Driving device, light emitting device, and driving method

A driving device that includes a temperature monitoring circuit, a headroom voltage monitoring circuit, a power supply voltage monitoring circuit, and a control unit. The temperature monitoring circuit detects a temperature of a drive circuit that drives a light emitting element in a test light emission period of the light emitting element. The headroom voltage monitoring circuit detects a headroom voltage of the drive circuit in the test light emission period. The power supply voltage monitoring circuit detects a power supply voltage supplied to the light emitting element in the test light emission period. The control unit adjusts the power supply voltage in the test light emission period according to an input/output potential difference of the light emitting element varying depending on the temperature of drive circuit so as to obtain a headroom voltage necessary and sufficient for causing a prescribed drive current to flow through the light emitting element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 and claims the benefit of PCT Application No. PCT/JP2021/008775, having an international filing date of 5 Mar. 2021, which designated the United States, which PCT application claimed the benefit of Japanese Patent Application No. 2020-061967, filed 31 Mar. 2020, the entire disclosures of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a driving device, a light emitting device, and a driving method.

BACKGROUND ART

A ranging device of a time of flight (ToF) method using a light emitting element, such as a semiconductor laser, is required to emit laser light having a higher output with a pulse having a higher frequency in order to extend a measurement distance and improve safety. A driving device that drives the light emitting element needs to optimize a drive current of the light emitting element in a case where the laser light having the higher output is emitted with the pulse having the higher frequency.

For this reason, there is a driving device that causes a light emitting element to perform test light emission before distance measurement is performed, performs control to suppress variation of a drive current of the light emitting element in a test light emission period, and then, causes the light emitting element to perform main light emission for the distance measurement (see, for example, Patent Document 1).

CITATION LIST

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, the conventional driving device has room for improvement in terms of low power consumption.

Therefore, the present disclosure proposes a driving device, a light emitting device, and a driving method capable of reducing power consumption of a light emitting element.

Solutions to Problems

According to the present disclosure, a driving device is provided. The driving device includes a temperature monitoring circuit, a headroom voltage monitoring circuit, a power supply voltage monitoring circuit, and a control unit. The temperature monitoring circuit detects a temperature of a drive circuit that drives a light emitting element in a test light emission period of the light emitting element. The headroom voltage monitoring circuit detects a headroom voltage of the drive circuit in the test light emission period. The power supply voltage monitoring circuit detects a power supply voltage supplied to the light emitting element in the test light emission period. The control unit adjusts the power supply voltage in the test light emission period according to an input/output potential difference of the light emitting element that varies depending on the temperature of the drive circuit so as to obtain a headroom voltage necessary and sufficient for causing a prescribed drive current to flow through the light emitting element.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the same parts will be denoted by the same reference signs in each of the following embodiments, and the redundant description thereof will be omitted.

[1. Configuration Example of Ranging Module]

FIG.1is a diagram illustrating a configuration example of a ranging module according to an embodiment of the present disclosure. A ranging module100illustrated inFIG.1is a device that measures a distance to an object by a time of flight (ToF) method. The ranging module100emits laser light, receives the laser light reflected by the object, and measures the distance to the object on the basis of time from the emission of the laser light to the reception of the laser light or a phase difference between the emitted light and the reflected light.

The ranging module100includes a substrate111, an optical module112, a driving device (hereinafter, described as “LDD: Laser Diode Driver”)113, a lens114, a distance image sensor115, and a large scale integrated circuit (LSI)116.

The optical module112, the LDD113, the lens114, the distance image sensor115, and the LSI116are provided on the substrate111. The optical module112and the LDD113function as a light emitting device101that emits laser light.

The optical module112includes a light emitting element (hereinafter, described as “LD: Laser Diode”)121, a photo diode (PD)122, and a diffuser123. The LD121emits laser light having a predetermined wavelength. The LD121emits the laser light to be used to measure the distance to the object according to the control of the LDD113.

The PD122is a light receiving element that is used for measurement of the intensity of the laser light emitted from the LD121. The PD122outputs a light reception signal corresponding to the amount of received light. The PD122receives return light, which is a part of the laser light that is emitted from the LD121, is reflected by the diffuser123, and returns, and outputs the light reception signal corresponding to the amount of received return light.

