JP2002319208A - Method and device for magneto-optical reproduction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for a magneto-optical reproduction, in which waveform deviations caused by the characteristics of a medium and a recording and reproducing system is corrected, and recorded information is reproduced correctly. SOLUTION: A pattern is detected from reproduced signals and an amount of correction for waveform deviation generated, depending on the pattern, is computed from a prescribed equation. Reproduced signals are corrected based on the computed amount of correction. As for the methods for correction, there are two ways: one is to add to and to subtract from an offset with respect to amplitudes, and the other is to use interpolation in a time-axis direction. Moreover, it is possible to adaptively set the coefficients included in a correction equation from the amount of jitters generated, based on phase error signals obtained by reproducing known signal patterns.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical reproducing method and apparatus for reproducing information utilizing a magneto-optical effect.

[0002]

2. Description of the Related Art Conventionally, recording on a magneto-optical disk or the like
In a reproduction system, it is known that a waveform shift occurs in a recording signal or a reproduction signal due to characteristics of a medium. An outline of the waveform shift will be described with reference to FIG. In FIG.
(A) is a reproduced waveform, and (B) is a clock. Here, it is assumed that the reproduction waveform is sampled at the rising edge of the clock in the reproduction system. The symbol x in (A) is a sampling signal. When a waveform shift occurs due to the characteristics of the medium, when the level changes from the “H” level to the “L” level at the time k1 in FIG. Sampling of a reproduced waveform having a waveform shift causes performance degradation of a PLL loop and a decoding unit at a subsequent stage.

On the other hand, for example, Japanese Patent Application Laid-Open No. H10-500
No. 00 discloses a method of performing data detection determination after adding a predetermined positive offset value to reproduced data at a transition point where the level shifts from “H” level to “L” level. Japanese Patent Application Laid-Open No. 05-197957 discloses a method of measuring a recording pulse width or the like at the time of recording information and controlling a rising position to compensate for a waveform shift at the time of recording.

In a PLL loop (data PLL) based on a sample value of a reproduced signal, an erroneous detection occurs in a phase error signal due to a waveform shift. FIG. 17 schematically shows the phase error detection in the data PLL. Data P
In the LL, a phase error is obtained based on a sample value of an edge portion of the reproduction signal. In FIG. 17, reference numeral 920 denotes a reproduced signal, and .circleincircle. And .circle-solid. Represent sample values by a clock.

FIG. 1A shows a case where the phase of the clock is delayed with respect to the reproduced signal, and the phase error outputs a positive value.
(B) shows a case where the phases of the clocks match, and the phase error becomes zero. (C) is a case where the phase of the clock is advanced, and the phase error has a negative value. The PLL loop performs control based on the phase error signal. However, when a waveform shift 930 occurs with respect to the reproduction signal 920 as shown in (D), the phase error detected at the edge becomes ■, and an erroneous value is generated.

[0006]

However, in the above-mentioned Japanese Patent Laid-Open Publication No. Hei 10-50000, only the level change point is mentioned. For example, the waveform shift amount changes depending on the waveform pattern reaching the change point. I can't handle it. Here, when the “H” level section of the reproduced signal is a mark and the “L” level section is a space, if the waveform shift amount fluctuates depending on the space between the mark and the space, etc. Unless the correction amount of the waveform shift is set adaptively according to (recording mark length), a desired effect cannot be obtained.

Further, in the method of compensating for a waveform shift at the time of recording as described in Japanese Patent Application Laid-Open No. 05-197957, when the shortest mark length is shortened for high density recording, the recording shorter than the shortest mark length is performed. Due to the influence of the compensation by the pulse, the possibility of occurrence of bit loss or the like increases. Further, since the data PLL uses the edge portion of the reproduction signal, it is indispensable to appropriately correct the recording mark length in order to achieve desired performance. Therefore, it is not possible to cope with a waveform deviation of a reproduced signal only by correcting the level change point with a fixed correction amount as described in Japanese Patent Application Laid-Open No. 10-50000.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to correct a waveform shift caused by characteristics of a medium and a recording / reproducing system and to reproduce a recorded information accurately. And a device.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an information reproducing method for detecting a recording mark formed on a recording medium and generating a reproduction signal. The length is detected, and the reproduction signal is corrected with a correction amount corresponding to the detected mark length.

