JP3366658B2 - Magneto-optical disk playback device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto- optical disk reproducing apparatus, and more particularly to an optical disk on which information is recorded by an edge recording method.
The present invention relates to a device for reproducing already recorded information on a magnetic disk.

A recording / reproducing apparatus for a magneto-optical disk has rapidly spread from recording / reproducing image information to a code-recordable one for a computer due to its large capacity, interchangeability, high reliability and the like. In recent years, with the rapid development of multimedia, such a magneto-optical disk is required to be further miniaturized as a core memory to have a larger capacity and an improved transfer rate. An edge recording method has been proposed as one means.

In the above-mentioned edge recording method, when the recording data is a binary code string as shown in FIG. 4A, the light intensity is inverted only at the bit position of the value "1", as shown in FIG. A recording light beam emission pattern is created, and this is irradiated onto the magneto-optical disk as a recording light beam. As a result, one track on the medium plane of the magneto-optical disk can be read as shown in FIG.
As shown in (C), when the light intensity of the recording light beam is high, the temperature of the local position irradiated with the recording light beam rises, and the magnetic domain magnetized in the opposite direction to the surrounding magnetization direction by the external magnetic field. (Domains) C ₁ , C ₂ and C ₃ are formed.

The reproduction of the data thus recorded on the magneto-optical disk is performed by utilizing the magnetic Kerr effect, since the recorded data is recorded on the magneto-optical disk as a change in the magnetization direction. That is, since the polarization plane of the reflected light on the medium surface of the magneto-optical disk rotates according to the direction of recording magnetization, the recorded data is reproduced by discriminating the rotation direction of the polarization plane of the reflected light.

Therefore, at the time of reproduction, a reproduction light spot S is formed and scanned by narrowing the light beam with an objective lens on each track shown in FIG. 5A, and the rotation direction of the polarization plane of the reflected light obtained by this is controlled. Separately, a reproduced waveform as shown in FIG. The reproduction data having a predetermined bit period as shown in FIG. 5C is demodulated, which has a value "1" at the time when the center level of the reproduction waveform is crossed from this reproduction waveform and "0" at others.

In an edge recording type magneto-optical disk reproducing apparatus which records and reproduces based on the above-mentioned basic principle, the position of the edge of the magnetic domain is important, so that the magnetic domain recorded on the magneto-optical disk is important. It is necessary to be able to reproduce without being affected by the fluctuation of the edge position interval of the magnetic domains of the column.

[0007]

2. Description of the Related Art FIG. 6 shows a block diagram of an example of a magneto-optical disk device. In the figure, reference numeral 41 denotes a magneto-optical disk medium on which information is recorded by the edge recording method, and a magneto-optical head 4
A light beam is emitted from the second objective lens 43. This light beam is reflected by the magneto-optical disk medium 41, and the reflected light passes through the objective lens 43 and enters the magneto-optical head 42, where the magnetic Kerr effect is used as described above. ) Is converted into a reproduced signal waveform.

The reproduced signal waveform is supplied to the edge detection circuit 44, where the rising edge and the falling edge corresponding to the leading edge and the trailing edge of the recording magnetic domain are separately detected. The leading edge detection signal is supplied to the phase locked loop circuit (PLL) 45, and the trailing edge detection signal is supplied to the PLL 46 to extract the synchronous clock. The synchronous clocks respectively extracted by the PLLs 45 and 46 are supplied to the data separators 47 and 48 together with the edge detection signal, and the data are separated by the synchronous clocks here.

Both output data of the data separators 47 and 48 are temporarily stored in the buffers 49 and 50, respectively, and then the leading edge and trailing edge data are compared bit by bit from the head and a logical sum is obtained by the synthesizing circuit 51. After that, the data is input to the demodulation circuit 52 and is demodulated from the data which is the running length limiting code into the data which is the NRZ (non-return to zero) code.

By the way, the edge detection circuit 44 of the above-mentioned magneto-optical disk reproducing apparatus is conventionally constructed as shown in FIG. In the figure, the reproduction signal waveform input to the terminal 61 is supplied to a peak point detection circuit 62 to detect its peak point, and is also supplied to a bottom point detection circuit 63 to detect its bottom point. The detected peak point and bottom point are combined via resistors 64 and 65, converted into a midpoint level between the peak point and bottom point, and input to the comparator 66 as a slice level.

