Driving device, light emitting device, and driving method

Abstract

The present disclosure relates to a driving device (113) including a temperature monitoring circuit (33), a margin voltage monitoring circuit (37), a power supply voltage monitoring circuit (32), and a control unit (1). The temperature monitoring circuit (33) detects a temperature of a driving circuit (31) that drives a light emitting element (121) in a test light emitting period of the light emitting element (121). The margin voltage monitoring circuit (37) detects a margin voltage of the driving circuit (31) in the test light emitting period. The power supply voltage monitoring circuit (32) detects a power supply voltage supplied to the light emitting element (121) in the test light emitting period. The control unit (1) adjusts the power supply voltage in the test light emitting period in accordance with an input / output potential difference of the light emitting element (121) that varies depending on the temperature of the driving circuit (31) to obtain a margin voltage sufficient for a prescribed driving current to flow through the light emitting element (121).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a driving device, a light emitting device, and a driving method. BACKGROUND

[0002] A distance measuring device using a time-of-flight (ToF) method of a light emitting element such as a semiconductor laser requires emitting laser light with a higher output using a pulse with a higher frequency in order to extend a measurement distance and improve safety. In the case of emitting laser light with a higher output using a pulse with a higher frequency, a driving device that drives the light emitting element needs to optimize a driving current of the light emitting element.

[0003] Therefore, there is a driving device that causes a light emitting element to perform test light emission before distance measurement, performs control to suppress a change in a driving 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 distance measurement (for example, see Patent Literature 1).

[0004] LIST OF CITATIONS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2019-096642. SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, the conventional driving device has room for improvement in terms of low power consumption.

[0009] Therefore, the present disclosure proposes a driving device, a light emitting device, and a driving method that can reduce power consumption of a light emitting element.

[0010] SOLUTION TO PROBLEM

[0011] According to the present disclosure, a driving device is provided. The driving device includes a temperature monitoring circuit, a margin voltage monitoring circuit, a power supply voltage monitoring circuit, and a control unit. The temperature monitoring circuit detects a temperature of a driving circuit that drives a light emitting element in a test light emission period of the light emitting element. The margin voltage monitoring circuit detects a margin voltage of the driving 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 in accordance with an input / output potential difference of the light emitting element that varies depending on the temperature of the driving circuit so as to obtain a margin voltage that is necessary and sufficient for a prescribed driving current to flow through the light emitting element. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a diagram that shows a configuration example of a distance measuring module according to an embodiment of the present disclosure.

[0013] Figure 2 is a diagram showing a configuration example of an LDD according to an embodiment of the present disclosure.

[0014] Figure 3 is a circuit diagram showing a configuration example of a drive circuit according to an embodiment of the present disclosure.

[0015] Figure 4 is a circuit diagram showing a configuration example of a drive circuit according to an embodiment of the present disclosure.

[0016] Figure 5 is a diagram showing a relationship between a temperature, an LD current value, and a VOP according to an embodiment of the present disclosure.

[0017] Figure 6 is a diagram showing a modification example of a light emitting device according to an embodiment of the present disclosure.

[0018] Figure 7 is a timing chart showing an operation of an LDD according to an embodiment of the present disclosure.

[0019] Figure 8 is a flowchart showing an example of a process performed by a control unit of an LDD according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, in each of the following embodiments, the same parts are labeled with the same reference numerals and overlapping description is omitted.

[0021] [1. Configuration example of a distance measuring module]

[0022] Figure 1 is a diagram showing a configuration example of a distance measuring module according to an embodiment of the present disclosure. Figure 1 The distance measuring module 100 shown in FIG. 1 is a device that measures a distance to an object by a time of flight (ToF) method. The distance measuring module 100 emits laser light, receives laser light reflected by an object, and measures a distance to the object based on a time from emission of the laser light to reception of the laser light or a phase difference between emitted light and reflected light.

[0023] The distance measuring module 100 includes a substrate 111, an optical module 112, a drive device (hereinafter described as "LDD: Laser Diode Driver") 113, a lens 114, a distance image sensor 115, and a large scale integrated circuit (LSI) 116.

[0024] The optical module 112, the LDD 113, the lens 114, the distance image sensor 115, and the LSI 116 are provided on the substrate 111. The optical module 112 and the LDD 113 function as the light emitting device 101 that emits laser light.

[0025] The optical module 112 includes a light emitting element (hereinafter, described as "LD: Laser Diode") 121, a photodiode (PD) 122, and a diffuser 123. The LD 121 emits laser light having a predetermined wavelength. The LD 121 emits laser light for measuring a distance to an object in accordance with the control of the LDD 113.

[0026] The PD 122 is a light receiving element for measuring an intensity of the laser light emitted from the LD 121. The PD 122 outputs a light receiving signal corresponding to an amount of received light. The PD 122 receives return light that is a part of the laser light emitted from the LD 121, is reflected by the diffuser 123, and returns, and outputs a light receiving signal corresponding to an amount of the received return light.

