JP2005056476A - Optical disk drive and laser power control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform recording without deteriorating recording quality by eliminating a setting error when power varies in recording as in the case of daringly performing low-speed recording in order to prevent recording quality deterioration, for example, under conditions where originally high-speed recording is possible. <P>SOLUTION: The maximum voltage set value of a D/A converter is changed and set by using differential efficiency (S5, S7), and the maximum voltage set value of the D/A converter is changed and set according to the detected temperature of a semiconductor laser so as to put a limit thereon (S12, S14). Thus, for example, as in the case of intentionally performing low-speed recording to prevent the deterioration of recording quality under conditions where originally high-speed recording is possible, when power varies in recording, a set error is eliminated and more proper power is set. Further, there is no possibility that light with desired emission power is not emitted because the maximum voltage set value changed by using differential efficiency changes because of the change of differential efficiency due to temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical disc apparatus and a laser power control method.

  In a recordable optical disc such as CD-R (Compact Disc Recordable) and DVD (Digital Versatile Disc) -R or a rewritable optical disc such as CD-RW (Rewritable) and DVD-RW, for example, an organic dye-based recording material is formed by coating. Information is recorded by irradiating the disc with laser light to form recording pits.

  In order to stably form recording pits on an optical disk under constant conditions, a drive current of a semiconductor laser (hereinafter abbreviated as LD (Laser Diode) as appropriate) as a writing light source is used so that constant laser power is always obtained. Need to control.

  That is, in the recording of data in the optical disk apparatus, for example, in a CD-R, a recording film on the CD-R is irradiated with a laser beam having a strong light amount emitted from the LD as a light beam, and the thermal reaction causes a hole ( This is done by opening a pit. In CD-RW, it is performed by changing the crystal state of the recording film. On the other hand, the data written on the optical disk can be read from the amount of reflected light obtained when the recording film is irradiated with a weak amount of laser light emitted from the LD as a light beam.

  By the way, as described above, recording on the optical disk is performed by opening a pit on the optical disk with the light beam emitted from the LD, and the emission waveform of the laser light at this time is as shown in FIG.

  In FIG. 4, a first light emission power (light quantity level) P1 and a second light emission power (light quantity level) P2 higher than the first light quantity power are repeatedly emitted from the LD by digital modulation. When the second light emission power P2 is the recording power and is at the P2 level, a pit is formed. Further, the first light emission power P1 is a reproduction power, and the place at the P1 level becomes a space as it is. Further, in the CD-R, a third light emission power (light quantity level) P3 satisfying P3> P2 is provided as an extra power at the head portion of P2, and a recording power light emission waveform is generated with three values of P1, P2, and P3. Sometimes. That is, the pit edge is sharpened so that the third light emission power P3 is positioned at the top of the pit.

  Further, in a phase change type rewritable medium such as CD-RW, three values are also provided. However, by repeating the light emission power P3 and the light emission power P1 at high speed, the amorphous (non-crystallized) state and the light emission power P2 are set. Crystallize by sustaining. This is made to correspond to information data.

  In FIG. 4, the light emission waveform when data is reproduced from the optical disc before time t (light start) (left side) and the light emission waveform when data is recorded on the optical disc after time t (light start) (right side) are shown. Show. As described above, the power emitted from the LD when reproducing data on the optical disk is low, and the light emission is DC light emission. In general, P1 is about 1 mW. On the other hand, the power of the laser beam emitted from the LD during recording is high, and the level P2 is generally several mW to several tens mW. At the time of recording, pits are formed on the optical disk by repeating the light emission of these two light emission levels P1 and P2. For example, when recording is performed at 12 times the speed (12x) of CD-R, the recording power may be about 30 times the reproduction power (for example, the recording power is 30 mW when the reproduction power is 1 mW). .

  However, in recent years, both the reproduction speed and the recording speed have been further increased, and the recording speed may be 32x or 40x, which is faster than 12x described above. Therefore, when recording at such a speed, it is larger than 30 times the reproduction power.

  On the other hand, as high-speed recording becomes possible with an optical disk device, a model for an optical recording medium for high-speed correspondence is also emerging. Even if the manufacturer is the same, the media code is pre-embedded in each of the high-speed compatible media and non-compatible media. It has come to judge whether the media.

  Further, CD-R has a constant linear density, but in such media, recording is usually performed while rotating at a constant linear velocity (hereinafter referred to as CLV: Constant Linear Velocity). In this case, since the relative speed between the medium and the laser beam is always constant, the recording conditions such as the recording power and the recording pulse width to be set are determined before recording. The recording pulse width is determined in advance for each medium to be used, but the set recording power is determined in a specific area (trial writing area) in the innermost periphery, by performing trial writing with varying recording power. Using the optimum recording power, the entire surface is recorded at the same linear velocity without any problem. Obtaining the optimum recording power in this way is generally called Optimum Power Calibration (hereinafter referred to as OPC). The OPC method will not be described in detail here.

  By the way, since the light emission power of the LD changes due to a temperature rise or the like due to its own oscillation, the LD does not control the current for driving the LD while monitoring the LD output with the light receiving element in the optical disk device or the like. The light emission power will change. Therefore, in general, an optical disk apparatus that emits light at a high power as in recording requires a circuit that controls the light emission power of the LD to be constant. This is called Auto Power Control (hereinafter referred to as APC).

  FIG. 5 shows a configuration example of an LD drive control circuit that performs constant power control of light emission power. This constant power control is performed by digital control. In FIG. 5, the light incident on the PD 100 is output in the form of a current proportional to the amount of light by photoelectric conversion. However, the monitor by the PD 100 monitors a part of the laser beam from the LD 101, and most of the laser beam is applied to the recording film of the optical disc (not shown). Next, the current output from the PD 100 is converted into a voltage by the I / V converter 102 and output as a voltage value. In this output voltage, V (P1) corresponds to the first light emission level P1, and V (P2) corresponds to the second light emission level P2. Since the output at the time of recording is a signal in which V (P1) and V (P2) change alternately unlike at the time of reproduction, the signals are changed to V (P1) and V (P2) by the S / H circuits (sampling hold circuits) 103a and 103b. To be separated.

