Light-receiving device and electronic device

Abstract

To accurately receive desired light without being influenced by disturbance light.SOLUTION: A light receiving device includes: M pieces (M is an integer equal to or greater than 2) of light receiving elements corresponding to one pixel; and a control unit that controls a bypass voltage of the M pieces of receiving elements so that when N (N is an integer equal to or greater than 2 and smaller than the M) is set as a threshold, the number of light receiving elements, out of the M pieces of light receiving elements, that simultaneously detect light in a first period does not exceed the threshold.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] One embodiment of the present invention relates to a light receiving device and an electronic device.

Background Art

[0002] In autonomous driving and the like, it is common to use a ToF (Time of Flight) sensor to measure the distance to an object. The ToF sensor measures the distance based on the time difference between the time when the light projecting unit projects light and the time when the light reflected from the object by the light projecting unit is received.

[0003] When the object is far away, since the light intensity of the reflected light from the object becomes weak, it is necessary to increase the sensitivity of the light receiving device. By operating in Geiger mode using an avalanche photodiode as the light receiving device, a highly sensitive light receiving device capable of detecting weak light can be obtained.

[0004] However, when the sensitivity of the light receiving device is increased, there is a risk that ambient light such as sunlight may also be detected, making it impossible to accurately measure the distance.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] One aspect of the present invention provides a light receiving device and an electronic device that can accurately receive desired light without being affected by ambient light.

Means for Solving the Problems

[0007] In order to solve the above problems, according to one embodiment of the present invention, M (M is an integer of 2 or more) light receiving elements corresponding to one pixel, and A light receiving device is provided, which includes a control unit that controls the bias voltages of the M light receiving elements so that within a first period, the number of light receiving elements among the M light receiving elements that simultaneously detect light is not more than N (where N is an integer of 2 or more and less than M).

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of a light receiving device and an electronic device will be described with reference to the drawings. Hereinafter, the description will focus on the main constituent parts of the light receiving device and the electronic device, but the light receiving device and the electronic device may include constituent parts and functions not shown or described in the drawings. The following description does not exclude constituent parts and functions not shown or described in the drawings.

[0010] (First Embodiment) FIG. 1 is a block diagram showing a schematic configuration of a light receiving device 1 according to the first embodiment. As will be described later, the light receiving device 1 in FIG. 1 is used, for example, to receive reflected light from an object. The light receiving device 1 in FIG. 1 includes a light receiving unit 3 having a plurality of pixels 2 arranged in a one-dimensional or two-dimensional direction, and a control unit 4.

[0011] FIG. 2 is a circuit diagram showing the internal configuration of the pixel 2 in the light receiving device 1 of FIG. 1. As shown in FIG. 2, each pixel 2 in the light receiving unit 3 has a plurality of light receiving elements 5 connected in parallel. Each light receiving element 5 has a resistance element R and a SPAD 6 (Silicon Photon Avalanche Diode) connected in series between a first node and a second node. In this embodiment, it is assumed that the SPAD 6 operates in Geiger mode. Thereby, each light receiving element 5 can output an electrical signal obtained by photoelectrically converting one received photon. In this specification, the light receiving element 5 detecting one photon and outputting an electrical signal may be called firing. Once the light receiving element 5 fires, a reset operation is required, and until the reset operation is completed, new light cannot be received. The period from when the light receiving element 5 fires until it becomes possible to fire again is also called dead time. FIG. 2 only shows an example of the configuration of the light receiving element 5 and does not limit the configuration of the light receiving element 5. For example, an active quenching circuit or the like that controls the SPAD 6 using an active element instead of the resistor R may be used. Also, a configuration in which a plurality of light receiving elements 5 as shown in FIG. 2 are arranged in parallel and each terminal is connected is also an example, and the method of connecting the light receiving elements 5 in parallel is not limited. For example, the output of the SPAD 6 in the light receiving element 5 may be converted into a signal in the digital domain, and the outputs of the plurality of light receiving elements 5 may be added in the digital domain to obtain the output of the pixel 2.

