JP3824127B2 - Crosstalk reducing method and optical information reproducing apparatus in optical information reproducing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crosstalk reducing method and an optical information reproducing apparatus in an optical information reproducing apparatus, and more particularly to a crosstalk reducing method and an optical information reproducing apparatus in an optical information reproducing apparatus that reduce crosstalk between tracks.
[0002]
[Prior art]
In general, in the optical information reproducing apparatus, in order to increase the recording density of the optical recording medium, the track interval is reduced. In this case, the crosstalk between tracks from adjacent tracks becomes a problem.
[0003]
FIG. 4 is a block diagram showing a schematic configuration of a crosstalk reducing circuit provided in a conventional optical information reproducing apparatus in order to reduce the crosstalk between tracks.
[0004]
Normally, this type of crosstalk reduction circuit is composed of a main beam that irradiates a desired track of an optical recording medium and two sub-beams that irradiate the left and right positions of the desired track in the track direction. An optical system that irradiates an optical recording medium with three laser beams is configured.
[0005]
In FIG. 4, a photodetector 107 is a component of the above-described optical system, and includes a light receiving region A that receives reflected light of the main beam, and a light receiving region B and a light receiving region C that receive the reflected light of two sub beams, respectively. It has at least three light receiving areas.
[0006]
The crosstalk reduction circuit 2 is a delay circuit that corrects a deviation in detection time points caused by irradiation of three laser beams of light reception signals output from the light reception regions A, B, and C, respectively, back and forth in the track direction. 23a, 23b, an adder 21b for adding the light receiving signal of the light receiving region B output from the delay circuit 23b and the light receiving signal of the light receiving region C, an amplifier circuit 24 for amplifying the signal output from the adder 21b, and an amplifier circuit 24 And a subtractor 22c for subtracting the signal output from the light receiving area A output from the delay circuit 23a, and a desired track included in the light receiving signal output from the light receiving area A. It operates so as to reduce the crosstalk component from the adjacent tracks.
[0007]
[Problems to be solved by the invention]
However, in the above conventional crosstalk reduction circuit, the gain of the amplifier circuit 24 is set to a constant value unique to each optical information reproducing apparatus, so that the optimum gain of the amplifier circuit 24 for any optical recording medium is set. Could not be set.
[0008]
Therefore, the present invention provides a method capable of setting the gain of the amplifier circuit 24 to an optimum value for an arbitrary optical recording medium, and aims to improve the quality of a reproduced signal by reducing crosstalk between tracks. To do.
[0009]
[Means for Solving the Problems]
In order to achieve the above-described object, the present invention irradiates a recording track of an optical recording medium with a first laser beam, and each of two tracks adjacent to the recording track includes a second laser beam and a third laser. irradiating a beam from a first signal corresponding to the reflected light of the first laser beam from the optical recording medium, the second signal and the third laser corresponding to the reflected light of the second laser beam Information corresponding to the pit-land pattern recorded on the recording track is obtained based on a fifth signal obtained by subtracting a fourth signal obtained by amplifying the sum of the third signal corresponding to the reflected light of the beam with a predetermined gain. in the cross-talk reduction method in the optical information reproducing apparatus for reproducing the predetermined changing the gain predetermined pits recorded on the recording track - the in land pattern No. With advance plural detecting the level of the signal for each said gain determines the gain variation amount of the level of said fifth signal the detected becomes minimum as the optimum gain, said predetermined gain in the optimum gain determined the It is characterized by setting.
[0010]
By such a method, the amount of crosstalk components (intersymbol interference) from adjacent tracks included in the fifth signal becomes constant, so the amount of fluctuation in the level of the fifth signal is the amount of crosstalk from adjacent tracks. It becomes the component itself, and the crosstalk between tracks can be reduced easily and effectively.
[0011]
Note that the amount of variation can be obtained by, for example, the following three methods.
[0012]
1) Obtained from the ratio between the maximum level and the minimum level of the fifth signal corresponding to each gain.
[0013]
2) Obtain from the difference between the maximum level and the minimum level of the fifth signal corresponding to each gain.
[0014]
3) Obtain from the standard deviation of the fifth signal corresponding to each gain.
[0015]
Incidentally, the standard deviation of the first signal corresponds to the jitter of the reproduction signal.
[0016]
Further, the predetermined pit-land pattern is preferably a pattern in which a maximum length land sandwiches both ends of a minimum length pit. This is because a signal corresponding to the minimum length pit that is most susceptible to crosstalk can be extracted with the least influence from crosstalk (intersymbol interference) components from adjacent pits on the same track.
[0017]
In the crosstalk reduction method, the information on the recording track in a predetermined area of the optical recording medium is reproduced prior to the reproduction of information from the optical recording medium, and the optimum gain is obtained based on the reproduction of the information. Then, the predetermined gain is set with the obtained optimum gain.
