Light emitting device and measuring device

Abstract

To provide a light-emitting device capable of setting the charging time of a capacitive element when electric charges charged in the capacitive element connected in parallel with a light-emitting element are discharged to the light-emitting element to cause the light-emitting element to emit light.SOLUTION: A light-emitting device includes a light-emitting element, a switch element connected in series with the light-emitting element with the same electrode to drive the light-emitting element, a capacitive element connected in parallel with the light-emitting element to discharge charged electric charges to the light-emitting element, and a resistor element provided between the capacitive element and a power source for charging the capacitive element, all of which are formed on the same substrate.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a light emitting device and a measurement device. [Background technology]

[0002] Patent document 1 discloses a method for measuring depth that is insensitive to corrupted light caused by internal reflection, the method including: emitting light into a scene by a light source; performing a corrupted light measurement by controlling a first charge storage unit of the pixel to collect charge based on light impinging on the pixel during a first time period during which corrupted light impinges on the pixel but returning light from an object within the field of view of the pixel does not impinge on the pixel; removing a contribution from the corrupted light from one or more measurements affected by the corrupted light based on the corrupted light measurement; and determining the depth based on the one or more measurements from which the contribution from the corrupted light has been removed.

[0003] Patent Document 2 discloses a distance measurement device comprising a light-projecting unit which projects light onto an object, a light-receiving unit which receives light reflected or scattered by the object, a scanning unit which scans a scanning area with the light projected from the light-projecting unit, and a distance measurement unit which measures the time from when the light is projected by the light-projecting unit to when the light is received by the light-receiving unit, thereby measuring the distance to the object; the scanning area is divided into a plurality of divided areas, and one scan is defined as the period from when scanning of one of the divided areas begins to when scanning of all of the divided areas is completed. Based on a measurement value of a first divided area measured by the distance measurement unit during one scan and a measurement value of a second divided area measured prior to the measurement value of the first divided area, it is determined whether or not the measurement value of the first divided area can be used as the measurement result of the first divided area, and if it is determined that the measurement value of the first divided area can be used as the measurement result of the first divided area, the measurement value of the first divided area is output as the distance to the object in the first divided area.

[0004] Patent Document 3 discloses an optical flight type distance measuring device comprising: a first light source that emits a first light into a first light-emitting space; a light-receiving unit having a plurality of pixels that receives light by each pixel; a distance image acquisition unit that acquires a distance image showing the distance from the device to the object for each pixel by receiving light including a first reflected light of the first light reflected by the surface of the object during a light-emitting period in which the first light is repeatedly emitted from the first light source at the light-receiving unit; a brightness value image acquisition unit that acquires a brightness value image showing the brightness value for each pixel by receiving light including a second reflected light of a second light emitted from a second light source into a second light-emitting space including at least a part of the first light-emitting space so that the optical axis is different from that of the first light at the light-receiving unit during a non-light-emitting period in which the first light is not repeatedly emitted from the first light source; and a multipath detection unit that uses the distance image and the brightness value image to detect an area in which multipath occurs.

[0005] Patent Document 4 discloses a distance measurement device that has an emitter that emits a search light and a light-receiving unit that receives the reflected light of the search light, and that measures the distance to an object that reflects the search light based on the reflected light received by the light-receiving unit.The distance measurement device is characterized in that an area centered on the emitter where the intensity of scattered light generated when the search light passes through or is reflected by water droplets having a diameter larger than the wavelength of the search light exceeds the noise level of the light-receiving unit is defined as a strong scattering area, and the light-receiving unit is installed at a position outside the strong scattering area, and a shading means is provided to block converging scattered light that converges in a specific direction and scattered light that attempts to enter the light-receiving unit at an incident angle larger than the converging scattered light. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-219400 A [Patent Document 2] JP 2019-028039 A [Patent Document 3] JP 2017-15448 A [Patent Document 4] JP 2007-333792 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a light-emitting device and a measuring device that can set the charging time of a capacitive element when causing a light-emitting element to emit light by discharging electric charge stored in a capacitive element connected in parallel to the light-emitting element to the light-emitting element. [Means for solving the problem]

[0008] The light-emitting device of the first embodiment includes a light-emitting element, a switch element connected in series with the light-emitting element via the same electrode as the light-emitting element and for driving the light-emitting element, a capacitive element connected in parallel with the light-emitting element and for discharging stored electric charge to the light-emitting element, and a resistive element provided between the capacitive element and a power source for charging the capacitive element, which are formed on the same substrate.

[0009] The light emitting device of the second aspect is the light emitting device of the first aspect, wherein the capacitance value of the capacitive element and the resistance value of the resistive element are set to match the minimum light emission interval of the pulsed light emitted from the light emitting element.

[0010] A light emitting device according to a third aspect is the light emitting device according to the first or second aspect, wherein the base material is aluminum nitride.

