Semiconductor laser driving device

Abstract

The initial setting circuit (11) holds an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element (2). The differential amplifier (17) acquires, from the first light detection element (3), a measured light amount indicating the amount of light generated by the semiconductor laser element (2), and outputs a difference signal indicating the difference between the measured light amount and a target light amount. A correction circuit (13) corrects the initial setting value on the basis of the difference signal and generates a corrected setting value. The current generation circuit generates a drive current having a magnitude corresponding to the initial setting value or the correction setting value, and supplies the drive current to the semiconductor laser element (2). During an operation period in which the semiconductor laser element (2) is operated by continuously or intermittently supplying a drive current having a magnitude corresponding to the initial setting value or the correction setting value to the semiconductor laser element (2), the correction circuit (13) corrects the semiconductor laser element (2) on the basis of the difference signal. The correction setting value is generated or updated so as to reduce the difference between the measured light amount and the target light amount.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor laser driving device, a semiconductor laser driving method, and a distance measuring device. Background Art

[0002] Generally, the amount of light of a semiconductor laser element increases or decreases according to the temperature change of the element. In order to compensate for the change in the amount of light of a semiconductor laser element, for example, the technologies of Patent Documents 1 and 2 are disclosed. Patent Document 1 discloses that a fixed light output is obtained by taking into account the attenuation (droop) characteristics of a semiconductor laser element used in an image forming device such as a laser printer and a digital copier. Patent Document 2 discloses that the light amount correction accuracy is improved by performing a light amount correction corresponding to the change in the characteristics of a semiconductor laser element used in an image display device such as a laser scanning display in real time.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 5672845

[0006] Patent Document 2: Japanese Patent No. 5125390 Summary of the invention

[0007] Problems to be solved by the invention

[0008] Semiconductor laser elements are not only used in image forming devices and image display devices, but are also sometimes used in distance measuring devices such as ToF (Time of Flight) sensors. The ToF sensor measures the distance from the ToF sensor to the object based on the transmission time of light from radiating light toward the object to being reflected by the object. The ToF sensor can process three-dimensional information including not only distance information in the Z direction but also planar information in the XY direction.

[0009] The semiconductor laser element used in the ToF sensor continuously generates short-width light pulses in order to accurately measure the transmission time of light. In addition, the attenuation caused by the reflection in the object and the attenuation during transmission will affect the sensing of the light detection element. Therefore, it is necessary to generate a sufficiently large amount of light from the semiconductor laser element. Generally speaking, compared with the semiconductor laser element used in the image forming device or the image display device, the semiconductor laser element used in the ToF sensor requires driving with a large current and high speed according to the distance and accuracy. However, when the semiconductor laser element is driven with a large current and high speed, the increase in temperature caused by the heat of the semiconductor laser element itself becomes significant. Therefore, it is required that even if the temperature of the semiconductor laser element changes due to the heat of the semiconductor laser element itself or other heat sources present in the utilization environment of the semiconductor laser element, it is not easy to produce a change in the amount of light of the semiconductor laser element.

[0010] The object of the present disclosure is to provide a semiconductor laser driving device and a semiconductor laser driving method, which are not likely to cause a change in the light amount of the semiconductor laser element even if the temperature of the semiconductor laser element changes due to the heat of the semiconductor laser element itself or other heat sources. Furthermore, the object of the present disclosure is to provide a distance measuring device having such a semiconductor laser driving device.

[0011] Means for solving problems

[0012] A semiconductor laser driving device according to one aspect of the present disclosure is a semiconductor laser driving device that drives a semiconductor laser element, and includes:

[0013] an initial setting circuit for holding an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element;

[0014] a differential amplifier that obtains a measurement light amount representing the amount of light generated by the semiconductor laser element from the first light detection element and outputs a difference signal representing a difference between the measurement light amount and the target light amount;

[0015] a correction circuit, which corrects the initial setting value based on the difference signal to generate a corrected setting value; and

[0016] a current generating circuit that generates a driving current having a magnitude corresponding to the initial setting value or the correction setting value and supplies the driving current to the semiconductor laser element,

[0017] During the period in which the semiconductor laser element is operated by continuously or intermittently supplying the driving current having a magnitude corresponding to the initial setting value or the correction setting value, the correction circuit generates or updates the correction setting value based on the difference signal in a manner that reduces the difference between the measured light amount and the target light amount.

