Light-receiving device and distance measurement device

Abstract

To provide a light reception device capable of reducing power consumption and a distance measurement device.SOLUTION: A light reception device according to an embodiment comprises a plurality of pixels. Each pixel comprises a photoelectric conversion element capable of detecting incident photons, and a power source unit for changing a voltage applied across two ends of the photoelectric conversion element.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] Embodiments of the present invention relate to a light receiving device and a distance measuring device.

Background Art

[0002] A distance measuring device called LIDAR (Light Detection and Ranging) is known. In this distance measuring device, a laser beam is irradiated onto a measurement object, and based on the output of a light receiving device having a plurality of photodiodes such as an avalanche photodiode (APD), the intensity of the reflected light reflected by the measurement object is converted into a time-series measurement signal. Thereby, based on the time difference between the time point when the laser beam is emitted and the time point when the reflected light is received by the light receiving device, the distance to the measurement object is measured.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, background light such as sunlight is constantly received and multiplied including the background light. For this reason, photodiodes that receive only background light are also used to multiply unnecessary light such as background light, and there is a risk that the power consumption of the light receiving device increases.

[0005] The problem to be solved by the present invention is to provide a light receiving device and a distance measuring device capable of suppressing the power consumption of the light receiving device.

Means for Solving the Problems

[0006] The light receiving device according to this embodiment includes a plurality of pixels. Each pixel has a photoelectric conversion element capable of detecting the incidence of photons, and a power supply unit that changes the applied voltage at both ends of the photoelectric conversion element.

Brief Description of the Drawings

[0007]

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Mode for Carrying Out the Invention

[0008] Hereinafter, a light receiving device and a distance measuring device according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the following embodiments are examples of the embodiments of the present invention, and the present invention is not construed as being limited to these embodiments. In the drawings referred to in the present embodiment, the same parts or parts having similar functions are denoted by the same reference numerals or similar reference numerals, and repeated descriptions thereof may be omitted. Also, the dimensional ratios in the drawings may be different from the actual ratios for convenience of explanation, or a part of the configuration may be omitted from the drawings.

[0009] (First Embodiment) FIG. 1 is a diagram showing a schematic overall configuration of a driving support system according to the present embodiment. As shown in FIG. 1, the driving support system 1 performs driving support based on a distance image. The driving support system 1 includes a distance measurement system 2, a driving support device 500, an audio device 502, a braking device 504, and a display device 506. The distance measurement system 2 generates a distance image and a speed image of the measurement target 10, and includes a distance measurement device 5 and a measurement information processing device 400.

[0010] The distance measurement device 5 measures the distance to the measurement target 10 using a scanning method and a TOF (Time Of Flight) method. More specifically, the distance measurement device 5 includes a light emitting unit 100, an optical mechanism system 200, and a measurement unit 300.

[0011] The light emitting unit 100 intermittently emits a laser beam L1. The optical mechanism system 200 irradiates the measurement target 10 with the laser beam L1 emitted by the light emitting unit 100, and makes the reflected light L2 of the laser beam L1 reflected on the measurement target 10 enter the measurement unit 300. Here, the laser beam means light having the same phase and frequency. Also, the reflected light L2 means light in a predetermined direction among the scattered light by the laser beam L1.

[0012] The measurement unit 300 measures the distance to the measurement target 10 based on the reflected light L2 received via the optical mechanism system 200. That is, this measurement unit 300 measures the distance to the measurement target 10 based on the time difference between the time when the emission unit 100 irradiates the measurement target 10 with the laser light L1 and the time when the reflected light L2 is measured. The measurement information processing device 400 performs noise reduction processing and outputs distance image data based on the distances to a plurality of measurement points on the measurement target 10. Part or all of the measurement information processing device 400 may be incorporated in the housing of the distance measurement device 5.

[0013] The driving support device 500 supports the driving of the vehicle according to the output signal of the measurement information processing device 400. The driving support device 500 is connected to an audio device 502, a braking device 504, a display device 506, and the like.

[0014] The audio device 502 is, for example, a speaker and is arranged at a position where it can be heard from the driver's seat inside the vehicle. The driving support device 500 generates an audio such as "It is 5 meters to the object" in the audio device 502 based on the output signal of the measurement information processing device 400. Thereby, even when the driver's attention is decreased, for example, it is possible to arouse the driver's attention by listening to the audio.

[0015] The braking device 504 is, for example, an auxiliary brake. The driving support device 500 brakes the vehicle in the braking device 504 based on the output signal of the measurement information processing device 400 when the object approaches to a predetermined distance, for example, 3 meters.

[0016] The display device 506 is, for example, a liquid crystal monitor. The driving support device 500 displays an image on the display device 506 based on the output signal of the measurement information processing device 400. Thereby, it becomes possible to more accurately grasp external information by referring to the image displayed on the display device 506 even in, for example, backlight conditions.

[0017] Next, based on FIG. 2, a more detailed configuration example of the light emitting unit 100, the optical mechanism system 200, and the measurement unit 300 of the distance measurement device 5 according to the present embodiment will be described. FIG. 2 is a diagram showing a configuration example of the distance measurement device 5 according to the first embodiment. As shown in FIG. 2, the distance measurement device 5 includes a light emitting unit 100, an optical mechanism system 200, a measurement unit 300, and a measurement information processing device 400. Here, among the scattered light L3, the scattered light in a predetermined direction is referred to as the reflected light L2. The block diagram shown in FIG. 2 is an example of signals, and the order and wiring are not limited thereto.