[0011] A light emitting device according to a fourth aspect is the light emitting device according to any one of the first to third aspects, wherein the substrate is an inorganic substrate having a thickness of 100 μm or more and 500 μm or less and a thermal conductivity of 100 W / m·K or more.

[0012] A light emitting device according to a fifth aspect is the light emitting device according to the first or second aspect, wherein the base material is an organic base material having a thickness of less than 100 μm and a thermal conductivity of 1 W / m·K or more.

[0013] A light emitting device according to a sixth aspect is the light emitting device according to any one of the first to fifth aspects, further comprising a plurality of pairs of the light emitting element and the switch element.

[0014] A light emitting device according to a seventh aspect is the light emitting device according to the sixth aspect, in which signal wiring from a control unit that outputs a control signal for controlling a plurality of the switch elements to the plurality of the switch elements is branched into equal lengths.

[0015] The light emitting device according to an eighth aspect is the light emitting device according to the sixth or seventh aspect, further comprising a same cathode electrode, to which the cathodes of the plurality of light emitting elements are connected, provided on the base material.

[0016] A measuring device according to a ninth aspect includes a light emitting device according to any one of the first to eighth aspects, a light receiving element that receives reflected light of light emitted from the light emitting device toward a measured object, and a measurement unit that measures a distance to the measured object by time of flight in a direct method from the amount of light received by the light receiving element. Effect of the Invention

[0017] According to the first and ninth aspects, when the light-emitting element is made to emit light by discharging electric charge stored in a capacitive element connected in parallel to the light-emitting element to the light-emitting element, the charging time of the capacitive element can be set.

[0018] According to the second aspect, it is possible to adjust the emission interval of the pulsed light.

[0019] According to the third aspect, it is possible to dissipate heat generated by the light emission of the light emitting element.

[0020] According to the fourth aspect, compared to a case where the thermal conductivity of the base is less than 100 W / m·K, the ability to dissipate heat generated by the light emission of the light-emitting element is improved.

[0021] According to the fifth aspect, the light emitting device can be made more compact than when the thickness of the base is 100 μm or more.

[0022] According to the sixth aspect, the amount of emitted light can be increased compared to the case where one set of a light emitting element and a switch element is used.

[0023] According to the seventh aspect, deviation in the light emission timing of each light emitting element can be suppressed, compared to a case where the signal wirings vary in length.

[0024] According to the eighth aspect, it is possible to prevent deviation in the light emission timing of each light emitting element, compared to the case where the cathode electrodes are separate. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram for explaining relaxation oscillation. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of a measurement device. [Diagram 3] FIG. 2 is a block diagram showing a configuration of a main part of an electrical system of the measuring device. [Figure 4] FIG. [Diagram 5] FIG. 2 is a circuit diagram of the measurement device. [Figure 6] 1A is a plan view of the heat dissipation substrate, FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A, and FIG. 1C is a cross-sectional view taken along line BB of FIG. [Figure 7] FIG. 4 is a plan view of an electrode on the back surface side of the heat dissipation base material. [Figure 8] 11 is a diagram for explaining signal wiring having a configuration including a plurality of pairs of light sources and FET elements. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an example of an embodiment of the disclosed technology will be described in detail with reference to the drawings.

[0027] Among measurement devices that measure the three-dimensional shape of a measurement target, there are devices that measure the three-dimensional shape based on the so-called ToF (Time of Flight) method, which uses the time of flight of light. In the ToF method, the time from when light is emitted from a light source of the measurement device to when the irradiated light is reflected by the measurement target and received by a three-dimensional sensor (hereinafter referred to as a 3D sensor) of the measurement device is measured, and the three-dimensional shape is identified by measuring the distance to the measurement target. Note that an object whose three-dimensional shape is measured is referred to as a measurement target. A measurement target is an example of an object to be detected. Furthermore, measuring distance may be referred to as distance measurement, and measuring three-dimensional shape may be referred to as three-dimensional measurement, 3D measurement, or 3D sensing.

[0028] There are two types of ToF method: direct method and phase difference method (indirect method). The direct method is a method in which a pulsed light that is emitted for a very short time is irradiated onto the object to be measured, and the time it takes for the light to return is measured. The phase difference method is a method in which a pulsed light is periodically blinked, and the time delay when multiple pulsed lights go back and forth between the object to be measured and the object is detected as a phase difference.

[0029] Such a measuring device is mounted on a portable information processing device and is used for face authentication of a user who is trying to access the device. Conventionally, a method of authenticating a user by a password, a fingerprint, an iris, or the like has been used in a portable information processing device. In recent years, a method of authenticating a user with higher security has been required. Therefore, a measuring device that measures a three-dimensional shape has come to be mounted on a portable information processing device. That is, a three-dimensional image of the face of the user who has accessed the device is acquired, and it is identified whether or not the access is permitted, and only when it is authenticated that the user is permitted to access the device, the use of the device (portable information processing device) is permitted.

[0030] Furthermore, such a measuring device is also applicable to cases where the three-dimensional shape of an object to be measured is continuously measured, such as in augmented reality (AR).

