Distance measuring device

Abstract

To suppress errors in distance measurement.SOLUTION: A distance measuring device according to one embodiment includes: an emission unit configured to emit pulse light; a photodetector configured to detect reflected light from a target object of the pulse light; an analog processing unit configured to generate received light data on the basis of the detected reflected light; and a digital processing unit configured to measure a distance to the target object on the basis of the received light data. The emission unit is configured to sequentially emit the first pulse light and the second pulse light in which at least one of a peak and a pulse width is different from that of the first pulse light. The digital processing unit is configured to add first received light data corresponding to the first pulse light and second received light data corresponding to the second pulse light, and to measure the distance on the basis of the added data.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The embodiment relates to a distance measurement device. [Background technology]

[0002] Distance measurement devices called LiDAR (light detection and ranging) are known. LiDAR irradiates a target object with laser light and detects the intensity of the light reflected from the target object using a sensor (photodetector). Then, LiDAR measures the distance from the LiDAR to the target object based on the time change of the light intensity signal output from the sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-329902 A [Patent Document 2] International Publication No. 2022 / 264504 [Patent Document 3] Patent No. 7238343 Summary of the Invention [Problem to be solved by the invention]

[0004] Suppresses errors in distance measurement. [Means for solving the problem]

[0005] A distance measurement device according to an embodiment includes an emission unit that emits pulsed light, a photodetector that detects reflected light of the pulsed light from an object, an analog processing unit that generates received light data based on the detected reflected light, and a digital processing unit that measures a distance to the object based on the received light data. The emission unit is configured to emit a first pulsed light and a second pulsed light having at least one of a peak and a pulse width different from that of the first pulsed light in this order. The digital processing unit is configured to add up the first received light data corresponding to the first pulsed light and the second received light data corresponding to the second pulsed light, and measure the distance based on the added data. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a distance measurement device according to a first embodiment. [Diagram 2] FIG. 2 is a plan view showing an example of a planar layout of the photodetector according to the first embodiment. [Diagram 3] FIG. 2 is a block diagram showing an example of the configuration of a pixel according to the first embodiment. [Figure 4] FIG. 2 is a circuit diagram showing an example of the configuration of a pixel according to the first embodiment. [Diagram 5] 1A to 1C are schematic diagrams showing an example of the structure of an avalanche photodiode according to the first embodiment and the operation principle of a SPAD. [Figure 6] FIG. 2 is a block diagram showing an example of the configuration of a digital processing unit according to the first embodiment. [Figure 7] 5 is a flowchart showing an example of a distance measurement operation in the distance measurement device according to the first embodiment. [Figure 8] 3 is a waveform diagram showing an example of various signals related to a distance measurement operation in the distance measurement device according to the first embodiment. [Figure 9] FIG. 11 is a block diagram showing an example of the configuration of a synthesis calculation unit according to the second embodiment. [Figure 10] 10 is a flowchart showing an example of a distance measurement operation in the distance measurement device according to the second embodiment. [Figure 11]10 is a waveform diagram showing an example of various signals related to a distance measurement operation in the distance measurement device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, the embodiments will be described with reference to the drawings. In the following description, components having the same function and configuration are given common reference symbols. When multiple components having a common reference symbol are to be distinguished from one another, a subscript is added to the common reference symbol. When no particular distinction is required between multiple components, only the common reference symbol is added to the multiple components, and no subscript is added.

[0008] 1. First embodiment A distance measurement device according to the first embodiment will be described. The distance measurement device according to the first embodiment is, for example, a LiDAR that uses a laser to measure the distance to an object, and includes a photodetector that is a photomultiplier (semiconductor photon-multiplier, particularly a silicon photon-multiplier (SiPM)) that can be integrated on a semiconductor substrate.

[0009] 1.1 Configuration The configuration of the distance measurement device according to the first embodiment will be described.

[0010] 1.1.1 Distance measurement device FIG. 1 is a block diagram showing an example of the configuration of a distance measurement device according to the first embodiment.

[0011] 1, the distance measurement device 1 is configured to be able to measure the distance to a target object TG. The distance measurement device 1 may correspond to, for example, a part of an in-vehicle system (not shown). The target object TG is, for example, a tangible object such as another vehicle, a pedestrian, or an obstacle that exists in front of, behind, or to the side of the vehicle in which the distance measurement device 1 is mounted.

[0012] The distance measurement device 1 includes a control unit 10, a light emitting unit 20, a light receiving unit 30, and a digital processing unit 40.

[0013] The control unit 10 includes, for example, a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an oscillator. The ROM stores programs and the like used for the operation of the distance measurement device 1. The CPU controls the emission unit 20, the light receiving unit 30, and the digital processing unit 40 according to the programs stored in the ROM. The RAM is used as a working area for the CPU. The oscillator is used to generate intermittent pulse signals. The oscillator is configured to alternately generate two types of pulse signals that differ from each other in at least one of the amplitude and the pulse width, for example.

[0014] The emission unit 20 intermittently generates and emits laser pulses. The emitted laser pulses are irradiated onto the object TG and are used to measure the distance between the distance measurement device 1 and the object TG. Hereinafter, the laser pulses emitted from the emission unit 20 are also referred to as "emitted light Le." The emitted light Le reflected by the object TG is also referred to as "reflected light Lr." The emission unit 20 includes, for example, driving circuits 21 and 22, a light source 23, an optical system 24, and a mirror 25.

[0015] The drive circuit 21 generates an intermittent drive current in response to a pulse signal input from the oscillator of the control unit 10. The drive circuit 21 supplies the generated intermittent drive current to the light source 23. That is, the drive circuit 21 functions as a current supply source for the light source 23. Specifically, the drive circuit 21 supplies two types of drive currents, which differ from each other in at least one of the current value and the supply time, to the light source 23 based on two types of pulse signals input from the oscillator of the control unit 10.