  Here, the sample signal 1 in the S / H circuit 103a is a signal that always turns on the analog switch 104a in the S / H circuit 103a at the time of reproduction, and at the time of recording, it emits light at the recording light amount level P1, or The analog switch 104a in the sampling and holding circuit 103a is turned on only for a shorter period, and the analog switch 104a in the S / H circuit 103a is turned off and the capacitor 105a is used for the period of light emission at the reproduction light quantity level P2. Control is performed so that only the voltage Vs (P1) corresponding to the light amount level P1 for reproduction is extracted by the amplifier 106a.

  On the other hand, the sample signal 2 in the S / H circuit 103b is a signal that always turns off the analog switch 104b in the S / H circuit 103b during reproduction, and during recording, a period during which light is emitted at the recording light quantity level P2, or The analog switch 104b in the S / H circuit 103b is turned on only for a shorter period, and the analog switch 104b in the S / H circuit 103b is turned off and the capacitor 105b is used for the period during which light is emitted at the reproduction light quantity level P1 during recording. Control is performed so that only the voltage Vs (P2) corresponding to the light amount level P2 is extracted by the amplifier 106b.

  The Vs (P1) and Vs (P2) separated from the output voltage of the I / V converter 102 by the S / H circuits 103a and 103b are input to the comparators 107a and 107b, respectively. The comparator 107a compares the voltage signal Vs (P1) with a predetermined reference voltage level Vref1, and the comparator 107b similarly compares the voltage signal Vs (P2) with a predetermined reference voltage level Vref2. And comparing. From these comparators 107a and 107b, signals indicating only whether the input voltage signal is larger or smaller than the respective reference voltage levels, that is, binary values (digital values) are output and read by the CPU 108. It has become.

  Data is sent from the CPU 108 to a D / A converter 109a that converts a digital value into an analog value, and a voltage proportional to the inputted data is output as an analog voltage signal from the D / A converter 109a. Further, a voltage value proportional to the output is converted into a current signal by the V / I converter 110a and output. Similarly, data is also sent from the CPU 108 to the D / A converter 109b, and a voltage proportional to the input data is output from the D / A converter 109b as an analog voltage signal. Further, a voltage proportional to this output is output. The value is converted into a current signal by the V / I converter 110b and output.

  Furthermore, the output currents of the respective V / I converters 110a and 110b are amplified by the current amplifiers 111a and 111b. At the time of reproduction, the switch 112 is turned on by the LDON signal so that the output of the current amplifier 111a is added to the current. The light flows to the LD 115 through the device 114 and is emitted from the LD 115 as the light level P1. Further, at the time of recording, the switch 113 is turned on by the write pulse superimposed signal, so that the output of the current amplifier 111b is added to the output current from the current amplifier 111a by the current adder 114 and flows to the LD 115. Emits light as a recording light level P2.

  By the way, when reproduction is started, the CPU 108 first outputs data 0 to the D / A converter 109a. Thereby, the current corresponding to the light emission power of the LD 115 starts from zero. The CPU 108 gradually increases the data output to the D / A converter 109a until the output of the comparator 107a is inverted (that is, until Vs (P1) becomes larger than Vref1). Thereafter, the data output to the D / A converter 109a is always varied so that the output of the comparator 107a is constantly inverted (that is, Vs (P1) = Vref1). Thereby, the reproduction power emitted from the LD 115 is kept at a constant level as shown in FIG.

  Similarly, FIG. 7 shows a state from the start of recording until the recording power level is kept constant. In FIG. 7, the CPU 108 sets the output of the D / A converter 109b to 0 during the reproduction light emission. Next, when recording light emission is started, the CPU 108 increases the data output to the D / A converter 109b by one or a predetermined amount. Along with this, a current proportional to the output voltage of the D / A converter 109b is superimposed on the LD 115 as a recording power current on a current proportional to the output voltage of the D / A converter 109a. The output voltage of the S / H circuit 103b is also increased by a predetermined amount. Then, when the output voltage of the S / H circuit 103b eventually exceeds Vref2, the output of the comparator 107b is inverted. When reversed, the CPU 108 sends the data moved in the opposite direction to the previous one to the D / A converter 109b. As a result, the current of the LD 115 decreases and the comparator 107b is inverted. When reversed, the CPU 108 operates the D / A converter 109b in a direction opposite to the previous direction, and so on, so that the output voltage of the S / H circuit 103b and Vref2 always straddle (hereinafter referred to as this). In this way, the state where the output voltage and the reference voltage cross over each other is referred to as “settling state”). As a result, a laser beam having a substantially constant light amount level P2 is emitted from the LD 115.

  With the feedback loop configured as described above, a certain level of power light determined by the reference voltage is emitted from the LD 115. The relationship between the reference voltages of the comparators 107a and 107b and P1 or P2 is obtained in advance in the form of a relational expression, for example, in the manufacturing process. At this time, the relational expression obtained in advance is used for power control or the like during actual recording. In other words, if it is desired to vary the power emitted from the LD 115, light can be emitted with that power by setting a reference voltage for a certain predetermined power, and thus can be realized by varying this reference voltage.

  The example shown in FIG. 5 is digital control using the CPU 108 and the D / A converters 109a and 109b, but the same applies to analog control. That is, the APC is not limited to such digital control, but signals from the S / H circuits 103a and 103b are input to an error amplifier or the like, and compared with the reference voltage by the error amplifier or the like, there is a deviation from the reference voltage. Sometimes the error amplifier can perform power control even by analog control that outputs a voltage that corrects the deviation to the V / I converters 110a and 110b. In this way, in both analog control and digital control, the light emission power of the LD 115 is monitored, and the drive current to the LD 115 is controlled so that the predetermined light quantity levels P1 and P2 are compared with the reference voltage to become the reference voltage. It is the same operation.