[0018] Effects of the Invention

[0019] According to the semiconductor laser driving device according to one aspect of the present disclosure, even if the temperature of the semiconductor laser element changes due to heat generated by the semiconductor laser element itself or other heat sources, the light intensity of the semiconductor laser element can be less likely to change. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a block diagram showing the structure of the semiconductor laser driving device 1 according to the first embodiment.

[0021] Figure 2 It is shown by Figure 1 FIG. 1 is a graph showing an example of characteristics of light quantity with respect to current of a semiconductor laser element 2 driven by a semiconductor laser driving device 1 .

[0022] Figure 3 It is shown by Figure 1 FIG. 2 is a graph showing an example of a temporal change in the amount of light of a semiconductor laser element 2 driven by a semiconductor laser driving device 1 .

[0023] Figure 4 It is shown Figure 1 A timing chart showing an operation example of the semiconductor laser driving device 1.

[0024] Figure 5 It is shown Figure 1 1 is a timing chart of another operation example of the semiconductor laser driving device 1.

[0025] Figure 6 It is a block diagram showing the structure of a semiconductor laser driving device 1A according to a first comparative example.

[0026] Figure 7 1 is a block diagram showing a configuration of a semiconductor laser driving device 1B according to a second comparative example.

[0027] Figure 8 It is shown by Figure 6 A semiconductor laser driving device 1A or Figure 7 FIG. 2 is a graph showing an example of a temporal change in the amount of light of the semiconductor laser element 2 driven by the semiconductor laser driving device 1B.

[0028] Fig. 9 It is a block diagram showing a configuration of a semiconductor laser driving device 1C according to a modification of the first embodiment.

[0029] Fig.10 It is a block diagram showing the structure of a distance measurement device 20 according to the second embodiment. DETAILED DESCRIPTION

[0030] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The same structural elements are denoted by the same reference numerals across the various drawings.

[0031] [First embodiment]

[0032] [Structure of the first embodiment]

[0033] Figure 1 1 is a block diagram showing the structure of a semiconductor laser driving device 1 according to the first embodiment. The semiconductor laser driving device 1 supplies a driving current Iop to a semiconductor laser element 2 to drive the semiconductor laser element 2. The semiconductor laser driving device 1 obtains a measurement light amount indicating the amount of light generated by the semiconductor laser element 2 from a light detection element 3, and determines the magnitude of the driving current based on the measurement light amount.

[0034] The semiconductor laser element 2 is, for example, a laser diode. The light detecting element 3 is, for example, a photodiode. The light detecting element 3 may be provided separately from the semiconductor laser element 2 or may be integrated with the semiconductor laser element 2.

[0035] The semiconductor laser driving device 1 includes an initial setting circuit 11, a digital / analog converter (DAC) 12, a correction circuit 13, a digital / analog converter (DAC) 14, a switch 15, a reference voltage source 16, and a differential amplifier 17. Each component of the semiconductor laser driving device 1 operates according to a clock signal Sclk supplied from the outside.

[0036] The initial setting circuit 11 maintains an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element 2. The initial setting value is a combination of a digital code value Sbi representing the magnitude of the bias current Ibi and a digital code value Smod0 representing the magnitude of the modulation current Imod. The bias current Ibi can also be set to be equal to the minimum value of the current at which the semiconductor laser element 2 starts to emit light, that is, the threshold current Ith. When the current flowing through the semiconductor laser element 2 is less than the threshold current Ith, the semiconductor laser element 2 does not emit light at all, or hardly emits light. The bias current Ibi and the modulation current Imod are set so that when their sum flows through the semiconductor laser element 2, the light amount of the semiconductor laser element 2 is equal to the target light amount. The initial setting circuit 11 performs APC (Automatic Power Control) based on the difference signal Sdiff (described later) output from the differential amplifier 17 according to the control signal Sinit, thereby predetermining the digital code values ​​Sbi and Smod0. The initial setting circuit 11 stores the digital code values ​​Sbi and Smod0 in an internal memory 11m.