The comparator 66 compares the above-mentioned slice level with the reproduced signal waveform from the terminal 61, and when the reproduced signal waveform is above the slice level, it is logical "1", and when it is below the slice level, it is logical "0". Convert to binary signal. The leading edge / trailing edge separation circuit 67 detects both the rising edge and the falling edge of the binary signal separately, and outputs the rising edge detection signal to the terminal 68 as the leading edge edge detection signal, and the falling edge. The detection signal is output to the terminal 69 as a trailing edge detection signal.

[0012]

However, the actual reproduced signal waveform has a pit length (recording domain length) as shown in FIG.
As becomes longer, the amplitude tends to change greatly as shown by a1 → a2 → a3. In FIG.
The playback waveform is large and the pit interval is large.
In the returned part, (d) is almost at the leading and trailing edges of the pit.
The corresponding position can be detected. However, the pit length is small
The part where the playback waveform is repeated with a large pit interval.
Since the peak level is low, (d) is in front of the pit.
Lower near the bottom level than the positions corresponding to the edges and trailing edge
Detect the position. Therefore, the original leading edge position and trailing edge position
Clock synchronization is taken for each off position
The data is separated. This state continued as shown in Fig. 9.
After that, a reproduction waveform with the same pit length and pit interval
When the reproduced signal waveform has a change in amplitude as shown by the solid line a in FIG. 9, the bottom waveform has a small change as shown by b in FIG. The peak waveform changes greatly as indicated by c in the figure, so that the midpoint level (slice level) of the peak point and the bottom point also greatly changes as indicated by a chain double-dashed line d in the figure. Therefore, as shown in FIG. 10, when the amplitude of the reproduced signal waveform a changes significantly, the actual midpoint level changes as indicated by the chain double-dashed line d with respect to the broken line e indicating the change in the midpoint level up to that point. Therefore, the difference f is reproduced as a deviation of the detection position.

Further, even if there is such a shift, the shift can be absorbed because the sync clock can follow if it is a shift that changes gently. However, since this shift occurs in the frequency band of data, the sync clock is I can't follow and I can't remedy.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a magneto- optical disk reproducing apparatus which solves the above problems by allowing a synchronous clock to follow the deviation of the detection position. And

[0015]

FIG. 1 shows a block diagram of the principle of the present invention. According to the present invention, a reproduction signal waveform obtained from a magneto- optical disk on which an information signal is recorded by an edge recording method is supplied, and first and second edges respectively corresponding to the leading edge and the trailing edge of a recording domain of the magneto- optical disk. Generate a detection signal,
Magneto- optical disk reproduction in which synchronous clocks are separately extracted from the first and second edge detection signals, data is separately detected, and both detected data are combined to obtain a reproduction information signal. In the apparatus, as a circuit for obtaining the first and second edge detection signals from the reproduced signal waveform, a detection means 11, a reference signal generation circuit 12, a level comparison circuit 13 and a separation circuit 14 are provided as shown in FIG. It is what

Here, the detecting means 11 detects the peak point and the bottom point of the reproduced signal waveform, respectively. Reference signal generating circuit 12 detects the hand stage 11 yo Ri of the detection signal is supplied, the level corresponding to the midpoint between said detected peak point and the bottom point, tracking allows the frequency of the circuit for extracting the synchronization clock Generates and outputs a reference signal limited to a frequency band equal to or lower than the upper limit frequency of.

The level comparison circuit 13 compares the reproduced signal waveform and the reference signal in level to generate a binary signal. The separation circuit 14 separately outputs the first and second edge detection signals from the binary signal.

[0018]

According to the present invention, since the reference signal generating circuit 12 is to generate a reference signal whose frequency band is limited to tracking frequency band of the circuit for extracting the synchronization clock, recording domains on a magneto-optical disk Is large,
Therefore , even if the amplitude change of the reproduced signal waveform is large, the fluctuation of the reference signal can be suppressed to such an extent that the circuit for extracting the synchronous clock can follow it. Therefore, even if the reproduction signal waveform detection position shifts due to the fluctuation of the reference signal, the synchronization clock also has the same phase, so that the detection position shift with respect to the synchronization clock can be ignored.