The diffuser123is a diffusion member provided such that the laser light emitted from the LD121satisfies a safety standard defined by International Electrotechnical Commission (IEC) or the like. The laser light emitted from the LD121passes through the diffuser123to become diffused light. A part of the laser light is reflected by the diffuser123, and the return light is received by the PD122.

The LDD113supplies a drive current to the LD121to control driving of the LD121. Furthermore, the LDD113performs auto power control (APC) for controlling the intensity of the laser light emitted from the LD121on the basis of the light reception signal received from the PD122.

The lens114forms an image of reflected light, which is the laser light emitted from the LD121and reflected from the object, on a light receiving surface of the distance image sensor115. The distance image sensor115is a distance image sensor of a ToF method, and detects the distance (depth) to the object for each pixel. For example, the distance image sensor115detects the phase difference between the laser light emitted from the LD121and the reflected light from the object for each pixel, and outputs information indicating the phase difference to the LSI116.

The LSI116controls the LDD113and the distance image sensor115. Furthermore, the LSI116derives the distance to the object on the basis of the information regarding the phase difference input from the distance image sensor115. Note that the configuration of the ranging module100illustrated inFIG.1is an example, and other configurations may be used as long as the distance measurement using the Tof method can be performed.

[2. Configuration Example of LDD]

Next, a configuration example of the LDD113will be described with reference toFIG.2.FIG.2is a diagram illustrating a configuration example of the LDD according to the embodiment of the present disclosure. As illustrated inFIG.2, the LDD113includes a control unit1, a DCDC converter2, and a laser diode driver integrated circuit (LDDIC)3.

The LDDIC3includes a drive circuit (hereinafter, described as a “driver31”), a power supply voltage (hereinafter, described as “LDVCC”) monitoring circuit32, a temperature monitoring circuit33, a selector34, an AD converter35, and a logic circuit36. The driver31includes a metal oxide semiconductor (MOS) transistor and a headroom (hereinafter, described as “HR”) voltage monitoring circuit37.

The control unit1is connected to the DCDC converter2and the LDDIC3. The DCDC converter2is connected to an anode of the LD121and the LDVCC monitoring circuit32. Furthermore, the DCDC converter2is connected to a ground with a capacitor124interposed therebetween. The LD121has a cathode connected to the driver31.

Note that the control unit1is connected to the LSI116although not illustrated herein. The control unit1controls the operation of the DCDC converter2in accordance with the control of the LSI116to adjust LDVCC of a direct current to be supplied to the LD121. Furthermore, the control unit1turns on a MOS transistor in the driver31and supplies a drive current to the LD121to cause the LD121to emit light in accordance with the control of the LSI116.

Here, a configuration example of the driver31will be described with reference toFIGS.3and4.FIGS.3and4are circuit diagrams illustrating the configuration example of the drive circuit according to the embodiment of the present disclosure. As illustrated inFIG.3, the driver31includes two NMOS transistors Tr1and Tr2. The NMOS transistors Tr1and Tr2are connected in series between the cathode of the LD121whose anode is connected to a wiring to which LDVCC is supplied and the ground.

The driver31turns on the NMOS transistors Tr1and Tr2and causes a drive current (hereinafter, referred to as “LD current”) to flow through the LD121, thereby causing the LD121to emit light. Furthermore, the driver31turns off the NMOS transistors Tr1and Tr2to stop the light emission of the LD121.

Note that the light emission of the LD121can also be controlled by a driver31aillustrated inFIG.4. The driver31aincludes two PMOS transistors Tr4and Tr5. The PMOS transistors Tr4and Tr5are connected in series between a wiring to which LDVCC is supplied and the anode of the LD121. The LD121has a cathode connected to the ground.

The driver31aturns on the PMOS transistors Tr4and Tr5and causes an LD current to flow through the LD121, thereby causing the LD121to emit light. Furthermore, the driver31aturns off the PMOS transistors Tr4and Tr5to stop the light emission of the LD121. The driver31illustrated inFIG.2may be configured by the driver31aillustrated inFIG.4.

