JP3225669B2 - Laser driving method in optical recording apparatus and its driving apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical recording apparatus, and more particularly to a laser drive capable of performing phase change recording with a high recording density and a large number of rewrites, particularly in a phase change type optical recording apparatus. The method and its driving device.

[0002]

2. Description of the Related Art Conventionally, as this type of optical recording system, for example, a light transmitting substrate having a pre-groove for tracking servo, a recording layer made of an optical recording material laminated on the upper surface of the substrate, and An optical recording (phase change optical recording) system and a magneto-optical recording system using an optical recording medium having an inorganic dielectric layer laminated on the upper and lower surfaces of the leverage recording layer to protect the recording layer are known. I have. In particular, for writing and erasing on a phase change type optical recording medium, usually, a high-power circular laser spot is formed into a rectangular pulse, and the recording layer is irradiated, and the irradiated portion of the recording layer is melted by the recording material. The irradiation site is changed from a crystalline state (crystal phase) to an amorphous state (amorphous phase) by heating to a temperature equal to or higher than the temperature Tm and then quenching, and when erasing the written information, a light source is used. Irradiating the recording layer with a low-power circular laser spot from the recording medium by driving the recording layer with a rectangular pulse wave, heating the recording material to a temperature higher than the crystallization temperature Tx and lower than the melting point, and then slowly By cooling, a so-called one-beam overwrite recording / erasing method of changing an irradiated portion from an amorphous state (amorphous phase) to a crystalline state (crystalline phase) is employed.

As a recording material for forming a recording layer of an optical recording medium utilizing such a phase change between a crystalline phase and an amorphous phase, for example, a Ge—Sb—Te system, In
-Ge-Te based thin film materials are known. For example,
Ge-Sb-Te-based materials can be erased at high speed even if the time required for erasing is 100 ns or less, and the crystallization temperature is 150 ° C. or more, and the stability of the amorphous phase is low. It has been reported to have the advantage of being high [IEICE, cpm 87-88 (19
87)].

[0004] In order to increase the recording density in such a rewritable optical recording system and realize a further increase in capacity,
A pit edge recording method has been studied instead of the conventional pit position recording method. In this method, the recording is reproduced by detecting the positions of both ends of the recording mark. Since the recording density is 1.5 to 2 times as compared with the conventional pit position recording in which the center position of the recording pit is detected,
Actively studied (optical disc technology, radio technology company). Among the pit edge recording methods, multi-pulse recording has attracted particular attention. This is because in conventional pit edge recording, a mark is formed by irradiating a rectangular pulse having a length corresponding to the mark length at the time of mark formation, whereas in multi-pulse recording, a single recording mark is formed. This is a method of irradiating a plurality of pulses having a short width to form a recording mark thereof (JP-A-63-3004)
No. 36, Optical Memory Symposium '90 pp77-
78). This multi-pulse recording method can reduce the thermal load because the medium is not heated more than necessary at the time of mark formation.

When pit edge recording is performed using multi-pulses, a mechanism for generating a high-speed pulse train is required. For example, Ohno, et al. [Multipulss
eRecording Method for PWM
Recording on an Erasable
Phase Change Optical Dis
k (Jpn. J. Appl. Phys., v
ol. 30, no. 4, 77, 1991)], a method is employed in which the edge of a normal mark length-modulated signal sequence is detected and a recording pattern previously stored on a memory is output.

This recording method will be described with reference to FIGS. In FIG. 7, the input is EFM code or RL
This signal is PWM (mark length) modulated using a recording code such as L (2, 7) or RLL (1, 7). In addition,
The details of the EFM code, the RLL (2, 7) and (1, 7) codes are publicly known and will be omitted. The clock signal is PW
It has a period smaller than the minimum width of the M-modulated signal. The leading edge detection circuit 1 detects the leading edge of the PWM modulation signal and sends a leading edge detection signal to the pattern generator 3. The trailing edge detection circuit 2 detects the falling edge of the PWM modulation signal and sends a trailing edge detection signal to the pattern generator 3. The pattern memory 4 holds a multi-pulse train obtained in advance by an experiment or the like as a bit train in units of the clock signal period. The pattern generator 3 synchronizes the pattern memory 4 with the clock signal from the timing of the leading edge detection signal.
And starts outputting the recording pulse train. The pattern generator 3 stops outputting the recording pulse train at the timing of the trailing edge detection signal.