  FIG. 8 shows a characteristic diagram of LD driving current versus light emission power. As can be seen from this figure, the light emission power from the LD and the LD drive current show a linear function characteristic above a certain threshold value Ith. The gradient when the relationship between the light emission power and the LD drive current is a linear function is called “differential efficiency”.

  Therefore, for example, when the differential efficiency during APC control is obtained, it can be obtained from the value of the D / A converter 109b that is in a settling state at each power when light is emitted with at least two set powers.

  As described above, the fact that the light emission power changes means that the light emission power changes due to the characteristics of the LD even at the same current value, that is, the differential efficiency changes. Accordingly, when the differential efficiency is small even with the same power, a large LD drive current is required, and when the differential efficiency is large, the LD drive current is small.

  Therefore, when the differential efficiency changes, in order to emit light with the same power, the setting of the LD drive current, that is, the setting of the D / A converter 109 must be changed.

  By the way, in the settling state, binary values are repeated, but when the resolution of the original D / A converter 109 is rough, the error becomes larger than when the resolution is fine. That is, the setting error is determined by the resolution of the D / A converter 109 for setting the reference voltage.

The voltage that can be set by the D / A converter 109 can be divided into 2 ⁸ = 256 with respect to the voltage width that can be set if, for example, the specification of the D / A converter 109 is 8 bits, and 2 ¹⁰ = if the specification is 10 bits. It can be divided into 1024.

  Accordingly, the voltage setting maximum value here corresponds to the maximum value of the voltage width, and the larger the number of bits, the finer the resolution, but the larger the number of bits, the higher the cost, so the D / A converter with coarse resolution. The possibility of having to use comes out. Of course, since the LD drive current increases as the voltage setting maximum value increases, the set maximum value has increased in recent years.

  Incidentally, according to Patent Document 1, in order to be able to detect the target light output accurately and in a short time even in a deteriorated laser diode, the target setting is made by changing the current setting step from the differential efficiency. Proposals have been made so that the current can be set in a short time.

JP 11-296886 A

  Incidentally, as described above, since higher-speed recording has become possible in recent years, it has become necessary to cause the LD to emit light with high power. However, despite the fact that the recording speed that can be set by the optical disk device is higher in this way, there are actually users who think that the recording quality is better at lower speeds, especially in audio-related recording. There are many cases where recording is attempted at a lower recording speed.

  However, when the recording power is high during the actual recording operation, the value of Vref2 set in the D / A converter 109b is large, so the error of P2 with respect to the set Vref2 is small, but the recording power is the maximum power. In particular, the resolution of the D / A converter 109b is the same, so that the error of P2 with respect to the set Vref2 becomes large. That is, it shows that light emission becomes rough. For example, if the maximum power is 50 mW and an attempt is made to record at a recording power of 10 mW, the error will be five times that when the light is simply emitted at 50 mW. The fact that the light emission power becomes rough means that the recording quality is lowered, and therefore the recording quality is lowered at a low power. As described above, when the recording speed was low and the maximum light emission power was not high as before, there was almost no setting error, and there was no problem that the light emission power became rough due to the difference in the light emission power. Are expected to increase.

  Incidentally, according to Patent Document 1, since the step of changing the setting of the LD drive current according to the differential efficiency is changed, even if the differential efficiency changes, for example, it can be set accurately when viewed only on the high power side, When the power is low, the setting error is large, so even if the step is changed, the correct setting value cannot be reached.

  The object of the present invention is set when the recording power is different, for example, when recording is performed at a low speed so that the recording quality is not deteriorated under the condition that the high-speed recording can be performed originally. It is an object to provide an optical disc apparatus and a laser power control method capable of performing recording without eliminating errors and degrading recording quality.

  An optical disc apparatus according to a first aspect of the present invention is a drive source for rotationally driving a recordable optical disc, an optical pickup having a semiconductor laser and an objective lens and irradiating the optical disc with laser light, and for recording on the optical disc. Semiconductor laser drive control apparatus for emitting light by digitally modulating the semiconductor laser as two laser light levels, ie, a first light level P1 and a second light level P2 larger than the first light level P1 The semiconductor laser drive control device detects a light emission power of the laser light output from the semiconductor laser, and outputs a current signal corresponding to the light emission power, and the light emission power detection Current voltage conversion means for converting the current signal output from the means into a voltage signal and outputting the voltage signal, and the level of the voltage signal Comparison means for comparing with a preset reference voltage level, light quantity level adjustment means for adjusting the light quantity level of the semiconductor laser according to the comparison result of the comparison means, and voltage signal output from the light quantity level adjustment means Drive current supply means for supplying a drive current to the semiconductor laser having voltage-current conversion means for converting the current signal into a current signal and current amplification means for amplifying the current signal output from the voltage-current conversion means A temperature detection means for detecting the temperature of the semiconductor laser; a differential efficiency calculation means for calculating the differential efficiency of the semiconductor laser; and a maximum voltage signal output from the light amount level adjustment means to the voltage-current conversion means. The set value is changed and set according to the differential efficiency of the semiconductor laser and the temperature of the semiconductor laser detected by the temperature detecting means. Comprising the maximum setting change control means.

  Accordingly, the voltage maximum set value is changed and set based on the differential efficiency, and the voltage maximum set value is changed and set depending on the detected temperature of the semiconductor laser. Even when the recording power is different, such as when trying to record at a low speed so that the recording quality does not deteriorate under conditions where high-speed recording can be performed, setting errors can be eliminated and more appropriate. In addition, it is possible to prevent the maximum voltage setting value changed by the differential efficiency from being unable to emit light at a desired light emission power because the differential efficiency has changed due to the temperature.

  According to a second aspect of the present invention, in the optical disc apparatus according to the first aspect, a ratio between a differential efficiency when the objective lens of the optical pickup is focus servo-off and a differential efficiency when the focus servo is on is obtained in advance. The differential efficiency calculation means obtains the differential efficiency in a state where the objective lens of the optical pickup is focus servo-off prior to the recording operation, and the focus servo on based on the ratio obtained in advance with the differential efficiency as an initial value. The differential efficiency at the equivalent time is calculated, and the maximum set value change control means changes and sets the maximum set value of the voltage signal in accordance with the calculated differential efficiency at the time when the focus servo is equivalent and the temperature of the semiconductor laser. did.

