression (1), the reproduction signal may slightly deteriorate due to the influence of crosstalk from an adjacent track. Therefore, in the present embodiment, in order to eliminate the influence of the crosstalk, a crosstalk canceling process using the sub beams LL and L2 is performed. That is, the sub beams L1, L
2 are located on both tracks next to each other,
The output signals of the photoelements 5e and 5f, into which the respective sub-beam reflected lights enter, are multiplied by appropriate constants K1 and K2 by the variable gain amplifiers 11 and 12, and then added to the adder 1.
The signals are added to each other by 3 and finally subtracted from the signal of the main beam by the subtractor 14 and output to the reproducing unit 28 as the reproduced signal HF via the switch 15. Constant K
If L and K2 are properly selected, the crosstalk components from both adjacent tracks can be completely removed.

The switch 15 selects whether or not to output a signal after the above-described crosstalk cancellation processing, based on the signal K3. When reproducing information on a low-density recording medium, the output of the adder 10 is selected. Should be output as it is. The type of the optical disk 100 is identified by an optical disk identification unit (not shown), and the result is sent to the switch 15 as a signal K3.

In FIG. 1, the sub-beams L1, L2
In the crosstalk canceling process using the reflected light, the output signals of the photoelements 5e and 5f are directly multiplied and added / subtracted. However, due to the design of the optical system, the main beam L0 and the sub beam L0
1, L2 may need to be irradiated separately in the track tangential direction. In such a case, delay adjustment (time difference correction) for correcting the mutual beam delay is required before the addition / subtraction processing. A specific method of this delay adjustment will be described later as a third embodiment.

Next, tracking error detection will be described. In the optical disk device of the present embodiment, when reproducing a high-density signal, a phase difference detection method suitable for a high-density medium is used. That is, the main beam reflected light is divided into four by the photo elements 5a, 5b, 5c, and 5d,
Each is output as an electric signal. An element pair (photo element 5a) arranged diagonally
And 5c and photo elements 5b and 5d)
Are binarized by comparators 16 and 17, respectively, the mutual phase is detected by a phase comparator 6, and after smoothing by a low-pass filter 7,
The signal is output as a tracking error signal TE via the switch 9. The tracking control unit 25 moves the optical head in the radial direction, and controls tracking of the beam based on the tracking error signal TE. The track jump drive means 26 controls the actuator 24 that moves the position of the objective lens 4 to perform a track jump.

Even when reproducing a low-density signal,
This phase difference detection method can be used. However, if the track pitch is still wider with respect to the elliptical beam, a no-signal area is formed between the track and the adjacent track, and noise may be added to the phase difference tracking error signal. That is, the comparator 16,
17 operates with a signal having a noise level in a no-signal region, and a phase difference between noise pulses may be output as a false tracking error signal. Therefore, in the present embodiment, the sub-beams L1 and L2 are used as cross beams for canceling crosstalk during reproduction of a high-density signal, and the sub-beams L1 and L2 are used as sub-beams for detecting a so-called three-beam tracking error signal during reproduction of a low-density signal. It can be used (Fig. 4). That is, the photo elements 5e, 5
The output signal of f becomes a difference signal by the difference calculator 8 and
It is output as a beam tracking error signal. The switch 9 switches between the phase difference tracking error signal and the three-beam tracking error signal.

Incidentally, the intensity of the sub-beam in the present embodiment is sufficient if it is possible to secure an SN ratio sufficient to remove weak crosstalk from an adjacent track.
It is sufficient that each is about 10% of the main beam. In other words, the beam from the laser light source 1 is split into sub-beams by the diffraction grating 2, and the light loss of the main beam due to this is about 20%. When a conventional hologram is used (the light loss is about 40 to 50%) Less than in Further, according to the present embodiment, as shown in FIG. 3, since an originally elliptical laser beam passes through the objective lens 4 in almost the same form in order to obtain an elliptical beam, a so-called aperture by the objective lens is used. The transmission efficiency from the laser light source 1 to the optical disk 100 is improved, with less "blur".

