JPH05101470A - Magneto-optical disk reproducing device - Google Patents

Abstract

PURPOSE:To provide a magneto-optical disk reproduction device that reproduces an already recorded information from a magneto-optical disk to which information is recorded by a pit edge recording method and compensates the effect caused by the variations in edge position interval using a smaller number of delay lines. CONSTITUTION:A leading edge detection signal which corresponds to the leading edge of the magnetic domain on the medium and a trailing edge detection signal which corresponds to the trailing edge of the above mentioned magnet domain, both of which are outputted from an edge detecting circuit 12, are supplied to a variable delay circuit 14, respectively. The variable delay circuit 14 changes the mutual time interval of these edge detection signals in accordance with the output detection values of an amplitude detecting circuit 13 which detects the amplitudes of reproduced signals.

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 apparatus for reproducing recorded information from a magneto-optical disk on which information is recorded by a pit edge recording system.

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, a pit edge recording method (or simply an edge recording method) has been proposed as one of the techniques for further increasing the capacity and the transfer rate of the magneto-optical disk.

FIG. 6 shows the principle of rewriting a magneto-optical disk. As shown in FIG. 1A, the external magnetic field generator 1 first applies a magnetic field to the magneto-optical disk medium 2 in a direction in which the N-pole side approaches the medium surface of the magneto-optical disk 2. The objective lens 3 is formed on the medium surface of the magneto-optical disk 2 rotating in this state.
When the erasing light beam 4 is squeezed and incident through the laser beam, the temperature of the local position where the erasing light beam 4 is irradiated rises and the magnetization is inverted, so that the magnetization direction is changed as indicated by the downward arrow in FIG. Are aligned in one direction. As a result, the medium portion 5 of the magneto-optical disk 2 is erased.

Next, as shown in FIG. 6 (B), the direction of the magnetic field applied by the external magnetic field generator 1 to the erased portion of the magneto-optical disk 2 is made opposite to that at the time of erasing, and the light intensity is changed by the information to be recorded. The recording light beam 6 modulated to be large or small is focused by the objective lens 3 and irradiated onto the medium surface of the magneto-optical disk 2. At this time, when the light intensity of the recording light beam is high, the temperature of the local position irradiated with the recording light beam rises,
The magnetization is inverted and the magnetization is magnetized in the direction opposite to that at the time of erasing.

On the other hand, when the light intensity of the recording light beam is small, the irradiation position of the light beam on the magneto-optical disk 2 is not heated, so that the magnetization reversal is not performed and the magneto-optical disk 2 is not.
The magnetization direction of remains the same as when erased. As a result, information to be recorded is written on the surface of the magneto-optical disk medium shown by 7 in FIG. 6 (B).

In the pit edge recording method described above, when the recording data is a binary code string as shown in FIG. 7A, the light intensity is inverted only at the bit position of the value "1".
The recording light beam emission pattern shown in FIG.
This is irradiated onto the magneto-optical disk 2 as the recording light beam 6. As a result, the recording domain (magnetic domain) of one track on the medium plane of the magneto-optical disk 2 is shown in FIG.
As shown in.

In reproducing the data recorded on the magneto-optical disk 2 in this manner, the recorded data is recorded on the magneto-optical disk 2.
Since it is recorded as a change in the magnetization direction, the magnetic Kerr effect is used. That is, since the polarization plane of the reflected light on the medium surface of the magneto-optical disk 2 rotates according to the recording magnetization direction, the recorded data is reproduced by discriminating the rotation direction of the polarization plane of the reflected light.

Therefore, at the time of reproduction, the reproduction beam spot 7 is formed and scanned by narrowing the light beam with the objective lens on each track shown in FIG. 8A, 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 reproduced data is demodulated as shown in FIG. 8C, in which the value at the time when the reproduced waveform crosses the center level of the reproduced waveform is "1" and the other is "0".

In a pit-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 the information is recorded on the magneto-optical disk. It is necessary to reproduce without being affected by the change in the edge position interval of the magnetic domain of the magnetic domain array.

