Ranging device and ranging method

Abstract

A ranging device according to the present invention comprises a light reception unit and a conversion unit. The light reception unit receives, as return light, reference light reflected by an object. The conversion unit switches, in accordance with the distance to the object or the light intensity of the return light, a detection method for light reception timing of the return light between an edge detection method and a level detection method.

Description

Distance measuring device and distance measuring method

[0001] The present invention relates to a distance measuring device and a distance measuring method.

[0002] Distance measuring devices called LiDAR (Light Detection and Ranging) are becoming essential for autonomous driving and other applications. LiDAR outputs light such as infrared pulses as reference light and detects the reference light reflected by an object as returned light. LiDAR converts the light intensity data of the returned light into a pulse signal and detects the reception timing of the returned light (e.g., the flight time of the reference light from when it is output from the light source unit to when it is received by the light receiving unit) based on the edge or level (amplitude) of the pulse signal. LiDAR measures the distance to the object based on the reception timing.

[0003] International Publication No. 2020 / 149173

[0004] It is known that when detecting returned light, the amount of light attenuates depending on the distance to the object. It is also known that the shape of the histogram (the distribution of light intensity over time) varies significantly between high-reflectivity and low-reflectivity objects. For this reason, optimization is performed by changing the calculation coefficient and judgment threshold according to the distance. A method of adding the level signals of multiple pixels is also used to improve the SNR. However, conventional methods focus on how to process the obtained information (signal processing and addition processing of the sampling results), and do not attempt to optimize the operating mode itself.

[0005] Therefore, the present disclosure proposes a distance measuring device and a distance measuring method that can obtain highly accurate distance measurement results by optimizing the operation mode.

[0006] According to the present disclosure, there is provided a distance measuring device including a light receiving unit that receives reference light reflected by an object as return light, and a conversion unit that switches a detection method for detecting the reception timing of the return light between an edge detection method and a level detection method depending on the distance to the object or the amount of the return light. Also, according to the present disclosure, there is provided a distance measuring method implemented by the distance measuring device.

[0007] FIG. 1 is a diagram showing an example of the system configuration of a distance measuring system. FIG. 2 is a diagram showing an example of a histogram. FIG. 3 is a diagram showing an example of the system configuration of a distance measuring system. FIG. 4 is a diagram showing an example of the configuration of a distance measuring device. FIG. 5 is a diagram for explaining the operation of a pixel. FIG. 6 is a diagram for explaining the operation of a pixel. FIG. 7 is a diagram for explaining a method for detecting the timing of light reception. FIG. 8 is a diagram for explaining a method for detecting the timing of light reception. FIG. 9 is a diagram showing an example of a process for switching the detection method depending on the distance to an object to be measured. FIG. 10 is a diagram showing an example of a process for switching the detection method depending on the amount of returned light.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following embodiments, the same components are designated by the same reference numerals, and redundant description will be omitted.

[0009] The description will be given in the following order: [1. System Configuration Example] [2. Range Finder Configuration Example] [3. Pixel Operation] [4. Light Reception Timing Detection Method] [5. Processing Flow] [6. Modification Example] [7. Effects]

[0010] 1 and 3 are diagrams showing an example of the system configuration of a distance measuring system DM.

[0011] The distance measurement system DM performs distance measurement using a direct ToF (Time Of Flight) method as an example of a distance measurement method. In the direct ToF method, a reference light beam emitted from the light source unit 2 and reflected by the object to be measured SB is received as a return light beam. The emission timing of the reference light beam (time t ０ ) and the timing of receiving the returning light (time t １ ) and measures the distance to the object to be measured SB.

[0012] For example, the distance measuring system DM includes a distance measuring device 1, a light source unit 2, a light receiving unit 3, a control unit 4, an optical system 5, and a storage unit 6. The light source unit 2 outputs pulsed light as reference light. For example, a VCSEL (Vertical Cavity Surface Emitting Laser) that emits laser light as a surface light source is used as the light source unit 2. However, the light source unit 2 is not limited to this, and may be one that scans a laser diode array in a one-dimensional direction, or one that scans a single laser diode in two-dimensional directions.