Characteristics of the drive circuit are affected unless the drivers31and31asecure an HR voltage equal to or higher than a certain voltage, and it is difficult for the drivers31and31ato cause a prescribed LD current according to the specifications to flow through the LD121and to cause the LD121to emit light with a desired output intensity. For this reason, the control unit1needs to set LDVCC such that the HR voltage can be sufficiently secured with respect to an input/output potential difference (hereinafter, described as “VOP”) of the LD121when a desired LD current flows.

The HR voltage is a voltage corresponding to a potential difference between the cathode of the LD121and the ground in the driver31illustrated inFIG.3. Furthermore, the HR voltage is a voltage corresponding to a potential difference between the wiring to which LDVCC is supplied and the anode of the LD121in the driver31aillustrated inFIG.4.

However, VOP varies under the influence of temperature variation. Furthermore, LDVCC also varies under the influence of the temperature variation. For this reason, for example, when VOP increases due to the temperature variation in the drivers31and31a, it is difficult to secure a sufficient HR voltage, and it is difficult to cause the desired LD current to flow through the LD121.

Here, a relationship among the temperature of the drive circuit, an LD current value, and VOP will be described with reference toFIG.5.FIG.5is a view illustrating the relationship among the temperature, the LD current value, and VOP according to the embodiment of the present disclosure. As illustrated inFIG.5, in a case where a prescribed LD current is caused to flow, VOP increases as the temperature increases and decreases as the temperature decreases.

For this reason, when the LDD113tries to cause an LD current having the prescribed LD current value in a case where a room-temperature state is switched to a high-temperature state, it is difficult to secure a sufficient HR voltage unless LDVCC is increased, and it is difficult to cause the desired LD current to flow through the LD121.

For this reason, the sufficient HR voltage has been secured by increasing LDVCC excessively to some extent, for example, in the case where the room-temperature state is switched to the high-temperature state. However, power is wastefully consumed in a case where LDVCC is higher than a minimum voltage required to cause the desired LD current to flow, and there is room for improvement in terms of low power consumption.

Therefore, the control unit1of the LDD113has a configuration for adjusting LDVCC according to VOP of the LD121that varies depending on the temperature of the driver31or31aso as to obtain the HR voltage that is necessary and sufficient for causing the prescribed LD current to flow through the LD121. Returning toFIG.2, the configuration for adjusting LDVCC to secure the necessary and sufficient HR voltage will be described.

The LDD113performs a process of adjusting LDVCC to secure the necessary and sufficient HR voltage in a test light emission period of the LD121. Specifically, the HR voltage monitoring circuit37detects an HR voltage of the driver31and outputs the detected HR voltage to the selector34.

The HR voltage monitoring circuit37detects a potential difference between the cathode of the LD121and the ground as the HR voltage and outputs the HR voltage to the selector34. Note that, in the case of the driver31aillustrated inFIG.4, the HR voltage monitoring circuit37detects the potential difference between the wiring to which LDVCC is supplied and the anode of the LD121as the HR voltage and outputs the HR voltage to the selector34.

The LDVCC monitoring circuit32detects LDVCC supplied to the LD121and outputs the detected LDVCC to the selector34. The temperature monitoring circuit33detects a temperature of the driver31and outputs the temperature to the selector34. Note that, in a case where the driver31aillustrated inFIG.4is provided in the LDD113, the temperature monitoring circuit33detects a temperature of the driver31aand outputs the temperature to the selector34.

The selector34sequentially selects signals one by one from three analog signals according to the HR voltage from the HR voltage monitoring circuit37, LDVCC from the LDVCC monitoring circuit32, and the temperature of the temperature monitoring circuit33, and outputs the selected signal to the AD converter35.

The AD converter35converts the analog signal according to the HR voltage, the analog signal according to LDVCC, and the analog signal according to the temperature sequentially input from the selector34into digital signals, and outputs the digital signals to the logic circuit36.

The logic circuit36converts the digital signals input from the AD converter35into information indicating a level of the HR voltage, information indicating a level of LDVCC, and information indicating the level of the temperature, respectively, and outputs the information to the control unit1.