[0010]

2. Description of the Related Art In FIG. 9, the present applicant has previously filed Japanese Patent Application No. 3-573.
The block diagram of an example of the magneto-optical disk reproducing apparatus proposed in No. 28 is shown. In the figure, an optical head 40 is a device equipped with a known optical system and circuit system for obtaining a reproduction signal from a magneto-optical disk recorded by the pit edge recording method described above, and the optical head 40 edge-processes the reproduction signal. It is supplied to the detection circuit 41.

The edge detection circuit 41 separately detects the edges of the reproduced signal corresponding to the leading edge and the trailing edge of the recording domain, and detects the leading edge detection signal from the delay line 4.
2 and the counter 43 and supplies the trailing edge detection signal as a reset pulse to the counter 43 and the latch circuit 44.
To the synthesizing circuit 45.

The delay line 42 is supplied with the edge detection signal of the leading edge, delays this by an integral multiple of the counter clock period, and outputs it. That is, the delay line 42
From the plurality of output terminals, the delay signals delayed from the minimum one cycle to the maximum n + 1 cycles of the counter clock and having different delay times are output in parallel. The parallel output delay signals are supplied to the multiplexer 46, respectively.

The counter 43 is an n + 1 (n is a natural number) base counter, and is supplied with a count clock of n + 1 pulses per data bit period from a PLL 47, which will be described later, at the trailing edge of the trailing edge detection signal. After resetting, the count clock counts up and the count value is supplied to the latch circuit 44. The latch circuit 44 is reset when the trailing edge edge detection signal falls, and latches the count value from the counter 43 when the leading edge edge detection signal falls and the multiplexer 4
The select signal is supplied to 4.

The multiplexer 46 selects the delay signal input terminal designated by the count value i supplied from the latch circuit 44 and supplies the delay signal to the synthesis circuit 45.

That is, the leading edge detection signal is delayed to synchronize the leading edge detection signal with the trailing edge detection signal.

The PLL 47 generates a clock (a count clock is a frequency obtained by dividing this clock) synchronized with the rising and falling edges of the composite signal and supplies it to the data separator 48. The data separator 48 separates the data using the clock and supplies the separated data to the demodulation circuit 49 together with the clock. The demodulation circuit 49 converts the separated data, which is the running length limit code (PLLC), into NRZ.
Demodulate to a (non-return-to-zero) code signal.

[0017]

By the way, upon recording, there is thermomagnetic writing in which a recording light beam is selectively heated to form a recording magnetic domain. Therefore, first, if the recording light beam is irradiated with the same power when the environmental temperature changes, the temperature distribution does not become the same, the size of the magnetic domains formed changes, and the position intervals of the edges change, so that correct recording cannot be performed. Further, due to variations in sensitivity of the magneto-optical disk medium within the medium or variations in sensitivity between the medium, variations in the size of the magnetic domain formed even if the temperature distribution is the same.
Further, the formed magnetic domain has a shape called a teardrop shape as shown in FIG. 7C, and a deviation occurs in the detection position between the shape of the leading edge and the shape of the trailing edge of the magnetic domain.

However, according to the reproducing apparatus proposed by the present applicant, the delay line 42 is configured to obtain a plurality of delay times, the counter 43 synchronized with the PLL 47 counts the data, and Since the optimum delay time of the delay line is selected from the counter value, the above problem is solved.

However, the above proposed apparatus requires a large number of delay times and a large number of delay lines in order to give an accurate amount of delay in addition to performing complicated measurement. Further, in the above proposed apparatus, the edge detection signal of the leading edge of the domain is delayed with reference to the edge detection signal of the trailing edge of the domain, so it can be corrected when the size of the domain is larger than the standard. It cannot be corrected for a change such that the domain size becomes smaller than the standard, such as when recording at a very low temperature.

The present invention has been made in view of the above points,
It is an object of the present invention to provide a magneto-optical disk reproducing apparatus capable of reproducing by correcting the influence of the change in the edge position interval with a small number of delay lines.

[0021]

FIG. 1 shows a block diagram of the principle of the present invention. In the figure, the optical head 11 reproduces the recorded signal of the magneto-optical disk recorded by the edge recording method,
A reproduction signal waveform having edges corresponding to the leading edge and the trailing edge of each magnetic domain of the magnetic domain array formed on the magneto-optical disk is obtained.

