JP3094726B2 - Waveform equalization method and waveform equalizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform equalization method and a waveform equalizer for a reproduced signal in an information input / output device for recording and reproducing information using light.

[0002]

2. Description of the Related Art In order to increase the density of information recorded on an information storage medium, if the mark length is made shorter than the diameter of the spot where the light beam is converged, it becomes difficult to reproduce information. The influence of the information recorded at the position immediately before and after the position of appears strongly. The effect of the information recorded at the positions before and after this is generally called intersymbol interference and degrades the characteristics of information reproduction. As one method of reducing intersymbol interference, a method using a waveform equalizer is known. FIG. 12 shows a configuration of a circuit system of a waveform equalizer using a conventional delay circuit. The input terminal 60 receives an electric signal output from the photodetector after the light irradiated to a desired position on the information storage medium is received by the photodetector. The signal input from the input terminal 60 enters the delay circuit 52 and is delayed by a time τ _u . Further, the delay circuit 5
2 is input to the delay circuit 53 and the time τ
_u get a delay. By extracting signals from before, between, and behind these two delay circuits 52 and 53, the time τ
Three signals with information separated by _u are obtained. Time τ _u
Are the light spot diameter on the information storage medium and the relative moving speed v of the light beam and the information storage medium on the information storage medium.
Determined from the distance T _u on the information storage medium tau _u = T
_{It has a u} / v relationship. That is, three signals having information recorded at positions separated by the distance _Tu are obtained. The signal from the input terminal 60 and the output signal from the delay circuit 64 are each input to the attenuating circuit 51 and are attenuated to the extent of intersymbol interference from adjacent positions. The output signal from the delay circuit 52 and each output signal from the attenuation circuit 51 are input to the arithmetic circuit 67. The arithmetic circuit 67 subtracts each output signal from the attenuation circuit 51 from the output signal from the delay circuit 52. An output signal from the arithmetic circuit 67 is output to an output terminal 80. As described above, the output terminal 80 receives the input signal delayed by the time τ, and obtains a signal from which the intersymbol interference has been removed to some extent. In an optical system in which the wavelength λ of the light source is 680 nm and the NA of the objective lens is 0.6, the basic period T = the shortest mark length =
When reproducing digital information recorded with the shortest space length = 0.425 μm, two eye patterns obtained as a result of waveform equalization by the waveform equalizer shown in FIG.
3 (a) and 3 (b). In FIG. 13A (conventional example a), the signal is increased by a factor of 0.05 by the attenuation circuit 51.
In (b) (conventional example b), the signal is set to 0.
It was assumed to be 30 times. Further, the delay time of the delay circuits 52 and 53 is determined as τ _u = τ, where T _u = T. Where time τ
Is determined from the diameter of the light spot on the information storage medium and the relative moving speed v between the light beam on the information storage medium and the information storage medium, and the distance T on the information storage medium and τ = T / v Have a relationship. The timing at which the desired position is located at an odd multiple of T / 2 from the end of the mark or space recorded on the information storage medium is t0, and the timing shifted by τ / 2 from t0 is before and after t1, t1. The timing shifted by .tau. / 4 is referred to as t2. In FIG. 13, an area A is an eye used when performing normal code detection, an area B,
C is an eye used when performing code detection with a partial response. Here, the normal code detection is a code detection method of determining digital information based on whether a signal is larger or smaller than a certain threshold at a timing t0. The amplitude of the entire signal is I, the amplitude of the region A at the timing t0 is IA, the amplitude of the timing t1 of the regions B and C is IB and IC, and the amplitude of the timing t2 of the region A is IA1. IA /
Let I, IB / I, IC / I, and the aperture ratio of the eye at the timing t2 of the area A be IA1 / I. When the conventional waveform equalizer is used, the aperture ratio of the eye in the conventional example a is 29%,
The opening ratio of the eye at the timing t2 of the region A is 20%, and the opening ratio of the eye in the conventional example b is 43% and 43%, respectively.
13%, 7%, and the aperture ratio of the eye at the timing t2 of the region A is 12%.

[0003]

However, in the above-described configuration, when the pit length is shortened, the intersymbol interference cannot be sufficiently removed. In FIG. 13A, the area A
The opening ratio of the eye at timing t0 is not so large,
As shown in FIG. 13B, there is a problem in that if the aperture ratio of the eye at the timing t0 in the region A is to be increased, the aperture ratio of the eye at the timing t2 is sharply reduced.

In view of the foregoing, the present invention provides a waveform equalization method and a waveform equalizer that effectively removes intersymbol interference, reduces variations caused by intersymbol interference, and increases an eye opening ratio used when performing normal code detection. An object is to provide an equalizer.