[0013] The reference light emitted from the light source unit 2 is reflected by the object under test SB. The light receiving unit 3 receives the reference light reflected by the object under test SB as returned light. The light receiving unit 3 has multiple light receiving elements. The light receiving elements convert the returned light into an electrical signal by photoelectric conversion and output a signal corresponding to the returned light. The multiple light receiving elements are arranged two-dimensionally to form a single light receiving surface. The optical system 5 guides light incident from outside to the light receiving surface. Note that although silicon is used for the photoelectric conversion unit, Ge or Ga may also be used for the photoelectric conversion unit to resolve the trade-off between PDE (Photon Detection Efficiency) and jitter.

[0014] The control unit 4 controls the overall operation of the distance measuring system DM. For example, the control unit 4 supplies a trigger (light emission trigger) to the distance measuring device 1 to make the light source unit 2 emit light. The distance measuring device 1 makes the light source unit 2 emit light at a timing based on the light emission trigger, and also outputs a time t ０ The control unit 4 sets a pattern for distance measurement in the distance measuring device 1 in response to, for example, an external instruction.

[0015] The distance measuring device 1 calculates the time from light emission to light reception (t １ -t ０ ) for the light receiving time t ｍ (See FIG. 2). The distance measuring device 1 acquires the light reception time t ｍ The distance measuring device 1 classifies the light beams into classes (bins) and generates a histogram. Based on the histogram, the distance measuring device 1 calculates the distance D to the object SB. For example, the distance D to the object SB can be calculated by the following equation: D=c×(t １-t ０ ) / 2. Information indicating the distance D is stored in the storage unit 6.

[0016] 2 is a diagram showing an example of a histogram. In FIG. 2, the horizontal axis indicates bins, and the vertical axis indicates the frequency of each bin. The bins are divided into groups based on the light receiving time t ｍ In the example of FIG. 2, bin #0 is 0≦t ｍ < d, bin #1 is d≦t ｍ < 2 × d, bin #2 is 2 × d ≦ t ｍ <3×d, ..., bin #(N-2) is (N-2)×d≦t ｍ <(N-1)×d. The exposure time of the light receiving unit 3 is set to time t ｅｐ In this case, t ｅｐ = N × d.

[0017] The ranging device 1 integrates the time-resolved data of the returned light generated for each shot and generates a histogram. A shot refers to the signal processing of the returned light performed for one light emission. The ranging device 1 detects the presence or absence of returned light in each bin for each light emission and acquires discrete data for each detected bin as time-minute data. The ranging device 1 performs multiple shots in one frame period. The ranging device 1 accumulates the time-resolved data of all shots and acquires the frequency FQ of each bin.

[0018] The light receiving unit 3 also receives light other than the reference light. An example of light other than the reference light is ambient light. The portion indicated by the range LE in the histogram includes an ambient light component. Ambient light is randomly incident on the light receiving unit 3 and becomes noise in distance measurement. On the other hand, light based on the reference light appears as an active light component LA. The bin corresponding to the frequency of peaks in the active light component LA is the bin corresponding to the distance D to the object SB to be measured. The distance measuring device 1 calculates the distance D to the object SB to be measured by obtaining a representative time of that bin (for example, the time at the center of the bin) as the time of flight of the reference light.

[0019] 2. Example of the Configuration of the Distance Measuring Device FIG. 4 is a diagram showing an example of the configuration of the distance measuring device 1. As shown in FIG.

[0020] The ranging device 1 includes a pixel array unit 100, a ranging processing unit 101, a pixel control unit 102, an overall control unit 103, a clock generation unit 104, an emission timing control unit 105, and an interface (I / F) 106. The pixel array unit 100, the ranging processing unit 101, the pixel control unit 102, the overall control unit 103, the clock generation unit 104, the emission timing control unit 105, and the interface (I / F) 106 are arranged on, for example, a single semiconductor chip.

