WO2024013948A1

WO2024013948A1 - Semiconductor laser drive device

Info

Publication number: WO2024013948A1
Application number: PCT/JP2022/027745
Authority: WO
Inventors: 一貴竹内
Original assignee: 日清紡マイクロデバイス株式会社
Priority date: 2022-07-14
Filing date: 2022-07-14
Publication date: 2024-01-18

Abstract

In the present invention, an initial setting circuit (11) holds an initial setting value corresponding to a preset target light amount of a semiconductor laser element (2). A differential amplifier (17) acquires, from a first optical detection element (3), a measured light amount indicating the light amount generated by the semiconductor laser element (2), and outputs a difference signal indicating the difference between the measured light amount and the target light amount. A correction circuit (13) generates a correction setting value by correcting the initial setting value on the basis of the difference signal. A current generating circuit generates and supplies to the semiconductor laser element (2) a drive current having a magnitude corresponding to the initial setting value or the corrected setting value. The correction circuit (13), during an operation period in which the drive current having a magnitude corresponding to the initial setting value or the corrected setting value is continuously or intermittently supplied to the semiconductor laser element (2) to operate the semiconductor laser element (2), generates or updates the corrected setting value on the basis of the difference signal so as to reduce the difference between the measured light amount and the target light amount.

Description

Semiconductor laser drive device

The present disclosure relates to a semiconductor laser driving device, a semiconductor laser driving method, and a distance measuring device.

In general, the amount of light from a semiconductor laser element increases or decreases depending on the temperature change of the element. In order to compensate for changes in the amount of light from a semiconductor laser element, techniques disclosed in

Patent Documents

1 and 2, for example, have been disclosed. Patent Document 1 discloses that a constant optical output is obtained by taking into consideration the droop characteristics of a semiconductor laser element used in an image forming apparatus such as a laser printer and a digital copying machine. Patent Document 2 discloses that light amount correction accuracy is improved by performing light amount correction in real time according to changes in characteristics of a semiconductor laser element used in an image display device such as a laser scan display.

Patent No. 5672845 Patent No. 5125390

Semiconductor laser elements may be applied not only to image forming devices and image display devices, but also to 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 propagation time of the light from when the light is emitted toward the object until it is reflected back by the object. The ToF sensor can handle three-dimensional information including not only distance information in the Z direction but also plane information in the XY directions.

A semiconductor laser element for a ToF sensor continuously generates short-width optical pulses in order to accurately measure the propagation time of light. Furthermore, since attenuation due to reflection at the target object and attenuation during propagation affect the sensing of the photodetector element, it is necessary to generate a sufficiently large amount of light from the semiconductor laser element. In general, semiconductor laser devices for ToF sensors are required to be driven with a large current and at high speed depending on distance and accuracy, compared to semiconductor laser devices for image forming devices or image display devices. However, when the semiconductor laser element is driven with a large current and at high speed, the temperature increases significantly due to heat generated by the semiconductor laser element itself. Therefore, even if the temperature of the semiconductor laser element changes due to the heat generated by the semiconductor laser element itself or other heat sources present in the environment in which the semiconductor laser element is used, there is a need to make it difficult for the amount of light from the semiconductor laser element to change.

An object of the present disclosure is to provide a semiconductor laser driving device and a semiconductor laser driving method in which the amount of light from a semiconductor laser element is unlikely to change even if the temperature of the semiconductor laser element changes due to heat generation of the semiconductor laser element itself or other heat sources. There is a particular thing. Furthermore, an object of the present disclosure is to provide a distance measuring device including such a semiconductor laser driving device.

A semiconductor laser driving device according to one aspect of the present disclosure includes:
A semiconductor laser drive device that drives a semiconductor laser element,
an initial setting circuit that holds an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element;
a differential amplifier that obtains a measured light amount indicating the light amount generated by the semiconductor laser element from a first photodetecting element and outputs a difference signal indicating the difference between the measured light amount and the target light amount;
a correction circuit that corrects the initial setting value based on the difference signal to generate a correction setting value;
a current generation circuit that generates a drive current having a magnitude corresponding to the initial setting value or the correction setting value and supplies it to the semiconductor laser element;
During an operation period in which the correction circuit operates the semiconductor laser device by continuously or intermittently supplying the drive current having a magnitude corresponding to the initial setting value or the correction setting value to the semiconductor laser device, Based on 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.

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 generation of the semiconductor laser element itself or other heat sources, it is possible to make it difficult to cause a change in the amount of light of the semiconductor laser element. can.