[0027] The diffuser 123 is a diffusing member that is provided so that the laser light emitted from the LD 121 satisfies a safety standard defined by the International Electrotechnical Commission (IEC) or the like. The laser light emitted from the LD 121 passes through the diffuser 123 to become diffused light. A part of the laser light is reflected by the diffuser 123, and the return light is received by the PD 122.

[0028] The LDD 113 supplies a drive current to the LD 121 to control driving of the LD 121. Further, the LDD 113 performs automatic power control (APC) for controlling an intensity of the laser light emitted from the LD 121 based on a light receiving signal received from the PD 122.

[0029] The lens 114 forms an image of the reflected light, which is the laser light emitted from the LD 121 and reflected from an object, on a light receiving surface of the distance image sensor 115. The distance image sensor 115 is a distance image sensor of the ToF method, and detects a distance (depth) to an object for each pixel. For example, the distance image sensor 115 detects a phase difference between the laser light emitted from the LD 121 and the reflected light from the object for each pixel, and outputs information indicating the phase difference to the LSI 116.

[0030] The LSI 116 controls the LDD 113 and the distance image sensor 115. Further, the LSI 116 derives a distance to an object based on information about the phase difference input from the distance image sensor 115. Note that the configuration of the distance measuring module 100 shown in Figure 1 the configuration of the distance measuring module 100 shown in FIG. 1 is one example, and other configurations can be used as long as distance measurement using the ToF method can be performed.

[0031] [2. Configuration example of LDD]

[0032] Next, a configuration example of the LDD 113 will be described with reference to Figure 2 Figure 2 is a diagram illustrating a configuration example of the LDD according to an embodiment of the present disclosure. As Figure 2 indicated, the LDD 113 includes a control unit 1, a DCDC converter 2, and a laser diode driver integrated circuit (LDDIC) 3.

[0033] The LDDIC 3 includes a driver circuit (hereinafter, described as "driver 31"), a power supply voltage (hereinafter, described as "LDVCC") monitoring circuit 32, a temperature monitoring circuit 33, a selector 34, an AD converter 35, and a logic circuit 36. The driver 31 includes a metal oxide semiconductor (MOS) transistor and a headroom (hereinafter, described as "HR") voltage monitoring circuit 37.

[0034] The control unit 1 is connected to the DCDC converter 2 and the LDDIC 3. The DCDC converter 2 is connected to a positive electrode of the LD 121 and the LDVCC monitoring circuit 32. In addition, the DCDC converter 2 is connected to a ground through a capacitor 124. The LD 121 has a negative electrode connected to the driver 31.

[0035] In addition, although not illustrated, the control unit 1 is connected to the LSI 116. The control unit 1 controls the operation of the DCDC converter 2 to adjust the LDVCC of the direct current to be supplied to the LD 121 in accordance with the control of the LSI 116. Further, the control unit 1 turns on the MOS transistor in the driver 31 and supplies a driving current to the LD 121 to cause the LD 121 to emit light in accordance with the control of the LSI 116.

[0036] Here, a configuration example of the driver 31 will be described with reference to Figure 3 and Figure 4 Figure 3 and Figure 4 is a circuit diagram illustrating a configuration example of the driver circuit according to an embodiment of the present disclosure. As Figure 3 indicated, the driver 31 includes two NMOS transistors Tr1 and Tr2. The NMOS transistors Tr1 and Tr2 are connected in series between a negative electrode of the LD 121 and a ground, and a positive electrode of the LD 121 is connected to a wiring to which the LDVCC is supplied.

[0037] ​​The driver 31 turns on the NMOS transistors Tr1 and Tr2 and causes a drive current (hereinafter, referred to as an "LD current") to flow through the LD 121, thereby causing the LD 121 to emit light. Further, the driver 31 turns off the NMOS transistors Tr1 and Tr2 to stop the emission of light from the LD 121.

[0038] Note that the emission of light from the LD 121 can also be controlled by a driver 31a illustrated in Figure 4 . The driver 31a includes two PMOS transistors Tr4 and Tr5. The PMOS transistors Tr4 and Tr5 are connected in series between a wiring that supplies the LD VCC and the anode of the LD 121. The cathode of the LD 121 is grounded.

[0039] The driver 31a turns on the PMOS transistors Tr4 and Tr5 and causes the LD current to flow through the LD 121, thereby causing the LD 121 to emit light. Further, the driver 31a turns off the PMOS transistors Tr4 and Tr5 to stop the emission of light from the LD 121. Figure 2 The driver 31 illustrated in Figure 4 can be configured by the driver 31a illustrated in

[0040] The characteristics of the drive circuit are affected unless the driver 31 and 31a ensure the HR voltage equal to or higher than a certain voltage, and the driver 31 and 31a are difficult to cause the LD current according to the prescribed regulation to flow through the LD 121 and cause the LD 121 to emit light having a desired output intensity. For this reason, the control unit 1 needs to set the LD VCC so that the input / output potential difference (hereinafter, described as "VOP") with respect to the LD 121 can sufficiently ensure the HR voltage when the desired LD current flows.