(Embodiment 2) An optical disk apparatus according to Embodiment 2 of the present invention will be described below. FIG. 5 is a block diagram of the optical disk device. In FIG. 5, a laser light source 1, a diffraction grating 2, a half mirror 3, a photodetector 5, variable gain amplifiers 11, 12, an adder 10, an adder 13, a subtractor 14, and a switch 15 are equivalent to those shown in FIG. Has functions.

A feature of this optical disk device is that the laser light source 1 is first made to emit a pulse by the modulator 201, and information is recorded on the optical disk 200 by the laser pulse at this time. Also, the photo element 5a
A so-called push-pull tracking error signal PTE is generated using the difference calculator 19 from the outputs of the first and second elements 5b and the outputs of the photoelements 5c and 5d. Further, a difference signal is generated by the difference calculator 18 from the light receiving signals of the sub-beams (outputs of the photo elements 5e and 5f), and thereby the push-pull tracking error signal PTE is corrected by the subtractor 20.

A groove (groove) as shown in FIG. 6 is formed in advance on the optical disc 200, and information is recorded while the laser beam tracks thereon. In this case, the tracking error signal is detected by using a so-called push-pull method that detects a difference in intensity of light diffracted and scattered by an edge of the groove in a direction perpendicular to the track. However, in the case of the push-pull system, an offset due to an imbalance in light amount is likely to occur, and if an off-track occurs due to this, there is a problem that information is not recorded at the track center. For example, as shown in FIG. 6, when information is recorded in the groove G0 using the main beam L0, information is recorded in the adjacent groove G1 and information is not recorded in the groove G2 on the opposite side. And the crosstalk from both causes imbalance in the amount of reflected light. That is, the groove G1 side is darkly reflected, and as a result, the tracking position moves from the track center to the groove G2 side. Naturally, the information is recorded at a position shifted from the track center.

Therefore, in the present embodiment, the grooves G1,
The light amount imbalance is corrected using the sub-beams L1 and L2 applied to G2, respectively. That is, the sub beam L1 for scanning the groove G1 on which information is recorded.
The resulting reflected light is weaker than the reflected light obtained from the sub-beam L2 that scans the groove G2 on which information is not recorded. Therefore, an unbalance amount is generated in the output of the difference calculator 18. Therefore, the unbalance amount is removed from the push-pull tracking error signal PTE using the subtractor 20.
As a result, the crosstalk amount is canceled irrespective of recording / non-recording of the adjacent track, and a tracking error signal without offset can be detected.

(Embodiment 3) Next, a description will be given of a third embodiment of the above-described time difference correction for correcting delay between beams. The sub-beam L described above
1. When the crosstalk cancel function using L2 is actually configured, the following problems occur in practical use. That is, if the main beam L0 and the sub-beams L1 and L2 can be arranged on a straight line orthogonal to the track, there is no particular problem with the configuration shown in FIG. 1, but such a configuration cannot be taken in practice. In other words, if the main beam and the sub beam are arranged in the direction orthogonal to the track, the interval between the beams becomes substantially the track pitch, and it becomes difficult to separate them at the light receiving unit.
Accordingly, each sub-beam must be sufficiently separated from the main beam in the track tangential direction, in other words, must be arranged on a straight line obliquely intersecting the track. At this time, a time difference corresponding to the distance in the tangential direction occurs in the reproduction signal of each beam.

[0024] These problems have been pointed out, and some solutions have been proposed. For example, in Japanese Unexamined Patent Publication No. 7-176052, a variable delay means is inserted in a reproduction system of each beam, a crosstalk correlation between respective reproduction signals is calculated, and a delay amount is determined so that the correlation becomes maximum. I do. In addition, Japanese Patent Application Laid-Open No. 5-11510
In Japanese Patent Laid-Open Publication No. 6 (1999) -1994, identification marks arranged in a line in a direction orthogonal to tracks over a plurality of tracks on an optical disk are formed in advance, and the amount of correction delay is determined from the timing at which each beam scans the identification marks on each track. . However, it is difficult to detect and correct the time difference accurately because the method based on the correlation operation does not provide sufficient detection sensitivity. There is a problem that is subject to the restrictions of. Therefore, in the present embodiment, the time difference correction, which is a practical problem of the three-beam crosstalk canceller, will be described below.
A time difference between beams is accurately detected for an optical disk having a general format such as a CD or a DVD, and the time difference between beams is accurately corrected.

