Light-source-driving device, light-emitting device, and distance-measuring system

Abstract

[Problem] To make it possible to suppress any deviation of light emission timing. [Solution] A light-source-driving device according to the present invention comprises: a first transistor for generating an electric current to be channeled through a light-emitting element; a second transistor for switching and controlling whether to allow the first transistor to generate the electric current; a third transistor for stopping emission of light by the light-emitting element; and a fourth transistor for switching and controlling whether to allow the third transistor to stop the emission of light by the light-emitting element.

Description

Light source driving device, light emitting device and ranging system

[0001] The present disclosure relates to a light source driving device, a light emitting device, and a distance measuring system.

[0002] A light-emitting device known as a VCSEL (Vertical Cavity Surface Emitting Laser) is known. A VCSEL is a light-emitting device that emits light resonated in a resonator disposed in the normal direction of a semiconductor substrate surface from a surface in the normal direction of the substrate surface. In recent years, VCSELs have been attracting attention as light sources for measuring the distance to an object using, for example, an STL (Structured Light) method or a ToF (Time of Flight) method.

[0003] In a light source driving device that drives a VCSEL, it is necessary to shorten the rise time and fall time of the current flowing through the light emitting element to improve distance measurement accuracy. For example, an assist circuit is known that shorts both ends of the light emitting element to make the fall waveform of the current flowing through the light emitting element steeper. Patent Document 1 discloses a light source driving device that includes an assist circuit and a delay circuit that dynamically adjusts the delay time of a drive control signal to adjust the timing of turning off the current to the light emitting element and the timing of shorting the light emitting element.

[0004] Japanese Patent Application Laid-Open No. 2021-22689

[0005] The transistors that make up the assist circuit and the transistors in the drive circuit that drives the light-emitting element are generally high-voltage transistors. The transistor that generates the current that flows to the light-emitting element is connected to the main path. A low-voltage transistor that switches whether or not current flows to the main path is connected to the main path.

[0006] High-voltage transistors operate slower than low-voltage transistors. This means that the transistors that make up the assist circuit and the low-voltage transistors in the main path are prone to misalignment in their on / off timing. Because individual transistors have PVT (process, voltage, temperature) variations, the PVT variations are greater between high-voltage transistors and low-voltage transistors, which can cause fluctuations in the light emission timing of multiple light-emitting elements included in the VCSEL.

[0007] In Patent Document 1, the drive circuit is delayed to match the assist circuit in order to adjust the phase between the drive circuit and the assist circuit. However, because the delay amount of the assist circuit is large, the delay of the drive circuit also becomes large, causing a delay in driving the light-emitting element. This delay varies due to PVT variations.

[0008] Therefore, the present disclosure provides a light source driving device, a light emitting device, and a distance measuring system that can suppress deviations in light emission timing.

[0009] In order to solve the above problem, according to the present disclosure, there is provided a light source driving device comprising: a first transistor that generates a current flowing in a light-emitting element; a second transistor that switches between controlling whether or not the first transistor generates the current; a third transistor that stops the light emission of the light-emitting element; and a fourth transistor that switches between controlling whether or not the third transistor stops the light emission of the light-emitting element.

[0010] The third transistor may shape a waveform of a current flowing through the light emitting element when the light emitting element stops emitting light.

[0011] The second transistor may have a lower breakdown voltage than the first transistor, and the fourth transistor may have a lower breakdown voltage than the third transistor.

[0012] The third transistor and the fourth transistor may be cascode-connected, and the first transistor and the second transistor may be cascode-connected.

[0013] The semiconductor device may further include a bias generation circuit that generates a bias signal to be input to the gate of the third transistor, the bias generation circuit generating the bias signal based on a predetermined reference voltage, and the reference voltage being supplied to the drain or source of the fourth transistor.

[0014] The bias generation circuit may include an impedance circuit that generates the bias signal according to the reference voltage, and a current source that passes a predetermined current through the impedance circuit, and the bias signal may have a voltage level based on the reference voltage and a voltage drop that occurs in the impedance circuit according to the current.

[0015] The bias generating circuit may include an impedance circuit that generates the bias signal by dividing the reference voltage.

[0016] The bias generating circuit may include a capacitor connected between the gate of the third transistor and the reference voltage node.

[0017] The device may include a plurality of third transistors that stop the light emission of a plurality of light-emitting elements, respectively; and a plurality of fourth transistors that switch and control the third transistors to determine whether or not to stop the light emission of the plurality of light-emitting elements, wherein the bias generation circuit supplies the bias signal common to the third transistors, and an individual switch control signal is input to each gate of the fourth transistors.

[0018] The power supply may further include a first buffer circuit that buffers a first pulse signal that controls switching of the fourth transistor, the first buffer circuit having a withstand voltage corresponding to a withstand voltage of the second transistor.

[0019] The first buffer circuit may include a transistor having a lower withstand voltage than the third transistor.

[0020] The power supply may further include a second buffer circuit that buffers a second pulse signal that controls switching of the second transistor.

[0021] The second buffer circuit may have a withstand voltage corresponding to the withstand voltage of the second transistor.

[0022] The first transistors, the second transistors, the third transistors, and the fourth transistors may be arranged in one direction.

[0023] The plurality of first transistors, the plurality of third transistors, and the plurality of fourth transistors may be arranged in this order along a first direction, and each of the plurality of second transistors and the corresponding first transistor may be arranged along a second direction intersecting the first direction.

[0024] The fourth transistor may be a thin film transistor.

[0025] The first transistor and the second transistor may be N-type MOS (Metal Oxide Semiconductor) transistors, the third transistor and the fourth transistor may be P-type MOS transistors, the source of the fourth transistor may be connected to a first reference voltage node, the drain of the fourth transistor may be connected to the source of the third transistor, the source of the third transistor may be connected to the drain of the first transistor and the cathode of the light-emitting element, the source of the first transistor may be connected to the drain of the second transistor, and the source of the second transistor may be connected to a second reference voltage node.

[0026] The present disclosure also provides a light emitting device including: a light emitting section having a plurality of the light emitting elements that perform surface emission; and a light source driving device that drives the light emitting section.

[0027] The light emitting unit may be a vertical cavity surface emitting laser (VCSEL).

[0028] Furthermore, according to the present disclosure, there is provided a ranging system comprising: a light emitting device that emits a pulsed light signal; a light receiving unit that receives a reflected light signal from an object onto which the light signal is irradiated; and a ranging unit that measures the distance to the object based on the light signal emitted by the light emitting device and the reflected light signal received by the light receiving unit.

[0029] FIG. 1 is a circuit diagram showing a first configuration example of a light source driving device according to a first embodiment of the present disclosure. FIG. 2 is a circuit diagram showing a second configuration example of a light source driving device according to a first embodiment of the present disclosure. FIG. 3 is a circuit diagram showing a third configuration example of a light source driving device according to a first embodiment of the present disclosure. FIG. 4 is a circuit diagram showing a fourth configuration example of a light source driving device according to a first embodiment of the present disclosure. FIG. 5 is a circuit diagram showing a bias generation circuit according to the first configuration example. FIG. 6 is a circuit diagram showing a bias generation circuit according to the second configuration example. FIG. 7 is a circuit diagram showing a fifth configuration example of a light source driving device according to the first embodiment of the present disclosure. FIG. 8 is a circuit diagram showing a configuration of a light source driving device according to a comparative example. FIG. 9 is a diagram showing two buffer circuits of a light source driving device according to a comparative example. FIG. 10 is a circuit diagram showing a configuration of a light source driving device according to a second embodiment of the present disclosure. FIG. 11 is a timing chart of signals when a parasitic capacitor occurs in the light source driving device according to the first embodiment of the present disclosure. FIG. 12 is a block diagram showing a first configuration example of a light source driving device according to a third embodiment of the present disclosure. FIG. 13 is a block diagram showing a second configuration example of a light source driving device according to a third embodiment of the present disclosure. FIG. 14 is a block diagram showing a configuration example of a distance measuring system according to a fourth embodiment of the present disclosure. FIG. 15 is an explanatory diagram of an STL system. It is an explanatory diagram of the distance measurement principle of the STL method. It is a block diagram showing an example of a schematic configuration of a vehicle control system. It is an explanatory diagram showing an example of the installation positions of a vehicle outside information detection unit and an imaging unit.

[0030] Hereinafter, embodiments of a light source driving device, a light emitting device, and a ranging system will be described with reference to the drawings. The following description will focus on the main components of the light source driving device, the light emitting device, and the ranging system, but the light source driving device, the light emitting device, and the ranging system may include components and functions that are not shown or described. The following description does not exclude components and functions that are not shown or described.