Reference numeral 12 denotes an edge detection circuit, which is an optical head 11.
On the basis of the output reproduction signal waveform of 1., a leading edge detection signal corresponding to the leading edge of the magnetic domain and a trailing edge detection signal corresponding to the trailing edge of the magnetic domain are generated and output.

An amplitude detection circuit 13 detects the amplitude of the output reproduction signal waveform of the optical head 11.

The variable delay circuit 14 provides a delay time for varying the relative time interval between the leading edge detection signal and the trailing edge detection signal output from the edge detection circuit 12 according to the output detection value of the amplitude detection circuit 13. To do.

The synthesizing circuit 15 synthesizes the leading edge detection signal and the trailing edge detection signal extracted from the variable delay circuit 14, respectively.

The demodulation means 16 demodulates the recorded signal from the combined signal output from the combining circuit 15.

[0027]

In the present invention, the leading edge detection signal and the trailing edge detection signal from the edge detection circuit 12 are delayed by the variable delay circuit 14 according to the amplitude value of the reproduced signal waveform. Here, the reproduced signal waveform becomes as shown by a, b, and c as the edge shift amount increases, as shown in FIG. That is, as can be seen from FIG. 2, the amplitude of the reproduction signal changes according to the edge shift amount.

Therefore, the present invention pays attention to the relationship between the amplitude of the reproduction signal and the edge shift amount, and determines the delay time of the variable delay circuit 14 according to the amplitude value of the reproduction signal waveform. The relative time interval between and is changed to a predetermined value. Further, in the present invention, the variable delay circuit 14 can be constituted by only two delay lines having a fixed delay time and a voltage control type delay line having a variable delay time. The demodulation means 16 includes a PLL 21 and a data separator 22.
And a demodulation circuit 23.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 3 shows a block diagram of an embodiment of the present invention. In the figure, the same components as those in FIG. 1 are designated by the same reference numerals. In FIG. 3, the optical head 11 and the edge detection circuit 12 have the same circuit configuration as the optical head 40 and the edge detection circuit 41, respectively. Further, the PLL 21, the data separator 22 and the demodulation circuit 23 are also the PLL 4 of FIG.
7, the data separator 48 and the demodulation circuit 49 have the same configuration.

In FIG. 3, the reproduction signal obtained by reproducing the magneto-optical disk on which information is recorded by the edge recording method with the optical head 11 is supplied to the edge detection circuit 12 and corresponds to the leading edge of the magnetic domain. 4 (A) and the trailing edge detection signal shown in FIG. 4 (C), which corresponds to the trailing edge of the magnetic domain, are supplied to the amplitude detection circuit 13, where the amplitude (of one cycle The peak value of the waveform) is retained.

A first delay circuit 31 delays the leading edge detection signal from the edge detection circuit 12 by a predetermined time td.
It consists of a delay line with a fixed delay time. 32
Is a second delay circuit, which is composed of a delay line having a variable delay time for delaying the trailing edge detection signal from the edge detection circuit 12 within a range of 0 to 2td. As this delay time variable delay line, for example, a voltage control type delay line manufactured by JPC Corporation can be used. The first and second delay circuits 31 and 32 constitute the variable delay circuit 14 described above.

The delay time of the second delay circuit 32 is determined according to the amplitude value of the reproduced signal waveform. Here, the relationship between the amplitude Vg (unit V) of the reproduction signal and the edge shift amount Δt (unit ns) is represented by the equation Δt = −300 · Vg−140 (1) as indicated by the broken line I in FIG. It was confirmed experimentally.

Therefore, from the relationship of the above equation, the delay time td (unit n
The relationship between s) and the reproduced signal amplitude Vg is td = 300 · Vg−220 (2) as shown by the solid line II in FIG. Therefore, the delay time td and the reproduced signal amplitude V of the equation (2)
In order to obtain the relationship with g, the gain Ka and the offset value Ko of the amplifier 33 of FIG. 3 are determined, and the delay time of the second delay circuit 32 is set to 0 by the reproduction signal passed through this amplifier 33.
Variable control is performed within a range of up to 2td.