[0012] Since the pixel 2 in FIG. 2 has a plurality of light receiving elements 5, it is also called a SiPM (Silicon Photomultiplier). Hereinafter, an example in which the number of light receiving elements 5 included in one pixel 2 is M (M is an integer of 2 or more) will be described.

[0013] By applying a bias voltage higher than the breakdown voltage of the SPAD6, which is the light-receiving element 5, to the cathode of the SPAD6, the light-receiving element 5 is driven in Geiger mode. By controlling the bias voltage applied to the SPAD6, the sensitivity of the SPAD6 can be adjusted.

[0014] The control unit 4 shown in FIG. 1 controls the bias voltages of the M light-receiving elements 5 in the pixel 2 so that the number of light-receiving elements 5 having a number equal to or greater than a threshold value with N (N is an integer greater than or equal to 2 and less than M) of the M light-receiving elements 5 within a predetermined period do not simultaneously detect light. In this way, in the first period, the control unit 4 adjusts the bias voltage so that less than N light-receiving elements 5 in the pixel 2 simultaneously detect light, so there is no risk of the light-receiving element 5 saturating within the first period, and the distance to the object can be accurately measured.

[0015] The first period is, for example, a period shorter than the interval during which the light-projecting unit (not shown in FIG. 1) irradiates the object with light. More specifically, for example, when measuring the distance, the first period is set to a period including the timing at which the reflected light from the object is received.

[0016] The M light-receiving elements require the elapse of a dead time period from detecting the first light until they can newly detect the second light. The state where N or more light-receiving elements simultaneously detect light means that N light-receiving elements simultaneously belong to the dead time period.

[0017] FIG. 3 is a diagram showing the characteristics of the light receiving unit 3. The horizontal axis in FIG. 3 is the bias voltage of the light receiving elements 5 in each pixel 2, and the vertical axis is the output of each pixel 2. In the present embodiment, as the light receiving element 5, an SPAD 6 operating in the Geiger mode is assumed. When each SPAD 6 detects light, it cannot detect new light during the subsequent dead time period. Therefore, when all the SPADs 6 in the pixel 2 detect light, no more light can be received, and this state is called the saturation state. The saturation state corresponds to the maximum output in FIG. 3. When each pixel 2 reaches the saturation state, it cannot receive new light for a while. Therefore, it is necessary to adjust the bias voltage of each light receiving element 5 so that each pixel 2 does not reach the saturation state.

[0018] The output of the pixel 2 on the vertical axis in FIG. 3 represents the number of light receiving elements 5 that have detected light among the M light receiving elements 5 in the pixel 2. As shown in the figure, by changing the bias voltage of the light receiving element 5, the output of each pixel 2 can be changed. The characteristic curve in FIG. 3 is a linear region where the output of the pixel 2 changes almost linearly within a period of low bias voltage. When the bias voltage increases, most of the light receiving elements 5 detect light, so the degree of change in the output of the pixel 2 becomes gentle. The slope of the linear region of the characteristic curve in FIG. 3 is determined by ambient light such as sunlight, manufacturing variations of the light receiving elements 5, temperature, crosstalk between the light receiving elements 5, and the like.

[0019] The higher the bias voltage of the light receiving element 5, the higher the sensitivity of the light receiving element 5, and it becomes possible to receive even weak light. On the other hand, it also becomes easier to detect ambient light such as sunlight, and the ratio of noise included in the electrical signal photoelectrically converted by the light receiving element 5 increases. In addition, the SPAD 6 may output an electrical signal that becomes noise even when it does not receive light. In particular, when the sensitivity of the SPAD 6 is increased, the noise tends to increase. Furthermore, due to the influence of the firing of the surrounding SPADs 6, a phenomenon called crosstalk may occur in which other SPADs 6 fire. On the other hand, when the bias voltage of the light receiving element 5 is lowered, weak light cannot be detected, and the sensitivity decreases.

