JP2001084592A - Method and device for recording multi-valued information, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make removable the influence of an inter-code interference and to make reducible reproduction errors by determining necessary irradiating energy in specific information units according to the relation between multi- valued information in a specific information unit and pieces of multi-valued information in both information units adjacent to the information. SOLUTION: A shift register 1 receives a recording data train having four values, stores information (i) to be recorded in a register 1b, and stores pieces (j) and (k) of information to be recorded before and behind the place where the information (i) is recorded in registers 1a and 1c. A D/A converting means 2 outputs a signal Pi having recording power corresponding to the information value (i). A recording power correcting means 3 supplies, as a correction quantity dP, a quantity which is proportional to the difference between the information value (i) to be recorded and the mean value of the pieces (j) and (k) of information before and behind the information value (i) to a subtractor 4. The output Pi-dP of the substractor 4 is supplied to the laser light source 6a of an optical head 6 through a laser driver 5 and the laser light source 6a emits light with power corresponding to the output Pi-dP.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multivalued information recording method, apparatus and recording medium for recording multivalued information on an optical recording medium whose characteristics change according to irradiation energy.

[0002]

2. Description of the Related Art In recent years, the density of optical disks has been increasing. In general, binary recording is used for optical discs capable of recording and reproducing information, such as CD-Rs and DVD-RAMs, which are widely used today.

That is, a laser power corresponding to 1-bit digital information, ie, “0” and “1”, is radiated to the recording surface of an optical disk, and a recording film formed on the recording surface, for example, a so-called GeTeSb compound. The phase change film is crystallized or made amorphous, and information is recorded based on the change in reflectance.

In other words, binary, that is, 1-bit information is recorded in one information unit, that is, in a unit of division on the medium (for example, a length on the recording surface corresponding to one clock) when information is recorded. can do.

On the other hand, in recent years, a multivalued information recording method has been proposed. For example, as disclosed in JP-A-6-309720, the laser power is switched to three or more values, and a mark having a corresponding thickness is formed on a recording medium. For example, 2-bit information “0 (00)”, “1”
If marks having different thicknesses are formed using four-level laser powers corresponding to (01) "," 2 (10) ", and" 3 (11) ", double information can be recorded per information unit. You can do it.

[0006]

However, as described above, if a mark having a thickness equivalent to four values is simply recorded, a reproduction error may occur due to intersymbol interference when reproducing the mark. .

That is, when reproducing the quaternary information, for example, 2-bit information "0", "2" is obtained by the reproduction signal amplitude which changes according to the thickness of each mark.
1 ”,“ 2 ”, or“ 3 ”is determined.
When the reproduced signal amplitude fluctuates due to intersymbol interference from an adjacent information mark, for example, it may be determined that “2” should be determined and “3”.

However, intersymbol interference is not a problem unique to multi-level recording but also exists in conventional binary recording. However, in the case of binary recording, there is a margin corresponding to the amplitude difference of the reproduction signal caused by the presence or absence of the mark, but in the case of quaternary, there is only a margin obtained by dividing the amplitude difference into four equal parts. It becomes more severe.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a multilevel information recording method and the like that can eliminate the influence of intersymbol interference and reduce reproduction errors.

[0010]

According to the present invention, there is provided a multi-valued information recording method for recording multi-valued information by changing energy applied to an information unit on a recording medium. Is a multivalued information recording method for determining the irradiation energy to be applied to a predetermined information unit in accordance with the relationship between the two information units adjacent to the multivalued information.

The present invention also provides a multi-valued information recording method for changing the width of a mark to be recorded by changing the power of light applied to an information unit on a recording medium, thereby recording multi-valued information. And a multivalued information recording method for changing the irradiation time of the light in a relationship opposite to the power of the light when recording a mark in the information unit.

Further, the present invention provides a multi-level information recording apparatus for recording multi-level information by changing energy applied to an information unit on a recording medium, wherein the register stores multi-level information to be recorded, Determining means for determining the irradiation energy to be applied to the predetermined information unit according to the relationship between the multivalued information in the information unit and the multivalued information of both information units adjacent thereto, and the determined irradiation And an optical head for irradiating the recording medium with energy.

Further, the present invention provides a recording medium having an information unit in which information is recorded in a multi-valued manner by irradiation with different energy, wherein the multi-valued information in the predetermined information unit and the adjacent two-valued information are stored. Is a recording medium in which the state of a mark recorded in a predetermined information unit is adjusted according to the relationship between the information unit and the multi-valued information.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A multi-value information recording method according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an apparatus for realizing a multilevel information recording method according to an embodiment of the present invention. The method and apparatus will be described below.