  Therefore, based on the differential efficiency when the focus servo is turned off, the differential efficiency when the focus servo is turned on is recalculated, the maximum voltage setting value is changed accordingly, and the maximum voltage setting value is limited by the detection temperature of the semiconductor laser. The setting error can be eliminated, the setting error can be eliminated, the power can be set more appropriately, and the voltage setting maximum value changed by the differential efficiency has changed by the temperature. It is possible to prevent the light from becoming unable to be emitted.

  According to a third aspect of the present invention, in the optical disc apparatus according to the second aspect, the differential efficiency calculation means further acquires the differential efficiency during a recording operation in which the objective lens of the optical pickup is in focus servo-on, and the maximum setting The value change control means changes and sets the maximum set value of the voltage signal in accordance with the obtained differential efficiency when the focus servo is turned on and the temperature of the semiconductor laser.

  Therefore, by recalculating the differential efficiency during recording, changing and setting the maximum voltage setting value accordingly, and changing the setting so as to limit the maximum voltage setting value based on the detected temperature of the semiconductor laser, the setting error is eliminated. Therefore, it is possible to set a more appropriate power, and it is possible to prevent the light from being unable to emit light at a desired light emission power because the voltage maximum setting value changed by the differential efficiency is changed by the temperature.

  According to a fourth aspect of the present invention, in the optical disc apparatus according to any one of the first to third aspects, the maximum set value change control means is configured to output a maximum voltage signal corresponding to the temperature of the semiconductor laser during a short recording operation. Changed the setting value change. According to a fifth aspect of the present invention, in the optical disc apparatus according to the fourth aspect, the short-time recording operation is a test writing process for obtaining an optimum recording power of the semiconductor laser.

  Accordingly, during a short-time recording operation such as OPC (trial writing process), since the recording quality is affected by the change in the maximum voltage setting value, the recording quality can be prevented by not changing the voltage maximum setting value. Can be made to have no effect.

  According to a sixth aspect of the present invention, at least two light quantities of a first laser light level P1 and a second light quantity level P2 larger than the first light quantity level P1 are used as laser light to irradiate a recordable optical disk. A laser power control method in which light is emitted after being digitally modulated at a level, wherein the light emission power of the laser light output from the semiconductor laser is detected, and a current signal corresponding to the light emission power is converted into a voltage by a current-voltage conversion means. The signal is converted into a signal, the level of the converted voltage signal is compared with a preset reference voltage level by a comparison unit, and the light level of the semiconductor laser is adjusted by a light amount level adjustment unit according to the comparison result of the comparison unit. When performing automatic power control processing to adjust, the light amount level adjusting means outputs to drive the semiconductor laser For the voltage / current converting means for converting the voltage signal into a current signal, the maximum set value of the voltage signal output by the light amount level adjusting means is changed according to the differential efficiency of the semiconductor laser and the detected temperature of the semiconductor laser. Includes processing to set.

  Accordingly, the voltage maximum set value is changed and set based on the differential efficiency, and the voltage maximum set value is changed and set depending on the detected temperature of the semiconductor laser. Even when the recording power is different, such as when trying to record at a low speed so that the recording quality does not deteriorate under conditions where high-speed recording can be performed, setting errors can be eliminated and more appropriate. In addition, it is possible to prevent the maximum voltage setting value changed by the differential efficiency from being unable to emit light at a desired light emission power because the differential efficiency has changed due to the temperature.

  According to the optical disk apparatus of the first aspect of the invention, the voltage maximum set value is changed and set by differential efficiency, and the voltage maximum set value is changed and set according to the detected temperature of the semiconductor laser. For example, even when the recording power is different, such as when trying to record at a low speed so as not to deteriorate the recording quality under the condition that the high-speed recording can be performed by capability originally. The setting error can be eliminated, the power can be set more appropriately, and the maximum voltage setting value changed by the differential efficiency is prevented from being unable to emit light at the desired light emission power because the differential efficiency has changed due to the temperature. You can also

  According to the second aspect of the present invention, in the optical disk device according to the first aspect, the differential efficiency when the focus servo is on is recalculated based on the differential efficiency when the focus servo is off, and the maximum voltage setting value is changed and set accordingly. In addition, the setting error can be eliminated by changing the setting so as to limit the maximum voltage setting value according to the detected temperature of the semiconductor laser. Since the efficiency of the voltage setting maximum value changes depending on the temperature, it is possible to prevent the light from being emitted with a desired light emission power.

  According to a third aspect of the present invention, in the optical disc apparatus according to the second aspect, the differential efficiency is recalculated during recording, the maximum voltage setting value is changed and set accordingly, and the maximum voltage is determined according to the detected temperature of the semiconductor laser. By changing the setting to limit the setting value, setting errors can be eliminated, more appropriate power can be set, and the maximum voltage setting value changed by the differential efficiency has changed due to temperature. It is possible to prevent the light from being emitted with a desired light emission power.

  According to the fourth aspect of the present invention, in the optical disk apparatus according to any one of the first to third aspects, the maximum voltage is maintained during a short recording operation like the OPC (trial writing process) of the fifth aspect. In the case where the recording quality is affected by the change of the setting value, it is possible to prevent the recording quality from being affected by not changing the maximum voltage setting value.

  According to the sixth aspect of the invention, the maximum voltage setting value is changed and set based on the differential efficiency, and the maximum voltage setting value is changed and set depending on the detected temperature of the semiconductor laser. Therefore, even if the power at the time of recording is different, such as when trying to record at a low speed so that the recording quality does not deteriorate under the condition that high-speed recording can be performed originally, the setting error Can be set to a more appropriate power, and it is possible to prevent the maximum voltage setting value changed by the differential efficiency from being unable to emit light at a desired light emission power because the differential efficiency has changed due to the temperature. .