[0018]
Further, the present invention irradiates the first laser beam on the recording track of the optical recording medium, by irradiating respectively the second laser beam and a third laser beam into two tracks adjacent to the recording track, wherein Corresponds to the second signal corresponding to the reflected light of the second laser beam and the reflected light of the third laser beam from the first signal corresponding to the reflected light of the first laser beam from the optical recording medium. Information reproducing apparatus for reproducing information corresponding to a pit-land pattern recorded on the recording track based on a fifth signal obtained by subtracting a fourth signal obtained by amplifying the sum of the third signal and the third signal with a predetermined gain. in the predetermined changing the gain predetermined pits recorded on the recording track - detecting hands in advance plural detecting the level of said fifth signal in the land pattern for each said gain If, the amount of variation in the level of said fifth signal detected by the detection means determined as the optimal gain the gain becomes minimum; and a gain setting means for setting the predetermined gain in the optimum gain determined the It is characterized by.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a crosstalk reducing method and an optical information reproducing apparatus in an optical information reproducing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
[0020]
An optical disk reproducing apparatus will be described as an example of the optical information reproducing apparatus.
[0021]
FIG. 2 is a block diagram showing a schematic configuration of an optical pickup generally used in an optical disc reproducing apparatus having a crosstalk reducing circuit.
[0022]
In general, this type of optical pickup has an optical system configured to emit a total of three laser beams, one main beam and two sub-beams. A structure for generating a laser beam or a structure for generating one laser beam emitted from one laser diode by dividing it into at least three laser beams by a diffraction grating is known. In this embodiment, a description will be given by applying a more general optical system configured to divide one laser beam emitted from one laser diode into at least three laser beams by a diffraction grating.
[0023]
One laser beam emitted from the laser diode 101 is converted into parallel light by the collimator lens 102, enters the diffraction grating 103, and is at least 3 of 0th-order diffracted light used as the main beam and ± 1st-order diffracted light used as the sub beam. Divided into laser beams of books. The light beam divided by the diffraction grating 103 passes through the beam splitter 104, converges on the recording surface of the optical disc 4 through the objective lens 105, and is aligned linearly and at equal intervals by the 0th order diffracted light and the ± 1st order diffracted light. Three beam spots are formed on the recording surface. The 0th-order diffracted light and ± 1st-order diffracted light reflected by the recording surface include information recorded on the recording surface in its optical characteristics, and again enter the objective lens 105 to become parallel light. The light is reflected in the direction and forms an image on the photodetector 107 through the condenser lens 106.
[0024]
FIG. 3 shows a recording track (hereinafter referred to as a track) of the optical disc 4, a beam spot formed by condensing three laser beams emitted from the optical pickup on the optical disc 4, and each beam spot is the optical disc 4. The relationship with the signal read from is shown.
[0025]
In FIG. 3, a beam spot m by 0th-order diffracted light for signal reproduction is arranged on a desired track 4A of the optical disk. The beam spot s1 due to the + 1st order diffracted light is disposed on the outer peripheral land adjacent to the track 4A, and the beam spot s2 due to the −1st order diffracted light is disposed on the inner peripheral land adjacent to the track 4A.
[0026]
The beam spots s1 and s2 are arranged at a distance d from the beam spot m before and after the track direction in order to eliminate mutual interference. The beam spots s1 and s2 are formed on the photodetector 107 of each beam spot generated by this arrangement. The shift of the detection time point in is corrected by the delay circuits 23a and 23b. That is, the signal Sa output from the delay circuit 23a and the signal Sb output from the delay circuit 23b are the positions m ′ and s1 ′ on the same radius line where the beam spot s2 that scans the last of the three beam spots is located. Is a signal read by the beam spot m and the beam spot s1.
[0027]
When the track pitch of the optical disk 4 is narrowed for high density, a part of the beam spot m leaks into the adjacent outer track 4B and the adjacent inner track 4C of the desired track 4A. The signal Sa read from the optical disc 4 includes the signal mB and the signal mC recorded on the track 4B and the track 4C in addition to the desired signal mA recorded on the track 4A (Sa = mA + mB + mC). mC becomes a crosstalk component and becomes a factor of deteriorating the quality of a desired signal mA.
[0028]
Similarly, when the track pitch of the optical disk 4 is narrowed, a part of the beam spot s1 leaks into the track 4A and the track 4B, and a part of the beam spot s2 leaks into the track 4A and the track 4C. Therefore, the signal Sb read by the + 1st order diffracted light from the optical disc 4 includes the signal sA and the signal sB recorded on the track 4A and the track 4B (Sb = sA + sB). 4A and the signal sA and the signal sC recorded on the track 4C are included (Sc = sA + s C ).
