JP2005347477A - Semiconductor laser driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that the correct optical output of an LD (Laser Diode) can not be obtained when the characteristics of a driving current to the optical output of LD is provided with non-linearity. <P>SOLUTION: The optical output from a semiconductor laser 4 in response to the set value of a DAC for setting a driving current has non-linearity. The optical output of the semiconductor laser 4 is controlled by the differential quantum efficiency of the semiconductor laser 4 and an approximate optical output resolution. In this case, the approximate optical output resolution is obtained by dividing an inclination of the driving current of the semiconductor laser 4 determined by the DAC for setting driving current and the DAC for setting full scale, to the optical output into arbitrary divisions and multiplying the differential quantum efficiency by the inclination which are operated in each division. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser driving device used in an optical disk device such as a CD-R driving device, a CD-RW driving device, a DVD-R driving device, a DVD-RW driving device, a DVD-RAM driving device, and a DVD + RW driving device. About.

  In an optical disc apparatus that records information on an optical disc as a recording medium by optical modulation of a laser beam from a semiconductor laser (laser diode, hereinafter referred to as LD), high-speed recording and high recording density accompanying an increase in the amount of information in recent years In addition, due to high reliability, the optical modulation of the laser light is indispensable to control by making the optical modulation multi-pulse, multi-level optical output, or the like.

  FIG. 3 shows an optical waveform for recording on a phase change recording medium as an example of a recording waveform from a semiconductor laser. Conventional recording from a semiconductor laser to a recording medium is performed by marking a phase change type recording medium or the like with a multi-pulse LD emission waveform (hereinafter referred to as a multi-pulse waveform) generated based on an EFM (Eight Fourteen Modulation) modulation code. It is done by forming. In particular, in order to perform recording on a phase change recording medium, the recording layer of the recording medium is heated by the optical output Pw of the semiconductor laser and rapidly cooled by the optical output Pb of the semiconductor laser, thereby forming a mark shape on the recording layer of the recording medium. In forming and erasing the mark shape on the recording layer of the recording medium, the recording layer temperature of the recording medium needs to be set to the crystallization temperature by the optical output Pe of the semiconductor laser.

  For this reason, the multi-pulse waveform includes the optical output Pb for emitting the LD, the optical outputs Pw and Pb for forming the mark shape on the recording medium, the optical output Pe for erasing the mark shape on the recording medium, and the recording It is formed from four types of power of optical output Pr for reading the mark shape on the medium. As shown in FIG. 3, the drive current Iop for emitting each of the light outputs Pw, Pb, Pe, and Pr emits LD with Iop = Ibias + Iw, Ibias + Ib, Ibias + Ie, and Ibias + Ir. Thus, optical outputs Pw, Pb, Pe, and Pr are obtained. Normally, Ibias is set to a current value that causes the LD to emit light, that is, about the threshold current Ith of the LD.

  As is well known in the art, the LD, which is a light source, does not emit light even when driven at a threshold current Ith or less, but emits laser light when driven at a current exceeding the threshold current Ith. The differential quantum efficiency (or slope efficiency) η representing the threshold current Ith and the light output Po versus the drive current Iop in the laser emission region shown in FIG. 2 differs depending on the type of LD. Furthermore, even with the same LD, as shown in FIG. 2, for example, the differential quantum efficiency decreases (η → η ′ in FIG. 2) or the threshold current increases (Ith → Ith in FIG. ') Changes the drive current Iop for obtaining the optical output Po.

  Between the start of recording and the end of recording, the differential quantum efficiency η and the threshold current Ith fluctuate due to changes in LD temperature and time. That is, variations in the LD's differential quantum efficiency η and threshold current Ith due to elements, temperature fluctuations, etc. cause the optical output from the LD to the recording medium to fluctuate, leading to a decrease in writing quality and a writing error. FIG. 2 shows changes in Ith and η due to temperature fluctuation of a general LD. When the temperature of the LD rises (TL → TH), as shown in FIG. 2, the drive current (threshold current) Ith necessary for the LD to enter the light emitting state increases, and the differential quantum efficiency η decreases.

  In a conventional semiconductor laser drive circuit, as a method for preventing variations and temperature fluctuations due to elements of the differential quantum efficiency η and threshold current Ith of the LD, a part of the laser beam output of the LD is received by a light receiving element (monitor diode). APC (Auto Power Control) is used to monitor the drive current of the LD so that the optical output power of the LD becomes a desired power from the monitor signal.

