Photoelectric conversion device

Abstract

To provide a photoelectric conversion device that can acquire accurate distance information.SOLUTION: A photoelectric conversion device has: a light receiving unit that generates a light receiving signal according to incident light through photoelectric conversion; a time-digital conversion unit that executes time-digital conversion of periodically performing an operation to output a time count value indicating the time elapsed from light emission from a light source device until input of the light receiving signal, every time a predetermined period elapses within a first distance measurement period; a weight determination unit that acquires a count value indicating the number of times of the time-digital conversion performed within the first distance measurement period, and outputs a weighted value on the basis of the count value; and a frequency distribution generation unit that uses the weighted value in the addition of frequency in generation of the frequency distribution of the count values.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a photoelectric conversion device. [Background technology]

[0002] Patent Document 1 discloses a distance measuring device that measures the distance to an object by repeatedly emitting light from a light source and receiving light, including reflected light from the object, with a light receiving element. Patent Document 1 also discloses a process for generating a frequency distribution based on a count value indicating the time from light emission to the incidence of a photon and a weight determined based on the number of reactions of the light receiving element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-001764 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a photoelectric conversion device such as that described in Patent Document 1, there are cases where it is required to obtain distance information with higher accuracy.

[0005] An object of the present invention is to provide a photoelectric conversion device capable of acquiring highly accurate distance information. [Means for solving the problem]

[0006] According to one disclosure of this specification, there is provided a photoelectric conversion device that includes a light receiving unit that generates a light receiving signal corresponding to incident light by photoelectric conversion, a time-to-digital conversion unit that performs time-to-digital conversion periodically every time a predetermined period elapses within one ranging period to output a time count value indicating the elapsed time from the light emission of a light source device to the input of the light receiving signal, a weight determination unit that acquires a count value indicating the number of times the time-to-digital conversion was performed within one ranging period and outputs a weight value based on the count value, and a frequency distribution generation unit that uses the weight value to add frequencies to generate a frequency distribution of the count values. Effect of the Invention

[0007] According to the present invention, a photoelectric conversion device capable of acquiring highly accurate distance information is provided. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing a schematic configuration of a distance measuring device according to a first embodiment. [Diagram 2] 2 is a block diagram showing the configuration of a light receiving section and a distance measuring section according to the first embodiment. FIG. [Diagram 3] 1 is a diagram showing the configuration and operation of a pixel according to a first embodiment; [Figure 4] 2 is a block diagram showing the configuration of a distance measuring unit according to the first embodiment. FIG. [Diagram 5] 4 is a table showing an example of setting weight values ​​according to the first embodiment. [Figure 6] 4 is a graph showing an example of generation of a frequency distribution according to the first embodiment. [Figure 7] FIG. 11 is a block diagram showing the configuration of a distance measuring unit according to a second embodiment. [Figure 8] 13 is a table showing an example of setting weight values ​​according to the second embodiment. [Figure 9] FIG. 11 is a block diagram showing the configuration of a distance measuring unit according to a third embodiment. [Figure 10] 13 is a graph showing an example of generation of a frequency distribution according to the third embodiment. [Figure 11]FIG. 13 is a schematic diagram of a light detection system according to a fourth embodiment. [Figure 12] FIG. 13 is a schematic diagram of a device according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same elements or corresponding elements in multiple drawings are denoted by the same reference numerals, and the description thereof may be omitted or simplified.

[0010] [First embodiment] Fig. 1 is a block diagram showing a schematic configuration of a distance measuring device 1 according to the first embodiment. As shown in Fig. 1, the distance measuring device 1 has a light receiving device 2, a light source device 3, and a signal processing device 4. The light receiving device 2 has a light receiving unit 20 and an optical system 26. The light source device 3 has a light emitting unit 30. The signal processing device 4 has a control unit 40 and a distance measuring unit 41.

[0011] It should be noted that the configuration of the distance measuring device 1 shown in this embodiment is an example, and the configuration of the distance measuring device 1 is not limited to the illustrated configuration. For example, the light source device 3 may be disposed outside the distance measuring device 1. Even in this case, the light emitting unit 30 operates in response to a control signal from the control unit 40. The configuration and operation of the distance measuring device 1 described in this embodiment can also be applied to other photoelectric conversion devices that generate signals by photoelectric conversion. Examples of photoelectric conversion devices include an imaging device and a focus detection device.

[0012] The distance measuring device 1 is a device that measures the distance to the object X to be measured using technology such as LiDAR (Light Detection And Ranging). The distance measuring device 1 measures the distance from the distance measuring device 1 to the object X based on the time difference between when light is emitted from the light source device 3 and when the reflected light from the object X is received by the light receiving device 2. The distance measuring device 1 can also measure the distance at multiple points two-dimensionally by emitting light to a predetermined distance measuring range including the object X and receiving the reflected light by a pixel array. This allows the distance measuring device 1 to measure and output the distribution of the distance from the distance measuring device 1 to the object X in the distance measuring range.

[0013] The light received by the light receiving device 2 includes ambient light such as sunlight, disturbance light from other light sources, and the like, in addition to the reflected light from the object X. The distance measuring device 1 repeatedly performs an operation of measuring the time difference between the emission of light and the reception of the reflected light as a time count value multiple times. The distance measuring device 1 then generates a frequency distribution in which the light reception count value of the pulse based on the incident light is associated with each of the multiple time count values. The distance measuring device 1 then performs distance measurement with reduced influence of ambient light, etc., by using a method of determining that the reflected light is incident during the time interval of the time count value corresponding to the maximum light reception count value.

[0014] The signal processing device 4 may include a processor that performs arithmetic processing of digital signals, a memory that stores digital signals, and a control circuit that controls the operations of the light receiving device 2 and the light source device 3. The control unit 40 outputs a control signal that controls the light emission timing of the light emitting unit 30, a control signal that controls the operation timing of the light receiving unit 20, and a control signal that controls the operation timing of the distance measuring unit 41.