[0029]
Therefore, by performing the following calculation using the signals Sb and Sc read by the ± 1st order diffracted light, the crosstalk component contained in the signal Sa read by the 0th order diffracted light can be reduced.
[0030]
Sa-k (Sb + Sc)
= (MA + mB + mC) -k {(sA + sB) + (sA + sC)} (1)
The expression (1) is modified as follows.
[0031]
Sa-k (Sb + Sc)
= (MA + mB + mC) −k (2 × sA + sB + sC)
= (MA-2k * sA) + {mB + mC-k (sB + sC)} (2)
Therefore, the quality of the desired signal mA can be ensured by finding the value of k that minimizes the absolute value of {mB + mC−k (sB + sC)} which is a term indicating the crosstalk component in the equation (2). .
[0032]
FIG. 1 is a schematic block diagram showing an embodiment of a crosstalk reducing circuit according to the present invention.
[0033]
In FIG. 1, the same reference numerals as those in FIG. 4 indicate the same components as those in FIG. Note that the crosstalk reduction circuit 2 electrically realizes the expression (1).
[0034]
The crosstalk reduction circuit 2 includes a gain control circuit 3 and tracks information in a predetermined area of the optical disk 4 in order to adjust the gain of the variable gain amplification circuit 24 before reproducing information from the optical disk 4. Perform test playback to play back.
[0035]
FIG. 4 is a flowchart for explaining the operation of the gain control circuit 3. A method for adjusting the gain of the variable gain amplifying circuit 24 will be described with reference to FIG.
[0036]
When the optical disk 4 is inserted, the gain control circuit 3 sets the gain of the variable gain amplifier circuit 24 to K1 (steps 301 and 302), and starts test reproduction. When a signal pattern corresponding to 14T land-3T pit-14T land (hereinafter referred to as L14-P3-L14) is detected in the reproduction signal S (step 303), a signal corresponding to 3T pit in this signal pattern (hereinafter referred to as P3 signal). ) Is detected (step 304). The gain control circuit 3 repeats N times detection of the signal level of the P3 signal every time L14-P3-L14 is detected in the gain K1 (steps 303 to 307), and N detected in this repetition. The signal levels of the P3 signals are stored in correspondence with the gain K1 (step 306).
[0037]
Next, a fluctuation amount C1 of the level of the N P3 signals detected with respect to the gain K1 is obtained (step 308). Here, the amount of fluctuation in the level of the N P3 signals is, for example, 1) The difference between the signal Smax having the highest level and the signal Smin having the lowest level among the N P3 signals.
[0038]
2) The ratio between the signal Smax having the highest level and the signal Smin having the lowest level among the N P3 signals.
[0039]
3) Standard deviation of N P3 signals.
[0040]
Any of these can be adopted.
[0041]
Next, the gain control circuit 3 repeats the above steps while changing the gain of the variable gain amplifying circuit 24 to K2, K3,..., KM, and the amount of change C2 in the signal level of the N P3 signals with respect to each gain. , C3,..., CK are calculated (steps 302 to 310).
[0042]
FIG. 5 is a diagram illustrating an example of a storage area included in the gain control circuit 3.
[0043]
As shown in FIG. 5, the gain control circuit 3 repeats steps 302 to 310 of the flowchart shown in FIG. 4, thereby detecting the levels S1j to SNj of the N P3 signals detected with respect to the gain Kj and the variation amount Cj thereof. Are sequentially stored.
[0044]
Finally, the gain control circuit 3 detects the gain Kj that gives the smallest amount of fluctuation Cj from the N level fluctuation amounts C1 to CN calculated as the optimum gain Kopt for the optical disc 4 (step S1). 311), the gain Kopt is set as the gain K of the variable gain amplifier circuit 24 (step 312), and the test reproduction is finished.
[0045]
According to the above method, since a predetermined signal (3T pit) is extracted from a predetermined pit-land pattern (14T land-3T pit-14T land), the pits before and after the predetermined signal (3T pit) are included. The crosstalk component from the signal, that is, the intersymbol interference component is substantially constant. In other words, the factor that fluctuates the signal level of the predetermined signal (3T pit) is limited to the crosstalk between tracks, and therefore reproduction is performed by finding the value of the gain K of the gain variable amplifier circuit 24 that minimizes the fluctuation amount. The inter-track crosstalk component included in the signal sequence S can be sufficiently reduced.
[0046]
In the above embodiment, the method for reducing crosstalk in the optical disc reproducing apparatus has been described. However, this method for reducing crosstalk can be applied to general optical information reproducing apparatuses such as an optical card reader.