In FIG. 1, a recording information sequence having four values is supplied to a shift register 1 first. Information i to be recorded is stored in the register 1b among the registers constituting the shift register 1. Registers 1a,
1c stores information j and k, which are recorded before and after the place where the information i is recorded.

Reference numeral 2 denotes DA conversion means, which is an information value i (=
0, 1, 2, 3) is output with a signal Pi having an amplitude corresponding to the recording power corresponding to the recording power. The signal Pi is supplied to the laser light source 6a of the optical head 6 via the laser driver 5, and the laser light source 6a emits light at a power corresponding to the signal Pi.

That is, when there is no correction according to the present invention, light is emitted with powers P0, P1, P2, and P3 corresponding to information values i = 0, 1, 2, and 3, as shown in FIG. The laser light emitted from the laser light source 6a is emitted from the objective lens 6b.
Thus, the light is focused on the information track 70 formed on the recording surface of the optical disk 7.

A phase change film is formed on the recording surface of the optical disk 7, and has a width (thickness) corresponding to each recording power.
Marks M0, M1, M2, M3 having the following are formed along the track 70.

When the marks thus recorded are reproduced, signals of amplitude levels L0, L1, L2 and L3 corresponding to the width of each mark are obtained as shown in FIG. If the amplitude of the reproduced signal is detected, a quaternary value, ie, 1
Two bits of information can be obtained per information unit.

However, as described in the section of the prior art, when the linear recording density (density in the track tangential direction) of one information unit is sufficiently low as shown in FIG. Can be detected independently.
However, when the marks are brought close to each other to increase the linear recording density, intersymbol interference occurs.

Whether or not intersymbol interference is a problem depends on the diameter of the focused laser beam used for recording or reproduction. 1
If the length of the information unit is approximately the same as or smaller than the diameter of the focused laser beam, it is better to consider that significant intersymbol interference occurs.

The problem of the conventional example will now be described in more detail. As an example, as shown in FIG.
Minimum power P0 between marks M41 and M42 written with
If there is a mark M11 written with
Are reproduced, the signal levels of the marks M41 and M42
As a result of being pulled by the intersymbol interference from, the level increases from the original level L0. Here, if an error in the increasing direction occurs due to the influence of noise or the like, the mark M11
May be erroneously determined as level L1.

Therefore, in the present embodiment, when an arbitrary mark is recorded, a correction according to the recording amplitude of an adjacent mark is made by using the recording power correcting means 3.

FIG. 4 shows this state. That is, when information values i = 3, 0, and 3 are sequentially recorded, when the information value i = 0 is recorded, recording is performed by the subtracter 4 at a power dP lower than the power P0.

As a result, a mark M11 'smaller than the mark M11 in FIG. 3 is recorded on the track 70.

Even if the mark 11 'is reduced or lost in this way, the reproduction level at the timing when the mark M11' is reproduced increases due to the intersymbol interference between the marks M41 and M42 and becomes the level L0. Is detected.

The specific operation of the recording power correction means 3 is, for example, information j before and after an information value i to be recorded.
And the average of k is i ′, ie,

[0029]

Assuming that i ′ = (j + k) / 2, an amount proportional to the difference between the average value and the information value i is a correction amount dP, that is,

[0030]

## EQU2 ## What is supplied to the subtractor 4 as dP = c.times. (I'-i) may be considered.

Here, c is a constant.

The recording power correcting means 3 calculates the number (1)
As a result of the operation as in (2), a larger correction amount dP is generated as the difference between the information value i to be recorded and the information values j and k of the marks adjacent thereto increases.

Of course, the larger the level difference between adjacent marks,
Since it should be subject to large code interference, the number (1),
The correction effect of (2) acts in a direction to just cancel the intersymbol interference.

The above processing will be described in more detail.
First, the multivalued information sequences i (1) to i (8) to be recorded are PA i (1) i (2) i (3) i (4) i (5) i (6) i (7) i (8) PA 0 2 3 3 0 3 2 1 0 0

Here, the first and last PAs (= 0) are so-called preambles and postambles. That is,
In order to determine the correction amount of the recording power according to the equations (1) and (2), information values before and after the information value are necessary.
Since there is no information before this, PA = 0 is added for convenience. The same is true for the tail. Note that these additions are ignored during reproduction.