FIG. 1 is a block diagram showing the configuration of a semiconductor laser driving device 1 according to a first embodiment. 2 is a graph illustrating an example of the characteristics of the amount of light with respect to the current of the semiconductor laser element 2 driven by the semiconductor laser driving device 1 of FIG. 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 the semiconductor laser driving device 1 of FIG. 1. FIG. 2 is a timing chart showing an example of the operation of the semiconductor laser driving device 1 of FIG. 1. FIG. 2 is a timing chart showing another example of the operation of the semiconductor laser driving device 1 of FIG. 1. FIG. FIG. 2 is a block diagram showing the configuration of a semiconductor laser driving device 1A according to a first comparative example. FIG. 2 is a block diagram showing the configuration of a semiconductor laser driving device 1B according to a second comparative example. 7 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 drive device 1A of FIG. 6 or the semiconductor laser drive device 1B of FIG. 7. FIG. It is a block diagram showing the composition of semiconductor laser drive device 1C concerning a modification of a 1st embodiment. It is a block diagram showing the composition of distance measuring device 20 concerning a 2nd embodiment.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Like components are designated with the same reference numerals throughout the drawings.

[First embodiment]
[Configuration of first embodiment]
FIG. 1 is a block diagram showing the configuration of a semiconductor laser driving device 1 according to the first embodiment. The semiconductor laser driving device 1 supplies a driving current Iop to the semiconductor laser element 2 to drive the semiconductor laser element 2. The semiconductor laser driving device 1 obtains a measured light amount indicating the amount of light generated by the semiconductor laser element 2 from the photodetector element 3, and determines the magnitude of the drive current based on the measured light amount.

The semiconductor laser element 2 is, for example, a laser diode. The photodetector element 3 is, for example, a photodiode. The photodetector element 3 may be provided separately from the semiconductor laser element 2 or may be integrated with the semiconductor laser element 2.

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. Be prepared. Each component of the semiconductor laser driving device 1 operates according to a clock signal Sclk supplied from the outside.

The initial setting circuit 11 holds 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 may be set equal to, for example, the minimum value of the current at which the semiconductor laser element 2 starts emitting light, that is, the threshold current Ith. When the current flowing through the semiconductor laser device 2 is smaller than the threshold current Ith, the semiconductor laser device 2 does not emit light at all or hardly emit light. The bias current Ibi and the modulation current Imod are set so that when the sum of them flows through the semiconductor laser device 2, the light amount of the semiconductor laser device 2 becomes equal to the target light amount. The initial setting circuit 11 predetermines the digital code values Sbi and Smod0 by executing APC (Auto Power Control) based on the difference signal Sdiff (described later) output from the differential amplifier 17 in accordance with the control signal Sinit. . The initial setting circuit 11 stores digital code values Sbi and Smod0 in an internal memory 11m.

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

The correction circuit 13 corrects the digital code value Smod0 based on the difference signal Sdiff (described later) output from the differential amplifier 17 in accordance with 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.

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

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

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, 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. Further, when the switch 15 is turned off, only the bias current Ibi is supplied to the semiconductor laser element 2.

The photodetector element 3 generates a measurement voltage that indicates the magnitude of the measured light amount. A reference voltage source 16 generates a reference voltage indicating the magnitude of the target light amount. The differential amplifier 17 acquires the measured voltage from the photodetector element 3, the reference voltage from the reference voltage source 16, and outputs a difference signal Sdiff indicating the difference between the measured light amount and the target light amount. The differential amplifier 17 is, for example, an operational amplifier. As described above, the initial setting circuit 11 determines the initial setting value in advance 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.

The semiconductor laser driving device 1 has at least two periods having different operation modes, that is, an initial setting period and an operation period. During the initial setting period, the semiconductor laser driving device 1 determines an initial setting value corresponding to the target light amount by gradually increasing the driving current Iop from zero. During the operation period, the semiconductor laser driving device 1 operates the semiconductor laser device 2 by continuously or intermittently supplying the semiconductor laser device 2 with a drive current Iop having a magnitude corresponding to the initial setting value or the correction setting value. . During the operation period, the correction circuit 13 generates or updates a correction setting value based on the difference signal Sdiff so as to reduce the difference between the measured light amount and the target light amount. As a result, the magnitude of the drive current Iop can be corrected during the operation period, and therefore, even if the temperature of the semiconductor laser element 2 changes due to heat generation of the semiconductor laser element 2 itself or other heat sources, the magnitude of the drive current Iop can be corrected. Changes in the amount of light can be made less likely to occur.

