JPH0227547A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To suppress the dynamic range of a circuit which performs the reproduction of recording information at required minimum by arranging an area for recording at least on one side out of first and second saturation levels at the front of each unit recording area at every unit recording area. CONSTITUTION:Segment constitution in one sector of a magneto-optical disk on which plural unit recording areas having prescribed recording quantities are arranged in circumferential direction is formed in such a way that an emboss pit including the information of a sync mark, a sector address, and a track address is formed, and the first half three bytes of a reserve area consisting of eighth to 13th bytes following the area are set as the areas for recording an erasure saturation level, and the latter half three bytes as the areas for recording a recording saturation level. And the area for recording at least on one side out of the first and second saturation levels is arranged at the front of each unit recording area at every unit recording area. In such a way, it is possible to suppress the dynamic range of the circuit which performs the reproduction of the recording information at the required minimum.

Description

[Detailed description of the invention] Technical field The present invention relates to a magneto-optical disk.

BACKGROUND ART In recent years, read-only and write-once optical discs have been put into practical use, and rewritable optical discs are also about to be put into practical use. In any of these types of optical discs, the track pitch is very narrow, about 1 to 2 μm, so concave or convex bits or grooves are previously formed on the disc to follow the tracks. - By diffraction of the light that is irradiated onto the disk and reflected by these bits or grooves, it is possible to detect the relative positional relationship in the disk radial direction between the track and the beam spot for information reading, thereby tracking the beam spot to follow the track. Can be used as a servo. Bits are also used for information needed to record or reproduce data and to generate locks, information to partition sectors, information to access sectors, information to partition the inside of a sector into blocks, etc. These various types of information are read by diffraction of light by the bits. As described above, the bits which are formed in advance on the disk and whose purpose is to obtain information by diffraction of light are called embossed bits.

Examples of the arrangement (so-called format) of the embossed bits on the disk are shown in FIGS. 4 to 7.

In the format shown in FIGS. 4 to 7, a virtually spiral track formed on the disk is divided into 1376 equiangular segments per rotation. Furthermore, one sector is composed of 43 consecutive segments. Therefore, one track (one track) consists of 32 sectors.

FIG. 4 is a diagram showing a segment configuration within one sector. Every segment consists of a 2-byte servo area and a 16-byte header area or data area, a total of 18 bytes. The first segment has a 16-byte header area, and the second to 43rd segments have a 16-byte data area. Note that one byte of all bytes in the servo area, header area, and data area is divided into 15 channel bits.

FIG. 5 is a diagram showing the configuration of the servo area.

One segment of servo area consists of 2 bytes.

The bytes constituting the servo area are respectively referred to as a first servo byte and a second servo byte. Two embossed bits are formed in the first servo bite. These are formed to be shifted from the virtual track center by about 1/4 track pitch in opposite directions in the radial direction of the disk. The first wobbled pit PWI is formed at the position of the third or fourth channel bit while being switched every 16 tracks, and the second wobbled pit PW2 is formed at the position of the eighth channel bit.

Using these two wobbled pits, a tracking error signal can be generated in a sampling manner once per segment. That is, when the beam spot passes through the virtual track center, it passes between the two wobbled pits, so the degree of diffraction in each wobbled pit is equal, and the reflected light is also equal. Therefore, the tracking error signal obtained by taking the difference between the signals obtained by photoelectrically converting the amount of reflected light is zero (no error). Further, when the beam spot passes through the track with a deviation from the center of the virtual track, a difference occurs in the reflected light from the two wobbled pits, so a tracking error signal corresponding to the direction and amount of deviation is obtained. Since there are 1.376 segments in one rotation, the tracking error signal obtained by sampling at each servo byte is almost equivalent to one obtained continuously, making it possible to perform tracking servo. .