  For example, Patent Document 1 describes details of a conventional LD driving device that performs such APC. In this LD driving device, the fluctuation of the threshold current Ith due to the LD temperature fluctuation is corrected by adding a bias current to the LD driving current so that the LD optical output becomes a constant optical output, The fluctuation of the differential quantum efficiency η due to the temperature fluctuation of the LD is output by a digital-to-analog converter (hereinafter referred to as PWDAC) corresponding to the recording power value of the selected register, and flows to the LD, and the k-folding control signal Is applied as a reference current to the PWDAC via a full-scale digital-analog converter (hereinafter referred to as a full-scale DAC), and the k-fold control signal is changed to change the inclination of the optical output of the LD with respect to the set value of the full-scale DAC. It is possible to correct by making the constant.

JP 2000-306255 A

  On the other hand, in the optical disk apparatus, with the demand for higher recording speed, the rotational speed of the recording medium is improved and the optical output Pw necessary for mark formation continues to increase. Further, in the recording medium, it is essential to improve the resolution of the optical output Pw for forming the recording mark (margin of appropriate optical output) as well as the recording sensitivity of the recording medium. However, especially in the phase change recording medium, it is difficult to widen the recording speed margin due to the characteristics of the recording material, and the increase in the maximum output of the light output Pw for forming the mark shape It is necessary to improve both output accuracy and control.

However, in the LD driving apparatus described in Patent Document 1 described above, the full scale of the PWDAC is set with reference to Pw, and the optical output of the set value of the PWDAC vs. the LD is made constant so that the variation in the differential quantum efficiency η and the temperature fluctuation are reduced. The absorption control method has the following problems 1 and 2.
Problem 1 is that when the linearity accuracy of the set value of the PWDAC versus the LD optical output is insufficient due to the characteristics of the LD, an error occurs in the actual optical output of the LD in the control of the recording current value by the above-described full-scale DAC. It is in that point.
Problem 2 is that when Pw increases as the recording speed increases, Pw is set to be large as a full-scale reference by the full-scale DAC, so that the resolution is reduced by Pw.

Hereinafter, Problem 1 will be described with reference to FIG.
FIG. 4 shows the LD driving current Iop versus optical output characteristics when the LD driving current Iop versus optical output Po has non-linearity due to the characteristics of the LD. The LD optical output Po = Pw necessary for forming a mark on the recording medium is used as a reference for the full-scale DAC. Here, since the setting value of PWDAC with respect to Pw is 8 bits, the optical output shown in FIG. 4 is maximum when the input Dw of PWDAC is FF′h. Further, Ibias is added to each of the recording current values Iw and Ie so that Ibias becomes equal to the threshold current Ith when the input Dw (DACdata) of PWDAC is 00′h.

  Conventionally, when the LD is driven with a current equal to or higher than the threshold current Ith, the optical output of the LD is controlled on the assumption that the differential quantum efficiency η increases linearly with the gradient as shown by the dotted line in FIG. . However, when the LD drive current versus optical output is non-linear due to LD characteristics or the like, that is, a curve as shown by a solid line in FIG. 4, for example, the optical output Pe for erasing the mark on the phase change recording medium is The actual light output Pe and Pe ′ predicted as the slope η are shifted by ΔPe, and accurate information recording on the recording medium is not performed.

  Also, if the drive current at which the optical output of the LD for forming the mark shape on the recording medium is increased by δIw due to the higher recording speed, the accuracy of the drive current per bit decreases by δ / 256. To do. That is, as shown in FIG. 5, the reference current of the PWDAC from the full-scale DAC is changed to Pw as described above, even though the optical output Pw necessary for mark formation is increased by increasing the recording speed. As a reference, the light output accuracy per 1 bit varies. Furthermore, in the high-speed recording medium, as described above, the sensitivity of the recording layer to the optical output of the LD is improved in order to support high-speed recording, but on the other hand, by improving the recording layer sensitivity and increasing the recording speed. The light output accuracy such as the light output Pw for forming an appropriate mark shape has become severe.

  The present invention makes it possible to accurately control the LD optical output even if the LD driving current versus the optical output has non-linearity due to the LD characteristics and the like, and further improve the setting accuracy of the LD optical output and It is an object of the present invention to provide a semiconductor laser driving device that can achieve stability and can simplify the control of the set value of the drive current setting DAC and the LD light output.

  In order to achieve the above object, the invention according to claim 1 is characterized in that the differential quantum efficiency detection means for detecting the differential quantum efficiency of the semiconductor laser and the differential quantum efficiency signal output from the differential quantum efficiency detection means are calculated. Bias current setting means for outputting a bias current substantially equal to the threshold current of the semiconductor laser, a driving current setting digital / analog converter for outputting the driving current of the semiconductor laser, and the driving current setting digital / analog conversion A full-scale setting digital / analog converter for setting the full scale of the detector, and a current adding means for adding the bias current from the bias current setting means and the driving current from the driving current setting digital-analog converter. In the semiconductor laser driving device comprising, for the set value of the digital-analog converter for setting the drive current When the optical output output from the semiconductor laser has non-linearity, the differential quantum efficiency of the semiconductor laser, the driving current setting digital-analog converter, and the full-scale setting digital-analog converter The semiconductor laser is determined by the approximate optical output resolution obtained from the product of the differential quantum efficiency and the slope calculated for each section, by dividing the slope of the drive current versus the optical output of the semiconductor laser determined by It has a function of controlling the light output of the.