[0037] The digital / analog converter 12 converts the digital code value Sbi into a bias current Ibi having a corresponding current value.

[0038] The correction circuit 13 corrects the digital code value Smod0 based on the difference signal Sdiff (described later) output from the differential amplifier 17 according to the control signal Srun, and generates a corrected digital code value Smod. The correction circuit 13 stores the digital code values ​​Smod0 and Smod in an internal memory 13m.

[0039] In this specification, the combination of the digital code values ​​Sbi and Smod is also referred to as a “corrected setting value.” In other words, the correction circuit 13 corrects the initial setting value based on the difference signal Sdiff to generate the corrected setting value.

[0040] The digital / analog converter 14 converts the digital code value Smod into a modulation current Imod having a corresponding current value.

[0041] The switch 15 passes or cuts off the modulation current Imod according to the control signal Son. Therefore, when the switch 15 is turned on (ON), the sum of the bias current Ibi and the modulation current Imod is supplied as the drive current Iop to the semiconductor laser element 2. In addition, when the switch 15 is turned off (OFF), only the bias current Ibi is supplied to the semiconductor laser element 2.

[0042] The light detection element 3 generates a measurement voltage indicating the magnitude of the measured light quantity. The reference voltage source 16 generates a reference voltage indicating the magnitude of the target light quantity. The differential amplifier 17 obtains the measurement voltage from the light detection element 3, obtains the reference voltage from the reference voltage source 16, and outputs a difference signal Sdiff indicating the difference between the measured light quantity and the target light quantity. The differential amplifier 17 is, for example, an operational amplifier. As described above, the initial setting circuit 11 predetermines the initial setting value based on the difference signal Sdiff, and the correction circuit 13 corrects the initial setting value based on the difference signal Sdiff to generate a corrected setting value.

[0043] The semiconductor laser driving device 1 has at least two periods with different action modes, namely, an initial setting period and an action period. During the initial setting period, the semiconductor laser driving device 1 determines an initial setting value corresponding to a target light quantity by gradually increasing the driving current Iop from zero. During the action period, the semiconductor laser driving device 1 continuously or intermittently supplies a driving current Iop having a size corresponding to the initial setting value or the corrected setting value to the semiconductor laser element 2 to cause the semiconductor laser element 2 to operate. During the action period, the correction circuit 13 generates or updates the corrected setting value based on the difference signal Sdiff in a manner that reduces the difference between the measured light quantity and the target light quantity. Thus, the size of the driving current Iop can be corrected during the action period, so that even if the temperature of the semiconductor laser element 2 changes due to the heat of the semiconductor laser element 2 itself or other heat sources, it is not easy to produce a change in the light quantity of the semiconductor laser element 2.

[0044] The digital / analog converter 12, the digital / analog converter 14, and the switch 15 are an example of a current generating circuit that generates a drive current Iop having a magnitude corresponding to an initial setting value or a modified setting value and supplies it to the semiconductor laser element 2. The digital / analog converter 12 is an example of a first current source that generates a bias current Ibi. The digital / analog converter 14 and the switch 15 are an example of a second current source that generates a modulation current Imod.

[0045] [Operation of the First Embodiment]

[0046] Figure 2 It is shown by Figure 1A graph showing an example of the characteristics of the amount of light of a semiconductor laser element 2 driven by a semiconductor laser driving device 1 relative to the current. As mentioned above, when the current flowing through the semiconductor laser element 2 is less than the threshold current Ith, the semiconductor laser element 2 does not emit light at all or hardly emits light. If the current flowing through the semiconductor laser element 2 exceeds the threshold current Ith, the semiconductor laser element 2 begins to emit light, and then the amount of light increases in proportion to the increase in current. The bias current Ibi and the modulation current Imod1 are set so that when their sum flows through the semiconductor laser element 2, the amount of light of the semiconductor laser element 2 is equal to the target amount of light.