FIG. 7 shows a block diagram of the optical disk device in the present embodiment. The track formed on the optical disc 100 is irradiated with a total of three beams, the main beam L0 and the sub-beams L1 and L2, and the reflected light is transmitted to the optical head 20.
The photo elements 5g, 5
e and 5f convert it into a gas signal. The detection signals of these three beams are appropriately time-corrected by the delay elements 300 and 301, and then subjected to so-called crosstalk calculation processing by the addition / subtraction means 33 (corresponding to the adder 13 and the subtractor 14 in FIG. 1). , The leakage component from the adjacent track is removed.

At this time, if the time difference caused by the delay elements 300 and 301 cannot be completely corrected, not only the crosstalk is not sufficiently removed, but if the time error is large, the adjacent track component is added on. This degrades the SN ratio of the reproduced signal. In the present embodiment, the time error correction is executed by using frame marks provided at equal intervals in advance on the information track of the optical disc. The frame is one unit of the information recorded on the optical disk, and the frame mark is formed at the head of the information mark so as to be easily identified from other information mark groups. For example, in the case of DVD, the frame mark is 1456
It is provided for each bit, and the other information group is 3T to 1
A mark having a length of 1T (T is a channel bit length) is provided, whereas a mark having a length of 14T is provided. Therefore, if this frame mark can be detected by each beam, the time error of each beam can be accurately detected from the timing error at which the frame mark is detected. However, although the frame marks are formed at equal bit intervals, they need not be aligned in the track orthogonal direction. In other words, in order for the frame marks to be aligned in the orthogonal direction, the same number of information pits must be formed per track in all tracks (so-called CAV).
In the case of "DVD" or "CD", the information is recorded in CLV, so that the number of bits for one round of the track differs for each radial position.

Next, time correction using a frame mark will be described with reference to FIGS. In FIG. 8, first, the main beam L0 is tracking on the track T2, and the sub beam L1 is scanning on the track T0. On the track T0, the information mark group 103, the frame mark 101, the information mark group 104, and the frame mark 10
2 are formed. For example, in the case of a DVD, the information mark groups 103 and 104 are composed of random data having a mark length of 3T to 11T. On the other hand, the frame mark 10
1 and 102 are not included in the information mark group.
A mark having a length of 4T is included. In FIG. 7, the signal selector 40 switches the reproduction signals S0, S1, and S2 from the light receiving elements corresponding to the respective beams to switch the binarization circuit 50.
Is supplied to the frame mark detecting means 60 via the. The frame mark detecting means 60 detects a frame mark, and may be any device which, for example, sequentially counts the mark lengths of all input signal trains and outputs a pulse signal when 14T is detected. When the main beam L0 is tracking the track T2, that is, when the sub beam L1 is scanning on the track T0, as shown in FIG. 8, the signal selector 40 selects a reproduction signal based on the sub beam L1. Therefore, when the sub beam L1 scans the frame mark 101, the frame mark detection means 60 detects this and outputs a frame mark detection pulse FP. To simplify the explanation,
In FIG. 8, the function of selecting the reproduction signal S2 by the sub beam L2 is omitted.