[0031] The configurations, functions, methods, etc. described in the present embodiment described below can be applied not only to face recognition and augmented reality, but also to measuring the three-dimensional shape of other measurement objects.

[0032] The phase difference method is mainly used when the distance to the object to be measured is short, up to about 5 m. However, in order to expand the measurement range to long distances with the phase difference method, the driving frequency of the light source must be lowered, which reduces the measurement accuracy. For this reason, when the distance to the object to be measured is long, the direct method is mainly used. In this embodiment, a case where a three-dimensional shape is measured using the direct method will be described.

[0033] In the direct method, a single photon avalanche diode (SPAD) element is generally used in the 3D sensor, and the round trip time of the light pulse is directly measured by the SPAD element. When a SPAD element detects a single photon, it generates electrons in an avalanche fashion. The generated electrons are charged in the capacitance element of the 3D sensor. If the rise time from when the drive current is supplied to make the light source emit light to when it emits light is slow, the timing at which the SPAD element reacts will change depending on the amount of reflected light, even if the distance to the object to be measured is the same, resulting in measurement errors. Therefore, it is necessary to speed up the rise time from when the drive current is supplied to the light source to when it emits light.

[0034] When a light source is driven by current, a delay and oscillation of several GHz occurs in the time response waveform of the light due to a phase difference in the interaction between the light and the carriers. This is known as relaxation oscillation. Figure 1 shows an example of a relaxation oscillation waveform. As shown in Figure 1, after a drive current is supplied at t1, the optical output rises to several times the pulse height of the steady-state value in a short period of several tens of ps until light emission begins at t2. This operation is called gain switching. The sensitivity and accuracy of distance measurement using the direct method are determined by the peak power and rise time of the optical output.

[0035] For distance measurement in the direct method, the response of the optical output after the peak part (t2) of the rising edge of the light emission is unnecessary and is a waste of energy. In other words, the drive current supplied to the light source only needs to be large enough and have a pulse width sufficient for the rise of the optical output in the gain switching operation. For this reason, the drive current needs to be a large current with a pulse width of several hundred ps.

[0036] In the direct method, infrared pulse light of several tens of watts is required to measure distances of more than 10 m outdoors under strong daylight of 100 klx. For example, to generate pulse light with a pulse width of several hundreds of ps at a large current of 10 A, the inductance of the current path including the driving circuit of the light source must be minimized. At the same time, high-speed and high-precision distance measurement requires high-current pulse light to be emitted frequently, and heat generation from the light-emitting element becomes a problem. For this reason, the light source is mounted on a heat dissipation substrate (submount) made of a high thermal conductivity material such as AlN (aluminum nitride) to assist heat dissipation. However, mounting the heat dissipation substrate increases the inductance of the current path, degrading the pulse characteristics. Thus, in the light source for the direct method, it is a big challenge to achieve both high-speed, high-current driving and thermal characteristics.

[0037] When a light source mounted on a heat dissipation substrate on a wiring board is driven by a driving unit provided outside the heat dissipation substrate, the inductance of the current path is large, which results in a slow rise in light emission. The driving unit usually includes a high-speed pulse input circuit, a control circuit, an output circuit, etc., and occupies a large area. For this reason, it is difficult to mount it directly on the heat dissipation substrate.

[0038] In addition, the final stage of the output circuit usually drives a switching element such as an open drain FET element, but there are FET elements such as GaN (gallium nitride) elements that are small enough to be about 1 mm square on their own.

[0039] Therefore, in this embodiment, the FET element in the final stage of the output circuit is mounted on a heat dissipation base material, and this is driven by a signal generating circuit on the wiring board.

[0040] In addition, in order to drive a light source with a driving current of a sufficiently short pulse as a light source of the direct method, so-called resonant capacitance discharge type driving is desirable. In this case, a capacitor is connected in parallel with the series connection of the light emitting element and the FET element of the driving unit with a ground reference, and when the FET element is turned on, the light emitting element is driven by the discharge current of the capacitor charged with the power supply voltage, and a large current pulse of an extremely short duration can be obtained under the resonance condition of the capacitor, the light emitting element, the inductance of the current loop of the FET element, and the capacitance of the capacitor. In this embodiment, the power supply potential side of the capacitor is connected to the power supply via a resistive element, and is recharged with a time constant determined by the capacitance value of the capacitor and the resistance value of the resistive element, but details will be described later.

[0041] (Measuring device 1)

[0042] FIG. 2 is a block diagram illustrating an example of the configuration of a measurement apparatus 1 that measures a three-dimensional shape.

[0043] The measurement apparatus 1 includes an optical device 3 and a control unit 8. The control unit 8 controls the optical device 3. The control unit 8 includes a three-dimensional shape specifying unit 81 that specifies the three-dimensional shape of the object to be measured.