[0005]

In order to achieve the above object, a waveform equalizer of the present invention comprises an optical pickup head device and a first equalizer.
A series of tracks on an information storage medium, on which a digital information is recorded / reproduced substantially at an integral multiple of T when the basic period is T, comprising a signal processing circuit, a clock signal generating circuit, and a second signal processing circuit. A first position, and at least one position on the same track that is separated from the first position by an arbitrary integer multiple of T as a second position group, (1) the optical pickup head The device optically reads while relatively moving on the information storage medium, and outputs a first signal including information recorded on the information storage medium,
The first signal processing circuit includes a delay circuit, a group of N variable gain amplifier circuits, and an arithmetic circuit, and the delay circuit receives the first signal and is recorded at the first position. A main signal including information and an adjacent signal group including information recorded in the second position group are generated, and the variable gain amplifying circuit multiplies the adjacent signal group by a certain coefficient to compare with the main signal. Attenuating, the arithmetic circuit subtracts the attenuated adjacent signal from the main signal and outputs the result. (2) The optical pickup head device optically reads information recorded at the first position and the second position group simultaneously while relatively moving a series of tracks on the information storage medium. Outputting a main signal including information recorded at the first position and an adjacent signal group including information recorded at the second position group, wherein the first signal processing circuit outputs the first signal Receiving the signal group, comprising N variable gain amplifier circuits and an arithmetic circuit, wherein the variable gain amplifier circuit multiplies the adjacent signal group by a coefficient to attenuate the signal with respect to the main signal; Subtracts the attenuated adjacent signal from the main signal and outputs the result.

The clock signal generation circuit having the configuration of either (1) or (2), receiving the output signal, generates a clock signal synchronized with the information recorded on the information storage medium. The second signal processing circuit receives the clock signal and outputs the coefficient so that the coefficient of the variable gain amplifier circuit periodically changes in synchronization with information recorded on the information storage medium. Controls the variable gain amplifier circuit. It has the structure of.

[0007]

According to the present invention, by controlling the gain of the variable gain amplifying circuit to periodically change in synchronization with the information of the fundamental period T recorded on the information storage medium, the present invention provides It becomes a waveform equalizer capable of obtaining the removed signal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a waveform equalizer according to the present invention will be described in detail with reference to FIGS. In the embodiments, the same reference numerals are used when the same components as those in the conventional example can be used.

(First Embodiment) As a first embodiment of the present invention, one light beam is applied to a desired track as shown in FIG. Remove low frequency components of the signal by dynamic operation,
1 shows a configuration of an optical system of a waveform equalizer that processes and calculates a signal using a delay circuit to reduce intersymbol interference. The configuration of this optical system is well known.

A divergent beam 70 having linearly polarized light emitted from the semiconductor laser light source 1 becomes a parallel beam after passing through the collimator lens 2, passes through the polarizing beam splitter 3, passes through the λ / 4 plate 9, and becomes circularly polarized light. It becomes a beam, passes through the objective lens 8, and is focused on the information storage medium 4.
Information represented by marks or spaces is formed on the information storage medium 4 to form a track, and the light beam 70 condensed by the lens 8 is optically designed to be positioned on the track. The light beam 70 reflected and diffracted by the information storage medium 4 passes through the lens 8 again, passes through the λ / 4 plate 9, and has linear polarization light having a polarization direction different from that of the light beam emitted from the light source 1 by 90 degrees. It becomes a beam and enters the polarization beam splitter 3. The light beam 70 incident on the polarizing beam splitter 3 is reflected and guided to the cylindrical lens 6, and the light beam 70 transmitted through the cylindrical lens 6 becomes a light beam having astigmatism, which is condensed by the lens 7 and detected by the photodetector. 5 is received.

FIG. 2 shows the relationship between the photodetector 5 and the light beam 70 received by the photodetector 5 in the optical system shown in FIG. 1 and the configuration of the circuit system of the waveform equalizer. The photodetector 5 includes light receiving units 501 to 504. Light beam 70 is received by light receiving section 501
504 are received. By performing a desired operation on the signals output from the light receiving units 501 to 504, a focus error signal and a tracking error signal can be obtained. Here, the focus error signal is obtained by the astigmatism method, and the tracking error signal is obtained by the push-pull method. Although an arithmetic circuit for obtaining the focus error signal and the tracking error signal is omitted because it is difficult to understand the gist of the present invention, the focus error signal is obtained by summing the signals output from the light receiving units 501 and 503 and the light receiving unit 502. By performing a differential operation on the sum of the signals output from the light receiving units 501 and 502, the tracking error signal is calculated by subtracting the sum of the signals output from the light receiving units 501 and 502 from the sum of the signals output from the light receiving units 503 and 504. Each is obtained by performing a differential operation. The focus error signal and the tracking error signal are respectively supplied to the actuators 91 and 92 shown in FIG. 1 to perform focus and tracking control.

Information recorded on a desired track on the information storage medium 4 is obtained by adding signals output from the light receiving units 501 to 504 by an adding circuit 61.

An output signal from the adding circuit 61 is input to a differential operation circuit 620. Also, the reference signal generation circuit 621
Is also input to the differential operation circuit 620 and subjected to a subtraction process. As a result, the DC component of the signal from the adding circuit 61 is removed. The output from the differential operation circuit 620 is input to the delay circuit 63 and is delayed by the time τ. Further, the output signal from the delay circuit 63 is input to the delay circuit 64 and is delayed by the time τ. The temporal basic period τ is τ = T / v from the relative speed v between the optical pickup head device and the information storage medium and the basic period T of information recorded on the information storage medium.
Is determined by Here, the output signal from the delay circuit 63 becomes the main signal 63a, and the output signal from the delay circuit 64 and
The output signal from the operation calculation circuit 620 which is not delayed is the adjacent signal group 64a.