[0047] In addition, if the semiconductor laser element 2 is operated, the semiconductor laser element 2 itself generates heat, and the characteristics of the semiconductor laser element 2 (for example, the magnitude of the threshold current, the slope of the light quantity / current characteristic) change. Since the light quantity decreases according to the increase in temperature, even if the sum of the bias current Ibi and the modulation current Imod1 flows through the semiconductor laser element 2, the measured light quantity becomes less than the target light quantity. Therefore, the semiconductor laser driving device 1 generates a modulation current Imod2 obtained by increasing the modulation current Imod1. The modulation current Imod2 is set so that when the sum of the bias current Ibi and the modulation current Imod2 flows through the semiconductor laser element 2, the light quantity of the semiconductor laser element 2 is equal to the target light quantity.

[0048] When the measured current is greater than the target current, a modulation current Imod3 is generated by reducing the modulation current Imod1. The modulation current Imod3 is set so that when the sum of the bias current Ibi and the modulation current Imod3 flows through the semiconductor laser element 2, the light amount of the semiconductor laser element 2 is equal to the target light amount.

[0049] Figure 3 It is shown by Figure 1 A graph showing an example of the temporal change in the amount of light of a semiconductor laser element 2 driven by a semiconductor laser driving device 1. For example, when the semiconductor laser element 2 is used in a ToF sensor, the driving current Iop is intermittently supplied to the semiconductor laser element 2 at a period of tens of MHz, so that the semiconductor laser element 2 continuously generates short-width light pulses. However, as mentioned above, if the semiconductor laser element 2 is operated, the semiconductor laser element 2 itself generates heat, and there is a possibility that the amount of light gradually decreases. According to this embodiment, by correcting the size of the driving current Iop during the operation period, it is possible to prevent the amount of light of the semiconductor laser element 2 from changing.

[0050] Figure 4 It is shown Figure 1 A timing chart showing an operation example of the semiconductor laser driving device 1. Figure 4 The temporal changes of the control signals Sinit, Srun, Son, the clock signal Sclk, the digital code values ​​Snbi, Smod, and the light amount are shown.

[0051] In the initial state, the control signal Srun is at a low level (L), and the correction circuit 13 does not correct the input digital code value Smod0 but directly outputs it as the digital code value Smod. In the initial state, the control signal Son is at a low level, and the switch 51 is off.

[0052] When the control signal Sinit changes from a low level to a high level (H), the initial setting period begins, and the initial setting circuit 11 performs APC. The initial setting circuit 11 gradually increases the digital code value Sbi while referring to the difference signal Sdiff, and maintains the digital code value bi1 when the light quantity begins to increase at a rate higher than the predetermined rate of change. Next, the control signal Son changes from a low level to a high level, and the switch 15 is turned on. The initial setting circuit 11 gradually increases the digital code value Smod0 while referring to the difference signal Sdiff, and maintains the digital code value mod1 when the measured light quantity reaches the target light quantity. The initial setting circuit 11 uses the digital code values ​​bi and mod1 as the initial setting values ​​corresponding to the target light quantity, that is, as the digital code values ​​Sbi and Smod0 and maintains them. Thereafter, the control signals Sinit and Son change from a high level to a low level, and the initial setting period ends.

[0053] After that, the semiconductor laser driving device 1 starts an operation period for lighting the semiconductor laser element 2 for the desired task. The operation period includes a first time interval in which only the bias current Ibi is supplied to the semiconductor laser element 2, and a second time interval in which the sum of the bias current Ibi and the modulation current Imod is supplied to the semiconductor laser element 2 as the drive current Iop, and the first time interval and the second time interval are repeated alternately.

[0054] In the first operation section, the control signal Son is at a low level, and the switch 51 is turned off. On the other hand, in the second operation section, the control signal Son is at a high level, and the switch 51 is turned on.