Further, in a magneto-optical reproducing apparatus for detecting a recording mark formed on a recording medium and generating a reproduction signal, a means for detecting a mark length of the recording mark based on the reproduced signal, Means for correcting the reproduction signal with a correction amount corresponding to a mark length.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In all the following embodiments, a mark portion and a space portion of a signal are collectively referred to as a recording mark.

(First Embodiment) FIG. 1 is a block diagram showing the configuration of a first embodiment of a magneto-optical reproducing apparatus according to the present invention. In FIG. 1, reference numeral 101 denotes a magneto-optical disk serving as an information recording medium, and 102 denotes a spindle motor for rotating the magneto-optical disk 101 at a predetermined speed. A magnetic head 103 for generating a magnetic field modulated in accordance with a recording signal is provided on an upper surface of the magneto-optical disk 101, and an optical head 104 is provided on a lower surface thereof so as to face the magnetic head 103.

The optical head 104 irradiates a recording light beam to record information, or irradiates a reproducing light beam and detects reflected light from the medium to reproduce recorded information. At this time, a semiconductor laser (not shown) as a recording / reproducing light source and an optical sensor (not shown) for detecting reflected light from a medium are provided in the optical head 104. The semiconductor laser is driven by a laser drive circuit 108,
Information recording and reproduction are performed by controlling the light beam of the semiconductor laser for recording and reproduction. Further, a domain wall moving type magneto-optical medium is used as the magneto-optical disk 101, and information is reproduced by moving the domain wall. A detailed description of the reproducing method using the domain wall displacement type magneto-optical medium is omitted.

When recording information, the magneto-optical disk 10
1 is rotated at a predetermined speed by driving the spindle motor 102, and in this state, the recording data is
7 is supplied. The pre-encoder 107 modulates, for example, NRZI sequence data. The modulation signal output from the pre-encoder 107 is supplied to a magnetic head driver 106, and the magnetic head driver 106 generates a magnetic head 103 for generating an external magnetic field according to the modulation signal.
Drive. Thereby, the magnetic head 103 generates a magnetic field according to the modulation signal and applies the magnetic field to the magneto-optical disk 101. At the same time, data is recorded on the magneto-optical disk 101 by irradiating the magneto-optical disk 101 with a recording light beam from the optical head 104 according to a drive signal from the laser drive circuit 108.

On the other hand, at the time of reproducing information, the magneto-optical disk 101 is similarly controlled to rotate at a predetermined speed, and a light beam for reproduction is irradiated from the optical head 104 onto the magneto-optical disk 101. The reflected light from the magneto-optical disk 101 is detected by an optical sensor of the optical head 104,
A signal is generated. This RF signal is supplied to the AGC circuit 109 through the preamplifier 105, and the AGC circuit 109
In, gain control is performed according to the RF signal, and an RF signal having a predetermined amplitude is generated.

The reproduced RF signal processed by the AGC circuit 109 is converted into a digital signal by the A / D converter 110.
The RF digital signal converted into the digital signal is supplied to the waveform correction circuit 111 and the reproduction compensation circuit 114. The reproduction compensation circuit 114 includes a pattern detection circuit 115 and a correction amount generation circuit 116, detects a recording mark length of data from the RF digital signal, and generates a waveform shift correction signal corresponding to each recording mark length. The waveform correction circuit 111 corrects the RF digital signal based on the waveform shift correction signal supplied from the reproduction compensation circuit 114.

The corrected RF digital signal is supplied to a decoding circuit 1
12 and the decoding circuit 112 outputs the decoded data by detecting the difference. Although the decoded data is generated by the difference detection here, the PRM
A known decoding method such as L or bit by bit may be used.

Next, a description will be given of the operation of the reproduction compensation of the waveform deviation, which is a feature of the present embodiment. Reproduction compensation circuit 114
Is composed of a pattern detection circuit 115 and a correction amount generation circuit 116. FIG. 2 shows the configuration of the pattern detection circuit 115.
Shown in In FIG. 2, reference numeral 201 denotes a difference circuit which outputs a difference value of the RF digital signal. Reference numeral 202 denotes a pattern measurement circuit that measures a space between a mark and a space as a recording mark length. The operation will be described with reference to FIG.