[0021] The overall control unit 103 controls the overall operation of the distance measuring device 1 in accordance with, for example, a pre-installed program. The overall control unit 103 can also execute control in accordance with an external control signal supplied from outside. The clock generation unit 104 generates one or more clock signals used in the distance measuring device 1 based on a reference clock signal supplied from outside. The light emission timing control unit 105 generates a light emission control signal indicating the light emission timing in accordance with a light emission trigger signal supplied from outside. The light emission control signal is supplied to the light source unit 2 and also to the distance measurement processing unit 101.

[0022] The pixel array section 100 includes a plurality of pixels 10, 10, ... arranged in a two-dimensional lattice pattern. Each pixel 10 includes a light receiving element that receives returning light. The pixel array section 100 has a light receiving section 3 configured by a plurality of light receiving elements.

[0023] The operation of each pixel 10 is controlled by the pixel control unit 102 in accordance with instructions from the overall control unit 103. For example, the pixel control unit 102 can control the readout of pixel signals from each pixel 10 for each block including (p × q) pixels 10, with p pixels in the row direction and q pixels in the column direction. The pixel control unit 102 can read pixel signals from each pixel 10 by scanning each pixel 10 in the row direction and then in the column direction, using the block as a unit. This is not a limitation, and the pixel control unit 102 can also control each pixel 10 individually. Furthermore, the pixel control unit 102 can set a predetermined region of the pixel array unit 100 as a target region and set pixels 10 included in the target region as pixels 10 from which pixel signals are to be read out.

[0024] The pixel signals read out from each pixel 10 are supplied to a ranging processing unit 101. The ranging processing unit 101 includes a conversion unit 110, a generation unit 111, and a signal processing unit 112.

[0025] The pixel signals read out from each pixel 10 and output from the pixel array unit 100 are supplied to the conversion unit 110. Here, the pixel signals are read out asynchronously from each pixel 10 and supplied to the conversion unit 110. That is, the pixel signals are read out from the light receiving elements in accordance with the timing at which light is received in each pixel 10 and output.

[0026] The conversion unit 110 converts the pixel signals supplied from the pixel array unit 100 into digital information. That is, the pixel signals supplied from the pixel array unit 100 are output in accordance with the timing at which light is received by the light receiving element included in the pixel 10 to which the pixel signal corresponds. The conversion unit 110 converts the supplied pixel signals into time information indicating the timing.

[0027] The generation unit 111 generates a histogram based on the time information into which the pixel signals are converted by the conversion unit 110. Here, the generation unit 111 counts the time information based on the unit time d set by the setting unit 113, and generates a histogram.

[0028] The signal processing unit 112 performs predetermined arithmetic processing based on the histogram data generated by the generation unit 111, and calculates, for example, distance information. For example, the signal processing unit 112 creates a curve approximation of the histogram based on the histogram data generated by the generation unit 111. The signal processing unit 112 detects peaks in the curve obtained by approximating the histogram, and can calculate the distance D based on the detected peaks.

[0029] When performing curve approximation of a histogram, the signal processing unit 112 can perform filtering on the curve obtained by approximating the histogram. For example, the signal processing unit 112 can suppress noise components by performing low-pass filtering on the curve obtained by approximating the histogram.

[0030] The distance information obtained by the signal processing unit 112 is supplied to the interface 106. The interface 106 outputs the distance information supplied from the signal processing unit 112 to the outside as output data. As the interface 106, for example, a Mobile Industry Processor Interface (MIPI) can be applied.

[0031] In the above description, the distance information calculated by the signal processing unit 112 is output to the outside via the interface 106, but this is not limited to this example. That is, the histogram data, which is the histogram data generated by the generation unit 111, may be output to the outside from the interface 106. In this case, the distance measurement condition information set by the setting unit 113 can omit information indicating the filter coefficients. The histogram data output from the interface 106 is supplied to, for example, an external information processing device and processed as appropriate.

