JP3366654B2 - 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 apparatus for reproducing recorded information from a magneto- optical disk on which information is recorded by a pit edge recording method.

2. Description of the Related Art Magneto-optical disk recording / reproducing devices are rapidly spreading from recording / reproducing of image information to those capable of recording codes for computers due to 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 speed of such a magneto-optical disk.

FIG. 6 shows the principle of rewriting a magneto-optical disk. As shown in FIG. 1A, first, the external magnetic field generator 1 applies a magnetic field to the magneto-optical disk medium 2 in a direction in which, for example, the N pole side approaches the medium surface of the magneto-optical disk 2. The objective lens 3 is provided on the medium surface of the magneto-optical disk 2 rotating in this state.
When the erasing light beam 4 is narrowed and incident through the interface, the temperature at a local position where the erasing light beam 4 is irradiated rises, magnetization reversal is performed, and the magnetization direction as shown by a downward arrow in FIG. Are aligned in one direction. Thus, the medium portion 5 of the magneto-optical disk 2 is erased.

[0006] Next, as shown in FIG. 6 (B), the direction of the applied magnetic field of the external magnetic field generator 1 is reversed with respect to the erased portion of the magneto-optical disk 2, 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 at the local position irradiated with the recording light beam rises,
The magnetization reversal is performed, and magnetization is performed in a direction opposite to that in the erase operation.

On the other hand, when the light intensity of the recording light beam is low, the irradiation position of the light beam on the magneto-optical disk 2 is not heated.
The magnetization direction at the time of erasing remains as it is. As a result, information to be recorded is written on the surface of the magneto-optical disk medium indicated by 7 in FIG. 6B.

Here, 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".
A recording light beam emission pattern shown in FIG.
This is irradiated onto the magneto-optical disk 2 as the recording light beam 6. Thereby, the recording domain (magnetic domain) of one track on the medium plane of the magneto-optical disk 2 is changed as shown in FIG.
It becomes as shown in.

[0007] The data recorded on the magneto-optical disk 2 in this manner is reproduced when the recorded data is read from the magneto-optical disk 2.
The change is recorded as a change in the magnetization direction, and is performed using the magnetic Kerr effect. That is, since the polarization plane of the reflected light on the medium surface of the magneto-optical disk 2 rotates according to the direction of the recording magnetization, the recorded data is reproduced by discriminating the rotation direction of the polarization plane of the reflected light.

Accordingly, at the time of reproduction, a light beam is focused on each track shown in FIG. 8 (A) by an objective lens to form a reproduction light spot 7 and scanning is performed. Separately, a reproduced waveform as shown in FIG. The reproduction data as shown in FIG. 8 (C) is demodulated from this reproduction waveform at a point where the value crosses the center level of the reproduction waveform and the value is “1”, and the others are “0”.

In a pit edge recording type magneto-optical disk reproducing apparatus which is recorded and reproduced based on the above-described basic principle, the position of the edge of a magnetic domain is important. It is necessary to perform reproduction without being affected by a change in the edge position interval between the magnetic domains in the magnetic domain row.

[0010]

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

The edge detecting circuit 41 separately detects the edges of the reproduced signal corresponding to the leading edge and the trailing edge of the recording domain, and outputs the leading edge detecting signal to the delay line 4.
2 and the counter 43, and the trailing edge detection signal is used as a reset pulse as a reset pulse.
And to the synthesis circuit 45.

The delay line 42 is supplied with a leading edge detection signal, and outputs the signal after delaying it by an integral multiple of the counter clock cycle. That is, the delay line 42
From the plurality of output terminals, delayed signals having different delay times are output in parallel from the minimum one cycle of the counter clock to the maximum n + 1 cycle. This parallel output delay signal is supplied to each of the multiplexers 46.

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, when the trailing edge detection signal falls. After the reset, the count is incremented by the count clock, and the count value is supplied to the latch circuit 44. The latch circuit 44 is reset when the trailing edge detection signal falls, and latches the count value from the counter 43 when the leading edge detection signal falls.
4 is supplied with a select signal.

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

That is, by delaying the leading edge detection signal, the leading edge detection signal is synchronized with the trailing edge detection signal.

The PLL 47 generates a clock synchronized with the rise and fall of the synthesized signal (the count clock is a frequency-divided version of this clock) 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 extracts the NRZ from the separated data which is the running length limited code (PLLC).
The signal is demodulated into a (non-return-to-zero) code signal.