First, the reproduced waveform is, for example, as shown in FIG.
The signal is as shown in FIG. This is sampled by a clock generated by a PLL circuit (not shown),
It is supplied from the A / D converter 110 as a discrete digital signal. The crosses in FIG. 16A indicate the sampling signals as described above. The difference circuit 201 is A
A difference signal is generated from the RF digital signal supplied from the / D converter 110. This difference signal is obtained by subtracting the immediately preceding sampled signal value from the currently sampled signal value, and the generated difference signal has a signal waveform as shown in FIG.

The difference signal generated by the difference circuit 201 is supplied to a pattern measurement circuit 202,
In 02, ternary determination is performed on the difference signal. Specifically, as shown in FIG. 3, positive and negative threshold values T1 and T2 are set for the difference signal d (k), and the determination is performed by the following method.

D (k) .gtoreq.T1.fwdarw. "1" d (k) .ltoreq.T2.fwdarw. "-1" In addition to the above. "0". In the section of “0”, the counter value of the internal counter is incremented in synchronization with the clock (clock generated by the PLL loop). When the determination result changes from "1" or "-1" to "0", it means that the rising or falling edge of the reproduction signal is detected, and the counter value at that time is output. The recording mark length P is a value obtained by adding +1 to the output counter value. The pattern measuring circuit 202 measures the recording mark length in this way, resets the counter after outputting the recording mark length, and measures the next recording mark length.

In the pattern detection circuit 115, when the above-mentioned determination result changes from “1” to “0” as the signal F indicating the direction of the change of the rising and falling, “F = 1” as the rising portion When the determination result changes from “−1” to “0”, “F = 0” is output to the correction amount generation circuit 116 as a falling portion. Here, for example, as shown in FIG. 4A, when the pattern detection circuit 115 performs pattern detection on a section from time k2 to k3 of the difference signal, the pattern interval (recording) as shown in FIG. Mark length) P can be obtained. FIG. 4C shows the direction F of the change.

The correction amount generation circuit 116 generates a correction amount by the following equation (1) based on the signal supplied from the pattern detection circuit 115.

Y (i) = − A · P (i−1) + B · P (i) (1) A and B are predetermined correction coefficients set in advance, and P (i) is a current recording mark. The length, P (i-1), indicates the previous recording mark length. That is, the correction amount is calculated by multiplying the current recording mark length and the immediately preceding recording mark length by a predetermined correction coefficient and adding the values.

Here, in the magneto-optical recording, the temperature of the laser beam irradiated portion of the magneto-optical recording medium reaches the Curie point due to the irradiation of the laser beam during recording, and the magnetization disappears. However, magnetization exists at a peripheral portion where the temperature has not risen to the Curie point, and there is a floating magnetic field caused by the magnetization. The domain wall as the recording mark end is formed at the rear end in the light beam traveling direction. When the domain wall as the recording mark end is formed, these floating magnetic fields are superimposed on the modulation magnetic field applied from outside by a magnetic head for forming the domain wall. Acts in shape. The magnitude of the stray magnetic field varies depending on the distance between the domain wall formed immediately before and the domain wall to be formed next, that is, the length of a recording mark to be formed and the length of a mark located before that. Therefore,
The strength of the stray magnetic field acting on the domain wall formation site differs depending on the mark length (or mark length sequence) to be recorded.

Further, the position where the domain wall is formed is determined based on the relationship between the temperature and the magnetic field strength. Here, the laser beam intensity and the magnetic field intensity applied from the magnetic head are kept in a steady state,
If the recording mark length or the recording mark length sequence is different, the superimposed floating magnetic field strength is different, so the magnetic field strength applied to the magnetic domain forming position is the magnetic field strength from the magnetic head +
The intensity of the stray magnetic field, which is substantially the intensity of the magnetic field applied to the magnetic domain forming portion, differs depending on the length of the recording mark or the length of the recording mark. As a result, a phenomenon in which the domain wall formation position differs depending on the recording mark length appears.