[0031] 1 is a circuit diagram showing a first configuration example of a light source driving device 1 according to a first embodiment of the present disclosure. The light source driving device 1 is connected to a plurality of light emitting elements 20. The light source driving device 1 includes a transistor (first transistor) 11, a transistor (second transistor) 12, a transistor (third transistor) 13, a transistor (fourth transistor) 14, a transistor 15, a transistor 16, and a current source 17.

[0032] The light-emitting element 20 is one of a plurality of light-emitting elements 20 included in, for example, a VCSEL. The plurality of light-emitting elements 20 are provided, for example, in a VCSEL chip. Meanwhile, the light source driving device 1 is provided, for example, in a driver chip. The light source driving device 1 drives the plurality of light-emitting elements 20 individually. In this specification, a unit of the light source driving device 1 that drives each light-emitting element 20 is called a channel 2. Figure 1 illustrates the circuit configuration of two channels 2. The circuit of one channel 2, excluding the light-emitting element 20, is the minimum configuration of the light source driving device 1.

[0033] The transistors 11, 12, 15, and 16 are, for example, N-channel field effect transistors (FETs), and the transistors 13 and 14 are, for example, P-channel FETs.

[0034] The transistor 11 generates a current that flows through the light-emitting element 20. The source of the transistor 11 is connected to the drain of the transistor 12. The drain of the transistor 11 is connected to the drain of the transistor 13 and the cathode of the light-emitting element 20. The gate of the transistor 11 is connected to the gate and drain of the transistor 15.

[0035] The transistors 11 and 15 constitute a current mirror circuit 3. The current mirror circuit 3 causes a current proportional to the current flowing between the drain and source of the transistor 15 to flow between the drain and source of the transistor 11. In other words, the light emission drive current value of the light emitting element 20 is determined by the current mirror circuit 3.

[0036] The transistor 12 controls whether or not the transistor 11 generates a current that flows through the light-emitting element 20. The source of the transistor 12 is connected to, for example, a ground wiring (second reference voltage node). A signal (second pulse signal) Main_SW is input to the gate of the transistor 12. The transistor 12 is turned on when, for example, a high-level signal Main_SW is input, causing the transistor 11 to generate a current.

[0037] As described above, the transistors 11 and 12 are used to make the light-emitting element 20 emit light. In this specification, the transistors 11 and 12 are also referred to as a drive circuit 4. The transistors 11 and 12 are cascode-connected between a connection node with the light-emitting element 20 and a ground wiring.

[0038] The transistor 13 stops the light emission of the light emitting element 20 and shapes the waveform of the current flowing through the light emitting element 20 when the light emitting element 20 stops emitting light. The source of the transistor 13 is connected to the drain of the transistor 14. A predetermined bias signal Assist_Bias is input to the gate of the transistor 13.

[0039] The transistor 14 controls switching of whether or not to cause the transistor 13 to stop light emission of the light-emitting element 20. The source of the transistor 14 is connected to, for example, a power supply (VPOS) wiring (first reference voltage node). A signal (first pulse signal) Assist_SW is input to the gate of the transistor 14. The transistor 14 is turned on when, for example, a low-level signal Assist_SW is input, causing the transistor 13 to stop light emission of the light-emitting element 20.

[0040] The source of the transistor 14 may be connected to the anode of the light-emitting element 20. In this case, when the transistor 14 is turned on, the anode and cathode of the light-emitting element 20 are short-circuited, and the light-emitting element 20 can stop emitting light.

[0041] As described above, the transistors 13 and 14 are used to stop the light emission of the light emitting element 20. In this specification, the transistors 13 and 14 are also referred to as an assist circuit (stop circuit) 5. The transistors 13 and 14 are cascode-connected between the connection node with the light emitting element 20 and the power supply (VPOS) wiring.

[0042] The signals Main_SW and Assist_SW are supplied from a timing adjustment unit, which will be described later.

[0043] Since the transistor 13 is directly connected to the light-emitting element 20, it must be configured as an element with a high withstand voltage (for example, withstand voltage of 3.3 V, 5 V, or 10 V). On the other hand, the transistor 14 can be configured as an element with a low withstand voltage (for example, withstand voltage of 1.1 V). The transistor 14 can be configured as, for example, a thin film transistor (TFT).

[0044] Similarly, the transistor 11 is made up of a high-voltage element (for example, 3.3 V, 5 V, or 10 V), and the transistor 12 is made up of a low-voltage element (for example, 1.1 V).

[0045] The transistors 11 to 14 are arranged for each light emitting element 20. One light emitting element 20 and the transistors 11 to 14 corresponding to the light emitting element 20 form one channel 2.

[0046] The transistors 15 and 16 control the current flowing between the drain and source of the plurality of transistors 11 based on the current generated by the current source 17. The source of the transistor 15 is connected to the drain of the transistor 16. The source of the transistor 16 is connected to, for example, a ground wiring. A predetermined bias voltage is applied to the gate of the transistor 16. One end of the current source 17 is connected to the drain and gate of the transistor 15. The other end of the current source 17 is connected to, for example, a power supply wiring.

[0047] The light-emitting element 20 is used, for example, as a light source in a distance measurement system. To improve distance measurement accuracy, it is necessary to make the signal waveform of the light pulse signal from the light-emitting element 20 steeper. The light pulse signal from the light-emitting element 20 has a rising edge corresponding to the timing at which the transistor 12 turns on and a falling edge corresponding to the timing at which the transistor 14 turns on. By using the transistors 12 and 14, the light-source driving device 1 can make the signal waveform of the light pulse signal steeper.

[0048] In order to improve the distance measurement accuracy, it is desirable to minimize the delay between when the high-level signals Main_SW and Assist_SW are input and when the light emitting element 20 starts and stops emitting light. It is also desirable to minimize the variation in the delay between when the light emitting element 20 starts emitting light and when it stops emitting light.

[0049] The light source driving device 1 according to the present disclosure is characterized in that the switching of the assist circuit 5 is performed by a low-voltage transistor 14. By making the transistor 14 low-voltage, sensitivity to changes in the signal level of the signal Assist_SW can be improved, and the delay until the light emitting element 20 stops emitting light can be reduced. Furthermore, by making the withstand voltage of the transistor 14 substantially the same as that of the transistor 12, the variability in the delay until the light emitting element 20 starts emitting light and the delay until the light emitting element 20 stops emitting light can be reduced.

[0050] 2 is a circuit diagram showing a second configuration example of the light source driving device 1 according to the first embodiment of the present disclosure. The light source driving device 1a shown in FIG. 2 differs from the light source driving device 1 shown in FIG. 1 in that it includes a buffer circuit (first buffer circuit) 30 that buffers (shapes the waveform of) the signal Assist_SW and inputs it to the gate of the transistor 14. Note that the transistors 15 and 16 and the current source 17 are not shown in FIG. 2. Furthermore, in this specification, the transistors 13 and 14 and the buffer circuit 30 may be referred to as an assist circuit 5.

[0051] The buffer circuit 30 includes inverters 31 and 32. A signal Assist_SW is input to the input terminal of the inverter 31. An output terminal of the inverter 31 is connected to the input terminal of the inverter 32. An output terminal of the inverter 32 inputs the signal Assist_SW to the gate of the transistor 14. The inverters 31 and 32 are connected to a power supply (VPOS) wiring and a virtual ground (VGND) wiring. FIG. 2 illustrates an example in which the buffer circuit 30 is configured with two inverters 31 and 32, but the present invention is not limited to this, and the buffer circuit 30 may have three or more inverters. Note that one or more positive logic buffer amplifiers may be provided instead of the inverters 31 and 32.

[0052] Because the transistor 14 according to the present disclosure has a low breakdown voltage, the transistors constituting the buffer circuit 30 also have a low breakdown voltage. Specifically, the inverters 31 and 32 can be configured with core transistors with a lower breakdown voltage than the transistor 13, for example, a breakdown voltage of 1.1 V. The voltage level of the virtual ground VGND is set to, for example, VPOS-1.1 V. This allows the amount of delay in the buffer circuit 30 to be reduced compared to when the buffer circuit 30 is configured with high breakdown voltage transistors.

[0053] 3 is a circuit diagram showing a third configuration example of the light source driving device 1 according to the first embodiment of the present disclosure. The light source driving device 1b shown in FIG. 3 differs from the light source driving device 1a shown in FIG. 2 in that it includes a buffer circuit (second buffer circuit) 40 that buffers (shapes the waveform of) the signal Main_SW and inputs it to the gate of the transistor 12. In this specification, the transistors 11 and 12 and the buffer circuit 40 may be referred to as a driving circuit 4.