[0020] Therefore, it is desirable to set the bias voltage of the light receiving element 5 as high as possible without causing the pixel 2 to saturate. Thus, as shown by the dashed line in FIG. 3, the control unit 4 according to the present embodiment sets a threshold value (also referred to as a saturation threshold value) for the output of the pixel 2, and adjusts the bias voltage of each light receiving element 5 in the pixel 2 so that the output of the pixel 2 does not exceed the threshold value within the first period. In this specification, it is assumed that bias voltages of the same voltage level are applied to all the light receiving elements 5 in one pixel 2.

[0021] The control unit 4 sets the first period so as to include the period during which the light emitted by the light projecting unit is reflected by the object and received by the light receiving element 5, and sets the bias voltage so that the number of light receiving elements 5 that detect light within the set first period does not exceed the threshold value. As a result, the reflected light from the object can be received by the light receiving unit 3 without leakage, and the accuracy of distance measurement can be improved.

[0022] Further, when there are a plurality of pixels 2 arranged in a one-dimensional or two-dimensional direction, the control unit 4 may individually control the bias voltage for each pixel 2. This is because there may be differences in the characteristics of detecting light for each pixel 2.

[0023] As described above, in the first embodiment, since the bias voltage of each light receiving element 5 in the pixel 2 is adjusted so that the output of the pixel 2 does not saturate, the reflected light from the object can be received without leakage, and the pixel 2 is less likely to be affected by disturbing light such as sunlight.

[0024] (Second Embodiment) The light receiving device 1 according to the second embodiment has the same block configuration as that in FIG. 1, but the operation of the control unit 4 is different from that in the first embodiment. Also, the pixel 2 according to the first embodiment includes at least two light receiving elements 5, but the pixel 2 according to the present embodiment only needs to include one or more light receiving elements 5. Hereinafter, it is assumed that the pixel 2 has M (M is an integer of 1 or more) light receiving elements 5.

[0025] The control unit 4 according to this embodiment controls the bias voltage of the M light-receiving elements 5 so that the total number of times the M light-receiving elements 5 detect light within the first period does not exceed a predetermined threshold value. That is, the control unit 4 controls the bias voltage of each light-receiving element 5 so that the number of light-receiving elements 5 that detect light within the pixel 2 during the first period is less than the threshold value.

[0026] The first period is a period longer than the interval at which the light-projecting unit irradiates the object with light. In this embodiment, it is assumed that light is received multiple times. For example, the first period is set within a period during which the light-projecting unit intermittently projects light multiple times and the light reflected by the object is sequentially received.

[0027] As described above, in this embodiment, since the light-receiving element 5 assumes reception of light multiple times, only one light-receiving element 5 may be provided within the pixel 2. Based on the result of one light-receiving element 5 receiving light multiple times, the bias voltage of that light-receiving element 5 can be controlled. Further, when a plurality of light-receiving elements 5 are provided within the pixel 2, based on the result of the plurality of light-receiving elements 5 receiving light multiple times, the bias voltages of these light-receiving elements 5 can be controlled.

[0028] The threshold value is set to a value such that all the light-receiving elements 5 within the light-receiving element 5 do not detect light during the first period. Since the control unit 4 controls the bias voltage of each light-receiving element 5 so that the number of light-receiving elements 5 that receive light during the first period is less than the threshold value, there is no possibility of missing light received from the object, and the distance to the object can be accurately measured.

[0029] Further, when there are a plurality of pixels 2 arranged in a one-dimensional or two-dimensional direction, the control unit 4 may individually control the bias voltage based on the light reception results multiple times for each pixel 2. This is because there may be differences in the characteristics of detecting light for each pixel 2.

[0030] Thus, in the second embodiment, based on the result of the light-receiving unit 3 receiving light multiple times, the bias voltage of each light-receiving element 5 in the pixel 2 is controlled. Therefore, for example, when measuring the distance to an object based on the results of receiving light multiple times, the problem of the output of the pixel 2 saturating during the distance measurement does not occur, and the distance measurement can be performed accurately.

[0031] (Third Embodiment) The light-receiving device 1 according to the third embodiment has the same block configuration as that in FIG. 1, but the operation of the control unit 4 is different from that in the first and second embodiments.