The control unit1includes a microcomputer including a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like, and various circuits. Note that some or all of the control unit1may be configured by hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA).

The control unit1adjusts LDVCC by controlling the operation of the DCDC converter2as the CPU executes a program stored in the ROM using the RAM as a work area.

For example, the control unit1stores in advance the information indicating the relationship among the temperature, the LD current value, and the VOP illustrated inFIG.5. The control unit1can calculate VOP in a case where the prescribed LD current flows at the temperature detected by the temperature monitoring circuit33by referring to the information indicating the relationship among the temperature, the LD current value, and VOP.

Even if LDVCC varies due to the temperature variation, the control unit1can acquire LDVCC when the temperature has been detected by the temperature monitoring circuit33from the LDVCC monitoring circuit32. Furthermore, the control unit can acquire the HR voltage when the temperature has been detected by the temperature monitoring circuit33from the HR voltage monitoring circuit37.

For this reason, the control unit1can adjust LDVCC in the test light emission period according to VOP of the LD121that varies depending on the temperature of the driver31so as to obtain the HR voltage that is necessary and sufficient for causing the prescribed LD current to flow through the LD121.

In this manner, the control unit1supplies the LD121with the minimum required LDVCC in order to secure the HR voltage required to cause the prescribed (for example, in the specifications) LD current to flow through the LD121. Therefore, the control unit1does not wastefully set LDVCC high, the power consumption of the LD121can be reduced.

Furthermore, the light emitting device101can also be downsized according to the LDD113. Next, a configuration of a light emitting device that can be downsized by adopting the driver31will be described with reference toFIG.6.FIG.6is a view illustrating a modified example of the light emitting device according to the embodiment of the present disclosure.

Although the LDD113and the optical module112are placed flat on the same plane on the substrate111in the light emitting device101illustrated inFIG.1, a light emitting device101aaccording to the modified example has a structure in which the optical module112is stacked on the LDD113as illustrated inFIG.6.

Therefore, the light emitting device101acan reduce the occupied area on the substrate111as compared with the case where the LDD113and the optical module112are placed flat on the same plane on the substrate111, and thus, can be downsized.

Furthermore, in the light emitting device101a, a temperature of the LDD113in the lower layer increases due to heat generated by light emission of the optical module112in the upper layer, but a minimum required LDVCC is supplied to the LD121by the driver31provided in the LDD113, and thus, various costs and power can be reduced.

[3. Operation Example of LDD]

Next, an operation example of the LDD113will be described with reference toFIG.7.FIG.7is a timing chart illustrating operations of the LDD according to the embodiment of the present disclosure. InFIG.7, from the top, a supply timing of the LD current, a reception timing of the light reception signal of the PD, a detection timing of the HR voltage, a temperature detection timing of the drive circuit, and a detection timing of LDVCC are sequentially illustrated in time series.

As illustrated inFIG.7, an operation period of the LDD113is roughly divided into a test light emission period (adjustment period) and a ranging period (actual operation period) period. The LDD113repeatedly executes an operation in the test light emission period and an operation in the ranging period. Note thatFIG.1illustrates an operation in a first test light emission period and the operation in the ranging period.

The LDD113repeats an operation of causing the LD121to perform test light emission in a test period, performing the APC and adjustment and correction of LDVCC, and then, causing the LD121to perform main light emission with a high-frequency pulse for distance measurement.

For example, the LDD113causes the LD121to perform test light emission in a period from time t1to time t2, and performs the APC on the basis of the light reception signal output from the PD122in this period. Thereafter, the LDD113causes the LD121to perform test light emission in a period from time t3to time t4, and detects the HR voltage in this period (step S1).

Subsequently, the LDD113detects the temperature of the driver31in a period from time t4to time t5(step S2). Thereafter, the LDD113detects LDVCC in a period from time t5to time t6(step S3).

Then, the LDD113performs adjustment and correction of the HR voltage in a period from time t6to time t7before entering the ranging period (step S4). At this time, the LDD113adjusts the HR voltage by adjusting LDVCC according to VOP of the LD that varies depending on the temperature of the driver31so as to obtain the HR voltage that is necessary and sufficient for causing the prescribed LD current to flow through the LD121.