[0015] The light source device 3 is a device that emits light such as laser light to the outside of the distance measuring device 1. The light emitting unit 30 of the light source device 3 includes, for example, a semiconductor laser diode as a light source. The light emitting unit 30 emits laser light having a predetermined pulse width based on a control signal from the control unit 40. This laser light is diffused by an optical system such as a diffusion plate, and is irradiated to a predetermined range.

[0016] The optical system 26 includes optical elements such as lenses that form an image of incident light on the light receiving unit 20. Reflected light generated by the laser light emitted from the light emitting unit 30 being reflected by the object X forms an image on the light receiving unit 20 via the optical system 26.

[0017] The light receiving unit 20 is, for example, a photoelectric conversion device including an avalanche photodiode (hereinafter referred to as APD) as a photoelectric conversion element. In this case, when one photon is incident on the APD and an electric charge is generated, one pulse is generated by avalanche multiplication. However, the light receiving unit 20 may be, for example, a photoelectric conversion element using another photodiode.

[0018] The distance measuring unit 41 generates a frequency distribution based on the electrical signal output from the light receiving unit 20. The distance measuring unit 41 also generates distance information indicating the distance from the distance measuring device 1 to the object X based on the frequency distribution.

[0019] 2 is a block diagram showing the configuration of the light receiving unit 20 and the distance measuring unit 41 according to the first embodiment. The light receiving unit 20 has a pixel array 21 and a pixel driving unit 22. The distance measuring unit 41 has a column processing unit 410, a transfer unit 420, and a distance calculation unit 430.

[0020] In the pixel array 21, a plurality of pixels 210 are arranged in a plurality of rows and a plurality of columns. Each of the plurality of pixels 210 has a photoelectric conversion unit 211 including a photoelectric conversion element, and a pixel circuit 212. The photoelectric conversion unit 211 generates a signal according to incident light. The signal generated by the photoelectric conversion unit 211 of each pixel 210 is shaped into a pulse signal in the pixel circuit 212. The pixel circuit 212 outputs the pulse signal to the column processing unit 410 via a signal line 24 arranged for each column of the pixel array 21.

[0021] The pixel driving unit 22 supplies a control signal to each of the plurality of pixel circuits 212 based on a control signal supplied from the control unit 40. The pixel driving unit 22 supplies a control signal to each pixel circuit 212 for each row via a driving line 23 provided for each row of the pixel array 21. The pixel driving unit 22 may include logic circuits such as a shift register and an address decoder. In this way, the pixel driving unit 22 selects a row for outputting a signal from the pixel circuit 212 to the column processing unit 410.

[0022] The column processing units 410 are arranged to correspond to each column of the pixel array 21. A timing control signal such as a clock signal is input from the control unit 40 to each of the multiple column processing units 410. The column processing units 410 are signal processing circuits that perform processing such as time-to-digital conversion on the pulse signals output from the pixel circuits 212. The signals output from the column processing units 410 for each column are input to the transfer unit 420.

[0023] The transfer unit 420 is a transfer circuit that sequentially transfers the signals of each column output from the column processing unit 410 to the distance calculation unit 430 based on a control signal supplied from the control unit 40.

[0024] The distance calculation unit 430 is a signal processing circuit that processes the signal input from the transfer unit 420. The distance calculation unit 430 may be arranged on the semiconductor chip on which the column processing unit 410 is arranged, or may be arranged on a different semiconductor chip (for example, a signal processing circuit chip such as a digital front end).

[0025] 2 shows a circuit configuration in which the column processing unit 410 processes output signals from multiple pixels 210 in the same column, and the distance calculation unit 430 processes output signals from all pixels 210 in the pixel array 21, but the configuration is not limited to this. For example, a signal processing circuit equivalent to the column processing unit 410 may be arranged corresponding to each of the multiple pixels 210, and a signal processing circuit equivalent to the distance calculation unit 430 may be arranged corresponding to each of the multiple pixels 210. Furthermore, a signal processing circuit equivalent to the distance calculation unit 430 may be arranged corresponding to each column of the pixel array 21, similar to the column processing unit 410.

[0026] 2, the pixel array 21 includes a plurality of pixels 210 arranged two-dimensionally, but is not limited thereto. For example, the arrangement of the plurality of pixels 210 may be one-dimensional. Also, the light receiving unit 20 may include only a single pixel 210.

[0027] Furthermore, the function of the pixel circuit 212 does not necessarily have to be provided for each pixel 210. For example, one pixel circuit 212 may be shared by a plurality of pixels 210. In this case, the pixel circuit 212 provides a signal processing function to the plurality of pixels 210 by sequentially processing signals output from the plurality of photoelectric conversion units 211.

[0028] Fig. 3(a) is a diagram showing the configuration of a pixel 210 according to the first embodiment. Figs. 3(b) and 3(c) are diagrams showing the operation of the pixel 210. The pixel 210 has a photoelectric conversion unit 211, a quenching element 213, a waveform shaping unit 214, and a selection circuit 215. The quenching element 213, the waveform shaping unit 214, and the selection circuit 215 correspond to the pixel circuit 212 shown in Fig. 2.

[0029] The photoelectric conversion unit 211 is an APD, and generates charges according to incident light by photoelectric conversion. An electric potential VL is supplied to the anode of the photoelectric conversion unit 211. The cathode of the photoelectric conversion unit 211 is connected to a first terminal of the quench element 213 and an input terminal of the waveform shaping unit 214. A electric potential VH higher than the electric potential VL supplied to the anode is supplied to a second terminal of the quench element 213. As a result, a reverse bias voltage is supplied to the anode and cathode of the photoelectric conversion unit 211 such that the photoelectric conversion unit 211 performs an avalanche multiplication operation. When electric charges are generated by incident light in the photoelectric conversion unit 211 to which the reverse bias voltage is supplied, the electric charges cause avalanche multiplication, and an avalanche current is generated.