In the present embodiment, a waveform shift occurring depending on the recording mark length is corrected based on such a phenomenon. That is, as shown in equation (1), 1
The previous recording mark length and the current recording mark length are each multiplied by a predetermined correction coefficient, the sum thereof is calculated as a correction amount, and the waveform deviation of the reproduction signal is corrected based on the correction amount. . In equation (1), the correction coefficients A and B are desirably obtained in advance by an experiment. When the recording medium is shipped, the correction coefficients A and B may be recorded in advance on a control track of a disk and read out. The data may be written to the ROM of the device and read out.

In the waveform correction circuit 111, the RF digital signal supplied from the A / D converter 110 is delayed, and the RF digital signal is delayed based on the correction amount Y obtained from the correction amount generation circuit 116 and the signal F indicating the direction of change. Correct the signal. FIG. 5 shows an outline of the correction. FIG. 5A shows the waveform of the reproduced signal, and ● indicates a sampling point. FIG.
The dashed line in (A) is a waveform after correction, and * indicates a sampling point after correction. FIG. 5B shows a difference signal before correction, and FIG.
(C) is the difference signal after the correction.

The waveform correction circuit 111 calculates the offset amount S of the signal amplitude based on the correction amount Y, and when the change direction F is "1" (when the reproduced signal falls), the offset amount near the change point. If S is subtracted and the change direction F is “0” (when the reproduction signal rises), the offset amount S is added near the change point. The offset amount S is S = KY
Obtained in (i). Note that K is a coefficient. The corrected RF digital signal is supplied to the decoding circuit 112. Here, the decoding circuit 112 performs a decoding process by detecting a difference.

FIG. 6A shows a difference signal with respect to the corrected RF digital signal, and FIG. 6B shows decoded data. In the difference detection, "1" is output when the difference signal is equal to or more than the positive threshold value T1, "0" when the difference signal is equal to or less than the negative threshold value T2, otherwise, the same value as the immediately preceding decoded data is output. . By performing such correction, decoding errors due to waveform shift can be reduced.

Next, a specific reproducing operation of this embodiment will be described with reference to FIG. 7A is an RF digital signal, FIG. 7B is a clock, FIG. 7C is a differential signal, FIG. 7D is a pattern interval, FIG. 7E is a direction of change, and FIG. ) Is a gate for setting a correction section, FIG. 7G is a correction offset amount, and FIG. 7H is a digital signal after correction. Here, when a reproducing light beam is applied to the rotating magneto-optical disk 101 from the optical head 104, the optical head 104 detects reflected light from the magneto-optical disk 101 to generate a reproduction signal, and the preamplifier 105 , AG
The signal is supplied to the A / D converter 110 via the C circuit 109. In the A / D converter 110, as shown in FIG.
The F digital signal is output in synchronization with the clock of FIG. 7B and supplied to the pattern detection circuit 115.

In the pattern detection circuit 115, FIG.
A difference signal as shown in FIG. 7C is generated, and at the same time, the recording mark length P is calculated based on the counter value synchronized with the clock in FIG. Further, the pattern detection circuit 115 detects the direction of the rise / fall from the value of the difference signal in FIG. 7C, and changes from 1 → 0 of the difference signal as shown in FIG. Is output as 0 → 1 and for the difference signal −1 → 0, the direction of change is 1 → 0.

In the correction amount generation circuit 116, the correction amount is calculated by the equation (1) based on the recording mark length P of FIG.
Is output as shown in FIG. The waveform correction circuit 111 applies a predetermined delay to the RF digital signal obtained from the A / D converter 110, and
As shown in (F), a correction gate for controlling the section for correcting the RF digital signal is internally generated based on the signal from the correction amount generation circuit 116, and the correction gate is offset with respect to the amplitude of the RF digital signal in the correction gate section. Is added or subtracted. That is,
The correction gate signal shown in FIG. 7F is created corresponding to the edge of the RF digital signal, and the addition and subtraction of the offset are performed within the section of "1" of the correction gate signal. As described above, FIG.
As shown in (H), the reproduction signal indicated by the broken line is corrected to the reproduction signal indicated by the solid line, and the waveform shift can be corrected.