  The best mode for carrying out the present invention will be described with reference to FIGS. The present embodiment shows an example of application to an optical disc apparatus for a write-once optical disc 1 as a recordable CD-R (CD-Recordable) that can be written only once and conforms to a CD format. A configuration example of the drive device is shown in FIG. FIG. 1 is a schematic block diagram showing the configuration of the optical disk apparatus (drive apparatus).

  The schematic configuration and operation of the optical disc apparatus will be described with reference to FIG. First, in a CD-based disc, a data string is represented by the presence or absence of a hole called a pit on a disc substrate, and a laser beam is applied to this to read data by a change in reflected light. This data string is arranged in a spiral on the disk substrate like a record. This spirally arranged line is called a track, and the distance between adjacent tracks is 1.6 μm.

  Such an optical disk 1 is rotationally driven by a spindle motor 2 as driving means. The spindle motor 2 is controlled by the motor driver 3 and the servo means 4 so that the linear velocity is constant (CLV) or the rotational speed is constant (CAV). The linear velocity can be changed in stages. The optical pickup 5 includes a semiconductor laser, an optical system, a focusing actuator, a tracking actuator, a light receiver, a position sensor, and the like, which will be described later, and irradiates the recording surface of the optical disc 1 with laser light.

  The optical pickup 5 can be moved in the sledge direction (disk radial direction) by a seek motor (not shown). These focusing actuators, tracking actuators, and seek motors are controlled by the motor driver 3 and the servo means 4 so as to position the laser spot at a target location on the optical disk 1 based on signals obtained from the light receiver and the position sensor.

  At the time of data reproduction, a reproduction signal obtained by the optical pickup 5 is amplified by a read amplifier 6 and subjected to equalizer processing or binarization (digitization) processing, and then input to a CD decoder 7 for EFM demodulation. That is, the EFM signal is data obtained by modulating 8-bit data into 14-bit data so that it can be easily reproduced or recorded optically. The EFM demodulated data is subjected to deinterleaving (reordering processing) and error correction processing. Do. Further, the data after the deinterleaving and error correction processing is input to the CD-ROM decoder 8 to perform error correction processing for improving data reliability.

  Thereafter, the data processed by the CD-ROM decoder 8 is temporarily stored in the buffer RAM 10 by the buffer manager 9 and transferred to the host side at once by the interface 11 such as ATAPI or SCSI when it is prepared as sector data. In the case of music data, the data output from the CD decoder 7 is input to the D / A converter 12 to extract an analog audio signal.

  On the other hand, at the time of data recording, when data transferred from the host via the interface 11 such as ATAPI or SCSI is received, the data is temporarily stored in the buffer RAM 10 by the buffer manager 9. Recording starts when a certain amount of data accumulates in the buffer RAM 10, but before that, the laser spot is positioned at the writing start point. The writing start point is obtained by an ATIP (Absolute Time In Pre-groove) signal which is a wobble signal preliminarily carved on the optical disc 1 by meandering tracks (pregrooves). The ATIP signal is time information indicating an absolute address on the optical disc. The ATIP decoder 13 extracts the ATIP signal information, detects an ATIP error, and measures the ATIP signal detection error rate.

  The synchronization signal generated by the ATIP decoder 13 is input to the CD encoder 14 so that data can be written at an accurate position. Data in the buffer RAM 10 is subjected to error correction code addition and interleaving (rearrangement) by the CD-ROM encoder 15 and the CD encoder 14, and then EFM-modulated. The data is transferred to the optical disk 1 through the laser control circuit 16 and the optical pickup 5. To be recorded.

  Such an optical disk apparatus includes a microcomputer 20 including a CPU 17, a ROM 18, and a RAM 19 for controlling the operation of each unit described above.

  Here, in the present embodiment, the emission waveform of the semiconductor laser includes the second light amount level P2 and the second light amount level for recording for forming recording pits in accordance with the case shown in FIG. This is an application example in the case of using a waveform that is digitally modulated at two light quantity levels, which are smaller than P2 and does not form a recording pit, and a first light quantity level P1, and alternately emits light.

  Next, an example of the circuit configuration of the semiconductor laser drive control device centered on the laser control circuit 16 will be described with reference to FIG. The basic configuration is the same as that shown in FIG. First, light reception for monitoring, which is provided in the optical pickup 5 and directly or indirectly receives a part of the emitted light (which may be front light or rear light) with respect to a semiconductor laser (LD) 21 to be controlled. An element (PD) 22 is provided. The PD 22 outputs a current proportional to the optical power incident on the PD 22. Here, the PD 22 functions as light emission power detecting means for detecting the light emission power of the laser light output from the LD 21 and outputting a current signal corresponding to the light emission power.

  An I / V converter (current / voltage conversion means) 23 for converting the current signal into a voltage signal is provided on the output side of the PD 22. On the output side of the I / V converter 23, as one system, a sampling hold circuit (S / H circuit) 24a and a comparator (comparing means) 25a are sequentially connected, and the output of the comparator 25a is input to the CPU 17. ing. Here, the sample signal 1 in the S / H circuit 24a is a signal that always turns on the analog switch 26a in the S / H circuit 24a at the time of reproduction, and at the time of recording, it emits light at the recording light level P2, or The analog switch 26a in the sampling hold circuit 24a is turned on only for a shorter period, and the analog switch 26a in the S / H circuit 24a is turned off and the capacitor 27a is used during the period of light emission at the reproduction light quantity level P2. Control is performed so that only the voltage Vs (P1) corresponding to the light amount level P1 for reproduction is extracted by the amplifier 28a. A reference voltage level Vref1 for the light amount level P1 is set for the comparator 25a.