  According to a second aspect of the present invention, in the semiconductor laser driving circuit according to the first aspect, the full-scale setting digital / analog converter may arbitrarily set the full-scale of the driving current setting digital-analog converter. Thus, the optical output resolution of the semiconductor laser is arbitrarily set.

  According to a third aspect of the present invention, in the semiconductor laser drive circuit according to the first or second aspect, the optical output resolution of the semiconductor laser is arbitrarily set by arbitrarily setting the number of divisions of the tilt. It is.

  According to a fourth aspect of the present invention, in the semiconductor laser drive circuit according to the third aspect, the number of divisions of the slope is 2 to the nth power, and the multiplier is less than or equal to the number of bits of the digital / analog converter for setting the drive current. Is.

  According to a fifth aspect of the present invention, in the semiconductor laser drive circuit according to any one of the first to fourth aspects, the function of canceling the variation in the differential quantum efficiency of the semiconductor laser by keeping the approximate optical output resolution constant. It is what has.

  According to a sixth aspect of the present invention, there is provided a differential quantum efficiency detection means for detecting a differential quantum efficiency of a semiconductor laser, and a threshold current of the semiconductor laser calculated from a differential quantum efficiency signal output from the differential quantum efficiency detection means. Bias current setting means for outputting substantially the same bias current, a digital / analog converter for setting the drive current for outputting the drive current of the semiconductor laser, and a full scale for setting the full scale of the digital / analog converter for setting the drive current Scale setting digital-to-analog converter, driving current biasing means for adding a predetermined bias current to the driving current, adding the driving current from the driving current biasing means and the bias current from the bias current setting means A semiconductor laser driving device comprising a current adding means, wherein the driving current bias means is the driving power supply. It is to slightly smaller than the current corresponding to the bias current to be added to the desired light output of the semiconductor laser.

  According to a seventh aspect of the invention, in the semiconductor laser drive circuit according to the sixth aspect, the bias setting means and the drive current bias means are common.

  According to an eighth aspect of the present invention, in the semiconductor laser driving circuit according to any one of the first to seventh aspects, the parameter of the optical output of the semiconductor laser by the driving current setting digital-analog converter is a recording medium. The calculation is performed at a part where writing is not performed by the optical output of the semiconductor laser.

  The invention according to claim 9 is the semiconductor laser drive circuit according to any one of claims 1 to 7, further comprising a parameter storage unit, and the optical output of the semiconductor laser by the digital-analog converter for setting the drive current. These parameters are calculated at the time of factory shipment inspection test and stored in the parameter storage unit.

  According to a tenth aspect of the present invention, in the semiconductor laser driving circuit according to any one of the first to ninth aspects, at least the driving current setting digital-analog converter and the full-scale setting digital-analog converter are provided. It is provided for each optical output of the semiconductor laser.

According to the present invention, even if the LD drive current vs. optical output characteristic has non-linearity due to the LD characteristic, more accurate optical output control is possible by dividing and approximating this.
According to the present invention, the optical output resolution setting can be arbitrarily and flexibly controlled even if the LD driving current versus the LD optical output characteristic is nonlinear due to the LD characteristic.

According to the present invention, the optical output resolution can be controlled with higher accuracy even if the LD drive current versus the optical output has nonlinearity due to the LD characteristics.
According to the present invention, it is possible to suppress variation in the differential quantum efficiency of the LD even if the LD driving current versus optical output has nonlinearity due to the LD characteristics.
According to the present invention, even if the optical output of the LD increases, the optical output resolution is not affected, and more accurate optical output control can be arbitrarily set.

According to the present invention, the chip area can be further reduced, and the cost can be reduced.
According to the present invention, it is possible to achieve higher reliability and higher optical output of the LD.
According to the present invention, highly accurate light output control is possible for each light output of the LD.