[0041] The HR voltage is a voltage corresponding to the potential difference in the driver 31 between the cathode of the LD 121 and the ground as illustrated in Figure 3 . Further, the HR voltage is a voltage corresponding to the potential difference in the driver 31a between the wiring that supplies the LD VCC and the anode of the LD 121 as illustrated in Figure 4

[0042] However, the VOP varies under the influence of temperature variation. Further, the LD VCC also varies under the influence of temperature variation. For this reason, for example, when the VOP increases due to the temperature variation of the driver 31 and 31a, it is difficult to ensure sufficient HR voltage, and it is difficult to cause the desired LD current to flow through the LD 121.

[0043] Here, the relationship between the temperature of the drive circuit, the LD current value, and the VOP will be described with reference to Figure 5 . Figure 5 is a graph illustrating the relationship between the temperature, the LD current value, and the VOP according to the embodiment of the present disclosure. As illustrated in​Figure 5 As shown, in a case where a prescribed LD current is caused to flow, VOP increases as the temperature increases and decreases as the temperature decreases.

[0044] For this reason, when the LDD 113 attempts to switch from the room temperature state to the high temperature state, it is difficult to secure a sufficient HR voltage unless the LDVCC is increased, and it is difficult to cause the desired LD current to flow through the LD 121.

[0045] For this reason, for example, in a case where the room temperature state is switched to the high temperature state, a sufficient HR voltage is secured by excessively increasing the LDVCC to some extent. However, in a case where the LDVCC is higher than the minimum voltage required to cause the desired LD current to flow, power is wastefully consumed, and there is room for improvement in terms of low power consumption.

[0046] Therefore, the control unit 1 of the LDD 113 has a configuration for adjusting the LDVCC in accordance with the VOP of the LD 121 that varies depending on the temperature of the driver 31 or 31a, in order to obtain a necessary and sufficient HR voltage for causing a prescribed LD current to flow through the LD 121. Returning Figure 2 A configuration for adjusting the LDVCC to secure a necessary and sufficient HR voltage will be described.

[0047] The LDD 113 performs a process of adjusting the LDVCC to secure a necessary and sufficient HR voltage at the time of test light emission of the LD 121. Specifically, the HR voltage monitoring circuit 37 detects the HR voltage of the driver 31 and outputs the detected HR voltage to the selector 34.

[0048] The HR voltage monitoring circuit 37 detects the potential difference between the negative electrode of the LD 121 and the ground as the HR voltage and outputs the HR voltage to the selector 34. Note that, in the case of the driver 31a shown in Figure 4 , the HR voltage monitoring circuit 37 detects the potential difference between the wiring that supplies the LDVCC and the positive electrode of the LD 121 as the HR voltage and outputs the HR voltage to the selector 34.

[0049] The LDVCC monitoring circuit 32 detects the LDVCC supplied to the LD 121 and outputs the detected LDVCC to the selector 34. The temperature monitoring circuit 33 detects the temperature of the driver 31 and outputs the temperature to the selector 34. Note that, in the case of the driver 31a provided in the LDD 113 shown in Figure 4 , the temperature monitoring circuit 33 detects the temperature of the driver 31a and outputs the temperature to the selector 34.

[0050] The selector 34 selects the signals one by one from among the three analog signals in order from the HR voltage from the HR voltage monitoring circuit 37, the LD VCC from the LD VCC monitoring circuit 32, and the temperature from the temperature monitoring circuit 33, and outputs the selected signal to the AD converter 35.

[0051] The AD converter 35 converts the analog signal according to the HR voltage, the analog signal according to the LD VCC, and the analog signal according to the temperature, which are sequentially input from the selector 34, into digital signals, and outputs the digital signals to the logic circuit 36.

[0052] The logic circuit 36 converts the digital signals input from the AD converter 35 into information indicating the level of the HR voltage, information indicating the level of the LD VCC, and information indicating the level of the temperature, respectively, and outputs the information to the control unit 1.

[0053] The control unit 1 includes 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 unit 1 can be configured by hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA).

[0054] When the CPU executes a program stored in the ROM using the RAM as a work area, the control unit 1 adjusts the LD VCC by controlling the operation of the DCDC converter 2.

[0055] For example, the control unit 1 stores information indicating the relationship between the temperature, the LD current value, and the VOP shown in FIG. 6 in advance. The control unit 1 is able to calculate the VOP in the case where the prescribed LD current flows at the temperature detected by the temperature monitoring circuit 33 by referring to the information indicating the relationship between the temperature, the LD current value, and the VOP. Figure 5

[0056] Even if the LD VCC changes due to a change in temperature, the control unit 1 can acquire the LD VCC from the LD VCC monitoring circuit 32 when the temperature monitoring circuit 33 has detected the temperature. Further, the control unit can acquire the HR voltage from the HR voltage monitoring circuit 37 when the temperature monitoring circuit 33 has detected the temperature.

[0057] To this end, the control unit 1 is able to adjust the LD VCC in the test light emission period in accordance with the VOP of the LD 121 that changes depending on the temperature of the driver 31 so as to obtain the HR voltage that is necessary and sufficient for causing the prescribed LD current to flow through the LD 121.