[0016] The driving circuit 22 generates a driving current in accordance with the control of the control unit 10. The driving circuit 22 supplies the generated driving current to the mirror 25. That is, the driving circuit 22 functions as a power supply circuit for the mirror 25.

[0017] The light source 23 is a laser light source such as a laser diode. The light source 23 intermittently emits a laser pulse (emitted light Le) based on an intermittent drive current supplied from the drive circuit 21. Specifically, the light source 23 alternately emits two types of emitted light Le having at least one of a pulse peak and a pulse width different from each other based on two types of drive current supplied from the drive circuit 21. The emitted light Le is incident on the optical system 24.

[0018] The optical system 24 includes a plurality of lenses and optical elements. The optical system 24 may include a beam shaper, a beam splitter, and the like. The optical system 24 is disposed on the optical path of the emitted light Le from the light source 23. The optical system 24 collimates the emitted light Le and guides it to the mirror 25.

[0019] The mirror 25 reflects the outgoing light Le guided by the optical system 24 based on a driving current supplied from the driving circuit 22. For example, the reflecting surface of the mirror 25 is configured to rotate or oscillate about two intersecting axes. The outgoing light Le reflected by the mirror 25 is irradiated onto the target TG.

[0020] The light receiving unit 30 converts the light incident on the distance measurement device 1 into a digital signal. The light receiving unit 30 transfers the converted digital signal to the digital processing unit 40 as a light receiving result. The light receiving unit 30 is used to detect reflected light Lr that intermittently enters the distance measurement device 1. The light receiving unit 30 includes, for example, an optical system 31, a photodetector 32, and an analog processing unit 33.

[0021] The optical system 31 includes at least one lens. The optical system 31 collects the reflected light Lr incident on the distance measurement device 1 onto the photodetector 32.

[0022] The photodetector 32 is, for example, a photomultiplier that can be integrated on a semiconductor substrate. The photodetector 32 includes a photomultiplier element using a semiconductor. The photodetector 32 converts the reflected light Lr collected by the optical system 31 into an analog signal using the photomultiplier element. The analog signal converted by the photodetector 32 is transferred to the analog processing unit 33.

[0023] The analog processing unit 33 is an AFE (analog front end). The analog processing unit 33 converts the analog signal transferred from the photodetector 32 into a digital signal. Specifically, the analog processing unit 33 includes, for example, a trans-impedance amplifier (TIA), an analog to digital converter (ADC), and a time-correlated single photon counter (TCSPC), etc. The analog processing unit 33 sends the generated digital signal to the digital processing unit 40.

[0024] The digital processing unit 40 measures the time when the light receiving unit 30 detects the reflected light Lr based on the digital signal transferred from the light receiving unit 30. The digital processing unit 40 measures the distance between the distance measurement device 1 and the target TG based on the time when the emitted light Le is emitted from the emission unit 20 and the time when the light receiving unit 30 detects the reflected light Lr.

[0025] The time when the emitted light Le is emitted from the emission unit 20 is notified, for example, from the control unit 10. The timing of incidence of the reflected light Lr is determined, for example, based on the rise time of a digital signal. Such a distance measurement method is also called a ToF (time of flight) method.

[0026] The digital processing unit 40 sends the measured distance measurement data to a downstream image processing circuit (not shown). The downstream image processing circuit generates image data in which the distance measurement data is mapped over the area to be measured by the distance measurement device 1, based on the distance measurement data. The generated image data is referenced by a control program of a vehicle or the like equipped with the distance measurement device 1, for example.

[0027] With the above-described configuration, the distance measurement device 1 can measure the distance to the target TG.

[0028] 1.1.2 Photodetectors Next, the configuration of the photodetector according to the first embodiment will be described. (Flat layout) FIG. 2 is a plan view showing an example of a planar layout of the photodetector according to the first embodiment.

[0029] 2, the photodetector 32 includes, for example, a plurality of pixels PX arranged in a matrix shape extending in the row and column directions on a semiconductor substrate. Each of the plurality of pixels PX is arranged so that its position can be specified by a column address associated with the column direction and a row address associated with the row direction.

[0030] In the example of FIG. 2, in the photodetector 32, the m-th pixel PX in the row direction RA and the n-th pixel PX in the column direction CA is a pixel PX<m、n> (0≦m≦M, 0≦n≦N, M and N are arbitrary integers). In the following, for convenience of explanation, a plurality of pixels PX <m>is the row address <m>, corresponding to a plurality of pixels PX located at the nth position along the column direction CA. <n>is the column address <n>The following description will be given assuming that the above corresponds to the above.

[0031] Each of the multiple pixels PX includes at least one photomultiplier element. For example, a single-photon avalanche diode is used as the photomultiplier element. Hereinafter, the single-photon avalanche diode is also referred to as a "SPAD (single-photon avalanche diode)". The function of the SPAD will be described in detail later. When multiple SPADs are provided in the pixel PX, the multiple SPADs are arranged in a matrix shape spreading in the row direction and column direction within the pixel PX, for example. A pixel PX including multiple SPADs is also referred to as a silicon photomultiplier element (SiPM).

[0032] The number of pixels PX and SPADs included in the photodetector 32 is not limited to the number shown in FIG. 2 and can be designed to be any number. The planar shape of each of the pixels PX and the SPADs does not necessarily have to be square. The shape of the pixels PX can change depending on the shape and arrangement of the SPADs included in each pixel PX. For example, in each pixel PX, the number of SPADs arranged in the row direction and the number of SPADs arranged in the column direction may be different. The photodetector 32 may use pixels PX of different shapes. The shape of the SPADs may be other shapes, for example, rectangular. (pixels) FIG. 3 is a block diagram showing an example of the configuration of a pixel according to the first embodiment.