[0055] In addition, in the first action interval, the control signal Srun is set to a low level. In this case, the correction circuit 13 does not perform correction of the digital code value Smod0 based on the difference signal Sdiff. When the digital code value Smod is consistent with the digital code value Smod0 of the initial setting value (time interval t3~t4), the correction circuit 13 maintains the digital code value Smod as it is. When the digital code value Smod is corrected to a value different from the digital code value Smod0 of the initial setting value (time interval t5~t6), the correction circuit 13 may also change the corrected setting value in a manner close to the initial setting value at each specified cycle of the clock signal Sclk. Figure 4 In the example, the digital code value Smod is reduced to approach the digital code value mod1. This is because, considering that the modulation current Imod is not supplied to the semiconductor laser element 2 over a specified time, the temperature of the semiconductor laser element 2 drops, and therefore the corrected digital code value Smod becomes too large relative to the target light amount. On the other hand, in the second action interval, the control signal Srun is set to a high level. In this case, the correction circuit 13 corrects the digital code value Smod0 based on the difference signal Sdiff in a manner that reduces the difference between the measured light amount and the target light amount, thereby generating a corrected digital code value Smod. Figure 4 In the example, the digital code value Smod gradually increases.

[0056] In the case where the digital code value Smod0 is not corrected by the correction circuit 13, Figure 4 As shown by the bottom dashed line (“no correction”), the light quantity may gradually decrease. According to this embodiment, by correcting the magnitude of the drive current Iop during the operation period, the light quantity of the semiconductor laser element 2 can be less likely to change.

[0057] The cycle and step width (step width in Japanese) of changing the digital code value by the initial setting circuit 11 and the correction circuit 13 may also be determined according to the application and use environment of the semiconductor laser element 2 .

[0058] Figure 5 It is shown Figure 1 The timing chart of another operation example of the semiconductor laser driving device 1. The correction circuit 13 keeps the current immediately before the transition from the second time interval to the first time interval ( Figure 5 At time t5) the digital code value Smod is Figure 5 In the example of , the correction circuit 13 holds the digital code value mod2 as the digital code value Smod. When the first time interval is transferred to the second time interval ( Figure 5At time t6, the semiconductor laser driving device 1 generates a driving current Iop having a magnitude corresponding to the digital code values ​​Sbi and Smod held, and supplies it to the semiconductor laser element 2. For example, when the first time interval and the second time interval are alternated in a short cycle, the temperature change of the semiconductor laser element 2 during the period when the modulated current Imod is not supplied to the semiconductor laser element 2 can be ignored. In this case, by holding the digital code value Smod when the semiconductor laser element 2 was turned on in the immediately previous cycle, it is possible to reduce the change in the amount of light when the semiconductor laser element 2 is turned on next time.

[0059] [Comparative Example]

[0060] Figure 6 1 is a block diagram showing the structure of a semiconductor laser driving device 1A according to a first comparative example. The semiconductor laser driving device 1A has Figure 1 The semiconductor laser driving device 1 is a structure in which the correction circuit 13 is removed. Figure 6 The structure is used, for example, to drive a semiconductor laser element for a general image forming device or an image display device. The image forming device and the image display device scan a frame including an image area and a non-image area in a raster scan manner. When the non-image area is being scanned, the semiconductor laser driver 1A can correct the light amount of the semiconductor laser element 2 according to the ambient temperature by forcibly lighting the semiconductor laser element 2 and performing APC. However, after performing APC, for example, when the image area is being scanned, the semiconductor laser driver 1A cannot correct the light amount of the semiconductor laser element 2. Therefore, in Figure 6 In the structure, the light intensity of the semiconductor laser element 2 may increase or decrease according to the temperature change of the semiconductor laser element 2.