Also, one embossed bit is formed in the second servo byte exactly on the virtual track center at the position of the twelfth channel bit. This is the clock bit P
It is called C. The clock bit PC is located at a fixed position in each servo byte, one per segment, so by synchronizing the PLL with a signal that is reproduced from this bit at regular intervals, a clock with the frequency of the channel bit rate is generated. can do. Modulation is performed using this clock when recording data, and demodulation is performed using this clock when reproducing data as well.

Note that since there is a mirror surface between PW2 and PC, it is possible to generate a stable focus error in a sampling manner that is not affected by the presence or absence of bits.

In addition, the interval between PW2 and PC is an interval (19 channel bits) that cannot occur in the 4/15 modulation mode described later, so segment synchronization can be performed by detecting this interval. It is possible.

FIG. 6 is a diagram showing the configuration within the header area. 1st
The sink mark of the cutting tool is formed by an embossed bit. The sync mark is formed with bits on the 2nd, 7, 8, and 9 channel bits, and is 4/15 as described later.
In the modulation method modulation diameter conversion table, this is a special pattern that does not correspond to any NRZ data. Therefore,
By detecting this, sector synchronization can be performed. The second byte is a sector address within one track, and the third to seventh bytes are track addresses within a disk, formed by embossed bits. These are modulated using a 4/15 modulation method, which will be described later, for each byte.

The 8th to 13th bytes are reserve areas whose uses have not been determined, and are mirror surfaces without emboss bits.

The 14th to 16th bytes are laser power control areas, and are initially mirror surfaces without embossed bits. When recording or erasing on a disc, it is desirable to use appropriate optical power, but in this area it is permissible to emit recording or erasing power on a trial basis from the optical pickup and correct the output power based on that. has been done.

FIG. 7 is a diagram showing the data area. The data area is 1
It is 6 bytes long, and in the unrecorded state is a mirror surface without embossed bits. NRZ data is modulated one byte at a time using the 4/15 modulation method described later and recorded in this area. In the case of the write-once type, recording involves physical changes such as holes in the recording film. In the case of a rewritable disk that utilizes the magneto-optical effect (hereinafter referred to as a magneto-optical disk), such a physical change does not occur, but it does involve a change in which the direction of the magnetic field of the recording film is reversed.

The data area in one sector is 16x42-672.
There are bytes, which consist of user data, error correction codes, etc., but the details will not be described here.

Next, the 4/15 modulation method will be explained with reference to FIG. 4/15 modulation method 1 byte is converted into 15 channel bits, and from these 15 places, the original 258
For the NRZ data on the street, there are 4 locations (2 odd and even 2 locations each) that correspond one-to-one using the conversion table.
One place at a time. However, the 15th channel bit is excluded. ). That is, in the case of a write-once type, an operation such as making a hole in the recording film is performed, and in the case of a magneto-optical disc, the direction of magnetization of the recording film is reversed. Note that, as in the example shown in Figure 8, the marks are next to each other (see 12.13.1).
4 channel bits), but there is always a gap of at least two channel bits (10th and 11th channel bits) between marks (9th and 12th channel bits) that are not adjacent to each other. However, as an exception, there are cases where the 14th channel bit of one byte and the 1st channel bit of the next byte become a mark, leaving only one channel bit (15th channel bit) between them, but the 15th channel bit was originally marked. Therefore, there is no problem during demodulation.

Next, demodulation of data using 4/15 modulation method will be explained. FIG. 8 shows reproduced waveforms corresponding to the marks.

In addition, in the case of drilling records, the reflected light at the mark position is darker than the reflected light at the unmarked position (mirror surface).
Also, some media that are not perforated undergo the opposite change.

However, demodulation is possible if there is a difference between the level at the mark position and the level at the mirror surface due to the 4/15 modulation method.
It is assumed that the reproduced waveform in FIG. 8 is not bright in the upper part of the figure, but simply shows the voltage level at a certain point in the demodulation circuit.