In the case where this is to be recorded by the conventional method, it is only necessary to irradiate the optical disk with power corresponding to each information value, for example, P0 = 4 mW P1 = 5 mW P2 = 6 mW P3 = 7 mW. As a result, a mark having a width corresponding to the input power is formed on the optical disk.

Next, a specific procedure of the correction according to the present invention will be described. First, the average values i (1) ′ to i (8) ′ of the preceding and succeeding information obtained by Expression (1) are i (1) ′ i (2) ′ i (3) ′ i (4) ′ i (5) 'i (6)' i (7) 'i (8)' 1.0 2.5 1.0 3.0 1.0 2.0 1.0 0.5 Further, the correction amounts dP1 to dP8 [mW]
Is c = 0. Assuming that 2 [mW], dP (1) dP (2) dP (3) dP (4) dP (5) dP (6) dP (7) dP (8) -0.2 0.1 -0.4 0.6 -0.4 0.0 0.0 0.1 is obtained. The value of c varies depending on the material of the recording film and the recording density. Therefore, for the powers P (1) to PP (8) [mW] to be irradiated when each information is recorded, the correction amount is subtracted from the predetermined power, and P (1) P (2) P (3) P (4) P (5) P (6) P (7) P (8) 6.2 5.9 7.4 3.4 7.4 6.0 5.0 3.9

In the above results, i (4) and i (8) are both "0", but the recording power is 3.4 m each.
W and 3.9 mW. These results are naturally derived from the size of the marks adjacent to each other.

As described above, according to the present embodiment, when an arbitrary mark is recorded, correction according to the recording amplitude of an adjacent mark is performed so that an error due to intersymbol interference does not occur during signal reproduction. Alternatively, it is possible to realize a multivalued information recording method capable of greatly reducing errors.

Incidentally, the recording power correcting means 3, the D / A converting means 2, and the subtractor 4 are examples of the determining means of the present invention.

In the present embodiment, the power according to the multi-valued information to be recorded is generated by using the DA converter 2, but the characteristic of the DA converter 2 is linear with respect to the input information. Need not be. That is, the characteristics of the recording film formed on the optical disk 7 often have nonlinear characteristics with respect to the laser power to be irradiated.
Rather, it may be better to have a characteristic that cancels out the nonlinearity.

In the first embodiment, it is assumed that the size of the recording mark changes almost linearly with respect to the recording power, and as a result, it is sufficient to correct by the equation (2). Hate. Actually, there is a case where a higher power than the proportional relationship is required due to the influence of thermal diffusion on the optical disk or the like. For example, if the recording mark width (the information value to be recorded) and the power required to form it have a squared relationship, instead of equation (2),

[0043]

## EQU3 ## The recording power correction amount must be determined based on the relationship dP = c × (i ′ ² −i ² ).

Needless to say, the output of the DA conversion means 2 is 0 when a mark having an information value i = 0 is recorded.
(That is, no laser emission). Rather,
Conversely, at the lowest level information value i = 0,
Rather than forming no mark at all, the mark must have a certain width as shown in FIG. This is because, as described above, in order to remove intersymbol interference from adjacent tracks, the lowest level information value i = 0.
However, the recording power must be further reduced, and if recording is performed at a power of 0 (or a power that does not form a mark) from the beginning (no mark is formed), the power is further reduced and the code This is because interference cannot be removed.

In the present embodiment, the laser irradiation power (P0 to P3) is changed when forming a mark corresponding to multi-valued information, or the power (dP) is changed when correcting intersymbol interference. However, since the energy that actually contributes to the formation of a mark on the recording film is energy determined by power × time, the irradiation time may be changed instead of the irradiation power, for example.

Further, as described above, in this embodiment, as shown in FIGS. 2 to 4, when recording one information unit, the recording time is kept constant and the power of the laser light is changed. However, even when only the power is changed and the irradiation time is kept constant, the recording length changes. Because, in fact, the power distribution of the laser beam on the recording film is almost circular and the Gaussian shape is the strongest at the center. Conversely, when the laser power is increased to increase the mark width, the mark length tends to increase at the same time. Then, the energy of the regenerated light will not meet the target.

Therefore, as shown in FIG. 5, it is better to change the irradiation time at the same time as changing the power according to each multi-value information.

That is, if the laser irradiation time is long when a thin mark is recorded, and the irradiation time is short if a thick mark is recorded, marks of an equal length can be formed in each information unit. .