[0032] The distance measuring device 1 has a configuration in which a light-receiving chip and a logic chip are stacked. The light-receiving chip has a plurality of light-receiving elements arranged in a two-dimensional lattice pattern. The transistors and inverters of the pixels 10 are formed on the logic chip. The light-receiving elements are connected to the logic chip via a copper-copper connection (CCC) or the like. The light-receiving chip and the logic chip may be arranged on the same substrate, or may be arranged separately on different substrates. Furthermore, a substrate including a DRAM or a chip for machine learning may be stacked on the light-receiving chip and the logic chip, resulting in a three-layer or more layer configuration.

[0033] 5 and 6 are diagrams for explaining the operation of the pixel 10. The pixel 10 includes, for example, a SPAD (Single Photon Avalanche Diode) 2000 as a light receiving element. Fig. 5 shows the configuration of the pixel 10 taking into account the parasitic capacitance Cca. The pixel 10 includes the SPAD 2000, a current source 2001, and an inverter 2002.

[0034] The SPAD2000 converts incident photons into an electrical signal through photoelectric conversion and outputs a pulse corresponding to the incident photons. When a large negative voltage that generates avalanche multiplication is applied to the cathode, the electrons generated in response to the incidence of a single photon undergo avalanche multiplication, resulting in a large current flow. By utilizing this characteristic of the SPAD2000, the incidence of a single photon can be detected with high sensitivity.

[0035] 5, the anode of SPAD 2000 is connected to a voltage (-Vbd), and the cathode is connected to one end of a current source 2001. The other end of the current source 2001 is connected to a voltage Ve, and supplies a reference current Iref to the SPAD 2000 in the direction from the other end to the one end. An inverter 2002 and a parasitic capacitance Cca are connected to the cathode of the SPAD 2000.

[0036] The parasitic capacitance Cca is the parasitic capacitance at the cathode terminal of the SPAD 2000, and is the sum of the capacitance of the PN junction between the anode and cathode of the SPAD 2000, the element capacitance of the current source 2001 and the inverter 2002, and the parasitic capacitance associated with the wiring.

[0037] FIG. 6 is a diagram showing the operation of the pixel 10 when a photon is received by the SPAD 2000. In FIG. 6, the vertical axis represents voltage and the horizontal axis represents time. The cathode voltage Vc of the SPAD 2000 is at a predetermined initial voltage value until a photon is received. Furthermore, the voltage between the anode and cathode of the SPAD 2000 is at a voltage (-Vbd). When the SPAD 2000 receives a photon (at time t ０ ), avalanche multiplication occurs, a large current flows from the cathode to the anode, and the cathode voltage Vc drops.

[0038] When the cathode voltage Vc drops to the voltage (-Vbd) (at time t １), avalanche multiplication stops, and charging of the cathode of the SPAD 2000 begins with the reference current Iref from the current source 2001. This charging of the cathode of the SPAD 2000 is called recharging. Recharging takes a certain amount of time based on a time constant determined by the parasitic capacitance Cca. When the cathode voltage Vc of the SPAD 2000 returns to the initial voltage value (time t ２ ), the recharge operation is completed. In the SPAD2000, the period of this recharge operation is a period during which no photons can be detected, and is called dead time.

[0039] Here, the slope of the change in the cathode voltage Vc during recharging of the SPAD 2000 is proportional to the reference current Iref, as shown in the following equation (2): If the reference current Iref is large, the dead time is shortened, and if the reference current Iref is small, the dead time is lengthened.

[0040] The inverter 2002 converts the cathode voltage Vc of the SPAD 2000 to a threshold Vc ｔｈ The output signal Vinv is output based on the result of a comparison with the cathode voltage Vc (e.g., 1 / 2Vc). This generates a pulse corresponding to the reception of photons by the SPAD 2000. The width of this pulse depends on the slope of the cathode voltage Vc described above, and the pulse width becomes narrower as the slope becomes steeper and wider as the slope becomes gentler. Note that the output signal Vinv can be regarded as, for example, a signal that inverts the change in the cathode voltage Vc.