An output signal from the differential operation circuit 620 is input to a variable gain amplifier 65, an output signal from the delay circuit 64 is input to a variable gain amplifier 66, and a signal multiplied by a certain coefficient k is output. Is done. The main signal 63a and the output signals from the variable gain amplifying circuits 65 and 66 are
7 is input. The arithmetic circuit 67 subtracts the adjacent signal group 64a multiplied by k from the main signal 63a. Arithmetic circuit 67
Are obtained from an output terminal 80. The signal output from the output terminal 80 is demodulated as a reproduced waveform at the timing of a clock signal obtained from an output terminal 81 described later. The signal from the arithmetic circuit 67 is input to a clock extracting circuit 68, and a clock signal 68a having a period τ synchronized with the information recorded on the information storage medium 4 is extracted.
The clock signal 68a is output to the clock signal output terminal 81 and to the signal processing circuit 69. The signal processing circuit 69 controls the variable gain amplifiers 65 and 66 so that the gains of the variable gain amplifiers 65 and 66 change periodically in synchronization with the clock signal 68a.

FIG. 3 shows an example of how the gains of the variable gain amplifier circuits 65 and 66 are changed. When a mark or space is arranged on the track as shown in FIG. 3A and the light spot moves in the direction of the arrow, the signal obtained from the terminal 80 changes as shown in FIG. 3B. In FIG. 3B, the horizontal axis represents time, and the vertical axis represents signal intensity. FIG. 3C shows a clock signal 68a obtained from the clock extraction circuit 68, and FIG.
(D) shows how the gains of the variable gain amplifier circuits 65 and 66 change. In FIG. 3D, the horizontal axis represents time, and the vertical axis represents gain. The timing at which the desired position is located at an odd multiple of T / 2 from the end of the mark or space recorded on the information storage medium is t0, and the timing shifted by τ / 2 from t0 is before and after t1, t1. The timing shifted by .tau. / 4 is referred to as t2.

In this embodiment, the gain at the timing t0 is k
a, control is performed so that the gain at timing t1 becomes a triangular wave with kb (ka> kb).

In an optical system in which the wavelength of the light source is λ = 680 nm and the NA of the objective lens is 0.6, the basic period T = the shortest mark length =
FIG. 4 shows an eye pattern obtained by using the waveform equalizer shown in this embodiment when reproducing digital information recorded with the shortest space length = 0.425 μm. In FIG. 4, the gains of the variable gain amplifier circuits 65 and 66 are ka = 0.30, k
b = 0.05. In FIG. 4, as in FIG. 13, an area A is an eye used when performing normal code detection, an area B,
C is an eye used when performing code detection with a partial response. Here, the normal code detection is a code detection method of determining digital information based on whether a signal is larger or smaller than a certain threshold at a timing t0. The amplitude of the entire signal is I, the amplitude of the region A at the timing t0 is IA, the amplitude of the timing t1 of the regions B and C is IB and IC, and the amplitude of the timing t2 of the region A is IA1. IA /
Let I, IB / I, IC / I, and the aperture ratio of the eye at the timing t2 of the area A be IA1 / I. When the waveform equalizer of this embodiment is used, the aperture ratios of the eyes are 41%, 49%, and 4%, respectively.
3%. When the conventional waveform equalizer of FIG. 12 is used, the aperture ratios of the eyes in the conventional example a are 29%, 49%, and 43%, respectively.
%, And 43%, 13% and 7% in Conventional Example b, respectively. Further, the opening ratio of the eye at the timing t2 in the region A is 23% in the present embodiment, and 20% in the conventional example a in the conventional example.
%, And 12% in Conventional Example b.

In the case of the conventional example a, the region A is at timing t0,
Both t2 are not so large. In the case of the conventional example b, the eye aperture ratio at the time t0 in the region A is large, but when the timing is shifted to t2, the eye aperture ratio sharply decreases.

When the waveform equalizer shown in this embodiment is used,
The opening ratio of the eye at the timing t0 in the region A is inferior to that of the conventional example b, but is remarkably improved as compared with the conventional example a. Therefore, a noise margin at the time of code detection becomes large. Also,
The opening ratio of the eye at the timing t2 is greatly improved compared to the two conventional examples. That is, it is possible to increase the aperture ratio of the eye at the timing t2 while keeping the aperture ratio of the eye at the timing t0 large. When the aperture ratio of the eye at a position shifted from the timing t0 of the area A (for example, at the timing t2) increases, the margin for the fluctuation of the detection timing when performing the code detection increases. As described above, the error rate when reproducing the information recorded on the information storage medium is reduced.

Further, the aperture ratios of the eyes in the regions B and C are substantially the same as those of the prior art a having a large aperture ratio. For this reason, a noise margin when code detection is performed with a partial response is increased, an error rate when reproducing information recorded on an information storage medium is reduced, and information can be reproduced with high reliability.

As a special effect of this embodiment, since the gain may be changed as a triangular wave, the signal processing circuit 69 and the variable gain amplifying circuits 65 and 66 can be realized by simple circuits.