[0018] The light emitting unit 100 includes a light source 11, an oscillator 11a, a first drive circuit 11b, a control unit 16, a clock generator 16a, and a second drive circuit 16b.

[0019] The optical mechanism system 200 includes an irradiation optical system 202 and a light receiving optical system 204. The irradiation optical system 202 includes a lens 12, a first optical element 13, a lens 13a, and a mirror (reflection device) 15.

[0020] The light receiving optical system 204 includes a second optical element 14 and a mirror 15. That is, these irradiation optical system 202 and light receiving optical system 204 share the mirror 15.

[0021] The measurement unit 300 includes a photodetector 17, a lens 18a, a first amplifier 18, a light receiving device 19, and a first distance measurement unit 150. Here, as an existing method of scanning light, the mirror 15 is used here, but in addition to using the mirror 15, there is a method of rotating the distance measurement device 5 (hereinafter referred to as the rotation method). Also, as another existing scanning method, there is an OPA method (Optical Phased array). Since the present embodiment does not depend on the method of scanning light, the light may be scanned by the rotation method or the OPA method.

[0022] The oscillator 11a of the output unit 100 generates a pulse signal based on the control of the control unit 16. The first drive circuit 11b drives the light source 11 based on the pulse signal generated by the oscillator 11a. The light source 11 is a laser light source such as a laser diode, and intermittently emits laser light L1 in response to the drive by the first drive circuit 11b.

[0023] Next, the emission pattern of the light source 11 in one frame will be described with reference to FIG. 3. Here, a frame means a combination of emissions of the laser light L1 that is periodically repeated. FIG. 3 is a diagram schematically showing the emission pattern of the light source 11 in one frame. In FIG. 3, the horizontal axis indicates time, and the vertical lines indicate the emission timings of the light source 11. The upper figure is a partial enlarged view of the lower figure. As shown in this FIG. 3, the light source 11 intermittently and repeatedly emits the laser light L1(n) (0 ≦ n < N) at intervals of, for example, T = several microseconds to several tens of microseconds. Here, the laser light L1 emitted at the nth time is denoted as L1(n). N indicates the number of irradiations of the laser light L1(n) for measuring the measurement target 10 in one frame. When the irradiation for one frame is completed, the irradiation for the next frame starts from L1(0).

[0024] As shown in FIG. 2, on the optical axis O1 of the irradiation optical system 202, the light source 11, the lens 12, the first optical element 13, the second optical element 14, and the mirror 15 are arranged in this order. Thereby, the lens 12 collimates the laser light L1 that is intermittently emitted and guides it to the first optical element 13.

[0025] The first optical element 13 transmits the laser light L1 and makes a part of the laser light L1 enter the photodetector 17 along the optical axis O3. The first optical element 13 is, for example, a beam splitter. In this embodiment, although it has the first optical element 13, it is not limited thereto. For example, a configuration without the first optical element 13 may be used.

[0026] The second optical element 14 further transmits the laser beam L1 that has passed through the first optical element 13 and causes the laser beam L1 to be incident on the mirror 15. The second optical element 14 is, for example, a half mirror.

[0027] The mirror 15 has a reflecting surface 15a that reflects the laser beam L1 intermittently emitted from the light source 11. The reflecting surface 15a is rotatable, for example, about two rotation axes RA1 and RA2 that intersect each other. As a result, the mirror 15 periodically changes the irradiation direction of the laser beam L1.

[0028] The control unit 16 has, for example, a CPU (Central Processing Unit), and performs control to continuously change the tilt angle of the reflecting surface 15a according to a clock signal supplied from the clock generator 16a on the second drive circuit 16b. That is, the clock generator 16a generates a clock signal and supplies it to the control unit 16 and the like.

[0029] The second drive circuit 16b drives the mirror 15 according to the drive signal supplied from the control unit 16. That is, the control unit 16 controls the second drive circuit 16b to change the irradiation direction of the laser beam L1.

[0030] Next, based on FIG. 4, the irradiation direction of the laser light L1 in one frame will be described. FIG. 4 is a schematic diagram showing an enlarged view of the irradiation positions of the laser light L1 on the measurement target 10 in one frame. As shown in this FIG. 4, the reflecting surface 15a (FIG. 2) changes the irradiation direction for each laser light L1 and irradiates discretely along a plurality of substantially parallel straight-line paths P1 to Pm (m is a natural number of 2 or more) on the measurement target 10. In this way, the distance measuring device 5 according to the present embodiment irradiates the measurement target 10 once while changing the irradiation direction O(n) (0 ≦ n < N) of the laser light L1(n) (0 ≦ n < N) for each frame f(m) (0 ≦ m < M). Here, the irradiation direction of the laser light L1(n) is denoted as O(n). That is, in the distance measuring device 5 according to the present embodiment, the laser light L1(n) is irradiated once in the irradiation direction O(n). Since the irradiation direction O(n) (0 ≦ n < N) is the same in each frame, the irradiation direction O(n) (0 ≦ n < N) in the m-th frame and the irradiation direction O(n) (0 ≦ n < N) in the (m - 1)-th frame coincide. In this way, the laser light L1(n) according to the present embodiment may be irradiated sequentially one by one as shown in FIG. 4, but is not limited thereto, and a plurality of points may be irradiated simultaneously.