[0041] 7 and 8 are diagrams for explaining a method for detecting the timing of light reception.

[0042] Known methods for detecting the timing of light reception include a level detection method and an edge detection method. The level detection method detects the presence or absence of light reception based on the level (voltage value) of a pixel signal. The edge detection method detects the presence or absence of light reception based on a change point (edge: for example, the rising position of a pixel signal) in the pixel signal. When pixel signals are read out block by block, the level or edge of the composite signal of all pixels 10 in the block (a signal obtained by combining the pixel signals of all pixels 10) is used for determination.

[0043] The level detection method and the edge detection method each have their advantages and disadvantages. As described above, when the distance to the object under test SB or the amount of returned light changes, the shape of the histogram and the noise level change. As a result, the detection accuracy of each method also changes. For this reason, the conversion unit 110 switches the method for detecting the timing of receiving the returned light between the edge detection method and the level detection method depending on the distance to the object under test SB or the amount of returned light.

[0044] For example, the level detection method adds up pulse signals (pixel signals) including the pulse width. This results in a high SNR. However, as the amount of light increases, the pulse width widens. If the center of the pulse is detected as the light-receiving timing, a measurement error occurs depending on the pulse width. On the other hand, the edge detection method detects the edge of the pulse signal as the light-receiving timing of the returned light. This allows accurate detection of the light-receiving timing regardless of the amount of light. However, as the amount of light decreases, the method becomes more susceptible to noise, resulting in a lower SNR.

[0045] Each detection method has a distance range suitable for detection. Therefore, highly accurate distance measurement results can be obtained by adopting an appropriate detection method according to the distance. For example, when the object to be measured SB is a close-distance object, the conversion unit 110 adopts an edge detection method as the method for detecting the light reception timing. When the object to be measured SB is a long-distance object, the conversion unit 110 adopts a level detection method as the method for detecting the light reception timing (see FIG. 8).

[0046] Hereinafter, the detection mode for detecting the timing of light reception using the edge detection method will be referred to as the edge detection mode. The detection mode for detecting the timing of light reception using the level detection method will be referred to as the level detection mode. The distance (mode switching distance) that serves as the reference for switching the detection mode can be set arbitrarily by the system developer based on the preferred distance range for each method. For example, the distance at which the flight time of the reference light is 1 μsec (150 m) is set as the mode switching distance. An object that is at a distance from the light receiving unit 3 that is equal to or shorter than the mode switching distance is considered to be a close-distance object, and an object that is at a distance from the light receiving unit 3 that is farther than the mode switching distance is considered to be a long-distance object.

[0047] 5. Processing Flow FIG. 9 is a diagram showing an example of a process for switching the detection method depending on the distance to the object to be measured SB.

[0048] The conversion unit 110 performs various settings based on default settings. For example, the conversion unit 110 sets the detection mode for light reception timing to edge detection mode (step S1). The conversion unit 110 sets a mode switching distance (step S2).

[0049] The distance measuring device 1 measures the distance to the object SB based on the time of flight of the reference light (step S3). The conversion unit 110 determines whether the distance to the object SB exceeds the mode switching distance (step S4). This determination can be made based on the elapsed time from the time the reference light is emitted. For example, the distance is calculated as the product of the elapsed time and the speed of light c. By comparing the calculated distance with the mode switching distance, it is possible to determine whether the distance to the object SB exceeds the mode switching distance.

[0050] If the distance to the object SB is equal to or less than the mode switching distance (step S4: No), the distance measuring device 1 continues measuring the distance while maintaining the detection mode in the edge detection mode. If the distance to the object SB exceeds the mode switching distance (step S4: Yes), the conversion unit 110 sets the detection mode to the level detection mode (step S5). The distance measuring device 1 performs distance measurement in the level detection mode (step S6).

[0051] The distance measuring device 1 repeats the above process until distance measurement is completed (step S7). When signal processing for all pixels 10 and all shots is completed, the distance measuring device 1 determines that distance measurement is completed.