[0030] There are two operation modes when a reverse bias voltage is supplied to the photoelectric conversion unit 211: Geiger mode and linear mode. The Geiger mode is a mode in which the photoelectric conversion unit 211 operates with a potential difference between the anode and the cathode that is greater than the breakdown voltage, and the linear mode is a mode in which the photoelectric conversion unit 211 operates with a potential difference between the anode and the cathode that is close to or less than the breakdown voltage.

[0031] An APD operated in Geiger mode is called a SPAD (Single Photon Avalanche Diode). In this case, for example, the potential VL is −30 V and the potential VH is 1 V. The photoelectric conversion unit 211 may be operated in either a linear mode or a Geiger mode. In the case of a SPAD, the potential difference is larger than that of an APD in linear mode, and the effect of avalanche multiplication is prominent, so a SPAD is preferable.

[0032] The quench element 213 functions as a load circuit (quench circuit) during signal multiplication by avalanche multiplication. The quench element 213 suppresses the potential supplied to the photoelectric conversion unit 211 to suppress avalanche multiplication (quench operation). The quench element 213 also returns the potential supplied to the photoelectric conversion unit 211 to the potential VH by passing a current corresponding to the potential drop caused by the quench operation (recharge operation). The quench element 213 may be a resistive element or a MOS transistor. When the quench element 213 is a MOS transistor, a constant potential may be input to the gate of the MOS transistor. When the quench element 213 is a MOS transistor, a recharge operation may be performed at a constant cycle by inputting a periodic pulse signal to the gate of the MOS transistor.

[0033] The waveform shaping unit 214 shapes the potential change of the cathode of the photoelectric conversion unit 211 obtained when a photon is detected, and outputs a pulse signal. For example, an inverter circuit is used as the waveform shaping unit 214. Although an example using one inverter as the waveform shaping unit 214 is shown in Fig. 3(a), the waveform shaping unit 214 may be a circuit in which a plurality of inverters are connected in series, or may be another circuit having a waveform shaping effect.

[0034] 2 supplies a control signal to the selection circuit 215 via the drive line 23. In response to this control signal, the selection circuit 215 switches between electrical connection and non-connection between the output terminal of the waveform shaping unit 214 and the signal line 24. The selection circuit 215 may include, for example, a switch, a buffer circuit, etc.

[0035] Next, the operation of the pixel 210 will be described with further reference to Figures 3(b) and 3(c). As shown in Figure 3(a), a connection node between the photoelectric conversion unit 211, the quenching element 213, and the input terminal of the waveform shaping unit 214 is referred to as node A. Also, as shown in Figure 3(a), a connection node between the output terminal of the waveform shaping unit 214 and the selection circuit 215 is referred to as node B.

[0036] FIG. 3(b) is a graph showing the time change of the potential of node A in FIG. 3(a). FIG. 3(c) is a graph showing the time change of the potential of node B in FIG. 3(a). In the period from time t0 to time t1, a voltage of VH-VL is applied to the photoelectric conversion unit 211 in FIG. 3(a). When a photon is incident on the photoelectric conversion unit 211 at time t1, avalanche multiplication occurs in the photoelectric conversion unit 211. As a result, an avalanche current flows through the quench element 213, and the potential of node A drops. Thereafter, the amount of potential drop becomes larger, and the voltage applied to the photoelectric conversion unit 211 gradually decreases. Then, at time t2, the avalanche multiplication in the photoelectric conversion unit 211 stops. As a result, the potential of node A does not drop below a certain value. Thereafter, during the period from time t2 to time t3, a current flows to node A from the node at potential VH to compensate for the potential drop, and at time t3, node A settles to its original potential.

[0037] In the above process, the potential of node B becomes high level during the period when the potential of node A is lower than a certain threshold. In this way, the waveform of the drop in the potential of node A caused by the incidence of a photon is shaped by the waveform shaping unit 214 and output as a pulse to node B. This pulse signal is input to the column processing unit 410 via the selection circuit 215 and the signal line 24.

[0038] Next, the configuration and operation of the distance measuring unit 41 will be described in more detail. Fig. 4 is a block diagram showing the configuration of the distance measuring unit 41 according to this embodiment. Fig. 4 shows functional blocks of one pixel 210 out of the multiple pixels 210, one column processing unit 410 corresponding to the one pixel 210, and a distance calculation unit 430. The column processing unit 410 has a time-to-digital conversion unit (TDC) 411. The distance calculation unit 430 has a weight determination unit 431 and a frequency distribution generation unit 432.

[0039] The pixels 210 of the light receiving unit 20 output a pulse signal, which is a light receiving signal corresponding to the incident light, to the column processing unit 410. The pulse signal output from the pixels 210 is input to the time digital conversion unit 411. The time digital conversion unit 411 counts the pulses of the clock signal input from the control unit 40 to perform time counting, and generates a time count value whose value increases by one every time a predetermined time elapses. The time digital conversion unit 411 starts the time count in synchronization with the light emission timing of the light emission unit 30, and outputs the time count value at the timing when the pulse signal indicating the incident light is input from the pixels 210 to the frequency distribution generation unit 432. As a result, the time digital conversion unit 411 performs an output operation of a time count value indicating the elapsed time from the light emission of the light emission unit 30 to the input of the pulse signal indicating the incident light.

[0040] The light emission in the light-emitting unit 30 and the light reception in the pixel 210 are performed periodically every time a predetermined period elapses within one ranging period. Therefore, the output operation of the time count value in the time-to-digital conversion unit 411 is also performed periodically every time a predetermined period elapses within one ranging period. Hereinafter, the time count value generated corresponding to the Nth (N is an integer) light emission within one ranging period may be denoted as "TC(N)".

