JPH08221902A - Waveform equalizing device - Google Patents

Abstract

PURPOSE: To perform information reproduction of high reliability by setting the optimal equalizing coefficient even for the nonlinear distortion of a reproducing signal generated when an optical disk is inclined in an optical disk device. CONSTITUTION: Since a nonlinear distortion generated in a reproducing signal due to the inclined angle of an optical disk is known, an inclined angle detecting circuit 108 detects the inclined angle of the optical disk before the data reproduction. A coefficient arithmetic circuit 109 calculates the optimal equalizing coefficient for the nonlinear distortion based on the inclined angle of the optical disk detected by the inclined angle detecting circuit 108 and outputs it to multipliers 103, 104. Consequently, the equalizing coefficient is optimally set even for the reproducing signal having the nonlinear distortion due to the inclination of the optical disk, the probability of occurrence of erroneous detection of code due to the interference between codes is reduced and highly reliable information reproduction is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform equalizer for suppressing intersymbol interference in an optical disk device, by setting an equalization coefficient corresponding to a reproduction signal having a non-linear distortion caused by the inclination of the optical disk to perform waveform equalization. The present invention relates to a waveform equalizer that can perform highly reliable information reproduction by performing the operation.

[0002]

2. Description of the Related Art An optical disk device is a memory device for recording / reproducing information by using a laser beam, and has a feature that an optical disk as a recording medium has a large recording capacity and is hardly affected by scratches and dust. There is.

Generally, the frequency characteristic of a reproduced signal from an optical disk exhibits a characteristic of rapidly deteriorating in a high frequency range, and thus can be regarded as a kind of low-pass filter. If an attempt is made to increase the recording density of the data recorded on the optical disk in order to increase the recording capacity of the optical disk, it will inevitably be used near the upper limit of the frequency band, and when reading adjacent marks, the respective reproduced waveforms interfere with each other. Is likely to occur, resulting in a detection error. This phenomenon is intersymbol interference, and in order to reduce intersymbol interference to zero, it is necessary to satisfy the Nyquist characteristic obtained from the resolution of the optical system. When intersymbol interference occurs, the probability that a code detection error will occur at the time of data identification becomes high, which makes it difficult to reproduce information with high reliability. Therefore, in general, when increasing the recording density without improving the optical system resolution by shortening the laser wavelength or increasing the lens aperture ratio,
A waveform equalizer is used that suppresses the influence of intersymbol interference by emphasizing the high frequency band of the deteriorated reproduction signal.

As a waveform equalizer for suppressing the influence of intersymbol interference, a 3-tap transversal filter as shown in FIG. 7 is known as an example of a simple waveform equalizer. In FIG. 7, the reproduction signal from the optical disk (not shown) input from the input terminal 106 is delayed by the delay circuits 101 and 10.
Delayed by 2. Further, the reproduced signal is the multiplier 103,
The tap coefficient is multiplied by 104. The multiplication result by the multiplier and the reproduction signal delayed by the delay circuit are added by the adder 1
05 is added and output from the output terminal 107.
Delay time of delay circuits 101 and 102 and multipliers 103 and 1
As shown in FIG. 8, the reproduced signal equalized by properly setting the tap coefficient of 04 has almost no intersymbol interference at adjacent discrimination points in the isolated waveform. Therefore, even when intersymbol interference occurs in the reproduced signal, intersymbol interference is removed when performing code detection by the equalization processing, and highly reliable information reproduction is possible.

[0005]

In the conventional waveform equalizer, the case where an isolated waveform of a reproduced signal has a linear characteristic that is symmetrical with respect to a peak is generally examined. Therefore, the multiplier 103 shown in FIG. 7 is used. , 104 tap coefficient C
It was general that -1, C + 1 had the same value.

However, in an actual optical disc device, the optical disc is slightly inclined with respect to the pickup due to the warp of the recording medium, the inclination of the turntable, and the like. When the optical disc is tilted, the spot of the laser light imaged on the optical disc is deformed due to the influence of the aberration of the optical system and the reproduction signal of the optical disc has a non-linear distortion. Therefore, the isolated reproduction signal waveform when the optical disc is tilted is, for example, as shown in FIG.
As shown in FIG. 10, the waveform becomes asymmetrical with respect to the peak. When the tap coefficients C-1 and C + 1 are equalized as in the conventional case, as shown in FIG. However, there is a problem that the intersymbol interference at the + τ discrimination point does not become 0 and the probability of occurrence of a detection error during data discrimination increases.

