JP2000113595A - Crosstalk removing method and crosstalk removing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically adjust the subtraction ratio in a crosstalk removing method by which a sub signal which is the cause of the crosstalk is subtracted at a certain ratio from a reproducing signal. SOLUTION: A crosstalk removing signal 12a and the sub signal 11 are binarized and a coincidence detecting signal 16a of both is outputted with a coincidence detecting means 16. When the time for making both coincided is long, the subtraction ratio is increased, upon judging that a crosstalk component from the sub signal 11 remains in the crosstalk removing signal 12a. Conversely, when the time for making both coincided is long, the subtraction ratio is decreased, upon judging that the crosstalk component is excessively reduced. Further, an error generation timing signal 21a is produced from the exclusive OR of a signal before and after a PLL of the binarization crosstalk removing signal 14a, and the matching detection is performed only within the error generation timing, thereby deciding the subtraction ratio with higher accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an information recording / reproducing apparatus and an information communication apparatus, and more particularly to a method and an apparatus for removing crosstalk.

[0002]

2. Description of the Related Art In recent years, the practical use of digital versatile discs (hereinafter abbreviated as DVD) has greatly expanded the storage capacity of optical discs, and has made it possible to record high-quality, long-time moving picture information. There are also signs of commercialization of high-definition video broadcasting, and research and development of large-capacity storage devices are being actively pursued. Optical discs such as compact discs (hereinafter abbreviated as CDs) and DVDs are widely used as external storage devices for computers. However, since the performance of computers has rapidly increased, the fields of information processing and information communication have been increasing. Also, there is a strong demand for higher density optical disks.

In order to increase the capacity of an optical disk, information is reproduced from smaller pits. The pit size is limited by the light spot size determined by the wavelength of the light source of the optical pickup for reading the information and the numerical aperture of the condenser lens. Is done. When the pit size in the linear direction on the spirally arranged tracks is reduced below the limit, a sufficient signal amplitude cannot be obtained, and when the interval between the tracks is reduced below the limit, the distance from the adjacent track decreases. Accurate signal reproduction is hindered by crosstalk.

As a technique for achieving higher density beyond this limit, various crosstalk removing methods for reducing crosstalk generated when the track interval is reduced have been proposed. For example, in the method disclosed in Japanese Patent Application Laid-Open No. 4-69820, two other sub-spots are generated in addition to a main light spot for reading a signal from an information track,
These sub-spots irradiate adjacent right and left adjacent tracks, and extract a crosstalk component from each reflected light to remove a crosstalk component from a signal from the main light spot. In the method disclosed in Japanese Patent Application Laid-Open No. 7-320295, a sub-spot having two peaks is generated, the positions of the peaks are made to coincide with the adjacent left and right adjacent tracks, and crosstalk from the adjacent track is generated. The components are extracted simultaneously.

[0005]

In the above-described conventional crosstalk elimination method, a method of determining a weighting coefficient when a signal from a sub spot is subtracted from a signal from a main spot becomes a problem. Taking a case where a disc with a slightly different track interval is reproduced as an example, when the track interval is small, the crosstalk component is larger, and it is necessary to subtract the sub spot signal at a large rate. Not only the track interval, but also the optimum weighting coefficient differs for each disk to be reproduced and for each reproducing apparatus, such as the pit width of the disk and the size of the light spot. Also, when playing the same disc with the same playback device, the disc tilt, defocus,
Since the optimum weighting coefficient changes successively because the track deviation changes during reproduction, it is necessary to optimize the weighting coefficient in real time.

As a method of optimizing the weighting coefficient, Japanese Patent Application Laid-Open No. 9-180374 discloses a method of sequentially calculating a correlation coefficient between a main signal and a sub-signal and using the correlation coefficient as a weighting coefficient. However, to sequentially calculate the correlation coefficient between two signals requires a high-speed sample-and-hold circuit and a large-scale arithmetic circuit, and there are problems such as an increase in size and cost of the device. Japanese Patent Application Laid-Open No. 9-320200 discloses a method of determining a weighting coefficient from the value of a sub signal at the moment when a main signal crosses zero.
Similarly, there is a problem that a high-speed sample and hold circuit is required. Also, JP-A-5-205280 discloses that
Although a method of providing a crosstalk component detection pit on an optical disc and learning an optimal weighting coefficient is disclosed, there is a problem that the detection pit reduces the capacity of the optical disc.

