JPH0944849A - Reproducing method for optical information recording medium and reproducing device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly reproduce a signal from an optical information recording medium, in which information is loaded, by a displacement of a mark in the vertical direction of a track, without influence by an external factor. SOLUTION: The displacement position of a reproduced mark is detected by comparing it with that of the reproduced mark immediately before. Namely, by calculating a difference between the peak value of a mark displacement signal at the marking part of the synchronizing signal detected from the synchronizing signal extract circuit 9 and the peak value detection circuit 15 and the peak value of the mark displacement signal detected just before and stored in a preceding peak value storage circuit 16, and by making the quotient of this difference divided by the number of the mark displacement positions to be a threshold value for detecting the mark displacement of the data part, the mark displacement of the data part is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing method and a reproducing apparatus for an optical information recording medium for optically recording information, and more particularly to the presence or absence of a mark which substantially changes the reflected light amount of irradiated light. The present invention relates to a reproducing method and a reproducing apparatus for an optical information recording medium, in which information is recorded by both the displacement of a mark in the track orthogonal direction with respect to the center of the information track.

[0002]

2. Description of the Related Art Conventionally, in order to increase the amount of information recorded on an optical information recording medium such as an optical disk, not only information based on the presence or absence of a mark that substantially changes the reflected light amount of irradiated light but also the center of the information track. On the other hand, there has been proposed a method of recording information by slightly displacing the mark in the direction orthogonal to the track. In such an optical information recording medium, it is meaningless unless the total recording capacity of the presence or absence of a mark and the displacement of the mark is increased in proportion to the complexity of the system. Therefore, the amount of displacement of the mark in the direction orthogonal to the information track must be an extremely small amount that is sufficiently smaller than the period of the information track so as not to widen the track pitch of the information track.

As a method for detecting such a slight displacement of the mark, Japanese Patent Application Laid-Open No. 4-74317 discloses the following method. On the recording medium, the marks are modulated so that the ratio of the average value of the number of marks displaced in one direction and the number of marks displaced in the other direction with respect to the center of the information track becomes a predetermined value. Displace and record. Then, at the time of reproduction, the difference between the output signals respectively output from the two parts of the photodetector is compared with a threshold value to perform waveform shaping, and the average value of the waveform shaped signal is set to a predetermined value. Playback is performed while controlling the value.

[0004]

However, as described above, the displacement in the direction orthogonal to the track is a minute amount,
The mark displacement detection signal is affected by various external factors during reproduction. For example, there are lens shift, crosstalk, track shift, focus shift, tilt, etc., and these external factors cause disturbance in the mark displacement detection signal (hereinafter referred to as the mark displacement signal). In particular, since lens shift and crosstalk are serious problems, it is necessary to set the threshold value for detecting the mark displacement in the track orthogonal direction so as not to be influenced by the above factors.

FIG. 4 shows how the mark displacement signal is disturbed by the lens shift. In the figure, the mark M recorded on the information track is displaced in one of the left and right directions with respect to the center A of the information track, and an example in which binary information due to the displacement of the mark M is recorded is shown. The mark displacement signal S1 in the figure shows the case of reproduction by an ideal optical system without lens shift, and it can be seen that the polarity is inverted corresponding to the displacement of the mark M in the left-right direction. In the case of such a mark displacement signal, the threshold value is
For example, it is possible to detect the mark displacement by setting it to 0V.

On the other hand, when a lens shift is applied to the optical system, the mark displacement signal becomes S2 shown in FIG.
As shown in the figure, it can be seen that the peak value of the amplitude of the mark displacement signal S2 changes according to the displacement direction of the mark M and the mark length of the mark M. However, this peak value changes depending on the lens shift amount and shift direction even if the mark length is the same, so the threshold value for detecting mark displacement requires control according to the lens shift amount and shift direction. is there. Although crosstalk is improved to some extent by optimally setting the track pitch and the mark displacement amount, it remains as a fluctuation component of the mark displacement detection value.

Regarding the setting of the threshold value, Japanese Patent Laid-Open No. 4-74
As described in Japanese Patent No. 317, there is a method of controlling by negatively feeding back the result of binarizing the mark displacement, but this method cannot deal with lens shift and crosstalk, and is not realistic. Absent. Although a method of performing differential detection by grouping marks to be recorded as described in the publication can be considered, the degree of freedom in modulation is limited, and differential detection may be performed depending on the size of the grouping unit. There is a problem in that the magnitude of signal disturbance exceeds the detection selection criterion, and there is a high possibility that a detection error will occur.