An object of the present invention is to solve such a problem and to perform reliable waveform equalization on a reproduced signal waveform having a non-linear distortion due to an aberration or the like generated when an optical disc is tilted. An object of the present invention is to provide a waveform equalizer for reproducing information with high property.

[0008]

In order to achieve the above object, the present invention provides a waveform equalizing means capable of individually changing the equalization coefficient and an inclination angle detecting means for detecting the inclination angle of an optical disk. And an equalization coefficient setting means for setting the equalization coefficient of the waveform equalization means according to the optical disc tilt angle detected by the tilt angle detection means.

Alternatively, a specific signal extraction means for extracting a specific signal from the optical disk reproduction signal before the waveform equalization processing is performed by the waveform equalization means, and a reproduction signal extracted by the specific signal extraction means. A signal amplitude sampling means for sampling a specific signal amplitude in the
A waveform distortion amount detecting means for detecting a distortion amount of a reproduction signal by comparing a specific signal amplitude sampled by the signal amplitude sampling means with a reference signal amplitude, and detected by the waveform distortion amount detecting means. Equalization coefficient correcting means for correcting the reference equalization coefficient based on the reproduction signal distortion amount so as to be the optimum equalization coefficient for the reproduction signal distortion and outputting it to the waveform equalization means.

[0010]

According to the present invention, the inclination angle of the optical disk is detected by the inclination angle detecting means prior to the data reproduction of the optical disk, and the equalization coefficient setting means uses the detected inclination angle to cause the nonlinear distortion of the reproduction signal due to the inclination angle of the optical disk. The optimum equalization coefficient according to is output to the waveform equalization means capable of individually setting the equalization coefficient. Therefore, the waveform equalizing means can perform optimum waveform equalization even for the non-linear distortion of the reproduced signal due to the inclination of the optical disc during data reproduction, suppress intersymbol interference, and perform highly reliable information reproduction. You can do it.

Further, the specific signal extraction means extracts the specific signal from the optical disk reproduction signal before the waveform equalization processing is performed by the waveform equalization means. The specific signal amplitude in the extracted reproduction signal is sampled by the signal amplitude sampling means and compared with the reference signal amplitude in the waveform distortion amount detection means to detect the distortion amount of the reproduction signal.
On the basis of the reproduction signal distortion amount detected by the waveform distortion amount detection means, the equalization coefficient correction means corrects the reference equalization coefficient to be the optimum equalization coefficient for the reproduction signal distortion, and performs the waveform equalization. Since it is output to the means, it is possible to perform optimum waveform equalization even with respect to the nonlinear distortion of the reproduction signal due to the tilt of the optical disc, suppress intersymbol interference, and perform highly reliable information reproduction.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the equalizer of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram showing a first embodiment of a waveform equalizer of the present invention. In FIG. 1, 101 and 102 are delay circuits, 103 and 104 are multipliers for multiplying a reproduction signal by an equalization coefficient input from the outside, 105 is an adder, and 106 is a reproduction signal from an optical disk (not shown). Is an input terminal, 107 is an output terminal for outputting a reproduction signal after equalization to a signal processing system (not shown), 108 is a tilt angle detection circuit for detecting a tilt angle of an optical disk (not shown), and 109 is the tilt angle detection The equalization coefficients C-1 and C + output to the multipliers 103 and 104 according to the tilt angle of the optical disk output from the circuit 108.
It is a coefficient calculation circuit for calculating 1.

In the figure, delay circuits 101, 102,
The multipliers 103 and 104 and the adder 105 constitute a 3-tap transversal filter as a waveform equalization circuit, and a reproduction signal from an optical disk (not shown) is input to the waveform equalization circuit from the input terminal 106, and the like. Conversion processing is performed. At that time, since the tap coefficients C-1 and C + 1 of the multipliers 103 and 104 are externally controlled, that is, the equalization coefficient is controlled by the coefficient calculation circuit 109, the equalization characteristics can be changed. The reproduction signal equalized by the 3-tap transversal filter is output from the output terminal 107 to the signal processing system.