[0019]

FIG. 2 is a block diagram of the first embodiment of the present invention.
FIG. 2 shows an embodiment of the edge detection circuit 44 in the magneto-optical disk device shown in FIG. 6, in which the terminal 20 shown in FIG. 2 is a magneto-optical disk medium in which information is recorded by the edge recording method described above. FIG. 5B obtained by reproducing with a magneto-optical head
A reproduction signal waveform as shown in is input.

This reproduced signal waveform has a peak point detection circuit 2
1, supplied to the bottom point detection circuit 22 and the comparator 27, respectively. The peak point detection circuit 21 and the bottom point detection circuit 22 constitute the detection means 11, and detect the peak point and the bottom point of the reproduced signal waveform by a known method.
The peak point signal showing the upper envelope of the reproduced signal waveform extracted from the peak point detection circuit 21 is the band limiting filter 2
3 is supplied. Further, the bottom point signal, which is extracted from the bottom point detection circuit 22 and indicates the lower envelope of the reproduction signal waveform, is supplied to the band limiting filter 24.

The band limiting filters 23 and 24 together with the mixing resistors 25 and 26 are the reference signal generating circuit 1 described above.
Make up 2. The band limiting filters 23 and 24 are
A filter circuit for limiting (attenuating) a high frequency component above the upper limit frequency of the trackable frequency range of the PLLs 45 and 46 of FIG. 6 for extracting the synchronous clock from the edge detection signal, for example, the upper limit frequency of the trackable frequency range. Is a first-order low-pass filter having a cut-off frequency of.

The peak point signal and the bottom point signal whose high frequency components have been attenuated by the band limiting filters 23 and 24 are combined via the mixing resistors 25 and 26, respectively. As a result, a signal at the midpoint level between the peak point signal level and the bottom point signal level is taken out as a reference signal from the connection point of the mixing resistors 25 and 26 by the resistance voltage division of the mixing resistors 25 and 26. Therefore, even if the reproduced signal waveform has a large amplitude change as shown by a in FIG. 10, this reference signal has a higher frequency band than the conventional reference signal (slice level) shown by d in FIG. Since the frequency component is limited, the fluctuation is further suppressed, and the waveform becomes a waveform approximate to the waveform indicated by e in the figure.

The comparator 27 is the level comparison circuit 1 described above.
3, a binary signal of logic "1" is generated and output when the reproduced signal waveform from the terminal 20 is equal to or higher than the reference signal level and is lower than the reference signal level. This binary signal is supplied to the leading edge and trailing edge separating circuit 28 which constitutes the above-mentioned separating circuit 14, where the rising edge and the falling edge are detected respectively, and the rising edge detection signal is the above-mentioned recording magnetic domain. For example, the first edge detection signal indicating the reproduction time of the leading edge is output to the terminal 29, while the falling edge detection signal is detected as the second edge detection signal indicating the reproduction time of the trailing edge of the recording magnetic domain. It is output to 30.

According to this embodiment, even if the reproduced signal waveform has a large amplitude change due to the data pattern, the fluctuation of the amplitude of the reference signal causes the synchronization clock to be extracted from the first and second edge detection signals. PLL (45, 4 in FIG. 6
Since the frequency is within the trackable frequency range of 6), the deviation of the detection position of the reproduced signal waveform with respect to the synchronization clock can be ignored, and therefore data with few errors can be detected.

Next, a second embodiment of the present invention will be described. FIG. 3 is a block diagram of the second embodiment of the present invention. In FIG. 3, the same components as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 3, the mixing resistors 31 and 32 and the band limiting filter 33 are the reference signal generating circuit 12 described above.
Are configured.

The peak point signal extracted from the peak point detection circuit 21 and the bottom point signal extracted from the bottom point detection circuit 22 are combined via the mixing resistors 31 and 32, respectively, and the detected peak point is obtained. It is converted to a signal at the level of the middle point with the bottom point. The midpoint level signal is supplied to the band limiting filter 33.