[0061] Figure 7 : is a block diagram showing the structure of a semiconductor laser driving device 1B according to a second comparative example. Figure 1 The semiconductor laser driving device 1B includes a correction circuit 13B and a memory 18. The memory 18 stores a predetermined pattern for correcting the digital code value Smod0. The correction circuit 13B corrects the digital code value Smod0 based on the pattern read from the memory 18 and generates a corrected digital code value Smod. Figure 7The structure assumes that the surrounding environment of the semiconductor laser element will not change significantly, such as laser printers and digital copiers, and requires the premise that the light amount of the semiconductor laser element 2 can be estimated according to the temperature change of the semiconductor laser element 2. Therefore, the use environment is not necessarily fixed, and in the case of unpredictable environmental changes, such as ToF sensors, Figure 7 The structure cannot follow the changes in the light intensity of the semiconductor laser element 2.

[0062] Figure 8 It is shown by Figure 6 A semiconductor laser driving device 1A or Figure 7 FIG. 1 is a graph showing an example of a temporal change in the amount of light of the semiconductor laser element 2 driven by the semiconductor laser driving device 1B. Figure 6 as well as Figure 7 With the structure, when the semiconductor laser element 2 is operated, the semiconductor laser element 2 itself generates heat, and there is a possibility that the light intensity will gradually decrease.

[0063] On the other hand, according to the semiconductor laser driving device 1 of the present embodiment, by correcting the magnitude of the driving current Iop during the operation period, as shown in FIG. Figure 3 As described above, the light quantity of the semiconductor laser element 2 is unlikely to change. In addition, according to the semiconductor laser driving device 1 involved in this embodiment, as Figure 7 As shown, the correction pattern pre-stored in the storage device can be used to follow any light quantity change according to the use environment. In addition, the semiconductor laser driving device 1 according to this embodiment can respond immediately even to a sudden change in light quantity.

[0064] [Modification of the first embodiment]

[0065] Fig. 9 1 is a block diagram showing a configuration of a semiconductor laser driving device 1C according to a modification of the first embodiment. Figure 1 The semiconductor laser driving device 1 has an initial setting circuit 11, and the semiconductor laser driving device 1C has an initial setting circuit 11C. The initial setting circuit 11C does not execute APC, and stores a predetermined initial setting value in an internal memory 11m. Since APC is not executed, Figure 1 can reduce costs compared to the previous situation.

[0066] [Second embodiment]

[0067] Fig.101 is a block diagram showing a configuration of a distance measurement device 20 according to the second embodiment. The distance measurement device 20 includes a semiconductor laser driving device 1 , a semiconductor laser element 2 , a photodetection element 3 , a photodetection element 4 , and a processing circuit 5 . Fig.10 A semiconductor laser driving device 1, a semiconductor laser element 2, and a light detecting element 3 and Figure 1 The corresponding components of the distance measuring device 20 are configured in the same manner. The light detecting element 4 obtains the reflected light amount indicating the amount of light generated by the semiconductor laser element 2 and reflected by the object 30. The processing circuit 5 calculates the distance from the distance measuring device 20 to the object 30 based on the reflected light amount. The processing circuit 5 generates Figure 1 The clock signal Sclk and the control signals Sinit, Srun, and Son of the distance measuring device 20 are, for example, a ToF sensor that obtains a three-dimensional image of the object 30 observed from the distance measuring device 20. The distance measuring device 20 includes the semiconductor laser driving device 1 involved in the first embodiment, so that even if the temperature of the semiconductor laser element 2 changes due to the heat generated by the semiconductor laser element 2 itself or other heat sources, the light amount of the semiconductor laser element 2 is not easily changed. Therefore, the distance measuring device 20 can calculate the distance from the distance measuring device 20 to the object 30 with high accuracy.

[0068] [Other Modifications]

[0069] exist Figure 4 as well as Figure 5 In the above description, the digital code value Smod of the correction setting value is generated so as to be larger than the digital code value Smod0 of the initial setting value. However, the digital code value Smod may be generated so as to be smaller than the digital code value Smod0 depending on the usage environment of the semiconductor laser element 2.

[0070] In consideration of a significant change in the threshold current Ith, the initial setting circuit 11 may perform APC again.