Therefore, the present invention has been made by paying attention to the above points, and an optical information recording medium which bears information by the displacement of the mark in the direction orthogonal to the track can be properly used regardless of the influence of external factors. It is intended for signal reproduction.

[0009]

The present invention provides, as means for achieving the above object, "the presence or absence of a mark that gives a substantial change in the amount of reflected light to the irradiated light, and the direction in the direction orthogonal to the information track. In a reproducing method of an optical information recording medium in which information is recorded by bearing both information on the displacement of the mark and the displacement of the reproduced mark, the displacement position of the reproduced mark is detected by comparison with the displacement position of the previously reproduced mark. A reproducing method of an optical information recording medium characterized by the above.

As a result of repeated studies by the inventor of the present invention, the reproduced mark M _i and the previous mark M even if the lens shift occurs.
It was found that the relative change in the detected value with _i-1 was not affected by the lens shift. That is, as shown in FIG. 5, the peak value P _i of the mark displacement signal at the mark M _i ,
The peak value P of the mark displacement signal at the immediately preceding mark M _{i-1
It has been found} that when the difference from _i-1 is D1 for the mark displacement signal S1 and D2 for the mark displacement signal S2, D1 and D2 have almost the same value. In addition,
As shown in FIG. 6, it is known that the difference D between the average values H is substantially the same when the average value of the amplitude of the mark displacement signal at the mark portion is used. Therefore, if the displacement amount of the current mark M _i is determined based on the relative displacement with respect to the mark displacement of the immediately preceding mark M _i−1 , even for the lens shift that has the greatest influence on the detection of the mark displacement. It is possible to detect with high accuracy.

[0011]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing the structure of a first embodiment of a reproducing apparatus for an optical information recording medium of the present invention. A reproducing apparatus 101 shown in FIG. 1 includes an optical pickup 51 including a semiconductor laser 2, a beam splitter 3, an objective lens 4 and the like, and an optical information recording medium (hereinafter referred to as a recording medium) 1 obtained from the optical pickup 51.
The signal processing unit 52 is configured to perform various kinds of signal processing by using reflected light from the electric signal as an electric signal.

Information is recorded on the recording medium 1 by optically readable marks such as an optical disk and an optical card, and it is detachable from the reproducing device 101. The mark M recorded on the recording medium 1 is recorded by being displaced in the track orthogonal direction with respect to the center line A of the information track as shown in FIG. 2, and by this displacement, binary information is recorded. ing. The displacement of the mark M is sufficiently smaller than the period (track pitch) of the information track and is a small amount of discrete value. Further, the mark M is formed, for example, as a pit having an uneven shape corresponding to information on the surface of the light transmissive substrate so that the reflected light amount is substantially changed with respect to the irradiated light.

Further, at a predetermined position of the recording medium 1, a reference signal in which a mark M having a predetermined length is arranged at a position most displaced to one side and a position most displaced to the other is recorded. Have a section. Usually, at a predetermined position on an optical information recording medium such as an optical disc, a sync signal for bit synchronization in which marks of a predetermined length are continuously recorded is recorded, and the mark length is the data length. It is longer than the section. Since the amplitude of the mark displacement signal increases as the mark length increases, it is desirable to use the synchronization signal for bit synchronization as the reference signal. Therefore, in the recording medium 1, this synchronization signal is used as the reference signal, and the mark M is arranged at the position most displaced to one side and the position most displaced to the other in the synchronization signal portion. That is, since the recording medium 1 records binary information by mark displacement as shown in FIG. 2, the displacement positions of the marks M are one each on the left and right sides of the information track center A. Is set. Therefore, in the case of the recording medium 1, the sync signal is displaced laterally with respect to the center A of the information track for recording.

The displacement position of the mark M is, for example, 1 on the left and right with the information track center position and the information track center A interposed therebetween.
Similarly, in the case of setting a total of three values, the marks of the synchronization signal are similarly recorded at the position most displaced to one side and the position most displaced to the other, that is, the displacement positions on the left side and the right side with respect to the center of the information track. . Also, depending on the mark displacement, 4
Similarly, in the case of recording information equal to or more than the value, the synchronization signal is similarly recorded at the position most displaced to one side and the position most displaced to the other side. In the case of the present embodiment, the displacement direction of the mark is either left or right with respect to the information track center A. Therefore, in the following description, this displacement direction is referred to as the mark displacement polarity.

The optical pickup 51 in the reproducing apparatus 101 shown in FIG. 1 condenses the laser light output from the semiconductor laser 2 with the objective lens 4 and irradiates the recording medium 1 with the beam, and the beam splitter 3 records the recording medium. The reflected light from 1 is guided to the photodetector 5 of the signal processing unit 52. A mechanism for moving the optical pickup 52 in a direction orthogonal to the information track and a mechanism for focus / tracking servo are not shown.