In addition, in the case of magneto-optical disks, it is not a mirror level, but
This is the erasure level. For demodulation, it is sufficient to specify the positions of marks in two of the odd numbered places and 21 of the even numbered places among the first to fourteenth channel bits of a certain byte.

Therefore, for example, by performing A/D conversion at the bit center of the first to fourteenth channel bits and comparing the magnitudes of the obtained digital data, the position of the mark can be specified. For example, in the example of FIG. 8, 1.3, 5, 7, 9.11.
Among the 13 channel bits, the 13th channel bit has the highest level, and the 9th channel bit has the second highest level. (In this example, there is a mark on the 14th channel bit and the 1st channel bit of the next byte, so the level of the 15th channel bit may be higher than the level of the 9th channel bit, but the 15th channel bit may not become a mark.) (Since there are no marks, they are not compared in size, and therefore do not cause a problem in demodulation.) In other words, it can be seen that among the odd-numbered bits, there are marks on the 9th and 13th channel bits. Similarly, No. 2゜4.6, 8.10.1
2. Among the 14 even channel bits, the 12th
．． It can be seen that there is a mark on the 14th channel bit.

The original NRZ data can be demodulated from these four marks using the conversion table.

In short, demodulation of the 4/15 modulation method is based on comparing the reproduction levels at the center of each channel bit.

Next, an outline of the magneto-optical disk will be explained.

First, as with write-once optical discs, portions that will become embossed pits are created on a glass master disc using a mask ring, and a stamper is created by electroforming.

Next, using this stubber as a mold, a polycarbonate resin or the like is injection molded to produce a substrate on which the embossed bits are transferred. Next, a thin film of TbFeCo alloy or the like is formed as a recording film on this substrate by a method such as sputtering to obtain a magneto-optical disk as shown in FIG.

The recording film 1 of the magneto-optical disk as shown in FIG. 9 produced in this way usually has a uniform reflectance of about several tens of percent. Therefore, light of uniform intensity is reflected in the mirror surface portion 2 without embossed pits.

Further, in the embossed bit portion 3, the amount of reflected light is approximately several tens of percent of that of the mirror surface portion 2 due to a diffraction phenomenon.

Note that 4 is a substrate.

Next, an outline of the recording principle of a magneto-optical disk will be explained. In the initial state where a recording film is formed by a method such as sputtering as described above, the magnetic domains of the recording film are randomly arranged upward and downward in a direction perpendicular to the film surface. Generally, a magnetic field Hm stronger than the coercive force Ha of the film is applied to the disk in this initial state to align the direction of magnetization in one direction (erasing direction). This creates a disc with no signal (completely erased). This disk has a magneto-optical disk device (hereinafter referred to as a drive).
When recording information with , it is weaker than Hc and the direction is Hm.
While applying a magnetic field Hr opposite to the above, a strong recording beam is irradiated only when a mark is to be recorded on a channel bit.

Then, the temperature of that part rises and the coercive force becomes smaller than Hr, so the magnetization direction is reversed, and after the beam spot passes, the magnetization direction of that part becomes Hr, and a mark cannot be recorded. That means that.

When erasing recorded data using a drive, a strong erasing beam is applied while applying a magnetic field He that is weaker than He and in the same direction as Hm. As a result, in the portion irradiated with the erasing beam, the direction of the magnetic field becomes a no-signal state (erased state) regardless of the presence or absence of a mark. In other words, the mark has been erased.

During reproduction, a linearly polarized reproduction beam, which is weaker than the recording beam or erasing beam, is irradiated. The plane of polarization of the reflected light is slightly rotated by the Kerr effect, but the direction of rotation depends on the direction of magnetization. By detecting this with an analyzer, converting it into a change in intensity, and photoelectrically converting it, it is possible to obtain the potential difference between the mark location and the non-mark location.

Note that a differential optical system is generally used as a reproduction signal detection optical system of a magneto-optical pickup.