[0032] The pixel 2 according to the third embodiment has M (M is an integer of 1 or more) light-receiving elements 5. The control unit 4 controls the bias voltage of the M light-receiving elements 5 in the pixel 2 so that the output of the pixel 2 within the first period does not become equal to or higher than a predetermined threshold value.

[0033] The control unit 4 controls the bias voltage of each light-receiving element 5 in the pixel 2 so that the output of the pixel 2 within the first period becomes equal to or lower than the threshold value indicated by the broken line in FIG. 2. The length of the first period is not particularly limited.

[0034] According to the third embodiment, by adjusting the bias voltage of each light-receiving element 5 in the pixel 2, saturation of the output within the pixel 2 can be prevented.

[0035] (Fourth Embodiment) The fourth embodiment relates to the processing operation of the control unit 4 according to the first to third embodiments described above. More specifically, in the fourth embodiment, it relates to a specific method for determining whether the pixel 2 is saturated.

[0036] FIG. 4 is a block diagram in which a histogram generation unit 7 is added to the light receiving device 1 of FIG. 1. The histogram generation unit 7 generates a histogram representing the relationship between the number of light receiving elements 5 that detected light among the M light receiving elements 5 within the first period and the frequency of occurrence of that number. In FIG. 4, a light projecting unit (not shown) projects light repeatedly at a predetermined time interval. Therefore, the histogram generation unit 7 generates a histogram by the light projecting unit projecting light a plurality of times and the light receiving device 1 receiving the reflected light obtained by the projected light being reflected by the object.

[0037] FIG. 5 is a diagram showing an example of the histogram generated by the histogram generation unit 7. The horizontal axis in FIG. 5 is the output of pixel 2, and the vertical axis is the frequency of occurrence. The output of pixel 2 on the horizontal axis refers to the number of light receiving elements 5 that detected light. The frequency of occurrence on the vertical axis is sometimes also referred to as the occurrence probability.

[0038] Based on the histogram generated by the histogram generation unit 7, the control unit 4 sets the bias voltage so that the frequency of occurrence when the number of light receiving elements 5 that detected light among the M light receiving elements 5 is maximized is equal to or less than a predetermined value.

[0039] The signal received by the light receiving element 5 includes both reflected light from the object and ambient light. Since the reflected light from the object is the light that should originally be received, it is necessary for the output of pixel 2 to be maximized when the reflected light from the object is received. That is, the output of pixel 2 should not be maximized at the timing when the reflected light from the object is not received. Therefore, the control unit 4 obtains the average and variance of the output of pixel 2 within a predetermined period based on the histogram, calculates the probability that the output of pixel 2 is maximized, and if the probability is equal to or less than a predetermined value, determines that the output of pixel 2 does not saturate, and if it is greater than the predetermined value, determines that the output of pixel 2 saturates. When the control unit 4 determines that the output of pixel 2 saturates, it lowers the bias voltage so that the probability that the output of pixel 2 is maximized is equal to or less than a predetermined value.

[0040] Note that the control unit 4 may set the bias voltage so that the frequency of occurrence of the output of pixel 2 slightly deviated from the maximum output of pixel 2 in the histogram shown in FIG. 5 is equal to or less than a predetermined value, taking into account manufacturing variations of the light receiving device 1 and the like.

[0041] To generate a histogram as shown in FIG. 5, multiple light projections and receptions are required, which takes time. Therefore, a histogram is created in advance, a threshold value is set based on the histogram, and it is determined whether the output of pixel 2 is saturated based on whether the average output of pixel 2 within the first period exceeds the threshold value. If it is determined that the output of pixel 2 is saturated, the bias voltage may be adjusted.

[0042] Further, the control unit 4 may detect the maximum output of pixel 2 within the first period without using a histogram, and determine that pixel 2 is not saturated if the maximum output of pixel 2 is less than a predetermined threshold value, and determine that pixel 2 is saturated if the maximum output of pixel 2 is equal to or greater than the threshold value. In this case, the control unit 4 sets the bias voltage of the light receiving element 5 so that the maximum output of pixel 2 within the first period does not exceed the threshold value. In this method, since the control unit 4 only needs to monitor the maximum output of pixel 2, the processing operation of the control unit 4 is facilitated, and for example, when the control unit 4 is configured by hardware, the circuit scale can be reduced.