In this way, the leading edge detection signal shown in FIG. 4 (B) extracted from the first delay circuit 31 and the trailing edge shown in FIG. 4 (D) extracted from the second delay circuit 32. The detection signals are respectively supplied to the combining circuit 15 and combined, and after being converted into signals as shown in FIG. 4 (E), they are input to the PLL 21.

Thereafter, in the same manner as in the conventional case, the data separator 22 separates the data and the clock on the basis of the signal taken out from the PLL 21 in synchronization with the combined signal, and demodulated into the NRZ signal by the demodulation circuit 23 using these. It

As described above, according to this embodiment, changes and variations in write power due to deterioration of the laser diode in the optical head 11, changes in environmental temperature, variations in sensitivity among magneto-optical disks to be reproduced, etc. It is possible to correct the reproduction data interval variation due to the change in the size of each magnetic domain (domain) of the magnetic domain array caused by the above, by a simple configuration with only two delay lines, and to perform accurate reproduction.

[0037]

As described above, according to the present invention, since the relative time interval between the leading edge detection signal and the trailing edge detection signal is made variable, changes and variations in write power, changes in environmental temperature, and magneto-optical characteristics. Even if the domain size changes smaller than the standard due to variations in sensitivity between discs, it is possible to correct and play back without being affected by edge position interval changes.
Further, since it requires only two delay lines, it has a feature that it can be configured more simply than the reproducing apparatus proposed by the present applicant.

[Brief description of drawings]

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

FIG. 2 is a diagram showing examples of reproduced signal waveforms.

FIG. 3 is a block diagram of an embodiment of the present invention.

FIG. 4 is a time chart for explaining the operation of FIG.

FIG. 5 is a diagram showing a relationship between a reproduction signal amplitude and edge shift or the like.

FIG. 6 is a diagram illustrating a rewriting principle of a magneto-optical disk.

FIG. 7 is a diagram showing a basic principle (recording) of conventional edge recording.

FIG. 8 is a diagram showing a basic principle (reproduction) of conventional edge recording.

FIG. 9 is a block diagram of an example of a playback device previously proposed by the applicant.

[Explanation of symbols]

 11 optical head 12 edge detection circuit 13 amplitude detection circuit 14 variable delay circuit 15 combining circuit 16 demodulation means

Claims (3)

[Claims] 1. A reproduced signal which reproduces a recorded signal of a magneto-optical disk recorded by an edge recording system and has edges corresponding to the leading edge and the trailing edge of each magnetic domain of a magnetic domain array formed on the magneto-optical disk. An optical head (11) for obtaining a waveform, and a leading edge detection signal corresponding to the leading edge of the magnetic domain and a trailing edge detection signal corresponding to the trailing edge of the magnetic domain based on the output reproduction signal waveform of the optical head (11). An edge detection circuit (12) for generating and outputting respectively, an amplitude detection circuit (13) for detecting the amplitude of the output reproduction signal waveform of the optical head (11), and an output detection value of the amplitude detection circuit (13). Accordingly, a variable delay circuit (14) for giving a delay time for varying the relative time interval between the leading edge detection signal and the trailing edge detection signal output from the edge detection circuit (12), and the variable delay circuit (14). Leading edge detection retrieved from No. and trailing edge detection signals respectively synthesized synthesis circuit (15)
And a demodulation means (16) for demodulating a recorded signal from an output combined signal of the combining circuit (15). 2. The variable delay circuit (14) includes a first delay circuit (31) for delaying one edge detection signal of the leading edge detection signal and the trailing edge detection signal by a predetermined time td, and the other edge. The light according to claim 1, further comprising a second delay circuit (32) that delays the detection signal in accordance with the output detection value of the amplitude detection circuit (13) in the range of 0 to 2td. Magnetic disk player. 3. The first delay circuit (31) is a delay line having a fixed delay time, and the second delay circuit (3).
3. The magneto-optical disk reproducing apparatus according to claim 2, wherein 2) is a voltage-controlled delay line with variable delay time.