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

[Operation of the first embodiment]
FIG. 2 is a graph showing an example of the characteristics of the amount of light with respect to the current of the semiconductor laser element 2 driven by the semiconductor laser driving device 1 of FIG. As described above, when the current flowing through the semiconductor laser device 2 is smaller than the threshold current Ith, the semiconductor laser device 2 does not emit light at all or hardly emit light. When the current flowing through the semiconductor laser device 2 exceeds the threshold current Ith, the semiconductor laser device 2 starts emitting light, and thereafter the amount of light increases in proportion to the amount of increase in the current. The bias current Ibi and the modulation current Imod1 are set so that when the sum thereof flows through the semiconductor laser device 2, the light amount of the semiconductor laser device 2 becomes equal to the target light amount.

Note that when the semiconductor laser device 2 is operated, the semiconductor laser device 2 itself generates heat, and the characteristics of the semiconductor laser device 2 (for example, the magnitude of the threshold current, the gradient of the light amount/current characteristics) change. Since the amount of light decreases as the temperature rises, even if the sum of the bias current Ibi and modulation current Imod1 flows through the semiconductor laser element 2, the measured amount of light becomes smaller than the target amount of light. Therefore, the semiconductor laser driving device 1 generates a modulation current Imod2 that is an increased modulation current Imod1. Modulation current Imod2 is set so that when the sum of bias current Ibi and modulation current Imod2 flows through semiconductor laser device 2, the light amount of semiconductor laser device 2 becomes equal to the target light amount.

Furthermore, when the measured current is larger than the target current, a modulation current Imod3 is generated by reducing the modulation current Imod1. Modulation current Imod3 is set so that when the sum of bias current Ibi and modulation current Imod3 flows through semiconductor laser device 2, the light amount of semiconductor laser device 2 becomes equal to the target light amount.

FIG. 3 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 1 of FIG. For example, when using the semiconductor laser element 2 in a ToF sensor, by intermittently supplying the driving current Iop to the semiconductor laser element 2 at a frequency of several tens of MHz, the semiconductor laser element 2 continuously emits short-width optical pulses. occurs. However, as described above, when the semiconductor laser element 2 is operated, the semiconductor laser element 2 itself generates heat, and the amount of light may gradually decrease. According to this embodiment, by correcting the magnitude of the drive current Iop during the operation period, it is possible to make it difficult for the amount of light from the semiconductor laser element 2 to change.

FIG. 4 is a timing chart showing an example of the operation of the semiconductor laser driving device 1 of FIG. 1. FIG. 4 shows temporal changes in the control signals Sinit, Srun, and Son, the clock signal Sclk, the digital code values Snbi and Smod, and the amount of light.

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 and outputs it as it is as the digital code value Smod. Further, in the initial state, the control signal Son is at a low level, and the switch 51 is turned off.

When the control signal Sinit transitions from low level to high level (H), the initial setting period starts, and the initial setting circuit 11 executes APC. The initial setting circuit 11 gradually increases the digital code value Sbi while referring to the difference signal Sdiff, and holds the digital code value bi1 when the amount of light starts to increase at a rate higher than a predetermined rate of change. Next, the control signal Son transitions from low level to high level, and 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 holds the digital code value mod1 when the measured light amount reaches the target light amount. The initial setting circuit 11 holds the digital code values bi and mod1 as initial setting values corresponding to the target light amount, that is, as the digital code values Sbi and Smod0. After that, the control signals Sinit and Son transition from high level to low level, and the initial setting period ends.

Thereafter, the semiconductor laser driving device 1 starts an operation period in which the semiconductor laser element 2 is turned on for a desired task. The operation period includes a first time period in which only the bias current Ibi is supplied to the semiconductor laser device 2, and a second time period in which the sum of the bias current Ibi and the modulation current Imod is supplied as the drive current Iop to the semiconductor laser device 2. and repeating the first and second time intervals alternately.

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

Furthermore, in the first operation period, the control signal Srun is set to low level. In this case, the correction circuit 13 does not correct the digital code value Smod0 based on the difference signal Sdiff. When the digital code value Smod matches the initial setting value digital code value Smod0 (time interval t3 to 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 initial setting value digital code value Smod0 (time interval t5 to t6), the correction circuit 13 initializes the correction setting value every predetermined period of the clock signal Sclk. It may be changed so as to approach the value. In the example of FIG. 4, the digital code value Smod is reduced so as to approach the digital code value mod1. This is because if the modulation current Imod is not supplied to the semiconductor laser device 2 for a predetermined period of time, the temperature of the semiconductor laser device 2 will drop, and the corrected digital code value Smod is considered to become excessive with respect to the target light amount. be. On the other hand, in the second operation period, 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 so as to reduce the difference between the measured light amount and the target light amount, and generates a corrected digital code value Smod. In the example of FIG. 4, the digital code value Smod gradually increases.