The reproduced signal (D1) once by the frame mark
When 01) is detected, the mark interval measuring means 70 is activated, and counts the time until the next reproduction signal (D102) by the frame mark is detected. The mark interval measuring means 70 includes, for example, flip-flops 700 and 701, gates 702 and 703, and a counter 704, as shown in FIG. First, when the first frame mark detection pulse FP (D101) is received, the outputs of the flip-flops 700 and 701 become H level and L level, respectively.
Level, the frame mark detection pulse passes through the gate 702 as it is, and the start pulse CSTRT
Then, the counter 701 is started. The start pulse CSTRT is also sent to the track jump driving means 111, and the track jump driving means 111
The track jump is executed by the tracking actuator 204 of 00. As a result, as shown in FIG. 8, the main beam L0 jumps from the track T2 to the track T0. Also, the start pulse CSTRT
Is also sent to the switching control means 120, and the switching control means 1
Reference numeral 20 controls the signal selector 40 to switch its output from a reproduced signal S1 based on the sub-beam L1 to a reproduced signal S0 based on the main beam L0.

Next, when the frame mark FP (102) is detected (by the main beam L0), the flip-flop 7
The outputs of 00 and 701 become H level and H level, respectively. Then, the gate 703 is opened, the frame mark detection pulse becomes the stop pulse CSTOP, and the counter 701 is stopped. The count value at that time is set to N. Here, the frame mark 101 and the frame mark 1
02 is provided at a predetermined interval, and if the same beam is reproduced continuously without causing a track jump, a predetermined count value is always obtained. This value is M. For example, in the case of a DVD, when the above-mentioned interval is measured by a channel clock, M = 1456 is always obtained.

Therefore, by comparing the count value N obtained by the above-mentioned means with the predetermined count value M, it is possible to know the time difference between the reproduced signals of the respective beams. That is, the reproduction means S0 and S1 have delay means 300,
A time delay is given in advance by 301, but if these are appropriate amounts, that is, the time difference corresponding to the distance between the main beam S0 and the sub beam S1 in the track tangential direction can be completely corrected, the count value ( N) = predetermined value (M). In other words, the error (N−M) between the count value and the predetermined value simply represents a correction error in time correction between beams. The predetermined value M is stored in the register 9
0 is stored.

The delay amount correcting means 110 includes a difference calculating means 80
The delay amount of each of the delay units 300 and 301 is set such that the error (NM) obtained by the above becomes zero. FIG. 9 shows a specific configuration example of the delay amount correction unit 110. The output signal of the photo element 5g is first converted into a digital signal by the AD converter 300a,
The shift register 300b sequentially gives a delay of one clock cycle for each rising edge of the clock CLK. The selector 300c is connected to the delay amount correcting unit 110.
, One output is selected from the register group constituting the shift register 300b, and the DA converter 300d converts the output again into an analog signal and outputs it as a reproduction signal S0. With the above configuration, the delay amount can be switched with one clock cycle accuracy. Note that the delay means 301 can also be constituted by similar means.

The method of performing the time correction of the main beam L0 and the sub-beam L1 has been described above, but the time correction of the main beam L0 and the sub-beam L2 can be similarly performed. For example, after the above processing is completed, the flip-flop and the counter of the mark interval measuring means 70 are reset once, and first, the frame mark 101 is set by the sub beam L2.
Is reproduced, a track jump is executed, and the main beam L0
, The delay amount of the delay means 300, 301 may be set so that the difference between the count value M between the frame marks and the predetermined value N at that time becomes zero. The delay amount of the delay element 301 is set again by the delay means 30 previously set by the above-described processing.
This is because the relative delay amounts of 0 and 301 must be maintained.

If the delay amount of each of the delay means 300 and 301 is set to an appropriate amount for the main beam L0 and the sub-beams L1 and L2, the crosstalk is appropriately removed by the addition / subtraction means 33. The signal from which the crosstalk has been removed is supplied to a PLL circuit 22 via a binarization circuit 21.
Thereby, the data component DATA and the clock CLK are separated and transmitted to a subsequent processing circuit such as a digital video decoder. The PLL clock is supplied to the counter 704 as well as the subsequent processing circuit. D earlier
In the case of VD, the predetermined value M = 1456 has been described, but this is a value when counting between frame marks with a channel clock that is a source of a reproduced signal. When the PLL circuit 22 is operating, the clock CLK generated thereby corresponds to this channel clock.