[0007]

In order to solve this problem, the crosstalk removing method of the present invention uses a crosstalk removing signal obtained by subtracting a signal from an adjacent track at a certain rate from a signal from a reproduction target track. Means for generating, means for binarizing the crosstalk elimination signal to output a binarized crosstalk elimination signal, and means for binarizing a signal from an adjacent track to output a binarized second channel signal , Binarized crosstalk removal signal and binarized second
Means for detecting coincidence with the channel signal, and the time during which the binarized crosstalk elimination signal and the binarized second channel signal coincide, and the binarized crosstalk elimination signal and the binarized second channel signal Means for comparing the time when they do not coincide with each other and changing the ratio of the subtraction by the subtraction means.

According to the crosstalk removing method of the present invention,
With a simple circuit configuration, the weighting coefficient is sequentially optimized without sacrificing the capacity of the optical disk, and a good crosstalk removing operation can be realized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A crosstalk removing method according to the present invention will be described below with reference to the drawings.

FIG. 1A shows an example of an optical pickup using a crosstalk removing method.
No. 95 describes this in detail. FIG. 1 (b)
3 is a diagram showing spots formed on the optical disc 34. FIG. The light emitted from the semiconductor laser 31 is a quarter
The light is split into two polarization components by the wave plate 32, and one polarization component is not given any phase change by the polarization phase filter 33, and forms a normal diffraction-limited light spot (main spot 35) on the optical disc 34. , Playback target track 3
Irradiate 9. The other polarization components are given phase steps of 0 and π by the polarization phase filter 33, and form an optical spot (sub-spot 36) having two peaks on the optical disk 34 as shown in FIG. Then, the tracks 37 and 38 adjacent to both sides of the reproduction target track are irradiated. The reflected light from the optical disk 34 is split by the polarizing beam splitter 40 into two.
The light from the main spot 35 is detected by the photodetector 41, the light from the sub-spot 36 is detected by the photodetector 42, and the two photodetectors are the signals on the track 39 to be reproduced. (A main signal 41a) and a signal on both adjacent tracks 37 and 38 (sub signal 42a).

At this time, when a high-density optical disc with a reduced track interval is being reproduced, the signals from the adjacent tracks 37 and 38 are included in the signal from the reproduction target track 39 as crosstalk. This crosstalk component can be removed by subtracting the sub-signal 42a from the 41a at a certain ratio. The crosstalk elimination method of the present invention provides a method for sequentially maintaining the subtraction ratio at an ideal value in such a crosstalk elimination apparatus. Although the optical pickup described in Japanese Patent Application Laid-Open No. 7-320295 has been exemplified here, the crosstalk removing method of the present invention can be used for an optical pickup that detects a signal on an adjacent track by another method. Further, the present invention is not limited to an optical disk, and can be used in a magnetic disk reproducing device or a receiving device of an information communication system having a plurality of channels.

Next, FIG. 2 shows an example of an apparatus for realizing the crosstalk removing method of the present invention. In the case where the removal of crosstalk is realized in the optical disk reproducing apparatus, FIG.
The main signal 10 represents a reproduction signal from a signal track to be reproduced, and the sub-signal 11 represents a reproduction signal from an adjacent track. Assume that a signal recorded on a track to be reproduced is M, a signal recorded on an adjacent track is S, the main signal 10 is M + δS, and the sub signal 11
Is assumed to be represented by S, the crosstalk elimination signal 12a becomes
(M + δS) −δS = M, and an ideal crosstalk removing operation is realized. Here, the crosstalk component from another track is originally included in the sub signal 11, but the crosstalk component included in the main signal 10 is sufficiently smaller than the main signal M if the condition of δ << 1 is satisfied. In this case, the calculation of the ideal subtraction ratio may not be affected.