[0041] The control unit 40 outputs an operation count value indicating the number of times that the emission of light and the generation of the time count value have been repeated in the past within one distance measurement period to the weight determination unit 431. Hereinafter, the operation count value input to the weight determination unit 431 corresponding to the Nth emission of light and the generation of the time count value within one distance measurement period may be represented as "N".

[0042] The weight determination unit 431 determines a weight value used for weighting the light reception count value in generating the frequency distribution, based on the operation count value N input from the control unit 40. The weight determination unit 431 outputs the determined weight value to the frequency distribution generation unit 432.

[0043] The frequency distribution generating unit 432 generates a frequency distribution based on the time count value and the weight value. The frequency distribution is data in which each time count value is associated with a light receiving count value obtained by counting the number of times the time count value is input. Each time a time count value and a weight value are input, the frequency distribution generating unit 432 updates the frequency distribution by adding a value equal to the number of weight values ​​to the light receiving count value of the time count value.

[0044] When the light emitting unit 30 emits light and the light receiving unit 20 receives light a predetermined number of times within one distance measurement period, the frequency distribution generating unit 432 completes the generation of the frequency distribution. The frequency distribution generating unit 432 generates distance information from the generated frequency distribution using a predetermined algorithm. This algorithm may, for example, detect a maximum value of the light receiving count value from the frequency distribution and calculate distance information from a time count value corresponding to the maximum value. Note that the frequency distribution generating unit 432 may output the frequency distribution as it is without calculating the distance information. In this case, a process of calculating distance information from the frequency distribution may be performed in an external signal processing device. Alternatively, the time-to-digital converting unit 411 may output the time count value to the outside, and the weight determining unit 431 may output the weight value to the outside, in which case the external signal processing device has a function of performing the process of the frequency distribution generating unit 432.

[0045] Next, a specific example of the processing performed in the distance measuring unit 41 of this embodiment will be described with reference to Fig. 5, Fig. 6(a) and Fig. 6(b). Fig. 5 is a table showing an example of setting weight values ​​according to this embodiment. In the example of Fig. 5, the weight determination unit 431 determines the weight value based on the value of the operation count value N. In the example of Fig. 5, the set value (total number of operations) of the total number of times that the operations of emitting light and outputting the time count value are repeated within one distance measurement period is set to 4000. In other words, the value range of the operation count value N is 1 or more and 4000 or less.

[0046] The weight determination unit 431 sets the weight value by referring to a table showing the correspondence between the action count value N and the weight value as shown in Fig. 5. As shown in Fig. 5, when the action count value N is 1 or more and 1000 (first threshold value) or less, the weight determination unit 431 determines the weight value to be "1" (first weight value) and outputs it to the frequency distribution generation unit 432. When the action count value N is 1001 or more and 2000 (second threshold value) or less, the weight determination unit 431 determines the weight value to be "2" (second weight value) and outputs it to the frequency distribution generation unit 432. When the action count value N is 2001 or more and 3000 (third threshold value) or less, the weight determination unit 431 determines the weight value to be "4" (third weight value) and outputs it to the frequency distribution generation unit 432. Furthermore, when the operation count value N is equal to or greater than 3001 and equal to or less than 4000 (the total number of operations), the weight determination unit 431 determines the weight value to be "8" (fourth weight value) and outputs it to the frequency distribution generation unit 432. In this way, the weight determination unit 431 sets a larger weight value for measurements performed later in one ranging period.

[0047] In the above example, the weight value is a value that can be expressed as 2M (M is an integer), such as "1" (20), "2" (21), "4" (22), and "8" (23). As described above, the value of M varies depending on the operation count value N. By setting the weight value to an integer power of 2 in this way, the calculation process can be performed by bit shift calculation, and the calculation process can be simplified. However, the setting of the weight value is not limited to these, and it may be a value such as "3" that cannot be expressed as 2M. In addition, the weight value may be set to a fraction such as "1 / 2" under some conditions, and in this case, the contribution of the time count value that satisfies the condition to the frequency distribution can be reduced. That is, the above-mentioned M may be a negative integer. In addition, the weight value may be set to "0" under some conditions, and in this case, the time count value that satisfies the condition can be prevented from being reflected in the frequency distribution.

[0048] Figures 6(a) and 6(b) are graphs showing an example of frequency distribution generated according to this embodiment. The horizontal axis of Figures 6(a) and 6(b) is the time count value, and the vertical axis of Figures 6(a) and 6(b) is the light-receiving count value. Figures 6(a) and 6(b) show the light-receiving count value corresponding to each time interval in the form of a bar graph.

[0049] FIG. 6(a) shows an example of a frequency distribution obtained when weighting is not performed by the weight determination unit 431 and the frequency distribution generation unit 432. As shown in FIG. 1, the object X may be moving. An example of such an object X is a moving body such as a vehicle. In this example, the object X is assumed to be moving in a direction approaching the distance measuring device 1. In this case, the distance between the object X and the distance measuring device 1 gradually shortens while repeated measurements are performed within one distance measuring period, and the flight time of light also gradually shortens. Therefore, as shown in FIG. 6(a), a frequency distribution is generated in which a large light receiving count value is obtained in a wide range of time count values, making the true distance to the object X at the time of distance measuring unclear. In addition, the maximum value of the light receiving count value also becomes small, and the S / N ratio decreases. Therefore, the accuracy of extracting the maximum light receiving count value decreases, and the distance measuring accuracy may decrease.

[0050] FIG. 6(b) shows an example of a frequency distribution obtained when weighting is performed by the weight determining unit 431 and the frequency distribution generating unit 432. FIG. 6(b) also shows a schematic diagram of a frequency distribution update process performed when the frequency distribution generating unit 432 receives a weight value corresponding to the time count value TC(N). At this time, the frequency distribution generating unit 432 adds the light receiving count value corresponding to the time count value TC(N) by the number of weight values. For example, when the weight value is "8", the frequency distribution generating unit 432 adds 8 to the light receiving count value corresponding to the time count value TC(N) to update the frequency distribution. In FIG. 6(b), a white box indicates a light receiving count value that has already been added before the Nth measurement, and a hatched box indicates a light receiving count value added in the Nth measurement.

