JPH06251375A - Laser driver and drive system in optical recorder - Google Patents

Abstract

PURPOSE:To make possible high speed driving of a laser source through a simple structure by selecting a plurality of multipulse serieses depending on the length of a record mark, subjecting the multipulse series thus selected to P/S conversion, and driving a laser source based on a multipulse pattern obtained by modulating the sum of the plurality of multipulse serieses. CONSTITUTION:An ON/OFF decision circuit 7 decides 1/0 of a PWM signal based on an output from a run length decision circuit 6. When the circuit 7 makes a decision of '1' for next output, pattern memories 9a, 9b load a multipluse(MP) serieses determined by an output from the circuit 6 to shift registers 10a, 10b. Gate circuits 11a, 11b are switched by means of a clock counter 8 and output MP patterns A, B. Level setting circuits 12a, 12b set predetermined recording levels of the outputs A, B and an adder 13 produces a modulated sum of MPs which is then fed to a laser drive circuit 14. Consequently, a laser light source 15 is driven based on an MP pattern.

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 phase change type optical recording apparatus which is capable of performing a phase change recording with a high recording density and a large number of rewritings. A method and its drive device.

[0002]

2. Description of the Related Art Conventionally, as an optical recording system of this kind, for example, an optically transparent 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 if necessary, An optical recording (phase change type optical recording) system and a magneto-optical recording system are known which utilize an optical recording medium provided with an inorganic dielectric layer which is laminated on both upper and lower surfaces of a lever recording layer to protect the recording layer. There is. In particular, for writing and erasing on a phase change type optical recording medium, usually, a high-power circular laser spot is made into a rectangular pulse and irradiated onto the recording layer, and the irradiated portion of this recording layer is melted at the recording material. By heating to a temperature of Tm or higher and then rapidly cooling, the irradiated portion is changed from a crystalline state (crystalline phase) to an amorphous state (amorphous phase), and at the time of erasing the written information, a light source is used. The circular laser spot of low output from is driven by a rectangular pulse wave to irradiate the recording layer, and is heated to a temperature not lower than the crystallization temperature Tx of the recording material at the irradiated portion of the recording and lower than the melting point, and then slowly. A so-called one-beam overwrite recording / erasing method is adopted in which the irradiated portion is changed from an amorphous state (amorphous phase) to a crystalline state (crystalline phase) by cooling.

As a recording material for forming a recording layer of an optical recording medium utilizing such a phase change between a crystal phase and an amorphous phase, for example, Ge-Sb-Te system, In
Thin film materials such as —Ge—Te system 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 high. It has been reported to have the advantage of being high [Electronic Society of Japan, cpm 87-88 (19).
87)].

In order to increase the recording density and further increase the capacity in such a rewritable optical recording system,
Instead of the conventional pit position recording method, a pit edge recording method is being studied. This method is a method of reproducing the recording by detecting the positions of both ends of the recording mark. Since the recording density is 1.5 to 2 times that of the conventional pit position recording which detects the center position of the recording pit,
Actively researched (optical disc technology, radio technology company). And, among the pit edge recording methods, multi-pulse recording is particularly attracting attention. This is because in conventional pit edge recording, a mark is formed by irradiating a rectangular pulse with a length corresponding to the mark length when forming a mark, whereas in multi-pulse recording, a pulse is formed in order to form one recording mark. This is a method of forming a recording mark by irradiating a plurality of pulses having a short width (Japanese Patent Laid-Open No. 63-3004).
36, Optical Memory Symposium '90 pp77-
78). In this multi-pulse recording method, the medium is not heated more than necessary at the time of mark formation, so that the thermal load can be reduced.

By the way, in the case of pit edge recording with multi-pulses, a mechanism for generating a high-speed pulse train is required. For example, Ohno, et al. [Multipulses
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 of detecting an edge of a normal mark length modulated signal sequence and outputting a recording pattern previously stored in a memory is adopted.