  FIG. 1 shows Embodiment 1 of an information recording / reproducing apparatus to which the present invention is applied. A recording medium 1 for recording / reproducing information is held by a spindle motor 2 and rotated. Examples of the recording medium 1 include optical disks such as a phase change recording medium, an organic dye-based recording medium, and a magneto-optical recording medium. Here, an optical disk is used. The optical pickup 3 includes an LD 4 as a light source that emits laser light for recording and reproducing information, and an optical that irradiates the surface of the optical disc 1 with light from the LD 4 to form a light spot of about 1 micron. A system (not shown, but in the optical pickup 3), a photodetector 5 for performing light spot control such as information reproduction, autofocus, track tracking, etc. using reflected light from the optical disc 1, and an LD 4 A laser driver 6 for driving, and recording and reproducing information on the optical disc 1; The optical pickup 3 constitutes a linear motor (not shown) for positioning the optical pickup 3 itself in the radial direction of the optical disc 1 at high speed.

  In general, an optical disk apparatus as an information recording / reproducing apparatus conforms to a standard of a host computer (hereinafter abbreviated as a host) 7 such as a personal computer or a workstation, and SCSI (Small Computer System Interface) or ATAPI (AT Attached Packet Interface). The interface control circuit 9 is composed of a microcomputer and the like, which is connected by an interface cable, decodes a command including instructions and information data from the host 7 by the interface control circuit 8 in the optical disc apparatus. The optical pickup 3 and the spindle motor 2 are controlled in accordance with the command decoded in step 8, and information recording, reproduction, and seek operations on the optical disc 1 are executed.

  The arithmetic / control circuit 9 calls an adjustment value stored in advance corresponding to the reproduction or recording of information from a storage circuit 10 such as a ROM made of a semiconductor memory, calculates the command value corresponding to that time, and calculates it. Is commanded to the laser driver 6 using, for example, a serial I / F or the like to obtain a target light emission amount from the LD 4. The adjustment value stored in the storage circuit 10 may be stored in a storage unit (not shown) built in the laser driver 6. The photodetector 5 receives the reflected light from the optical disc 1 and outputs an optical output signal to the arithmetic / control circuit 9. The arithmetic / control circuit 9 calculates a control signal for controlling the rotational speed of the spindle motor 2 from the light output signal from the light detector 5 and controls the spindle motor 2 by this control signal.

The arithmetic / control circuit 9 calculates the differential quantum efficiency of the LD 4 from the light intensity of at least two of the LD 4 obtained from the optical output signal from the photodetector 5 and the drive current Iop of the LD 4 at that time. The differential quantum efficiency detection means 11 is provided on a substrate (not shown) that incorporates the means 11 (see FIG. 6) or is mounted on the arithmetic / control circuit 9 or the like.
The LD driving apparatus according to the first embodiment includes a laser driver 6 on the optical pickup 3, a photodetector 5, and a part of the arithmetic / control circuit 9.

  This LD drive device includes a drive current setting DAC that sets a drive current to the LD4, a full scale setting DAC that sets the full scale of the drive current setting DAC, and a set value pair LD4 of the drive current setting DAC. Corresponding to the non-linearity of the optical output characteristics, there is provided computing means which is means for storing / calculating / setting the set values of the drive current setting DAC and the full scale setting DAC. As a result, the LD driving device can obtain a light output sufficiently approximated to the nonlinearity as described above, and can perform more accurate light output control.

  FIG. 6 shows a configuration example of the LD driving device according to the first embodiment. In FIG. 6, the same components as those in FIG. Each drive current setting DAC 601 to 604 is provided corresponding to Pw, Pe, Pr, and Pb (Ibias) shown in FIG. 3, and each drive current setting DAC 602 to 604 corresponding to Pw, Pe, and Pr is full. Full scale setting DACs 605 to 607 for changing the scale are provided. FIG. 7 shows drive currents that can be set by the drive current setting DACs 602 to 604 and the full scale setting DACs 605 to 607.

  That is, from FIG. 7, the slopes of the drive currents Iw, Ie, Ir are arbitrarily changed for each of the drive current setting DACs 602 to 604 according to the setting command from the arithmetic / control circuit 9 (a → a ′ in FIG. 7). be able to. Each of the drive current setting DACs 601 to 604 outputs each of the drive currents Iw, Ie, Ir, and Ib (Ibias) in accordance with a setting command from the arithmetic / control circuit 9, and the full scale setting DACs 605 to 607 are for setting each drive current. The full scales of the drive currents Iw, Ie, Ir from the DACs 601 to 604 are changed by setting commands from the arithmetic / control circuit 9, respectively. The light output characteristic of the set value pair LD4 of each of the drive current setting DACs 601 to 604 has non-linearity. The arithmetic / control circuit 9 includes the differential quantum efficiency of the LD 4 detected by the differential quantum efficiency detection means 11 and the drive current versus optical output characteristics of the LD 4 determined by the drive current setting DACs 602 to 604 and the full scale setting DACs 605 to 607. The slope of the laser is divided into arbitrary sections, the slope is linearly approximated, and the approximate optical output resolution obtained from the product of the differential quantum efficiency and the slope calculated for each section is kept constant, and the fluctuation of the differential quantum efficiency of LD4 The optical output of the LD 4 is controlled by controlling the drive current setting DACs 602 to 604 and the full scale setting DACs 605 to 607 so as to cancel.