[0017]

In recording, thermomagnetic writing is performed in which recording magnetic domains are formed by selectively heating with a recording light beam. 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 domain formed changes, and the position interval between edges changes, so that correct recording cannot be performed. Also, due to the sensitivity variation in the medium of the magneto-optical disk medium or the sensitivity variation between the media, the size of the magnetic domain formed varies even if the temperature distribution is the same.
Furthermore, 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, a plurality of delay times can be obtained by the delay line 42, and the data is counted by the counter 43 synchronized with the PLL 47. Since the optimum delay time of the delay line is selected from the counter value, the above problem is solved.

However, the above-described proposed device requires a large number of delay times and a large number of delay lines in order to provide an accurate delay amount in addition to performing a complicated measurement. Further, in the above proposed device, 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. Therefore, when the size of the domain is larger than the standard, it can be corrected. It cannot be corrected for a change in which the size of the domain becomes smaller than the standard, such as when recording at a very low temperature.

[0020] The present invention has been made in view of the above, be varied so that the edge position interval etc. with less delay line, optical magnetic playable by correcting the influence of the change
An object of the present invention is to provide a gas disk reproducing apparatus.

[0021]

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

Reference numeral 12 denotes an edge detection circuit,
Based on the output reproduced signal waveform, the front edge detection signal which corresponds to the leading edge of the recording domain, respectively generates and outputs the edge detection signal after corresponding to the trailing edge of the recording domain.

Reference numeral 13 denotes an amplitude detection circuit, and the optical head 11
The maximum amplitude during one cycle of the output reproduction signal waveform is detected.

The variable delay circuit 14 gives 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. I do.

The combining circuit 15 combines 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 output synthesized signal of the synthesis circuit 15.

[0027]

According to 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 in accordance with the amplitude value of the reproduced signal waveform. Here, as shown in FIG. 2, the reproduced signal waveform becomes as shown by a, b, and c as the edge shift amount increases. 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 focuses on the relationship between the amplitude of the reproduced signal and the edge shift amount, and adjusts the delay time of the variable delay circuit 14 in accordance with the amplitude value of the reproduced signal waveform with the leading edge detection signal and the trailing edge detection signal. Is varied so that the relative time interval with the predetermined value becomes 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-controlled 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]

FIG. 3 is a block diagram showing an embodiment of the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. 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 same configuration as the data separator 48 and the demodulation circuit 49.

In FIG. 3, a reproduced signal obtained by reproducing the magneto-optical disk on which information is recorded by the edge recording method by the optical head 11 is supplied to an edge detecting circuit 12, where the reproduced signal is supplied to the front edge of the magnetic domain. a leading edge signal that per, while being converted into an edge detection signal after Ru edge near <br/> other after magnetic domain, the amplitude detecting circuit 1
3 where the amplitude (the peak value of one cycle of the waveform) is held.

Reference numeral 31 denotes a first delay circuit, which is constituted by a delay line having a fixed delay time for delaying the leading edge detection signal from the edge detection circuit 12 by a predetermined time td0 . 32 is a second delay circuit, which is one round of the output reproduction signal waveform.
The delay time td of the trailing edge detection signal from the edge detection circuit 12 is variable in the range of 0 to 2 td 0 according to the maximum amplitude of the period.
It is composed of a variable delay time of the delay line for delaying delay time. As the delay line having a variable delay time, for example, a voltage-controlled delay line manufactured by JPC Corporation can be used. These 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 maximum amplitude between the periods of the reproduction signal waveform. Here, relationship between the reproduction signal amplitude Vg (unit V) and the edge shift amount Delta] t (unit ns) is as shown by a broken line I in FIG. 5 (A), Δt = -300 · Vg + 220 (1) made by the formula It was confirmed experimentally that it was expressed.