When reproducing data from the optical disk, the tilt angle detection circuit 108 detects the tilt angle of the optical disk before the waveform equalization processing is performed by the equalizer. The inclination angle detection circuit 108 can be realized by, for example, having a configuration shown in FIG. In FIG. 2, the position detecting element 203 detects the light receiving position of the reflected light of the light emitted by the light emitting element 202 with respect to the optical disc 201. The tilt angle calculation circuit 204 calculates and outputs the tilt angle θ of the optical disc 201 from the difference ΔX between the light receiving position of the reflected light from the optical disc 201 and the light receiving position of the reflected light when the optical disc is not tilted. The tilt angle θ of the optical disc detected by the tilt angle detection circuit 108 is output to the coefficient calculation circuit 109.

The coefficient calculation circuit 109 multiplies the multipliers 103, 10 by the tilt angle θ of the optical disc detected as described above.
The equalization coefficients C-1 and C + 1 output to 4 are calculated. Since the nonlinear distortion of the reproduced signal caused by the tilt angle of the optical disc can be known in advance by experiments, how much the equalization factor should be corrected when the optical disc has a tilt angle with respect to the equalization factor when the optical disc is not tilted. Whether or not the optimum equalization coefficient is obtained is created as a calculation table for the tilt angle. The coefficient calculation circuit 109 has this calculation table, and when data is reproduced from the optical disk, prior to data reproduction, the optimum equalization coefficient C− based on the inclination angle θ of the optical disk detected by the inclination angle detection circuit 108.
1, C + 1 is calculated using the above-mentioned calculation table and output to the multipliers 103, 104. In the waveform equalizer that performs the equalization process using the equalization coefficient output from the coefficient calculation circuit 109, even in the reproduction signal having the non-linear distortion due to the tilt of the optical disc as shown in FIG. The optimum waveform equalization coefficient that causes zero interference is performed.
Therefore, even with respect to a reproduced signal having a non-linear distortion due to the inclination of the optical disc, optimum waveform equalization can be performed by using the waveform equalizer of the first embodiment of the present invention.

As described above, by using the waveform equalizer according to the first embodiment of the present invention in the optical disc device, the equalization coefficient of the equalizer can be set even for a reproduced signal having a non-linear distortion due to the inclination of the optical disc. Since each can be set optimally, the probability of occurrence of code detection error due to inter-code interference can be reduced and highly reliable information reproduction can be performed.

Further, in the first embodiment, the constant equalization coefficient is corrected according to the inclination of the optical disk, but the equalization coefficient is automatically updated according to the change of the reproduction characteristic. Even when the automatic equalizer is used, the equalization coefficient updated by the equalization error as shown in FIG. 4 may be corrected by the coefficient correction circuit 403 to compensate the nonlinear distortion component with respect to the tilt angle of the optical disc. Then, the same effect can be obtained.

Next, a second embodiment of the present invention will be described with reference to the drawings. In the first embodiment of the present invention, the inclination angle detection circuit 108 detects the inclination angle of the optical disc,
The optimum equalization coefficient was set for the nonlinear distortion of the reproduction signal due to the tilt angle.In the second embodiment, the reference reproduction signal when the optical disk is not tilted and the reproduction signal during data reproduction are compared. , The amount of distortion of the reproduced signal is detected. The optimum equalization coefficient is set based on the detected distortion amount and the equalization processing is performed.

FIG. 5 is a circuit block diagram showing a second embodiment of the waveform equalizer of the present invention. In FIG. 5, 101,
102 is a delay circuit, 103 and 104 are multipliers for multiplying a reproduction signal by an equalization coefficient input from the outside, 105
Is an adder, 106 is an input terminal for inputting a reproduction signal from an optical disk (not shown), 107 is an output terminal for outputting the reproduction signal after equalization to a signal processing system (not shown), 50
Reference numeral 1 is a specific signal extraction circuit for extracting a specific signal from the reproduction signal before equalization processing, 502 is a waveform sampler for sampling the amplitude of the specific signal extracted by the specific signal extraction circuit 501, and 503 is A distortion amount detection circuit for detecting the distortion amount of the reproduction signal waveform by comparing the amplitude of the specific signal waveform sampled by the waveform sampler 502 with the reference reproduction signal amplitude, and 504 is detected by the distortion amount detection circuit 503. The optimum equalization coefficients C-1 and C for a reproduced signal having distortion are corrected by correcting the equalization coefficient in the case of no distortion, which is set in advance by the distortion amount of the reproduced signal thus reproduced.
A coefficient correction circuit for outputting +1 to the multipliers 103 and 104. The same parts as those in FIG. 1 are designated by the same reference numerals.