  Each of the drive current setting DACs 602 to 604 and the full scale setting DACs 605 to 607 is provided with switches 608, 609, 610, and these switches 608, 609, 610 are turned on / off by a signal from the arithmetic / control circuit 9. . The drive currents from the full-scale setting DACs 605 to 607 are alternatively selected by the switches 608, 609, and 610 and input to the current adding circuit 611, where the bias current Ib (Ibias from the drive current setting DAC 601 is set. ) And supplied to the LD 4, an optical output having a waveform as shown in FIG. 3 is output from the LD 4. The photodetector 5 detects the front light of the LD 4 and the reflected light from the recording medium 1 and feeds back the detection signal to the arithmetic / control circuit 9.

  The arithmetic / control circuit 9 calculates a bias current substantially equal to the threshold current of the LD 4 (equal to or slightly larger than the threshold current) from the differential quantum efficiency detected by the differential quantum efficiency detection means 11. By issuing a command to the drive current setting DAC 601 to output a bias current Ib (Ibias) substantially equal to the threshold current of LD4 (equal to or slightly larger than the threshold current). Apply APC.

  FIG. 8 shows the set value PwDACdeta of the drive current setting DAC 604 versus the optical output Po when the set value of the drive current setting DAC 604 versus the optical output characteristic of the LD 4 has nonlinearity. However, since Abia is applied to Ibias as described above, the drive current Iop to LD4 when PwDAC = 00′h in FIG. 8 is Ibias. The characteristics of the setting value PwDACdeta of the optical output Po of the LD4 versus the DAC 604 for setting the driving current have nonlinearity due to the nonlinearity of the setting value of the driving current setting DAC604 to the optical output characteristic of the LD4 due to the characteristics of the LD4. .

  802 in FIG. 8 indicates a set value (input value) PwDACdeta versus optical output Po of a drive current setting DAC obtained by approximating a full-scale of Pw with a primary straight line as a target optical output reference of LD4 as in the prior art. In the first embodiment, the arithmetic / control circuit 9 divides the 8-bit set values 00′h to FF′h of the drive current setting DACs 602 to 604 by 2 to the nth power as indicated by a dotted line 801 in FIG. The number of divided bits n is arbitrary (the number of divided bits n is 8 or less), and the differential quantum efficiency η in any divided section such as each divided section D1'h to D2'h or D2'h to D3'h Then, an approximate light output resolution aη that is the product of the slopes a by the drive current setting DACs 602 to 604 and the full scale setting DACs 605 to 607 is obtained. A dotted line 801 in FIG. 8 indicates the set value PwDACdeta of the drive current setting DACs 602 to 604 and the optical output Po of the LD4 when n = 2. The approximate linear resolution aη of each divided section is calculated by the calculation / control circuit 9, and the drive current setting DACs 602 to 604 in each divided section are calculated by the respective drive current setting DACs 602 to 604 and full scale setting DACs 605 to 607 in FIG. By arbitrarily setting the slope of the light output characteristic of the set value LD4, the light output of the LD4 can be accurately controlled even when the light output characteristic has non-linearity.

  Further, FIG. 9 is an enlarged view of a part of FIG. 8 (one divided section), and the setting values D1′h to D2′h of the driving current setting DAC whose vertical axis is 8 bits are shown in FIG. 11 represents the ratio of the approximate optical output resolution aη and the approximate optical output resolution error δaη when interpolated with n = 3 or n = 4 as shown in FIG. 11, and the horizontal axis indicates the setting of the drive current setting DAC. It represents the value PwDACdeta. That is, by making it possible to arbitrarily set the division number of the set values of the drive current setting DACs 602 to 604 in the arithmetic / control circuit 9, a desired light output resolution can be set arbitrarily.

  Further, by using the above approximate optical output resolution aη, even if the drive current resolution of the drive current setting DACs 602 to 604 has non-linearity, the arithmetic / control circuit 9 satisfies a ′ = aη / η ′. By setting a 'to the full scale setting DAC 605 to 607 and changing the full scale of the drive current setting DACs 602 to 604 with the full scale setting DAC 605 to 607, the optical output resolution accuracy can be improved with respect to the temperature fluctuation of the differential quantum efficiency. Stabilization can be realized.