This recording method will be described with reference to FIGS. 7 and 8. In Fig. 7, input is EFM code or RL
The signal is PWM (mark length) modulated using a recording code such as L (2,7) or RLL (1,7). In addition,
Details of the EFM code, RLL (2,7) and (1,7) code are publicly known and will be omitted. The clock signal is PW
It has a period equal to or smaller than the minimum width of the M modulation signal. The leading edge detection circuit 1 detects the rising edge of the PWM modulation signal and sends the leading edge detection signal to the pattern generator 3. The trailing edge detection circuit 2 detects the trailing edge of the PWM modulation signal and sends the trailing edge detection signal to the pattern generator 3. The pattern memory 4 holds a multi-pulse train previously obtained by an experiment or the like as a bit train with the cycle of the clock signal as a unit. The pattern generator 3 synchronizes with the clock signal from the timing of the leading edge detection signal, and the pattern memory 4
The bit train of is read out and the output of the recording pulse train is started. Further, the pattern generator 3 stops the output of the recording pulse train at the timing of the trailing edge detection signal.

For example, FIG. 8 shows the prior art document (Ohno,
Other), the bit string of the pattern memory is read using the clock signal C of 50 ns cycle,
The multi-pulse train B is output by using the leading edge and the trailing edge of the input mark-modulated PWM modulation signal A as a trigger, and the multi-pulse that is obtained in advance by experiments or the like is used.

[0008]

By the way, when the pit edge recording method is used, it has been difficult to put it into practical use until now 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 as a result of rewriting many times. What is the movement of recording material?
This is a phenomenon in which the recording material gradually moves along the track in the disc traveling direction or in the opposite direction when recording and erasing are repeated. If the movement of the recording material is large, the recording margin and the optimum laser power will change due to the change in the film thickness due to the movement, or in the worst case, the recording material will be lost, and recording will be impossible. The media is damaged. In particular, in the pit edge recording method, a long mark is used, and therefore, when a rectangular pulse having a length corresponding to the mark length is irradiated, the heat load is large and the mass transfer thereof is remarkable. Moreover, even if the thermal load is reduced and the mass transfer is reduced by using the above-mentioned multi-pulse recording, it is still insufficient.

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

As this gradually increasing pulse, for example, the pulse shape shown in FIG. 9 is conceivable, but as shown in FIG. 9 (b) filed as Japanese Patent Application No. 3-336254 already filed by the present applicant, for example. Effective pulse shapes are effective. Note that the recording pulse shape shown in FIG. 9A is equivalently obtained by sending a pulse that is sufficiently shorter than the recording signal width T to the laser drive circuit. However, for example, the rotation speed is 3,60
When recording with an RLL (2,7) code on a 3.5-inch optical disk conforming to the ISO standard of 0 rpm, the minimum time width of the recording mark is 135 ns, and therefore it is necessary to control the pulse in units of 5 ns. Further, each waveform shown in FIG. 9B also requires control in units of 10 ns.

A pit edge recording method using this gradually increasing pulse is shown in FIG. For example, when the RLL (2,7) code is used, a recording method in which a gradual increase pulse is first radiated, and then a rectangular pulse is radiated corresponding to each 0.5T until a trailing edge is recorded (see FIG. a)) and a method in which all pulses are gradually increasing pulses (only 4T is shown in FIG.
Various recording methods such as (shown in (b)) are possible.

It should be noted that the conventional multi-pulse generation method cannot support a high-speed pulse modulation method such as the above-mentioned method using the gradually increasing pulse. This is because, in the above-described gradually increasing pulse method, it is necessary to output a bit string having a width of 5 ns or 10 ns, but it is not possible to read the bit string serially from the memory element at such a speed and perform synchronous output in a consumer product level technique. Have difficulty.
Moreover, in the above-described gradually increasing pulse system, it is possible 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 the trigger as described in FIG. 8 cannot be applied. 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 is generally obtained equivalently by sending a pulse sufficiently short to the recording signal width T to the laser drive circuit, but ideally it is a multi-valued signal. The laser source should be driven by a pulse modulated with a level. However, in the case of performing multi-pulse recording by driving a laser with a pulse modulated at a multi-valued level, it is necessary to control the recording level at a higher speed, which is more difficult with the conventional multi-pulse generation method.