[0031] As shown in FIG. 2, on the optical axis O2 of the light receiving optical system 204, in the order in which the reflected light L2 is incident, the reflecting surface 15a of the mirror 15, the second optical element 14, the lens 18a, and the light receiving device 19 are arranged. Here, the optical axis O1 is the focal axis of the lens 12 passing through the central position of the lens 12. The optical axis O2 is the focal axis of the lens 18a passing through the central position of the lens 18a.

[0032] The reflecting surface 15a causes the reflected light L2 traveling along the optical axis O2 among the scattered light L3 scattered on the measurement target 10 to be incident on the second optical element 14. The second optical element 14 changes the traveling direction of the reflected light L2 reflected by the reflecting surface 15a and causes it to be incident on the lens 18a of the measurement unit 300 along the optical axis O2. The lens 18a condenses the reflected light L2 incident along the optical axis O2 onto the light receiving device 19.

[0033] On the other hand, the traveling direction of the light reflected in a direction different from that of the laser beam L1 among the scattered light L3 is deviated from the optical axis O2 of the light receiving optical system 204. Therefore, even if the light reflected in a direction different from the optical axis O2 among the scattered light L3 enters the light receiving optical system 204, it enters at a position deviated from the incident surface of the light receiving device 19. In contrast, among the ambient light such as sunlight scattered by some object, there is light traveling along the optical axis O2, and these lights randomly enter the incident surface of the light receiving device 19 and become random noise.

[0034] In addition, in FIG. 2, for the sake of clarity, the optical paths of the laser beam L1 and the reflected beam L2 are shown separately, but actually they may overlap. Also, the optical axis O1 is shown as the optical path of the center of the light beam of the laser beam L1. Similarly, the optical axis O2 is shown as the optical path of the center of the light beam of the reflected beam L2.

[0035] FIG. 5A is a diagram showing a configuration example of the measurement unit 200 that measures via an optical system 200b different from the optical mechanism system 200a. The optical mechanism system 200a has the same configuration as the output side of the optical mechanism system 200, and includes, for example, a lens 12, a first optical element 13, a lens 13a, and a mirror (reflection device) 15. On the other hand, the optical system 200b is an optical system having, for example, a plurality of objective lenses. Thus, the output unit 100 side and the measurement unit 200 side may each have an independent optical system.

[0036] FIG. 5B is a diagram showing an example of measuring the configuration of the distance measuring device 5 shown in FIG. 2 via a system different from the optical mechanism system 200. As shown in FIG. 5B, the return light L2 from the measurement target 10 is different from the configuration example of the distance measuring device 5 shown in FIG. 2 at the point where it is imaged via the mirror 14a and the lens 18a.

[0037] FIG. 6 is a block diagram showing a configuration example of the light receiving device 19. As shown in FIG. 6, the light receiving device 19 has a plurality of pixels 190b. Each pixel 190b includes a photodiode (PD) 180, a reverse bias power supply 182, a switch 184, and a detection circuit 186. Also, the PD 180, the reverse bias power supply 182, the plurality of switches 184, and the detection circuit 186 are connected in series. That is, the reverse bias power supply 182 is connected to one end (low potential side) of the anode side of the PD 180, and one end of the switch 184 is connected to the other end of the cathode side of the PD 180. Further, the voltage of the ranging unit side power supply 1900 is applied to the other end of the cathode side of the PD 180. Note that the reverse bias power supply 182 according to the present embodiment corresponds to the first power supply, and the ranging unit side power supply 1900 corresponds to the second power supply. Also, the photodiode (PD) 180 may be simply referred to as PD 180 hereinafter.

[0038] The PD 180 is, for example, a photoelectric conversion element that converts a single photon into an electrical signal. This photoelectric conversion element is constituted by, for example, a Geiger mode avalanche photodiode (APD: Avalanche Photo Diod). The avalanche photodiode is a light receiving element that increases the light receiving sensitivity by utilizing a phenomenon called avalanche multiplication. The avalanche photodiode used in the Geiger mode is generally used together with a quenching element and is called a single-photon avalanche photodiode (SPAD: Single-Photon Avalanche Diode). That is, the avalanche diode is a diode that increases the light receiving sensitivity by causing avalanche breakdown at a specific reverse voltage. The avalanche photodiode made of silicon is sensitive to light having a wavelength of, for example, 200 nm to 1000 nm.

[0039] Note that PD180 is not limited to an avalanche photodiode. For example, it may be composed of a silicon photomultiplier (SiPM). A silicon photomultiplier is a photon counting device that integrates a plurality of single photon avalanche diodes (SPADs). Also, PD180 may be configured by arranging a plurality of photodiodes, avalanche breakdown diodes (ABDs), silicon photomultipliers made of compound semiconductors, and the like. A photodiode is composed of, for example, a semiconductor that acts as a photodetector.

[0040] The reverse bias power supply 182 switches a plurality of reverse bias voltages and applies them to one end of PD180. On the other hand, the ranging unit side power supply 1900 switches a plurality of voltages and applies them to the other end of PD180. The switch 184 is, for example, a transistor. The switch 184 electrically connects or disconnects PD180 and the detection circuit 186.