[0071] [Summary of Implementation Methods]

[0072] The semiconductor laser driving device 1 involved in the first embodiment of the present disclosure is a semiconductor laser driving device 1 that drives a semiconductor laser element 2, and includes: an initial setting circuit 11, a differential amplifier 17, a correction circuit 13, and a current generating circuit. The initial setting circuit 11 maintains an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element 2. The differential amplifier 17 obtains a measured light amount representing the light amount generated by the semiconductor laser element 2 from the first light detection element 3, and outputs a difference signal Sdiff representing the difference between the measured light amount and the target light amount. The correction circuit 13 corrects the initial setting value based on the difference signal Sdiff to generate a corrected setting value. The current generating circuit generates a driving current Iop having a size corresponding to the initial setting value or the corrected setting value, and supplies it to the semiconductor laser element 2. During the operation period in which the semiconductor laser element 2 is operated by continuously or intermittently supplying a driving current Iop having a size corresponding to the initial setting value or the correction setting value, the correction circuit 13 generates or updates the correction setting value based on the difference signal Sdiff in a manner that reduces the difference between the measured light amount and the target light amount.

[0073] According to the semiconductor laser driving device 1 involved in the second embodiment of the present disclosure, the semiconductor laser driving device 1 involved in the first embodiment can also be configured as follows. The current generating circuit includes: a first current source that generates a bias current Ibi, and a second current source that generates a modulation current Imod. The operation period includes a first time interval and a second time interval that alternate with each other. In the first time interval, the current generating circuit supplies the bias current Ibi to the semiconductor laser element 2. In the second time interval, the current generating circuit supplies the sum of the bias current Ibi and the modulation current Imod to the semiconductor laser element 2 as a driving current Iop.

[0074] According to the semiconductor laser driving device 1 according to the third aspect of the present disclosure, the semiconductor laser driving device 1 according to the first or second aspect may be configured as follows: In the first time interval, the correction circuit 13 changes the correction setting value so as to approach the initial setting value at every predetermined cycle.

[0075] According to the semiconductor laser driving device 1 involved in the fourth aspect of the present disclosure, the semiconductor laser driving device 1 involved in the first or second aspect can also be configured as follows. The correction circuit 13 holds the correction setting value immediately before the transition from the second time interval to the first time interval. When the transition from the first time interval to the second time interval occurs, the current generating circuit generates a driving current Iop having a magnitude corresponding to the held correction setting value and supplies it to the semiconductor laser element 2.

[0076] According to the semiconductor laser driving device 1 according to the fifth aspect of the present disclosure, the semiconductor laser driving device 1 according to one of the first to fourth aspects may be configured as follows: The initial setting circuit 11 determines an initial setting value in advance based on the difference signal Sdiff.

[0077] According to the semiconductor laser driving device 1C according to the sixth aspect of the present disclosure, the semiconductor laser driving device 1 according to one of the first to fourth aspects may be configured as follows: The initial setting circuit 11C holds a predetermined initial setting value.

[0078] The distance measuring device 20 involved in the seventh embodiment of the present invention comprises: a semiconductor laser driving device 1 involved in one of the first to seventh embodiments; a semiconductor laser element 2; a first light detection element 3, which obtains a measurement light amount representing the amount of light generated by the semiconductor laser element 2; a second light detection element 4, which obtains a reflected light amount representing the amount of light generated by the semiconductor laser element 2 and reflected by an object; and a processing circuit 5, which calculates the distance to the object based on the reflected light amount.

[0079] The semiconductor laser driving method involved in the eighth mode of the present disclosure is a semiconductor laser driving method for driving a semiconductor laser element 2, comprising the following steps. The method includes: a step of maintaining an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element 2. The method includes: obtaining a measurement light amount representing the light amount generated by the semiconductor laser element 2 from a first light detection element, and outputting a difference signal Sdiff representing the difference between the measurement light amount and the target light amount. The method includes: a step of correcting the initial setting value based on the difference signal Sdiff, generating a correction setting value, and a step of generating a drive current Iop having a size corresponding to the initial setting value or the correction setting value, and supplying it to the semiconductor laser element 2. The step of generating the correction setting value includes: during the operation period in which the drive current Iop having a size corresponding to the initial setting value or the correction setting value is continuously or intermittently supplied to the semiconductor laser element 2 to cause the semiconductor laser element 2 to operate, based on the difference signal Sdiff, generating or updating the correction setting value in a manner that reduces the difference between the measurement light amount and the target light amount.