[0058] ​In this way, the control unit 1 supplies the LD 121 with the minimum required LDVCC so as to ensure the HR voltage required to cause the prescribed (e.g., in the specification) LD current to flow through the LD 121. Thus, the control unit 1 does not wastefully set the LDVCC high, and it is possible to reduce the power consumption of the LD 121.

[0059] Further, according to the LDD 113, the light emitting device 101 can also be downsized. Next, a configuration of a light emitting device that can be reduced in size by employing the driver 31 will be described with reference to Figure 6 Figure 6 is a view that shows a modification example of the light emitting device according to the embodiment of the present disclosure.

[0060] Although the LDD 113 and the optical module 112 are placed flat on the same plane on the substrate 111 in the light emitting device 101 shown in Figure 1 , the light emitting device 101a according to the modification example has a structure in which the optical module 112 is stacked on the LDD 113 as shown in Figure 6

[0061] Thus, compared to the case in which the LDD 113 and the optical module 112 are placed flat on the same plane on the substrate 111, the light emitting device 101a can reduce the area occupied on the substrate 111, and thus can reduce the size thereof.

[0062] Further, in the light emitting device 101a, the temperature of the LDD 113 in the lower layer increases due to the heat generated by the light emission of the optical module 112 in the upper layer, but the minimum required LDVCC is supplied to the LD 121 by the driver 31 provided in the LDD 113, and thus, it is possible to reduce various costs and power.

[0063] [3. Operation example of LDD]

[0064] Next, an operation example of the LDD 113 will be described with reference to Figure 7 Figure 7 is a timing chart that shows the operation of the LDD according to the embodiment of the present disclosure. In Figure 7 , from the top, the supply timing of the LD current, the reception timing of the light reception signal of the PD, the detection timing of the HR voltage, the temperature detection timing of the drive circuit, and the detection timing of the LDVCC are shown in time series order.

[0065] As shown in Figure 7 , the operation period of the LDD 113 is roughly divided into a test light emission period (adjustment period) and a ranging period (actual operation period) period. The LDD 113 repeatedly performs the operation in the test light emission period and the operation in the ranging period. Note that, Figure 1 ​​​Operations in the first test light emitting period and operations in the ranging period are shown.

[0066] The LDD 113 repeatedly causes the LD 121 to perform test light emission in the test period, perform adjustment and correction of the APC and the LDVCC, and then causes the LD 121 to perform main light emission with high-frequency pulses for distance measurement.

[0067] For example, the LDD 113 causes the LD 121 to perform test light emission for a period from time t1 to time t2, and performs APC based on the light reception signal output from the PD 122 for the period. Thereafter, the LDD 113 causes the LD 121 to perform test light emission for a period from time t3 to time t4, and detects the HR voltage for the period (step S1).

[0068] Subsequently, the LDD 113 detects the temperature of the driver 31 for a period from time t4 to time t5 (step S2). Thereafter, the LDD 113 detects the LDVCC for a period from time t5 to time t6 (step S3).

[0069] Then, the LDD 113 performs adjustment and correction of the HR voltage for a period from time t6 to time t7 before entering the ranging period (step S4). At this time, the LDD 113 adjusts the HR voltage by adjusting the LDVCC in accordance with the VOP of the LD which varies depending on the temperature of the driver 31, to obtain the HR voltage which is required and sufficient for causing the prescribed LD current to flow through the LD 121.

[0070] Then, after the ranging period ends, the LDD 113 causes the LD 121 to perform test light emission to perform APC, and detection of the HR voltage, temperature detection of the driver 31, detection of the LDVCC, and adjustment and correction of the HR voltage.

[0071] Here, the ranging period in which the LD 121 performs main light emission exists between the first test period and the second test period. For this reason, the temperature of the driver 31 is higher in the second test period than in the first test period.

[0072] Therefore, the LDVCC also varies, and the input-output voltage characteristics of the NMOS transistors Tr1 and Tr2 of the driver 31 also vary. As a result, it is necessary to ensure that the HR voltage which causes the prescribed LD current to flow through the LD 121 also varies between the first test period and the second test period.

[0073] For this reason, even if the LDD 113 adjusts the LDVCC so as to ensure the same HR voltage as that ensured in the first test period during the second test period, there is a case where the LD 121 has difficulty in setting the HR voltage which is required and sufficient for causing the prescribed LD current to flow.

[0074] Accordingly, the control unit 1 of the LDD 113 corrects the LDVCC based on the amount of change in the temperature of the driver 31 detected by the temperature monitoring circuit 33 in the test light emission period before and after the main light emission of the LD 121 and the correction coefficient of the LDVCC according to the amount of change in the temperature.

[0075] For example, the control unit 1 stores in advance a table in which the amount of change in the temperature of the driver 31 is associated with the amount of change in the necessary and sufficient HR voltage changed by the temperature change. Then, the control unit 1 calculates the difference between the temperature of the driver 31 detected in the first test period and the temperature of the driver 31 detected in the second test period.