  On the output side of the I / V converter 23, a sampling hold circuit (S / H circuit) 24b and a comparator (comparison means) 25b are sequentially connected as the other system, and the output of the comparator 25b is input to the CPU 17. Has been. The sample signal 2 in the S / H circuit 24b is a signal that always turns off the analog switch 26b in the S / H circuit 24b at the time of reproduction, and at the time of recording, it emits light at the recording light level P2, or from that period. The analog switch 26b in the S / H circuit 24b is turned on only for a short period, and the analog switch 26b in the S / H circuit 24b is turned off and the light quantity level is set by the capacitor 27b during the period when light is emitted at the reproduction light quantity level P1 during recording. Control is performed so that only the voltage Vs (P2) corresponding to P2 is extracted by the amplifier 28b. A reference voltage level Vref2 for the light amount level P2 is set for the comparator 25b.

  The Vs (P1) and Vs (P2) separated from the output voltage of the I / V converter 23 by the S / H circuits 24a and 24b are input to the comparators 25a and 25b, respectively. The comparator 25a compares the voltage signal Vs (P1) with a predetermined reference voltage level Vref1, and the comparator 25b similarly compares the voltage signal Vs (P2) with a predetermined reference voltage level Vref2. And comparing. From these comparators 25a and 25b, signals indicating only whether the input voltage signal is large or small with respect to the respective reference voltage levels, that is, binary values (digital values) are output and read by the CPU 17. It has become.

  Data is sent from the CPU 17 to a D / A converter 29a that converts a digital value into an analog value, and a voltage proportional to the input data is output from the D / A converter 29a as an analog voltage signal. Further, a voltage value proportional to the output is converted into a current signal by the V / I converter 30a and output. Similarly, data is also sent from the CPU 17 to the D / A converter 29b, and a voltage proportional to the input data is output from the D / A converter 29b as an analog voltage signal. Further, a voltage proportional to this output is output. The value is converted into a current signal by the V / I converter 30b and output.

  Furthermore, the output currents of the respective V / I converters 30a and 30b are amplified by the current amplifiers 31a and 31b, but the switch 32 is turned on by the LDON signal during reproduction so that the output of the current amplifier 31a adds the current. The light flows from the LD 21 to the LD 21 through the device 34 as the light amount level P1. Further, at the time of recording, the switch 33 is turned on by the write pulse superimposed signal so that the output of the current amplifier 31b is added to the output current from the current amplifier 31a by the current adder 34 and flows to the LD21. Emits light as a recording light level P2.

  Note that the sample signals 1 and 2, the LDON signal, and the write pulse superimposed signal, which are timing control signals, are each output by the CD encoder 14.

  Further, in FIG. 3, the CPU 17 that controls the voltage to the V / I converters 30a and 30 so that the reference voltage is compared with the reference voltage is the APC unit 35, and the V / I converters 30a and 30b and the subsequent ones. An LD driver unit (driver) 36 as drive current supply means is used. Further, the CPU 17 and the D / A converters 29a and 29b constitute a digital control light amount level adjusting means.

  Further, in the present embodiment, a temperature sensor 37 is provided as a temperature detecting means that is disposed in the vicinity of the LD 21 and measures the temperature of the LD 21. The detection value of the temperature sensor 37 (sensor output value = analog value) is converted into a digital value by the A / D converter 38 and read by the CPU 17. At this time, how many degrees the value read by the CPU 17 is is determined as the specification of the temperature sensor 37. However, since there are actually variations, etc., each device has a predetermined value. It can be grasped more accurately if it is examined.

  The D / A converters 29a and 29b can change the maximum value of the voltage that can be set (the maximum setting value of the voltage signal), and the CPU 17 sets how much the maximum setting value is to be set. Further, the D / A converters 29a and 29b are predetermined in the specification such as 100 LSB and 500 LSB, for example. Naturally, the larger this value, the finer the resolution.

  Further, as a prior process, a ratio between the differential efficiency of the LD 21 when the focus servo of the objective lens in the optical pickup 5 is turned off and the differential efficiency of the LD 21 when the focus servo is turned on is obtained in the form of a relational expression. Keep it. The reason why such a relational expression is obtained is that the differential efficiency may change when the focus servo is turned on / off. In advance, how much the differential efficiency differs when the focus servo is turned on / off is determined through experiments or the like. In obtaining this relational expression, it is desirable that data can be taken from as many drives as possible. The ratio relational expression obtained in this way is written in advance in the firmware or stored in the memory 18 or the like.

  The relationship between the light emission power difference and temperature is also examined in advance. For example, a value acquired by the temperature sensor 37 when light is emitted at a certain power (Pini) and a value acquired by the temperature sensor 37 when light is emitted at another power (Pother) are stored. At this time, the larger the number of samples acquired by the temperature sensor 37 in Pother, the better. Further, the light emission at the power Pini is acquired by the temperature sensor 37 when the Pother is further changed so as to be different from the value acquired first by changing the environmental temperature or the like. At this time, the difference between Pini and Pother in a certain table may be stored for each temperature of Pini, or some relational expression may be obtained.

  The processing for obtaining the relationship between the differential efficiency of the focus servo on / off and the processing for examining the relationship between the power difference and the temperature may be obtained in advance and are considered to be independent of each other. Good.

  In addition, the relational expression between the reference voltage and power in the manufacturing process is also examined in advance.

  In such a configuration, an outline of a light emission power control operation example executed by the CPU 17 by a program stored in the ROM 18 will be described with reference to a flowchart shown in FIG. First, it is assumed that the processing as described above as the preliminary processing has already been performed in the appropriate order in steps S1 to S3.

  Thereafter, when actually performing the recording operation on the optical disc 1, first, the focus servo is turned on to perform the recording using the optical disc 1, and the tracking servo is turned on to determine what type of the optical disc 1 is. Before the focus servo is turned on, that is, in the state where the focus servo is turned off, the LD 21 is caused to emit light with two different write powers and the differential efficiency ηini is obtained from the power at that time and the LD drive current. The LD drive current at this time does not directly measure the current to the LD 21 but is a value obtained by converting the current value from the set value of the D / A converter 29b set by APC, which is determined in advance at the time of design. Is. At the same time, the temperature when the light is emitted with this power is acquired by the temperature sensor 37. The value acquired at this time is defined as LDTEMPini. Based on the differential efficiency ηini, the differential efficiency when the focus servo is turned on is calculated based on a relational expression stored in advance, and this differential efficiency is defined as ηA.