If the digital code value Smod0 is not corrected by the correction circuit 13, the amount of light may gradually decrease as shown by the broken line at the bottom of FIG. 4 ("no correction"). According to this embodiment, by correcting the magnitude of the drive current Iop during the operation period, it is possible to make it difficult for the amount of light from the semiconductor laser element 2 to change.

The period and step width for changing the digital code value by the initial setting circuit 11 and the correction circuit 13 may be determined depending on the application and usage environment of the semiconductor laser device 2.

FIG. 5 is a timing chart showing another example of the operation of the semiconductor laser driving device 1 of FIG. 1. The correction circuit 13 holds the digital code value Smod immediately before the transition from the second time interval to the first time interval (time t5 in FIG. 5). In the example of FIG. 5, the correction circuit 13 holds the digital code value mod2 as the digital code value Smod. When transitioning from the first time period to the second time period (time t6 in FIG. 5), the semiconductor laser driving device 1 generates a driving current Iop having a magnitude corresponding to the held digital code values Sbi and Smod. It is generated and supplied to the semiconductor laser device 2. For example, when the first and second time periods are alternated at short intervals, temperature changes in the semiconductor laser device 2 during the period in which the modulation current Imod is not supplied to the semiconductor laser device 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 prevent a change in the amount of light from occurring when the semiconductor laser element 2 is turned on next time.

[Comparative example]
FIG. 6 is a block diagram showing the configuration of a semiconductor laser driving device 1A according to a first comparative example. The semiconductor laser driving device 1A has a configuration in which the correction circuit 13 is removed from the semiconductor laser driving device 1 of FIG. The configuration of FIG. 6 is used, for example, to drive a semiconductor laser element for a general image forming apparatus or image display apparatus. The image forming device and the image display device scan a frame including an image area and a non-image area using a raster scan method. When scanning a non-image area, the semiconductor laser driving device 1A corrects the light intensity of the semiconductor laser element 2 according to the ambient temperature by forcibly turning on the semiconductor laser element 2 and executing APC. be able to. However, after performing APC, the semiconductor laser driving device 1A cannot correct the light amount of the semiconductor laser element 2, for example, when scanning an image area. Therefore, in the configuration of FIG. 6, the amount of light from the semiconductor laser element 2 may increase or decrease depending on the temperature change of the semiconductor laser element 2.

FIG. 7 is a block diagram showing the configuration of a semiconductor laser driving device 1B according to a second comparative example. The semiconductor laser driving device 1B includes a correction circuit 13B and a memory 18 in place of the correction circuit 13 in FIG. 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. The configuration shown in FIG. 7 assumes applications such as laser printers and digital copying machines where the surrounding environment of the semiconductor laser element does not change significantly, and has the characteristic that the light amount of the semiconductor laser element 2 increases or decreases according to the temperature change of the semiconductor laser element 2. Requires the precondition that it can be inferred. Therefore, when the usage environment is not always constant and unpredictable environmental changes occur, such as with a ToF sensor, the configuration shown in FIG. 7 cannot follow changes in the amount of light from the semiconductor laser element 2.

FIG. 8 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 drive device 1A of FIG. 6 or the semiconductor laser drive device 1B of FIG. 7. According to the configurations shown in FIGS. 6 and 7, when the semiconductor laser element 2 is operated, the semiconductor laser element 2 itself generates heat, and the amount of light may gradually decrease.

On the other hand, according to the semiconductor laser driving device 1 according to the present embodiment, by correcting the magnitude of the driving current Iop during the operation period, the amount of light of the semiconductor laser element 2 changes as described with reference to FIG. can be made less likely to occur. Further, according to the semiconductor laser driving device 1 according to the present embodiment, as shown in FIG. 7, it is possible to follow any change in light amount depending on the usage environment, without being limited to the correction pattern stored in advance in the storage device. I can do it. Further, according to the semiconductor laser driving device 1 according to the present embodiment, it is possible to immediately respond to a sudden change in the amount of light.