[0033] In FIG. 3, one pixel PX in the photodetector 32<m,n> The photodetector 32 corresponds to the pixel PX<m,n> As a configuration corresponding to the above, the row selection line RSL <m>and the column selection line CSL<m,n> The photodetector 32 also includes terminals VSUB, DOUT, and OUT. The photodetector 32 is connected to a power supply circuit 50 via the terminals VSUB, DOUT, and OUT. A low impedance element R is connected between the terminal OUT and the power supply circuit 50. The low impedance element R is, for example, a low impedance resistor or transistor.

[0034] The power supply circuit 50 is a circuit that supplies a voltage for driving each pixel PX. For example, the power supply circuit 50 supplies a voltage to each pixel PX via terminals VSUB, OUT, and DOUT. The details of the connection between each pixel PX and the terminals VSUB, OUT, and DOUT will be described later. The power supply circuit 50 may be included in the photodetector 32.

[0035] Column selection line CSL<m,n> is pixel PX<m,n> The column selection line CSL is connected to the<m,n> is pixel PX<m,n> The photodetector 32 transfers a column selection signal to the column selection line CSL. For example, the photodetector 32 is provided with a column selection line CSL for each pixel PX.

[0036] Row selection line RSL <m>is the row address <m>The row selection line RSL is connected to multiple pixels PX that share the same row selection line RSL. <m>transfers a row selection signal to the pixels PX. The photodetector 32 is provided with a plurality of row selection lines RSL, for example, corresponding to the number of pixels PX arranged in the row direction RA.

[0037] Each pixel PX includes, for example, k SPADs 51 (51-1, ..., and 51-k), a selection circuit 52, and a shift circuit 53 (k is an integer equal to or greater than 1). Each of the k SPADs 51 is the smallest unit of an element used for detecting light. The output of each of the k SPADs 51 is input to the selection circuit 52.

[0038] The selection circuit 52 selects the column selection line CSL<m,n> and row selection line RSL <m>The selection circuit 52 selects the pixel PX<m,n> In the selected state, the selection circuit 52 selects the pixel PX<m,n> When the pixel PX<m,n> The light reception result at the pixel PX is not output to the analog processing unit 33. In the following, a pixel PX in a selected state is also called a "selected pixel PX." A pixel PX in a non-selected state is also called a "non-selected pixel PX."

[0039] The shift circuit 53 shifts the pixel PX<m,n> The column selection signal input to the pixel PX<m+1,n> Column selection line CSL connected to<m+1,n> , pixel PX<m+1,n-1> Column selection line CSL connected to<m+1,n-1> , or pixel PX<m+1,n+1> Column selection line CSL connected to<m+1,n+1> Transfer to.

[0040] Each of the control signals R_Shiftx and L_Shiftx is generated by, for example, the control unit 10. The control signal R_Shiftx is a signal for shifting a part of a region (selected pixel region PSR) formed by at least one selected pixel PX in the region in which the pixels PX are arranged in the +CA direction. The control signal L_Shiftx is a signal for shifting a part of the selected pixel region PSR in the -CA direction. In the example of FIG. 3, a case where the shift function of the shift circuit 53 is applied to the column selection line CSL is shown, but this is not limited to this. For example, the shift function of the shift circuit may be applied to the row selection line RSL. Also, the photodetector 32 may have two shift circuits for one pixel PX, so that the shift function of the shift circuit may be applied to both the column selection line CSL and the row selection line RSL.

[0041] FIG. 4 is a circuit diagram showing an example of the configuration of a pixel according to the first embodiment.

[0042] 4 shows the circuit configurations of k SPADs 51 and a selection circuit 52 in the pixel PX. Note that the k SPADs 51 each have the same configuration. Of the k SPADs 51, only SPADs 51-1 and 51-k are shown in FIG.

[0043] The SPAD 51-1 includes an avalanche photodiode APD1, a protection resistor Rs1, a diode RD1, and a quench resistor Rq1. The SPAD 51-k includes an avalanche photodiode APDk, a protection resistor Rsk, a diode RDk, and a quench resistor Rqk. The selection circuit 52 includes P-type transistors PM0 and PM1.

[0044] An anode AEL of the avalanche photodiode APD1 is connected to the terminal VSUB. A cathode CEL of the avalanche photodiode APD1 is connected to a first end of a protection resistor Rs1. A second end of the protection resistor Rs1 is connected to a node N1-1. A diode RD1 is a rectifier diode. A cathode of the diode RD1 is connected to the node N1-1. An anode of the diode RD1 is connected to a node N2. A first end of a quench resistor Rq1 is connected to the node N1-1. A second end of the quench resistor Rq1 is connected to a node N3.

[0045] An anode AEL of the avalanche photodiode APDk is connected to the terminal VSUB. A cathode CEL of the avalanche photodiode APDk is connected to a first end of a protection resistor Rsk. A second end of the protection resistor Rsk is connected to a node N1-k. The diode RDk is a rectifier diode. A cathode of the diode RDk is connected to the node N1-k. An anode of the diode RDk is connected to a node N2. A first end of a quench resistor Rqk is connected to the node N1-k. A second end of the quench resistor Rqk is connected to a node N3.

[0046] In this manner, the k SPADs 51-1 to 51-k are connected in parallel to each of the nodes N2 and N3.

[0047] The node N2 is connected to the terminal DOUT. The voltage supplied to the terminal DOUT is a constant voltage. The constant voltage supplied to the terminal DOUT is set to a voltage lower than, for example, the sum of the voltage at which avalanche breakdown stops in the avalanche photodiode APD1 and the threshold voltage of the diode RD1, ..., and the sum of the voltage at which avalanche breakdown stops in the avalanche photodiode APDk and the threshold voltage of the diode RDk.

[0048] The source of P-type transistor PM0 is connected to node N3. The body of P-type transistor PM0 is supplied with voltage VDD. The voltage VDD is a power supply voltage. The gate of P-type transistor PM0 is input with a column selection signal from a column selection line CSL. The source of P-type transistor PM1 is connected to the drain of P-type transistor PM0. The body of P-type transistor PM1 is supplied with voltage VDD. The gate of P-type transistor PM1 is input with a row selection signal from a row selection line RSL. The drain of P-type transistor PM1 is connected to terminal OUT.