Although not particularly shown, this method divides the reflected light from the disk into two systems using a polarizing beam splitter, and by taking the difference between the respective photoelectrically converted signals, it obtains a magneto-optical reproduction signal and eliminates semiconductor laser noise and disk noise. It is well known that the in-phase noise such as minute reflection unevenness from the optical system is suppressed, and that it is indispensable as an optical system for reproducing magneto-optical signals. Note that the reproduced signal of the embossed pit is obtained by summing the two systems of signals.

When demodulating data recorded on a magneto-optical disk having the format described above, segment synchronization is first performed by detecting the interval between the embossed pits of PW2 and PC shown in FIG. Sector synchronization is performed by detecting the sync mark shown in FIG. As shown in FIG. 8, by performing A/D conversion on the magneto-optical signal reproduction waveform of each byte and comparing the sizes, it is possible to determine whether the recorded mark (i.e. direction of magnetization is changed from the erased state). (inverted channel bits)
Since the position of the data can be known, it is possible to demodulate the recorded data.

Generally, on an optical disc, data is not recorded sequentially but randomly in each sector, which is the minimum unit of recording.

Therefore, it is naturally possible that a recorded sector appears after consecutive unrecorded sectors.

A magneto-optical disk device (hereinafter referred to as
In the drive (referred to as a drive), the playback signal is obtained by detecting minute changes in the Kerr rotation angle, so the amplitude of the signal read by the pickup is also very small, so the signal is increased to enable subsequent signal processing. Amplification is required, and for this purpose an AC coupled amplifier (hereinafter referred to as an AC amplifier) must be used. AC like this
FIG. 10 shows a circuit that performs demodulation processing after amplification by an amplifier.

In FIG. 10, a magneto-optical reproduction signal a (in the case of a differential optical system, a signal obtained by taking the difference between two channels) output from a pickup (not shown) is amplified by an amplifier 5, and then is amplified by a capacitor C1. The signal is supplied to an analog/digital (hereinafter abbreviated as A/D) converter 6 via the converter 6. A resistor R is connected between the input terminal of the A/D converter 6 and the ground.
1 is connected. After the magneto-optical reproduction signal a is converted into digital data by the A/D converter 6, it is supplied to a demodulation circuit (not shown) and subjected to Te4/15 demodulation processing.

By the way, in the case of a magneto-optical disk, in a completely erased part, the direction of magnetization is aligned in a certain direction, and conversely, in a part that is completely recorded over a sufficiently long section, the direction of magnetization is erased. They are aligned in opposite directions, and there are two saturated states. However, in the initial state of the disk where the recording film was formed by sputtering etc.,
Since the direction of magnetization is random, it is in an undefined state between a completely erased state and a completely recorded state.

Now, just by forming a recording film in this way, the retention force of the film is H.
The waveform of the magneto-optical reproduction signal a obtained by the pickup in the vicinity of the recorded sector for a disk that has not been subjected to the entire erasing operation by applying a magnetic field Hm stronger than C is as shown in FIG. 11(A). .

Since neither recording nor erasing is performed in the unrecorded sector, the level of the magneto-optical reproduction signal a is an undefined level between the recording saturation level vR corresponding to the recording saturation state and the erasing saturation level Vε corresponding to the erasing saturation state. level. Therefore,
The level of the magneto-optical reproduction signal a obtained from an unrecorded sector may be very close to the recording saturation level vR, and the waveform may be as shown by the solid line, or the level may be very close to the erase saturation level vE. As a result, the waveform may become as shown by the dashed line. On the other hand, in the recorded sector, the data is erased by the -degree drive and then a mark is recorded in the channel bit corresponding to the data, so the level of the magneto-optical reproduction signal a is the same as the recording saturation level VR and the erasing saturation level Vε. It changes depending on the mark position between. Note that here, the level difference between the recording saturation level VR and the erasing saturation level VE is assumed to be e.