[Modification of the first embodiment]
FIG. 9 is a block diagram showing the configuration of a semiconductor laser driving device 1C according to a modification of the first embodiment. The semiconductor laser driving device 1C includes an initial setting circuit 11C in place of the initial setting circuit 11 of the semiconductor laser driving device 1 of FIG. The initial setting circuit 11C does not execute APC and holds predetermined initial setting values in the internal memory 11m. By not performing APC, costs can be lower than in the case of FIG.

[Second embodiment]
FIG. 10 is a block diagram showing the configuration of a distance measuring device 20 according to the second embodiment. The distance measuring device 20 includes a semiconductor laser drive device 1 , a semiconductor laser element 2 , a photodetection element 3 , a photodetection element 4 , and a processing circuit 5 . The semiconductor laser drive device 1, semiconductor laser element 2, and photodetector element 3 in FIG. 10 are configured in the same manner as the corresponding components in FIG. The photodetector element 4 acquires the amount of reflected light that indicates the amount of light generated by the semiconductor laser device 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 amount of reflected light. The processing circuit 5 generates the clock signal Sclk and control signals Sinit, Srun, and Son shown in FIG. The distance measuring device 20 is, for example, a ToF sensor that acquires a three-dimensional image of the object 30 viewed from the distance measuring device 20. Since the distance measuring device 20 includes the semiconductor laser driving device 1 according to the first embodiment, even if the temperature of the semiconductor laser device 2 changes due to heat generation of the semiconductor laser device 2 itself or other heat sources, the semiconductor laser Changes in the light amount of the element 2 can be made less likely to occur. Therefore, the distance measuring device 20 can calculate the distance from the distance measuring device 20 to the target object 30 with high accuracy.

[Other variations]
In FIGS. 4 and 5, a case has been described in which 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, depending on the usage environment of the semiconductor laser device 2, the digital code value Smod may be generated to be smaller than the digital code value Smod0.

If it is considered that the threshold current Ith has changed significantly, the initial setting circuit 11 may re-execute APC.

[Summary of embodiments]
A semiconductor laser driving device 1 according to a first aspect 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 generation circuit. Equipped with 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 a measured light amount indicating the light amount generated by the semiconductor laser element 2 from the first photodetector element 3, and outputs a difference signal Sdiff indicating 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 generation circuit generates a drive current Iop having a magnitude corresponding to the initial set value or the corrected set value and supplies it to the semiconductor laser element 2 . The correction circuit 13 corrects the difference during an operation period in which the semiconductor laser device 2 is operated by continuously or intermittently supplying the drive current Iop having a magnitude corresponding to the initial setting value or the correction setting value to the semiconductor laser device 2. Based on the signal Sdiff, a correction setting value is generated or updated so as to reduce the difference between the measured light amount and the target light amount.

According to the semiconductor laser driving device 1 according to the second aspect of the present disclosure, the semiconductor laser driving device 1 according to the first aspect may be configured as follows. The current generation circuit includes a first current source that generates a bias current Ibi and a second current source that generates a modulation current Imod. The operating period includes a first time period and a second time period that alternate with each other. In the first time period, the current generation circuit supplies the bias current Ibi to the semiconductor laser device 2. In the second time period, the current generation circuit supplies the sum of the bias current Ibi and the modulation current Imod to the semiconductor laser device 2 as the drive current Iop.

According to the semiconductor laser drive device 1 according to the third aspect of the present disclosure, the semiconductor laser drive device 1 according to the first or second aspect may be configured as follows. The correction circuit 13 changes the correction setting value so as to approach the initial setting value at predetermined intervals in the first time interval.

According to the semiconductor laser drive device 1 according to the fourth aspect of the present disclosure, the semiconductor laser drive device 1 according to the first or second aspect may be configured as follows. The correction circuit 13 holds the correction setting value immediately before the transition from the second time period to the first time period. The current generation circuit generates a drive current Iop having a magnitude corresponding to the held correction setting value and supplies it to the semiconductor laser element 2 when transitioning from the first time period to the second time period.

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.

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 predetermined initial setting values.

A distance measuring device 20 according to a seventh aspect of the present disclosure includes a semiconductor laser driving device 1 according to one of the first to seventh aspects, a semiconductor laser element 2, and an amount of light generated by the semiconductor laser element 2. A first photodetector element 3 that obtains a measured light amount indicating the amount of light emitted by the semiconductor laser element 2 and reflected by the object, and a second photodetector element 4 that obtains the amount of reflected light that indicates the amount of light generated by the semiconductor laser element 2 and reflected by the object. and a processing circuit 5 that calculates the distance to the target object based on the distance to the target object.