Further, by removing the DC component of the signal before the variable gain amplifying circuit as in this embodiment, even if a DC offset signal is superimposed on the signal from the optical pickup head device, the offset is removed in advance. Therefore, even if the gain of the variable gain amplifying circuit changes with time, the margin for eye jitter is not narrowed.

In the present embodiment, since the optical pickup head device needs only one beam, both the optical system and the light source can have a simple configuration. Further, by realizing the delay circuit in an analog manner, it can be realized with a small number of circuit elements.

In this embodiment, the differential operation with respect to the reference signal is performed to remove the DC component.
If the generated signal is changed according to the situation in 21, it is possible to cope with various offsets and obtain a good signal.

It is also possible to change the gain sinusoidally. In this case, the signal processing circuit 69 and the variable gain amplifier circuits 65 and 66 can be realized by simple circuits. As an effect, it is possible to obtain an eye opening ratio substantially equal to that of a triangular wave.

In this embodiment, the waveform equalization is performed based on the information recorded at three different positions by two delay circuits. However, the waveform equalization is performed at more different positions by using more delay circuits. It is of course possible to perform waveform equalization on the basis of the information obtained, and it is also possible to perform waveform equalization on the basis of information recorded at two different positions using only one delay circuit. When this is expressed using a mathematical expression, when N is an arbitrary natural number and i is a natural number equal to or less than N, the i-th variable gain amplifier outputs a signal obtained by multiplying the input signal by k _i , and a desired track Is a main signal including information recorded at a desired position of S (0), a signal including information recorded at a position x away from the desired position is S (x), and n ₁ to n ₁
n _N is an integer other than 0 that does not overlap each other,
S (n ₁ · T), S (n ₂ · T)..., S (n _N · T): S (0) −k ₁ · S (n ₁ · T) −k ₂ · S (n ₂ · T)... −k _N · S (n _N · T) The waveform equalization can be performed by outputting the signal. In general, the amplitude and average value of the coefficient k to be applied to a signal including information recorded at a position far from a desired position in an adjacent signal group is a signal including information recorded at a position near a desired position. May be made smaller than the amplitude and average value of the coefficient k to be multiplied. As a result, the waveform equalization method and waveform equalizer of the present invention are effective even when intersymbol interference occurs in a wide range or when intersymbol interference occurs asymmetrically in front and back.

In the present embodiment, an example has been shown in which a delay circuit for outputting a signal delayed for a predetermined time is processed in an analog manner. However, the signal is digitized by an analog / digital converter, stored in a memory, and stored in a memory. It is also effective to read out from the memory after a lapse of time, and perform digital / analog conversion and output. Further, it is also possible to realize the same operation as that shown in the present invention by converting a digitized signal into digital data by a digital numerical operation processing device.

In this embodiment, the variable gain amplifying circuit performs non-inverting amplification and performs signal subtraction by the arithmetic circuit 67. However, the variable gain amplifying circuit performs inverting amplification.
Needless to say, the same effect can be obtained by the addition by the arithmetic circuit, and the arithmetic circuit and the variable gain amplifier circuit may be realized by the same element.

In this embodiment, controlling the gain of the variable gain amplifier circuit and controlling the coefficient to be applied to the adjacent signal group are the same.

(Second Embodiment) As a second embodiment, a variable gain amplifying circuit having a different gain changing method will be described. The configurations of the optical system and the circuit system are the same as in the first embodiment. The same symbols are used as in FIGS.

The signal processing circuit 69 controls the gains of the variable gain amplifying circuits 65 and 66 to change in a broken line in synchronization with the clock signal 68a. This is shown in FIG. 5A to 5C are the same as FIGS. 3A to 3C.
FIG. 5D shows how the gains of the variable gain amplifier circuits 65 and 66 change in this embodiment. In FIG. 5D, the horizontal axis is time,
The vertical axis represents the gain. The timing at which the desired position is located at an odd multiple of T / 2 from the end of the mark or space recorded on the information storage medium is defined as t0, t0 to τ /.
The timing shifted by 2 is shifted by τ before and after t1 and t1, respectively.
The timing shifted by / 4 is defined as t2. In the present embodiment, the gain has ka at timing t0, kb (ka> kb) at timing t1, and gain kc at timing t2.
have.

FIG. 6 shows an eye pattern obtained when the waveform equalizer shown in this embodiment is used under the same conditions as in the first embodiment. In FIG. 6, the gains of the variable gain amplifier circuits 65 and 66 are changed in a polygonal manner so that ka = 0.30, kb = 0.05, and kc = 0.20. In FIG. 6, symbols A, B,
C, I, IA, IB, IC, and IA1 are common to FIGS. When the waveform equalizer of the present embodiment is used, the aperture ratios of the eyes are 41%, 49%, and 43%, respectively. Further, the aperture ratio of the eye at the timing t2 in the area A is 2 in the case of the present embodiment.
4%.

When the waveform equalizer shown in this embodiment is used,
The eye opening ratio of each region is almost the same as in the first embodiment,
The aperture ratio of the eye at the timing t2 in the region A is improved as compared with the first embodiment. For this reason, the noise margin at the time of code detection becomes large, and at the same time, the margin for fluctuation in detection timing when code detection is performed becomes larger than that of the first embodiment. Therefore, the error rate when reproducing the information recorded on the information storage medium is reduced.