The waveform of the input signal S to the A/D converter 6 to which the magneto-optical reproduction signal a is supplied via the AC-coupled capacitor C1 is as shown in FIG. 11(B). While reading an unrecorded sector, regardless of whether the level of the magneto-optical reproduction signal a is near vR or near VE, the A/D
The level of the input signal to the converter 6 is approximately equal to the ground level. However, when the beam spot for reading information moves to the recorded sector, if the level of the magneto-optical reproduction signal a just before that is close to the VR level, the level of the input signal S is approximately -e and the ground level. The waveform becomes as shown by the solid line. Furthermore, when the beam spot for reading information moves to a recorded sector, if the level of the magneto-optical reproduction signal a immediately before that is a level near vE, the level of the input signal A is approximately the ground level and +e.
The waveform changes between , and the waveform becomes as shown by the dashed line.

Therefore, it is necessary to use an A/D converter 6 having a dynamic range of 2e even though the maximum signal amplitude is only e. In order to widen the dynamic range of the A/D converter while maintaining good resolution, one extra bit is required, but as in this example, if the period of each channel bit is short (the number of disk rotations is 3)
An A/D converter that performs A/D conversion at a speed of about 90 ns (in the case of 0 RPS) becomes extremely expensive if the number of bits increases even by one bit.

Therefore, it is conceivable to apply a magnetic field Hm stronger than the coercive force He of the film to the disk on which the recording film has been formed by sputtering to erase the entire surface. By doing so, the level of the magneto-optical reproduction signal a in the unrecorded sector shown in FIG. will always change between the ground level and +0. However, in order to erase the entire disk, a magnetic field Hm that is sufficiently stronger than the coercive force He of the film is required.
(Generally, the Hc of the recording film is set to be quite large in order to avoid being affected by leakage magnetic flux from the drive actuator, spindle motor, etc., so the Hm required to overcome this is extremely large. ) must be applied to the entire surface of the disk without fail, and the equipment for that purpose becomes large-scale. Furthermore, since it takes a lot of man-hours to erase each disc one by one and inspect it, this increases the cost of the disc. Another possibility is to raise the temperature of the disk and erase the entire surface using a magnetic field weaker than Hm, but if the substrate is made of resin, there are restrictions on the temperature, and of course it requires equipment and time to raise the temperature. It becomes.

Furthermore, even if the entire area is erased, if the recorded sector continues for a very long time, a sag due to AC coupling will gradually appear in the input signal of the A/D converter 6, as shown in FIG. Therefore, the dynamic range must be larger than e.

Furthermore, although the explanation has been made assuming that e is constant, since the medium of optical discs is replaceable, it is necessary for the drive to be able to play discs with various variations. Therefore, it is necessary to set the dynamic range of the A/D converter to the maximum value of e, and if the value of e becomes small due to variations,
The resolution of the /D converter would be reduced, which could lead to a worsening of the error rate.

Summary of the Invention The present invention has been made in view of the above points, and includes:
It is an object of the present invention to provide a magneto-optical disk that makes it possible to minimize the dynamic range of a circuit that reproduces recorded information.

In order to achieve the above object, in the magneto-optical disk according to the present invention, an area for recording at least one of the first and second saturation levels is arranged in front of each unit recording area. .

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 3.

As shown in FIG. 1, the segment configuration within one sector of the magneto-optical disk according to the present invention is similar to the formats shown in FIGS. 4 to 7. Further, in the header area, embossed bits containing information such as a sync mark, a sector address, and a track address are formed as in the formats shown in FIGS. 4 to 7, and a laser power control area is also provided. However, in this example, the first three bytes of the 8th to 13th byte reserve area following the area where the embossed bit corresponding to the track address is formed are an area for recording the erase saturation level, and the latter 3 bytes are an area for recording the erase saturation level. The byte is an area for recording at the recording saturation level.