  That is, when performing reading or writing, a laser beam is focused on the track of the optical disc 1 in advance to focus, the objective lens is controlled in the focused state (focus servo on), and the laser is further recorded in the groove where data is written. The objective lens is controlled so that the light follows (tracking on). Only in this state can the information recorded on the optical disc 1 be read. Here, normally, in order to obtain the differential efficiency η, the LD 21 is caused to emit light at several set powers, and a linear approximation expression is obtained from the LD drive current value obtained by APC at that time, that is, the value of the D / A converter 29b. Obtain the slope as the differential efficiency. However, since the recording is actually performed on the write once optical disc 1 in the focus servo ON state at this time, in the present embodiment, the differential efficiency is obtained before the focus servo is turned on, that is, in the focus servo OFF state, and this is differentiated. The initial efficiency value is ηint. Then, the differential efficiency corresponding to the focus servo on is calculated as ηA based on the relational equation of the differential η at the time of focus servo on / off measured in advance. That is, it can be seen from the differential efficiency ηint when the focus servo is turned off what differential efficiency is actually obtained when recording on the optical disc 1.

  Next, it is assumed that the track-on and mount operations are actually finished and OPC is performed. The mounting operation is to apply laser light to the optical disk 1 to turn on the focus servo, and to obtain necessary information from the optical disk 1 after the tracking servo is turned on. However, the description is omitted here. Prior to light emission by such OPC, the maximum voltage set value is changed and set for the D / A converter 29b using the differential efficiency ηA corresponding to the focus servo-on calculated as described above (S5). That is, since the voltage setting maximum value of the voltage signal output from the D / A converter 29b to the V / I converter 30b is changed according to the differential efficiency ηA, setting errors can be eliminated and the differential efficiency ηA As a result, the LD driving current flows as much as possible, and the resolution of the D / A converter 29b changes. Therefore, the setting error from this point can be made as small as possible, and the appropriate power can be obtained with higher accuracy. It becomes possible to set.

  After changing and setting the maximum voltage setting value, the OPC operation is actually executed (S6). That is, the reference voltage corresponding to the power set by OPC is set according to the value obtained in the manufacturing process or the like, and the LD 21 is caused to emit light. In this OPC operation, light is emitted at several powers to obtain an optimum power, but there are various methods for obtaining the optimum power, but these are well-known matters and will not be described in detail here. During this OPC operation, the voltage setting maximum value is not changed from the relationship between LDTEMPini, power, and temperature. The reason for this will be described later. Also, the differential efficiency during actual recording is obtained from the set power of the OPC operation and the LD drive current set value obtained by the APC at that time. The differential efficiency at this time is ηB.

  After the OPC operation is completed, the voltage setting maximum value of the D / A converter 29b is changed and set based on the differential efficiency ηB (S7). Thus, by recalculating the differential efficiency during recording (during trial writing) and resetting the voltage setting maximum value of the D / A converter 29b accordingly, the setting error can be further eliminated, and more Appropriate power can be set.

  Next, in the actual recording operation, a reference voltage Vref2 corresponding to the optimum recording power obtained by OPC is set for the comparator 25b (S8).

  Here, from the difference between the set power when the set power and the differential efficiency ηB are obtained and the LDTEMPini, how much the temperature fluctuates when the light is emitted with the optimum recording power is obtained and is set as LDSHIFT (S9).

  Next, using LDth that is set in advance as a threshold for whether or not to change the voltage maximum setting value from the difference due to temperature fluctuation, it is determined whether or not the fluctuation temperature LDSHFT is larger than this threshold LDth ( If it is larger than the threshold value LDth (Y in S10), the maximum voltage setting value is changed (S11), and the recording operation is started (S12).

  Even after the start of the recording operation, the temperature of the LD 21 is measured by the temperature sensor 37 at regular intervals. Let LDSHIFT_WRITE be the difference between the temperature and LDTEMPini at this time. It is determined whether or not the difference LDSHIFT_WRITE is larger than the threshold value LDth (S13). If the difference LDSHIFT_WRITE is larger than the threshold value LDth (Y in S13), the maximum voltage setting value is changed (S14). This process is repeated until the recording operation is completed.

  Therefore, in the process shown in FIG. 3, the processes of steps S4 and S6 are executed as a function of the differential efficiency calculation means, and the processes of steps S5, S9, S11, and S14 are executed as a function of the maximum set value change control means.

  Here, the point which considers the detected temperature of LD21 by the process mentioned above is demonstrated. Even if the differential efficiency is measured in advance before recording as described above, the temperature of the LD 21 when the differential efficiency is obtained must be high in advance, such as when the difference between the power emitted at this time and the power during actual recording is large. For example, the temperature change of the LD 21 may be small during actual recording, but if the temperature of the LD 21 when the differential efficiency is obtained is low, the temperature change becomes large when the light is actually emitted, and the differential efficiency also changes. Will also grow. Therefore, a temperature sensor 37 is provided for the LD 21, and the temperature of the LD 21 when light is emitted with a certain power is measured in advance by experiments or the like, and how much temperature fluctuation occurs when the light emission power is changed. Check it out. That is, when the LD 21 is caused to emit light in order to actually obtain the differential efficiency, the temperature is also measured at the same time.

  Further, when recording, if there is a temperature difference from the difference between the recording power when determining the recording power and the power emitted during differential efficiency measurement and the detected temperature of the LD 21 measured when determining the differential efficiency, The maximum voltage setting value is changed so as not to become smaller than a certain value when the value becomes larger than a certain value, that is, as shown in step S11, a limit is set.

  By doing in this way, it does not emit light with the set power because the change in differential efficiency increases with temperature, and an appropriate power can be set more accurately.