[0051] As described above, the weight value determined by the weight determination unit 431 is set to a larger value for measurements performed later in one distance measurement period. Therefore, by generating a frequency distribution by weighting using this weight value, a frequency distribution is obtained in which the light reception count value corresponding to the measurement performed later in one distance measurement period is emphasized, as shown in Fig. 6(b). Therefore, even if the object X is moving, the maximum value of the light reception count value can be extracted with high accuracy, and distance measurement accuracy can be improved.

[0052] As described above, according to this embodiment, the weight determination unit 431 acquires an action count value indicating the number of times that the action of outputting a time count value has been repeated in the past within one distance measurement period, and determines a weight value based on the action count value. By applying this weight value to the generation of the frequency distribution, the influence of the variation in the light reception count value caused by the movement of the object X is reduced. Therefore, according to this embodiment, a photoelectric conversion device capable of acquiring highly accurate distance information is provided. Furthermore, by performing weighted addition of the light reception count value in the frequency distribution using the method of this embodiment, it is possible to perform distance measurement with high accuracy.

[0053] 5, the range of the action count value is divided into four intervals, and four types of weight values ​​are set, but the number of intervals of the action count value may be 3 or less, or may be 5 or more. In that case, when the number of intervals of the action count value is M, the weight determination unit 431 may set the weight values ​​to 20, 21, ..., 2M-1 according to the action count value.

[0054] In this embodiment, an example is described in which the object X moves toward the distance measuring device 1, but the same effect can be obtained even if the object X moves away from the distance measuring device 1. In addition, the same effect can be obtained when the object X is stationary and the distance measuring device 1 is moving, or when both the object X and the distance measuring device 1 are moving.

[0055] Generally, in an apparatus or system that uses the distance measurement results obtained by the distance measuring device 1, newer distance information is often more important than older distance information. Therefore, it is desirable to set the weight value to a larger value for the measurement performed later within one distance measurement period, as shown in Fig. 5. However, this is not limited to this, and it is sufficient that the weight value is set to be different depending on the operation count value.

[0056] In this embodiment, the weight determination unit 431 refers to a table showing the correspondence between the operation count value N and the weight value, and sets different weight values ​​depending on whether the operation count value is equal to or less than a threshold value defined in the table or is greater than the threshold value. By performing processing by referring to a table prepared in advance, the calculation speed is increased compared to the case where calculation processing is performed each time the weight determination processing is performed. However, the method of determining the weight is not limited to this. For example, the weight determination unit 431 may determine the weight value by a function with the operation count value N as an independent variable. In this case, it is easy to change the processing according to the situation such as the external environment of the distance measuring device 1.

[0057] [Second embodiment] In this embodiment, a modified example will be described in which the weighting value is dynamically changed according to the set value of the total number of times that the operation of emitting light and outputting the time count value is repeated within one distance measurement period (total number of operations). In this embodiment, the description of elements common to the first embodiment may be omitted or simplified.

[0058] Fig. 7 is a block diagram showing the configuration of the distance measurement unit 41 according to this embodiment. As shown in Fig. 7, the control unit 40 outputs to the weight determination unit 431 a total operation number NM, which is a setting value of the total number of times that the operation of emitting light and outputting the time count value is repeated within one distance measurement period.

[0059] The weight determination unit 431 determines a weight value used for weighting the light reception count value in generating the frequency distribution, based on the operation count value N and the total operation number NM input from the control unit 40. The weight determination unit 431 outputs the weight value to the frequency distribution generation unit 432.

[0060] Fig. 8 is a table showing an example of setting weight values ​​according to this embodiment. In the example of Fig. 8, the correspondence between the action count value N and the weight value changes dynamically depending on the value of the total action number NM. That is, the weight determination unit 431 determines the weight value based on both the action count value N and the total action number NM. In the example of Fig. 8, the action of emitting light and outputting the time count value is performed the number of times equal to the total action number NM, so the value range of the action count value N is 1 or more and NM or less.

[0061] 8, when the action count value N is 1 or more and (NM*1 / 4) (first threshold value) or less, the weight determination unit 431 determines the weight value to be "1" (first weight value) and outputs it to the frequency distribution generation unit 432. When the action count value N is (NM*1 / 4+1) or more and (NM*2 / 4) (second threshold value) or less, the weight determination unit 431 determines the weight value to be "2" (second weight value) and outputs it to the frequency distribution generation unit 432. When the action count value N is (NM*2 / 4+1) or more and (NM*3 / 4) (third threshold value) or less, the weight determination unit 431 determines the weight value to be "4" (third weight value) and outputs it to the frequency distribution generation unit 432. Furthermore, when the operation count value N is equal to or greater than (NM*3 / 4+1) and equal to or less than the total number of operations NM, the weight determination unit 431 determines the weight value to be "8" (fourth weight value) and outputs it to the frequency distribution generation unit 432. In this way, the weight determination unit 431 sets a larger weight value for measurements performed later in one ranging period. Furthermore, since the first to third thresholds at which the weight value is switched are set to be proportional to the total number of operations NM, the first to third thresholds change at a constant rate with respect to changes in the total number of operations NM.

[0062] The value of the total number of operations NM affects the trade-off relationship between distance measurement accuracy and the time required for measurement, so the optimal value may change depending on the usage environment, purpose, etc. of the distance measuring device 1. When the total number of operations NM changes due to a change in the settings of the distance measuring device 1, the range of the value of the operation count value N also changes, so it is desirable to change the threshold value at which the weight value is switched accordingly. In this embodiment, the threshold value at which the weight value is switched in the weight determination unit 431 dynamically changes depending on the total number of operations NM. This allows the threshold value to be changed appropriately depending on the total number of operations NM, and the weight value is determined appropriately. Therefore, a photoelectric conversion device capable of acquiring highly accurate distance information is provided.