Further, as a method for reducing the mass transfer of the recording material, a technique of selecting and using a pulse waveform in which the power level at the start of pulse irradiation for recording mark formation is 50% higher than the power level at the end of irradiation is selected. 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 gradually increasing pulse method. However, even if an attempt is made to change the pattern of the multi-pulse train consisting of this pulse waveform according to the recording mark length, the pulse sequence cannot be selected unless the recording mark length is determined in advance.

Further, in the pit edge recording, the jitter characteristic is deteriorated due to the change of the recording power margin and the edge position due to the material movement of the recording material. Has been proposed (Masayuki Arai et al. "1.3 Gbyte 130 mm optical modulation overwrite magneto-optical disk system", MAG-92-1).
90, p69-76). When such a bias level control 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 of each pulse is set to zero, only 4T is displayed in FIG. 11B, but the bias level only at the trailing edge of the last pulse of the multi-pulse. Shows the case where is 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 is intended to solve the above-mentioned problems. It is possible to obtain a pulse train at a high speed with a simple structure, and a multi-pulse pattern can be selected according to the recording mark length, and the pulse train can be gradually increased. An object of the present invention is to provide a laser driving method and its driving device in an optical recording device capable of driving a laser light source using a multi-pulse pattern modulated at a multi-valued level even in multi-pulse recording using a pulse or the like. .

[0017]

That is, the laser driving method in the optical recording apparatus of the present invention is such that a recording layer formed of an optical recording material is irradiated with pulsed laser light emitted from a laser light source, and the mark length is increased. When performing multi-pulse recording by modulation, the recording mark length is discriminated in advance, a plurality of multi-pulse sequences are selected and read out in parallel based on the discriminated mark length, and then the read multi-pulse sequences are read. Outputs serially in synchronization with each clock signal, sets a predetermined recording level, then generates a modulated multi-pulse pattern by adding and modulating these multiple multi-pulse series, and based on the modulated multi-pulse pattern It is characterized by driving a laser light source.

Further, the laser driving device in the optical recording device of the present invention irradiates the recording layer formed of the optical recording material with the pulsed laser light emitted from the laser light source,
A laser driving device in an optical recording device for performing multi-pulse recording by mark length modulation, comprising mark length discriminating means for discriminating a recording mark length, a plurality of pattern storing means for storing a multi-pulse series pattern, and discriminated mark lengths. A plurality of read means for selecting a multi-pulse series from each pattern storage means in parallel based on the above, and a plurality of serially outputting the plurality of multi-pulse series read by each read means in synchronization with a clock signal. The output means, a plurality of level setting circuits for setting the recording level of the multi-pulse series output from each output means, an adder for adding the multi-pulse series output from each level setting circuit, and an adder Laser for driving a laser light source based on a modulated multi-pulse pattern that is added and modulated And it is characterized in that it comprises a drive circuit.

The outline of the present invention will be described with reference to FIGS. 2, 3 and 4 by taking an example of using an RLL (2,7) code (minimum run length 2, maximum run length 7) as a PWM (mark length) modulation code. It will be described based on. As described above, it is necessary to determine the recording mark length, that is, the run length of the recording signal, in order to perform high-speed multi-pulse recording at multi-valued levels. FIG. 2 shows the coding process of the RLL (2,7) code in a tree structure. When the number in the circle in the figure is a binary input (NZ) to the RLL (2,7) modulator.
R signal), and at each of A, B, C, D, E, F, and G nodes, the RLL (2,7) sequence is determined.