The PLL clock further includes delay means 300,
It is also supplied to 301. The reason is described below. This optical disk device is intended to correct the position error in the track tangential direction of each of the main beam L0 and the sub-beams L1 and L2 on the time axis. The condition is that the signal reproduction speed is a constant value. When the speed of the reproduction signal changes due to a change in the rotation speed of the optical disc 100 or the like, it is necessary to reset the optimum delay amount accordingly. The above-described time difference correction may be performed each time, but information cannot be reproduced during the correction processing, so that during that time, time is wasted and the performance of the entire system is significantly impaired. Therefore, in this optical disk apparatus, means for changing the delay amount of the delay means 300 and 301 in proportion to the speed of the reproduced signal is used. Originally, the PLL circuit 22 generates a clock signal synchronized in frequency with the reproduction signal. As described above, the delay means 300 (301) is configured as shown in FIG.
The time interval is measured in the clock cycle, and a delay of an integral multiple of the clock cycle is given. Therefore, as long as the PLL circuit 22 operates, the delay amount changes according to the speed of the reproduction signal. In other words, once the time difference correction processing is performed at a certain predetermined reproduction speed (in the PLL operating state), the crosstalk cancellation processing can always be executed in an optimum state even if the reproduction speed changes.

However, if the time difference correction process is executed in the PLL operation state, a time error occurs between the reproduced signals of the main beam and the sub beam in the transition period when the time correction is completed. Executing the talk cancellation process rather causes the reproduction signal to deteriorate as described above, and as a result, the PLL circuit 22 is likely to be unlocked. Therefore, in the present embodiment, switches 31 and 32 are inserted into the paths of the reproduced signals S1 and S2 by the sub-beams, respectively, so that the crosstalk processing can not be performed. Although the sequence of opening and closing the switches 31 and 32 is not specifically illustrated, for example, if the control signal CTCON is supplied so as to open both switches during execution of the time difference correction processing and close both switches after the processing is completed. Good.

Also, during a track jump, since a signal passes through a non-information section between tracks on which information is recorded, PLL disturbance due to noise is likely to occur.
Noise with a waveform very similar to the frame mark may also appear. Therefore, during the track jump period, the hold pulse (HO) is output from the track jump drive circuit 111.
LD), and the PLL circuit 22 and the frame mark detection means 60 should be temporarily stopped.

As described above, according to the present embodiment, it is possible to accurately correct the time difference between beams by reproducing frame marks provided at equal intervals on the same track while sequentially jumping tracks. , It is possible to always execute the optimal crosstalk cancellation processing.

In the present embodiment, the tracking is always performed only on the main beam. However, the tracking may be performed on the sub beam as appropriate. For example,
Regardless of whether it is the main or the sub, the operation may be performed on the beam reproducing the track T0. This is effective when the sub beam is not arranged on the adjacent track (for example, slightly closer to the main beam).

In this embodiment, the counter 7
03 is operated by the PLL clock, but the signal may not be synchronized with the reproduction signal as long as it uniquely represents the frame mark interval. For example, before entering the time difference correction processing, the frame mark interval may be measured in advance using the same beam on the same track, and the value at that time may be stored in the register 9 as the predetermined value M. Although the delay unit 300 is shown in FIG. 9 as an example, if the addition / subtraction unit 33 and the PLL circuit 22 are digitally configured, the DA conversion may not be performed again after the AD conversion.

In this embodiment, first, the sub beam L
After the frame mark 101 was detected in step 1, the track jump was performed, and the frame mark 102 was detected in the main beam L0. However, even if the processing is started from the main beam L0, the purpose of the time difference correction of the present embodiment is not lost.
Note that the three-beam crosstalk canceling process of the present embodiment is suitable for a case where reproduction is performed using a beam spot having an elliptical shape long in the direction perpendicular to the track, as described above. It is also useful in reproduction using a circular beam spot.