Accordingly, from the relationship of the equation, the delay time Δtd (unit n
s) and the reproduced signal amplitude Vg are shown by a solid line II in FIG.
Δtd = 300 · Vg−220 (2) Therefore, the gain Ka and the offset value Ko of the amplifier 33 in FIG. 3 are determined so that the relationship between the delay time Δtd and the reproduction signal amplitude Vg in the equation (2) is obtained.
The delay time of the second delay circuit 32 is variably controlled within the range of 0 to 2td0 by the reproduced signal passed through the second delay circuit 32 . At this time,
During the quasi-delay time td0, the amplitude Vg of a recording pit having a fixed length
Corresponds to the edge shift calculated using equation (2)
Equation (3) is obtained by adding the edge shift amount Δtd.
It can be represented by an equation as shown by td = Δtd + td0 (3)

FIG . 4 is a time chart for explaining the operation of FIG.
Show. A reproduced signal obtained by reproducing with the optical head 11 is:
Supplied to the edge detection circuit 12, where the leading edge of the magnetic domain is
A front edge signal shown in FIG. 4 (A), which corresponds, per the trailing edge of the magnetic domain
FIG. 4 which is converted into the trailing edge detection signal shown in FIG .
The leading edge detection signal shown in FIG.
4 (B), and is supplied to the synthesizing circuit 15 after being delayed.
It is. Also, the trailing edge detection signal shown in FIG.
As shown in FIG. 4D, the delay circuit 31 synthesizes the signals.
It is supplied to the circuit 15. The synthesizing circuit 15 shown in FIG.
The leading edge detection signal shown in FIG.
The signal is synthesized to generate a signal as shown in FIG.
L21. At this time, the second delay circuit 3
1 indicates that the delay amount is based on the signal from the amplitude detection circuit 13.
Controlled.

Thereafter, in the same manner as in the prior art, the data and the clock are separated by the data separator 22 based on the signal taken out from the PLL 21 in synchronization with the synthesized signal, and the NRZ signal is demodulated by the demodulation circuit 23 using these. You.

As described above, according to the present 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, and the like. The variation in the reproduction data interval due to the change in the size of each magnetic domain (domain) of the magnetic domain row caused by the above can be corrected by a simple configuration requiring only two delay lines, and accurate reproduction can be performed.

[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 disk Even if the size of the domain changes smaller than the standard due to the variation in sensitivity between the two, it can be corrected and reproduced without being affected by the change in the edge position interval.
Since only two delay lines are required, the present invention has the advantage that it can be configured more easily than the reproducing apparatus proposed in the present application.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing each example of a reproduction signal waveform.

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

FIG. 4 is a time chart for explaining the operation of FIG. 3;

FIG. 5 is a diagram illustrating a relationship between a reproduced signal amplitude and an edge shift or the like.

FIG. 6 is a diagram illustrating the principle of rewriting 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 reproducing apparatus proposed by the present applicant.

[Explanation of symbols]

11 Optical head 12. Edge detection circuit 13 Amplitude detection circuit 14 Variable delay circuit 15 Synthesis circuit 16 Demodulation means

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-134839 (JP, A) JP-A-2-46544 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11/10-11/105 G11B 7/00-7/0065

Claims (3)

(57) [Claims] 1. A reproducing the already recorded signals of the recorded magnetooptical di <br/> disk in edge recording method, having an edge corresponding to the leading and trailing edges of the recording domains formed on the optical disk An optical head for obtaining a reproduction signal waveform; and a leading edge detection signal corresponding to a leading edge of the recording domain and a trailing edge detection signal corresponding to a trailing edge of the recording domain based on an output reproduction signal waveform of the optical head. An edge detection circuit for generating and outputting a signal; an amplitude detection circuit for detecting a maximum amplitude of one cycle of an output reproduction signal waveform of the optical head; and an output of the edge detection circuit according to an output detection value of the amplitude detection circuit. A variable delay circuit for providing a delay time that varies a relative time interval between the leading edge detection signal and the trailing edge detection signal; and combining the leading edge detection signal and the trailing edge detection signal extracted from the variable delay circuit. Synthesis circuit When magneto-optical disk reproducing apparatus characterized by comprising a demodulation means for demodulating a recorded signal from an output composite signal of the combining circuit. 2. A variable delay circuit comprising: a first delay circuit that delays one of the leading edge detection signal and the trailing edge detection signal by a predetermined time; and the other edge detection signal detects the amplitude of the other edge detection signal. 2. The magneto- optical disk reproduction device according to claim 1, further comprising a second delay circuit that delays by a delay time variable in a range of 0 to 2 times the predetermined time according to an output detection value of the circuit. apparatus. 3. The delay circuit according to claim 2, wherein the first delay circuit is a delay line having a fixed delay time, and the second delay circuit is a voltage-controlled delay line having a variable delay time. Magneto- optical
Qi disk playback device.