[0041] The detection circuit 186 converts the electrical signal output by the PD 180 into a time-series luminance signal at a predetermined sampling interval. This detection circuit 186 has, for example, an amplifier and an AD converter. As the amplifier, a transimpedance amplifier (TIA) or the like that converts and amplifies the current signal of the PD 180 into a voltage signal is used. The AD converter (ADC: Analog to Digital Convertor) samples the measurement signal amplified by the amplifier at a plurality of sampling timings and converts it into a digital time-series luminance signal corresponding to the irradiation direction of the laser beam L1. That is, the AD converter samples the measurement signal amplified by the amplifier. In this way, the digital signal obtained by sampling the electrical signal based on the reflected light L2 at a predetermined sampling interval is referred to as a time-series luminance signal. That is, the time-series luminance signal is a series of values obtained by sampling the temporal change of the reflected light L2 at a predetermined sampling interval. The detection circuit 186 supplies the time-series luminance signal to the signal processing unit 22. Note that the detection circuit 186 may be configured within the signal processing unit 22. Further, the detection circuit 186 may be configured for each of the plurality of pixels 190b.

[0042] The signal processing unit 22 is configured by, for example, a logic circuit including an MPU (Micro Processing Unit), and measures the distance based on the time difference between the timing at which the optical detector 17 detects the laser beam L1 and the timing at which the light receiving device 19 detects the reflected light L2.

[0043] FIG. 7 is a diagram showing an example of the amplification factor with respect to the applied voltage of the PD 180. The horizontal axis represents the voltage applied between the two terminals of the PD 180, and the vertical axis represents the amplification factor. As shown in FIG. 7, the higher the amplification factor, the better the SNR (Signal Noise Ratio) is improved, and as a result, the device performance is improved. However, simply increasing the voltage increases the power consumption.

[0044] Therefore, in this embodiment, for example, the light receiver approval voltage is set within the range shown in FIG. 8. FIG. 8 is a table showing an example of the reverse bias voltage of the reverse bias power supply 182, the voltage of the ranging unit side power supply 1900, and the light receiver approval voltage applied across both ends of the PD180. In this way, the reverse bias power supply 182 applies a reverse bias voltage of, for example, -30 volts or -10 volts to one end of the PD180. On the other hand, a voltage of, for example, 0 volts or 5 volts is applied as the voltage of the ranging unit side power supply to the other end of the PD180. In this way, in this embodiment, the inter-terminal voltage of the PD180 of the pixel 190b used for measurement during normal measurement is set to, for example, 35 volts, and the voltage in the non-measurement case is set to, for example, 10 volts within a range where power consumption can be suppressed.

[0045] Referring to FIG. 7 again, when the inter-terminal voltage is 10 volts, the amplification factor approaches 0. As a result, it becomes possible to reduce the power consumption of the PD180 of the non-measurement pixel T1 close to 0. In this way, by reducing the inter-terminal voltage of the PD180 at the end of the non-measurement pixel T1 to a low voltage, power consumption is suppressed. Also, for the measurement pixel T3, the switch 184 is in a connected state. On the other hand, for the non-measurement pixel T1, the switch 184 is in a non-connected state. Among the pixels 190b according to this embodiment, the pixels used for measurement are referred to as measurement pixels T3, the pixels not used for measurement are referred to as non-measurement pixels T1, and the pixels in the measurement preparation state are referred to as preparation pixels T2.

[0046] FIG. 9 is a diagram schematically showing an example of the distribution of the measurement pixels T3 and non-measurement pixels T1 of the PD180 arranged two-dimensionally. As shown in FIG. 9, by switching the applied voltage of the reverse bias power supply 182, it is possible to set any pixel 190b as the measurement pixel T3 and any pixel 190b as the non-measurement pixel T1.

[0047] FIG. 10 is a block diagram showing a more detailed configuration example of pixel 190b. As shown in FIG. 10, pixel 190b is composed of a high withstand voltage side element and a low withstand voltage side element. In FIG. 10, PD180, a reverse bias power supply 182 corresponding to PD180, a switch 184, and a ranging unit side power supply 1900 are illustrated. Detection circuit 186, signal processing unit 22, etc. are composed of low withstand voltage side elements in order to perform logical operations and the like. For this reason, the ranging unit side power supply 1900 is also composed of low withstand voltage elements.

[0048] The reverse bias power supply 182 includes a plurality of DC / DC converters 1860, 1880, a plurality of capacitors 1900, 1920, and a switch 194. One end of capacitor 1900 is connected to DC / DC converter 1860 and switch 194, and the other end is connected to one end of the ranging unit side power supply 1900. One end of capacitor 1920 is connected to DC / DC converter 188 and switch 184, and the other end is connected to one end of the ranging unit side power supply 1900.

[0049] DC / DC converter 1860 outputs a voltage of -10 volts from the ground. As a result, charges corresponding to the potential of -10 volts from the ground are accumulated in capacitor 1900. Similarly, DC / DC converter 192 outputs a voltage of -30 volts from the ground. As a result, charges corresponding to the potential of -10 volts from the ground are accumulated in capacitor 1920. Switch 194 switches the connection between DC / DC converter 1860, DC / DC converter 1920, and PD180. In this case, fluctuations in the switching voltage can be suppressed by the stored charges of capacitors 1900 and 1920. Also, switch 194 is, for example, a transistor.