The semiconductor laser driving method according to the eighth aspect of the present disclosure is a semiconductor laser driving method for driving the semiconductor laser element 2, and includes the following steps. The method includes the step of maintaining an initial setting value corresponding to a predetermined target light amount of the semiconductor laser device 2. The method includes the steps of acquiring a measured light amount indicating the light amount generated by the semiconductor laser element 2 from the first photodetecting element, and outputting a difference signal Sdiff indicating the difference between the measured light amount and the target light amount. This method includes the steps of correcting the initial setting value based on the difference signal Sdiff to generate a correction setting value, and generating a drive current Iop having a magnitude corresponding to the initial setting value or the correction setting value to drive the semiconductor laser device 2. including the step of supplying. The step of generating the correction setting value is an operation of operating the semiconductor laser device 2 by continuously or intermittently supplying the driving current Iop having a magnitude corresponding to the initial setting value or the correction setting value to the semiconductor laser device 2. The period includes generating or updating a correction setting value based on the difference signal Sdiff so as to reduce the difference between the measured light amount and the target light amount.

1,1A to 1C Semiconductor laser driver 2 Semiconductor laser element 3 Photodetector element 4 Photodetector 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 Target object

Claims

A semiconductor laser drive device that drives a semiconductor laser element,
an initial setting circuit that holds an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element;
a differential amplifier that obtains a measured light amount indicating the light amount generated by the semiconductor laser element from a first photodetecting element and outputs a difference signal indicating the difference between the measured light amount and the target light amount;
a correction circuit that corrects the initial setting value based on the difference signal to generate a correction setting value;
a current generation circuit that generates a drive current having a magnitude corresponding to the initial setting value or the correction setting value and supplies it to the semiconductor laser element;
During an operation period in which the correction circuit operates the semiconductor laser device by continuously or intermittently supplying the drive current having a magnitude corresponding to the initial setting value or the correction setting value to the semiconductor laser device, generating or updating the correction setting value based on the difference signal so as to reduce the difference between the measured light amount and the target light amount;
Semiconductor laser drive device.
The current generation circuit includes a first current source that generates a bias current and a second current source that generates a modulation current,
The operating period includes a first time period and a second time period that alternate with each other,
In the first time period, the current generation circuit supplies the bias current to the semiconductor laser element,
In the second time period, the current generation circuit supplies the sum of the bias current and the modulation current to the semiconductor laser device as the drive current.
The semiconductor laser driving device according to claim 1.
The correction circuit changes the correction setting value so as to approach the initial setting value at every predetermined period in the first time interval.
The semiconductor laser driving device according to claim 2.
The correction circuit holds the correction setting value immediately before transition from the second time period to the first time period,
The current generation circuit generates a drive current having a magnitude corresponding to the held correction setting value and supplies it to the semiconductor laser element when transitioning from the first time period to the second time period. do,
The semiconductor laser driving device according to claim 2.
The initial setting circuit predetermines the initial setting value based on the difference signal.
A semiconductor laser driving device according to claim 1.
the initial setting circuit holds the initial setting value determined in advance;
A semiconductor laser driving device according to claim 1.
A semiconductor laser driving device according to claim 1;
a semiconductor laser element;
a first photodetection element that obtains a measurement light amount indicating the light amount generated by the semiconductor laser element;
a second photodetection element that obtains an amount of reflected light indicating the amount of light generated by the semiconductor laser element and reflected by the object;
and a processing circuit that calculates the distance to the object based on the amount of reflected light.
Distance measuring device.
A semiconductor laser driving method for driving a semiconductor laser element, the method comprising:
holding an initial setting value corresponding to a predetermined target light amount of the semiconductor laser element;
acquiring a measured light amount indicating the light amount generated by the semiconductor laser element from a first photodetecting element, and outputting a difference signal indicating the difference between the measured light amount and the target light amount;
correcting the initial setting value based on the difference signal to generate a correction setting value; and generating a drive current having a magnitude corresponding to the initial setting value or the correction setting value and supplying it to the semiconductor laser element. and a step of
The step of generating the correction setting value includes operating the semiconductor laser device by continuously or intermittently supplying the drive current having a magnitude corresponding to the initial setting value or the correction setting value to the semiconductor laser device. generating or updating a correction setting value based on the difference signal so as to reduce the difference between the measured light amount and the target light amount during the operation period to
Semiconductor laser driving method.