[0054] The buffer circuit 40 has inverters 41 and 42. A signal Main_SW is input to the input terminal of the inverter 41. An output terminal of the inverter 41 is connected to the input terminal of the inverter 42. An output terminal of the inverter 42 inputs the signal Main_SW to the gate of the transistor 12. FIG. 3 illustrates an example in which the buffer circuit 40 is configured with two inverters 41 and 42, but this is not limiting and a configuration having three or more inverters may also be used. Note that one or more positive logic buffer amplifiers may be provided instead of the inverters 41 and 42.

[0055] Because the transistor 12 according to the present disclosure has a low withstand voltage, the inverters 41 and 42 can be configured with low withstand voltage elements (for example, core transistors with a withstand voltage of 1.1 V) similar to the inverters 31 and 32. By configuring the inverters 41 and 42 with transistors with the same withstand voltage as the inverters 31 and 32, for example, it is possible to reduce PVT variations in the buffer circuits 30 and 40. This reduces variations in the amount of delay in the buffer circuits 30 and 40, and suppresses deviations in the light emission timing of the light-emitting element 20.

[0056] In order to make the delay amounts of the buffer circuits 30 and 40 approximately the same, it is not necessary to configure the inverters 41 and 42 with the same elements as the inverters 31 and 32, and the design of the buffer circuits 30 and 40 is arbitrary.

[0057] 4 is a circuit diagram showing a fourth configuration example of the light source driving device 1 according to the first embodiment of the present disclosure. The light source driving device 1c shown in FIG. 4 differs from the light source driving device 1 of FIG. 1 in that it includes a bias generation circuit 50 that generates a bias signal Assist_Bias. One end of the bias generation circuit 50 is connected to the gates of the plurality of transistors 13, and the other end is connected to a power supply (VPOS) wiring. The bias generation circuit 50 supplies a common bias signal Assist_Bias to the plurality of transistors 13. Note that the transistors 15 and 16 and the current source 17 are not shown in FIG. 4.

[0058] As described above, a common bias signal Assist_Bias is input to the gates of each transistor 13 of multiple channels 2, but an individual signal Assist_SW is input to the gates of each transistor 14 of each channel 2, so that the assist circuit 5 of each channel 2 can be controlled individually, and the timing at which the light-emitting element 20 of each channel 2 stops emitting light can be controlled individually.

[0059] The specific configuration of the bias generation circuit 50 in FIG. 4 is arbitrary. Representative configuration examples will be described below. FIG. 5A is a circuit diagram of a bias generation circuit 50a according to a first configuration example. The bias generation circuit 50a shown in FIG. 5A generates a bias signal Assist_Bias based on a predetermined reference current. The bias generation circuit 50a includes a current source 51 and an impedance element 52. The impedance element 52 is, for example, a resistive element. The current source 51 generates a reference current. A voltage drop occurs in the impedance element 52 due to the current generated by the current source 51. A bias signal Assist_Bias having a voltage level corresponding to this voltage drop and the power supply voltage VPOS is generated.

[0060] 5B is a circuit diagram of a bias generation circuit 50b according to a second exemplary configuration. The bias generation circuit 50b shown in FIG. 5B generates the bias signal Assist_Bias based on a reference voltage, specifically, the power supply voltage VPOS, that has a higher voltage level than the bias signal Assist_Bias. The bias generation circuit 50b includes impedance elements 53 and 54. The bias generation circuit 50b divides the power supply voltage VPOS using the impedance elements 53 and 54 to generate the bias signal Assist_Bias. For example, variable resistors may be used as the impedance elements 53 and 54 to dynamically adjust the voltage division ratio of the power supply voltage VPOS.

[0061] Fig. 6 is a circuit diagram showing a fifth configuration example of the light source driving device 1 according to the first embodiment of the present disclosure. The light source driving device 1d shown in Fig. 6 differs from the light source driving device 1b shown in Fig. 3 in that it includes a timing adjustment unit 61, a phase detection unit 62, and a timing control unit 63 for dynamically adjusting the input timing of the signals Main_SW and Assist_SW.

[0062] The timing adjustment unit 61 adjusts the input interval of the signals Main_SW and Assist_SW. A pulse signal indicating a light emission period is input to the timing adjustment unit 61 as an input signal IN from a circuit in a preceding stage (e.g., a control circuit). This input signal IN is a signal generated at a timing based on, for example, a frame synchronization signal. The timing adjustment unit 61 generates the signals Main_SW and Assist_SW from the input signal IN and inputs them to the buffer circuits 40 and 30, respectively.

[0063] The phase detection unit 62 receives the signals Main_SW and Assist_SW from the buffer circuits 40 and 30, respectively. The phase detection unit 62 is configured, for example, with a D-flip-flop circuit or the like. The phase detection unit 62 receives, for example, the signal Assist_SW as a clock input and the signal Main_SW as a D input, and obtains a phase comparison signal oPD as a Q output. Note that the phase detection unit 62 may also receive the signal Main_SW as a D input and the signal Assist_SW as a clock input.

[0064] When the D-flip-flop judges based on the rising edge of the clock input, either the signal Main_SW or the signal Assist_SW that rises at the timing when phase comparison is to be performed may be used as the clock input, thereby reducing the need for a buffer for pulse inversion.

[0065] The phase comparison signal oPD is input to the timing control unit 63. The timing control unit 63 is configured by, for example, a logic circuit, a central processing unit (CPU), etc. The timing control unit 63 generates a timing adjustment signal TA based on the phase comparison signal oPD and supplies it to the timing adjustment unit 61.

[0066] 6 can detect the phase difference between the signals Main_SW and Assist_SW when the signal delay amount in the buffer circuits 30 and 40 varies due to environmental factors such as temperature and power supply voltage state. Furthermore, the timing control unit 63 can adjust the input interval of the signals Main_SW and Assist_SW to the timing adjustment unit 61 in accordance with the detection result of the phase detection unit 62.

[0067] 6 may also include a level shifter or the like that adjusts the signal levels of the signals Main_SW and Assist_SW in accordance with the thresholds of the transistors 12 and 14. Furthermore, when a level shifter is provided in one of the signal paths of the signals Main_SW and Assist_SW, a dummy circuit or the like that provides a delay equivalent to that of the level shifter may be provided in the other signal path.

[0068] 7A is a circuit diagram showing the configuration of a light source driving device 100 according to a comparative example. The light source driving device 100 differs from the light source driving device 1 of FIG.

[0069] 7A uses a transistor 13 to control whether or not to stop light emission of the light-emitting element 20. A signal Assist_SW is input to the gate of the transistor 13. The source of the transistor 13 is connected to the power supply (VPOS) wiring. When a low-level signal Assist_SW is input, the transistor 13 turns on and stops light emission of the light-emitting element 20.

[0070] The light source driving device 100 can control the timing of when the light emitting element 20 starts and stops emitting light, similar to the light source driving device 1 of FIG.

[0071] On the other hand, since the transistor 13 is directly connected to the light-emitting element 20, it must be configured with a high-voltage resistance element. The transistor 13 is less sensitive to changes in the signal level of the signal Assist_SW than the transistor 13 in Figure 1, and there is a large delay until the light emission of the light-emitting element 20 stops. This makes it difficult to make the optical pulse signal of the light-emitting element 20 steep, and this deteriorates the distance measurement accuracy.

[0072] 7B is a diagram showing buffer circuits 40 and 110 of a light source driving device 100 according to a comparative example. The buffer circuit 110 buffers (shapes the waveform of) the signal Assist_SW and inputs it to the gate of the transistor 13. The buffer circuit 110 includes inverters 111 and 112.

[0073] Since the transistor 13 according to the comparative example has a high withstand voltage, the inverters 111 and 112 in the buffer circuit 110 also need to be configured with transistors with a high withstand voltage (for example, 3.3 V withstand voltage). The voltage level of the virtual ground VGND is set to, for example, VPOS-3.3 V.

[0074] Compared to the inverters 111 and 112 for the transistor 13, the inverters 41 and 42 for the transistor 12 are configured with elements having a low withstand voltage, and therefore PVT variations become large in the buffer circuits 40 and 110. As a result, the delay until the signal Assist_SW is input to the transistor 13 becomes larger than the delay until the signal Main_SW is input to the transistor 12, which increases the lag in the timing at which the light emitting element 20 stops emitting light, and deteriorates the distance measurement accuracy.

[0075] Even if the delay amount of the buffer circuit 40 is increased to make the delay amounts of the buffer circuits 40 and 110 the same, the start of light emission of the light emitting element 20 is delayed, resulting in a deterioration in distance measurement accuracy.