[0043] As described above, in the fourth embodiment, by using a histogram showing the correspondence between the output of pixel 2 and the frequency of occurrence, the bias voltage of the light receiving element 5 that prevents the output of pixel 2 from saturating can be set relatively easily. Also, even without using a histogram, by monitoring the maximum output of pixel 2, the bias voltage can be set so that the maximum output of pixel 2 is equal to or less than the threshold value.

[0044] (Fifth Embodiment) The fifth embodiment sets the bias voltage by a method different from that of the fourth embodiment. The light receiving device 1 according to the fifth embodiment has the same block configuration as in FIG. 1, but the processing operation of the control unit 4 is different from that of the fourth embodiment.

[0045] The control unit 4 according to the fifth embodiment searches for an optimal bias voltage by sequentially changing the bias voltage from the initial voltage a plurality of times. FIG. 6 is a diagram showing an example in which the bias voltage of the light receiving element 5 is sequentially (stepwise) decreased from the initial voltage a plurality of times. The horizontal axis in FIG. 6 represents the time when the bias voltage is applied to the light receiving element 5, and the vertical axis represents the bias voltage. In the period t1, the bias voltage is set to the initial voltage V0, and in the period t2, the bias voltage is set to a voltage V1 that is one step lower than the initial voltage V0. Thereafter, the bias voltage is decreased stepwise a plurality of times at predetermined intervals. The initial voltage of the bias voltage set in the period t1 is the maximum voltage applied within the control period, and it is assumed that a larger bias cannot be applied if the pixel does not saturate even with this bias.

[0046] When the control unit 4 applies the bias voltage to the light receiving element 5, it detects whether or not the light receiving element 5 saturates. By sequentially decreasing the bias voltage stepwise from the initial voltage, the number of light receiving elements 5 that detect light decreases. For example, when there are M (M is an integer of 2 or more) light receiving elements 5 in the pixel 2, the control unit 4 sets, as a threshold, the case where N (N is an integer of 1 or more and less than M) of the M light receiving elements 5 detect light, and sets the bias voltage at that time for each light receiving element 5 in the pixel 2.

[0047] As shown in FIG. 6, while sequentially decreasing the bias voltage stepwise, by counting the number of light receiving elements 5 that detect light in the pixel 2, the bias voltage of each light receiving element 5 in the pixel 2 can be set when a predetermined number of light receiving elements 5 in the pixel 2 detect light.

[0048] In FIG. 6, in addition to the control period in which the bias voltage is set while sequentially decreasing the bias voltage stepwise, a ranging period for measuring the distance to the object is provided. The control period is provided between the ranging periods.

[0049] In FIG. 6, an example of gradually decreasing the bias voltage from the initial voltage is shown, but the bias voltage may be gradually increased from the initial voltage. In this case, the initial voltage is the voltage given as the minimum within the control period, and it is assumed that if the pixel is saturated even with this bias, a smaller bias cannot be given.

[0050] When the control unit 4 gradually decreases the bias voltage from the initial voltage in multiple steps, the control unit 4 may set the bias voltage that first satisfies the threshold condition and then stop the subsequent bias voltage change process. Alternatively, when the control unit 4 gradually increases the bias voltage from the initial voltage in multiple steps, when the threshold condition is first no longer satisfied, the control unit 4 may set the bias voltage immediately before that and then stop the subsequent bias voltage change process.

[0051] Each time the light projecting unit intermittently irradiates light, the control unit 4 may gradually change the bias voltage. Alternatively, each time the light projecting unit irradiates light multiple times, the control unit 4 may gradually change the bias voltage.

[0052] Also, the voltage width when changing the bias voltage may be the same or different. Also, the bias voltage may be changed according to a certain voltage pattern. The voltage pattern in this case does not necessarily have to be a voltage pattern that monotonically increases or decreases, and may be a voltage pattern in which the voltage level changes irregularly (for example, randomly). Also, the bias voltage may be dynamically changed by a binary search method or the like to set the maximum bias voltage at which pixel 2 does not saturate.