In FIG. 5, the reproduction signal from the optical disk (not shown) input from the input terminal 106 is delayed by the delay circuits 101 and 102, the multipliers 103 and 104, and the adder 105.
The reproduction signal equalized by the 3-tap transversal filter configured by is output from the output terminal 107 to the signal processing system.

The reproduced signal input from the input terminal 106 in FIG. 5 is input to the specific signal extraction circuit 501. In this embodiment, since the non-linear distortion of the reproduction signal due to the inclination of the optical disc is detected by comparing the reproduction signal waveform with the reference reproduction signal when the optical disc is not inclined as described above, the distortion amount of the reproduction signal is In order to obtain, it is necessary to specify the reference reproduction signal. Therefore, the specific signal extraction circuit 501 extracts a specific signal for observing the reproduced signal distortion from the reproduced signal. The specific signal to be extracted is a specific signal for non-linear distortion detection in the recording format because it is easy to extract a specific signal such as a sync signal included in the reproduced signal whose existence position is fixed in advance for bit synchronization. An area in which is recorded may be provided.

In the present embodiment, the specific signal extraction circuit 501 extracts an isolated pit, which is recorded at a constant cycle like a clock pit in the format of the optical disk device of the sample servo system, as a specific signal. As shown in FIG. 6, since the specific signal exists in the reproduction signal 601 at a constant cycle, if the detection pulse 602 is generated, it is possible to easily extract only the specific signal from the reproduction signal 601 and obtain the extraction signal 603.

The signal amplitude of the specific signal extracted by the specific signal extraction circuit 501 is sampled by the waveform sampler 502 and output to the distortion amount detection circuit 503. In order to remove the influence of the noise component contained in the reproduced signal, The waveform sampler 502 may perform sampling a plurality of times and output sample values obtained by averaging to the distortion amount detection circuit 503.

The distortion amount detection circuit 503 is a waveform sampler 50.
By comparing the specific signal amplitude sampled by 2 with the reference signal amplitude, the amount of distortion of the reproduction signal caused by the tilt of the optical disc is detected. In that case, the maximum amplitude at the center of the solitary wave is used to eliminate the fluctuation of the absolute value of the amplitude due to the fluctuation of the optical disk reflectivity and the gain of the detection system amplifier, and only the amplitude change due to the waveform distortion is corrected as the distortion due to the optical disk tilt. Output to the circuit 504.

The coefficient correction circuit 504 is a distortion amount detection circuit 50.
Based on the distortion amount due to the tilt of the optical disc detected in 3, the optimum equalization coefficient when the optical disc is not tilted is corrected to be the optimum equalization factor for the reproduction signal in which the nonlinear distortion due to the tilt of the optical disc is generated. To calculate. Optimal equalization coefficients C-1, C + 1 for the reproduced signal having the detected nonlinear distortion
Is output to the multipliers 103 and 104. Therefore, even when a nonlinear distortion occurs in the reproduction signal due to the tilt of the optical disc, the waveform equalization apparatus according to the second embodiment of the present invention can perform optimum waveform equalization.

As described above, by using the waveform equalizer according to the second embodiment of the present invention in the optical disc device, the equalization coefficient of the equalizer can be set even for a reproduction signal having a non-linear distortion due to the inclination of the optical disc. Since each can be set optimally, the probability of occurrence of code detection error due to inter-code interference can be reduced and highly reliable information reproduction can be performed.

Although the equalization circuit is a 3-tap transversal filter in the above first and second embodiments, the same effect can be obtained by applying the present invention even when the number of taps is 3 or more. Obtainable. Further, in the first and second embodiments, the equalizing circuit is explained as an analog circuit, but the same effect can be obtained even if it is a digital equalizing circuit.