[0076] The control unit 1 derives the necessary and sufficient HR voltage that changes depending on the calculated temperature difference based on the table, calculates the correction coefficient that needs to be multiplied by the LDVCC to obtain the derived HR voltage, and multiplies the adjusted LDVCC by the correction coefficient to correct the LDVCC. Accordingly, the LDD 113 can more accurately set the necessary and sufficient HR voltage.

[0077] Note that the LDD 113 performs the processing in the order of the detection of the HR voltage, the temperature detection of the driver 31, and the detection of the LDVCC in the example shown in Figure 7 , but the order of the detection of the HR voltage, the temperature detection of the driver 31, and the detection of the LDVCC can be changed to any order.

[0078] [4. Processing performed by control unit]

[0079] Next, the processing performed by the control unit 1 of the LDD 113 will be described with reference to Figure 8 . Figure 8 is a flowchart showing an example of the processing performed by the control unit of the LDD according to the embodiment of the present disclosure.

[0080] As shown in Figure 8 , the control unit 1 first performs a background light measurement processing (step S101). In the background light measurement processing, according to the control of the LSI 116, the control unit 1 sets the LD 121 in a non-light emission state, and holds the amount of received light corresponding to the light reception signal output from the PD 122 as the light amount of the background light.

[0081] Subsequently, the control unit 1 performs APC1 according to the control of the LSI 116 (step S102). In the APC1, the control unit 1 supplies the LD 121 with a first LD current that is slightly larger than the LD current with which the LD 121 enters the light emission state from the non-light emission state, to cause the LD to emit light, and holds a first received light amount corresponding to the light reception signal output from the PD 122.

[0082] Thereafter, the control unit 1 supplies a second LD current, which is slightly larger than the first LD current, to the LD 121 to cause the LD to emit light, and holds a second received light amount corresponding to the light reception signal output from the PD 122.

[0083] Here, the emission intensity of the LD 121 linearly increases with an increase in the LD current until the LD current exceeds a certain threshold current. Further, when the LD current exceeds the certain threshold current, the emission intensity of the LD 121 non-linearly increases with an increase in the LD current.

[0084] Using this characteristic of the LD 121, when the second LD current, which is equal to or smaller than the threshold current, is reduced to the first LD current, the control unit 1 calculates and holds a maximum LD current at which the LD 121 does not emit light, based on a reduction rate at which the second received light amount is reduced to the first received light amount.

[0085] Subsequently, the control unit 1 performs APC2 in accordance with the control of the LSI 116 (step S103). In the APC2, the control unit 1 calculates a target LD current, which is an LD current in a case where laser light is emitted from the LD 121 to an actual ranging object.

[0086] Because it is necessary to irradiate a distant object with laser light and receive its reflected light in the ranging module 100, a desired intensity of laser light of the LD 121 used at the time of ranging (hereinafter, referred to as a target intensity) is extremely high.

[0087] Therefore, an LD current for emitting laser light having the target intensity from the LD 121 exceeds the linear portion and is included in the non-linear portion. Therefore, in the non-linear portion of the LD current, the control unit 1 supplies a third LD current, which is slightly smaller than the target LD current (obtained by assuming an object in advance), to the LD 121 to cause the LD to emit light, and holds a third received light amount corresponding to the light reception signal output from the PD 122.

[0088] Thereafter, the control unit 1 supplies a fourth LD current, which is slightly larger than the target LD current, to the LD 121 to cause the LD to emit light, and holds a fourth received light amount corresponding to the light reception signal output from the PD 122.

[0089] Then, when the third LD current is increased to the fourth LD current, the control unit 1 calculates and holds the target LD current, based on a non-linear increase rate at which the third received light amount is increased to the fourth received light amount.

[0090] Subsequently, the control unit 1 executes the APC1 check processing (step S104). In the APC1 check processing, the control unit 1 supplies the LD 121 with the maximum LD current held in the APC1 and for which the LD 121 does not emit light to cause the LD to emit light, and holds the second received light amount corresponding to the light reception signal output from the PD 122.

[0091] Then, in a case where the difference between the held received light amount and the light amount of the background light is within the determined value, the control unit 1 determines that the maximum LD current held in the APC1 and for which the LD 121 does not emit light is appropriate. On the other hand, in a case where the difference between the held received light amount and the light amount of the background light exceeds the determined value, the control unit 1 determines that an error has occurred, and ends the processing. In a case where the control unit 1 does not determine that an error has occurred in step S104, the processing proceeds to step S105.

[0092] In step S105, the control unit 1 executes the APC2 check processing. In the APC2 check processing, the control unit 1 determines whether the diffuser 123 is properly set, and whether the target LD current is appropriate.

[0093] The control unit 1 supplies the LD 121 with the target LD current held in the APC2 to cause the LD to emit light, and holds the second received light amount corresponding to the light reception signal output from the PD 122. Then, the control unit 1 calculates the difference between the held received light amount and the light amount of the background light.

[0094] At this time, if the diffuser 123 is properly set, a part of the laser light emitted from the LD 121 is reflected by the diffuser 123 and enters the PD 122. Therefore, the difference between the received light amount held in the APC2 check processing and the light reception amount of the background light increases.