Then, after the end of the ranging period, the LDD113causes the LD121to perform test light emission to perform the APC, and the detection of the HR voltage, the temperature detection of the driver31, the detection of LDVCC, and the adjustment and correction of the HR voltage.

Here, the ranging period in which the LD121performs the main light emission is present between the first test period and the second test period. For this reason, the temperature of the driver31is higher in the second test period than in the first test period.

Therefore, LDVCC also varies, and input-output voltage characteristics of the NMOS transistors Tr1and Tr2of the driver31also vary. As a result, the HR voltage that needs to be secured to cause the prescribed LD current to flow through the LD121also varies between the first test period and the second test period.

For this reason, even if the LDD113adjusts LDVCC so as to secure the same HR voltage as the HR voltage secured in the first test period during the second test period, there is a case where it is difficult for the LD121to set the HR voltage necessary and sufficient for causing the prescribed LD current to flow.

Therefore, the control unit1of the LDD1corrects LDVCC on the basis of the amount of temperature variation of the driver31detected by the temperature monitoring circuit33in the test light emission period before and after the main light emission of the LD121and a correction coefficient of LDVCC according to the amount of temperature variation.

For example, the control unit1stores, in advance, a table in which the amount of temperature variation of the driver31is associated with the amount of change in the necessary and sufficient HR voltage changed by the temperature variation. Then, the control unit1calculates a difference between the temperature of the driver31detected in the first test period and the temperature of the driver31detected in the second test period.

The control unit1derives the necessary and sufficient HR voltage varying depending on the calculated temperature difference on the basis of the table, calculates the correction coefficient that needs to be multiplied to LDVCC in order to obtain the derived HR voltage, and multiplies the adjusted LDVCC by the correction coefficient to correct LDVCC. Therefore, the LDD113can more accurately set the necessary and sufficient HR voltage.

Note that the LDD113executes the processing in the order of the detection of the HR voltage, the temperature detection of the driver31, and the detection of LDVCC in the example illustrated inFIG.7, but the order of the detection of the HR voltage, the temperature detection of the driver31, and the detection of LDVCC can be changed to any order.

[4. Processing Executed by Control Unit]

Next, processing executed by the control unit1of the LDD133will be described with reference toFIG.8.FIG.8is a flowchart illustrating an example of the processing executed by the control unit of the LDD according to the embodiment of the present disclosure.

As illustrated inFIG.8, the control unit1first executes a background light measurement process (step S101). In the background light measurement process, the control unit1sets the LD121in a non-light emitting state, and holds the amount of received light corresponding to a light reception signal output from the PD122as a light amount of background light according to the control of the LSI116.

Subsequently, the control unit1executes APC1 according to the control of the LSI116(step S102). In the APC1, the control unit1supplies a first LD current slightly greater than the LD current at which the LD121enters a light emitting state from a non-light emitting state to the LD121to cause the LD to emit light, and holds a first amount of received light corresponding to a light reception signal output from the PD122.

Thereafter, the control unit1supplies a second LD current slightly greater than the first LD current to the LD121to cause the LD to emit light, and holds a second amount of received light corresponding to a light reception signal output from the PD122.

Here, a light emission intensity of the LD121increases linearly with an increase in the LD current until the LD current exceeds a certain threshold current. Furthermore, the light emission intensity of the LD121increases non-linearly with the increase in the LD current when the LD current exceeds the certain threshold current.

Using such characteristics of the LD121, the control unit1calculates and holds a maximum LD current at which the LD121do not emit light on the basis of a reduction rate at which the second amount of received light is reduced to the first amount of received light when the second LD current equal to or less than the threshold current is reduced to the first LD current.

Subsequently, the control unit1executes APC2 according to the control of the LSI116(step S103). In the APC2, the control unit1calculates a target LD current that is an LD current in a case where laser light is emitted from the LD121to an actual ranging object.

Since it is necessary to irradiate a distant object with laser light and receive reflected light thereof in the ranging module100, a desired intensity (hereinafter, referred to as target intensity) of the laser light of the LD121used at the time of ranging is extremely high.