The band limiting filter 33 has the same circuit configuration as the band limiting filters 23 and 24, and limits the band of the signal at the midpoint level to the frequency band that can be followed by the PLLs 45 and 46, and uses that signal as a reference signal. Supply to the comparator 27. Therefore, this embodiment can also generate a reference signal similar to that of the first embodiment. Therefore, as in the case of the first embodiment, even if there is a large amplitude change in the reproduced signal waveform, a reference signal with a gentle level fluctuation can be generated and stable. In addition, accurate data detection can be performed. Further, since only one band limiting filter 33 is required in this embodiment, the circuit configuration can be simplified as compared with the first embodiment.

[0028]

As described above, according to the present invention, even if the amplitude of the reproduced signal waveform greatly changes depending on the data pattern, the fluctuation of the reference signal can be suppressed to a level that the synchronous clock extraction circuit can follow. The deviation of the position of the reproduced signal waveform with respect to the synchronous clock can be ignored, and therefore data detection with less errors than in the past can be performed, which contributes to high-density recording / reproduction of the magneto- optical disk. It has features such as large size.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

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

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a recording principle of an edge recording method.

FIG. 5 is an explanatory diagram of a reproducing principle of a magneto-optical disk recorded by an edge recording method.

FIG. 6 is a block diagram of an example of a magneto-optical disk reproducing device.

FIG. 7 is a configuration diagram of an example of a main part of a conventional magnetic disk device.

FIG. 8 is a diagram for explaining an amplitude change of a reproduction signal waveform.

FIG. 9 is a diagram illustrating a change in slice level when a reproduced signal waveform changes in amplitude.

FIG. 10 is a diagram showing a shift of an edge detection position due to an amplitude change of a reproduction signal waveform.

[Explanation of symbols]

11 detection means 12 reference signal generation circuit 13 level comparison circuit 14 separation circuit 23, 24, 33 band limiting filter 25, 26, 31, 32 mixing resistor 40 edge detection circuit 45, 46 phase locked loop circuit (PL
L)

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-63-213121 (JP, A) JP-A-62-12957 (JP, A) JP-A-2-46544 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G11B 11/10-11/105 G11B ^7/ 00-7/0065

Claims (3)

(57) [Claims] 1. A reproduction signal waveform obtained from a magneto- optical disk on which an information signal is recorded by an edge recording system is supplied, and first and second corresponding to a leading edge and a trailing edge of a recording domain of the magneto- optical disk, respectively. Of the first and second edge detection signals, the synchronous clocks are separately extracted from the first and second edge detection signals, the data is detected separately, and the detected data are combined to obtain a reproduction information signal. In a magnetic disk reproducing apparatus, a detection means for detecting a peak point and a bottom point of the reproduction signal waveform, respectively, and a detection signal from the detection means are supplied to the detected midpoint between the peak point and the bottom point. A reference signal generation circuit for generating and outputting a reference signal in which a corresponding level is limited to a frequency band equal to or lower than an upper limit frequency of a trackable frequency of the circuit for extracting the synchronous clock, and the reference signal generation circuit Level comparison circuit for generating a binary signal by comparing the level of the output reference signal with the reproduced signal waveform, and the first and second levels from the output binary signal of the level comparison circuit.
Of the magneto-optical disk reproducing apparatus, characterized in that it comprises a separation circuit for edge detection signal outputted separately. 2. The reference signal generation circuit includes a first band limiting filter for limiting a band of a peak point signal detected by the detecting means to the frequency band, and a bottom point signal detected by the detecting means. A second band limiting filter that limits the band to the frequency band, and output signals of the first and second band limiting filters are respectively synthesized, and the midpoint level of these signal levels is used as the reference signal. 2. The magneto- optical disk reproducing apparatus according to claim 1, comprising first and second resistors for taking out. 3. The first and second resistors, wherein the reference signal generating circuit synthesizes the signal levels of the peak point and the bottom point detected by the detecting means, and extracts the signal at the midpoint level thereof. 2. The magneto- optical disk reproducing apparatus according to claim 1, further comprising a band limiting filter that limits the band of the midpoint level signal to the frequency band and outputs the reference signal.