[0095] On the other hand, in a case where the diffuser 123 is disengaged, a part of the laser light emitted from the LD 121 is not reflected by the diffuser 123, and thus does not impinge on the PD 122. Therefore, the received light amount held in the APC2 check processing and the light reception amount of the background light are substantially equal.

[0096] Therefore, in a case where the difference between the received light amount held in the APC2 check processing and the light reception amount of the background light exceeds the determined value, the control unit 1 determines that the diffuser 123 is properly set. On the other hand, in a case where the difference between the received light amount held in the APC2 check processing and the light reception amount of the background light is within the determined value, the control unit 1 determines that an error has occurred, and ends the processing.

[0097] Thereafter, the control unit 1 calculates a difference between the received light amount held in the APC2 check processing and the target light amount. The target light amount is an amount of light detected by the PD 122 when laser light having a target intensity is emitted from the LD 121, and is obtained in advance, for example, by actual measurement or calculation.

[0098] In a case where the difference between the received light amount held in the APC2 check processing and the target light amount is within a determination threshold, the control unit 1 determines that the target LD current held in the APC2 is appropriate. Further, in a case where the difference between the received light amount held in the APC2 check processing and the target light amount exceeds the determination threshold, the control unit 1 determines that an error has occurred, and ends the processing.

[0099] In a case where it is not determined that an error has occurred in step S105, the control unit 1 causes the processing to proceed to step S106. In step S106, the control unit 1 executes the HR voltage measurement processing. In the HR voltage measurement processing, the control unit 1 detects the HR voltage of the driver 31.

[0100] Subsequently, the control unit 1 executes the drive circuit temperature measurement processing (step S107). In the drive circuit temperature measurement processing, the control unit 1 detects the temperature of the driver 31. Thereafter, the control unit 1 executes the LD VCC measurement processing (step S108). In the LD VCC measurement processing, the control unit 1 detects the LD VCC supplied to the LD 121.

[0101] Then, the control unit 1 executes the HR voltage adjustment and correction processing (step S109). In the HR voltage adjustment and correction processing, the control unit 1 adjusts and corrects the LD VCC so that the HR voltage becomes a necessary and sufficient HR voltage for causing a prescribed LD current to flow through the LD 121, in accordance with the VOP of the LD 121 that varies depending on the temperature of the driver 31 or 31a.

[0102] Thereafter, the control unit 1 repeats the operation of causing the LD 121 to perform main light emission with a high-frequency pulse for ranging, starts ranging (step S110), and ends the processing. Thereafter, the control unit 1 starts the processing again from step S101.

[0103] Note that the description has been given in the above-described embodiment regarding a case where the control unit 1 detects the temperature of the driver 31, the HR voltage, and the LD VCC under the control of the LSI 116, and adjusts the LD VCC in the test light emission period in accordance with the VOP of the LD 121 that varies depending on the temperature of the driver 31 so as to obtain a necessary and sufficient HR voltage for causing a prescribed LD current to flow through the LD 121, but this is an example.

[0104] For example, a configuration can be employed in which the control unit 1 does not follow the control of the LSI 116, and the control unit 1 individually detects the temperature of the driver 31, the HR voltage, and the LDVCC, and adjusts the LDVCC in the test light emission period in accordance with the VOP of the LD 121 that varies depending on the temperature of the driver 31, so as to obtain the HR voltage that is necessary and sufficient for a prescribed LD current to flow through the LD 121.

[0105] [5. Effects]

[0106] The LDD 113, which is an example of a driving device, includes the temperature monitoring circuit 33, the HR voltage monitoring circuit 37, the LDVCC monitoring circuit 32, and the control unit 1. The temperature monitoring circuit 33 detects the temperature of the driver 31 that drives the LD 121 in the test light emission period of the LD 121. The HR voltage monitoring circuit 37 detects the HR voltage of the driver 31 in the test light emission period. The LDVCC monitoring circuit 32 detects the LDVCC supplied to the LD 121 in the test light emission period. The control unit 1 adjusts the LDVCC in the test light emission period in accordance with the VOP of the LD 121 that varies depending on the temperature of the driver 31, so as to obtain the HR voltage that is necessary and sufficient for a prescribed LD current to flow through the LD 121. Thus, the LDD 113 can reduce the power consumption of the LD 121 by supplying the minimum required LDVCC to the LD 121 so that a prescribed (e.g., in a specification) LD current flows through the LD 121.

[0107] The driver 31 includes the NMOS transistors Tr1 and Tr2 connected in series between the ground and the negative electrode of the LD 121, and the positive electrode of the LD 121 is connected to a wiring that supplies the LDVCC thereto. The HR voltage monitoring circuit 37 detects the potential difference between the negative electrode of the LD 121 and the ground as the HR voltage. Thus, the LDD 113 can reduce the power consumption of the LD 121 in a case where the LD 121 is disposed at a preceding stage of the driver 31.

[0108] The driver 31a includes the PMOS transistors Tr4 and Tr5 connected in series between a wiring that supplies the LDVCC and the positive electrode of the LD 121, and the negative electrode of the LD 121 is connected to the ground. The HR voltage monitoring circuit detects the potential difference between the wiring that supplies the LDVCC and the positive electrode of the LD 121 as the HR voltage. Thus, the LDD 113 can reduce the power consumption of the LD 121 in a case where the LD 121 is disposed at a subsequent stage of the driver 31a.