Therefore, the LD current for emitting the laser light having the target intensity from the LD121exceeds the linear section and is included in the non-linear section. Therefore, in the non-linear section of the LD current, the control unit1supplies a third LD current slightly less than the target LD current, obtained assuming the object in advance, to the LD121to cause the LD to emit light, and holds a third amount of received light corresponding to a light reception signal output from the PD122.

Thereafter, the control unit1supplies a fourth LD current slightly greater than the target LD current to the LD121to cause the LD to emit light, and holds a fourth amount of received light corresponding to a light reception signal output from the PD122.

Then, the control unit1calculates and holds the target LD current on the basis of a non-linear increase rate at which the third amount of received light is increased to the fourth amount of received light when the third LD current is increased to the fourth LD current.

Subsequently, the control unit1executes an APC1 check process (step S104). In the APC1 check process, the control unit1supplies the maximum LD current which is held in the APC1 and at which the LD121does not emit light to the LD121to cause the LD to emit light, and holds the second amount of received light corresponding to the light reception signal output from the PD122.

Then, in a case where a difference between the held amount of received light and the light amount of background light is within a determination value, the control unit1determines that the maximum LD current which is held in the APC1 and at which the LD121does not emit light is appropriate. On the other hand, in a case where the difference between the held amount of received light and the light amount of the background light exceeds the determination value, the control unit1determines that an error occurs and ends the processing. In a case where the control unit1does not determine that an error occurs in step S104, the processing proceeds to step S105.

In step S105, the control unit1, the control unit1executes an APC2 check process. In the APC2 check process, the control unit1determines whether or not the diffuser123is normally set and whether or not the target LD current is appropriate.

The control unit1supplies the target LD current held in the APC2 to the LD121to cause the LD to emit light, and holds the second amount of received light corresponding to the light reception signal output from the PD122. Then, the control unit1calculates a difference between the held amount of received light and the light amount of background light.

At this time, if the diffuser123is set normally, a part of laser light emitted from the LD121is reflected by the diffuser123and enters the PD122. For this reason, the difference between the amount of received light held in the APC2 check process and the light reception amount of background light increases.

On the other hand, in a case where the diffuser123is disengaged, a part of the laser light emitted from the LD121is not reflected by the diffuser123, and thus, is not incident on the PD122. For this reason, the amount of received light held in the APC2 check process and the light reception amount of background light are substantially equal.

Therefore, the control unit1determines that the diffuser123is normally set in a case where the difference between the amount of received light held in the APC2 check process and the light reception amount of background light exceeds a determination value. On the other hand, in a case where the difference between the amount of received light held in the APC2 check process and the light reception amount of background light is within the determination value, the control unit1determines that an error occurs and ends the processing.

Thereafter, the control unit1calculates a difference between the amount of received light held in the APC2 check process and a target light amount. The target light amount is a light amount detected by the PD122when laser light having the target intensity is emitted from the LD121, and is obtained in advance by actual measurement or calculation, for example.

In a case where the difference between the amount of received light held in the APC2 check process and the target light amount is within a determination threshold, the control unit1determines that the target LD current held in the APC2 is appropriate. Furthermore, in a case where the difference between the amount of received light held in the APC2 check process and the target light amount exceeds the determination threshold, the control unit1determines that an error occurs and ends the processing.

In a case where it is not determined that an error occurs in step S105, the control unit1causes the processing to proceed to step S106. In step S106, the control unit1executes an HR voltage measurement process. In the HR voltage measurement process, the control unit1detects the HR voltage of the driver31.

Subsequently, the control unit1executes a drive circuit temperature measurement process (step S107). In the drive circuit temperature measurement process, the control unit1detects the temperature of the driver31. Thereafter, the control unit1executes an LDVCC measurement process (step S108). In the LDVCC measurement process, the control unit1detects LDVCC supplied to the LD121.

Then, the control unit1executes an HR voltage adjustment and correction process (step S109). In the HR voltage adjustment and correction process, the control unit1adjusts and corrects LDVCC according to VOP of the LD121that varies depending on the temperature of the driver31or31asuch that the HR voltage becomes a necessary and sufficient HR voltage for causing a prescribed LD current to flow through the LD121.