[0052] [6. Modifications] In the above-described embodiment, the detection method is switched depending on the distance to the object under test SB. However, the conversion unit 110 can also switch the detection method based on the amount of returning light. For example, when the amount of returning light is low, the conversion unit 110 employs the edge detection method as the method for detecting the light-receiving timing. When the amount of returning light is high, the conversion unit 110 employs the level detection method as the method for detecting the light-receiving timing.

[0053] The light intensity (mode switching light intensity) that serves as the basis for switching the detection mode can be set arbitrarily by the system developer based on the preferred light intensity range for each method. For example, a light intensity equal to or less than the mode switching light intensity may be set as a low level, and a light intensity greater than the mode switching light intensity may be set as a high level.

[0054] As mentioned above, the shape of the histogram differs between high-reflectivity objects and low-reflectivity objects. The level detection method uses pulse width information in addition to the arrival timing of photons, so distance measurement errors are likely to occur in cases where the pulse width is long, such as when measuring the distance to a highly reflective object. The edge detection method does not use pulse width information, so measurement errors due to the strength of the returning light are less likely to occur, but the SNR is low. Each method has its advantages and disadvantages, so highly accurate distance measurement results can be obtained by adopting an appropriate detection method depending on the amount of returning light.

[0055] FIG. 10 is a diagram showing an example of a process for switching the detection method depending on the amount of returned light.

[0056] The converter 110 determines the level of the amount of light of the return light in the next frame based on the level of the amount of light of the return light in the previous frame (step S11). For example, if the amount of light of the return light in the previous frame is high, the converter 110 determines that the amount of light of the return light in the next frame will be high. If the amount of light of the return light in the previous frame is low, the converter 110 determines that the amount of light of the return light in the next frame will be low. The converter 110 determines the amount of light of the return light for each pixel 10. Based on the determination result, the converter 110 selects a detection method (detection mode) for each pixel 10 (step S12).

[0057] In the example of FIG. 10 , the detection method is selected for each pixel 10. However, the detection method may also be selected for each block. A block is a partial region within the pixel array unit 100 that is configured by a plurality of pixels 10. That is, the conversion unit 110 can determine the amount of returned light for each pixel 10 or for each block. The conversion unit 110 switches the detection method for each pixel 10 or for each block based on the determination result.

[0058] The level of the light amount can be determined based on the cumulative value of the signal amount detected for each shot. For example, the conversion unit 110 monitors the signal amount calculated for each shot. The conversion unit 110 determines that the light amount of the returned light is at a high level when the signal amount (cumulative value of the signal amount) during distance measurement exceeds a switching criterion. The switching criterion can be set as a value corresponding to the mode switching light amount.

[0059] The distance measuring device 1 performs distance measurement in the selected detection mode for each pixel 10 (steps S13 to S14). When signal processing for all pixels 10 and all shots is completed, the distance measuring device 1 completes distance measurement.

[0060] [7. Effects] The distance measuring device 1 has a light receiving unit 3 and a conversion unit 110. The light receiving unit 3 receives the reference light reflected by the object under test SB as returned light. The conversion unit 110 switches the detection method for the timing of receiving the returned light between an edge detection method and a level detection method depending on the distance to the object under test SB or the amount of returned light.

[0061] According to this configuration, an appropriate operation mode is selected depending on the distance to the object SB or the amount of returned light, thereby obtaining highly accurate distance measurement results.

[0062] The converter 110 employs an edge detection method as a method for detecting the timing of light reception when the object SB to be measured is a short-distance object, and employs a level detection method as a method for detecting the timing of light reception when the object SB to be measured is a long-distance object.

[0063] According to this configuration, an appropriate detection method is adopted depending on the distance to the object to be measured SB.

[0064] The conversion unit 110 employs the edge detection method as a method for detecting the timing of light reception when the amount of returned light is low, and employs the level detection method as a method for detecting the timing of light reception when the amount of returned light is high.

[0065] According to this configuration, an appropriate detection method is adopted depending on the amount of returned light.