[0050] The ranging unit side power supply 1900 switches between 0 volts and 5 volts. Similar to the reverse bias power supply 182 for example, the ranging unit side power supply 1900 is also composed of a plurality of DC / DC converters and a plurality of capacitors. In this case, the capacitance of the capacitor of the ranging unit side power supply 1900 is smaller than that of the reverse bias power supply 182. The transistors constituting the switch also have a low breakdown voltage. The control unit 16 (see FIG. 2) controls the reverse bias power supply 182, the switch 184, and the ranging unit side power supply 1900.

[0051] FIG. 11 is a table showing an operation example of the power supply voltage of the comparative example. That is, FIG. 10 shows a general example of the reverse bias voltage, the voltage of the ranging unit side power supply, and the light receiver applied voltage applied across both ends of the PD180. In the comparative example, the reverse bias voltage is an example fixed at -30 volts. As the voltage of the ranging unit side power supply 1900, for example, 0 volts or 5 volts is applied. In such a case, even if the voltage of the ranging unit side power supply 1900 is set to 0 volts, 30 volts is applied across the terminals of the PD180, so that the PD180 maintains a magnification several times that (see FIG. 7). If the ranging unit side power supply 1900 during non-measurement can be made -20 volts, the voltage across the terminals of the PD180 can be suppressed to about 10 volts. However, the ranging unit side power supply 1900 is on the low breakdown voltage side, and it is difficult to realize a change from 0 volts to -20 volts. As can be seen from these, in order to vary the voltage across the terminals by about 20 volts, it is necessary to adjust with the power supply of the high breakdown voltage side circuit, that is, the reverse bias power supply 182.

[0052] FIG. 12 is a table showing an operation example of a power supply voltage including a preparation operation by the control unit 16 (see FIG. 2). That is, this FIG. 12 shows an example of a reverse bias voltage, the voltage of the ranging unit side power supply 1900, and the light receiver approval voltage (voltage between terminals) applied across both ends of the PD180. As described above, the pixel 190b has a preparation pixel T2 (the pixel to be measured next) as a pixel in an intermediate operation state between the measurement pixel T3 and the non-measurement pixel T1. In the preparation pixel T2, the reverse bias voltage is set to -30 volts, the voltage of the ranging unit side power supply 1900 is set to, for example, 0 volts, and the light receiver approval voltage is set to 30 volts. The measurement pixel T3 connects the switch 184. On the other hand, for the non-measurement pixel T1 and the preparation pixel T2, the switch 184 is not connected. Also, as shown in FIG. 12, by setting the preparation pixel T2 to be measured next to an intermediate voltage, it is possible to shorten the response time required for voltage control. Thereby, it is possible to relax the constraints on the response speed of the DC / DC converters 1860 and 1880 (see FIG. 10).

[0053] FIG. 13 is a diagram showing an example of the distribution of the measurement pixel T3, the preparation pixel T2, and the non-measurement pixel T1 of the PD180 arranged in a two-dimensional manner. As shown in FIG. 13, by switching the combination of the applied voltages of the reverse bias power supply 182 and the ranging unit side power supply 1900 under the drive control of the control unit 16, any pixel 190b can be set as either the measurement pixel T3, the preparation pixel T2, or the non-measurement pixel T1.

[0054] FIG. 14 is a diagram schematically showing the time change of the driving state of three vertical pixels. The arrow G18 indicates the pixels in three vertical columns, and the horizontal axis indicates time. As shown in FIG. 14, for example, it is possible to change the positions of the measurement pixel T3, the preparation pixel T2, and the non-measurement pixel T1 in accordance with the time change of the position of the imaging object. In this way, by the drive control of the control unit 16 for the light receiving device 19, it is also possible to change the positions of, for example, the measurement pixel T3, the preparation pixel T2, and the non-measurement pixel T1 according to the passage of time.

[0055] FIG. 15 is a block diagram showing a configuration example of the light receiving device 19a. As shown in FIG. 15, this light receiving device 19a is different from the light receiving device 19 shown in FIG. 6 in that it has a plurality of reverse bias power supplies 182a and b and switches 185 for connecting or disconnecting between the reverse bias power supplies 182a and b and the PD 180. The reverse bias power supply 182a can be switched, for example, between 0, -10, and -20 volts. Also, the reverse bias power supply 182b can be switched, for example, between -20 and -30 volts. Thereby, reverse bias voltages of 0, -10, -20, and -30 volts can be applied to each PD 180. In this way, a plurality of reverse bias voltages may be prepared and configured such that the voltage can be selected by the switch 185 for each pixel.

[0056] FIG. 16 is a block diagram showing a configuration example of the light receiving device 19b. As shown in FIG. 16, the light receiving device 19b is different from the light receiving device 19 shown in FIG. 6 in that reverse bias power supplies 182c and d are connected to a plurality of PDs 180. The reverse bias power supplies 182c and d can be switched, for example, between -10 and -30 volts. Thereby, in the light receiving device 19b, the bias voltage is switched for each of the plurality of PDs 180.