Thereafter, the control unit1repeats an operation of causing the LD121to perform the main light emission with a high-frequency pulse for distance measurement, starts the distance measurement, and ends the processing. Thereafter, the control unit1starts the processing again from step S101.

Note that the description has been given in the above-described embodiment regarding the case where, under the control of the LSI116, the control unit1detects the temperature, the HR voltage, and LDVCC of the driver31, and adjusts LDVCC in the test light emission period according to VOP of the LD121that varies depending on the temperature of the driver31so as to obtain the HR voltage that is necessary and sufficient for causing the prescribed LD current to flow through the LD121, but this is an example.

For example, a configuration may be adopted in which the control unit1does not follow the control by the LSI116, and the control unit1alone detects the temperature of the driver31, the HR voltage, and LDVCC and adjusts LDVCC in the test light emission period according to VOP of the LD121that varies depending on the temperature of the driver31so as to obtain the HR voltage that is necessary and sufficient for causing the prescribed LD current to flow through the LD121.

The LDD113, which is an example of a driving device, includes the temperature monitoring circuit33, the HR voltage monitoring circuit37, the LDVCC monitoring circuit32, and the control unit1. The temperature monitoring circuit33detects the temperature of the driver31that drives the LD121in the test light emission period of the LD121. The HR voltage monitoring circuit37detects the HR voltage of the driver31in the test light emission period. The LDVCC monitoring circuit32detects LDVCC supplied to the LD121in the test light emission period. The control unit1adjusts LDVCC in the test light emission period according to VOP of the LD121that varies depending on the temperature of the driver31so as to obtain the HR voltage that is necessary and sufficient for causing the prescribed LD current to flow through the LD121. Therefore, the LDD113can reduce the power consumption of the LD121by supplying the minimum required LDVCC to the LD121in order to cause the prescribed (for example, in the specifications) LD current to flow through the LD121.

The driver31includes the NMOS transistors Tr1and Tr2connected in series between the ground and the cathode of the LD121whose anode is connected to the wiring to which LDVCC is supplied. The HR voltage monitoring circuit37detects the potential difference between the cathode of the LD121and the ground as the HR voltage. Therefore, the LDD113can reduce the power consumption of the LD121in a case where the LD121is provided at a previous stage of the driver31.

The driver31aincludes the PMOS transistors Tr4and Tr5connected in series between the wiring to which LDVCC is supplied and the anode of the LD121whose cathode is connected to the ground. The HR voltage monitoring circuit detects the potential difference between the wiring to which LDVCC is supplied and the anode of the LD121as the HR voltage. Therefore, the LDD113can reduce the power consumption of the LD121in a case where the LD121is provided at a subsequent stage of the driver31a.

The control unit1adjusts LDVCC on the basis of the information indicating the relationship between the LD current of the LD121and VOP of the LD121that varies depending on the temperature of the driver31. Therefore, the LDD113can supply the minimum required LDVCC according to the temperature variation to the LD121, thereby causing the prescribed LD current to flow through the LD121.

The driver31repeats the operation of causing the light emitting element to perform the test light emission and the operation of causing the light emitting element to perform the main light emission for distance measurement. The control unit1corrects the power supply voltage on the basis of the amount of temperature variation of the driver31detected by the temperature monitoring circuit33in the test light emission period before and after the main light emission and the correction coefficient of LDVCC according to the amount of temperature variation. Therefore, the LDD113can more accurately set the necessary and sufficient HR voltage.

The light emitting device101includes the LD121, the temperature monitoring circuit33, the HR voltage monitoring circuit37, the LDVCC monitoring circuit32, and the control unit1. The LD121emits light for distance measurement. The temperature monitoring circuit33detects the temperature of the driver31that drives the LD121in the test light emission period of the LD121. The HR voltage monitoring circuit37and the HR voltage of the driver31are detected in the test light emission period. The LDVCC monitoring circuit32detects LDVCC supplied to the LD121in the test light emission period. The control unit1adjusts LDVCC in the test light emission period according to VOP of the LD121that varies depending on the temperature of the driver31so as to obtain the HR voltage that is necessary and sufficient for causing the prescribed LD current to flow through the LD121. Therefore, the light emitting device101can reduce the power consumption of the LD121by supplying the minimum required LDVCC to the LD121in order to cause the prescribed (for example, in the specifications) LD current to flow through the LD121.