[0063] In Fig. 8, an example in which the threshold value changes according to a function corresponding to the total number of operations NM is shown, but the present invention is not limited to this. For example, a plurality of types of tables in which the threshold value is fixed as shown in Fig. 5 may be prepared in advance, and the weight determination unit 431 may select one of the plurality of tables according to the total number of operations NM to determine the weight value. In this case, since a calculation using the total number of operations NM is not required, the processing is simplified. In addition, the weight determination unit 431 may determine the weight value according to a two-variable function with the operation count value N and the total number of operations NM as independent variables. In this case, it is easy to change the processing according to the situation such as the external environment of the distance measuring device 1.

[0064] [Third embodiment] In this embodiment, a modified example will be described in which the distance measuring device 1 outputs velocity information of the object X based on the frequency distribution. In this embodiment, the description of elements common to the first and second embodiments may be omitted or simplified.

[0065] Fig. 9 is a block diagram showing the configuration of the distance measuring unit 41 according to this embodiment. As shown in Fig. 9, the frequency distribution generating unit 432 generates and outputs, in addition to distance information, velocity information of the object X from the frequency distribution. The velocity information may be, for example, the speed of the object X (absolute value of the velocity) and the direction of the velocity of the object X.

[0066] 10(a), 10(b), and 10(c) are graphs showing an example of frequency distribution generated according to this embodiment. FIG. 10(a) shows an example of frequency distribution obtained when the object X moves in a direction approaching the distance measuring device 1, similar to FIG. 6(b). FIG. 10(b) shows an example of frequency distribution obtained when the object X moves in a direction away from the distance measuring device 1. Focusing on the vicinity of the maximum value of the light receiving count value in FIG. 10(a) and FIG. 10(b), the left-right asymmetry in the vicinity of the maximum value of the light receiving count value is significantly different between FIG. 10(a) and FIG. 10(b). When the object X moves in a direction approaching the distance measuring device 1, an asymmetric distribution spreading to the right is obtained as shown in FIG. 10(a). When the object X moves in a direction away from the distance measuring device 1, an asymmetric distribution spreading to the left is obtained as shown in FIG. 10(b). Therefore, the asymmetry of the variation in the frequency distribution contains information indicating the direction of the speed of the object X. In this way, the frequency distribution generating unit 432 can obtain the direction of the velocity of the object X based on the asymmetry of the variation in the frequency distribution.

[0067] FIG. 10(c) shows an example of a frequency distribution obtained when the object X moves in a direction approaching the distance measuring device 1. In the example of FIG. 10(c), the object X moves slower than in the example of FIG. 10(a). Focusing on the vicinity of the maximum value of the light reception count value in FIG. 10(a) and FIG. 10(c), the magnitude of the variation in the vicinity of the maximum value of the light reception count value is significantly different between FIG. 10(a) and FIG. 10(c). When the object X moves fast, a distribution with a large spread is obtained as shown in FIG. 10(a). When the object X moves slowly, a distribution with a small spread is obtained as shown in FIG. 10(c). Therefore, the magnitude of the variation in the frequency distribution includes information indicating the speed of the object X. In this way, the frequency distribution generating unit 432 can obtain the speed of the object X based on the magnitude of the variation in the frequency distribution.

[0068] As described above, according to this embodiment, the distance measuring device 1 can obtain the velocity information of the object X based on the frequency distribution. This velocity information may be used to improve the accuracy of distance measurement in a device or system that uses the distance measurement result obtained by the distance measuring device 1, or may be used for purposes other than distance measurement.

[0069] 10(a) and 10(b) are frequency distributions obtained when weighting is performed such that the weight value increases as the action count value increases, as in FIG. 5 or FIG. 8, but other frequency distributions may be obtained depending on the weighting settings. For example, it is assumed that weighting is performed such that the weight value decreases as the action count value increases. In this case, when the object X moves in a direction away from the distance measuring device 1, a frequency distribution as shown in FIG. 10(a) is obtained, and when the object X moves in a direction toward the distance measuring device 1, a frequency distribution as shown in FIG. 10(b) is obtained. Even in such a case, the frequency distribution generating unit 432 can obtain the direction of the object's speed based on the asymmetry of the variation in the frequency distribution.

[0070] [Fourth embodiment] Fig. 11 is a block diagram of a light detection system according to this embodiment, more specifically, a block diagram of a range image sensor including the range finder 1 described in the above embodiment.

[0071] 11, the distance image sensor 501 includes an optical system 502, a photoelectric conversion device 503, an image processing circuit 504, a monitor 505, and a memory 506. The distance image sensor 501 receives light (modulated light, pulsed light) emitted from a light source device 511 toward a subject and reflected from the surface of the subject. The distance image sensor 501 can obtain a distance image according to the distance to the subject, based on the time from emission to reception of light. The light source device 511 corresponds to the light source device 3 in the above-described embodiment.

[0072] The optical system 502 includes one or more lenses, guides image light (incident light) from a subject to the photoelectric conversion device 503, and forms an image on the light receiving surface (sensor unit) of the photoelectric conversion device 503. The optical system 502 corresponds to the optical system 26 in the above-described embodiment.

[0073] The light receiving unit 20 and distance measuring unit 41 of the above-described embodiment can be applied as the photoelectric conversion device 503. The photoelectric conversion device 503 supplies an image processing circuit 504 with a distance signal indicating a distance determined from a light reception signal.

[0074] Image processing circuit 504 (signal processing unit) performs image processing to construct a distance image based on the distance signal supplied from photoelectric conversion device 503. The distance image (image data) obtained by the image processing can be displayed on monitor 505 and stored (recorded) in memory 506.