[0044] Fig. 3 is a block diagram showing a hardware configuration of the control unit 8. As shown in Fig. 3, the control unit 8 includes a controller 12. The controller 12 includes a central processing unit (CPU) 12A, a read only memory (ROM) 12B, a random access memory (RAM) 12C, and an input / output interface (I / O) 12D. The CPU 12A, the ROM 12B, the RAM 12C, and the I / O 12D are connected to each other via a system bus 12E. The system bus 12E includes a control bus, an address bus, and a data bus.

[0045] In addition, a communication unit 14 and a storage unit 16 are connected to the I / O 12D.

[0046] The communication unit 14 is an interface for performing data communication with an external device.

[0047] The storage unit 16 is composed of a non-volatile rewritable memory such as a flash ROM, and stores a measurement program 16A for measuring the three-dimensional shape of a measurement object by a direct method. The CPU 12A loads the measurement program 16A stored in the storage unit 16 into the RAM 12C and executes it to configure a three-dimensional shape specification unit 81, which specifies the three-dimensional shape of the measurement object. The three-dimensional shape specification unit 81 is an example of a measurement unit.

[0048] The optical device 3 includes a light emitting device 4 and a 3D sensor 5. The light emitting device 4 includes a wiring board 10, a heat dissipation base material 100, a light source 20, a light diffusing member 30, a driving unit 50, a holding unit 60, and capacitors 70A and 70B. The heat dissipation base material 100 is an example of a base material. The light source 20 is an example of a light emitting element. The 3D sensor 5 is an example of a light receiving element. The capacitors 70A and 70B are an example of a capacitive element.

[0049] The heat dissipation base material 100 and the driving unit 50 of the light emitting device 4 are provided on the surface of the wiring board 10. Note that, although the 3D sensor 5 is not provided on the surface of the wiring board 10 in FIG. 2, it may be provided on the surface of the wiring board 10.

[0050] The light source 20, the capacitors 70A and 70B, and the holder 60 are provided on the surface of the heat dissipation base material 100. The light diffusing member 30 is provided on the holder 60. Here, the outer shape of the heat dissipation base material 100 and the outer shape of the light diffusing member 30 are assumed to be the same. Here, the surface refers to the front side of the paper surface of Fig. 2. More specifically, in the wiring board 10, the side on which the heat dissipation base material 100 is provided is referred to as the surface, front side, or front side.

[0051] The light source 20 is configured as a light-emitting element array in which a plurality of light-emitting elements are arranged two-dimensionally (see FIG. 4 described later). In this embodiment, the light source 20 will be described as a light-emitting element array having a plurality of light-emitting elements, but the light source 20 may be configured as having one light-emitting element. In this embodiment, the light-emitting element is a vertical cavity surface-emitting laser element VCSEL (Vertical Cavity Surface Emitting Laser) as an example. In the following, the light-emitting element will be described as a vertical cavity surface-emitting laser element VCSEL. In the following, the vertical cavity surface-emitting laser element VCSEL will be referred to as VCSEL. Since the light source 20 is provided on the surface of the heat dissipation base material 100, the light source 20 emits light perpendicularly to the surface of the heat dissipation base material 100 and in a direction away from the heat dissipation base material 100. In other words, the light-emitting element array is a surface-emitting laser element array. Note that a plurality of light-emitting elements in the light source 20 are arranged two-dimensionally, and the surface of the light source 20 that emits light may be referred to as an emission surface.

[0052] The light emitted by the light source 20 is incident on the light diffusion member 30. The light diffusion member 30 diffuses the incident light and emits it. The light diffusion member 30 is provided so as to cover the light source 20 and the capacitors 70A and 70B. That is, the light diffusion member 30 is provided at a predetermined distance from the light source 20 and the capacitors 70A and 70B provided on the heat dissipation base material 100 by the holding portion 60 provided on the surface of the heat dissipation base material 100 (see Figs. 6(B) and (C) described later). Therefore, the light emitted by the light source 20 is diffused by the light diffusion member 30 and irradiated to the measurement object. That is, the light emitted by the light source 20 is diffused by the light diffusion member 30 and irradiated to a wider range than when the light diffusion member 30 is not provided.

[0053] The 3D sensor 5 includes a plurality of light receiving elements, for example 640×480 light receiving elements, and outputs a signal corresponding to the time from when light is emitted from the light source 20 to when the light is received by the 3D sensor 5.

[0054] For example, each light receiving element of the 3D sensor 5 receives a pulsed reflected light (hereinafter, referred to as a received light pulse) from the object to be measured in response to the emitted light pulse from the light source 20, and accumulates a charge corresponding to the time until the light is received for each light receiving element. The 3D sensor 5 is configured as a CMOS structure device in which each light receiving element has two gates and a charge storage section corresponding to the gates. Then, by alternately applying pulses to the two gates, the generated photoelectrons are transferred at high speed to one of the two charge storage sections. Charges corresponding to the time difference between the emitted light pulse and the received light pulse are accumulated in the two charge storage sections. Then, the 3D sensor 5 outputs a digital value corresponding to the time difference between the emitted light pulse and the received light pulse for each light receiving element as a signal via an AD converter. That is, the 3D sensor 5 outputs a signal corresponding to the time from the timing when the light is emitted from the light source 20 to the timing when the light is received by the 3D sensor 5. That is, a signal corresponding to the distance to the object to be measured, that is, the three-dimensional shape of the object to be measured, is acquired from the 3D sensor 5. The AD converter may be included in the 3D sensor 5 or may be provided outside the 3D sensor 5.