An information processing method, performed by the control unit1, which is an example of a computer, including: detecting a temperature of the driver31that drives the LD121in a test light emission period of the LD121; detecting an HR voltage of the driver31in the test light emission period; detecting LDVCC supplied to the LD121in the test emission period; and adjusting LDVCC in the test light emission period according to VOP of the LD121that varies depending on the temperature of the driver31so as to obtain an HR voltage that is necessary and sufficient for causing a prescribed drive current to flow through the LD121. Therefore, the information processing method can reduce the power consumption of the LD121by supplying the minimum required LDVCC to the LD121in order to cause the prescribed (for example, in the specifications) LD current to flow through the LD121.

Note that the effects described in the present specification are merely examples and are not limited, and there may be other effects.

A driving device including:a temperature monitoring circuit that detects a temperature of a drive circuit that drives a light emitting element in a test light emission period of the light emitting element;a headroom voltage monitoring circuit that detects a headroom voltage of the drive circuit in the test light emission period;a power supply voltage monitoring circuit that detects a power supply voltage supplied to the light emitting element in the test light emission period; anda control unit that adjusts the power supply voltage in the test light emission period according to an input/output potential difference of the light emitting element that varies depending on the temperature of the drive circuit to obtain a headroom voltage necessary and sufficient for causing a prescribed drive current to flow through the light emitting element.

The driving device according to (1), in whichthe drive circuit includes a transistor connected in series between a ground and a cathode of the light emitting element having an anode connected to a wiring to which the power supply voltage is supplied, andthe headroom voltage monitoring circuit detects, as the headroom voltage, a potential difference between the cathode of the light emitting element and the ground.

The driving device according to (1), in whichthe drive circuit includes a transistor connected in series between a wiring to which the power supply voltage is supplied and an anode of the light emitting element having a cathode connected to a ground, andthe headroom voltage monitoring circuit detects, as the headroom voltage, a potential difference between the wiring to which the power supply voltage is supplied and the anode of the light emitting element.

The driving device according to any one of (1) to (3), in whichthe control unit adjusts the power supply voltage on the basis of information indicating a relationship between a drive current of the light emitting element varying depending on the temperature of the drive circuit and an input/output voltage difference of the light emitting element.

The driving device according to any one of (1) to (4), in whichthe drive circuit repeats an operation of causing the light emitting element to perform test light emission and an operation of causing the light emitting element to perform main light emission for distance measurement, andthe control unit corrects the power supply voltage on the basis of an amount of temperature variation of the drive circuit, detected by the temperature monitoring circuit in the test light emission period before and after the main light emission, and a correction coefficient of the power supply voltage according to the amount of temperature variation.

A light emitting device including:a light emitting element that emits light for distance measurement;a temperature monitoring circuit that detects a temperature of a drive circuit that drives the light emitting element in a test light emission period of the light emitting element;a headroom voltage monitoring circuit that detects a headroom voltage of the drive circuit in the test light emission period;a power supply voltage monitoring circuit that detects a power supply voltage supplied to the light emitting element in the test light emission period; anda control unit that adjusts the power supply voltage in the test light emission period according to an input/output potential difference of the light emitting element that varies depending on the temperature of the drive circuit to obtain a headroom voltage necessary and sufficient for causing a prescribed drive current to flow through the light emitting element.

A driving method including:detecting, by a computer, a temperature of a drive circuit that drives a light emitting element in a test light emission period of the light emitting element;detecting, by the computer, a headroom voltage of the drive circuit in the test light emission period;detecting, by the computer, a power supply voltage supplied to the light emitting element in the test light emission period; andadjusting, by the computer, the power supply voltage in the test light emission period according to an input/output potential difference of the light emitting element that varies depending on the temperature of the drive circuit to obtain a headroom voltage necessary and sufficient for causing a prescribed drive current to flow through the light emitting element.

REFERENCE SIGNS LIST