[0041]

According to the present invention, since a beam having a long shape in the direction perpendicular to the track is used, a low-density optical disk can be reproduced with high compatibility from a high-density optical disk with a simple configuration. By irradiating three elliptical beams onto three adjacent tracks and performing a crosstalk canceling process as appropriate, compatibility can be ensured for information having different recording densities. Also,
By correcting the crosstalk offset from the adjacent track mixed in the push-pull tracking error signal obtained from the main beam with the sub beam reflected light applied to the adjacent track, the offset of the offset regardless of whether the adjacent track is recorded or unrecorded is corrected. No tracking error signal can be detected. In addition, the main beam and the sub beam reproduce frame marks in the same track while sequentially repeating track jumps, and correct the delay amount according to the difference between the measured frame mark interval at that time and the frame mark interval in the format. As a result, the time difference between the beams can be accurately detected. In addition, since the delay means has a shift register configuration synchronized with the PLL clock, the time difference can always be provided with an appropriate correction amount even if the reproduction speed changes, and a highly accurate and stable crosstalk cancellation can be achieved. Processing can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical disk device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation in this embodiment.

FIG. 3 is a main part configuration diagram for explaining an operation in this embodiment.

FIG. 4 is a main part configuration diagram for explaining the operation in this embodiment.

FIG. 5 is a block diagram of an optical disc device according to a second embodiment of the present invention.

FIG. 6 is an operation explanatory diagram in this embodiment.

FIG. 7 is a block diagram of an optical disc device according to a third embodiment of the present invention.

FIG. 8 is a timing chart for explaining an operation of time difference correction according to the embodiment.

FIG. 9 is a block diagram illustrating an example of a delay unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Diffraction grating 4 Objective lens 5 Photodetector 6 Phase comparator 9, 15 Switch 11, 12 Variable gain amplifier 20 Modulator 22 PLL circuit 100 Optical disk 200 Optical head 300, 301 Delay means 40 Signal selector 60 Frame mark detection means 70 Mark Interval measuring means 90 register 110 delay amount correcting means 111 track jump driving means

Claims (15)