[0057] FIG. 17 is a block diagram showing a configuration example of the light receiving device 19c. As shown in FIG. 17, the light receiving device 19c is connected between a plurality of reverse bias power supplies 182a and b and a plurality of PDs 180 via switches 185a and b. The switches 185a and b select one of the reverse bias power supplies 182a and b. The reverse bias power supply 182a can be switched, for example, between 0 and -10 volts. Also, the reverse bias power supply 182b can be switched, for example, between -20 and -30 volts. Thereby, reverse bias voltages of 0, -10, -20, and -30 volts can be applied to each of the plurality of PDs 180. In this way, a plurality of reverse bias voltages may be prepared and configured such that the voltage can be selected by the switches 185a and b for each of the plurality of pixels.

[0058] FIG. 18 is a block diagram showing a configuration example of the control unit 16. As shown in FIG. 18, the control unit 16 includes a mechanism control unit 160a, a drive mode setting unit 160b, a voltage control unit 160c, and a determination unit 160d. As described above, the mechanism control unit 160a controls the oscillator 11a and the second drive circuit 16b to control the irradiation position and irradiation timing of the laser light. The input / output unit (IF) 23 has a decoder function and a serial / parallel conversion function. Thereby, the control unit 16 can parallel-convert and decode the signal encoded by the control unit 16 and the serially-converted signal.

[0059] The voltage control unit 160c controls the voltage applied to the PD 180, and the connection and disconnection of the PD 180. The mode setting unit sets the operating state of the PD 180. The mode setting unit sets, for example, any one of a first mode, a second mode, and a third mode. For example, the mode setting unit sets each mode according to a control instruction from a higher-level device such as the driving assistance device 500 (see FIG. 1).

[0060] FIG. 19 is a time chart showing a control example of each mode. From the top, it shows the drive signal of the pixel, the reverse bias voltage in the first mode at the pixel C (190b), the distance measurement unit voltage, the reverse bias voltage in the second mode at the pixel C, the distance measurement unit voltage, the reverse bias voltage in the third mode at the pixel C, the distance measurement unit voltage, and the measurement type. The horizontal axis represents time.

[0061] The drive signal of the pixel indicates, at a high level, the drive timing of each PD 180 arranged in a row above as shown in FIG. 4. For example, the drive timing of each PD 180 of pixels A to D is indicated at a high level. That is, each PD 180 is driven in conjunction with the light reception position of the reflected laser L2.

[0062] Here, taking the driving of pixel C in the scanning method as an example, the first mode, the second mode, and the third mode will be described. The first mode is a mode in which the driving of pixel C is changed in time series with non-measured pixel T1 and measured pixel T3. That is, in the first mode, at the timing t12 of the end of the driving of the adjacent PD180 (pixel B), the voltage control unit 160c sets the reverse bias voltage to -30 volts and the ranging unit voltage to 5 volts, and drives pixel C as measured pixel T3.

[0063] In the second mode, it is a mode in which the driving is changed in time series with non-measured pixel T1, preparation pixel T2, and measured pixel T3. That is, in the second mode, at the timing t10 of the start of the driving of the adjacent PD180 (pixel B), the voltage control unit 160c sets the reverse bias voltage to -30 volts and drives pixel C as preparation pixel T2 from non-measured pixel T1. Then, at the timing t12 of the end of the driving of the adjacent PD180, the voltage control unit 160c sets the ranging unit voltage to 5 volts and drives pixel C as measured pixel T3 from preparation pixel T2.

[0064] The third mode is a mode in which this measurement is performed when sunlight or the like is not incident according to the result of pre-measurement. That is, in the third mode, at the timing t10 of the start of the driving of the adjacent PD180 (pixel B), the voltage control unit 160c sets the reverse bias voltage to -30 volts and drives pixel C as preparation pixel T2. If the voltage between the terminals of PD180 is 30 volts, normal measurement is difficult, but if there is a large amount of light such as sunlight, PD180 can perform multiplication. Thereby, the power consumption is suppressed. The determination unit 160d determines that sunlight is being received when PD180 of pixel C generates a current equal to or greater than a predetermined value in pre-measurement.

[0065] In the third mode, when the determination unit 160d determines that sunlight is being received, even if it is the start t14 of the measurement timing of pixel C, this measurement is not performed, and the ranging unit voltage is maintained at 0 volts. As a result, power consumption is suppressed. In this case, the voltage control unit 160c may set the reverse bias voltage to 0 volts at the end t12 of the measurement timing of pixel B, and use pixel C as the measurement pixel T3 instead of the preparation pixel T2. As a result, power consumption is further suppressed.

[0066] FIG. 20 is a flowchart showing an example of processing in the third mode. Here, with reference to FIG. 19, an example of driving pixels in a scanning method will be described. First, the drive mode setting unit 160b of the control unit 16 sets the third mode, and at the timing t10 of the start of driving the adjacent PD180, sets the reverse bias voltage to -30 volts, drives the PD180 as the preparation pixel T2, and performs pre-measurement (step S100).

[0067] Next, the current value generated by the PD180 is transmitted to the determination unit 160d (step S102). Then, the determination unit 160d determines whether the current value is less than or equal to a predetermined value (step S104). If the determination unit 160d determines that it is less than or equal to the predetermined value (Y in step S104), it controls the voltage control unit 160c, sets the ranging unit voltage to 5 volts, and drives the PD180 as the measurement pixel T3 instead of the preparation pixel T2 (step S106).