During reproduction of a signal from the optical disk, the defocus and the disc tilt change to change the main signal 10.
, The crosstalk component included in changes, so that it is necessary to always adapt the subtraction ratio δ to an optimal value in order to perform an ideal crosstalk canceling operation. First, a method of determining the subtraction ratio δ that has been conventionally proposed will be described.

Now, consider a case where the crosstalk component increases and the main signal 10 changes to M + δ1S (δ1> δ). At this time, the crosstalk removal signal 12a is (M + δ1
S) −δS = M + (δ1−δ) S, and (δ1−δ)
The crosstalk component of S remains. Here, in order to obtain an ideal subtraction ratio, the crosstalk removal signal 12a
And the correlation between the sub-signals 20a.
The signal M in the crosstalk removal signal 12a and the sub signal 20
Since the signal S on the track is different from the signal S in FIG.
The correlation of a reflects the correlation between (δ1−δ) S and the sub-signal S. Here, since δ1−δ takes a positive value, the crosstalk removal signal 12a and the sub-signal 19a show a positive correlation, and it can be seen that the ideal subtraction ratio is a value larger than the current subtraction ratio δ. That is, when the correlation between the crosstalk elimination signal 12a and the sub-signal 20a is positive, the subtraction ratio is increased, and when the correlation is negative, the subtraction ratio is decreased, so that the ideal subtraction ratio is always obtained according to the reproduction state. Following this, the crosstalk removing operation can be performed. However, the crosstalk cancellation signal 12a and the sub-signal 20
Since a has a wide signal band, a high-speed sample and hold circuit is required to calculate these correlations as described above, and there is a problem that the apparatus becomes expensive.

The crosstalk elimination method of the present invention is characterized in that an ideal crosstalk elimination operation can be realized only with a simple logic circuit or an integration circuit without using a high-speed sample and hold circuit. I do.
Hereinafter, a first embodiment of the crosstalk removing method of the present invention will be described with reference to FIG.

In the crosstalk removing method according to the present embodiment, as shown in FIG.
a and the sub-signal 19a are converted to signal binarizing means 1 respectively.
4 and 15 and the binarized crosstalk removal signal 14a
And a binary sub-signal 15a. Signal binarization means 1
Reference numerals 4 and 15 output a "1" level when the input analog signal is higher than a certain signal level (hereinafter, abbreviated as a slice level), and output a "0" level when the input analog signal is lower than the slice level. The slice level is automatically and sequentially adjusted so that the time at which the “1” level is output is equal to the time at which the “0” level is output.

The binarized crosstalk removing signal 12a and the binarized sub-signal 15a output from the signal binarizing units 14 and 15 are both input to the coincidence detecting unit 16. The coincidence detecting means 16 outputs a coincidence detection signal 16a having a "0" level when the input binarized crosstalk removal signal 14a and the binarized sub-signal 15a have the same output level, and a "1" level when they have different output levels. Output. At this time, when the crosstalk elimination signal 12a and the sub-signal 19a have a positive correlation, the time when the binarized crosstalk elimination signal 14a and the binarized sub-signal 15a are at the same level becomes longer, and the coincidence detection signal The time for 16a to reach the “0” level becomes longer. Conversely, when the crosstalk elimination signal 12a and the sub-signal 19a have a negative correlation, the time during which the coincidence detection signal 16a is at the "1" level becomes longer.

The match detection signal 16 from the match detection means 16
a is input to the polarity detecting means 17. Polarity detection means 1
7 compares the time when the coincidence detection signal 16a is at the "0" level with the time when the coincidence detection signal 16a is at the "1" level, and outputs a polarity signal 17a proportional to the ratio of the time when the coincidence detection signal 16a is at the "0" level. The coefficient determining means 13 internally holds the subtraction ratio δ and increases or decreases the subtraction ratio δ according to the polarity signal 17a, so that the subtraction ratio δ can always follow an ideal value.