[Claims] 1. An information reproducing apparatus for reproducing an optical disk having a first recording density and an optical disk having a second recording density lower than the first recording density, comprising a main beam and a plurality of adjacent tracks formed on the optical disk. from a light source for irradiating the sub-beams, and a light detecting element for detecting respective main beam and the sub beams of reflected light from the optical disk surface, based on a signal from the light detecting element and the reproducing unit to reproduce information of an optical disc The main beam generated by the light source has a dimension in the track tangential direction corresponding to the resolution of the optical disk of the first recording density, and has a shape elongated in the track perpendicular direction of the optical disk. The unit cancels a crosstalk component from an adjacent track included in a signal reproduced from the reflected light of the main beam by using a signal reproduced from the reflected light of the sub beam.
A two-disk optical information reproducing apparatus comprising a canceling means. 2. The optical information reproducing apparatus according to claim 1, wherein a ratio of a major axis to a minor axis of the main beam is 1.2 or more and 2.0 or less. 3. The reproducing section reproduces information recorded on an optical disc having a first recording density using a main beam and a sub beam using the first canceling means, and performs a second recording. 2. The optical information reproducing apparatus according to claim 1, wherein information recorded on an optical disk having a high density is reproduced using only a main beam. 4. A method according to claim 1, wherein a ratio of a width of a pit forming information on the optical disk of the first recording density to a width of a pit forming information on the optical disk of the second recording density is 1.5 to 2.0. The optical information reproducing apparatus according to claim 1, wherein: 5. A tracking control unit for controlling tracking of an optical head including the light source according to a tracking error signal generated based on an output signal from a light detection element, wherein the light source includes a main beam and a main beam. The optical disc is irradiated with two sub-beams, and the tracking control unit divides the reflected light of the main beam and reproduces the reflected light of the main beam when the information recorded on the optical disc of the first recording density is reproduced. A signal obtained by generating a tracking error signal from the mutual phase difference between the received signals and receiving reflected light of the sub-beam by the photodetector when reproducing information recorded on the optical disk of the second recording density. 2. The optical information reproducing apparatus according to claim 1, further comprising: a tracking error signal generating unit that generates a tracking error signal from the optical information. 6. A tracking control unit for controlling tracking of the light source by a tracking error signal generated based on an output signal from a photodetector, wherein the light source is provided on a surface of an optical disk having a track groove. A main beam and two sub-beams are irradiated on a plurality of adjacent tracks above, and the tracking control unit generates a push-pull tracking error signal from the reflected light of the main beam. And a second canceling means for canceling a crosstalk component from an adjacent track included in the push-pull tracking error signal obtained by the push-pull tracking error signal generating means using the reflected light of the sub-beam. The optical information reproducing apparatus according to claim 1. 7. In reproducing optical information from an optical disk having identification marks formed at predetermined intervals on a track, the first canceling means includes a reproducing signal based on a first beam irradiated by the light source and a second reproducing signal. Delay means for giving a relative time difference to a reproduced signal by a beam;
After the first identification mark is detected by the second beam, the second beam emitted by the light source is caused to jump to the track, and the time until the second identification mark is detected by the second beam is measured. And a delay amount determining means for determining a delay amount of the delay means according to a difference between the time measurement value and a time interval determined from the first and second identification mark intervals. The optical information reproducing apparatus according to claim 1, wherein: 8. The optical information reproducing apparatus according to claim 7, wherein said delay means sets a delay amount with a clock cycle as one unit. 9. The optical device according to claim 7, wherein said delay means has a function of sequentially transmitting a reproduction signal in accordance with a clock, and said clock is generated at least in synchronization with the reproduction signal. Information playback device. 10. A light source for irradiating a main beam and a sub-beam on a plurality of mutually adjacent tracks formed on an optical disk having identification marks formed on tracks at predetermined intervals, and And a photodetector that detects the reflected light of the main beam and the sub-beam, respectively, and corrects the time difference between the reproduction signal by the main beam and the reproduction signal by the sub-beam to reduce the crosstalk between tracks mixed in the main beam to the sub-beam. And a reproducing unit for obtaining a reproduced signal by the main beam. The reproducing unit irradiates a first beam to a first identification mark formed on an arbitrary track, and after a track jump, Irradiating a second beam on a second mark provided on the track at a predetermined interval with respect to the first identification mark, and irradiating the second mark with each beam. The time difference is corrected according to a difference between a time interval at which the first and second identification marks are detected and a time interval determined from the predetermined interval to cancel the inter-track crosstalk. Optical disc information reproducing apparatus. 11. The optical disk information reproducing apparatus according to claim 10, wherein said reproducing unit measures said time interval using a clock generated in synchronization with a signal reproduced from the optical disk. 12. The optical disk information reproducing apparatus according to claim 10, wherein the reproducing unit corrects the time difference using one cycle of a clock generated in synchronization with a signal reproduced from the optical disk as a correction unit. apparatus. 13. A method for reproducing optical information from an optical disk having tracks on which identification marks are formed at predetermined intervals by irradiating a plurality of adjacent tracks formed on the optical disk with a main beam and a sub-beam, An optical information reproducing method for correcting a time difference between a reproduction signal and a reproduction signal by a sub-beam and canceling out a crosstalk between tracks mixed into the main beam by using a sub-beam to obtain a reproduction signal by a main beam, The crosstalk between tracks is performed by irradiating a first beam on a first identification mark formed on an arbitrary track, and after a track jump, on the track at a predetermined interval with respect to the first identification mark. The second mark provided is irradiated with a second beam, and the time interval at which the first and second identification marks are detected by the respective beams is determined by the time interval. An optical disc information reproducing method, wherein the time difference is corrected and canceled according to a difference from a time interval determined from the predetermined interval. 14. The optical disk information reproducing method according to claim 13, wherein the time interval is measured using a clock generated in synchronization with a signal reproduced from the optical disk. 15. The optical disk information reproducing method according to claim 13, wherein the time difference is corrected using one cycle of a clock generated in synchronization with a signal reproduced from the optical disk as one correction unit.