[0076] In contrast, the light source driving device 1 in Fig. 1 etc. can use a low-voltage transistor 14 to control whether or not to stop the light emission of the light-emitting element 20. Because the transistor 14 is highly sensitive to changes in the signal level of the signal Assist_SW, the delay amount until the light emission of the light-emitting element 20 stops can be reduced, and can even be made substantially the same as the delay amount until the light-emitting element 20 starts to emit light. Furthermore, because the inverters 31 and 32 in Fig. 3 etc. can be configured using low-voltage elements, the delay amounts of the buffer circuits 30 and 40 can be made substantially the same without increasing the delay amount of the buffer circuit 40.

[0077] Compared to the light source driving device 100 according to the comparative example, the light source driving devices 1 to 1d according to the present disclosure can make the optical pulse signal of the light emitting element 20 steeper without delaying the start of light emission of the light emitting element 20, thereby improving distance measurement accuracy.

[0078] As described above, the light source driving devices 1 to 1d according to the present disclosure include a low-voltage transistor 14 in the assist circuit 5 for controlling the on / off switching of the high-voltage transistor 13. The light source driving devices 1 to 1d use this transistor 14 to control whether or not to stop the light emission of the light emitting element 20, thereby improving sensitivity to the signal Assist_SW and reducing the delay until the light emission of the light emitting element 20 stops. This reduces the variation in the delay until the light emitting element 20 starts to emit light and until the light emission stops, making it possible to make the optical pulse signal of the light emitting element 20 steeper regardless of PVT fluctuations.

[0079] 3 and the like can be configured using low-voltage transistors, the delay amounts of the buffer circuits 30 and 40 can be made substantially the same without increasing the delay amount of the buffer circuit 40. This makes it possible to make the optical pulse signal of the light-emitting element 20 steeper without delaying the start of light emission of the light-emitting element 20.

[0080] In particular, by applying the light source driving devices 1 to 1d according to the present disclosure to a distance measurement system, the distance measurement accuracy can be improved.

[0081] Second Embodiment Fig. 8 is a circuit diagram showing the configuration of a light source driving device 1d according to a second embodiment of the present disclosure. The light source driving device 1d in Fig. 8 differs from the light source driving device 1 in Fig. 1 in that it includes a capacitor 71 connected to the gate of the transistor 13. The capacitor 71 is provided to mitigate sudden fluctuations in the signal level of the bias signal Assist_Bias caused by a parasitic capacitor 72 (described later).

[0082] One end of the capacitor 71 is connected to the gate of the transistor 13 and the output terminal of the bias generating circuit 50. The other end of the capacitor 71 is connected to, for example, a power supply (VPOS) line.

[0083] A parasitic capacitor 72 exists between the drain and gate of the transistor 13 in the light source driving devices 1 to 1d according to the first embodiment. FIG. 9A is a timing chart of signals when the parasitic capacitor 72 exists in the light source driving devices 1 to 1d. When the signal Main_SW is turned on between times t1 and t2, a current is supplied to the light emitting element 20, causing the light emitting element 20 to emit light. This causes the cathode voltage Vcahode of the light emitting element 20 to decrease. When the cathode voltage Vcahode decreases, the signal level of the bias signal Assist_Bias drops sharply due to capacitive coupling by the parasitic capacitor 72.

[0084] A drop in the bias signal Assist_Bias may cause a drop in the drain voltage of the low-voltage transistor 14, which may result in the transistor 14 being destroyed due to an excess of the voltage.

[0085] 9B is a timing chart of signals when a parasitic capacitor 72 occurs in the light source driving device 1d according to the second embodiment. In the light source driving device 1d, even if the cathode voltage Vcahode drops due to light emission from the light emitting element 20, the bias signal Assist_Bias has a signal level that corresponds to the capacitance ratio between the capacitor 71 and the parasitic capacitor 72, thereby mitigating momentary fluctuations in the signal level of the bias signal Assist_Bias. This prevents damage to the transistor 14.

[0086] In this way, the light source driving device 1d according to the second embodiment of the present disclosure can suppress sudden fluctuations in the signal level of the bias signal Assist_Bias by connecting the capacitor 71 between the gate of the transistor 13 and the wiring of the power supply voltage VPOS through capacitive coupling by the parasitic capacitor 72, thereby preventing destruction of the low-voltage transistor 14 and the unexpected cessation of light emission of the light-emitting element 20.

[0087] Third Embodiment FIG. 10A is a block diagram showing a first configuration example of a light-source driving device 1 according to a third embodiment of the present disclosure. The light-source driving device 1 according to the third embodiment has multiple light-emitting units. Each light-emitting unit has multiple channels. In the example of FIG. 10A, one light-emitting unit has four channels A to D, but the number of channels included in one light-emitting unit is arbitrary. Furthermore, the number of light-emitting units included in the light-source driving device 1 is also arbitrary. The light-source driving device 1 can individually control the light-emitting modes of the multiple channels for each light-emitting unit. The light-emitting mode refers to any combination of lighting and extinguishing of the multiple channels included in one light-emitting unit.

[0088] 10A is a diagram showing the layout arrangement of transistors 11 to 14 and inverters 32 and 42 included in multiple light-emitting units. The drive circuit 4 (hereinafter also referred to as N-channel) is arranged in the upper part of Fig. 10A. The assist circuit 5 (hereinafter also referred to as P-channel) is arranged in the lower part of Fig. 10A.

[0089] Channel A in each light-emitting unit includes transistors 11a, 12a, 13a, and 14a, and inverters 32a and 42a. Channel B includes transistors 11b, 12b, 13b, and 14b, and inverters 32b and 42b. Channel C includes transistors 11c, 12c, 13c, and 14c, and inverters 32c and 42c. Channel D includes transistors 11d, 12d, 13d, and 14d, and inverters 32d and 42d.

[0090] One transistor each of 13a to 13d and 14a to 14d is provided for each light-emitting unit. Transistors 11a to 11d and 12a to 12d are provided corresponding to the multiple channels of each light-emitting unit. More specifically, channel A is provided with transistors 11a and 12a, channel B is provided with transistors 11b and 12b, channel C is provided with transistors 11c and 12c, and channel D is provided with transistors 11d and 12d. Each channel drives a separate light-emitting element 20. Note that the light-emitting elements 20 are not shown in FIG. 10A.

[0091] 10A , there are provided a region RG1 in which the transistors 11a to 11d of each channel of each light-emitting unit are arranged in order in the second direction Y, a region RG2 in which the transistors 12a to 12d of each channel of each light-emitting unit are arranged in order in the second direction Y, a region RG3 in which the transistors 13a to 13d of each light-emitting unit are arranged in order in the second direction Y, and a region RG4 in which the transistors 14a to 14d of each light-emitting unit are arranged in order in the second direction Y. In addition, between regions RG2 and RG3, there is provided a region RG5 in which the inverters 42a to 42d are arranged in order in the first direction X. Furthermore, at one end of region RG4 in the second direction Y, there is provided a region RG6 in which the inverters 32a to 32d are arranged in the first direction X.

[0092] The inverters 32a to 32d receive a signal Assist_SW from the inverter 31 and the timing adjustment unit 61. The inverters 42a to 42d receive a signal Main_SW from the inverter 41 and the timing adjustment unit 61. The light source driving device 1f in FIG. 10A is configured to include one inverter 31 and one inverter 41, but the light source driving device 1f may also be configured to include a plurality of inverters 31 and a plurality of inverters 41.

[0093] As shown in FIG. 10A , in the light source driving device 1f, the driving circuit 4 and the assist circuit 5 are arranged separately. Furthermore, the second buffer group (i.e., inverters 42a to 42d) of the driving circuit 4 is arranged adjacent to the assist circuit 5. The light source driving device 1f in FIG. 10A can suppress variations in the amount of signal delay by making the lengths of the signal wirings L1 and L2 approximately equal. This allows the buffer circuits 30 and 40 to input the signals Main_SW and Assist_SW to the transistors 12 and 14, respectively, at the input intervals of the signals Main_SW and Assist_SW adjusted by the timing adjustment unit 61.

[0094] 10B is a block diagram showing a second configuration example of a light-source driving device 1 according to a third embodiment of the present disclosure. The light-source driving device 1g shown in FIG. 10B differs from FIG. 10A in that the above-mentioned regions RG1 and RG2 are arranged close to each other in the first direction X. This allows the distance between regions RG1 and RG3 arranged along the second direction Y to be reduced.

[0095] Since current flows from the light emitting element 20 between the sources of the transistors 11a to 11d in the region RG1 and the drains of the transistors 12a to 12d in the region RG3, a shorter distance between the regions RG1 and RG3 can suppress deviation in light emission timing.

[0096] 10B, the transistors 11a to 11d in the region RG1 and the transistors 12a to 12d in the region RG2 are arranged close to each other in the first direction X, but the size of the high-voltage transistors 11a to 11d is larger than the size of the low-voltage transistors 12a to 12d. For this reason, it is necessary to provide a gap between each region of the transistors 12a to 12d in the second direction Y. A dummy transistor may be placed in this gap, or a capacitor connected between the gate of each of the transistors 11a to 11d and the ground wiring may be placed.