Although the signal delay means 18 is not essentially indispensable to the crosstalk removing method of the present invention, if the signal delay time in the variable subtraction means 12 cannot be ignored, the signal delay means 18 corrects the delay time. Then, an accurate crosstalk removing operation becomes possible. Filter 1
9 and 20 are not essentially indispensable to the present crosstalk elimination method. However, when the frequency characteristics of the signal detection path of the previous stage for extracting the main signal 10 and the signal detection path of the previous stage for extracting the sub-signal 11 are different. For example, the filter 19
By making the filter and the filter 20 have optimal characteristics, it is possible to compensate for the difference in frequency characteristics between the two signal detection paths.

FIG. 3 shows an example of a configuration for realizing the coincidence detecting means 16 and the polarity detecting means 17 in the crosstalk removing method shown in FIG. In this example, the coincidence detecting means 16 is realized by one stage of a logic circuit of an exclusive OR circuit 51, and the polarity detecting means 17 is realized by a low-pass filter 52 and a differential amplifier 53. As described above, the coincidence detecting means 16 and the polarity detecting means 17 can be realized with an inexpensive circuit configuration.

Next, a second embodiment of the crosstalk removing method of the present invention will be described. According to the second embodiment, a more accurate crosstalk removing operation can be performed than the crosstalk removing method described in the first embodiment.

As described above, the crosstalk removal signal 12
a is represented by M + (δ1−δ) S using the signal M of the track to be reproduced and the signal S of the adjacent track. Here, δ1S is a crosstalk component included in the main signal, δ1S
Represents a subtraction ratio in the variable subtraction means 12. At this time (δ
Since 1-δ) is sufficiently smaller than 1, the binarized crosstalk removal signal 14a is substantially determined by the signal M, and the contribution of the crosstalk component S to the crosstalk removal signal 14a is relatively small. That is, the output of the coincidence detecting means 17 is almost equal to the signal M of the track to be reproduced and the signal S of the adjacent track.
Is determined by whether or not they match. Where signal M and signal S
Since there is no correlation at all, if the match detection signal 16a is integrated for a sufficiently long time, the crosstalk component (δ1-δ)
A signal reflecting the correlation between S and S can be obtained. However, in this case, there is a problem that the time for convergence to the optimal subtraction ratio becomes relatively long. This problem is solved by the crosstalk removing method according to the second embodiment of the present invention.

FIG. 4 shows the configuration of an apparatus for realizing the crosstalk removing method according to the second embodiment. In the apparatus shown in FIG. 4, the binary crosstalk removal signal 14a obtained by the signal binarization means 14 is quantized in the time axis direction by the PLL circuit 22, thereby generating a time axis quantized signal 22a. An exclusive OR signal of the valued crosstalk removal signal 14a and the time axis quantized signal 22a is generated by the error occurrence timing detection means 21 and is used as an error occurrence timing signal 21a. At this time, the PLL
In order to compensate for the time delay caused by the circuit 22, the signal delay means 2 is provided before the error occurrence timing detection means 21.
3 are provided. Using the coincidence detecting means 16, a coincidence detection signal 16a is obtained as an exclusive OR of the binarized crosstalk removal signal 14a and the binarized sub-signal 15a, and the time when the coincidence detection signal 16a is at the "1" level is calculated. Although the crosstalk removing method according to the present embodiment is the same as the crosstalk removing method according to the first embodiment in terms of comparing the time at the “0” level, in the present embodiment, When comparing the times at both levels, the gate is gated with the above-mentioned error occurrence timing signal 21a, the coincidence detection signal 16a is made effective only when the error occurrence timing signal 21a is at the "0" level, and the error occurrence timing signal 2
The difference from the first embodiment is that the operation of the polarity detecting means 17 is stopped while the time 1a is at the "1" level.

The principle of operation of the crosstalk elimination method according to the present embodiment will be described based on signal waveforms at various points in the block diagram of FIG.