[0066] The converter 110 monitors the signal amount calculated for each shot. If the signal amount during distance measurement exceeds a switching criterion, the converter 110 determines that the amount of returned light is at a high level.

[0067] According to this configuration, the method for detecting the light reception timing can be appropriately switched depending on the amount of returned light.

[0068] The conversion unit 110 determines the level of the amount of light returned in the next frame based on the level of the amount of light returned in the previous frame.

[0069] According to this configuration, the detection method can be easily switched.

[0070] The conversion unit 110 determines the amount of returned light for each pixel 10 or for each block. A block is a partial area within the pixel array unit 100 that is made up of a plurality of pixels 10. The conversion unit 110 switches the detection method for each pixel 10 or for each block based on the determination result.

[0071] According to this configuration, an appropriate detection method is adopted for each location.

[0072] The effects described in this specification are merely examples and are not limiting, and other effects may also be present.

[0073] [Additional Notes] The present technology may also have the following configurations. (1) A distance measuring device having a light receiving unit that receives reference light reflected by an object as returned light, and a conversion unit that switches a detection method for the timing of receiving the returned light between an edge detection method and a level detection method depending on the distance to the object or the amount of light of the returned light. (2) The distance measuring device according to (1), wherein the conversion unit adopts the edge detection method as the detection method for the timing of receiving the light when the object is a close object, and adopts the level detection method as the detection method for the timing of receiving the light when the object is a long distance object. (3) The distance measuring device according to (1), wherein the conversion unit adopts the edge detection method as the detection method for the timing of receiving the light when the amount of light of the returned light is low, and adopts the level detection method as the detection method for the timing of receiving the light when the amount of light of the returned light is high. (4) The distance measuring device according to (3), wherein the conversion unit monitors the signal amount calculated for each shot, and determines that the amount of returned light is at a high level when the signal amount during distance measurement exceeds a switching criterion. (5) The distance measuring device according to (3), wherein the conversion unit determines the level of the amount of returned light for a next frame based on the level of the amount of returned light for a previous frame. (6) The distance measuring device according to (5), wherein the conversion unit determines the amount of returned light for each pixel or for each block consisting of a plurality of pixels, and switches the detection method for each pixel or each block based on the determination result. (7) A distance measuring method comprising: receiving reference light reflected by an object as returned light; and switching a detection method for the timing of receiving the returned light between an edge detection method and a level detection method according to the distance to the object or the amount of returned light.

[0074] 1 Range finding device 3 Light receiving unit 10 Pixel 110 Conversion unit SB Measurement target (object)

Claims

1. A distance measuring device having a light receiving unit that receives reference light reflected by an object as returned light, and a conversion unit that switches the detection method for the timing of receiving the returned light between edge detection and level detection depending on the distance to the object or the amount of the returned light.

2. The distance measuring device according to claim 1, wherein the conversion unit adopts the edge detection method as the method for detecting the timing of light reception when the object is a close-range object, and adopts the level detection method as the method for detecting the timing of light reception when the object is a long-range object.

3. The distance measuring device according to claim 1, wherein the conversion unit adopts the edge detection method as the detection method for the light reception timing when the amount of light of the returned light is at a low level, and adopts the level detection method as the detection method for the light reception timing when the amount of light of the returned light is at a high level.

4. The distance measuring device according to claim 3, wherein the conversion unit monitors the signal amount calculated for each shot, and determines that the light amount of the returned light is at a high level when the signal amount during distance measurement exceeds a switching criterion.

5. The distance measuring device according to claim 3, wherein the conversion section determines the level of the amount of light of the return light in the next frame based on the level of the amount of light of the return light in the previous frame.

6. The distance measuring device according to claim 5, wherein the conversion unit determines the amount of returned light for each pixel or for each block consisting of multiple pixels, and switches the detection method for each pixel or for each block based on the determination result.

7. A distance measuring method comprising: receiving reference light reflected by an object as returned light; and switching the detection method for the timing of receiving the returned light between an edge detection method and a level detection method depending on the distance to the object or the amount of the returned light.

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