(Second Embodiment) Next, a second embodiment of the present invention will be described. The second embodiment adaptively generates the above-described correction coefficient from the reproduced signal, and flexibly copes with a change in the correction coefficient due to an individual difference of a medium. Also, the waveform correction is performed by a method different from that of the first embodiment. FIG. 8 is a block diagram showing a configuration of the second exemplary embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals and have the same configuration and operation, and description thereof will be omitted.

In FIG. 8, a correction coefficient generation circuit 152 generates the correction coefficients A and B of the equation (1) adaptively. In addition, the reproduction compensation circuit 150 includes the pattern detection circuit 1
A correction amount Y is generated based on the recording mark length generated by the controller 15 and supplied to the waveform correction circuit 153. Here, the correction amount generation circuit 151 generates a correction amount using the correction coefficients A and B generated by the correction coefficient generation circuit 152. The waveform correction circuit 153 corrects the sample value near the edge based on the correction amount Y supplied from the correction amount generation circuit 151 and outputs the corrected value.

Next, the configuration and operation of each unit will be described. FIG. 9 is a block diagram showing a configuration of the correction coefficient generation circuit 152. In FIG. 9, reference numeral 901 denotes a reference area detection unit which detects a region where a predetermined recording mark sequence for generating a correction coefficient is recorded and starts a sequence for generating a correction coefficient. It is assumed that the recording mark sequence is recorded in a predetermined area set in advance.

When generating a correction coefficient, a CP (not shown) is used.
U or the like is controlled to reproduce a signal of a predetermined address, and the reproduced RF digital signal is converted into an A / D converter 11
0 is supplied to the reference area detection unit 901. When detecting a predetermined recording mark sequence from the RF digital signal, the reference area detecting unit 901 starts a process of generating a correction coefficient. A known method such as the above-described difference detection and PRML can be used for detecting the recording mark string.

The jitter detector 902 calculates a jitter by reproducing a predetermined record mark sequence, and generates a correction coefficient based on the calculated jitter. The operation of the jitter detector 902 will be described with reference to FIG. In FIG. 10, points ● and ○ are obtained by sampling the reproduction signal 910 with a PLL clock. The jitter detector 902 acquires a sample value of an edge portion as a phase error signal based on the signal of the reference area detector 901 and detects jitter based on the sample value.

Next, the jitter detecting operation will be described with reference to FIG. 11A is a reproduced signal (signal pattern) for detecting jitter, FIG. 11B is a PLL clock, FIG. 11C is a differential signal of the reproduced signal, and FIG.
Is a phase error signal obtained from the sample value of the point に shown in FIG. The jitter detector 902 detects the rising and falling edges of the signal pattern shown in FIG.
A phase error signal (D) is generated as shown in FIG. 10 from the gate section generated based on the differential signal of (C) and detected based on the differential signal.

Next, the jitter detector 902 selects a phase error signal obtained by a specific combination of recording mark arrays from the generated phase error signals, and generates a jitter signal. For example, as shown in FIG.
In a predetermined recording mark sequence of T-2T-2T-8T, 8
The phase error signals J3 and J4 obtained at the edge of the 2T pattern after T are selected. Since the detection of the signal pattern is performed by the above-described reference area detection unit 901, an 8T-2T pattern can be obtained from the detection result.

In the jitter detection, as shown in FIG. 12, the phase error signal J3 at the falling and rising portions of the 2T pattern is used.
And J4. When there is no waveform shift, the added value of J3 and J4 is "0", but when the length of the 2T pattern is changed due to the waveform shift, it changes to the plus and minus sides. As shown in the above example, the jitter detector 902 generates a jitter signal in a specific pattern from a predetermined recording mark sequence and calculates an average value thereof.

The correction coefficient calculating section 903 calculates the correction coefficient of the equation (1) from the generated jitter signal. Here, it is obtained in advance by the characteristics of the medium or the like (jitter signal).
It is assumed that the correction coefficients A and B are obtained by the equation (2) using the function K representing the relationship of-(correction coefficient).

Correction coefficient A = K _A (Jt), B = K _B (Jt) (2) Jt is a jitter signal obtained in the jitter detector 902. In some cases, the same effect can be obtained even when the correction coefficient A = B in the equation (1). In this case, only the correction coefficient A is calculated in the equation (2) to reduce the processing load. Is also possible. The generated correction coefficient is supplied to the correction amount generation circuit 151 of the reproduction compensation circuit 150.