FIG. 2 shows a drive for recording and reproducing information using a magneto-optical disk according to the present invention as shown in FIG.

In FIG. 2, 10 is a magneto-optical pickup;
A light receiving element 12.1 that receives light from both channels of the semiconductor laser 11 as a light source and the differential optical system and performs photoelectric conversion.
3 is built-in. The light receiving elements 12 and 13 detect, for example, laser beams emitted from the semiconductor laser 11 and reflected by the magneto-optical disk 15 through analyzers, and one detects the positive direction component of the Kerr rotation angle. , the other detects the negative direction component of the Kerr rotation angle. The magneto-optical disk 15 is rotated at a predetermined speed by a spindle motor 16 that is driven and controlled by a spindle servo circuit (not shown). The pickup 10 further includes a focus actuator and a tracking actuator, which are driven by a focus servo circuit and a tracking servo circuit. By these servo circuits etc., the semiconductor laser 1
The laser beam emitted from the magneto-optical disk 15 is accurately focused on the recording surface of the magneto-optical disk 15 to form a beam spot, and this beam spot accurately follows the track. It is omitted because it is not.

The outputs of the light receiving elements 12 and 13 are added by an adder 17 to form an embossed bit reproduction signal d. Also,
At the same time, the output of the light receiving elements 12 and 13 is
One is subtracted from the other to form the magneto-optical reproduction signal a.

The embossed bit reproduction signal d is supplied to a 4/15 demodulation circuit 19 and a synchronization circuit 20. The synchronization circuit 20 is configured to generate a segment synchronization signal and a sector synchronization signal based on the embossed bit reproduction signal d. The segment synchronization signal and sector synchronization signal output from the synchronization circuit 20 are supplied to a timing signal generation circuit 21. The timing signal generation circuit 21 is configured to generate various timing signals based on the segment synchronization signal and the sector synchronization signal and supply them to each section.

Furthermore, the 4/15 demodulation circuit 19 demodulates the portion of the embossed pit reproduction signal d corresponding to the embossed bits including the sector address and track address information in the header area using the timing signal from the timing signal generation circuit 21. It is configured to output data indicating a sector address and a track address.

On the other hand, the magneto-optical reproduction signal a is amplified by an amplifier 22 and then supplied to an A/D converter 24 and a sample-hold circuit 25 via an AC coupling capacitor C2 and an analog switch 23. An analog switch 26 and a resistor R are connected between the input terminal of the A/D converter 24 and ground.
2 are connected. The analog switches 23 and 26 are supplied with ON command signals f and g from the timing signal generation circuit 21. The sample hold circuit 25 also receives a sampling pulse h from the timing signal generation circuit 21.
is supplied.

The output j of the sample hold circuit 25 serves as a full scale input to the A/D converter 24.

The A/D converter 24 has a dynamic range set from the ground level to the full-scale input level. The output data of this A/D converter 24 is supplied to a 4/15 demodulation circuit 28.

Further, a drive signal is supplied to the semiconductor laser 11 in the pickup 10 from a drive circuit 29 .

The drive circuit 29 is supplied with a timing signal from the timing signal generation circuit 21 and the system controller 3
Various commands output from 0 and recording signals output from a 4/15 modulation circuit (not shown) are supplied. The drive circuit 29 constantly outputs a constant level signal having an amplitude corresponding to the low level laser power for reading information, and also has an amplitude corresponding to the laser power during erasing in response to an erasing command from the system controller 30. The drive pulse signal k is superimposed on the constant level signal in synchronization with the timing signal,
In response to a recording command, a drive pulse signal g having an amplitude corresponding to the laser power during recording is superimposed on a constant level signal according to a recording signal output from a 4/15 modulation circuit (not shown), and forced irradiation is performed. In response to the command, the above drive pulse signal g
The configuration is such that the signal is superimposed on a constant level signal.