[0068] Subsequently, the signal processing unit 22 (see FIG. 2) generates a distance value based on the time difference between the peak timing of the signal driven as the measurement pixel T3 and the emission timing of the measurement light (step S106). On the other hand, if the determination unit 160d determines that it is greater than or equal to the predetermined value (Y in step S104), it controls the voltage control unit 160c, sets the reverse bias voltage to 0 volts, and drives the PD180 as the non-measurement pixel T1 instead of the preparation pixel T2 (step S110). The signal processing unit 22 (see FIG. 2) does not perform signal processing on the pixel driven as the non-measurement pixel T1, and generates, for example, a NULL value as the distance value (step S106).

[0069] The drive mode setting unit 160b determines whether all pixels have been completed (step S112). When it is determined that the measurement of all pixels has been completed (Y in step S112), the process in the third mode is terminated. On the other hand, when the drive mode setting unit 160b determines that the measurement of the pixel has not been completed (N in step S112), it changes the drive target to the next pixel and repeats the process from step S100.

[0070] As described above, in the pre-measurement, if the current value is equal to or greater than a predetermined value, the drive mode setting unit 160b performs control to lower the inter-terminal voltage of the target pixel to the level of the non-measured pixel T3. Thereby, if the current value is equal to or greater than the predetermined value, sunlight or the like is incident on the target pixel, and normal distance measurement cannot be performed, so that the power consumption of the target pixel can be suppressed.

[0071] As described above, according to the present embodiment, the voltage applied across both ends of the PD180 can be configured to be changeable for each pixel 190b. Thereby, the power consumption of the pixels 190b that are not used for measurement, such as the preparation pixel T2 and the non-measured pixel T1, can be reduced more than that of the measurement pixel T3, and the power consumption of the light receiving device 19 can be suppressed.

[0072] (Second Embodiment) The driving assistance system 1 according to the second embodiment is different from the driving assistance system 1 according to the first embodiment in that the inter-terminal voltage is changed in accordance with the change in the characteristics of the PD180 due to the temperature variation of the light receiving device 19. Hereinafter, the differences from the driving assistance system 1 according to the first embodiment will be described.

[0073] FIG. 21 is a block diagram showing a configuration example of the distance measurement device 5 according to the second embodiment. The distance measurement device 5 according to the second embodiment is different from the distance measurement device 5 according to the first embodiment in that it further includes a temperature sensor 70. The temperature sensor 70 is disposed near the PD180 of the light receiving device 19, measures the ambient temperature of the PD180, and transmits it to the control unit 16. When the ambient temperature is equal to or higher than a predetermined temperature (for example, 30° C.), the drive mode setting unit 160b of the control unit 16 sets a high temperature mode in which the inter-terminal voltage is increased by, for example, 3 volts compared to the normal mode. On the other hand, when the ambient temperature is lower than the predetermined temperature, the inter-terminal voltage is set to the normal mode, which is, for example, 3 volts lower than the high temperature mode.

[0074] FIG. 22 is a diagram showing the temperature characteristics of the magnification factor with respect to the applied voltage. The horizontal axis represents the inter-terminal voltage (applied voltage), and the vertical axis represents the magnification factor. Line L22 shows the characteristics at low temperature, and line L24 shows the characteristics at high temperature. As described above, the magnification factor decreases as the temperature increases. Therefore, in this embodiment, control is performed to increase the inter-terminal voltage as the temperature increases.

[0075] FIGS. 23 to 27 are diagrams showing an example of the light receiving device 19 in which the drive mode setting unit 160b is configured to be able to vary the voltage between the PD180 terminals. FIG. 23 is a diagram showing a configuration example of the light receiving device 19d in which the reverse bias voltage can be changed to 30 V ± 3 V. That is, it is different from the light receiving device 19c shown in FIG. 17 in that the switch 184 is removed and the voltage settings of the reverse bias power supplies 182a and b are changed. That is, in the light receiving device 19d, the reverse bias voltage can be changed to 0 V, -30 V ± 3 V. Thereby, in the high temperature mode, the reverse bias voltage can be set to -33 V, and in the normal mode, the reverse bias voltage can be set to -30 V or -27 V.

[0076] FIG. 24 is a diagram showing a configuration example of the light receiving device 19e in which the reverse bias voltage can be further changed to -10 V and -20 V. That is, the reverse bias voltage of the light receiving device 19d shown in FIG. 23 can be further changed to -10 V and -20 V.

[0077] FIG. 25 is a diagram showing a configuration example of a light receiving device 19f in which the reverse bias voltage for a plurality of PD180s can be changed to 30 volts ± 3 volts. It is different from the light receiving device 19d shown in FIG. 23 in that the reverse bias voltage for a plurality of PD180s can be changed to 30 volts ± 3 volts.

[0078] FIG. 26 is a diagram showing a configuration example of a light receiving device 19g in which the voltage of the ranging unit side power supply 1900 can be changed by ± 3 volts. It is different from the light receiving device 19d shown in FIG. 23 in that the voltage of the ranging unit side power supply 1900 can be changed by ± 3 volts with respect to PD180. Thus, in the high temperature mode, for example, the voltage of the ranging unit side power supply 1900 can be set to 8 volts, and in the normal mode, the voltage of the ranging unit side power supply 190 can be set to 5 or 2 volts.