For example, FIG. 8 shows the above-mentioned prior art document (Ono,
The bit string of the pattern memory is read using the clock signal C having a period of 50 ns,
The multi-pulse train B is output using the leading edge and the trailing edge of the input mark-modulated PWM modulated signal A as a trigger, and the multi-pulse is obtained in advance by an experiment or the like.

[0008]

When the pit edge recording method is used, it has been difficult to put it to practical use because of the following problems. That is, there is a problem that the number of times of rewriting is limited because the recording material moves with rewriting many times. What is the transfer of recording material?
When recording and erasing are repeated, this is a phenomenon in which the recording material gradually moves along the track in the disk traveling direction or in the opposite direction. If the movement of the recording material is large, the recording margin and the optimal laser power will change due to the change in the film thickness accompanying the movement, or in the worst case, the recording material will run out, making recording impossible, The media will be damaged. In particular, since a long mark is used in the pit edge recording method, when a rectangular pulse having a length corresponding to the mark length is irradiated, the heat load is large, and the mass transfer appears remarkably. Further, even if the thermal load is reduced by using the above-described multi-pulse recording to reduce the mass transfer, it is still not enough.

Therefore, when forming a recording mark, the shape of the first recording pulse is a pulse shape in which the energy amount in the second half is larger than the energy amount in the first half with respect to the middle point of the irradiation pulse, or Further, by using a pulse in which the shape of the first and subsequent subsequent pulses is such that the energy amount in the second half is larger than the energy amount in the first half with respect to the middle point of the irradiation pulse, the mass transfer of the recording material can be reduced. It becomes possible. Hereinafter, a pulse shape in which the energy amount in the second half is larger than the energy amount in the first half with respect to the middle point of the irradiation pulse is abbreviated as “gradual increase pulse”.

As the gradually increasing pulse, for example, the pulse shape shown in FIG. 9 can be considered.
FIG. 9 already filed as Japanese Patent Application No. 3-336254.
The pulse shape as shown in (b) is effective. Note that the recording pulse shape shown in FIG. 9A can be equivalently obtained by sending a pulse that is sufficiently shorter than the recording signal width T to the laser drive circuit. However, for example, 3,600 rpm
RLL on 3.5 inch optical disc conforming to ISO standard
When recording with the (2,7) code, since the minimum time width of the recording mark is 135 ns, it is necessary to control the pulse in units of 5 ns. Also, control is required in units of 10 ns for each waveform shown in FIG.

FIG. 10 shows a pit edge recording method using this gradually increasing pulse. For example, when the RLL (2, 7) code is used, a recording method of irradiating a gradually increasing pulse first, and then irradiating each rectangular pulse one by one every 0.5T until a falling edge is recorded (FIG. 10 ( a)) or a method in which all the pulses are gradually increasing pulses (only 4T is shown in FIG. 10).
(Shown in (b)).

In the conventional multi-pulse generation method, a high-speed pulse modulation method such as the method using the above-described gradually increasing pulse cannot be used. This is because, in the above-described incremental pulse method, it is necessary to output a bit string having a width of 5 ns or 10 ns. However, reading a bit string serially from a memory element at such a speed and performing synchronous output is a technology of a consumer product level. Have difficulty.
In addition, in the above-described incremental pulse method, it is conceivable to change the pattern of the multi-pulse train according to the recording mark length.
The method using the leading edge and the trailing edge of the PWM modulation signal as a trigger as described with reference to FIG. 8 cannot be used. That is, the pulse sequence cannot be selected unless the recording mark length is determined in advance.