FIG. 13 shows the outline of the waveform correction of the second embodiment. The correction of the waveform according to the present embodiment is realized by signal interpolation. FIG. 13 shows a signal near the edge of the reproduction signal. A broken line indicates a reproduced signal waveform, and ● indicates a digital signal sampled by a PLL clock, which has a waveform shift due to medium characteristics and the like. Correction amount generation circuit 151
Calculates the correction amount Y based on the correction coefficient obtained by the correction coefficient generation circuit 152. Note that the correction amount Y can be obtained by Expression (1), but it is also possible to simply substitute Expression (3) with A = 0 in Expression (1).

Y (i) = B · P (i) (3) Here, the correction amount Y is calculated by the equation (3), and based on this, the interpolation coefficient G as shown in FIG. 13 is generated. Equation (3)
Is used, two adjacent recording mark lengths P (i) and P (i)
A memory or the like for holding (i-1) is not required, and the load of calculation can be reduced. Waveform correction circuit 153
, Sample values E2 ′ and E3 ′ corrected by linear interpolation are calculated from the sample values E1 to E3 of the edge portion and the interpolation coefficient G (indicated by Δ). For example, E2 'can be obtained by the following equation (4).

E2 ′ = (G / T) · E1 + ((T−G) / T) · E2 (4) T indicates an interval between sampling clocks. Here, a case of linear interpolation is shown, but other known interpolation methods can be used instead. As a result, the edge shift due to the waveform shift can be reduced, so that the factor of the decoding error can be eliminated and the recording density can be improved.

Although the waveform correction here is performed on the reproduced digital signal, when decoding is performed by detecting a difference, the same effect can be obtained by correcting the difference signal. Also, when decoding by PRML, it goes without saying that correction can be performed on the PR equalized waveform.

(Third Embodiment) Next, a third embodiment of the present invention will be described. In the present embodiment, the following is used as a calculation formula of the correction amount Y in the correction amount generation circuit 116 of FIG.

Y (i) = − A · (P (i−1) −R) + B · (P (i) −R) (5) where R represents a reference mark length. By generating the correction amount according to equation (5), the absolute value of the correction amount can be reduced. For example, when R = 2 in equation (5), the correction amount becomes “0” when the recording mark length is 2T. As a result, the fluctuation of the signal due to the correction can be distributed to the plus side and the minus side, so that the change from the original reproduction signal can be suppressed.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. FIG. 14 is a block diagram showing the configuration of the fourth embodiment of the present invention. FIG. 14 is different from FIG. 1 in that a data PLL 154 is added. Others are the same as FIG. The data PLL 154 generates a clock signal based on the reproduction signal whose waveform deviation has been corrected by the waveform correction circuit 111 in the same manner as in the first embodiment.

FIG. 15 is a block diagram showing a configuration of data PLL 154. In the figure, reference numeral 301 denotes a phase error detection unit which detects a phase error based on a sample value of a rising edge portion of a reproduction signal. Reference numeral 302 denotes a loop filter that removes unnecessary noise from the phase error signal and compensates for the reduction. A VCO 303 generates a clock signal having a frequency corresponding to the control voltage. The data PLL detects a phase error from an edge portion of the corrected reproduced signal, and supplies the detected signal as a VCO control signal after filtering. By using this as a loop, a clock synchronized with the reproduction signal can be obtained.

In the apparatus according to the present embodiment, the phase error is detected based on the reproduced signal in which the waveform deviation has been corrected.
The influence of erroneous detection as shown in (D) can be reduced, and an appropriate reproduced signal can be obtained. The method of detecting the phase error is not limited to the above, and other known techniques can be used.

[0053]

As described above, according to the present invention, the waveform of a reproduction signal is detected by detecting the length of a recording mark recorded on a recording medium and correcting the reproduction signal with a correction amount corresponding to the recording mark length. Since the shift can be corrected and the edge shift can be canceled, the recorded signal can be accurately reproduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a pattern detection circuit of FIG. 1;

FIG. 3 is a diagram for explaining ternary determination on a difference signal.