  Further, the optical output data of the set value of the drive current setting DACs 602 to 604 necessary for obtaining the appropriate number of divisions, that is, the interpolation straight line is written by, for example, the optical output of the LD 4 of the recording medium 1. The optical output data of the set value pair LD4 of the drive current setting DACs 602 to 604 corresponding to the number of divisions may be measured as described above using a portion that is not present, and stored in the internal register area of the ROM 10 or the laser driver 6 Further, the setting value of the driving current setting DACs 602 to 604 corresponding to the number of divisions as described above is used for the optical output data of the LD4 as described above by using the portion of the recording medium 1 that is not written by the LD4 optical output during the factory shipping test. The measurement data may be stored in the ROM 10.

According to the first embodiment, even if the set value of the drive current setting DACs 602 to 604 versus the optical output of the LD 4 has nonlinearity due to the characteristics of the LD 4, it is more accurate by dividing and approximating this. Light output control is possible.
According to the first embodiment, even if the set value of the drive current setting DACs 602 to 604 to the optical output of the LD4 has nonlinearity due to the characteristics of the LD4, the drive current setting is performed by the full scale setting DACs 605 to 607. The optical output resolution can be set by setting the full scale of the DACs 602 to 604 arbitrarily, or by setting the number of divisions of the slope to 2 to the nth power and making the multiplier less than the number of bits of the DACs 602 to 604 for setting the drive current. Optionally, more flexible control is possible.

According to the first embodiment, the drive current setting DACs 602 to 604 and the full scale setting are used even if the optical output of the LD4 optical output of the set values of the drive current setting DACs 602 to 604 is nonlinear due to the characteristics of the LD4. By arbitrarily setting the number of divisions of the inclination of the drive current versus the optical output of the LD 4 determined by the DACs 605 to 607, it becomes possible to control the optical output resolution with higher accuracy.
According to the first embodiment, even if the set value of the drive current setting DACs 602 to 604 versus the optical output of the LD 4 has nonlinearity due to the characteristics of the LD 4, the approximate optical output resolution is kept constant and the differential of the LD 4 is differentiated. It is possible to suppress variations in the differential quantum efficiency by canceling the fluctuations in the quantum efficiency.
According to the first embodiment, the relationship between the set values of the drive current setting DACs 602 to 604 and the optical output of the LD 4 is stored in advance, so that the optical output is more reliable and the optical output is more accurate. be able to.
According to the first embodiment, highly accurate light output control is possible for each light output of the LD 4.

Next, Embodiment 2 of the information recording / reproducing apparatus to which the present invention is applied will be described.
The second embodiment is provided with drive current bias setting means for obtaining a light output slightly smaller than the target light output in the first embodiment. As a result, the above-described non-linearity can be corrected, and the drive current setting DACs 602 to 600 that set the drive currents Iw, Ie, Ir by biasing the drive currents Iw, Ie, Ir of the LD 4. It is possible to reduce the number of bits of 604, and it is possible to prevent a decrease in optical output resolution due to the increase in the writing speed described above.

  FIG. 12 shows a configuration example of the second embodiment. 12, the same components as those in FIGS. 1 and 6 are denoted by the same reference numerals. In the second embodiment, drive current bias circuits 620 to 622 are provided as drive current bias setting means for outputting a bias current for obtaining a light output slightly smaller than the target light output of the LD 4 in the first embodiment. ing. The drive current bias circuits 620 to 622 generate bias currents for obtaining a light output slightly smaller than the target light output in response to a command from the arithmetic / control circuit 9.

  FIG. 13 shows the drive current versus optical output characteristics of the second embodiment. The target optical outputs of the LD 4 are Pr_target, Pe_target, and Pw_target, respectively. The bias currents Ir_bias, Ie_bias, and Iw_bias from each of the drive current bias circuits 620 to 622 are obtained from the drive current corresponding to the light output slightly lower than the target optical outputs Pr_target, Pe_target, and Pw_target by the calculation / control circuit 9, respectively. A value obtained by subtracting the bias current Ibias from the setting DAC 601 is set. The output from each of the DACs 605 to 607 for setting the full scale is added to the bias currents Ir_bias, Ie_bias, and Iw_bias from the drive current bias circuits 620 to 622, and the drive current is set by the current addition circuit 611 via the switches 608 to 610. The bias current Ibias from the DAC 601 is added, and the optical output of the LD 4 (optical output corresponding to the solid line portion in FIG. 13) is adjusted.

  Each of the drive current setting DACs 602 to 604 receives bias currents Ir_bias, Ie_bias, and Iw_bias from the drive current bias circuits 620 to 622 based on target optical outputs Pr_target, Pe_target, and Pw_target, respectively, according to a setting command from the arithmetic / control circuit 9. Each of the drive currents is output by subtracting the bias current Ibias from the drive current setting DAC 601 and the full scale setting DACs 605 to 607 correspond to the drive currents from the drive current setting DACs 601 to 604. Each scale is changed by a setting command from the arithmetic / control circuit 9. The drive current from each of the full-scale setting DACs 605 to 607 is added to the bias currents Ir_bias, Ie_bias, and Iw_bias from each of the drive current bias circuits 620 to 622, and the current addition circuit 611 applies a bias from the drive current setting DAC 601. By adding the current Ibias, an optical output having a waveform as shown in FIG. 3 is output from the LD 4.