The recording pulse shape using this gradually increasing pulse can be generally obtained equivalently by sending a pulse sufficiently short with respect to the recording signal width T to the laser driving circuit. The laser light source should be driven by a pulse whose level has been modulated. However, when multi-pulse recording is performed by driving a laser with a pulse modulated at a multi-level level, it is necessary to control the recording level at a higher speed, but this becomes more difficult with the conventional multi-pulse generation method.

As a technique for reducing mass transfer of a recording material, a technique is used in which a pulse waveform in which the power level at the start of pulse irradiation for forming a recording mark is 50% higher than the power level at the end of irradiation is selected and used. However, even if an attempt is made to select a multi-pulse train having such a pulse waveform, a conventional multi-pulse generation method is used, as in the case of the above-described incremental pulse method. However, even if an attempt is made to change the pattern of a multi-pulse train composed of this pulse waveform in accordance with the recording mark length, a pulse sequence cannot be selected unless the recording mark length is determined in advance.

Furthermore, jitter characteristics are degraded due to a change in recording power margin or edge position due to mass transfer of a recording material in pit edge recording. (A "1.3 Gbyte 130 mm light modulation overwrite magneto-optical disk system" by Masayuki Arai et al., MAG-92-1)
90, p69-76). When such control of the bias level is applied to the pit edge recording method using the above-mentioned gradually increasing pulse, the recording waveform is as shown in FIG. 11, for example. That is, in FIG. 11A, when the bias level at the trailing edge is set to zero for each pulse, while FIG. 11B shows only 4T, the bias level is shown only at the trailing edge of the last pulse of the multi-pulse. Is set to zero. However, in order to simultaneously control the bias level in addition to the above-described gradually increasing pulse and the like, high-speed control is required as in the case of the recording pulse.

The present invention has been made to solve the above-mentioned problems, and a pulse train can be obtained at a high speed with a simple structure, and a multi-pulse pattern can be selected according to a recording mark length. It is an object of the present invention to provide a laser driving method in an optical recording apparatus capable of driving a laser light source using a multi-pulse pattern modulated at a multi-level level even in multi-pulse recording using pulses and the like, and an object thereof. .

[0017]

That is, the laser driving method in the optical recording apparatus of the present invention irradiates a recording layer formed of an optical recording material with a pulse-like laser beam emitted from a laser light source to form a recording mark. Length is determined in advance, and a multi-pulse using a gradual increase pulse is performed based on the determined mark length.
A plurality of multi-pulse sequences including a pulse are selected and read out in parallel, and then the read out multi-pulse sequences are serially output in synchronization with a clock signal, respectively. A modulated multi-pulse pattern is generated by adding a plurality of multi-pulse sequences and modulating the multi-level at a multi-level.
The laser light source is driven based on a modulated multi-pulse pattern comprising

Further, the laser driving device in the optical recording apparatus of the present invention irradiates a recording layer formed of an optical recording material with pulsed laser light emitted from a laser light source,
A laser driving apparatus in an optical recording apparatus for performing multi-pulse recording according to the mark length modulation, the mark length discrimination means for discriminating a recording mark length, multi with increasing pulse
A plurality of pattern storage means for storing a multi-pulse sequence pattern including a pulse; a plurality of read means for selecting a multi-pulse sequence from each pattern storage means based on the determined mark length and reading out in parallel; A plurality of output means for serially outputting a plurality of multi-pulse sequences including a multi-pulse using a gradually increasing pulse in synchronization with a clock signal, and a multi-pulse sequence output from each output means. A plurality of level setting circuits for setting a recording level, an adder for adding a multi-pulse sequence output from each level setting circuit , and a modulation multi-pulse pattern added by the adder and modulated at a multi-level level A laser driving circuit for driving the laser light source.

[0019]

The outline of the present invention will be described by taking an example in which an RLL (2, 7) code (minimum run length 2, maximum run length 7) is used as a PWM (mark length) modulation code.
A description will be given based on FIGS. 2, 3 and 4. As described above, in order to perform multi-pulse recording at a high-speed multi-value level, it is necessary to determine the recording mark length, that is, the run length of the recording signal. Figure 2 is a representation of a RLL (2, 7) code encoding process in the tree structure, digits <br/> within a circle of FIG binarization input to RLL (2, 7) modulator ( NZR signal), and the RLL (2, 7) sequence is determined at each node of A, B, C, D, E, F, and G.