The photodetector 5 is composed of a photodiode or the like which converts light into an electric signal according to the light intensity,
The information track of the recording medium 1 is divided into the left and right directions. The detection signals output from each of the divided parts of the photodetector 5 are output to the adder 6 and the subtractor 13, respectively. The adder 6 outputs the detection signal for detecting the presence or absence of the mark, and the subtracter 13 outputs the detection signal for detecting the mark displacement.

The output signal from the adder 6 is binarized by the slice circuit 7, and the PLL circuit 8 and the mark detection circuit 1 are provided.
1 and the first demodulation circuit 10, respectively. PLL
The circuit 8 generates a clock pulse from the output signal from the slice circuit 7 and supplies it to the synchronization signal extraction circuit 9 and the sample pulse generation circuit 12. The sync signal extraction circuit 9 extracts the sync signal from the output signal of the slice circuit 7 and the clock pulse from the PLL circuit 8 and supplies it to the polarity determination circuit 17. Further, the mark detection circuit 11 determines the polarity of the output of the slice circuit 7 and supplies the result to the sample pulse generation circuit 12 and the peak detection circuit 15. The sample pulse generation circuit 12 generates a sample pulse for sampling the mark displacement signal from the clock pulse from the PLL circuit 8 and the output signal of the mark detection circuit 11 and supplies it to the sample hold circuit 14. This pulse is assumed to have been gated on the clock pulse at the mark.

On the other hand, the output of the subtractor 13 is supplied to the sample hold circuit 14. The sample hold circuit 14 receives the signal from the sample pulse generating circuit 12, samples and holds the output of the subtractor 13, and supplies the sample output to the peak detection circuit 15. The peak detection circuit 15 detects the peak value of the amplitude of the mark displacement signal within the mark from the output signals of the mark detection circuit 11 and the sample hold circuit 14. The output signal of the peak detection circuit 15 is output to the polarity determination circuit 17 and the previous peak storage circuit 16, and the previous peak storage circuit 16 stores the output signal from the peak detection circuit 15 as the previous peak value.

In the polarity determination circuit 17, the peak detection circuit 1
5 and the output value of the previous peak storage circuit 16 are compared to determine whether or not the displacement of the mark has changed, and the second demodulation circuit 18
To supply. At this time, the recording medium 1 is used as a criterion for determination.
The above-mentioned synchronization signal recorded at a predetermined position of is used. This will be described below.

In the polarity determination circuit 17, the output difference of the mark displacement signal of the sync signal from the output signals of the sync signal extraction circuit 9, the peak detection circuit 15, and the previous peak storage circuit 16 (see FIG. 4).
(D1 or D2) shown in FIG. 2 is detected, and the detected value is divided by the number of mark displacement positions (in the present embodiment, the number of mark displacement positions is two, so it is 1/2 of this detected value).
Is the threshold. Then, when reproducing the data portion, it is determined based on this threshold value whether or not the mark displacement positions of the peak detection circuit 15 and the previous peak storage circuit 16 have changed. Further, since the displacement direction of the mark is known in advance from the synchronization signal, the polarity determination circuit 17 determines the displacement of the mark in the data portion after that, using the mark displacement in the synchronization signal as a reference. Therefore, the detected threshold value and the mark displacement reference are stored in the storage means (not shown). When the above-mentioned synchronization signal is recorded in a plurality of portions of the recording medium 1, the threshold value and the mark displacement reference are updated for each synchronization signal.

Further, when the polarity judgment circuit 17 judges that the polarity of the mark displacement is reversed from the threshold value detected by the above operation and the reference of the mark displacement during reproduction of the data portion, the peak detection circuit 15 of the mark. The stored value update signal is output to the previous peak storage circuit 16 in order to store the output of the above in the previous peak storage circuit 16. In this way, the mark displacement polarity is determined by comparison with the immediately preceding mark displacement polarity, and the result is output to the second demodulation circuit 18.
Then, the difference between the peak value of the mark displacement signal of the reproduced mark and the previously detected peak value stored in the previous peak storage circuit 16 is compared with the detected threshold value to determine the mark displacement. Play the information.

The first demodulation circuit 10 demodulates the information depending on the presence or absence of the mark M, and the second demodulation circuit 18 demodulates the information based on the mark displacement, and the first demodulation circuit 10 and the second demodulation circuit. The signals demodulated by the circuit 18 are combined in the combining circuit 19 at the same timing and finally output as digital data recorded on the recording medium 1.