[0080] Explanation of symbols

[0081] 1, 1A~1C semiconductor laser driving device; 2 semiconductor laser element; 3 light detection element; 4 light detection element; 5 processing circuit; 11, 11C initial setting circuit; 11m memory; 12 digital / analog converter (DAC); 13, 13B correction circuit; 13m memory; n14 digital / analog converter (DAC); 15 switch; 16 reference voltage source; 17 differential amplifier; 18 memory; 20 distance measuring device; 30 object.

Claims

1. A semiconductor laser driving device, which is a semiconductor laser driving device for driving a semiconductor laser element, comprising: an initial setting circuit for holding an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element; a differential amplifier that obtains a measurement light amount representing the amount of light generated by the semiconductor laser element from the first light detection element and outputs a difference signal representing a difference between the measurement light amount and the target light amount; A correction circuit, which corrects the initial setting value based on the difference signal to generate a corrected setting value; as well as a current generating circuit that generates a driving current having a magnitude corresponding to the initial setting value or the correction setting value and supplies the driving current to the semiconductor laser element, During the period in which the semiconductor laser element is operated by continuously or intermittently supplying the driving current having a magnitude corresponding to the initial setting value or the correction setting value, the correction circuit generates or updates the correction setting value based on the difference signal in a manner that reduces the difference between the measured light amount and the target light amount.

2. The semiconductor laser driving device according to claim 1, wherein: The current generating circuit comprises: a first current source generating a bias current, and a second current source generating a modulation current. The action period includes a first time interval and a second time interval that alternate with each other. In the first time interval, the current generating circuit supplies the bias current to the semiconductor laser element. In the second time period, the current generating circuit supplies the sum of the bias current and the modulation current to the semiconductor laser element as the driving current.

3. The semiconductor laser driving device according to claim 2, wherein: In the first time interval, the correction circuit changes the correction setting value so as to approach the initial setting value at every predetermined cycle.

4. The semiconductor laser driving device according to claim 2, wherein: the correction circuit holds the correction setting value immediately before the transition from the second time interval to the first time interval, When the first time period shifts to the second time period, the current generating circuit generates a driving current having a magnitude corresponding to the held correction setting value and supplies the driving current to the semiconductor laser element.

5. The semiconductor laser driving device according to any one of claims 1 to 4, wherein: The initial setting circuit predetermines the initial setting value based on the difference signal.

6. The semiconductor laser driving device according to any one of claims 1 to 4, wherein: The initial setting circuit holds the predetermined initial setting value.

7. A distance measuring device comprising: The semiconductor laser driving device according to claim 1; Semiconductor laser components; a first light detecting element that acquires a measured light amount representing an amount of light generated by the semiconductor laser element; a second light detecting element for acquiring a reflected light amount indicating an amount of light generated by the semiconductor laser element and reflected by an object; as well as The processing circuit calculates the distance to the object based on the amount of reflected light.

8. A semiconductor laser driving method, which is a semiconductor laser driving method for driving a semiconductor laser element, comprising: a step of maintaining an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element; a step of acquiring a measurement light amount indicating the amount of light generated by the semiconductor laser element from a first light detection element, and outputting a difference signal indicating the difference between the measurement light amount and the target light amount; The step of modifying the initial setting value based on the difference signal to generate a modified setting value; as well as a step of generating a drive current having a magnitude corresponding to the initial setting value or the correction setting value and supplying the drive current to the semiconductor laser element, The step of generating the correction setting value includes: during the operation period in which the driving current having a size corresponding to the initial setting value or the correction setting value is continuously or intermittently supplied to the semiconductor laser element to cause the semiconductor laser element to operate, the correction setting value is generated or updated based on the difference signal in a manner that reduces the difference between the measured light amount and the target light amount.

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