In FIG. 2, when the first bit is "1" from the root indicating the start, the first bit is "0" and the second bit is "1" depending on whether the subsequent second bit is "1" or "0". In the case of "1", the following third bit is "1" or "0"
If the first and second bits are “0”, the third bit is “1”, the first, second, and third bits depend on whether the subsequent fourth bit is “1” or “0”. When the eyes are all “0”, the nodes A, B,
C, D, E, F, and G, and the correspondence of the RLL (2, 7) code corresponding to the original binary code is as follows: Binary code: RLL (2, 7) ) Code (11) (1000) (Node A) (10) (0100) (Node B) (011) (001000) (Node C) (010) (100100) (Node D) (0011) (00001000) (Node E) (0010) (00100100) (Node F) (000) (000100) (Node G)

For example, as shown in FIG. 6, when the binarized input (NRZ signal) is 111001101000011, ABCDEFG is used as a node shown in FIG.
And the corresponding RLL (2,7) code is 100001000000100010010000001
000. The run length (the number of consecutive 0s) of the RLL (2, 7) code corresponds to the mark length of the recording signal,
Since the boundary of the RLL (2, 7) code can be recognized from "1", when decoding, the code boundary (edge) can be read and decoded into a binary code.

To output the run length of the recording signal,
What is necessary is just to perform based on the state transition shown in FIG. That is, the determination of the run length is based on the detection of the nodes A to G,
State variable (the number of zeros following the bit is a 1) undetermined run as (numbers in circles in FIG. 3) to the next input, for example, for an input A, because it is 1 000 3, input B It carried out in the system to take a value of 2 because it is 01 00 against. In addition,
The state transition of FIG. 3 will be described. In the case of state 2, when inputs are B, D, F, and G, the number of undetermined runs is 2, so that the state is still 2, and in state 2, the inputs are A and C. , E, the number of undetermined runs is 3, so that the state transits to state 3. In the state 3, when the input is A, C, and E, the undetermined runs are 3, respectively, so that the state is still 3. When the input is B, D, F, and G in the state 3, the undetermined run is not determined. Since each run is 2, the state transits to state 2.

The output is the run length determined by the input, as shown in FIG. For example, in state 2, when the input is A, the first bit of the code of A is 1, so the undetermined 2 is determined, and the output is 2. In state 2, when D is input, the code of D is (1001)
00), the undetermined 2 is determined and the output becomes 2, and since the fourth bit of the D code is 1, the previous 2 of 00 is output. When F is input in state 3, the code of F is (00100100)
Therefore, 3 + 2 = 5 which has not been determined is output, and 2 is output. Note that, in the above example, the RLL (2, 7) code has been described, but a similar configuration is possible using other RLL (1, 7) codes or EFM codes.

Since the run length, that is, the recording mark length can be determined in advance, the pattern of the multi-pulse train is stored in the pattern memory corresponding to this, and the multi-pulse is read from the pattern memory using the run-length detection signal as an address. By doing so, a high-speed multi-pulse train can be generated, and a high-speed pulse modulation method using a gradually increasing pulse can be supported.

In particular, in the present invention, the pattern of the multi-pulse train is divided into a plurality of unit patterns for modulating the pattern according to the run length (recording mark length), and each unit pattern is separately stored in a plurality of pattern memories. In advance, multi-pulse trains each consisting of a predetermined unit pattern are read out in parallel from each pattern memory using the run-length detection signal as an address, and the read-out multi-pulse trains are set to levels and then added to achieve desired modulation. Since a multi-pulse pattern can be generated at a multi-value level, it is possible to more accurately cope with a high-speed pulse modulation method using a gradually increasing pulse or the like.
Therefore, since the laser light source can be driven based on the modulated multi-pulse pattern generated at such a high speed and at a multi-level level, the movement of the recording material can be reduced more accurately, and a phase change such as a large number of rewrites can be performed. Can be optically recorded.