In FIG. 2, when the first bit from the root indicating start is "1", the first bit is "0" and the second bit is "0" depending on whether the following second bit is "1" or "0". In case of "1", the following third bit is "1" or "0"
Depending on whether the 1st and 2nd bits are "0" and the 3rd bit is "1", the following 4th bit is "1" or "0". When all eyes are “0”, the nodes A, B, and
C, D, E, F, and G, and the correspondence of the original RLL (2,7) code corresponding to the 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 as the node shown in FIG.
The RLL (2,7) code corresponding to this sequence is 10000100000100010010000001
It will be 000. The run length (number of consecutive 0s) of this 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", the boundary (edge) of the code can be read and decoded into the binary code when decoding.

To output the run length of the recording signal,
It may be performed based on the state transition shown in FIG. That is, the run length determination is performed for the node detections A to G,
An undetermined run (the number of 0s following a bit that is 1) until the next input as a state variable (the number in the circle in FIG. 3), for example, since it is 1000 for input A, 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. When the inputs are B, D, F, and G in state 2, the number of undefined runs is 2, so the state is still 2. In state 2, the inputs are A and C. , E, the number of undetermined runs is 3, so the state transits to state 3. When the inputs are A, C, and E in state 3, the number of undetermined runs is 3, so the state is still 3. In state 3, when the inputs are B, D, F, and G, it is undetermined. 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 undefined 2 is fixed and the output is 2. In state 2, when D inputs, the code of D is (1001
00), the undecided 2 is decided and the output becomes 2, and since the 4th bit of the D code is 1, the preceding 2 by 00 is outputted. When F is input in state 3, the code for F is (00100100)
Therefore, 3 + 2 = 5 which has not been determined is output, and 2 is further output. In the above example, the RLL (2,7) code has been described, but the same configuration is possible by using other RLL (1,7) code or EFM code.

In this way, since the run length, that is, the recording mark length can be discriminated in advance, the pattern of the multi-pulse train is stored in the pattern memory correspondingly, and the multi-pulse is read out 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 gradually increasing pulses can be applied.

In particular, in the present invention, a unit pattern for modulating a pattern of a multi-pulse train corresponding to a run length (recording mark length) is divided into a plurality of unit patterns, and each unit pattern is separately stored in a plurality of pattern memories. Then, using the run-length detection signal as an address, a multi-pulse train consisting of a predetermined unit pattern is read out in parallel from each pattern memory, and the read-out multiple multi-pulse trains are level-set and then added to obtain the desired modulation. Since a multi-pulse pattern can be generated at multi-levels, it is possible to more accurately support a high-speed pulse modulation method using a gradually increasing pulse or the like.
Therefore, the laser light source can be driven based on the modulated multi-pulse pattern generated at such a high speed and multi-valued level as described above, so that the movement of the recording material can be more accurately reduced and the phase change, which is frequently rewritten, is performed. The optical recording of can be enabled.

[0026]

According to the present invention, after the recording mark length is discriminated in advance, a plurality of multi-pulse sequences corresponding to the recording mark length are selected, and the output of a shift register or the like is controlled in parallel from a memory device such as a ROM at high speed. Each is read out to the circuit, output serially based on the clock, and set to a predetermined recording level respectively, and then the laser light source is driven using a modulated multi-pulse pattern that is obtained by analog addition processing of these multiple multi-pulse series and modulation. . Therefore, it is possible to obtain a multi-pulse train (pattern) using a simple structure and at high speed according to the recording mark length, in particular, a multi-pulse train (pattern) using gradually increasing pulses, and to obtain a multi-pulse pattern modulated in this way. Based on this, laser driving becomes possible.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is used as a R modulation PWM code.
An example of using the LL (2,7) code will be described with reference to FIGS. 1 to 6. FIG. 1 is a block diagram showing an embodiment of a laser driving device according to the present invention. In this example,
It 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 shown in FIG.
Each node A to G is detected based on the encoding process of the RLL (2,7) code shown in FIG. The run-length determination circuit 6 receives the node detections A to G as an input 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 the inversion of the immediately preceding state as shown in FIG. The clock counter 8 counts the clock signal corresponding to the run length on the basis of the outputs of the run length judging circuit 6 and the ON / OFF judging circuit 7, and counts it while the PWM signal has a value of "1". Supply signals to the shift registers 10a and 10b,
The gate circuits 11a and 11b are closed while the PWM signal has a value of "0".