The aperture ratio of the eyes in the regions B and C is the first
Has the same eye opening ratio as that of the embodiment. Therefore, a noise margin when performing code detection with a partial response increases, and an error rate when reproducing information recorded on an information storage medium decreases.

The effect can be obtained by changing the gain other than that shown in the first and second embodiments. Although the circuit system becomes complicated, an eye opening with a stronger jitter margin can be obtained if the gain changes smoothly as the desired position moves.

(Third Embodiment) As a third embodiment, a case where a low-frequency component of a signal is removed using a low-frequency cutoff circuit will be described. FIG. 7 shows the configuration of the circuit system. The optical system is the same as that of the first embodiment. The shape of the light receiving portion of the photodetector 5 is the same as that of FIG. The output signal from the adding circuit 61 is input to the input terminal 60 in FIG.

The signal input from the input terminal 60 is input to the low frequency cutoff circuit 622 to remove the DC component. The output from the low frequency cutoff circuit 622 is input to the delay circuit 63 and is delayed by the time τ. Further, the output signal from the delay circuit 63 is input to the delay circuit 64 and is delayed by the time τ.
Here, the output signal from the delay circuit 63 becomes the main signal 63a, and the output signal from the delay circuit 64 and the low-frequency cutoff circuit 6
The output signal which does not receive the delay from the signal group 22 is the adjacent signal group 64a.
Becomes

An output signal from the low frequency cutoff circuit 622 is input to a variable gain amplifier 65, an output signal from the delay circuit 64 is input to a variable gain amplifier 66, and a signal multiplied by a certain coefficient k is output. Is done. The main signal 63a and the output signals from the variable gain amplifier circuits 65 and 66 are input to the arithmetic circuit 67. The arithmetic circuit 67 subtracts the adjacent signal group 64a multiplied by k from the main signal 63a. Arithmetic circuit 6
The signal output from 7 is obtained from terminal 80. The signal from the arithmetic circuit 67 is input to the clock extraction circuit 68, and the period τ synchronized with the information recorded on the information storage medium 4
Is extracted. Clock signal 68
a is output to the clock signal output terminal 81 and to the signal processing circuit 69. The signal processing circuit 69 periodically synchronizes with the clock signal 68a.
Variable gain amplifying circuit 6 so that the gains of
5, 66 are controlled.

In this embodiment, a DC component can be removed with a very simple circuit configuration by using a low-frequency cutoff circuit to remove a low-frequency component. An eye opening ratio comparable to that of the first or second embodiment can be obtained without reducing the margin for jitter.

(Fourth Embodiment) As a fourth embodiment, an example in which a low-frequency component of a signal is not removed will be described. FIG. 8 shows a configuration of a circuit system according to the fourth embodiment.

The signal from the input terminal 60 is input to the delay circuit 63 and the variable gain amplifying circuit 65 without removing the low frequency components of the signal. Thereafter, signals are processed in the same manner as in the first to third embodiments.

In this embodiment, when the DC component of the signal obtained from the optical pickup head device is smaller than the amplitude of the modulation by the code, the intersymbol interference can be effectively removed with a very simple circuit configuration. The specific eye opening ratio is substantially the same as in the first and second embodiments, and a great effect can be obtained.

(Fifth Embodiment) As a fifth embodiment, an example in which the load on the circuit system is reduced by using a multi-beam optical pickup head device will be described. FIG. 9 shows the configuration of the optical system.
Shown in

A method in which a plurality of light beam spots from a multi-beam optical pickup head device are formed on a track on an information storage medium, and the light from each spot is detected simultaneously and individually and weighted for calculation. Is disclosed in JP-A-2-282937.

In the optical system shown in FIG. 9, optical elements which can use the same optical elements as the optical system shown in FIG. 1 are denoted by the same reference numerals as the optical elements shown in FIG. The optical system shown in this embodiment differs from the optical system shown in the previous embodiment in that three light beams 70 to 72 from the semiconductor laser light sources 1, 11, and 12 having different wavelengths are applied to the information storage medium. It is.

Light beams having linearly polarized light emitted from the semiconductor laser light sources 1, 11, and 12 that generate light beams having different wavelengths are arranged adjacent to each other by two beam splitters 31. Light beam 70-7
Numeral 2 denotes a parallel beam after passing through the collimating lens 2, passing through the polarizing beam splitter 3, passing through the λ / 4 plate 9 to become a circularly polarized light beam, passing through the objective lens 8, and being collected on the information storage medium 4. Be lighted. Information represented by a mark or a space is formed on the information storage medium 4 and forms a track.
Reference numerals 72 are optically designed so as to be located on the same track. The light beams 70 to 72 reflected and diffracted by the information storage medium 4 pass through the lens 8 again, and
Is converted into a linearly polarized light beam having a polarization direction different from that of the light beam emitted from the light source 1 by 90 degrees, and enters the polarization beam splitter 3. The light beams 70 to 72 incident on the polarization beam splitter 3 are reflected and guided to the cylindrical lens 6, and the light beams 70 to 72 transmitted through the cylindrical lens 6 become light beams having astigmatism, and are condensed by the lens 7. ,
The light passes through the diffraction grating 10 and is received by the photodetector 50. Since the three light beams 70 to 72 have different wavelengths, the angles diffracted by the diffraction grating 10 are different from each other, and the three light beams can be largely separated from each other.
Thus, three light beams can be detected by different light receiving sections without overlapping.