[0049] With the above configuration, a common potential difference Vbias is applied from the anode AEL to the cathode CEL to each of the avalanche photodiodes APD1 to APDk in the selected pixel PX. The potential difference Vbias is, for example, a reverse bias in which the cathode CEL is at a higher potential than the anode AEL. The selected pixel PX outputs an output signal equivalent to the sum of the light reception results of the avalanche photodiodes APD1 to APDk from the drain of the P-type transistor PM1 based on the potential difference Vbias. Therefore, the selected pixel PX can function as the minimum output unit of the light reception result in the photodetector 32. Note that the connection order of the P-type transistors PM0 and PM1 may be reversed. In this case, the selected pixel PX outputs an output signal from the drain of the P-type transistor PM0. In addition, the non-selected pixel PX emits carriers to the terminal DOUT via the diodes RD1, ..., and RDk.

[0050] The pixel PX may further include an N-type transistor connected to the node N3. The N-type transistor of the non-selected pixel PX may be configured to discharge carriers accumulated in the node N3 to a power supply line VSS (not shown). The power supply line VSS is connected to, for example, the ground. For example, two N-type transistors are connected in parallel between the node N3 and the power supply line VSS. A column selection line CSL and a row selection line RSL are connected to the gates of the two N-type transistors. When the pixel PX is in a non-selected state, the voltage of either the column selection line CSL or the row selection line RSL becomes the "H" level. As a result, either one of the two N-type transistors connected in parallel between the node N3 and the power supply line VSS is turned on. As a result, carriers unnecessarily accumulated in the node N3 can be discharged to the power supply line VSS more easily than when the two N-type transistors are not connected to the node N3.

[0051] 1.1.3 APD Next, an example of the configuration of the avalanche photodiode APD and the operation principle of the SPAD will be described. Fig. 5 is a schematic diagram showing an example of the structure of the avalanche photodiode according to the first embodiment and the operation principle of the SPAD.

[0052] First, the configuration of the avalanche photodiode APD will be described. The avalanche photodiode APD includes, for example, a substrate 60, a p-type semiconductor layer 61, a p + The n-type semiconductor layer 62 and + The semiconductor layer 63 is a type semiconductor layer.

[0053] The substrate 60 is, for example, a p-type semiconductor substrate. + The n-type semiconductor layer 62 and + A type semiconductor layer 63 is laminated in this order. + The concentration of p-type impurities in the p-type semiconductor layer 62 is higher than the concentration of p-type impurities in the p-type semiconductor layer 61. + The n-type semiconductor layer 63 is a semiconductor layer doped with n-type impurities. + An electrode (not shown) is connected to the top of the type semiconductor layer 63 .

[0054] Next, the operation principle of the SPAD will be described. In the distance measurement device 1 according to the first embodiment, the substrate 60 side corresponds to the low potential power supply node SUB, and + The type semiconductor layer 63 corresponds to the high potential side (cathode).

[0055] During the light detection operation, a high negative voltage is applied to the anode AEL (i.e., the substrate 60 side) of the avalanche photodiode APD. In other words, a high reverse bias potential difference Vbias is applied to the avalanche photodiode APD. + The n-type semiconductor layer 62 + A strong electric field is generated between the n-type semiconductor layer 63 (that is, in the vicinity of the PN junction) (FIG. 5(1)).

[0056] Then, a depletion layer is formed from the PN junction toward the substrate 60 (FIG. 5(2)). This causes the avalanche photodiode APD to become capable of detecting an optical signal.

[0057] When the avalanche photodiode APD is irradiated with light, part of the light energy reaches the depletion layer (FIG. 5(3)). When the depletion layer is irradiated with light, pairs of electrons and holes, i.e., carriers, may be generated in the depletion layer (FIG. 5(4)). The carriers generated in the depletion layer drift due to an electric field generated by the reverse bias potential difference Vbias applied to the avalanche photodiode APD (FIG. 5(5)). For example, the holes of the generated carriers are accelerated toward the substrate 60 side. On the other hand, the electrons of the generated carriers are accelerated toward the PN junction side.

[0058] Electrons accelerated toward the PN junction collide with atoms under the strong electric field generated near the PN junction. The electrons colliding with the atoms then ionize the atoms, generating new electron-hole pairs. If the reverse bias potential difference Vbias applied to the avalanche photodiode APD exceeds the breakdown voltage of the avalanche photodiode APD, the generation of such electron-hole pairs is repeated. This phenomenon is called avalanche breakdown (Figure 5 (6)).

[0059] When an avalanche breakdown occurs, the avalanche photodiode APD discharges (Figure 5 (7)). This type of discharge is called a Geiger discharge. When a Geiger discharge occurs, a current flows to the terminal OUT via the cathode CEL. As a result, an electrical signal related to the Geiger discharge and the subsequent recovery is output from the avalanche photodiode APD, i.e., one SPAD.

[0060] Moreover, the current output from the avalanche photodiode APD flows, for example, through a quench resistor Rq. As a result, a voltage drop occurs at the terminal OUT (FIG. 5(8)). Such a voltage drop is also called quenching. When the potential difference Vbias of the reverse bias applied to the avalanche photodiode APD becomes less than the breakdown voltage due to quenching, the Geiger discharge stops.

[0061] After that, the capacitance of the PN junction of the avalanche photodiode APD is charged, and a recovery current flows. After the Geiger discharge stops and the avalanche phenomenon ends, the avalanche photodiode APD returns to a state where it can detect the next light.

[0062] As described above, the avalanche photodiode APD causes an avalanche breakdown in response to the incidence of light and outputs an electrical signal. This allows the photodetector 32 to detect the reception of light on a photon-by-photon basis. Hereinafter, a series of light detection operations corresponding to one avalanche breakdown in the avalanche photodiode APD is also referred to as one "light reception sequence."