FIG. 5A shows a pit pattern on a reproduction target track. The solid line in FIG. 5B shows the behavior of the crosstalk elimination signal 12a when the light spot traces on the pit pattern in FIG. 5A, and the crosstalk elimination signal 12a has a crosstalk component. Assume that it remains. The solid line in FIG. 5C is a binarized crosstalk elimination signal 14a obtained by binarizing the crosstalk elimination signal 12a, and the broken line in FIG. FIG. 5D shows an error generation timing signal 21a obtained by performing an exclusive OR operation on the binarized crosstalk removal signal 14a and the time axis quantized signal 22a. Show. Considering that the difference between the solid line and the broken line in FIG. 5C is an error caused by the remaining crosstalk, for example, the portions A and D in FIG.
It can be seen that negative crosstalk remains in portions B and C. Thus, the error occurrence timing signal 21a
Is at the "0" level, the polarity of the binarized crosstalk removal signal 14a represents the polarity of the remaining crosstalk component. By comparing the polarity of this signal with the binarized sub-signal 15a, the crosstalk It is determined whether the subtraction ratio is excessive or insufficient.
Can be made to follow the optimum value by increasing or decreasing the subtraction ratio.

The reason why the high-speed and high-accuracy crosstalk elimination operation can be performed by the crosstalk elimination method in the present embodiment is as follows. As is apparent from a comparison between FIGS. 5B, 5C and 5D, the error occurrence timing signal 2
When 1a is at "1" level, the polarity of the binarized crosstalk removal signal 14a is determined by the pit pattern of the track to be reproduced, and when the error occurrence timing signal 21a is at "0" level, the binary crosstalk removal signal 14a is set. The polarity of 14a is determined by the remaining crosstalk component. That is, only when the error occurrence timing signal 21a is negative, the coincidence detection signal 1
By outputting 6a, it is possible to reduce the influence of the pit pattern of the reproduction target track and extract only the crosstalk component.

The crosstalk elimination method using the main signal from the track to be reproduced and one sub-signal for extracting the signal from the adjacent track has been described with reference to the drawings. The crosstalk elimination method of the present invention is also effective for a crosstalk elimination method using two sub-signals for extracting track signals. In the above description, the polarities of the coincidence detection signal 16a and the error occurrence timing signal 21a are limited. However, the circuit configuration in which the “0” and “1” levels of the respective signals are inverted, and “positive” and “negative” signals are used. It goes without saying that the same operation can be realized by a circuit configuration using levels and the like. Further, the present invention is not limited to an optical disk, and can be used for a receiving device of an information communication device having a plurality of channels.

[0028]

As described above, according to the present invention, even when the mixing ratio of crosstalk varies in real time, a high-speed and high-accuracy crosstalk removing operation can be realized with an inexpensive circuit configuration.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a configuration of an optical pickup including a crosstalk removing device.

FIG. 2 is a block diagram showing a first embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a circuit that realizes a polarity detecting unit of the crosstalk removing method according to the present invention.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a conceptual diagram of a signal waveform at each point according to the second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Main signal 11 Sub signal 12 Variable subtraction means 12a Crosstalk removal signal 13 Coefficient determination means 14, 15 Signal binarization means 14a Binarization crosstalk removal signal 15a Binary subsignal 16 Match detection means 16a Match detection signal 17 Polarity detection means 17a Polarity detection signal 18 Signal delay means 19, 20 Filter 21 Error generation timing detection means 21a Error generation timing signal 22 PLL circuit 22a Time axis quantization signal 23 Signal delay means 31 Semiconductor laser 32 Quarter wave plate 33 Polarizing phase filter 34 Optical disk 35 Main spot 36 Sub spot 37, 38 Adjacent track 39 Track to be reproduced 40 Polarizing beam splitter 41, 42 Photodetector 41a Main signal 42a Sub signal

Claims (4)