[0055] As described above, the measurement device 1 diffuses the light emitted by the light source 20 and irradiates the object to be measured, and receives the light reflected from the object to be measured by the 3D sensor 5. In this manner, the measurement device 1 measures the three-dimensional shape of the object to be measured.

[0056] (Configuration of light source 20)

[0057] 4 is a plan view of light source 20. Light source 20 is configured by arranging multiple VCSELs in a two-dimensional array. In other words, light source 20 is configured as a light-emitting element array using VCSELs as light-emitting elements. The rightward direction on the paper is the x-direction, and the upward direction on the paper is the y-direction.

[0058] The direction perpendicular to the x and y directions is defined as the z direction. The front surface of the light source 20 refers to the front side of the paper, i.e., the surface on the +z direction side, and the back surface of the light source 20 refers to the back side of the paper, i.e., the surface on the -z direction side. The plan view of the light source 20 is a view of the light source 20 as seen from the front surface side.

[0059] To explain further, in the light source 20, the side on which an epitaxial layer functioning as a light emitting layer is formed is referred to as the front surface, front side, or front surface side of the light source 20.

[0060] A VCSEL is a light-emitting element that has an active region between a lower multilayer reflector and an upper multilayer reflector stacked on a semiconductor substrate, and emits laser light in a direction perpendicular to the surface. For this reason, VCSELs can be easily arrayed in two dimensions compared to edge-emitting lasers. The number of VCSELs included in the light source 20 is, for example, 100 to 1000. The multiple VCSELs are connected in parallel to each other and driven in parallel. The number of VCSELs is just an example, and may be set according to the measurement distance and the irradiation range.

[0061] An anode electrode 218 (see FIG. 5) common to the multiple VCSELs is provided on the front surface of the light source 20. A cathode electrode 214 (see FIG. 5) is provided on the back surface of the light source 20. In other words, the multiple VCSELs are connected in parallel. By connecting the multiple VCSELs in parallel and driving them, light with a higher intensity is emitted compared to when the VCSELs are driven individually.

[0062] Here, the shape of light source 20 as viewed from the front side (referred to as planar shape, the same applies below) is rectangular. The side surface on the -y direction side is referred to as side surface 21A, the side surface on the +y direction side as side surface 21B, the side surface on the -x direction side as side surface 22A, and the side surface on the +x direction side as side surface 22B. Side surface 21A and side surface 21B face each other. Side surface 22A and side surface 22B connect side surface 21A and side surface 21B, respectively, and face each other.

[0063] The center of the planar shape of the light source 20, that is, the center in the x and y directions, is defined as a center Ov.

[0064] (Driver 50 and capacitors 70A, 70B)

[0065] When it is desired to drive the light source 20 at higher speed, it is preferable to use low-side driving. Low-side driving refers to a configuration in which a driving element such as a MOS transistor is located on the downstream side of the current path of a driving target such as a VCSEL. Conversely, a configuration in which a driving element is located on the upstream side is called high-side driving.

[0066] Fig. 5 is a diagram showing an example of an equivalent circuit when the light source 20 is driven by low-side driving. Fig. 5 shows the VCSEL of the light source 20, the driving unit 50, the capacitors 70A and 70B, the resistive element 72, and a power supply 82. The power supply 82 is provided in the control unit 8 shown in Fig. 1. The power supply 82 generates a DC voltage with the + side being a power supply potential and the - side being a reference potential. The power supply potential is supplied to a power supply line 83, and the reference potential is supplied to a reference line 84. The reference potential may be a ground potential (sometimes referred to as GND; indicated as [G] in Fig. 5).

[0067] As described above, the light source 20 is configured by connecting a plurality of VCSELs in parallel. The anode electrode 218 of the VCSEL (see FIG. 4; indicated as [A] in FIG. 5) is connected to the power line 83.

[0068] The driving unit 50 includes a FET element 51 and a signal generating circuit 52 that turns on and off the FET element 51. The drain (indicated as [D] in FIG. 5) of the FET element 51 is connected to the cathode electrode 214 (see FIG. 4; indicated as [K] in FIG. 5) of the VCSEL. The FET element 51 is an example of a switch element.

[0069] The FET element 51 is, for example, a GaN (gallium nitride) FET element, but is not limited to this and may be an FET element made of other materials such as silicon.