[0026]

According to the present invention, after a recording mark length is determined in advance, a plurality of multipulse sequences corresponding to the recording mark length are selected, and output control of a shift register or the like is performed in parallel from a memory element such as a ROM at high speed. After reading out to each circuit, outputting in series based on a clock and setting each at a predetermined recording level, the laser light source is driven by using a modulated multi-pulse pattern obtained by performing analog addition processing of the plurality of multi-pulse sequences and modulating the same. . Therefore, it is possible to more accurately obtain a multi-pulse train (pattern) using a simple configuration and at a high speed in accordance with the recording mark length, particularly a multi-pulse train (pattern) using a gradually increasing pulse or the like. Based laser drive becomes possible.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described by using R as a PWM modulation code.
An example in which the LL (2, 7) code is used will be described with reference to FIGS. FIG. 1 is a configuration diagram showing one embodiment of a laser driving device according to the present invention. In this embodiment,
This shows an example in which a laser light source is driven at a ternary level during writing.

First, the RLL (2, 7) modulator 5 is configured as shown in FIG.
The detection of each node of A to G is performed based on the encoding process of the RLL (2, 7) code shown in FIG. The run length determination circuit 6 receives the detection of the nodes A to G and outputs the run length shown in FIG. 4 according to the principle described above. ON / OF
The F determination circuit 7 determines 1/0 of the PWM signal based on the output of the run length determination circuit 6. This is because 1/0 of the PWM signal is determined as an inversion of the immediately preceding state as shown in FIG. The clock counter 8 counts a clock signal corresponding to the run length based on the outputs of the run length determination circuit 6 and the ON / OFF determination circuit 7, and keeps counting the clock signal while the PWM signal takes a value of “1”. Supplying the signals to the shift registers 10a and 10b,
The gate circuits 11a and 11b are closed while the PWM signal takes a value of "0".

Here, the pattern memories 9a and 9b store the multi-pulse sequence determined by the output of the run length determination circuit 6 in the shift registers 10a and 10b when the ON / OFF determination circuit 7 sets the next output to 1. Load in parallel. That is, as shown in FIG.
The multi-pulse sequence E having a predetermined pattern in synchronization with the clock signal D from the clock counter 8 corresponding to the run length B by the load signals C of 0a and 10b.
a and Eb are respectively loaded. 5 shows signal waveforms, where A is a clock signal, B is a PWM signal, C is a load signal of the shift registers 10a and 10b, and D is a shift register 10a and 10
b, a clock signal to be supplied to the pattern memory 9a
And Eb is a pattern of a multi-pulse sequence output from the pattern memory 9b.

The gate circuits 11a and 11b output zero signals as outputs A and B while the gate is closed by the clock counter 8, and are selected by the pattern memories 9a and 9b while the gates are open. The multi-pulse patterns read out to the shift registers 10a and 10b are output as outputs A and B. The level setting circuits 12a and 12b adjust and set the recording level of each multi-pulse pattern output from each gate circuit to a predetermined value. The adder 13 adds and modulates each multi-pulse pattern whose level has been set by the level setting circuit. That is,
The multi-pulse sequences Ea and Eb after the level setting are added and modulated into a multi-pulse pattern F as shown in FIG. The modulated multi-pulse pattern F shown in FIG.
This corresponds to a multi-pulse using a gradually increasing pulse.

Then, the modulated multi-pulse pattern is input to the laser drive circuit 14, and the laser light source 15 is driven based on the multi-pulse pattern. Since the above operation is performed while the gate circuit 11 is outputting the PWM signal 0, no overhead is caused by the load operation.

Although the present embodiment shows an example of the configuration of an apparatus for driving a laser light source at a ternary level at the time of writing, the number of pattern memories, shift registers, and gate circuits is increased to increase the level at a higher multilevel level. It is possible to perform laser driving with modulated multi-pulses. Even in the case where laser driving is performed by pulse modulation in such a multi-valued manner, no time overhead is similarly generated.