Here, the pattern memories 9a and 9b store in the shift registers 10a and 10b the multi-pulse series determined by the output of the run-length judging circuit 6 when the ON / OFF judging circuit 7 sets the next output to 1, respectively. Load in parallel. That is, as shown in FIG.
By the load signal C of 0a and 10b, the multi-pulse sequence E having a predetermined pattern is synchronized with the clock signal D from the clock counter 8 in correspondence with the run length B.
a and Eb are loaded respectively. FIG. 5 shows respective signal waveforms. 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 clock counter 8 and shift registers 10a and 10b.
b is a clock signal supplied to b, Ea is a pattern memory 9a
From the pattern memory 9b, and Eb is a multi-pulse series pattern 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 being opened. 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 is set by the level setting circuit. That is,
The multi-pulse series 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. 5 is
It corresponds to the multi-pulse using the 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, the overhead due to the load operation does not occur.

In this embodiment, an example of the structure of the device for driving the laser light source at the three-valued level at the time of writing is shown. However, by increasing the pattern memory, the shift register and the gate circuit, it is possible to further increase the multi-valued level. It is possible to drive the laser with modulated multi-pulses. Even in the case where the laser driving is performed by pulse modulation with such multi-valued, the time overhead does not occur in the same manner.

Further, according to this system 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 set to zero as shown in FIG. 11A, the bias level at the trailing edge of each multi-pulse sequence is canceled to zero. It is realized by adding the laser drive pulse set to the polarity level.
By simultaneously adjusting such a bias level and driving the laser light source, the movement of the recording material can be further accurately reduced.

[0034]

As described above, according to the present invention, it is possible to perform pit edge recording particularly in a rewritable optical recording system such as a phase change recording system, and it is possible to determine the recording mark length in advance and to perform high speed recording. Since it can more accurately support the pulse modulation method, especially the pulse modulation method using gradually increasing pulses, etc., the movement of the recording material can be more surely reduced, and optical recording with a large number of rewritings can be performed. It is possible to provide an optical recording system and a high-quality optical recording system.

[Brief description of 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 a relationship between input and output 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 for explaining the operation of the present invention.

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

FIG. 8 is a diagram illustrating an 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 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 drive circuit, 15 ... Laser light source.

Claims (2)

[Claims] 1. A recording layer formed of an optical recording material is irradiated with pulsed laser light emitted from a laser light source,
When performing multi-pulse recording by mark length modulation, the recorded mark length is discriminated in advance, a plurality of multi-pulse sequences are selected based on the discriminated mark length and read in parallel, and then the read multi-pulses Generates a modulated multi-pulse pattern that is generated by adding a plurality of multi-pulse series and modulating them after setting the predetermined recording level while serially outputting each series in synchronization with the clock signal. A laser drive method in an optical recording device, characterized in that a laser light source is driven based on the above. 2. A recording layer formed of an optical recording material is irradiated with pulsed laser light emitted from a laser light source,
A laser driving device in an optical recording device for performing multi-pulse recording by mark length modulation, comprising mark length discriminating means for discriminating a recording mark length, a plurality of pattern storing means for storing a multi-pulse series pattern, and discriminated mark lengths. A plurality of read means for selecting a multi-pulse series from each pattern storage means in parallel based on the above, and a plurality of serially outputting the plurality of multi-pulse series read by each read means in synchronization with a clock signal. The output means, a plurality of level setting circuits for setting the recording level of the multi-pulse series output from each output means, an adder for adding the multi-pulse series output from each level setting circuit, and an adder Laser for driving a laser light source based on a modulated multi-pulse pattern that is added and modulated A laser driving device comprising: a driving circuit.