[0075] The range image sensor 501 configured in this manner can obtain an accurate range image by applying the configuration of the above-described embodiment.

[0076] [Fifth embodiment] 12(a) and 12(b) are block diagrams of devices related to the vehicle-mounted distance measuring device in this embodiment. The device 80 has a distance measuring unit 803, which is an example of the distance measuring device 1 in the above-mentioned embodiment, and a signal processing device (processing device) that processes a signal from the distance measuring unit 803. The device 80 has a distance measuring unit 803 that measures the distance to an object, and a collision determination unit 804 that determines whether or not there is a possibility of collision based on the measured distance. Here, the distance measuring unit 803 is an example of a distance information acquisition means that acquires distance information to the object. In other words, the distance information is information related to the distance to the object, etc. The collision determination unit 804 may use the distance information to determine the possibility of collision.

[0077] The device 80 is connected to a vehicle information acquisition device 810, and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. In addition, the device 80 is connected to a control ECU 820, which is a control device that outputs a control signal to generate a braking force for the vehicle based on the judgment result of the collision judgment unit 804. In addition, the device 80 is also connected to an alarm device 830 that issues an alarm to the driver based on the judgment result of the collision judgment unit 804. For example, when the judgment result of the collision judgment unit 804 indicates that there is a high possibility of a collision, the control ECU 820 performs vehicle control to avoid a collision and reduce damage by applying the brakes, releasing the accelerator, suppressing engine output, etc. The alarm device 830 warns the user by sounding an alarm such as a sound, displaying alarm information on the screen of a car navigation system, etc., and applying vibrations to a seat belt or steering wheel. These devices of the device 80 function as a mobile object control unit that controls the operation of controlling the vehicle as described above.

[0078] In this embodiment, the device 80 measures distances around the vehicle, for example, in front or behind. Fig. 12(b) shows the device when measuring distances in front of the vehicle (distance measurement range 850). A vehicle information acquisition device 810 as a distance measurement control means sends an instruction to the device 80 or distance measurement unit 803 to perform a distance measurement operation. With this configuration, the accuracy of distance measurement can be further improved.

[0079] Although the above describes an example of control to prevent collision with other vehicles, the present invention can also be applied to control of automatic driving by following other vehicles, control of automatic driving to prevent deviation from lanes, etc. Furthermore, the device is not limited to vehicles such as automobiles, but can be applied to moving bodies (moving devices) such as ships, aircraft, artificial satellites, industrial robots, and consumer robots. In addition, the present invention can be applied to devices that use object recognition or biometric recognition, such as intelligent transport systems (ITS) and surveillance systems, in addition to moving bodies.

[0080] [Modified embodiment] The present invention is not limited to the above-described embodiments and can be modified in various ways. For example, an example in which a part of the configuration of any of the embodiments is added to another embodiment, or an example in which a part of the configuration of any of the embodiments is replaced with a part of the configuration of another embodiment, is also an embodiment of the present invention.

[0081] The disclosure of this specification includes the complement of the concepts described in this specification. In other words, if the specification states, for example, that "A is B" (A=B), the specification is deemed to disclose or suggest that "A is not B" even if the statement that "A is not B" (A≠B) is omitted. This is because when it states that "A is B," it is assumed that the case that "A is not B" is taken into consideration.

[0082] The disclosure of this specification includes the following configurations. (Configuration 1) a light receiving unit that generates a light receiving signal according to incident light by photoelectric conversion; a time-to-digital conversion unit that performs time-to-digital conversion periodically at the lapse of a predetermined period within one distance measurement period to output a time count value indicating an elapsed time from light emission by a light source device to input of the light reception signal; a weight determination unit that acquires a count value indicating the number of times the time-to-digital conversion has been performed within the one ranging period, and outputs a weight value based on the count value; a frequency distribution generating unit that uses the weight value for frequency addition in generating a frequency distribution of the count value; A photoelectric conversion device comprising: (Configuration 2) The weight determination unit outputs a first weight value when the count value is equal to or smaller than a first threshold value, and outputs a second weight value larger than the first weight value when the count value is larger than the first threshold value. 2. The photoelectric conversion device according to configuration 1. (Configuration 3) The weight determination unit outputs the second weight value when the count value is greater than the first threshold value and equal to or less than a second threshold value, and outputs a third weight value greater than the second weight value when the count value is greater than the second threshold value. 3. The photoelectric conversion device according to configuration 2. (Configuration 4) The weight determination unit outputs the weight value by referring to a table indicating a correspondence relationship between the count value and the weight value. 4. The photoelectric conversion device according to any one of configurations 1 to 3. (Configuration 5) The weight determination unit outputs the weight value according to a function indicating a correspondence relationship between the count value and the weight value. 4. The photoelectric conversion device according to any one of configurations 1 to 3. (Configuration 6) the weight determination unit further acquires a total operation number which is a setting value of a total number of times that the time-to-digital conversion unit repeats an operation of outputting the time count value within one ranging period; The weight determination unit outputs the weight value further based on the total number of operations. 6. The photoelectric conversion device according to any one of configurations 1 to 5. (Configuration 7) The correspondence between the count value and the weight value is set to vary depending on the total number of operations. 7. The photoelectric conversion device according to configuration 6. (Configuration 8) the weight determination unit outputs a first weight value when the count value is equal to or less than a threshold value, and outputs a second weight value greater than the first weight value when the count value is greater than the threshold value; The threshold value is set to a different value depending on the total number of operations. 8. The photoelectric conversion device according to configuration 6 or 7. (Configuration 9) The threshold value is set to a larger value as the total number of operations increases. 9. The photoelectric conversion device according to configuration 8. (Configuration 10) The threshold is set to be proportional to the total number of operations. 10. The photoelectric conversion device according to configuration 8 or 9. (Configuration 11) The weight value is 2M (M is an integer), The value of M varies depending on the count value. 11. The photoelectric conversion device according to any one of configurations 1 to 10. (Configuration 12) The frequency distribution generating unit generates distance information based on the frequency distribution. 12. The photoelectric conversion device according to any one of configurations 1 to 11. (Configuration 13) The frequency distribution generating unit detects a maximum value of the count value, and generates the distance information based on a time count value corresponding to the maximum value. 13. The photoelectric conversion device according to configuration 12. (Configuration 14) The frequency distribution generating unit generates speed information of the object based on the frequency distribution. 14. The photoelectric conversion device according to any one of configurations 1 to 13. (Configuration 15) The frequency distribution generating unit obtains a speed of the object based on a magnitude of variation in the count value indicated by the frequency distribution. 15. The photoelectric conversion device according to configuration 14. (Configuration 16) The frequency distribution generating unit obtains a velocity direction of the object based on asymmetry of the variation of the count value indicated by the frequency distribution. 16. The photoelectric conversion device according to configuration 14 or 15. (Configuration 17) The light receiving portion includes an avalanche photodiode. 17. The photoelectric conversion device according to any one of configurations 1 to 16, (Configuration 18) The photoelectric conversion device according to any one of configurations 1 to 17, a signal processing unit that processes a signal output from the photoelectric conversion device; 1. An optical detection system comprising: (Configuration 19) The photoelectric conversion device according to any one of configurations 1 to 17, a signal processing unit that processes a signal output from the photoelectric conversion device; The light source device, 1. An optical detection system comprising: (Configuration 20) A mobile object, The photoelectric conversion device according to any one of configurations 1 to 17, a moving object control unit that controls the moving object based on distance information acquired by the photoelectric conversion device; A moving object comprising:

[0083] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) for implementing one or more of the functions.

[0084] It should be noted that the above-mentioned embodiments are merely examples of the implementation of the present invention, and the technical scope of the present invention should not be interpreted as being limited by these embodiments. In other words, the present invention can be implemented in various forms without departing from its technical concept or main features. [Explanation of symbols]

[0085] 1 Ranging device 20 Light receiving part 411 Time Digital Converter 431 Weight Determination Unit

Claims

1. a light receiving unit that generates a light receiving signal according to incident light by photoelectric conversion; a time-to-digital conversion unit that performs time-to-digital conversion periodically to output a time count value indicating an elapsed time from light emission by a light source device to input of the light receiving signal every time a predetermined period elapses within one distance measurement period; a weight determination unit that obtains a count value indicating the number of times the time-to-digital conversion is performed within one distance measurement period, and outputs a weight value based on the count value; a frequency distribution generating unit that uses the weight value for adding frequencies to generate a frequency distribution of the count values; A photoelectric conversion device comprising:

2. The weight determination unit outputs a first weight value when the count value is equal to or smaller than a first threshold value, and outputs a second weight value larger than the first weight value when the count value is larger than the first threshold value.

2. The photoelectric conversion device according to claim 1.

3. The weight determination unit outputs the second weight value when the count value is greater than the first threshold value and equal to or less than a second threshold value, and outputs a third weight value greater than the second weight value when the count value is greater than the second threshold value.

3. The photoelectric conversion device according to claim 2.

4. The weight determination unit outputs the weight value by referring to a table indicating a correspondence relationship between the count value and the weight value.

2. The photoelectric conversion device according to claim 1.

5. The weight determination unit outputs the weight value according to a function indicating a correspondence relationship between the count value and the weight value.

2. The photoelectric conversion device according to claim 1.

6. the weight determination unit further acquires a total operation number that is a setting value of a total number of times that the time-to-digital conversion unit repeats an operation of outputting the time count value within one ranging period; The weight determination unit outputs the weight value further based on the total number of operations.

2. The photoelectric conversion device according to claim 1.

7. The correspondence between the count value and the weight value is set to vary depending on the total number of operations.

7. The photoelectric conversion device according to claim 6.

8. the weight determination unit outputs a first weight value when the count value is equal to or less than a threshold value, and outputs a second weight value greater than the first weight value when the count value is greater than the threshold value; The threshold value is set to a different value depending on the total number of operations.

7. The photoelectric conversion device according to claim 6.

9. The threshold value is set to a larger value as the total number of operations increases.

9. The photoelectric conversion device according to claim 8.

10. The threshold is set to be proportional to the total number of operations.

9. The photoelectric conversion device according to claim 8.

11. The weight value is 2 Ｍ (M is an integer), The value of M varies depending on the count value.

2. The photoelectric conversion device according to claim 1.

12. The frequency distribution generating unit generates distance information based on the frequency distribution.

2. The photoelectric conversion device according to claim 1.

13. The frequency distribution generating unit detects a maximum value of the count value, and generates the distance information based on a time count value corresponding to the maximum value.

13. The photoelectric conversion device according to claim 12.

14. The frequency distribution generating unit generates speed information of the object based on the frequency distribution.

2. The photoelectric conversion device according to claim 1.

15. The frequency distribution generating unit obtains a speed of the object based on a magnitude of variation in the count value indicated by the frequency distribution.

15. The photoelectric conversion device according to claim 14.

16. The frequency distribution generating unit obtains a velocity direction of the object based on asymmetry of the variation of the count value indicated by the frequency distribution.

15. The photoelectric conversion device according to claim 14.

17. The light receiving portion includes an avalanche photodiode.

2. The photoelectric conversion device according to claim 1.

18. The photoelectric conversion device according to any one of claims 1 to 17, a signal processing unit that processes a signal output from the photoelectric conversion device; 1. An optical detection system comprising:

19. The photoelectric conversion device according to any one of claims 1 to 17, a signal processing unit that processes a signal output from the photoelectric conversion device; The light source device, 1. An optical detection system comprising:

20. A mobile object, The photoelectric conversion device according to any one of claims 1 to 17, a moving object control unit that controls the moving object based on distance information acquired by the photoelectric conversion device; A moving object comprising:

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