  Further, when recording is performed on the optical disc 1, since the temperature rises greatly because the writing is continued with the same power, the characteristics of the LD 21 change and the current required for the LD 21 changes even with the same power. In other words, the differential efficiency is high, but if this is a short time, it does not matter so much, but if the recording is performed for a long time, the fluctuation of the differential efficiency becomes large. Therefore, the temperature of the LD 21 is measured at the start of recording, and the temperature is measured every certain period. Therefore, when the temperature change from the start of recording exceeds a certain threshold value LDth, the voltage setting maximum value is changed and set as shown in step S14. By doing so, there is no shortage of light emission power due to changing the maximum voltage setting during recording.

  In general, an OPC process for obtaining an optimum recording power is performed before recording on the optical disc 1, and the differential efficiency when light is emitted by OPC is closer to the efficiency at the time of actual recording performed thereafter. However, in OPC processing, recording is performed with some power, and the difference in power may be large, but the recording time is short, so in OPC, recording ends before the differential efficiency changes significantly due to temperature changes. To do. Furthermore, since the time is short, it takes time to change and set the maximum voltage setting value. This set time may affect the recording if the recording speed is considerably high. Therefore, even if there is a difference in recording power in the power in the OPC, it is possible to prevent the recording quality from being affected in the OPC by not changing the differential efficiency so much. That is, during a short recording operation such as the OPC process, the maximum setting value of the voltage signal is not changed according to the detected temperature of the LD 21 as shown in step S6.

1 is a block diagram of an optical disc apparatus showing an embodiment of the present invention. It is a circuit diagram which shows the structure of a semiconductor laser drive control apparatus. It is a schematic flowchart which shows the example of control operation. It is a wave form diagram which shows the light emission waveform of the ternary system for general CD-R. It is a circuit diagram which shows the structure of the conventional semiconductor laser drive control apparatus. It is a wave form diagram which shows the rise control example at the time of reproduction | regeneration by digital APC control. It is a wave form diagram which shows the example of a rise control at the time of the recording by digital APC control. It is a current vs. power characteristic diagram of LD.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Drive source 5 Optical pick-up 16 Semiconductor laser drive control apparatus 21 Semiconductor laser 22 Light emission power detection means 23 Current voltage conversion means 25 Comparison means 29 Light quantity level adjustment means 30 Voltage current conversion means 31 Current amplification means 36 Drive current supply means 37 Temperature detection means

Claims (6)

A drive source for rotationally driving a recordable optical disc;
An optical pickup having a semiconductor laser and an objective lens and irradiating the optical disc with laser light;
As a laser beam to be irradiated for recording on the optical disk, a semiconductor laser is digitally modulated at two light amount levels of a first light amount level P1 and a second light amount level P2 larger than the first light amount level P1 to emit light. A semiconductor laser drive control device,
With
The semiconductor laser drive control device comprises:
A light emission power detecting means for detecting a light emission power of the laser light output from the semiconductor laser and outputting a current signal according to the light emission power;
Current-voltage conversion means for converting the current signal output from the light emission power detection means into a voltage signal and outputting the voltage signal;
A comparison means for comparing the level of the voltage signal with a preset reference voltage level;
A light amount level adjusting means for adjusting the light amount level of the semiconductor laser according to the comparison result of the comparing means;
A voltage-current converting means for converting the voltage signal output from the light amount level adjusting means into a current signal and outputting the current signal; and a current amplifying means for amplifying the current signal output from the voltage-current converting means. Drive current supply means for supplying a drive current to the laser;
Temperature detecting means for detecting the temperature of the semiconductor laser;
Differential efficiency calculating means for calculating the differential efficiency of the semiconductor laser;
The maximum set value of the voltage signal output from the light amount level adjusting means to the voltage-current converting means is changed and set according to the differential efficiency of the semiconductor laser and the temperature of the semiconductor laser detected by the temperature detecting means. A maximum set value change control means;
An optical disc apparatus comprising: The ratio between the differential efficiency when the focus servo is turned off and the differential efficiency when the focus servo is turned on is obtained in advance.
The differential efficiency calculation means obtains differential efficiency in a state where the focus servo of the objective lens of the optical pickup is turned off prior to a recording operation, and is equivalent to focus servo on based on the ratio obtained in advance using the differential efficiency as an initial value. Calculate the differential efficiency of the hour,
The maximum set value change control means changes and sets the maximum set value of the voltage signal according to the calculated differential efficiency when the focus servo is equivalent and the temperature of the semiconductor laser.
2. The optical disk apparatus according to claim 1, wherein The differential efficiency calculation means further acquires differential efficiency during a recording operation in which the objective lens of the optical pickup is focus servo-on,
The maximum set value change control means further changes and sets the maximum set value of the voltage signal according to the obtained differential efficiency when the focus servo is turned on and the temperature of the semiconductor laser.
3. The optical disk apparatus according to claim 2, wherein The maximum set value change control means does not perform the change setting of the maximum set value of the voltage signal according to the temperature of the semiconductor laser during a short recording operation,
4. An optical disc apparatus according to claim 1, wherein   5. The optical disk apparatus according to claim 4, wherein the recording operation for a short time is a test writing process for obtaining an optimum recording power of the semiconductor laser. As a laser beam to be radiated onto a recordable optical disc, a semiconductor laser is digitally modulated and emitted by at least two light levels, ie, a first light level P1 and a second light level P2 that is larger than the first light level P1. A laser power control method as described above,
The emission power of the laser beam output from the semiconductor laser is detected, a current signal corresponding to the emission power is converted into a voltage signal by a current-voltage conversion means, the level of the converted voltage signal and a preset reference When performing automatic power control processing for comparing the voltage level with the comparison means, and adjusting the light level of the semiconductor laser by the light quantity level adjustment means according to the comparison result of the comparison means,
For the voltage-current converter that converts the voltage signal output to drive the semiconductor laser by the light quantity level adjuster into a current signal, the maximum set value of the voltage signal output by the light quantity level adjuster is A laser power control method comprising a process of changing and setting according to a differential efficiency of a semiconductor laser and a detected temperature of the semiconductor laser.

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