Various commands output from the system controller 30 are as follows:
Furthermore, it is supplied to the magnetic field application circuit 32. Magnetic field application circuit 32
is configured to supply a drive signal according to a command to the coil of the magnetic field application mechanism.

The magnetic field application circuit 32 and the coil L apply an erasing magnetic field He of a predetermined strength when an erasing command is generated, and apply a recording magnetic field Hr whose direction is opposite to the erasing magnetic field He when a recording command or forced irradiation command is generated. Ru.

The system controller 30 includes a processor, a ROMSR
It is formed by a microcomputer such as AM. The system controller 30 is further supplied with output data of the 4/15 demodulation circuit 19. The system controller 30 generates various commands as described below using a processor that operates according to a program stored in advance in the ROM.

When recording data, the system controller 30
The sector in which data is to be recorded is detected based on the output data of the /15 demodulation circuit 19, and when the sector is detected, the area from the 8th byte to the 13th byte of the header area and The data area of each of the second to forty-third segments is detected and an erase command is sent to the drive circuit 29 and the magnetic field application circuit 32.

Then, when the beam spot passes over the sector to be recorded as shown in FIG. 3(A), the constant level signal constantly supplied to the semiconductor laser 11 is changed to the laser power during erasing as shown in FIG. 3(B). A drive pulse signal k having a corresponding amplitude is superimposed, and the data areas of the reserve area and the second to forty-third segments are put into an erased state.

Next, the system controller 30 detects the sector in which data is to be recorded again based on the output data of the 4/15 demodulation circuit 19, and when the sector is detected, the system controller 30 uses the timing signal to detect the sector in which data is to be recorded. After detecting the area and sending a forced irradiation command to the drive circuit 29 and the magnetic field application circuit 32, the data area of each of the second to 43rd segments is detected and a recording command is sent to the drive circuit 29 and the magnetic field application circuit 32. Send.

Then, as shown in FIG. 3(C), a driving pulse signal g having an amplitude corresponding to the laser power during recording is superimposed on the constant level signal constantly supplied to the semiconductor laser 11, and from the 11th byte of the header area Marks are recorded over the entire area up to the 13th byte, that is, the latter three bytes of the reserve area, and marks corresponding to the recording signal are recorded in the data areas of each of the second to 43rd segments.

As described above, the state of the track becomes as shown in FIG. 3(D).

Next, during playback, the system controller 30
A reading command is sent to the drive circuit 29 and the magnetic field application circuit 32. Then, only a constant level signal having an amplitude corresponding to the low level laser power for information reading is supplied to the semiconductor laser 11, and a magneto-optical reproduction signal a as shown in FIG. 3(E) is output from the subtraction circuit 18. Ru. The level of the magneto-optical reproduction signal a is the embossed bit that has not been erased! ! Although it is undefined in the laser power control section, the first three bytes of the reserve area are equal to the erase saturation level vE-, and the latter three bytes of the reserve area are equal to the recording saturation level vR. In addition, in the data area, the level of the magneto-optical reproduction signal a is
It changes between the erase saturation level VE and the recording saturation level VR.

At this time, as shown in FIG. 3(F), the ON command signal f is supplied to the analog switch 23 only during a period of 6 bytes in the reserve area and in each data area from the 2nd segment to the 43rd segment. For example, no abnormal charge is accumulated in the capacitor C2 due to the undefined level of the magneto-optical reproduction signal a. Also, analog switch 2
6 acts as a clamp circuit together with the capacitor C2, so if the ON command signal g is supplied to the analog switch 26 only during the second byte period of the reserve area as shown in FIG. The erase saturation level of the input signal C of the /D converter 24 is clamped to the ground level. Therefore, as shown in FIG. 3(H),
The recording saturation level of the last three bytes of the reserve area of the input signal C of the D converter 24 is +e, and the level of the input signal C of the A/D converter 24 in the data area changes between the ground level and +e. Become. Therefore, in the A/D converter 24, A/D conversion is performed regardless of whether the immediately preceding sector is unerased, erased, or recorded. The dynamic range of the D converter 24 should always be from the ground level to +e.