In the above embodiment, the threshold value is detected using the peak value P of the amplitude of the mark displacement signal at the mark portion. However, as shown in FIG. 6, the mark displacement signal at the mark portion is detected. The average value H _i of the amplitude of S2 (or S1),
It is also possible to detect H _i−1 and use the difference D2 (or D1) to detect the threshold value.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram schematically showing the structure of the second embodiment of the reproducing apparatus for the optical information recording medium of the present invention. The same components as those of the reproducing apparatus 101 of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.
The difference from the reproducing apparatus 101 is that the signal processing unit 53 includes a mark length detecting circuit 20 and a previous mark length storing circuit 21, and the polarity determining circuit 17 determines the mark length of the reproduced mark and the mark length of the previous reproduced mark. The criterion for polarity determination is changed according to Hereinafter, this point will be described.

When the mark length is relatively short with respect to the size (diameter) of the irradiated light spot, for example, as shown in FIG.
As shown in, the detected value of the mark displacement signal S1 or S2 becomes small. When it is desired to increase the recording density, it is desired to displace as many marks as possible to increase the amount of information, so that the shortest mark is also displaced to carry information. However, when the threshold value is uniquely determined as in the reproducing apparatus 101, the displacement of the mark having a short mark length may not be detected. However, if the threshold value is set in accordance with the short mark length, the S / N of detection will decrease.

Therefore, in the reproducing apparatus 102 shown in FIG.
The threshold is appropriately changed according to the mark length detection result of the mark length detection circuit 20. That is, FIG. 5 or FIG.
, The marks M _i and 1 in the mark displacement signal
It can be seen that the difference between the peak value or the average value at the mark portion with respect to the immediately preceding mark M _i-1 changes according to the mark lengths of the marks M _i and M _i-1 . Therefore, the mark M
By changing the threshold value for detecting the mark displacement according to the mark lengths of _i and the mark M _i−1 , it is possible to correctly detect the mark displacement of the short mark length.

The operation until the threshold value for detecting the mark displacement is calculated is the same as that of the reproducing apparatus 101.
The mark displacement detection in the data section is performed based on the threshold value calculated in the sync signal section.
Then, the threshold value is changed according to the mark length of the reproduced mark and the mark length of the previously reproduced mark as described above. This will be described below.

The mark length detection circuit 20 includes a PLL circuit 8
The clock generated in step 1 and the output signal from the mark detection circuit 11 are supplied, and the mark length is detected from them. The detection result of the mark length detection circuit 20 is output to and stored in the previous mark length storage circuit 21 and is also supplied to the polarity determination circuit 17. The polarity determination circuit 17 compares the output of the peak detection circuit 15 with a threshold value stored in a storage unit (not shown) to determine the polarity of the mark. At this time, the mark length of the reproduced mark M _i is detected from the output of the mark length detection circuit 20, and the previous mark length storage circuit 2
The mark length of the mark M _i-1 reproduced immediately before the output of 1 is detected. Then, it is determined polarity mark the mark length and the mark length of the mark M _i-1 of the mark M _i, and reproduced by changing the threshold based on the total value for example a total of. Then, the result is output to the second demodulation circuit 18. In the second demodulation circuit 18, the reproducing device 10
Similar to 1, the information based on the mark displacement is demodulated and the result is output to the synthesizing circuit 19. After that, the playback device 101
Is processed in the same way as.

In the above, the embodiment of the present invention has been described with reference to the mark displacement as a typical binary value.
The same configuration can be used for values, ... Also,
This is applicable even when a recording method is adopted in which the displacement amount is changed for a long mark within the same mark.

[0030]

According to the reproducing method and reproducing apparatus of the optical information recording medium of the present invention, the presence or absence of the mark which gives a substantial change in the reflected light amount to the irradiated light and the mark in the direction orthogonal to the information track. When reproducing an optical information recording medium in which information is recorded by carrying both the displacement and the displacement of the information, the displacement position of the reproduced mark is detected by comparing with the displacement position of the mark reproduced one time before. Therefore, it is possible to correctly reproduce the signal regardless of the influence of external factors such as lens shift.

When the displacement information is carried up to a mark having a short mark length, the threshold value is changed according to the mark length of the reproduced mark and the mark length of the previously reproduced mark. It becomes possible to satisfactorily detect a mark displacement of a short mark length in which the detected value of the displacement signal is small.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the structure of a first embodiment of a reproducing apparatus for an optical information recording medium of the present invention.

FIG. 2 is a diagram for explaining a mark recorded on the optical information recording medium in FIG.