Tracks on information storage medium 4 and light beam 7
The relationship between 0 and 72 is shown in FIG. FIG. 10 shows the information storage medium 4 in an enlarged manner. Reference numerals 82 and 83 denote marks and spaces on a track, and reference numerals 70 to 72 denote condensed light beams. The interval between the light beams converged on the information storage medium 4 is set to be substantially an integral multiple of the fundamental period T of the recorded information. In the drawing, the light beam intervals are arranged so as to be substantially equal to T.

The photodetector 50 in the optical system shown in FIG.
FIG. 11 shows the relationship between the light beams 70 to 72 received by the photodetector 50 and the configuration of the circuit system of the waveform equalizer. The photodetector 50 includes light receiving units 505 to 510. Light beam 70
Are the light receiving units 506 to 509, and the light beam 71 is the light receiving unit 50
At 5, the light beams 72 are respectively received by the light receiving units 510.
By performing a desired operation on the signals output from the light receiving units 506 to 509, a focus error signal and a tracking error signal can be obtained. Here, the focus error signal is obtained by the astigmatism method, and the tracking error signal is obtained by the push-pull method.

The signals from the light receiving units 506 to 509 are added by an adding circuit 61. The signal from the light receiving section 505 is input to the variable gain amplifier circuit 65, the signal from the light receiving section 510 is input to the variable gain amplifier circuit 66, and a signal multiplied by a certain coefficient k is output. Here, the addition circuit 6
1 becomes the main signal 63a, and the light receiving section 505
And the signal from the light receiving unit 510 becomes the adjacent signal group 64a. The main signal 63a and the output signals from the variable gain amplifier circuits 65 and 66 are input to the arithmetic circuit 67. The arithmetic circuit 67 subtracts the adjacent signal group 64a multiplied by k from the main signal 63a. The signal output from the arithmetic circuit 67 is
Obtained from The signal from the arithmetic circuit 67 is input to a clock extracting circuit 68, and a clock signal 68a having a period τ synchronized with the information recorded on the information storage medium 4 is extracted. The clock signal 68a is output to the clock signal output terminal 81 and to the signal processing circuit 69. The signal processing circuit 69 controls the variable gain amplifiers 65 and 66 so that the gains of the variable gain amplifiers 65 and 66 change periodically in synchronization with the clock signal 68a.

In this embodiment, a delay circuit is not required, so that the load on the circuit system can be greatly reduced, and intersymbol interference can be effectively removed.

In this embodiment, three semiconductor laser light sources for emitting light beams of different wavelengths are used as the light source. However, the information storage medium is irradiated with two or more light beams to sufficiently emit light beams at the time of detection. An optical pickup head device having a configuration other than that shown in this embodiment, such as a method using an array-type semiconductor laser light source that emits light beams having different wavelengths, may be used as long as it can be detected separately.

[0052]

As described above, according to the present invention,
The gain of the variable gain amplifying circuit is controlled so as to be periodically changed in synchronization with the information of the basic cycle T recorded on the information storage medium, and a signal including information on a position adjacent to a desired position is amplified by the variable gain amplifying circuit. By amplifying in a circuit and subtracting from information recorded in a desired position, a signal from which intersymbol interference has been removed is obtained. The eye pattern of the signal from which the intersymbol interference has been removed is not only large when the normal code detection is performed but also when the timing is shifted. Can be reduced, and information can be reproduced with a low error rate.

Further, the eyes at the time of performing the code detection by the partial response are greatly opened, and the information can be reproduced with a low error rate.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical system of a waveform equalizer according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a circuit system of a waveform equalizer according to a first embodiment of the present invention.

FIG. 3 shows information recorded on an information storage medium, a signal input to a clock extraction circuit, a clock signal output from the clock extraction circuit, and a gain of a variable gain amplification circuit according to the first embodiment of the present invention. Relationship diagram

FIG. 4 is a diagram of an eye pattern obtained by using the waveform equalizer shown in the first embodiment of the present invention.

FIG. 5 shows information recorded on an information storage medium according to a second embodiment of the present invention, a signal input to a clock extracting circuit, a clock signal output from the clock extracting circuit, and a gain of a variable gain amplifying circuit. Relationship diagram

FIG. 6 is a diagram of an eye pattern obtained by using the waveform equalizer according to the second embodiment of the present invention.

FIG. 7 is a configuration diagram of a circuit system of a waveform equalizer according to a third embodiment of the present invention.

FIG. 8 is a configuration diagram of a circuit system of a waveform equalizer according to a fourth embodiment of the present invention.

FIG. 9 is a configuration diagram of an optical system of a waveform equalizer according to a fifth embodiment of the present invention.

FIG. 10 is a diagram showing a relationship between positions of light spots on an information storage medium according to a fifth embodiment of the present invention.

FIG. 11 is a configuration diagram of a circuit system of a waveform equalizer according to a fifth embodiment of the present invention.