FIG. 4 is a diagram for explaining an operation of pattern detection.

FIG. 5 is a diagram for explaining a correction process of the waveform correction circuit of FIG. 1;

FIG. 6 is a diagram for explaining the decoding method of FIG. 1;

FIG. 7 is a timing chart illustrating the operation of the first embodiment.

FIG. 8 is a block diagram showing a second embodiment of the present invention.

FIG. 9 is a block diagram illustrating a correction coefficient generation circuit of FIG. 8;

FIG. 10 is a diagram for explaining phase error detection in FIG. 8;

11 is a diagram illustrating the operation of the correction coefficient generation circuit of FIG.

FIG. 12 is a diagram illustrating an outline of jitter detection in FIG. 8;

FIG. 13 is a diagram illustrating a correction process of the waveform correction circuit of FIG. 8;

FIG. 14 is a block diagram showing a fourth embodiment of the present invention.

FIG. 15 is a configuration diagram of a data PLL of FIG. 14;

FIG. 16 is a diagram for explaining a conventional waveform shift of a reproduced signal.

FIG. 17 is a diagram illustrating phase error detection in data PLL.

[Explanation of symbols]

 101 Magneto-optical disk 102 Spindle motor 103 Magnetic head 104 Optical head 105 Preamplifier 106 Magnetic head driver 107 Preencoder 108 Laser drive circuit 109 AGC circuit 110 A / D converter 111 Waveform correction circuit 112 Decoding circuit 114 Reproduction compensation circuit 115 Pattern detection circuit 116 correction amount generation circuit 150 reproduction compensation circuit 151 correction amount generation circuit 152 correction coefficient generation circuit 153 waveform correction circuit 154 data PLL 201 difference circuit 202 pattern measurement circuit 301 phase error detection section 302 loop filter 303 VCO 901 reference area detection section 902 jitter Detector 903 Correction coefficient calculator

Claims (12)

[Claims] In an information reproducing method for detecting a recording mark formed on a recording medium and generating a reproduction signal, a mark length of each recording mark is detected based on a reproduced signal, and the detected mark length is detected. A magneto-optical reproducing method, wherein the reproducing signal is corrected by a correction amount according to the following. 2. The magneto-optical reproducing method according to claim 1, wherein the correction amount is an amount for compensating a change in a recording mark edge due to a stray magnetic field. 3. The correction amount Y is Y = −A × P (i−
1) + B × P (i) (A, B: constant, P (i−1); mark length of the immediately preceding recording mark, P (i): mark length of the current recording mark) 3. The magneto-optical reproducing method according to claim 2, wherein: 4. The magneto-optical reproducing method according to claim 3, wherein A = B in the correction amount Y. 5. The magneto-optical reproducing method according to claim 3, wherein A = 0 in the correction amount Y. 6. The correction amount Y is represented by Y = −A × (P (i−
1) −R) + B × (P (i) −R) (A, B: constants,
P (i-1): mark length of previous recording mark, P
3. The magneto-optical reproducing method according to claim 2, wherein (i): a current mark length of the recording mark), and R: a reference mark length). 7. The magneto-optical reproducing method according to claim 1, wherein the correction is performed by adding or subtracting an offset corresponding to the correction amount to or from the reproduction signal. 8. The magneto-optical reproducing method according to claim 1, wherein the correction is performed by interpolating the reproduction signal with an interpolation coefficient corresponding to the correction amount. 9. The apparatus according to claim 2, wherein the constant is calculated based on a measured value of a jitter of a reproduced signal obtained when a predetermined recording mark train is reproduced. Magneto-optical reproduction method. 10. The magneto-optical reproducing method according to claim 1, wherein the recording medium is a domain wall displacement type magneto-optical recording medium. 11. An information reproducing apparatus for detecting a recording mark formed on a recording medium and generating a reproduction signal, comprising: means for detecting a mark length of the recording mark based on the reproduced signal; Means for correcting the reproduction signal by a correction amount corresponding to the length. 12. The magneto-optical reproducing apparatus according to claim 11, wherein the correction amount is an amount for compensating a change of a recording mark edge due to a stray magnetic field.