[0097] In the light source driving device 1g shown in FIG. 10B, the wiring connecting the sources of the transistors 11a to 11d and the drains of the transistors 12a to 12d can be shortened, thereby suppressing deviations in light emission timing.

[0098] In this way, the light source driving device 1f according to the third embodiment of the present disclosure can suppress deviations in the timing of stopping light emission by arranging the buffer circuit 40 near the assist circuit 5. Furthermore, the light source driving device 1g according to the third embodiment of the present disclosure can suppress deviations in the timing of light emission by shortening the length of the wiring connecting the transistor 11 and the transistor 12 in each channel. The layout according to the third embodiment can be applied to any of the light source driving devices 1 to 1e according to the first and second embodiments.

[0099] Fourth Embodiment The light source driving devices 1 to 1g according to the first to third embodiments can be applied to a distance measuring system. Fig. 11 is a block diagram showing an example configuration of a distance measuring system 80 according to a fourth embodiment of the present disclosure. The distance measuring system 80 of Fig. 11 measures the distance to an arbitrary subject S by irradiating the subject S with light and receiving the reflected light. The distance measuring system 80 includes a light emitting unit 81, a driving unit 82, a power supply circuit 83, a light emitting side optical system 84, a light receiving side optical system 85, a light receiving unit 86, a signal processing unit 87, a control unit 88, and a temperature detection unit 89.

[0100] The light-emitting unit 81 emits light from a plurality of light sources. The light-emitting unit 81 has the light-emitting elements 20 shown in Fig. 1 as each light source. The light-emitting unit 81 is configured such that the plurality of light-emitting elements 20 are arranged in a predetermined pattern, such as a matrix.

[0101] The driver 82 is configured to include a power supply circuit 83 for driving the light emitting unit 81. The power supply circuit 83 generates a power supply voltage for the driver 82 based on an input voltage from, for example, a battery (not shown) or the like provided in the distance measuring system 80. The driver 82 drives the light emitting unit 81 based on the power supply voltage. The light source driving devices 1 to 1g according to the first to third embodiments can be applied to the driver 82 and the power supply circuit 83, for example.

[0102] In this specification, the light emitting unit 81, the driving unit 82, and the power supply circuit 83 may be collectively referred to as a light emitting device.

[0103] Light emitted from the light-emitting unit 81 is irradiated onto a subject (object) S, which is the object of distance measurement, via a light-emitting side optical system 84. The light thus irradiated is reflected from the subject S and enters the light-receiving surface of a light-receiving unit 86 via a light-receiving side optical system 85.

[0104] The light receiving unit 86 is a light receiving element such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, and receives reflected light from the subject S that enters through the light receiving side optical system 85 as described above, converts it into an electrical signal, and outputs it.

[0105] The light receiving unit 86 performs processes such as CDS (Correlated Double Sampling) and AGC (Automatic Gain Control) on the electrical signal obtained by photoelectrically converting the received light, and then performs A / D (Analog / Digital) conversion on the electrical signal, and outputs the resulting digital data to the signal processing unit 87 at the subsequent stage.

[0106] Furthermore, the light receiving unit 86 in this example outputs a frame synchronization signal to the driving unit 82. This enables the driving unit 82 to cause the light emitting element in the light emitting unit 81 to emit light at a timing according to the frame period of the light receiving unit 86.

[0107] The signal processing unit 87 is configured as a signal processor, for example, a DSP (Digital Signal Processor), etc. The signal processing unit 87 performs various signal processes on the digital signal input from the light receiving unit 86.

[0108] The control unit 88 is configured with, for example, a microcomputer having a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., or an information processing device such as a DSP, and controls the drive unit 82 for controlling the light-emitting operation by the light-emitting unit 81, and controls the light-receiving operation by the light-receiving unit 86.

[0109] The control unit 88 has a function as a distance measurement unit 88a. The distance measurement unit 88a measures the distance to the subject S based on a signal input via the signal processing unit 87 (i.e., a signal obtained by receiving reflected light from the subject S). The distance measurement unit 88a in this example measures the distance to each part of the subject S in order to be able to identify the three-dimensional shape of the subject S. Note that the specific distance measurement method in the distance measurement system 80 will be described again later.

[0110] The temperature detection unit 89 detects the temperature of the light-emitting unit 81. The temperature detection unit 89 may be configured to detect temperature using, for example, a diode. In this example, information about the temperature detected by the temperature detection unit 89 is supplied to the drive unit 82, which enables the drive unit 82 to drive the light-emitting unit 81 based on the temperature information.

[0111] The distance measurement method used in the distance measurement system 80 may be, for example, a STL (Structured Light) method or a ToF (Time of Flight) method.

[0112] The STL method is a method for measuring distance based on an image of a subject S illuminated with light having a predetermined light / dark pattern, such as a dot pattern or a grid pattern.

[0113] Fig. 12A is an explanatory diagram of the STL method. In the STL method, pattern light Lp having a dot pattern such as that shown in Fig. 12A is irradiated onto a subject S. The pattern light Lp is divided into a plurality of blocks BL, and a different dot pattern is assigned to each block BL (dot patterns are arranged not to overlap between blocks BL).

[0114] 12B is an explanatory diagram of the distance measurement principle of the STL method. In this example, a wall W and a box BX placed in front of it are considered as the subject S, and pattern light Lp is irradiated onto the subject S. "G" in the diagram schematically represents the angle of view of the light receiving unit 86.

[0115] In addition, "BLn" in the figure denotes the light of a certain block BL in the pattern light Lp, and "dn" denotes the dot pattern of the block BLn projected on the light-receiving image by the light-receiving unit 86.

[0116] Here, if there is no box BX in front of the wall W, the dot pattern of the block BLn is projected at the position "dn'" in the figure in the received light image. In other words, the position at which the pattern of the block BLn is projected in the received light image differs depending on whether the box BX is present or not, and specifically, the pattern is distorted.

[0117] The STL method is a method for determining the shape and depth of the subject S by utilizing the fact that the irradiated pattern is distorted by the object shape of the subject S. Specifically, it is a method for determining the shape and depth of the subject S from the way the pattern is distorted.

[0118] When the STL system is adopted, for example, a global shutter type IR (Infrared) light receiving unit is used as the light receiving unit 86. In the case of the STL system, the distance measuring unit 88a controls the drive unit 82 so that the light emitting unit 81 emits pattern light, detects distortion of the pattern in the image signal obtained via the signal processing unit 87, and calculates the distance based on the distortion of the pattern.

[0119] Next, the ToF method is a method for measuring the distance to an object by detecting the time of flight (time difference) of light emitted from the light-emitting unit 81, reflected by the object, and reaching the light-receiving unit 86.

[0120] When the so-called direct ToF (dTOF) method is adopted as the ToF method, a SPAD (Single Photon Avalanche Diode) is used as the light receiving unit 86, and the light emitting unit 81 is pulse-driven. In this case, the distance measuring unit 88a calculates the time difference between light emission and reception of light emitted from the light emitting unit 81 and received by the light receiving unit 86, based on a signal input via the signal processing unit 87, and calculates the distance to each part of the subject S based on the time difference and the speed of light.

[0121] When the so-called indirect ToF (iTOF) method (phase difference method) is adopted as the ToF method, a light receiving unit capable of receiving, for example, IR light is used as the light receiving unit 86 .

[0122] In this way, the light source driving devices 1 to 1g according to the first to third embodiments can be applied to the driving unit 82 and the power supply circuit 83 in Fig. 11. This makes it possible to make the light emission pulse of the light emitting element 20 in the light emitting unit 81 steeper, thereby improving the distance measurement accuracy of the distance measurement system 80.

[0123] (Application Examples) The technology according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of moving body, such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, a robot, construction machinery, or agricultural machinery (tractor). Note that the technology according to the present disclosure is not necessarily limited to moving bodies, but can also be applied to mobile devices such as smartphones or tablets, or electronic devices such as PCs (Personal Computers).

[0124] 13 is a block diagram showing a schematic configuration example of a vehicle control system 7000, which is an example of a mobile object control system to which the technology according to the present disclosure can be applied. The vehicle control system 7000 includes a plurality of electronic control units connected via a communication network 7010. In the example shown in FIG. 13, the vehicle control system 7000 includes a drive system control unit 7100, a body system control unit 7200, a battery control unit 7300, an outside-vehicle information detection unit 7400, an inside-vehicle information detection unit 7500, and an integrated control unit 7600. The communication network 7010 connecting these multiple control units may be an in-vehicle communication network conforming to any standard, such as a Controller Area Network (CAN), a Local Interconnect Network (LIN), a Local Area Network (LAN), or FlexRay (registered trademark).