FIG. 12 is a configuration diagram of a circuit system of a waveform equalizer shown in the conventional example.

FIG. 13 is a diagram of an eye pattern obtained by using the waveform equalizer shown in the conventional example.

[Explanation of symbols]

 Reference Signs List 4 information storage medium 51 attenuation circuit 63 delay circuit 63a main signal 64 delay circuit 64a adjacent signal group 65 variable gain amplifier circuit 66 variable gain amplifier circuit 67 arithmetic circuit 68 clock extraction circuit 68a clock signal 69 signal processing circuit T basic cycle (distance) τ Basic period (time) t0 Normal code detection timing t1 Timing shifted by τ / 2 from t0 t2 Timing shifted by τ / 4 from t0

Claims (10)

(57) [Claims] 1. A waveform equalization method for removing intersymbol interference of a signal obtained by reading information recorded on an information storage medium on which digital information is recorded and reproduced substantially at an integral multiple of T, where T is a basic period. In the above, a desired position of a desired track is defined as a first position, and at least one position on the track separated from the first position by an arbitrary integral multiple of T other than 0 is defined as a second position group. Obtaining a main signal including information recorded in the first position, and an adjacent signal group including information recorded in the second position group, and multiplying the adjacent signal group by a predetermined coefficient. When the main signal is attenuated and the attenuated adjacent signal group is subtracted from the main signal, the coefficient is periodically changed in synchronization with information recorded on the information storage medium. Waveform equalization method. 2. A waveform equalizing method for removing intersymbol interference of a signal obtained by reading information recorded on an information storage medium on which digital information is recorded and reproduced substantially at an integral multiple of T, where T is a basic period. In the above, a desired position of a desired track is defined as a first position, and at least one position on the track separated from the first position by an arbitrary integral multiple of T other than 0 is defined as a second position group. Obtaining a main signal including information recorded in the first position and an adjacent signal group including information recorded in the second position group, removing low frequency components from the adjacent signal group, The adjacent signal group from which the low frequency component has been removed is multiplied by a predetermined coefficient to attenuate the main signal, and when the attenuated adjacent signal group is subtracted from the main signal, the signal is recorded on the information storage medium. The coefficient is synchronized with the information Waveform equalization method characterized by periodically changing. 3. The value of a coefficient to be multiplied to an adjacent signal group when a desired position is located at an odd multiple of T / 2 from an end of a mark or space recorded on an information storage medium is equal to a desired position. The waveform according to any one of claims 1 to 2, wherein the coefficient periodically changes so that the value of the coefficient is larger than a value of the coefficient when the distance is T / 2 from the position. Equalization method. 4. The waveform equalizing method according to claim 3, wherein the coefficient applied to the adjacent signal group changes periodically by a triangular wave function. 5. A waveform equalizer used when reproducing information using a light beam, comprising: an optical pickup head device, a first signal processing circuit, a clock signal generation circuit, and a second signal processing circuit. When the basic period is T, a desired position on a series of tracks on the information storage medium on which digital information is recorded and reproduced substantially at an integral multiple of T is set as a first position, and the first position is set on the track. At least one position apart from the position by any integer multiple of T other than 0 is defined as a second position group, and the optical pickup head device optically reads while relatively moving on the information storage medium. Outputting at least one first signal including information recorded on a track, wherein the first signal processing circuit receives the first signal,
Is an arbitrary natural number, i is a natural number less than or equal to N, and k _i is a real number greater than 0 and less than or equal to 1, the i-th variable gain amplifying circuit outputs a signal obtained by multiplying the input signal by the coefficient k _i. A variable gain amplifier circuit group, a delay circuit that outputs a signal obtained by delaying an input signal for a predetermined time, and an arithmetic circuit that performs addition or subtraction of two or more signals, and information recorded in the first position. Is defined as S (0), a signal including information recorded at a position separated by x from the first position is represented as S (x), and n _{1 to} n _N are non-zero and do not overlap with each other. As an integer, the adjacent signal group including the information recorded in the second position is represented by S (n ₁ · T), S (n ₂ · T),..., S (n _N · T)
A signal of S (0) −k ₁ · S (n ₁ · T) −k ₂ · S (n ₂ · T)... −k _N · S (n _N · T) The signal generation circuit generates and outputs a clock signal synchronized with the information recorded on the information storage medium. The second signal processing circuit receives the clock signal and records the clock signal on the information storage medium. A waveform equalizer characterized by periodically changing the coefficient in synchronization with information. 6. A waveform equalizer used for reproducing information using a light beam, comprising: an optical pickup head device, a first signal processing circuit, a clock signal generation circuit, and a second signal processing circuit. Assuming that the basic period is T, a desired position on a series of tracks on the information storage medium on which digital information is recorded and reproduced substantially at an integral multiple of T is defined as a first position, and the first position is determined on the same track. At least one position apart from the position by any integer multiple of T other than 0 is defined as a second position group, and the optical pickup head device moves the first position while relatively moving on the information storage medium. A position and the second position group are optically read simultaneously, and a main signal including information recorded at the first position and an adjacent signal group including information recorded at the second position group are read. Outputting the first signal processing Circuit, the N and any natural number, i