This is related to the above-mentioned non-linearity of the recording film and the necessity of the correction. In other words, if the irradiation time for recording a thick mark is simply shortened to make the lengths uniform, the energy (power × time) applied to the recording film naturally decreases. If the irradiation energy is reduced, a mark narrower than the width that should be formed is formed. Therefore, in the above case, in order to keep the irradiation energy constant, if the irradiation power is irradiated with a power higher than the proportional relationship, for example, as expressed by Expression (3), the width corresponding to each information value is increased. The mark can be formed correctly.

FIG. 6 is a circuit diagram for realizing the embodiment of FIG. Here, reference numeral 8 denotes a control means for changing the irradiation time of the light in a relation opposite to the power of the light when a mark is recorded in an information unit.

In the above embodiment, the relationship between the multi-valued information in a predetermined information unit and the multi-valued information values in both information units adjacent thereto is focused on the numerical value of the multi-valued information itself. The difference from the average was taken, but the present invention is not limited to this, and depends on the relationship between the energy to be irradiated in the information unit to be recorded and the energy to be irradiated in both adjacent information units. Even so,
The present invention includes. For example, in the above example, the information unit i
Regarding (3), the energy to be irradiated there is 7 mW
Since the energies of both the adjacent powers are 6 mW and 4 mW, the average is 5 mW, and the correction amount corresponding to (7-5) mW is subtracted from 7 mW.

The embodiment focusing on the irradiation energy as described above also includes the present invention of claim 1.

Further, the recording medium of the present invention is a recording medium having an information unit in which information is recorded in a multi-valued manner by being irradiated with different energy. Is a recording recording medium in which the state of a mark recorded in a predetermined information unit is adjusted in accordance with the relationship between the two information units adjacent to the multi-value information.

[0054]

As described above, according to the present invention, it is possible to realize a multi-valued information recording method with less intersymbol interference and less reproduction errors even when the density is increased.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus for realizing a multilevel information recording method according to an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram in the embodiment.

FIG. 3 is an operation explanatory diagram in the embodiment.

FIG. 4 is an operation explanatory diagram in the embodiment.

FIG. 5 is an operation explanatory diagram in the embodiment.

FIG. 6 is a diagram showing a multi-value information recording device according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shift register 2 DA conversion means 3 Recording power correction means 5 Laser driver 6 Optical head 6a Laser light source 7 Optical disk 70 Track 8 Control means

Claims (7)

[Claims] 1. A multi-valued information recording method for recording multi-valued information by changing the energy applied to an information unit on a recording medium, wherein the multi-valued information in the predetermined information unit and both information units adjacent to the predetermined information unit are recorded. A multi-valued information recording method for determining the irradiation energy to be applied to a predetermined information unit according to a relationship with multi-valued information. 2. The multi-valued information recording method according to claim 1, wherein the irradiation energy is light, and changing the irradiation energy changes power and / or irradiation time of the light. 3. Assuming that the reference information value recorded in the information unit is i and the average of the information values recorded in both adjacent information units is i ′, the irradiation energy is:
2. The multi-value information recording method according to claim 1, wherein the method is determined corresponding to (i'-i). 4. A multi-valued information recording method for changing the width of a mark to be recorded by changing the power of light applied to an information unit on a recording medium, thereby recording multi-valued information, A multi-valued information recording method for changing the irradiation time of the light in a relationship opposite to the power of the light when recording a mark on the mark. 5. A multi-level information recording apparatus for recording multi-level information by changing energy applied to an information unit on a recording medium, comprising: a register for storing multi-level information to be recorded; Determining means for determining the irradiation energy to be applied to the predetermined information unit in accordance with the relationship between the value information and the multi-value information of both adjacent information units; and a storage medium for determining the determined irradiation energy. Multi-valued information recording device comprising: an optical head for irradiating light. 6. A multi-valued information recording apparatus for changing the width of a mark to be recorded by changing the power of light applied to an information unit on a recording medium and thereby recording multi-valued information, A control unit for changing the irradiation time of the light in a relation opposite to the power of the light when recording a mark on the mark; and an optical head for irradiating the recording medium with light based on a signal determined by the control unit. Multi-value information recording device provided with. 7. A recording medium having an information unit in which information is recorded in a multi-valued manner by irradiating different energy, wherein the multi-valued information in the predetermined information unit and both information units adjacent thereto are A recording medium in which a state of a mark recorded in a predetermined information unit is adjusted according to a relationship with multi-value information.