Furthermore, if the sampling pulse h is supplied to the sample and hold circuit 25 only during the period of the fifth byte of the reserve area as shown in FIG. The level of a is equal to the recording saturation level vR, and the input signal C of the A/D converter 24 is obtained by clamping the magneto-optical reproduction signal a using the analog switch 26 and the capacitor C2 with respect to the ground level. Since it is a signal, +e is input to the sample and hold circuit 25.Therefore, as shown in FIG. 3(J), the level of the output j of the sample and hold circuit 25 is + for one sector thereafter.
held at e.

The output j of this sample hold circuit 25 is the full scale input of the A/D converter 24, so the A/D
In the D converter 24, the magneto-optical reproduction signal a is subjected to A/D conversion with the range from the erase saturation level VE to the recording saturation level vR as the full scale. Therefore, even if the level difference between the erase saturation level Vε and the recording saturation level vR changes due to variations between disks or drives, automatic gain control is performed so that A/D conversion is always performed within the optimal dynamic range. The action will take place.

Although the formats shown in FIGS. 4 to 7 have been described above, the present invention can be applied not only to the above formats but also to other formats, and the minimum unit of recording is A similar effect can be obtained by recording at least one of the erase saturation level and the recording saturation level in an area located before the data recording area in the sector.

Furthermore, in the above embodiment, erasing and recording were performed independently of each other, but it is also possible to perform so-called override, in which erasing and recording are performed at the same time. You can write both at the same time.

Furthermore, in the above embodiment, both the erase saturation level and the recording saturation level are recorded in the reserve area, but only one of the erase saturation level and the recording saturation level may be recorded. . However, in that case, automatic gain control cannot be achieved, but clamping is possible, so the dynamic range of the A/D converter can be reduced.

Effects of the Invention As detailed above, in the magneto-optical disk according to the present invention, an area for recording at least one of the first and second saturation levels is arranged in front of each unit recording area. Therefore, by clamping the portion of the signal read from the disk corresponding to one of the above to a predetermined level, the level of the signal obtained from each unit recording area is reduced from the predetermined level to the predetermined level by the difference between the first and second saturation levels. This makes it possible to minimize the dynamic range of the circuit that reproduces recorded information. Additionally, since there is no need to perform full erasing upon shipment of the disk, the manufacturing cost of the disk can be reduced.

Furthermore, by controlling the gain of the circuit that reproduces recorded information according to the difference between the first and second saturation levels, variations in the difference between the first and second saturation levels can occur due to variations between discs, etc. However, it is also possible to always perform A/D conversion in the optimum dynamic range in the circuit that reproduces the recorded information.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing an embodiment of the present invention.
FIG. 3 is a timing chart showing the operation of each part of the device shown in FIG. 2, and FIGS. 4 to 7 show the recording format of a conventional magneto-optical disk. 8 is a diagram showing the correspondence between the recording state of the data area and the waveform of the read signal, FIG. 9 is a sectional view showing the structure of a magneto-optical disk, and FIG. 10 is a conventional disk reproducing circuit. Block diagram showing FIG. 11 and 1
FIG. 2 is a waveform diagram showing the operation of each part of the circuit of FIG. 10. Explanation of symbols of main parts 10...Pickup 15...Disk 18...Subtractor 23.26...Analog switch 25...
...Sample hold circuit 21 ...Timing signal generation circuit 30 ...System controller Applicant Pioneer Corporation

Claims (1)

[Claims] A magneto-optical disk comprising a plurality of unit recording areas having a predetermined recording capacity arranged in a circumferential direction, the first and second unit recording areas having a predetermined recording capacity.
A magneto-optical disk characterized in that an area for recording at least one of the saturation levels is arranged in front of each of the unit recording areas.