[Claims] When a signal of a plurality of channels is received and at least one other signal of a second channel is subtracted from a signal of the first channel by a certain ratio to remove a crosstalk component, a subtraction ratio is determined. In a crosstalk elimination method for automatically optimizing, a binarized crosstalk elimination signal obtained by binarizing a crosstalk elimination signal obtained by subtracting a second signal from a first signal and a signal of a second channel are binarized. Generating a binarized second channel signal, further detecting the coincidence between the binarized crosstalk elimination signal and the binarized second channel signal, and comparing the binarized crosstalk elimination signal with the binary signal. Comparing the time when the binarized second channel signal coincides with the time when the binarized crosstalk removal signal does not coincide with the binarized second channel signal, and Traffic light When binarization second channel signal are overlapped time is longer than with non time matching matching increases the rate of subtracting, the binarizing said crosstalk cancellation signal binarized second
A crosstalk elimination method characterized by reducing the ratio of subtraction when the time during which the channel signal does not match is longer than the time during which the channel signal does not match. 2. A method for receiving signals of a plurality of channels, subtracting a signal of at least one other second channel from a signal of the first channel at a certain rate, and removing a crosstalk component when removing the crosstalk component. In a crosstalk elimination method for automatically optimizing, a binarized crosstalk elimination signal obtained by binarizing a crosstalk elimination signal obtained by subtracting a second signal from a first signal and a signal of a second channel are binarized. Generating a binarized binary channel signal, detecting the coincidence between the binarized crosstalk elimination signal and the binarized second channel signal, and converting the binarized crosstalk elimination signal in the time axis direction. A period during which the quantized time axis quantized signal and the binarized crosstalk signal coincide with each other is defined as an error occurrence period. In the error occurrence period, the binarized crosstalk removal signal and the binarized second H Comparing the time when the channel signal coincides with the time when the binary crosstalk removal signal and the binary second channel signal do not match during the error occurrence period, When the time during which the binarized crosstalk removal signal and the binarized second channel signal coincide is longer than the time during which they do not coincide, the subtraction ratio is increased, and the binarization is performed during the error occurrence period. A crosstalk elimination method, characterized in that the subtraction ratio is reduced when a time during which the crosstalk elimination signal does not match the binarized second channel signal is longer than a time during which the two do not match. 3. A method of receiving signals of a plurality of channels and subtracting a signal of at least one other second channel from a signal of the first channel at a certain rate to remove a crosstalk component. A crosstalk elimination apparatus for automatically optimizing means for binarizing a crosstalk elimination signal obtained by subtracting the signal of the second channel from the signal of the first channel to generate a binarized crosstalk elimination signal Means for binarizing the signal of the second channel to generate a binarized second channel signal; and performing coincidence detection between the binarized crosstalk removal signal and the binarized second channel signal. Means, a time during which the binarized crosstalk elimination signal and the binarized second channel signal coincide, and a coincidence between the binarized crosstalk elimination signal and the binarized second channel signal. Comparing means for comparing the time when the binary crosstalk removal signal and the binary second channel signal coincide with each other when the time during which the binary crosstalk removal signal matches the binary second channel signal is longer than the time during which the binary crosstalk removal signal does not match; Crosstalk comprising subtraction ratio variable means for reducing a ratio of subtraction when the time during which the binary crosstalk removal signal does not match with the binary second channel signal is longer than the time during which the signal does not match. Removal device. 4. A crosstalk removing apparatus that receives signals of a plurality of channels and subtracts a signal of at least one other second channel from a signal of a first channel at a certain ratio to remove a crosstalk component. Means for binarizing a crosstalk elimination signal obtained by subtracting the signal of the second channel from the signal of the first channel to generate a binary crosstalk elimination signal; and a signal of the second channel. Means for binarizing to generate a binarized second channel signal; means for detecting coincidence between the binarized crosstalk removal signal and the binarized second channel signal; Quantizing means for quantizing the removal signal in the time axis direction to generate a time axis quantized signal, and a period in which the time axis quantized signal and the binary crosstalk signal coincide with each other are defined as an error generation period, Wherein the serial error generation period the binarized crosstalk cancellation signal with 2
Comparison means for comparing a time when the binarized second channel signal coincides with a time when the binarized crosstalk removal signal and the binarized second channel signal do not coincide in the error occurrence period. And when the time during which the binarized crosstalk elimination signal and the binarized second channel signal match during the error occurrence period is longer than the time during which they do not match, the subtraction ratio is increased. Current ratio varying means for decreasing the subtraction ratio when the time during which the binary crosstalk removal signal does not match the binary second channel signal is longer than the time during which the binary crosstalk removal signal does not match during the period. Crosstalk removal device.