[0063] The structure of the avalanche photodiode APD is not limited to the structure shown in FIG. + The p-type semiconductor layer 62 may be omitted. + The n-type semiconductor layer 62 and + The thickness of each of the p-type semiconductor layers 63 may be changed as appropriate. The PN junction of the avalanche photodiode APD may be formed in the vicinity of the boundary with the substrate 60. In the structure of the avalanche photodiode APD, the p-type semiconductor layer and the n-type semiconductor layer may be reversed.

[0064] 1.1.4 Digital Processing Section FIG. 6 is a block diagram showing an example of the configuration of a digital processing unit according to the first embodiment.

[0065] As shown in FIG. 6, the digital processing unit 40 includes a preprocessing unit 41, a memory 42, a synthesis calculation unit 43, and a distance measurement unit 44.

[0066] The pre-processing unit 41 includes, for example, a finite impulse response filter (FIR filter) and a bit shifter, and performs pre-processing on the digital signal input from the analog processing unit 33. Specifically, the pre-processing unit 41 shapes the digital signal by the FIR filter. Then, the pre-processing unit 41 reduces the digit of the signal value increased by the FIR filter by the bit shifter. This makes it possible to shape the component corresponding to the laser pulse in the digital signal while suppressing an increase in the amount of memory required for storing data. The digital signal shaped by the pre-processing unit 41 is stored in the memory 42 as received light data. Note that the digital signal shaped by the pre-processing unit 41 may be directly passed to the synthesis calculation unit 43 without passing through the memory 42.

[0067] The memory 42 stores the light reception data generated by the pre-processing unit 41 for each pixel PX. The light reception data is stored, for example, as time-series data associated with the sampling time in the ADC in the analog processing unit 33. The memory 42 has a data capacity corresponding to at least two light reception sequences.

[0068] The synthesis calculation unit 43 executes synthesis calculation based on the light reception data stored in the memory 42. When the memory 42 does not store the light reception data, the synthesis calculation unit 43 executes synthesis calculation based on the light reception data passed from the pre-processing unit 41. In the first embodiment, the synthesis calculation unit 43 generates synthesis data (addition data) by performing weighted addition of two pieces of light reception data corresponding to two consecutive light reception sequences. That is, the size of the addition data is equivalent to one piece of light reception data corresponding to one light reception sequence. The two pieces of light reception data used to generate the addition data correspond to two types of output light Le that differ in at least one of the pulse width and the peak. The synthesis calculation unit 43 outputs the generated addition data to the distance measurement unit 44. Details of the calculation process by the synthesis calculation unit 43 will be described later.

[0069] The distance measurement unit 44 measures the distance between the distance measurement device 1 and the target TG based on the sampling time at the rising edge of the peak included in the added data and the emission trigger received from the control unit 10, and generates distance measurement data. The distance measurement unit 44 sends the generated distance measurement data to an external image processing circuit.

[0070] 1.2 Operation Next, the distance measurement operation in the distance measurement device according to the first embodiment will be described.

[0071] In the distance measurement operation of the distance measurement device according to the first embodiment, the light receiving unit 30 receives reflected light Lr corresponding to one laser pulse per light receiving sequence. The digital processing unit 40 generates sum data based on two pieces of light receiving data received in two consecutive light receiving sequences.

[0072] 1.2.1 Flowchart Fig. 7 is a flowchart showing an example of a distance measurement operation in the distance measurement device according to the first embodiment. Fig. 7 shows one cycle of processing from generation of multiple laser pulses to generation of one piece of distance measurement data corresponding to the multiple laser pulses.

[0073] When the distance measurement operation starts (START), the emission unit 20 emits a first laser pulse (emitted light Le) (S1).

[0074] The light receiving unit 30 receives the reflected light Lr of the first laser pulse emitted in the process of S1 in a first light receiving sequence (S2). The first light receiving data obtained in the process of S2 is stored in the memory 42.

[0075] After the process of S2, the emission unit 20 emits a second laser pulse that is different from the first laser pulse emitted in the process of S1 in at least one of the peak and the pulse width (S3).

[0076] The light receiving unit 30 receives the reflected light Lr of the second laser pulse emitted in the process of S3 in a second light receiving sequence following the first light receiving sequence (S4). The second light receiving data obtained in the process of S4 is stored in a memory area of ​​the memory 42 different from the memory area in which the first light receiving data is stored. Alternatively, the digital signal shaped by the pre-processing unit 41 may be directly passed to the synthesis calculation unit 43 without passing through the memory 42.

[0077] The synthesis calculation unit 43 generates added data by weighting the first light reception data obtained in the process of S2 and the second light reception data obtained in the process of S4 (S5). In the addition process, the synthesis calculation unit 43 may multiply each of the first light reception data and the second light reception data by a weighting coefficient of any magnitude. The weighting coefficient applied to the first light reception data and the weighting coefficient applied to the second light reception data may be equal to or different from each other. The calculation process by the synthesis calculation unit 43 may be performed, for example, on a memory area in which the first light reception data is stored. The second light reception data may be used to generate added data in the distance measurement operation of the next cycle, and therefore may be maintained in a state stored in the memory 42.

[0078] The distance measurement unit 44 generates distance measurement data based on the sum data obtained in the process of S5 (S6). Specifically, the distance measurement unit 44 generates distance measurement data based on the time difference between the emission trigger time notified from the control unit 10 and the sampling time at the rise of the peak included in the sum data.

[0079] When the process of S6 ends, the distance measurement operation ends (ends).

[0080] 1.2.2 Waveform diagram Fig. 8 is a waveform diagram showing an example of various signals related to the distance measurement operation in the distance measurement device according to the first embodiment. The upper part (A) of Fig. 8 shows the first laser pulse and the second laser pulse, which respectively correspond to the processes of S1 and S3 in Fig. 7. The middle part (B) of Fig. 8 shows the first light reception data and the second light reception data, which respectively correspond to the processes of S2 and S4 in Fig. 7. The lower part (C) of Fig. 8 shows the added data generated in the process of S5 in Fig. 7.