[0053] The bias search method is performed, for example, according to the following processing procedure. First, it is compared whether the output of pixel 2 saturates with the maximum adjustable bias voltage A and the minimum adjustable bias voltage B. If it does not saturate at the bias voltage A, the bias voltage A is set as the set value of the bias voltage. If it saturates at the bias voltage B, the bias voltage B is set as the set value of the bias voltage. If it saturates at the bias voltage A and does not saturate at the bias voltage B, it is examined whether the output of pixel 2 saturates at the bias voltage C = (A + B) / 2. If it saturates at the bias voltage C, the saturation state is examined at a bias voltage between the bias voltage C and the bias voltage B. If it does not saturate at the bias voltage C, the saturation state is examined at a bias voltage between the bias voltage C and the bias voltage A. By repeating such comparison processing of the saturation state, the error between the actual set value and the ideal set value of the bias voltage can be reduced in inverse proportion to the square of the number of processing steps.

[0054] When the control unit 4 measures the distance to the object, it controls the bias voltage of the light receiving element 5 in the pixel 2. However, the control of the bias voltage does not necessarily have to be performed every time the distance measurement is performed. For example, the bias voltage may be adjusted at a rate of once every time a plurality of distance measurements are performed.

[0055] FIG. 7 is a diagram showing a first example of the timing of the control period for adjusting the bias voltage and the ranging period for performing the distance measurement. In the first example of FIG. 7, the control period for adjusting the bias voltage is provided at a rate of once after four consecutive ranging periods for performing the distance measurement are provided. The frequency at which the bias voltage is adjusted is arbitrary. Also, in FIG. 7, the bias voltage is adjusted at regular intervals, but the bias voltage may be adjusted irregularly.

[0056] FIG. 8 is a diagram showing a second example of the adjustment timing of the bias voltage and the distance measurement timing. In the second example of FIG. 8, a first period and a second period are alternately arranged. In the first period, as in FIG. 7, each time a plurality of ranging periods are continuously provided, a control period is provided at a rate of once. In the second period, only a ranging period is provided. The time lengths of the first period and the second period are arbitrary, and the time lengths of the first period and the second period may change irregularly.

[0057] Thus, in the fifth embodiment, in order to make the number of light receiving elements 5 that detect light in pixel 2 be equal to or less than the threshold while changing the bias voltage step by step, an optimal bias voltage can be set relatively easily.

[0058] In addition, since the timing for adjusting the bias voltage can be arbitrarily set, the bias voltage can be adjusted periodically or irregularly at a timing that does not interfere with distance measurement. (Sixth Embodiment)

[0059] The light receiving device 1 according to the first to fifth embodiments described above can be incorporated into an electronic device that performs distance measurement by the ToF (Time of Flight) method. FIG. 9 is a block diagram showing a schematic configuration of an electronic device 21 including a light receiving module 24 incorporating the light receiving device 1 according to the present embodiment. The electronic device 21 in FIG. 9 includes a light projecting unit 22, a light control unit 23, a light receiving module 24, a signal processing unit 25, and an image processing unit 26. Among these, the light projecting unit 22, the light control unit 23, the light receiving module 24, and the signal processing unit 25 constitute a distance measurement device 27. The light receiving device 1 according to the first to fifth embodiments described above is mounted as at least a part of the light receiving module 24.

[0060] At least a part of the electronic device 21 in FIG. 1 can be configured by one or more semiconductor ICs (Integrated Circuits). For example, the signal processing unit 25 and the image processing unit 26 may be integrated inside one semiconductor chip, or the light receiving module 24 may be included in this semiconductor chip for integration. Further, the light projecting unit 22 may be included in this semiconductor chip for integration.

[0061] The light projecting unit 22 projects first light. The first light is, for example, laser light in a predetermined frequency band. Laser light is coherent light with aligned phase and frequency. The light projecting unit 22 intermittently projects the pulsed first light at a predetermined period. The period at which the light projecting unit 22 projects the first light is a time interval longer than the time required for the distance measuring device 27 to measure the distance based on one pulse of the first light.