[0079] FIG. 27 is a diagram showing a configuration example of a light receiving device 19h in which the voltage of the ranging unit side power supply 1900 can be changed by ± 3 volts. It is different from the light receiving device 19e shown in FIG. 24 in that the voltage of the ranging unit side power supply 1900 can be changed by ± 3 volts with respect to PD180. Thus, in the high temperature mode, for example, the voltage of the ranging unit side power supply 1900 can be set to 8 volts, and in the normal mode, the voltage of the ranging unit side power supply 190 can be set to 5 or 2 volts.

[0080] FIG. 28 is a block diagram showing an example in which a second control unit 160 is configured in the measurement unit 300. The distance measurement device 5 according to the second embodiment is different from the distance measurement device 5 according to the first embodiment in that the second control unit 160 is configured in the measurement unit 300. That is, the drive mode setting unit 160b, the voltage control unit 160c, and the determination unit 160d are configured in the second control unit 160 in the measurement unit 300. Thereby, the measurement unit 300 can perform a control operation only by receiving a control signal for interlocking with the control of the oscillator 11a and the driver 16b (see FIG. 2). Therefore, it is possible to further simplify the communication process.

[0081] As described above, according to the present embodiment, the inter-terminal voltage of the PD 180 is changed in accordance with the change in the characteristics of the PD 180 due to the temperature fluctuation of the light receiving devices 19d to 19h. Thereby, even when the characteristics of the PD 180 have temperature dependence, power control according to the measurement accuracy becomes possible, and the power consumption of the light receiving device can be suppressed.

[0082] As described above, some embodiments of the present invention have been described. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0083] 5: Distance measuring device, 16: Control unit, 19, 19a to 19h: Light receiving devices, 22: Signal processing unit, 160: Second control unit, 160a: Mechanism control unit, 160b: Drive mode setting unit, 160c: Voltage control unit, 160d: Determination unit, 180: Photodiode PD (photoelectric conversion element), 182, 182a, 182c, 182d: Reverse bias power supply (first power supply), 190: Distance measuring unit side power supply (second power supply), 190b: Pixel.

Claims

1. A distance measuring device comprising a plurality of pixels and a control unit, wherein the pixels include a photoelectric conversion element capable of detecting the incidence of photons, a first power supply for supplying a voltage to the anode side of the photoelectric conversion element, a second power supply that is independent of the first power supply and is capable of changing the voltage, and supplies a voltage to the cathode side of the photoelectric conversion element variably for each pixel or a plurality of pixels including the pixel, and the control unit controls at least one of the first power supply and the second power supply, and controls the voltage between the terminals of the photoelectric conversion element to be lower in the order of a measurement pixel used for measurement during normal measurement, a preparation pixel capable of doubling when the light amount exceeds a predetermined amount, and a non-measurement pixel that is not measured. A distance measuring device.

2. The distance measuring device according to claim 1, wherein the control unit controls the preparation pixel to be the non-measurement pixel when the preparation pixel generates a current equal to or greater than a predetermined value.

3. The control unit makes the variation range of the voltage with respect to the first power supply larger than the variation range of the voltage with respect to the second power supply, The distance measuring device according to claim 2, wherein the first power supply is configured in an element region on the high breakdown voltage side, and the second power supply is configured in an element region on the low breakdown voltage side.

4. The control unit makes the variation range of the voltage with respect to the first power supply smaller than the variation range of the voltage with respect to the second power supply, The distance measuring device according to claim 3, wherein the first power supply is configured in an element region on the high breakdown voltage side, and the second power supply is configured in an element region on the low breakdown voltage side.

5. The distance measuring device according to claim 4, wherein the first power supply supplies a voltage to the photoelectric conversion elements respectively included in the plurality of pixels.

6. The distance measuring device according to claim 5, wherein the control unit makes the absolute value of the voltage between the terminals in the measurement pixel larger than the voltage between the terminals in the non-measurement pixel.

7. The distance measuring device according to claim 5, wherein the control unit changes the magnitude of the voltage between the terminals in the preparation pixel in at least two steps.

8. The distance measuring device according to claim 5, wherein the control unit controls the preparation pixel to be the measurement pixel according to the magnitude of the output signal based on the photoelectric conversion element in the preparation pixel.

9. The distance measuring device according to claim 8, wherein the control unit controls the preparation pixel to be the measurement pixel when the output signal is less than a predetermined value.

10. The distance measuring device according to claim 8, wherein the control unit changes the magnitude of the voltage between the terminals according to the temperature of the photoelectric conversion element.

11. The distance measuring device according to claim 10, wherein the control unit increases the magnitude of the voltage between the terminals as the temperature of the photoelectric conversion element rises.

12. An irradiation optical system that irradiates a measurement object while changing the irradiation direction of the laser light, and a light receiving optical system that receives the reflected light of the laser light irradiated by the irradiation optical system. The distance measuring device according to claim 11, wherein the plurality of pixels convert the reflected light received through the light receiving optical system into an electrical signal.

13. The distance measuring device according to claim 12, wherein the photoelectric conversion element is an avalanche photodiode. ​

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