[0081] At time t1, a first laser pulse is emitted. The first laser pulse has a peak I1 and a pulse width W1.

[0082] From time t2 to time t3, the light receiving unit 30 executes a first light receiving sequence corresponding to a first laser pulse. In response to the first light receiving sequence, the first light receiving data Da is stored in the memory 42. The luminance of the first light receiving data Da has a peak B1.

[0083] At time t4, a second laser pulse is emitted. The second laser pulse has a peak I2 and a pulse width W2. At least one of the peak I2 and the pulse width W2 is different from the peak I1 and the pulse width W1. The pulse width of the laser pulse with the lower peak is shorter than the pulse width of the laser pulse with the higher peak. The example of FIG. 8 shows a case where the peak I2 of the second laser pulse is lower than the peak I1 of the first laser pulse, and the pulse width W2 of the second laser pulse is shorter than the pulse width W1 of the first laser pulse.

[0084] When the measurable distance is 300 m, the emission interval T1 from the first laser pulse to the second laser pulse is set to about 4 μs. The control unit 10 is configured to finely adjust the emission interval T1 with a time resolution shorter than the sampling time (e.g., 2.5 ns) in the light receiving unit 30.

[0085] From time t4 to time t5, the light receiving unit 30 executes a second light receiving sequence corresponding to a second laser pulse. The interval of the first light receiving sequence (period from time t2 to time t3) is approximately equal to the interval of the second light receiving sequence (period from time t4 to time 5). In response to the second light receiving sequence, the memory 42 stores second light receiving data Db. The luminance of the second light receiving data Db has a peak B2. When the peak I2 of the second laser pulse is lower than the peak I1 of the first laser pulse, the peak B2 of the second light receiving data Db is lower than the peak B1 of the first light receiving data Da. The slew rate of the light receiving data may change depending on the luminance. Therefore, each of the first light receiving data Da and the second light receiving data Db is corrected depending on the luminance.

[0086] Thereafter, the synthesis calculation unit 43 performs weighted addition on the first light reception data Da and the second light reception data Db to generate added data Dc.

[0087] The distance measurement unit 44 extracts a sampling time t7 at which the luminance of the added data Dc exceeds a threshold value Bth. The distance measurement unit 44 generates distance measurement data by calculating a time difference Δt between the time t7 and the rising time t1 of the laser pulse.

[0088] 8, the sampling time of the sum data Dc is associated with the sampling time of the first light reception data Da, but this is not limited thereto. For example, the sampling time of the sum data Dc may be associated with the sampling time of the second light reception data Db. In this case, the distance measurement unit 44 generates distance measurement data by calculating the time difference Δt between time t7 and the rising time t2 of the laser pulse.

[0089] 1.3 Effects of this embodiment According to the first embodiment, the emission unit 20 emits two types of laser pulses that differ in at least one of the peak and the pulse width. The synthesis calculation unit 43 performs weighted addition of the first light reception data Da corresponding to the first laser pulse and the second light reception data Db corresponding to the second laser pulse. The distance measurement unit 44 measures the distance to the target TG based on the added data. This makes it possible to improve the distance measurement accuracy while suppressing an increase in hardware size.

[0090] To supplement, the main factors of distance measurement error in LiDAR include errors due to insufficient time resolution and errors dependent on the amount of received light. If an attempt is made to interpolate the received light data to improve errors due to insufficient time resolution, the size of the hardware required for the interpolation process of the received light data (e.g., ADC, memory, and distance measurement calculation unit) increases. If an attempt is made to emit multiple laser pulses with different energies and measure the distance for each laser pulse in order to improve errors dependent on the amount of received light, the SNR decreases because low-energy laser pulses do not substantially contribute to the measurement during long-distance distance measurement. In addition, a solution to one issue may not be a solution to the other issue.

[0091] According to the first embodiment, the distance measurement is performed based on the sum of data from multiple light receptions. This makes it possible to suppress an increase in the hardware size required for processing the light reception data while improving the interpolation error. In addition, the energy of the laser pulse can be contributed to substantially all measurements, regardless of the measurement distance. This contributes to improving both the error due to insufficient time resolution and the error dependent on the amount of received light.

[0092] In addition, when the peak of one of two types of laser pulses differs from the peak of the other laser pulse, the pulse width of the one laser pulse is shorter than the pulse width of the other laser pulse. This makes it possible to suppress deterioration of the distance measurement accuracy even when the light reception data based on the laser pulse with a low peak, such as in short-distance distance measurement, significantly affects the distance measurement accuracy.

[0093] Furthermore, the emission unit 20 controls the emission interval T1 of the two types of laser pulses with a time resolution shorter than the sampling time of the light reception data in the analog processing unit 33. This makes it possible to optimize the emission interval T1 to a value that can suppress a decrease in distance measurement error according to an increase in the amount of received light.

[0094] 2. Second embodiment Next, a distance measurement device according to a second embodiment will be described. The second embodiment differs from the first embodiment in that a plurality of laser pulses are received in one light receiving sequence. The following mainly describes configurations and operations that differ from the first embodiment. Descriptions of configurations and operations equivalent to those of the first embodiment will be omitted as appropriate.

[0095] 2.1 Laser pulse emission interval In the second embodiment, the distance measurement device 1 is configured to emit multiple laser pulses at intervals shorter than the measurable distance. Specifically, for example, when the measurable distance is 300 m, the emission interval of multiple consecutive laser pulses is set to about 100 ns.

[0096] The control unit 10 is configured to finely adjust the emission interval with a time resolution shorter than the sampling time in the light receiving unit 30 (for example, 2.5 ns).

[0097] 2.2 Synthesis operation section FIG. 9 is a block diagram showing an example of the configuration of the synthesis calculation unit according to the second embodiment.