  The arithmetic / control circuit 9 calculates the differential quantum efficiency of the LD 4 detected by the differential quantum efficiency detection means 11 and the drive current versus optical output of the LD 4 determined by the drive current setting DACs 602 to 604 and the full scale setting DACs 605 to 607. Fluctuation of the differential quantum efficiency of LD4 by dividing the slope into arbitrary sections and linearly approximating the slope, and keeping the approximate optical output resolution obtained from the product of the differential quantum efficiency calculated for each section and the above slope constant. The optical output of the LD 4 is controlled by controlling the drive current setting DACs 602 to 604 and the full scale setting DACs 605 to 607 so as to cancel.

  As in the first embodiment, the drive current setting DACs 602 to 604 are provided with full-scale setting DACs 605 to 607, so that the slope of the solid line portion in FIG. 13 can be arbitrarily changed as in the first embodiment. . That is, the drive current of the LD 4 is raised by the drive current bias circuits 620 to 622 to the drive current corresponding to the vicinity of the target optical outputs Pr_target, Pe_target, and Pw_target, and the drive current setting DACs 602 to 604 and the full scale setting are set. The optical output of the LD 4 is controlled by the DACs 605 to 607 by fine adjustment.

  In the second embodiment, the range of the drive current adjusted by each of the drive current setting DACs 602 to 604 and the full scale setting DACs 605 to 607 is narrowed. That is, more accurate light output control is possible with each target light output Pr_target, Pe_target, Pw_target, and further, the drive current setting DAC 602 for each arbitrary divided section near each target light output Pr_target, Pe_target, Pw_target The optical output resolution can be set by the 604 and the full scale setting DACs 605 to 607 to perform more accurate control. In particular, when the writing speed to the recording medium 1 is increased, the Pw resolution can be obtained with higher accuracy than when the full scale of the drive current setting DACs 602 to 604 is determined based on the recording power Pw.

  Further, when the drive current setting DACs 601 to 604 and the full scale setting DACs 605 to 607 are mounted on the laser driver 6, the laser driver has a configuration in which the drive current bias circuits 620 to 622 and the Pb (Ibias) setting DAC 601 are shared. 6 chip area can be reduced. Furthermore, the number of bits of the DAC can be reduced by narrowing the drive current range by the drive current setting DACs 602 to 604. That is, in the second embodiment, the light output control can be simplified and the area occupied by the DAC in the laser driver 6 can be reduced. Each drive current bias circuit 620 to 622 outputs a bias current obtained by adding the bias current Ib (Ibias) to the bias current Ir_bias, Ie_bias, Iw_bias, respectively, when the drive current bias circuit 620 to 622 is shared with the drive current setting DAC 601. Configured.

  According to the second embodiment, the drive current bias circuits 620 to 622 set the bias current added to the drive current from the drive current setting DACs 602 to 604 to be slightly smaller than the desired optical output of the LD 4, whereby the light of the LD 4 Even if the output increases, the optical output resolution is not affected, and more accurate optical output control can be arbitrarily set.

According to the second embodiment, the chip area of the laser driver 6 can be further reduced, and the cost can be reduced.
According to the second embodiment, the relationship between the set values of the drive current setting DACs 602 to 604 and the optical output of the LD 4 is stored in advance, so that the optical output is more reliable and the optical output is more accurate. be able to.
According to the second embodiment, highly accurate light output control is possible for each light output of the LD 4.

It is a block diagram which shows Embodiment 1 of the information recording / reproducing apparatus to which this invention is applied. It is a characteristic view which shows the optical output versus drive current characteristic of LD. It is a wave form diagram which shows the example of the optical waveform for recording to a phase change type recording medium. It is a characteristic view which shows the drive current Iop of LD vs the optical output characteristic. It is a characteristic view which shows the optical output characteristic of set value DACdata of LD of prior art WPDAC. It is a block diagram which shows the structural example of the LD drive device in the said Embodiment 1. FIG. FIG. 5 is a characteristic diagram illustrating a relationship between a set value of a drive current setting DAC and a drive current of an LD according to the first embodiment. FIG. 6 is a characteristic diagram showing a set value PwDACdeta vs. optical output characteristic of the drive current setting DAC in the first embodiment. FIG. 9 is a partially enlarged view of FIG. 8. The figure which shows ratio of approximate optical output resolution aeta and error deltaaeta of approximate optical output resolution when interpolation between setting value D1'h-D2'h of drive current setting DAC in the above-mentioned embodiment 1 by division bit number n = 3 It is. The figure which shows ratio of approximate optical output resolution aeta and error deltaaeta of approximate optical output resolution when interpolation between setting value D1'h-D2'h of drive current setting DAC in the above-mentioned embodiment 1 by division bit number n = 4 It is. It is a block diagram which shows Embodiment 2 of this invention. It is a characteristic view which shows the drive current versus optical output characteristic of the second embodiment.