[0062] The light projecting unit 22 includes an oscillator 31, a light projection control unit 32, a light source 33, a first driving unit 34, and a second driving unit 35. The oscillator 31 generates an oscillation signal corresponding to the period for projecting the first light. The first driving unit 34 intermittently supplies power to the light source 33 in synchronization with the oscillation signal. The light source 33 intermittently emits the first light based on the power from the first driving unit 34. The light source 33 may be a laser element that emits a single laser light or a laser unit that emits a plurality of laser lights simultaneously. The light projection control unit 32 controls the second driving unit 35 in synchronization with the oscillation signal. The second driving unit 35 supplies a driving signal synchronized with the oscillation signal to the light control unit 23 according to an instruction from the light projection control unit 32.

[0063] The light control unit 23 controls the traveling direction of the first light emitted from the light source 33. Also, the light control unit 23 controls the traveling direction of the received second light.

[0064] The light control unit 23 includes a first lens 41, a beam splitter 42, a second lens 43, and a scanning mirror 44.

[0065] The first lens 41 condenses the first light emitted from the light projecting unit 22 and guides it to the beam splitter 42. The beam splitter 42 branches the first light from the first lens 41 in two directions and guides it to the second lens 43 and the scanning mirror 44. The second lens 43 guides the branched light from the beam splitter 42 to the light receiving module 24. The reason for guiding the first light to the light receiving module 24 is to detect the light projection timing in the light receiving module 24.

[0066] The scanning mirror 44 rotationally drives the mirror surface in synchronization with the drive signal from the second drive unit 35 within the light projection unit 22. Thereby, the reflection direction of the branched light (first light) that has passed through the beam splitter 42 and is incident on the mirror surface of the scanning mirror 44 is controlled. By rotationally driving the mirror surface of the scanning mirror 44 at a constant period, the first light emitted from the light control unit 23 can be scanned in at least one-dimensional direction. By providing the axis for rotationally driving the mirror surface in two directions, it is also possible to scan the first light emitted from the light control unit 23 in two-dimensional direction. FIG. 1 shows an example in which the first light projected from the electronic device 21 is scanned in the X direction and the Y direction by the scanning mirror 44.

[0067] When the object 20 exists within the scanning range of the first light projected from the electronic device 21, the first light is reflected by the object 20. Among the reflected light reflected by the object 20, at least a part thereof travels in the reverse direction along substantially the same path as the first light and is incident on the scanning mirror 44 within the light control unit 23. Although the mirror surface of the scanning mirror 44 is rotationally driven at a predetermined period, since the laser light propagates at the speed of light, the reflected light from the object 20 is incident on the mirror surface while the angle of the mirror surface of the scanning mirror 44 hardly changes. The reflected light from the object 20 incident on the mirror surface is received by the light receiving module 24.

[0068] The light receiving module 24 includes a photodetector 51, an amplifier 52, a third lens 53, a light receiving sensor 54, and an A / D converter 55. The photodetector 51 receives the light branched by the beam splitter 42 and converts it into an electrical signal. The light projection timing of the first light can be detected by the photodetector 51. The amplifier 52 amplifies the electrical signal output from the photodetector 51.

[0069] The third lens 53 forms an image of the laser light reflected by the object 20 on the light receiving sensor 54. The light receiving sensor 54 receives the laser light and converts it into an electrical signal. The light receiving sensor 54 can be applied with the light receiving device 1 according to the above-described first to fifth embodiments. The light receiving sensor 54 is also called a SiPM (Silicon Photomultiplier).

[0070] The A / D converter 55 samples the electrical signal output from the light receiving sensor 54 at a predetermined sampling rate and performs A / D conversion to generate a digital signal.

[0071] The signal processing unit 25 measures the distance to the object 20 that reflects the first light, and stores the digital signal corresponding to the second light in the storage unit 61. The signal processing unit 25 includes a storage unit 61, a distance measurement unit 62, and a storage control unit 63.