[0125] Each control unit includes a microcomputer that performs arithmetic processing according to various programs, a memory unit that stores the programs executed by the microcomputer or parameters used in various calculations, and a drive circuit that drives various devices to be controlled. Each control unit includes a network I / F for communicating with other control units via a communication network 7010, and a communication I / F for communicating with devices or sensors inside and outside the vehicle via wired or wireless communication. Figure 13 illustrates the functional configuration of the integrated control unit 7600, including a microcomputer 7610, a general-purpose communication I / F 7620, a dedicated communication I / F 7630, a positioning unit 7640, a beacon receiving unit 7650, an in-vehicle device I / F 7660, an audio / video output unit 7670, an in-vehicle network I / F 7680, and a memory unit 7690. Similarly, the other control units also include a microcomputer, a communication I / F, a memory unit, and the like.

[0126] The drivetrain control unit 7100 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 7100 functions as a control device for a drive force generating device for generating drive force for the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating braking force for the vehicle. The drivetrain control unit 7100 may also function as a control device for an ABS (Antilock Brake System) or an ESC (Electronic Stability Control), etc.

[0127] A vehicle state detection unit 7110 is connected to the drivetrain control unit 7100. The vehicle state detection unit 7110 includes at least one of a gyro sensor that detects the angular velocity of the axial rotational motion of the vehicle body, an acceleration sensor that detects the acceleration of the vehicle, or a sensor that detects the amount of operation of the accelerator pedal, the amount of operation of the brake pedal, the steering angle of the steering wheel, the engine rotation speed, the rotation speed of the wheels, etc. The drivetrain control unit 7100 performs arithmetic processing using signals input from the vehicle state detection unit 7110, and controls the internal combustion engine, the drive motor, the electric power steering device, the brake device, etc.

[0128] The body system control unit 7200 controls the operation of various devices equipped in the vehicle body according to various programs. For example, the body system control unit 7200 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as headlamps, backup lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves transmitted from a portable device that serves as a key or signals from various switches can be input to the body system control unit 7200. The body system control unit 7200 receives these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

[0129] The battery control unit 7300 controls the secondary battery 7310, which is the power supply source for the drive motor, in accordance with various programs. For example, information such as battery temperature, battery output voltage, or remaining battery capacity is input to the battery control unit 7300 from a battery device equipped with the secondary battery 7310. The battery control unit 7300 performs arithmetic processing using these signals, and controls the temperature regulation of the secondary battery 7310 or a cooling device or the like equipped in the battery device.

[0130] The outside vehicle information detection unit 7400 detects information outside the vehicle equipped with the vehicle control system 7000. For example, at least one of an imaging unit 7410 and an outside vehicle information detection unit 7420 is connected to the outside vehicle information detection unit 7400. The imaging unit 7410 includes at least one of a time-of-flight (ToF) camera, a stereo camera, a monocular camera, an infrared camera, and other cameras. The outside vehicle information detection unit 7420 includes at least one of an environmental sensor for detecting the current weather or climate, or a surrounding information detection sensor for detecting other vehicles, obstacles, pedestrians, etc. around the vehicle equipped with the vehicle control system 7000.

[0131] The environmental sensor may be, for example, at least one of a raindrop sensor that detects rain, a fog sensor that detects fog, a sunshine sensor that detects the degree of sunshine, and a snow sensor that detects snowfall. The surrounding information detection sensor may be at least one of an ultrasonic sensor, a radar device, and a LIDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) device. The imaging unit 7410 and the outside vehicle information detection unit 7420 may each be provided as an independent sensor or device, or may be provided as a device in which multiple sensors or devices are integrated.

[0132] 14 shows an example of the installation positions of the imaging unit 7410 and the vehicle exterior information detection unit 7420. The imaging units 7910, 7912, 7914, 7916, and 7918 are provided, for example, at least one of the front nose, side mirrors, rear bumper, back door, and upper part of the windshield inside the vehicle cabin of the vehicle 7900. The imaging unit 7910 provided on the front nose and the imaging unit 7918 provided on the upper part of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 7900. The imaging units 7912 and 7914 provided on the side mirrors mainly acquire images of the sides of the vehicle 7900. The imaging unit 7916 provided on the rear bumper or back door mainly acquires images of the rear of the vehicle 7900. The imaging unit 7918 provided on the upper part of the windshield inside the vehicle cabin is mainly used to detect leading vehicles, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc.

[0133] 14 shows an example of the imaging ranges of the imaging units 7910, 7912, 7914, and 7916. Imaging range a indicates the imaging range of the imaging unit 7910 provided on the front nose, imaging ranges b and c indicate the imaging ranges of the imaging units 7912 and 7914 provided on the side mirrors, respectively, and imaging range d indicates the imaging range of the imaging unit 7916 provided on the rear bumper or back door. For example, by overlaying the image data captured by the imaging units 7910, 7912, 7914, and 7916, a bird's-eye view image of the vehicle 7900 viewed from above can be obtained.

[0134] The outside vehicle information detection units 7920, 7922, 7924, 7926, 7928, and 7930 provided on the front, rear, sides, corners, and above the windshield inside the vehicle cabin of the vehicle 7900 may be, for example, ultrasonic sensors or radar devices. The outside vehicle information detection units 7920, 7926, and 7930 provided on the front nose, rear bumper, back door, and above the windshield inside the vehicle cabin of the vehicle 7900 may be, for example, LIDAR devices. These outside vehicle information detection units 7920 to 7930 are mainly used to detect preceding vehicles, pedestrians, obstacles, etc.

[0135] Returning to FIG. 13 , the explanation will be continued. The outside-vehicle information detection unit 7400 causes the imaging unit 7410 to capture an image outside the vehicle and receives the captured image data. The outside-vehicle information detection unit 7400 also receives detection information from the connected outside-vehicle information detection unit 7420. If the outside-vehicle information detection unit 7420 is an ultrasonic sensor, a radar device, or a LIDAR device, the outside-vehicle information detection unit 7400 emits ultrasonic waves or electromagnetic waves and receives information on the received reflected waves. Based on the received information, the outside-vehicle information detection unit 7400 may perform object detection processing or distance detection processing for people, vehicles, obstacles, signs, text on the road, etc. Based on the received information, the outside-vehicle information detection unit 7400 may also perform environment recognition processing for recognizing rainfall, fog, road conditions, etc. Based on the received information, the outside-vehicle information detection unit 7400 may also calculate the distance to an object outside the vehicle.

[0136] The outside vehicle information detection unit 7400 may also perform image recognition processing or distance detection processing to recognize people, vehicles, obstacles, signs, or characters on the road surface based on the received image data. The outside vehicle information detection unit 7400 may perform processing such as distortion correction or alignment on the received image data, and may also generate an overhead image or a panoramic image by combining image data captured by different image capturing units 7410. The outside vehicle information detection unit 7400 may also perform viewpoint conversion processing using image data captured by different image capturing units 7410.

[0137] The interior information detection unit 7500 detects information inside the vehicle. A driver state detection unit 7510 that detects the driver's state is connected to the interior information detection unit 7500, for example. The driver state detection unit 7510 may include a camera that captures an image of the driver, a biosensor that detects the driver's biometric information, or a microphone that collects sound from within the vehicle cabin. The biosensor is provided, for example, on the seat or steering wheel, and detects the biometric information of a passenger sitting in the seat or the driver gripping the steering wheel. The interior information detection unit 7500 may calculate the driver's level of fatigue or concentration based on the detection information input from the driver state detection unit 7510, or may determine whether the driver is dozing off. The interior information detection unit 7500 may perform processing such as noise canceling on the collected audio signal.

[0138] The integrated control unit 7600 controls the overall operation of the vehicle control system 7000 according to various programs. An input unit 7800 is connected to the integrated control unit 7600. The input unit 7800 may be implemented by a device that can be operated by a passenger, such as a touch panel, a button, a microphone, a switch, or a lever. Data obtained by voice recognition of a voice input through a microphone may be input to the integrated control unit 7600. The input unit 7800 may be, for example, a remote control device using infrared or other radio waves, or an externally connected device such as a mobile phone or a personal digital assistant (PDA) that can operate the vehicle control system 7000. The input unit 7800 may be, for example, a camera, in which case the passenger can input information using gestures. Alternatively, data obtained by detecting the movement of a wearable device worn by the passenger may be input. Furthermore, the input unit 7800 may include, for example, an input control circuit that generates an input signal based on information input by the passenger using the input unit 7800 and outputs the input signal to the integrated control unit 7600. Passengers and the like operate this input unit 7800 to input various data to the vehicle control system 7000 and to instruct processing operations.