[0109] The control unit 1 adjusts the LDVCC based on information indicating a relationship between an LD current of the LD 121 and a VOP of the LD 121 that varies according to a temperature of the driver 31. Thus, the LDD 113 can provide the LD 121 with a minimum required LDVCC according to the temperature variation, thereby causing a prescribed LD current to flow through the LD 121.

[0110] The driver 31 repeats the operation of causing the light emitting element to perform the test emission and the operation of causing the light emitting element to perform the main emission for distance measurement. The control unit 1 corrects the power supply voltage based on the amount of change in the temperature of the driver 31 detected by the temperature monitoring circuit 33 in the test emission period before and after the main emission and a correction coefficient of the LDVCC according to the amount of change in the temperature. Thus, the LDD 113 can more accurately set the necessary and sufficient HR voltage.

[0111] The light emitting device 101 includes the LD 121, the temperature monitoring circuit 33, the HR voltage monitoring circuit 37, the LDVCC monitoring circuit 32, and the control unit 1. The LD 121 emits light for distance measurement. The temperature monitoring circuit 33 detects the temperature of the driver 31 that drives the LD 121 in a test emission period of the LD 121. The HR voltage monitoring circuit 37 and the driver 31 detect the HR voltage in the test emission period. The LDVCC monitoring circuit 32 detects the LDVCC supplied to the LD 121 in the test emission period. The control unit 1 adjusts the LDVCC in the test emission period according to a VOP of the LD 121 that varies depending on the temperature of the driver 31, so as to obtain a necessary and sufficient HR voltage for causing a prescribed LD current to flow through the LD 121. Thus, the light emitting device 101 can reduce the power consumption of the LD 121 by providing the LD 121 with a minimum required LDVCC to cause a prescribed (e.g., in a specification) LD current to flow through the LD 121.

[0112] An information processing method performed by the control unit 1, the control unit 1 being an example of a computer, includes: detecting a temperature of a driver 31 that drives an LD 121 in a test emission period of the LD 121; detecting an HR voltage of the driver 31 in the test emission period; detecting an LDVCC supplied to the LD 121 in the test emission period; and adjusting the LDVCC in the test emission period according to a VOP of the LD 121 that varies depending on the temperature of the driver 31, so as to obtain a necessary and sufficient HR voltage for causing a prescribed LD current to flow through the LD 121. Thus, the information processing method can reduce the power consumption of the LD 121 by providing the LD 121 with a minimum required LDVCC to cause a prescribed (e.g., in a specification) LD current to flow through the LD 121.

[0113] Note that the effects described in this specification are merely examples and are not limiting, and other effects can be present.

[0114] Note that the present technology can also have the following configurations. (1)

[0116] A driving device includes:

[0117] a temperature monitoring circuit that detects a temperature of a driving circuit that drives a light emitting element during a test light emitting period of the light emitting element;

[0118] a margin voltage monitoring circuit that detects a margin voltage of the driving circuit during the test light emitting period;

[0119] a power supply voltage monitoring circuit that detects a power supply voltage supplied to the light emitting element during the test light emitting period; and

[0120] a control unit that adjusts the power supply voltage during the test light emitting period in accordance with an input / output potential difference of the light emitting element, which varies in accordance with the temperature of the driving circuit, to obtain a margin voltage that is necessary and sufficient for a prescribed driving current to flow through the light emitting element. (2)

[0122] The driving device according to (1), wherein

[0123] the driving circuit includes a transistor connected in series between a ground and a negative electrode of the light emitting element, the light emitting element has a positive electrode connected to a wiring that supplies a power supply voltage, and

[0124] the margin voltage monitoring circuit detects a potential difference between the negative electrode of the light emitting element and the ground as the margin voltage. (3)

[0126] The driving device according to (1), wherein

[0127] the driving circuit includes a transistor connected in series between a wiring that supplies a power supply voltage and a positive electrode of the light emitting element, the light emitting element has a negative electrode connected to a ground, and

[0128] the margin voltage monitoring circuit detects a potential difference between the wiring that supplies the power supply voltage and the positive electrode of the light emitting element as the margin voltage. (4)

[0130] The driving device according to any one of (1) to (3), wherein

[0131] the control unit adjusts the power supply voltage based on information indicating a relationship between a driving current of the light emitting element and an input / output voltage difference of the light emitting element, wherein the driving current of the light emitting element varies in accordance with the temperature of the driving circuit. (5)

[0133] The driving device according to any one of (1) to (4), wherein

[0134] The driving circuit repeats 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, and

[0135] The control unit corrects the power supply voltage based on the amount of change in the temperature of the driving circuit detected by the temperature monitoring circuit in the test light emission period before and after the main light emission and the correction coefficient of the power supply voltage according to the amount of change in the temperature. (6)

[0137] A light emitting device comprising:

[0138] a light emitting element that emits light for distance measurement;