Explanation of symbols

1 Recording medium 2 Spindle motor 3 Optical pickup 4 LD
5 Photodetector 6 Laser driver 7 Host 8 Interface control circuit 9 Arithmetic / control circuit 10 Memory circuit 11 Differential quantum efficiency detection means
601 to 604 Drive current setting DAC
605 to 607 DAC for full scale setting
608, 609, 610 switch
611 Current summing circuit
620 to 622 drive current bias circuit

Claims (10)

Differential quantum efficiency detection means for detecting the differential quantum efficiency of the semiconductor laser, and a bias current substantially equal to the threshold current of the semiconductor laser calculated from the differential quantum efficiency signal output from the differential quantum efficiency detection means is output. Bias current setting means, digital / analog converter for driving current setting for outputting the driving current of the semiconductor laser, and digital / analog conversion for full scale setting for setting the full scale of the digital / analog converter for setting the driving current A semiconductor laser driving device comprising: a current adding means for adding a bias current from the bias current setting means and a drive current from the driving current setting digital-analog converter;
When the optical output output from the semiconductor laser has non-linearity with respect to the setting value of the digital / analog converter for setting the driving current, the differential quantum efficiency of the semiconductor laser and the driving current setting The differential quantum efficiency calculated for each section obtained by dividing the slope of the optical output and the drive current of the semiconductor laser determined by the digital / analog converter and the full-scale setting digital / analog converter in an arbitrary section And a function of controlling the optical output of the semiconductor laser by an approximate optical output resolution obtained from the product of the inclination and the inclination.   2. The semiconductor laser drive circuit according to claim 1, wherein the full-scale setting digital / analog converter arbitrarily sets a full scale of the driving current setting digital-analog converter, thereby reducing the optical output resolution of the semiconductor laser. A semiconductor laser driving circuit having a function of arbitrarily setting   3. The semiconductor laser driving circuit according to claim 1, wherein the semiconductor laser driving circuit has a function of arbitrarily setting a light output resolution of the semiconductor laser by arbitrarily setting the number of divisions of the inclination. .   4. The semiconductor laser drive circuit according to claim 3, wherein the number of divisions of the slope is 2 to the nth power, and the multiplier is less than or equal to the number of bits of the digital / analog converter for setting the drive current. circuit.   5. The semiconductor laser drive circuit according to claim 1, wherein the semiconductor laser drive circuit has a function of canceling a variation in differential quantum efficiency of the semiconductor laser by keeping the approximate light output resolution constant. 6. Laser drive circuit. Differential quantum efficiency detection means for detecting the differential quantum efficiency of the semiconductor laser, and a bias for outputting a bias current substantially equal to the threshold current of the semiconductor laser calculated from the differential quantum efficiency signal output from the differential quantum efficiency detection means Current setting means, driving current setting digital / analog converter for outputting the driving current of the semiconductor laser, and full scale setting digital / analog converter for setting the full scale of the driving current setting digital / analog converter A semiconductor laser drive comprising: a driving current bias unit that adds a predetermined bias current to the driving current; and a current addition unit that adds the driving current from the driving current bias unit and the bias current from the bias current setting unit A device,
A semiconductor laser drive circuit, wherein the drive current bias means sets a bias current added to the drive current to be slightly smaller than a current corresponding to a desired optical output of the semiconductor laser.   7. The semiconductor laser drive circuit according to claim 6, wherein the bias setting means and the drive current bias means are common.   8. The semiconductor laser driving circuit according to claim 1, wherein the parameter of the optical output of the semiconductor laser by the digital / analog converter for setting the driving current depends on the optical output of the semiconductor laser of a recording medium. A semiconductor laser driving circuit characterized in that the calculation is performed in a portion where writing is not performed.   8. The semiconductor laser driving circuit according to claim 1, further comprising a parameter storage unit, wherein the parameter of the optical output of the semiconductor laser by the digital / analog converter for setting the driving current is measured in a factory shipment inspection test. A semiconductor laser driving circuit characterized in that it is calculated and stored in the parameter storage unit. 10. The semiconductor laser driving circuit according to claim 1, wherein at least the driving current setting digital / analog converter and the full scale setting digital / analog converter are provided for each optical output of the semiconductor laser. A semiconductor laser driving device provided in the above.

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