[0139] The storage unit 7690 may include a ROM (Read Only Memory) that stores various programs executed by the microcomputer, and a RAM (Random Access Memory) that stores various parameters, calculation results, sensor values, etc. The storage unit 7690 may also be realized by a magnetic storage device such as an HDD (Hard Disc Drive), a semiconductor storage device, an optical storage device, a magneto-optical storage device, or the like.

[0140] The general-purpose communication I / F 7620 is a general-purpose communication I / F that mediates communication with various devices present in the external environment 7750. The general-purpose communication I / F 7620 may implement a cellular communication protocol such as GSM (Global System of Mobile communications), WiMAX (registered trademark), LTE (Long Term Evolution), or LTE-Advanced (LTE-A), or other wireless communication protocols such as a wireless LAN (also referred to as Wi-Fi (registered trademark)) or Bluetooth (registered trademark). The general-purpose communication I / F 7620 may connect to a device (e.g., an application server or a control server) present on an external network (e.g., the Internet, a cloud network, or an operator-specific network) via, for example, a base station or an access point. In addition, the general-purpose communication I / F 7620 may connect to a terminal located near the vehicle (e.g., a terminal of a driver, pedestrian, or store, or an MTC (Machine Type Communication) terminal) using, for example, P2P (Peer To Peer) technology.

[0141] The dedicated communication I / F 7630 is a communication I / F that supports a communication protocol designed for use in vehicles. The dedicated communication I / F 7630 may implement a standard protocol such as WAVE (Wireless Access in Vehicle Environment), which is a combination of a lower layer IEEE 802.11p and an upper layer IEEE 1609, DSRC (Dedicated Short Range Communications), or a cellular communication protocol. The dedicated communication I / F 7630 typically performs V2X communication, which is a concept including one or more of vehicle-to-vehicle communication, vehicle-to-infrastructure communication, vehicle-to-home communication, and vehicle-to-pedestrian communication.

[0142] The positioning unit 7640 performs positioning by receiving, for example, GNSS signals from GNSS (Global Navigation Satellite System) satellites (for example, GPS signals from GPS (Global Positioning System) satellites), and generates position information including the latitude, longitude, and altitude of the vehicle. Note that the positioning unit 7640 may identify the current position by exchanging signals with a wireless access point, or may obtain position information from a terminal such as a mobile phone, PHS, or smartphone that has a positioning function.

[0143] The beacon receiving unit 7650 receives, for example, radio waves or electromagnetic waves transmitted from radio stations or the like installed on the road, and acquires information such as the current location, congestion, road closures, required travel time, etc. The function of the beacon receiving unit 7650 may be included in the dedicated communication I / F 7630 described above.

[0144] The in-vehicle device I / F 7660 is a communication interface that mediates connections between the microcomputer 7610 and various in-vehicle devices 7760 present in the vehicle. The in-vehicle device I / F 7660 may establish wireless connections using wireless communication protocols such as wireless LAN, Bluetooth (registered trademark), NFC (Near Field Communication), or WUSB (Wireless USB). Furthermore, the in-vehicle device I / F 7660 may establish a wired connection such as USB (Universal Serial Bus), HDMI (High-Definition Multimedia Interface), or MHL (Mobile High-Definition Link) via a connection terminal (and a cable, if necessary) not shown. The in-vehicle device 7760 may include, for example, at least one of a mobile device or a wearable device owned by a passenger, or an information device carried into or attached to the vehicle. The in-vehicle device 7760 may also include a navigation device that searches for a route to an arbitrary destination. The in-vehicle device I / F 7660 exchanges control signals or data signals with these in-vehicle devices 7760.

[0145] The in-vehicle network I / F 7680 is an interface that mediates communication between the microcomputer 7610 and the communication network 7010. The in-vehicle network I / F 7680 transmits and receives signals in accordance with a predetermined protocol supported by the communication network 7010.

[0146] The microcomputer 7610 of the integrated control unit 7600 controls the vehicle control system 7000 in accordance with various programs based on information acquired via at least one of the general-purpose communication I / F 7620, the dedicated communication I / F 7630, the positioning unit 7640, the beacon receiving unit 7650, the in-vehicle device I / F 7660, and the in-vehicle network I / F 7680. For example, the microcomputer 7610 may calculate control target values ​​for the driving force generating device, the steering mechanism, or the braking device based on the acquired information inside and outside the vehicle, and output control commands to the drivetrain control unit 7100. For example, the microcomputer 7610 may perform cooperative control aimed at realizing functions of an Advanced Driver Assistance System (ADAS), including vehicle collision avoidance or impact mitigation, following driving based on the following distance, vehicle speed maintenance driving, vehicle collision warning, vehicle lane departure warning, etc. In addition, the microcomputer 7610 may perform cooperative control for the purpose of autonomous driving, in which the vehicle travels autonomously without relying on driver operation, by controlling a driving force generating device, a steering mechanism, a braking device, etc. based on information acquired about the vehicle's surroundings.

[0147] The microcomputer 7610 may generate three-dimensional distance information between the vehicle and objects such as surrounding structures and people, and create local map information including information about the vicinity of the vehicle's current location, based on information acquired via at least one of the general-purpose communication I / F 7620, the dedicated communication I / F 7630, the positioning unit 7640, the beacon receiving unit 7650, the in-vehicle device I / F 7660, and the in-vehicle network I / F 7680. Furthermore, the microcomputer 7610 may predict dangers, such as a vehicle collision, the approach of a pedestrian, or entry into a closed road, based on the acquired information, and generate a warning signal. The warning signal may be, for example, a signal for generating a warning sound or turning on a warning lamp.

[0148] The audio / image output unit 7670 transmits at least one audio and / or image output signal to an output device capable of visually or audibly notifying vehicle occupants or the outside of the vehicle of information. In the example of FIG. 13 , an audio speaker 7710, a display unit 7720, and an instrument panel 7730 are illustrated as examples of the output devices. The display unit 7720 may include, for example, at least one of an on-board display and a head-up display. The display unit 7720 may have an AR (Augmented Reality) display function. The output device may also be other devices, such as headphones, a wearable device such as an eyeglass-type display worn by the occupant, a projector, or a lamp. When the output device is a display device, the display device visually displays results obtained by various processes performed by the microcomputer 7610 or information received from other control units in various formats, such as text, images, tables, and graphs. When the output device is an audio output device, the audio output device converts audio signals, such as reproduced audio data or acoustic data, into analog signals and audibly outputs the analog signals.

[0149] In the example shown in FIG. 13 , at least two control units connected via the communication network 7010 may be integrated into a single control unit. Alternatively, each control unit may be composed of multiple control units. Furthermore, the vehicle control system 7000 may include another control unit not shown. In the above description, some or all of the functions performed by one of the control units may be performed by another control unit. In other words, as long as information is transmitted and received via the communication network 7010, predetermined arithmetic processing may be performed by one of the control units. Similarly, a sensor or device connected to one of the control units may be connected to another control unit, and multiple control units may transmit and receive detection information to and from each other via the communication network 7010.

[0150] In the vehicle control system 7000 described above, the ranging system 80 according to this embodiment described using Fig. 11 can be applied to the image capturing unit 7410 of the application example shown in Fig. 13. For example, by applying the ranging system 80 of Fig. 11 to the ranging of the image capturing unit 7410, the ranging accuracy can be improved.