[0028]

As described above, according to the present invention,
Since the equalization coefficient of the equalizer can be optimally set by detecting the inclination angle of the optical disc even for a reproduction signal having nonlinear distortion due to the inclination of the optical disc,
It is possible to reduce the occurrence probability of code detection error due to inter-code interference and perform highly reliable information reproduction. Also, by comparing the specific signal amplitude extracted from the reproduction signal before equalization with the reference signal amplitude, the non-linear distortion of the reproduction signal caused by the tilt of the optical disc is detected, and the equalization coefficient of the equalizer is calculated as the non-linear distortion. By optimally setting each of the reproduction signals, it is possible to reduce the probability of occurrence of a code detection error due to inter-code interference and perform highly reliable information reproduction.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a first embodiment of a waveform equalizer according to the present invention.

FIG. 2 is a diagram showing a specific example of a tilt angle detection circuit in FIG.

FIG. 3 is a diagram showing an example in which optimum equalization is performed by a waveform equalizer of the present invention on a waveform having nonlinear distortion.

FIG. 4 is a circuit block diagram showing an embodiment when the first embodiment of the present invention is applied to an automatic equalizer.

FIG. 5 is a circuit block diagram showing a second embodiment of the waveform equalizer according to the present invention.

6 is a waveform diagram showing an operation of the specific signal extraction circuit in FIG.

FIG. 7 is a configuration diagram showing a 3-tap transversal filter.

FIG. 8 is a waveform diagram showing an operation of waveform equalization by a 3-tap transversal filter.

FIG. 9 is a waveform diagram showing an example of an isolated waveform when the optical disc has a non-linear distortion due to tilting.

FIG. 10 is a waveform diagram showing an example of a case where conventional waveform equalization is performed on a signal having nonlinear distortion.

[Explanation of symbols]

101, 102 ... Delay circuit, 103, 104 ... Multiplier,
105 ... Adder, 108 ... Inclination angle detection circuit, 109 ... Coefficient calculation circuit, 501 ... Specific signal extraction circuit, 502 ... Waveform sampler, 503 ... Distortion amount detection circuit, 504 ... Coefficient correction circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G11B 20/18 572 9558-5D G11B 20/18 572C // G11B 7/095 9368-5D 7/095 G (72) Inventor, Yoshio Suzuki, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa, Ltd., Institute of Visual Media, Hitachi, Ltd. (72) Inventor, Nakajima: 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa, Ltd. In-house

Claims (5)

[Claims] 1. A waveform equalizer for equalizing a reproduced signal from an optical disc, the waveform equalizing means capable of changing an equalization coefficient of the waveform equalizer, and recording / reproducing on / from an optical disc as a recording medium. For detecting the tilt angle of the optical disc with respect to the optical pickup for performing the optical pickup, and the tilt angle detecting means for determining the optimum equalization coefficient for the nonlinear distortion of the reproduction signal generated by the tilt of the optical disc. A waveform equalization device comprising: a coefficient calculation unit that calculates based on the detected tilt angle of the optical disc and outputs the calculated optical disc angle to the waveform equalization unit. 2. A waveform equalizer for equalizing the waveform of a reproduced signal from an optical disc, the waveform equalizing means capable of changing the equalization coefficient of the waveform equalizer, and a specific signal from the reproduced signal from the optical disc. Specific signal extraction means for extracting the waveform, waveform sampling means for sampling the amplitude of the specific signal extracted by the specific signal extraction means, and reproduction signal amplitude sampled by the waveform sampling means depending on the tilt of the optical disc. A waveform distortion amount detecting means for detecting a nonlinear distortion amount of a reproduced signal waveform, and a nonlinear distortion of the reproduced signal generated by the tilt of the optical disk based on the reproduced signal waveform distortion amount detected by the waveform distortion amount detecting means. Waveform and the like, which has an equalization coefficient correction means for correcting the equalization coefficient so as to obtain an optimum equalization coefficient and outputting it to the waveform equalization means. Apparatus. 3. The waveform equalizer according to claim 2, wherein the signal extracted by the specific signal extracting means is a sync signal included in a reproduction signal of the optical disc. 4. An optical disc device for performing waveform equalization using the waveform equalization device according to claim 2, wherein a specific signal for detecting a non-linear distortion of a reproduction signal due to an inclination of the optical disc extracted by said specific signal extracting means. A recording format of an optical disk having an area in which is recorded, and an optical disk device using the optical disk of the recording format. 5. An optical disc device for performing waveform equalization on a reproduction signal from an optical disc, wherein the waveform equalization device according to any one of claims 1, 2 and 3 performs waveform equalization processing.