Is a natural number less than or equal to N and k _i is a real number greater than 0 and less than or equal to 1, an i-th variable gain amplifier circuit is a group of N variable gain amplifier circuits that output a signal obtained by multiplying an input signal by a coefficient k _i And an arithmetic circuit for adding or subtracting two or more signals, wherein the main signal is S (0), and a signal including information recorded at a position x away from the first position is S (0). x)
Where n _{1 to} n _N are integers other than 0 that do not overlap each other, and the adjacent signal groups are S (n ₁ · T), S (n ₂ · T),.
As _{(n N · T), S} (0) -k 1 · S (n 1 · T) -k 2 · S (n 2 · T) ··· -k N · S (n N · T) comprising signal The clock signal generation circuit generates and outputs a clock signal synchronized with the information recorded on the information storage medium. The second signal processing circuit receives the clock signal and stores the information A waveform equalizer characterized by periodically changing the coefficient in synchronization with information recorded on a medium. 7. A method for reproducing information using a light beam.
The optical pickup head device, the first signal processing circuit, and the
A clock signal generation circuit and a second signal processing circuit.
A series of tracks on an information storage medium on which information is recorded and reproduced
The desired position on the track as the first position and
Away from the first position by any integer multiple of T other than 0
At least one position is defined as a second position group, and the optical pickup head device is provided on the information storage medium.
Optically read while moving relative to the track
Emitting at least one first signal containing the recorded information;
The first signal processing circuit receives the first signal, and
Is an arbitrary natural number, i is a natural number of N or less, and k_iTo
The i-th variable gain when a real number greater than 0 and less than 1
The amplifier circuit converts the input signal into a coefficient k_iOutput a signal multiplied by
N variable gain amplifier circuits and input signal delayed for a fixed time
A delay circuit that outputs the output signal, and a low-frequency
A third signal processing circuit for outputting a signal from which components have been removed
And an arithmetic circuit for adding or subtracting two or more signals
A main signal including information recorded in the first position.
S (0), and written at a position x away from the first position.
Removed low frequency components from signals containing recorded information
Denote the signal as S '(x), n₁~ N _NAre non-overlapping 0
Information recorded in the second position as an integer other than
Signal group from which low-frequency components have been removed
 S '(n₁・ T), S '(n_Two· T) ..., S '(n_N・ T)
And S (0) -k₁・ S '(n₁・ T) -k_Two・ S '(n_Two・ T) ・ ・ ・ -k_N・ S '(n_N.T), and the clock signal generation circuit records the information on the information storage medium.
Generating and outputting a clock signal synchronized with the received information, wherein the second signal processing circuit receives the clock signal
In synchronization with the information recorded on the information storage medium.
Waveform equalization characterized by periodically changing the coefficient
vessel. 8. A waveform equalizer used for reproducing information using a light beam, comprising: an optical pickup head device, a first signal processing circuit, a clock signal generation circuit, and a second signal processing circuit. Assuming that the basic period is T, a desired position on a series of tracks on the information storage medium on which digital information is recorded and reproduced substantially at an integral multiple of T is defined as a first position, and the first position is determined on the same track. At least one position apart from the position by any integer multiple of T other than 0 is defined as a second position group, and the optical pickup head device moves the first position while relatively moving on the information storage medium. A position and the second position group are optically read simultaneously, and a main signal including information recorded at the first position and an adjacent signal group including information recorded at the second position group are read. Outputting the first signal processing Circuit, the N and any natural number, i
Is a natural number less than or equal to N and k _i is a real number greater than 0 and less than or equal to 1, an i-th variable gain amplifier circuit is a group of N variable gain amplifier circuits that output a signal obtained by multiplying an input signal by a coefficient k _i A third signal processing circuit that outputs a signal obtained by removing a low-frequency component from an input signal, and an arithmetic circuit that performs addition or subtraction of two or more signals, wherein the main signal is S (0), A signal obtained by removing a low-frequency component from a signal including information recorded at a position separated by x from the first position is represented as S ′ (x), and n _{1 to} n _N are integers other than 0 that do not overlap each other. S ′ (n ₁ · T), S ′ (n ₂ · T),..., S ′ (n _N · T) are obtained by removing the low-frequency component from the adjacent signal group.
_{As, S (0) -k 1 ·} S '(n 1 · T) -k 2 · S' (n 2 · T) ··· -k N · S ' outputs (n _N · T) comprising signal The clock signal generation circuit generates and outputs a clock signal synchronized with the information recorded on the information storage medium, and the second signal processing circuit receives the clock signal and outputs the clock signal on the information storage medium. A waveform equalizer characterized by periodically changing the coefficient in synchronization with recorded information. 9. A coefficient multiplied by an adjacent signal group when a desired position is located at an odd multiple of T / 2 from an end of a mark or a space recorded on an information storage medium has a value of a desired position. The waveform according to any one of claims 5 to 8, wherein the coefficient changes periodically so that the value of the coefficient is larger than a value of the coefficient when the coefficient is located at a position separated by T / 2 from the position. Equalizer. 10. The waveform equalizer according to claim 9, wherein the coefficient applied to the adjacent signal group changes periodically with a triangular wave function.