[0070] The source of the FET element 51 (denoted as [S] in FIG. 5) is connected to a reference line 84. The gate of the FET element 51 is connected to a signal generating circuit 52. That is, the VCSEL and the FET element 51 of the driving unit 50 are connected in series between a power supply line 83 and a reference line 84. Under the control of the control unit 8, the signal generating circuit 52 generates an "H level" signal that turns the FET element 51 on and an "L level" signal that turns the FET element 51 off.

[0071] Capacitors 70A and 70B have one terminal connected to a power supply line 83 and the other terminal connected to a reference line 84. Here, when there are multiple capacitors 70, the multiple capacitors 70 are connected in parallel. That is, in Fig. 5, capacitors 70 are two capacitors 70A and 70B. Capacitors 70 are, for example, electrolytic capacitors or ceramic capacitors.

[0072] One terminal of each of the capacitors 70A and 70B is connected to one terminal of the resistor element 72. The other terminal of the resistor element 72 is connected to the + side of the power supply 82.

[0073] In this way, the capacitors 70A, 70B are connected in parallel to the light source 20, and discharge the stored charge to the light source 20. In addition, a resistive element 72 is provided between the capacitors 70A, 70B and the power source 82 that charges the capacitors 70A, 70B. The capacitance of the capacitors 70A, 70B is relatively small, for example, a capacitance that discharges all of the accumulated charge.

[0074] Next, a method for driving the light source 20, which is low-side driving, will be described.

[0075] First, assume that the signal generated by the signal generating circuit 52 in the driving unit 50 is at "L level." In this case, the FET element 51 is in an off state. In other words, no current flows between the source ([S] in FIG. 5) and drain ([D] in FIG. 5) of the FET element 51. Therefore, no current flows in the VCSEL connected in series with the FET element 51. In other words, the VCSEL does not emit light.

[0076] At this time, capacitors 70A and 70B are connected to power supply 82 via resistive element 72, the other terminal of resistive element 72 becomes the power supply potential, and the other terminal connected to reference line 84 becomes the reference potential. Therefore, a current flows (charge is supplied) from power supply 82 via resistive element 72 to capacitors 70A and 70B, and the capacitors are charged.

[0077] Next, when the signal generated by the signal generating circuit 52 in the driving unit 50 goes to "H level", the FET element 51 transitions from the OFF state to the ON state. Then, a closed loop is formed by the capacitors 70A, 70B and the series-connected FET element 51 and VCSEL, and the charge stored in the capacitors 70A, 70B is supplied to the series-connected FET element 51 and VCSEL. In other words, a driving current flows through the VCSEL, causing the VCSEL to emit light. This closed loop is a driving circuit that drives the light source 20.

[0078] Then, when the signal generated by the signal generating circuit 52 in the driving unit 50 goes to "L level" again, the FET element 51 transitions from the ON state to the OFF state. As a result, the closed loop (driving circuit) between the capacitors 70A, 70B and the FET element 51 and VCSEL connected in series becomes an open loop, and no driving current flows to the VCSEL. As a result, the VCSEL stops emitting light. Then, the capacitors 70A, 70B are charged by the charge supplied from the power source 82 via the resistive element 72.

[0079] As described above, each time the signal output by the signal generating circuit 52 transitions between "H level" and "L level," the FET element 51 repeatedly turns on and off, causing the VCSEL to repeatedly emit and not emit light. The repeated on and off of the FET element 51 is sometimes called switching.

[0080] The charging time (time constant) τ until capacitors 70A, 70B are charged to the power supply potential of power supply 82 after FET element 51 transitions from the on state to the off state is expressed by the following equation, where C is the capacitance value of the parallel circuit of capacitors 70A, 70B and R is the resistance value of resistor element 72.

[0081] τ = R C (1)

[0082] The charging time τ is set in accordance with the minimum value of the light emission interval of the pulsed light. Specifically, the charging time τ is set to be sufficiently smaller than the minimum value of the light emission interval of the pulsed light. That is, the capacitance value C of the parallel circuit of the capacitors 70A, 70B and the resistance value R of the resistive element 72 are set in accordance with the minimum value of the light emission interval of the pulsed light. The charging time τ is set to, for example, the time required for charging to 63.2% of the power supply voltage of the power supply 82.

[0083] (Heat dissipation base material 100)

[0084] Fig. 6(A) is a plan view of the heat dissipation base material 100. Fig. 6(B) is a cross-sectional view taken along line AA in Fig. 6(A). Fig. 6(C) is a cross-sectional view taken along line BB in Fig. 6(A).

[0085] Here, in FIG. 6(A), the right direction of the paper is the +X direction, the left direction of the paper is the -X direction, the top direction of the paper is the +Y direction, and the bottom direction of the paper is the -Y direction. The direction perpendicular to the X and Y directions (front direction of the paper) is the Z direction. And, for the heat dissipation base material 100 described below, the front direction of the paper (+Z direction) is called the front or front side, and the back direction of the paper (-Z direction) is called the back or back side. And, hereinafter, seeing through each component from the front side is called a top view. In FIG. 6(B), the right direction of the paper is the X direction, the back direction of the paper is the Y direction, and the top direction of the paper is the Z direction.