FIG. 3 is a diagram schematically showing the structure of a second embodiment of the reproducing apparatus for the optical information recording medium of the present invention.

FIG. 4 is a diagram showing how a mark displacement signal is disturbed due to lens shift.

FIG. 5 is a diagram for explaining the reproduction principle in FIG. 1 or FIG.

FIG. 6 is a diagram for explaining the reproduction principle in FIG. 1 or FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 recording medium (optical information recording medium) 9 reference signal extraction circuit (reference signal extraction means) 13 subtractor 14 sample hold circuit 15 peak value detection circuit (peak value detection means) 16 previous peak storage circuit (peak value storage means) 17 polarity determination circuit 20 mark length detection circuit (mark length detection means) 21 previous mark length storage circuit (mark length storage means) 101, 102 playback device

Claims (6)

[Claims] 1. An optical recording system in which information is recorded both by the presence or absence of a mark that gives a substantial change in the amount of reflected light to the irradiated light and the displacement of the mark in the direction orthogonal to the information track. In the reproducing method of the information recording medium, the reproducing position of the reproduced mark is detected by comparing with the displacement position of the previously reproduced mark. 2. A data section in which information is recorded by both the presence or absence of a mark that gives a substantial change in the amount of reflected light to the irradiated light and the displacement of the mark in the direction orthogonal to the information track. And a reference signal section for recording a reference signal in which a mark having a predetermined length is arranged at the most displaced position on one side and the most displaced position on the other side, in the reproducing method of the optical information recording medium, The difference between the peak value or the average value of the amplitude of the mark displacement signal at the mark portion of the reference signal and the peak value or the average value of the mark displacement signal of the reference signal reproduced one time before is detected, and this difference is detected. A reproducing method of an optical information recording medium, characterized in that a displacement position of a mark in the data portion is detected by using a value divided by the number of displacement positions as a threshold value. 3. The reproducing method for the optical information recording medium according to claim 2, wherein when the data portion is reproduced, the threshold is determined according to the mark length of the reproduced mark and the mark length of the preceding mark. A reproducing method of an optical information recording medium, characterized by changing a value. 4. Information is recorded in the data section by making information both responsible for the presence or absence of a mark that gives a substantial change in the amount of reflected light to the irradiated light and the displacement of the mark in the direction orthogonal to the information track. In the reproducing apparatus of the optical information recording medium having a reference signal portion for recording a reference signal in which the mark having a predetermined length and the most displaced position on one side and the most displaced position on the other side are arranged, Reference signal extracting means for extracting a signal, peak value detecting means for detecting the peak value of the mark displacement signal of the reproduced mark, and 1 obtained by this peak value detecting means.
And a peak value storage means for storing the peak value of the mark displacement signal of the reference signal reproduced before, and in the mark portion of the reference signal detected by the peak value detection means based on the output of the reference signal extraction means. The difference between the peak value of the mark displacement signal and the peak value of the previously detected mark displacement signal stored in the peak value storage means is calculated, and the difference is divided by the number of mark displacement positions to obtain the value. A reproducing apparatus for an optical information recording medium, which is used as a threshold value for detecting a mark displacement position of a data section. 5. The information is recorded in the data section by making the information both responsible for the presence or absence of a mark that gives a substantial change in the amount of reflected light to the irradiated light and the displacement of the mark in the direction orthogonal to the information track. In a reproducing apparatus for an optical information recording medium having a reference signal portion for recording a reference signal in which marks having a predetermined length are alternately arranged at a position most displaced to one side and a position most displaced to the other A reference signal extracting means for extracting the reference signal, an average value detecting means for detecting an average value of the amplitude of the mark displacement signal of the reproduced mark at the mark portion, and one before the peak value detecting means. An average value storage means for storing the average value of the amplitudes of the detected mark displacement signals, and in the mark portion of the reference signal detected by the average value detection means based on the output of the reference signal extraction means. Calculating an average value of the mark displacement signal, the difference between the average value of the detected mark displacement signal before one which is stored in the average value storage means,
A reproducing apparatus for an optical information recording medium, wherein a value obtained by dividing the difference by the number of mark displacement positions is used as a threshold value for detecting the mark displacement position of the data section. 6. A reproducing apparatus for an optical information recording medium according to claim 4 or 5, wherein mark length detecting means for detecting the length of the mark, and the mark preceding by the mark length detecting means. A mark length storage means for storing the mark length of the reproduced mark, and the mark length detected by the mark length detection means and the mark length of the previously reproduced mark stored in the mark length storage means. A reproducing apparatus for an optical information recording medium, wherein a threshold value for detecting a mark displacement in the data section is changed according to the above.