[0098] 9, the synthesis calculation unit 43 according to the second embodiment includes an FIR filter that receives received light data as input and outputs convolution data. Specifically, the synthesis calculation unit 43 according to the second embodiment includes a delay circuit 71, multipliers 72 and 73, and an adder 74.

[0099] The delay circuit 71 has an input terminal to which the received light data is supplied, and an output terminal connected to the input terminal of the multiplier 73. The delay circuit 71 has a function of delaying the input data by the emission interval between the first laser pulse and the second laser pulse, and outputting the data. Specifically, when the emission interval and the sampling time are 100 ns and 2.5 ns, respectively, the delay circuit 71 is configured to delay the input data by 100 / 2.5=40 samples, and output the data.

[0100] The multiplier 72 has an input terminal to which the received light data is supplied, and an output terminal connected to a first input terminal of the adder 74. The multiplier 72 has a function of amplifying or multiplying the input data by a coefficient H0 and outputting the result from the output terminal.

[0101] The multiplier 73 has an input terminal connected to the output terminal of the delay circuit 71, and an output terminal connected to a second input terminal of the adder 74. The multiplier 73 has a function of amplifying or multiplying input data by a coefficient H1 and outputting the result from the output terminal.

[0102] That is, the coefficients H0 and H1 are tap coefficients of the FIR filter. The ratio of the coefficients H0 and H1 is set to be approximately equal to the ratio of the peak I1 of the first laser pulse to the peak I2 of the second laser pulse, but is not limited thereto. The values ​​of the coefficients H0 and H1 may be set independently of each other.

[0103] Adder 74 has a first input terminal connected to the output terminal of multiplier 72, a second input terminal connected to the output terminal of multiplier 73, and an output terminal. Adder 74 outputs the convolution data from the output terminal.

[0104] 2.3 Flowchart Fig. 10 is a flowchart showing an example of a distance measurement operation in the distance measurement device according to the second embodiment. Fig. 10 corresponds to Fig. 7 in the first embodiment.

[0105] When the distance measurement operation starts (START), the emission unit 20 emits a first laser pulse (S11).

[0106] Next, the emission unit 20 emits a second laser pulse having at least one of the peak and the pulse width different from that of the first laser pulse emitted in the process of S11 (S12).

[0107] The light receiving unit 30 collectively receives the reflected light Lr of the first laser pulse and the second laser pulse emitted in the process of S11 in one light receiving sequence (S13). The collective light receiving data obtained in the process of S13 is stored in the memory 42.

[0108] The synthesis operation unit 43 performs a convolution operation on the batch light reception data obtained in the process of S13 to generate convolution data (S14).

[0109] The distance measurement unit 44 generates distance measurement data based on the convolution data obtained in the process of S14 (S15). Specifically, the distance measurement unit 44 generates distance measurement data based on the time difference between the emission trigger time notified from the control unit 10 and the sampling time at the rise of the peak included in the convolution data.

[0110] When the process of S15 ends, the distance measurement operation ends (ends).

[0111] 2.4 Waveform diagram Fig. 11 is a waveform diagram showing an example of various signals related to the distance measurement operation in the distance measurement device according to the second embodiment. Fig. 11 corresponds to Fig. 8 in the first embodiment. The upper part (A) of Fig. 11 shows the first laser pulse and the second laser pulse corresponding to the processes of S11 and S12 in Fig. 10, respectively. The middle part (B) of Fig. 11 shows batch light reception data corresponding to the process of S13 in Fig. 10. The lower part (C) of Fig. 11 shows convolution data generated in the process of S14 in Fig. 10.

[0112] At time t11, a first laser pulse is emitted. The first laser pulse has a peak I1 and a pulse width W1.

[0113] At time t12, a second laser pulse is emitted. The second laser pulse has a peak I2 and a pulse width W2. The relationship between the peaks I1 and I2 and the pulse widths W1 and W2 is the same as in the first embodiment. The example of FIG. 11 shows a case where the peak I2 of the second laser pulse is lower than the peak I1 of the first laser pulse, and the pulse width W2 of the second laser pulse is shorter than the pulse width W1 of the first laser pulse.

[0114] As described above, when the measurable distance is 300 m, the emission interval T2 from the first laser pulse to the second laser pulse is set to about 100 ns. The control unit 10 is configured to finely adjust the emission interval T2 with a time resolution shorter than the sampling time (e.g., 2.5 ns) in the light receiving unit 30.

[0115] From time t13 to time t14, the light receiving unit 30 executes a batch light receiving sequence for receiving the first laser pulse and the second laser pulse collectively. In response to the batch light receiving sequence, the memory 42 stores batch light receiving data Dd. The brightness of the batch light receiving data Dd has a peak B1 corresponding to the first laser pulse and a peak B2 corresponding to the second laser pulse. When the peak I2 of the second laser pulse is lower than the peak I1 of the first laser pulse, the peak B2 of the part of the batch light receiving data Dd corresponding to the second laser pulse is smaller than the peak B1 of the part of the batch light receiving data Dd corresponding to the first laser pulse. The slew rate of the light receiving data may change depending on the brightness. Therefore, the part of the batch light receiving data Dd corresponding to the first laser pulse and the part corresponding to the second laser pulse are each corrected according to the brightness.

[0116] Thereafter, the synthesis operation unit 43 executes a convolution operation on the collective light reception data Dd using the coefficients H0 and H1 to generate convolution data De.

[0117] As described above, the delay time of the delay circuit 71 in the synthesis calculation unit 43 is set to be approximately equal to the emission interval T2. As a result, peaks appear in the convolution data De at the sampling time corresponding to the first laser pulse, the sampling time corresponding to the second laser pulse, and the sampling time symmetrical to the sampling time corresponding to the first laser pulse with respect to the sampling time corresponding to the second laser pulse. Here, as described above, if the ratio of the coefficient H0 of the multiplier 72 and the coefficient H1 of the multiplier 73 in the synthesis calculation unit 43 is made approximately equal to the ratio of the peaks I1 and I2 (for example, 10:1), the peak corresponding to the second laser pulse becomes the largest among these three peaks.