[0151] The present technology may have the following configurations. (1) A light source driving device including: a first transistor that generates a current flowing through a light-emitting element; a second transistor that switches between controlling whether the first transistor generates the current; a third transistor that stops light emission of the light-emitting element; and a fourth transistor that switches between controlling whether the third transistor stops light emission of the light-emitting element. (2) The light source driving device according to (1), in which the third transistor shapes a waveform of a current flowing through the light-emitting element when the light-emitting element stops light emission. (3) The light source driving device according to (1) or (2), in which the second transistor has a lower withstand voltage than the first transistor, and the fourth transistor has a lower withstand voltage than the third transistor. (4) The light source driving device according to any one of (1) to (3), in which the third transistor and the fourth transistor are cascode-connected, and the first transistor and the second transistor are cascode-connected. (5) The light source driving device according to any one of (1) to (4), further comprising a bias generation circuit that generates a bias signal to be input to the gate of the third transistor, wherein the bias generation circuit generates the bias signal based on a predetermined reference voltage, and the reference voltage is supplied to the drain or source of the fourth transistor. (6) The light source driving device according to (5), wherein the bias generation circuit has: an impedance circuit that generates the bias signal according to the reference voltage; and a current source that flows a predetermined current through the impedance circuit, and the bias signal has a voltage level based on the reference voltage and a voltage drop occurring in the impedance circuit according to the current. (7) The light source driving device according to (5), wherein the bias generation circuit has an impedance circuit that generates the bias signal by dividing the reference voltage. (8) The light source driving device according to any one of (5) to (7), wherein the bias generation circuit has a capacitor connected between the gate of the third transistor and a node of the reference voltage.(9) The light source driving device according to any one of (5) to (8), comprising: a plurality of third transistors that respectively stop light emission of a plurality of light-emitting elements; and a plurality of fourth transistors that switch control the plurality of third transistors to determine whether or not to stop light emission of the plurality of light-emitting elements, wherein the bias generation circuit supplies the bias signal common to the plurality of third transistors, and an individual switching control signal is input to each gate of the plurality of fourth transistors. (10) The light source driving device according to any one of (1) to (9), comprising: a first buffer circuit that buffers a first pulse signal that controls switching of the fourth transistors, wherein the first buffer circuit has a withstand voltage corresponding to the withstand voltage of the second transistor. (11) The light source driving device according to (10), wherein the first buffer circuit includes a transistor having a withstand voltage lower than that of the third transistor. (12) The light source driving device according to (10) or (11), comprising: a second buffer circuit that buffers a second pulse signal that controls switching of the second transistor. (13) The light source driving device according to (12), wherein the second buffer circuit has a withstand voltage corresponding to the withstand voltage of the second transistor. (14) The light source driving device according to any one of (1) to (13), wherein the plurality of first transistors, the plurality of second transistors, the plurality of third transistors, and the plurality of fourth transistors are arranged along one direction. (15) The light source driving device according to any one of (1) to (13), wherein the plurality of first transistors, the plurality of third transistors, and the plurality of fourth transistors are arranged in this order along a first direction, and each of the plurality of second transistors and the corresponding first transistor are arranged along a second direction intersecting the first direction. (16) The light source driving device according to any one of (1) to (15), wherein the fourth transistor is a thin-film transistor.(17) The light source driving device according to any one of (1) to (16), wherein the first transistor and the second transistor are N-type MOS (Metal Oxide Semiconductor) transistors, the third transistor and the fourth transistor are P-type MOS transistors, a source of the fourth transistor is connected to a first reference voltage node, a drain of the fourth transistor is connected to the source of the third transistor, a source of the third transistor is connected to the drain of the first transistor and the cathode of the light-emitting element, a source of the first transistor is connected to the drain of the second transistor, and a source of the second transistor is connected to a second reference voltage node. (18) A light-emitting device comprising: a light-emitting unit having a plurality of the light-emitting elements that perform surface emission; and the light-source driving device according to any one of (1) to (17) that drives the light-emitting unit. (19) The light-emitting device according to (18), wherein the light-emitting unit is a VCSEL (Vertical Cavity Surface Emitting Laser). (20) A distance measurement system comprising: a light emitting device according to (18) or (19) that emits a pulsed light signal; a light receiving unit that receives a reflected light signal from an object irradiated with the light signal; and a distance measuring unit that measures the distance to the object based on the light signal emitted by the light emitting device and the reflected light signal received by the light receiving unit.

[0152] The aspects of the present disclosure are not limited to the individual embodiments described above, but include various modifications that may be conceived by those skilled in the art, and the effects of the present disclosure are not limited to the above-described contents. In other words, various additions, modifications, and partial deletions are possible within the scope of the conceptual idea and spirit of the present disclosure, which is derived from the contents defined in the claims and their equivalents.

[0153] 1, 1a, 1b, 1c, 1d, 1e, 1f, 1g, 100 light source driving device, 2 channel, 3 current mirror circuit, 4 driving circuit, 5 assist circuit, 11, 11a, 11b, 11c, 11d, 12, 12a, 12b, 12c, 12d, 13, 13a, 13b, 13c, 13d, 14, 14a, 14b, 14c, 14d, 15, 16 transistor, 17, 51 current source, 20 light emitting element, 30, 40, 110 buffer circuit, 31, 32, 32a, 32b, 32c, 32d, 41, 42, 42a, 42b, 42c, 42d, 111, 112 inverter, 50, 50a, 50b bias generation circuit, 52, 53, 54 impedance element, 61 Timing adjustment unit, 62 phase detection unit, 63 timing control unit, 71 capacitor, 72 parasitic capacitor, 80 distance measurement system, 81 light emitting unit, 82 driving unit, 83 power supply circuit, 84 light emitting side optical system, 85 light receiving side optical system, 86 light receiving unit, 87 signal processing unit, 88 control unit, 88a distance measurement unit, 89 temperature detection unit

Claims

1. A light source driving device comprising: a first transistor that generates a current flowing in a light-emitting element; a second transistor that switches between controlling whether or not the first transistor generates the current; a third transistor that stops the light emission of the light-emitting element; and a fourth transistor that switches between controlling whether or not the third transistor stops the light emission of the light-emitting element.

2. The light source driving device according to claim 1, wherein the third transistor shapes the waveform of the current flowing through the light emitting element when the light emitting element stops emitting light.

3. The light source driving device according to claim 1, wherein the second transistor has a lower breakdown voltage than the first transistor, and the fourth transistor has a lower breakdown voltage than the third transistor.

4. The light source driving device according to claim 1, wherein the third transistor and the fourth transistor are cascode-connected, and the first transistor and the second transistor are cascode-connected.

5. The light source driving device according to claim 1, further comprising a bias generation circuit that generates a bias signal to be input to the gate of the third transistor, the bias generation circuit generating the bias signal based on a predetermined reference voltage, and the reference voltage being supplied to the drain or source of the fourth transistor.

6. The light source driving device according to claim 5, wherein the bias generating circuit comprises: an impedance circuit that generates the bias signal according to the reference voltage; and a current source that supplies a predetermined current to the impedance circuit; and the bias signal has a voltage level based on the reference voltage and a voltage drop that occurs in the impedance circuit according to the current.

7. The light source driving device according to claim 5, wherein the bias generating circuit has an impedance circuit that generates the bias signal by dividing the reference voltage.

8. The light source driving device according to claim 5, wherein the bias generating circuit has a capacitor connected between the gate of the third transistor and the reference voltage node.

9. A light source driving device according to claim 5, comprising: a plurality of third transistors that respectively stop light emission of a plurality of light-emitting elements; and a plurality of fourth transistors that switch control the third transistors to determine whether or not to stop light emission of the plurality of light-emitting elements, wherein the bias generation circuit supplies the bias signal common to the third transistors, and an individual switching control signal is input to each gate of the fourth transistors.

10. The light source driving device according to claim 1, further comprising a first buffer circuit that buffers a first pulse signal that controls switching of the fourth transistor, the first buffer circuit having a withstand voltage corresponding to the withstand voltage of the second transistor.

11. The light source driving device according to claim 10, wherein the first buffer circuit has a transistor with a lower withstand voltage than the third transistor.

12. The light source driving device according to claim 10, further comprising a second buffer circuit that buffers a second pulse signal that controls switching of the second transistor.

13. The light source driving device according to claim 12, wherein the second buffer circuit has a withstand voltage corresponding to the withstand voltage of the second transistor.

14. The light source driving device according to claim 1, wherein the plurality of first transistors, the plurality of second transistors, the plurality of third transistors, and the plurality of fourth transistors are arranged along one direction.

15. The light source driving device according to claim 1, wherein the plurality of first transistors, the plurality of third transistors, and the plurality of fourth transistors are arranged in this order along a first direction, and each of the plurality of second transistors and the corresponding first transistor are arranged along a second direction intersecting the first direction.

16. The light source driving device according to claim 1, wherein the fourth transistor is a thin film transistor.

17. The light source driving device according to claim 1, wherein the first transistor and the second transistor are N-type MOS (Metal Oxide Semiconductor) transistors, the third transistor and the fourth transistor are P-type MOS transistors, the source of the fourth transistor is connected to a first reference voltage node, the drain of the fourth transistor is connected to the source of the third transistor, the source of the third transistor is connected to the drain of the first transistor and the cathode of the light-emitting element, the source of the first transistor is connected to the drain of the second transistor, and the source of the second transistor is connected to a second reference voltage node.

18. A light emitting device comprising: a light emitting section having a plurality of the light emitting elements that perform surface emission; and a light source driving device according to claim 1 that drives the light emitting section.

19. The light emitting device according to claim 18, wherein the light emitting portion is a VCSEL (Vertical Cavity Surface Emitting Laser).

20. A distance measurement system comprising: a light emitting device according to claim 18 that emits a pulsed light signal; a light receiving unit that receives a reflected light signal from an object onto which the light signal is irradiated; and a distance measuring unit that measures the distance to the object based on the light signal emitted by the light emitting device and the reflected light signal received by the light receiving unit.

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