[0047]
【The invention's effect】
As described above, according to the present invention, the recording track of the optical recording medium is irradiated with the first laser beam, and the second laser beam and the third laser are respectively applied to two tracks adjacent to the recording track. A second signal corresponding to the reflected light of the second laser beam and a third laser from the first signal corresponding to the reflected light of the first laser beam from the optical recording medium. Information corresponding to the pit-land pattern recorded on the recording track is obtained based on a fifth signal obtained by subtracting a fourth signal obtained by amplifying the sum of the third signal corresponding to the reflected light of the beam with a predetermined gain. In the optical information reproducing apparatus for reproducing, the level of the fifth signal in the predetermined pit-land pattern recorded on the recording track is changed for each gain by changing the predetermined gain. With multiple detection, determine the gain variation amount of the level of said fifth signal the detected becomes minimum as the optimum gain, and then, is setting the predetermined gain in the optimum gain determined said, any The crosstalk between tracks can be effectively reduced with respect to the optical disc.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a crosstalk reducing circuit according to the present invention.
FIG. 2 is a block diagram showing a schematic configuration of an optical pickup according to the present invention.
FIG. 3 is a diagram illustrating the basic principle of the present invention.
4 is a flowchart showing an example of the operation of the gain control circuit 3 of FIG.
FIG. 5 is a diagram illustrating an example of a storage area of the gain control circuit 3 of FIG. 1;
FIG. 6 is a block diagram showing a circuit configuration of a crosstalk reducing circuit in a conventional optical information storage device.
[Explanation of symbols]
2 Crosstalk reduction circuit 3 Gain control circuit 4 Optical disk 4A, 4B, 4C Track 21a, 21b Adder 22c Subtractor 23a, 23b Delay circuit 24 Variable gain amplifier circuit 101 Laser diode 102 Collimator lens 103 Diffraction grating 104 Beam splitter 105 Objective Lens 106 Condenser lens 107 Photo detector

Claims (7)

Irradiates the first laser beam on the recording track of the optical recording medium, the respective recording tracks on two adjacent tracks irradiated with the second laser beam and a third laser beam, said from the optical recording medium From a first signal corresponding to the reflected light of the first laser beam, a second signal corresponding to the reflected light of the second laser beam and a third signal corresponding to the reflected light of the third laser beam; In a crosstalk reducing method in an optical information reproducing apparatus for reproducing information corresponding to a pit-land pattern recorded on the recording track based on a fifth signal obtained by subtracting a fourth signal obtained by amplifying the sum of the signals with a predetermined gain ,
A plurality of levels of the fifth signal in a predetermined pit-land pattern recorded on the recording track by changing the predetermined gain are detected in advance for each gain;
Obtains the gain variation amount of the level of said fifth signal the detected becomes the smallest as the optimal gain,
The predetermined gain is set with the obtained optimum gain. A method for reducing crosstalk in an optical information reproducing apparatus. The amount of variation is
The crosstalk reduction method according to claim 1, wherein the crosstalk reduction method is obtained from a ratio between a maximum level and a minimum level of the plurality of fifth signals corresponding to each gain. The amount of variation is
Cross talk reduction method in the optical information reproducing apparatus according to claim 1, wherein the determining the difference between the maximum and minimum levels of the plurality of fifth signal corresponding to each gain. The amount of variation is
Cross talk reduction method in the optical information reproducing apparatus according to claim 1, wherein the obtaining the standard deviation of the plurality of fifth signal corresponding to each gain. The predetermined pit-land pattern is:
The method for reducing crosstalk in an optical information reproducing apparatus according to claim 1, wherein the maximum length land is sandwiched between both ends of the minimum length pit. Prior to reproduction of information from the optical recording medium, reproduction of information on a recording track in a predetermined area of the optical recording medium is performed,
The method for reducing crosstalk in an optical information reproducing apparatus according to claim 1, wherein the optimum gain is obtained based on reproduction of the information, and the predetermined gain is set with the obtained optimum gain. Irradiates the first laser beam on the recording track of the optical recording medium, the respective recording tracks on two adjacent tracks irradiated with the second laser beam and a third laser beam, said from the optical recording medium From a first signal corresponding to the reflected light of the first laser beam, a second signal corresponding to the reflected light of the second laser beam and a third signal corresponding to the reflected light of the third laser beam; In an optical information reproducing apparatus for reproducing information corresponding to a pit-land pattern recorded on the recording track based on a fifth signal obtained by subtracting a fourth signal obtained by amplifying
Detecting means for detecting in advance a plurality of levels of the fifth signal for each gain in a predetermined pit-land pattern recorded on the recording track by changing the predetermined gain;
Gain setting means for obtaining, as an optimum gain, a gain that minimizes the amount of fluctuation in the level of the fifth signal detected by the detection means, and setting the predetermined gain with the obtained optimum gain. An optical information reproducing apparatus.

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