[0086] 6(A) to 6(C), a light source 20, an FET element 51, capacitors 70A and 70B, and a resistive element 72 are provided on a surface of a heat dissipation base material 100. Then, a light diffusing member 30 is provided on a holding portion 60, as shown in FIGS.

[0087] The heat dissipating base material 100 is configured by providing a wiring layer that forms wiring made of metal such as copper (Cu) foil on an insulating base material such as aluminum nitride (AlN) having a thermal conductivity of 100 W / m·K or more. When an inorganic base material is used as the heat dissipating base material 100, the thickness is preferably at least 100 μm in terms of strength. Furthermore, if the thickness exceeds 500 μm, it becomes difficult to use in terms of inductance, so it is preferably 500 μm or less. In addition, it is more preferable that the thickness is 200 μm or less in terms of effective inductance of the current loop. That is, when an inorganic base material is used as the heat dissipating base material 100, the thickness is preferably 100 μm or more and 500 μm or less, preferably 100 μm or more and 200 μm or less.

[0088] Furthermore, when an organic base material is used as the heat dissipation base material 100, it is preferable to use a base material with high thermal conductivity, for example, a base material with a thermal conductivity of 1 to 5 W / m·K. Here, for example, when the thickness is about 10 μm, a base material with a thermal conductivity of 1 to 5 W / m·K can be used. Furthermore, in the case of an organic base material, unlike the case of an inorganic base material, it is preferable to use a base material with a thickness of less than 100 μm.

[0089] As shown in FIG. 6A, the light source 20 has a rectangular shape when viewed from above, and a cathode electrode 214 is provided in an area obtained by enlarging the light source 20. A part of the cathode electrode 214 extends in the -Y direction. The FET element 51 is provided on the extended cathode electrode 214, and the cathode electrode 214 and the drain [D] of the FET element 51 are connected. In other words, the FET element 51 is connected in series with the light source 20 by the same cathode electrode, and drives the light source 20.

[0090] The gate [G] of the FET element 51 is connected to a gate electrode 220 provided on the front surface side of the heat dissipation base material 100. The source [S] of the FET element 51 is connected to a ground electrode 222 provided on the front surface side of the heat dissipation base material 100.

[0091] 6(C), the gate electrode 220 is connected to a ground electrode 226 provided on the back surface of the heat dissipation base material 100 through a conductive via hole 224 that penetrates the heat dissipation base material 100. In addition, the ground electrode 222 is connected to a ground electrode 230 provided on the back surface of the heat dissipation base material 100 through a conductive via hole 228 that penetrates the heat dissipation base material 100.

[0092] In addition, an anode electrode 218 is provided on the front surface side of the heat dissipation base material 100 so as to surround three sides, the right side, left side, and upper side, of the light source 20. The right side and left side of the light source 20 are connected to the anode electrode 218 with a wire 232 by wire bonding.

[0093] A capacitor 70A is provided on the left side of the light source 20. One terminal of the capacitor 70A is connected to the anode electrode 218, and the other terminal is connected to the ground electrode 234. As shown in FIG. 6B, the ground electrode 234 is connected to a ground electrode 238 provided on the back side of the heat dissipation base material 100 through a conductive via hole 236 that penetrates the heat dissipation base material 100. A capacitor 70B is provided on the right side of the light source 20. One terminal of the capacitor 70B is connected to the anode electrode 218, and the other terminal is connected to a ground electrode 240. As shown in FIG. 6B, the ground electrode 240 is connected to the ground electrode 238 provided on the back side of the heat dissipation base material 100 through a conductive via hole 242 that penetrates the heat dissipation base material 100.

[0094] 6(A), a resistive element 72 is provided on the upper side of the capacitor 70B. One terminal of the resistive element 72 is connected to the anode electrode 218. The other terminal is connected to the power supply electrode 244. The power supply electrode 244 is connected to the power supply 82.

[0095] FIG. 7 is a top view of the ground electrodes 226, 238, and 244 provided on the back side of the heat dissipating substrate 100. As shown in FIG. 7, the ground electrodes are provided over almost the entire back side of the heat dissipating substrate 100. Therefore, the drive current for making the light source 20 emit light flows from the anode electrode 218 on the heat dissipating substrate 100 to the cathode electrode 214, and also flows in a path projected from the current path to the ground electrode 238 on the back side of the heat dissipating substrate 100. In addition, since the drain and source of the FET element 51 are directly connected on the heat dissipating substrate 100, the effective inductance of the current path is minimized. Therefore, it is possible to rapidly raise a pulse with a high current value and a short pulse width at a low power supply voltage. At the same time, the cathode electrode 214 connected to the light source 20 and the ground electrode 238 face each other on the front and back sides of the heat dissipating substrate 100 with high thermal conductivity, so that the heat generated by the light source 20 is efficiently dissipated to the ground electrode 238 side.