[0072] The distance measurement unit 62 measures the distance to the object 20 based on the first light and the reflected light. More specifically, the distance measurement unit 62 measures the distance to the object based on the time difference between the light projection timing of the first light and the light reception timing of the reflected light included in the second light received by the light receiving sensor 54. That is, the distance measurement unit 62 measures the distance based on the following formula (1). Distance = speed of light × (light reception timing of reflected light - light projection timing of first light) / 2 …(1)

[0073] In formula (1), the "light reception timing of the reflected light" is more precisely the light reception timing at the peak position of the reflected light. The distance measurement unit 62 detects the peak position of the reflected light included in the second light based on the digital signal generated by the A / D converter 55.

[0074] At least a part of the electronic device 21 according to the present embodiment can be implemented by SiP (Silicon in Package). FIG. 10 is a schematic perspective view showing an example in which the light receiving module 24 and the signal processing unit 25 are mounted on the substrate of the package. On the substrate 71 in FIG. 10, a first die 72 and a second die 73 are provided. On the first die 72, the light receiving sensor 54 in the light receiving module 24 of FIG. 1 is arranged. The light receiving sensor 54 is a SiPM 74 having the light receiving device 1 of the first to fourth embodiments described above. A plurality of SiPMs 74 are arranged in the X direction and the Y direction. On the second die 73, an A / D converter (ADC) 55 in the light receiving module 24 of FIG. 1 and the signal processing unit 25 are arranged. The pad 76 on the first die 72 and the pad 77 on the second die 73 are connected by a bonding wire 78.

[0075] In the layout diagram of FIG. 10, a plurality of SiPMs 74 are arranged on the first die 72. However, an active quenching circuit or a passive quenching circuit (AQs) for shortening the dead time of the APD may be arranged in association with each SiPM 74.

[0076] Aspects of the present disclosure are not limited to the individual embodiments described above, but also include various modifications that can be conceived by those skilled in the art, and the effects of the present disclosure are not limited to the above-described content. That is, various additions, changes, and partial deletions are possible without departing from the conceptual ideas and gists of the present disclosure derived from the content defined in the claims and their equivalents.

Description of Reference Numerals

[0077] 1 Light receiving device, 2 Pixel, 3 Light receiving section, 4 Control section, 5 Light receiving element, 6 SPAD, 7 Histogram generation section, 20 Object, 21 Electronic device, 22 Light projecting section, 23 Light control section, 24 Light receiving module, 25 Signal processing section, 27 Distance measurement device, 31 Oscillator, 32 Light projection control section, 33 Light source, 34 First drive section, 35 Second drive section, 41 First lens, 42 Beam splitter, 43 Second lens, 44 Scanning mirror, 51 Photodetector, 52 Amplifier, 53 Third lens, 54 Light receiving sensor, 55 A / D converter, 61 Storage section, 62 Distance measurement section, 63 Storage control section

Claims

1. M (M is an integer equal to or greater than 1) light receiving elements corresponding to one pixel; a control unit that controls bias voltages of the M light receiving elements so that an output of the pixel during a first period does not become equal to or exceeds a predetermined threshold; a histogram generating unit that generates a histogram that represents a relationship between the number of light receiving elements that detect light among the M light receiving elements within the first period and an occurrence frequency of the number, The control unit sets the bias voltage based on the histogram so that the occurrence frequency when the number of light receiving elements that detect light among the M light receiving elements is maximum is equal to or less than a predetermined value.

2. The light receiving device according to claim 1 , wherein the light receiving element has a characteristic that once it detects light, it cannot detect new light during a dead time period according to a circuit of the pixel.

3. 3. The light receiving device according to claim 1, wherein the light receiving element is an avalanche photodiode operating in a Geiger mode.

4. The light receiving device according to claim 1 , which receives a second light beam reflected by an object from the first light beam; an AD conversion unit that generates a digital signal corresponding to a light receiving signal received by the light receiving device; A storage unit that stores the digital signal; a distance measuring unit that measures a distance to the object based on a timing of projecting the first light and a timing of receiving the second light by the light receiving device.

5. A light projecting unit that projects the first light, The electronic device according to claim 4 , wherein the distance measurement unit acquires a projection timing of the first light.

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