[0139] a temperature monitoring circuit that detects a temperature of a driving circuit that drives the light emitting element in a test light emission period of the light emitting element;

[0140] a margin voltage monitoring circuit that detects a margin voltage of the driving circuit in the test light emission period;

[0141] a power supply voltage monitoring circuit that detects a power supply voltage supplied to the light emitting element in the test light emission period; and

[0142] a 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 to obtain a margin voltage that is necessary and sufficient for causing a prescribed driving current to flow through the light emitting element, the input / output potential difference of the light emitting element varying according to a temperature of the driving circuit. (7)

[0144] A driving method comprising:

[0145] detecting, by a computer, a temperature of a driving circuit that drives a light emitting element in a test light emission period of the light emitting element;

[0146] detecting, by the computer, a margin voltage of the driving circuit in the test light emission period;

[0147] detecting, by the computer, a power supply voltage supplied to the light emitting element in the test light emission period; and

[0148] adjusting, 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 to obtain a margin voltage that is necessary and sufficient for causing a prescribed driving current to flow through the light emitting element, the input / output potential difference varying according to a temperature of the driving circuit.

[0149] List of Reference Signs

[0150] 1 control unit

[0151] 2 DCDC converter

[0152] 3 LDDIC

[0153] 31, 31a drive circuit

[0154] 32 LDVCC monitoring circuit

[0155] 33 temperature monitoring circuit

[0156] 34 selector

[0157] 35 AD converter

[0158] 36 logic circuit

[0159] 37 HR voltage monitoring circuit

[0160] 100 distance measuring module

[0161] 101 light emitting device

[0162] 112 optical module

[0163] 113 LDD

[0164] 114 lens

[0165] 115 distance image sensor

[0166] 116 large scale integrated circuit

[0167] 121 LD

[0168] 122 PD

[0169] 123 diffuser

Claims

1. A driving device, comprising: A temperature monitoring circuit detects the temperature of the driving circuit that drives the light-emitting element during the test light-emitting period of the light-emitting element; A margin voltage monitoring circuit detects the margin voltage of the driving circuit during the test light emission period; A power supply voltage monitoring circuit detects the power supply voltage supplied to the light-emitting element during the test light-emitting period; as well as The control unit adjusts the power supply voltage during the test light-emitting period according to the input / output potential difference of the light-emitting element to obtain a sufficient margin voltage required for a specified drive current to flow through the light-emitting element, wherein the input / output potential difference of the light-emitting element varies according to the temperature of the drive circuit.

2. The driving device according to claim 1, wherein, The driving circuit includes a transistor connected in series between ground and the negative terminal of the light-emitting element, the light-emitting element having a positive terminal connected to a wiring supplying the power supply voltage, and The margin voltage monitoring circuit detects the potential difference between the negative electrode of the light-emitting element and the ground, and uses it as the margin voltage.

3. The driving device according to claim 1, wherein, The driving circuit includes a transistor connected in series between a wiring supplying the power supply voltage and the positive terminal of the light-emitting element, the light-emitting element having a negative terminal connected to ground, and The margin voltage monitoring circuit detects the potential difference between the wiring supplying the power supply voltage and the positive terminal of the light-emitting element, and uses this potential difference as the margin voltage.

4. The driving device according to claim 1, wherein, The control unit adjusts the power supply voltage based on information indicating the relationship between the driving current of the light-emitting element and the input / output potential difference of the light-emitting element, wherein the driving current of the light-emitting element varies according to the temperature of the driving circuit.

5. The driving device according to claim 1, wherein, The driving circuit repeatedly causes the light-emitting element to perform test light emission and to perform main light emission for distance measurement. The control unit corrects the power supply voltage based on the temperature change of the driving circuit detected by the temperature monitoring circuit during the test light emission period before and after the main light emission, and a correction factor of the power supply voltage based on the temperature change.

6. A light-emitting device, comprising: Light-emitting element, emitting light for distance measurement; A temperature monitoring circuit detects the temperature of the driving circuit that drives the light-emitting element during the test light-emitting period of the light-emitting element; A margin voltage monitoring circuit detects the margin voltage of the driving circuit during the test light emission period; A power supply voltage monitoring circuit detects the power supply voltage supplied to the light-emitting element during the test light-emitting period; as well as The control unit adjusts the power supply voltage during the test light-emitting period according to the input / output potential difference of the light-emitting element to obtain a sufficient margin voltage required for a specified drive current to flow through the light-emitting element, wherein the input / output potential difference of the light-emitting element varies according to the temperature of the drive circuit.

7. A driving method, comprising: The temperature of the driving circuit that drives the light-emitting element is detected by a computer during the test light-emitting period of the light-emitting element; The computer detects the margin voltage of the driving circuit during the test light emission period; The computer detects the power supply voltage supplied to the light-emitting element during the test light-emitting period; as well as The computer adjusts the power supply voltage during the test light-emitting period based on the input / output potential difference of the light-emitting element to obtain a sufficient margin voltage required for the specified driving current to flow through the light-emitting element. The input / output potential difference of the light-emitting element varies according to the temperature of the driving circuit.

Images