[0096] Although the embodiments have been described above, the technical scope of the present invention is not limited to the scope described in the above embodiments. Various modifications or improvements can be made to the above embodiments without departing from the gist of the invention, and such modifications or improvements are also included in the technical scope of the present invention.

[0097] Furthermore, the above-mentioned embodiments do not limit the inventions described in the claims, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. The above-mentioned embodiments include inventions at various stages, and various inventions are extracted by combining the multiple constituent elements disclosed. Even if some constituent elements are deleted from all the constituent elements shown in the embodiments, as long as the effect is obtained, the configuration from which these several constituent elements are deleted can be extracted as an invention.

[0098] For example, in the present embodiment, the case where one light source 20 and one FET element 51 are provided has been described, but a configuration having a plurality of pairs of light source 20 and FET element 51 may be used. In this case, a configuration may be used in which the signal wiring from the control unit 8 that outputs a control signal to control the plurality of FET elements 51 to the plurality of FET elements 51 is branched to have equal lengths. For example, as shown in FIG. 8, in the case of a configuration having two light sources 20A and 20B and two FET elements 51A and 51B, the signal wiring from the control unit 8 to the gates of the FET elements 51A and 51B is branched to have equal lengths so that the distance L1 from the control unit 8 to the gate of the FET element 51A and the distance L2 from the control unit 8 to the gate of the FET element 51B are the same. In addition, a configuration may be used in which the same cathode electrode 214 to which the cathodes of the light sources 20A and 20B are connected is provided on the heat dissipation base material 100. [Explanation of symbols]

[0099] 1. Measurement equipment 3 Optical equipment 4. Light-emitting device 5 3D Sensor 8. Control Unit 10 Wiring board 12 Controller 20 light source 50 Drive unit 51 FET element 52 Signal Generator Circuit 70A Capacitor 70B Capacitor 72 Resistance element 81 3D shape identification part 82 Power supply 83 Power line 84 Reference Line 100 Heat dissipation base material 214 Cathode Electrode 218 Anode Electrode

Claims

1. A light-emitting element; A drive unit including a switch element connected in series with the light emitting element through the same electrode as the light emitting element and for driving the light emitting element, and a signal generating circuit for turning on and off the switch element; a capacitance element connected in parallel to the light emitting element and discharging a charged charge to the light emitting element; a resistive element provided between the capacitive element and a power source that charges the capacitive element; Equipped with The light emitting element, the switch element, the capacitive element, and the resistive element are formed on the same heat dissipation substrate, and the signal generating circuit is not formed on the heat dissipation substrate. Light emitting device.

2. The capacitance value of the capacitive element and the resistance value of the resistive element are set in accordance with the minimum value of the light emission interval of the pulsed light emitted from the light emitting element. The light emitting device according to claim 1 .

3. The heat dissipation base material is aluminum nitride. The light emitting device according to claim 1 or 2.

4. The heat dissipation base material is an inorganic base material, has a thickness of 100 μm or more and 500 μm or less, and has a thermal conductivity of 100 W / m·K or more. The light emitting device according to any one of claims 1 to 3.

5. The heat dissipation base material is an organic base material, has a thickness of less than 100 μm, and has a thermal conductivity of 1 W / m·K or more. The light emitting device according to claim 1 or 2.

6. A plurality of pairs of the light emitting element and the switch element are provided. The light emitting device according to any one of claims 1 to 5.

7. Signal wiring from a control unit that outputs a control signal for controlling the plurality of switch elements to the plurality of switch elements is branched out to have equal lengths. The light emitting device according to claim 6.

8. The same cathode electrode to which the cathodes of the plurality of light-emitting elements are connected is provided on the heat dissipation base material. The light emitting device according to claim 6 or 7.

9. The switch element, the capacitance element, and the resistance element are provided on the same surface of the heat dissipation base material on which the light-emitting element is provided, an anode electrode that is provided in a planar shape on the same surface of the heat dissipation base material on which the light emitting element is provided, and that connects the capacitance element and the resistance element; a power supply electrode that is provided in a planar shape on the same surface of the heat dissipation base material on which the light emitting element is provided, and that connects the power supply and the resistance element; A plurality of ground electrodes are provided in a planar shape on a back surface of the heat dissipation base material on which the light emitting element is provided; The light emitting device according to claim 8 .

10. A drive current for causing the light emitting element to emit light flows from the anode electrode to the cathode electrode on the heat dissipation substrate, and a current also flows in a path obtained by projecting the current path onto a ground electrode. The light emitting device according to claim 9.

11. A light emitting device according to any one of claims 1 to 10; a light receiving element that receives reflected light of light emitted from the light emitting device to the object to be measured; a measurement unit that measures a distance to the object by a time of flight in a direct method from the amount of light received by the light receiving element; A measuring device equipped with

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