[0118] The distance measurement unit 44 extracts a sampling time t15 at which the maximum peak brightness of the convolution data De exceeds a threshold value Bth. The distance measurement unit 44 generates distance measurement data by calculating a time difference Δt between the time t15 and the rising time t12 of the laser pulse.

[0119] 2.3 Effects of this embodiment According to the second embodiment, the emission unit 20 is configured to generate the light reception data corresponding to the first laser pulse and the light reception data corresponding to the second laser pulse collectively as batch light reception data. This allows the distance measurement unit 44 to generate distance measurement data based on the batch light reception data generated in one light reception sequence. This allows the time required to generate distance measurement data to be shorter than when distance measurement data is generated based on two pieces of light reception data generated in two light reception sequences.

[0120] The synthesis calculation unit 43 also includes an FIR filter and performs a convolution calculation on the batch light reception data. The convolution calculation is performed based on the emission interval T2 between the first laser pulse and the second laser pulse. This allows the synthesis calculation unit 43 to generate convolution data having a maximum peak at a sampling time corresponding to one of the portion corresponding to the first laser pulse and the portion corresponding to the second laser pulse that appear in the batch light reception data. This allows distance measurement using two laser pulses to be performed without deteriorating the SNR, thereby improving distance measurement accuracy.

[0121] 3. Modifications In the above-described first embodiment, a case has been described in which the first light reception data and the second light reception data are stored in different memory areas in the memory 42, respectively, and then added together with a predetermined weighting coefficient in the synthesis calculation unit 43, but this is not limiting. For example, the first light reception data and the second light reception data may be multiplied by a predetermined weighting coefficient, respectively, and then added together and stored in the same memory area in the memory 42. This allows the hardware size of the memory 42 to be further reduced.

[0122] In the above-mentioned first and second embodiments, the case where the peak I1 of the first laser pulse is higher than the peak I2 of the second laser pulse has been described, but this is not limited thereto. For example, the peak I1 of the first laser pulse may be lower than the peak I2 of the second laser pulse. In this case, the pulse width W1 of the first laser pulse is shorter than the pulse width W2 of the second laser pulse.

[0123] For example, when the distance to the target is short, the brightness of the reflected light corresponding to the laser pulse with a high peak increases, and the output current time during reception may increase excessively. Therefore, in the second embodiment in which the emission interval T2 is relatively short, if the peak I1 of the first laser pulse is higher than the peak I2 of the second laser pulse, the output current time corresponding to the first laser pulse may interfere with the output current corresponding to the second laser pulse. In order to suppress such an increase in the output current time corresponding to the first laser pulse, it is possible to make the peak I1 of the first laser pulse lower than the peak I2 of the second laser pulse.

[0124] In the above-described first and second embodiments, a single piece of distance measurement data is generated based on two laser pulses, but the present invention is not limited to this. For example, a single piece of distance measurement data may be generated based on three or more laser pulses.

[0125] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0126] 1. Distance measuring device 10...Control section 20…Emission section 21, 22...Drive circuit 23…Light source 24...Optical system 25…Mirror 30...Light receiving section 31...Optical system 32...Photodetector 33...Analog processing section 40...Digital processing unit 41...Pretreatment section 42…Memory 43...Synthesis operation section 44…Distance measurement section 71...Delay circuit 72,72…Multiplier 74...Adder< / m> < / m> < / m> < / m> < / m> < / n> < / n> < / m> < / m>

Claims

1. an emission unit that emits pulsed light; a photodetector for detecting reflected light of the pulsed light from an object; an analog processing unit that generates light reception data based on the detected reflected light; a digital processing unit for measuring a distance to the object based on the received light data; Equipped with the emission unit is configured to emit a first pulsed light and a second pulsed light having at least one of a peak and a pulse width different from those of the first pulsed light in this order, The digital processing unit includes: adding first light reception data corresponding to the first pulsed light and second light reception data corresponding to the second pulsed light; measuring the distance based on the added data; It was configured as follows: Distance measuring device.

2. When a first peak of the first pulsed light is higher than a second peak of the second pulsed light, a first pulse width of the first pulsed light is longer than a second pulse width of the second pulsed light.

2. The distance measuring device according to claim 1.

3. The emission unit is configured to emit the second pulsed light after the first light reception data is generated.

2. The distance measuring device according to claim 1.

4. The digital processing unit includes: performing weighted addition on the first light reception data and the second light reception data; The distance is measured based on the weighted sum data. It was configured as follows:

4. The distance measuring device according to claim 3.

5. In the weighted averaging calculation, a first coefficient corresponding to the first light reception data is independent of a second coefficient corresponding to the second light reception data.

5. The distance measuring device according to claim 4.

6. The analog processing unit is configured to generate the first light reception data and the second light reception data collectively.

2. The distance measuring device according to claim 1.

7. The digital processing unit includes: Including a finite impulse response filter (FIR filter), The first light receiving data and the second light receiving data are input to the FIR filter to perform a convolution operation; determining the distance based on the convolved data; It was configured as follows:

7. The distance measuring device according to claim 6.

8. The digital processing unit is configured to execute the convolution operation based on an emission interval between the first pulsed light and the second pulsed light.

8. The distance measuring device according to claim 7.

9. The FIR filter has third and fourth coefficients that are independent of each other.

8. The distance measuring device according to claim 7.

10. a first peak of the first pulsed light is lower than a second peak of the second pulsed light; 7. The distance measuring device according to claim 6.

11. The control unit is further configured to adjust an emission interval between the first pulsed light and the second pulsed light from the emission unit with a time resolution shorter than a sampling time of the received light data in the analog processing unit.

2. The distance measuring device according to claim 1.

12. The analog processing unit includes an analog to digital converter (ADC) or a time-correlated single photon counter (TCSPC), 2. The distance measuring device according to claim 1.

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