Further, according to this method and apparatus, it is possible to simultaneously adjust the bias level of the laser light source. Specifically, for example, when the bias level at the trailing edge of each pulse is made zero as shown in FIG. 11A, the bias level at the trailing edge of each multipulse sequence is canceled to zero. This is realized by adding a laser drive pulse set to a desired polarity level.
By driving the laser light source while simultaneously adjusting the bias level, the movement of the recording material can be reduced more accurately.

[0034]

As described above, according to the present invention, pit edge recording can be performed particularly in a rewritable optical recording system such as a phase change recording system, and the length of a recording mark can be determined in advance. It can respond more accurately to pulse modulation methods, especially pulse modulation methods using gradually increasing pulses, so that the movement of recording material can be reduced more reliably, enabling optical recording with a large number of rewrites, and reliability. It is possible to provide an optical recording method and an optical recording apparatus having a high optical recording method.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a laser driving device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating encoding of an RLL (2, 7) code.

FIG. 3 is a state transition diagram of a run length determination circuit.

FIG. 4 is a diagram illustrating the input / output relationship of a run-length determination circuit.

FIG. 5 is a signal waveform diagram for explaining the operation of the present invention.

FIG. 6 is a diagram illustrating the operation of the present invention.

FIG. 7 is a diagram illustrating an example of a conventional modulation circuit.

FIG. 8 is a diagram illustrating the operation of a conventional modulation circuit.

FIG. 9 is a diagram showing a configuration example of a gradually increasing pulse.

FIG. 10 is a diagram showing an example of a recording waveform using a gradually increasing pulse.

FIG. 11 is a diagram showing an example of a recording waveform using a gradually increasing pulse and a zero-bias.

[Explanation of symbols]

5 RLL (2, 7) modulator, 6 run length determination circuit, 7 ON / OFF determination circuit, 8 clock counter, 9a, 9b pattern memory, 10a, 10b shift register, 11a, 11b Gate circuit, 12a,
12b: level setting circuit, 13: adder, 14: laser driving circuit, 15: laser light source.

Continuation of the front page (56) References JP-A-3-22223 (JP, A) JP-A-3-35424 (JP, A) JP-A-2-195538 (JP, A) JP-A-4-255913 (JP) , A) Patent 3161485 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B ^7/ 00-7/013 G11B 7/125

Claims (2)

(57) [Claims] A recording layer formed of an optical recording material is irradiated with a pulsed laser beam emitted from a laser light source.
When performing multi-pulse recording by mark length modulation, a recording mark length is determined in advance, and a plurality of multi-pulse sequences including a multi-pulse using a gradually increasing pulse are selected based on the determined mark length and read in parallel. Then
The read multi-pulse sequence is serially output in synchronization with the clock signal, and after setting to a predetermined recording level, the multi-pulse sequence is added and modulated at a multi-level level. A laser driving method in an optical recording apparatus, wherein a pulse pattern is generated, and a laser light source is driven based on a modulated multi-pulse pattern including multi-levels . 2. A recording layer formed of an optical recording material is irradiated with a pulsed laser beam emitted from a laser light source,
A laser driving apparatus in an optical recording apparatus for performing multi-pulse recording according to the mark length modulation, the mark length discrimination means for discriminating a recording mark length, increasing Pal
A plurality of pattern storage means for storing a multi-pulse sequence pattern including a multi-pulse using a pulse, and a plurality of read means for selecting a multi-pulse sequence from each pattern storage means based on the determined mark length and reading out in parallel. ,
Read in each read means, Ma with increasing pulse
A plurality of output means for serially outputting a plurality of multi-pulse sequences including multi-pulses in synchronization with a clock signal, a plurality of level setting circuits for setting a recording level of the multi-pulse sequence output from each output means, and each level An adder that adds the multi-pulse sequences output from the setting circuit, and a laser drive circuit that drives the laser light source based on a modulated multi-pulse pattern that has been added and modulated at a multi-level level by the adder. A laser drive device.