Measurement device, processing device, and measurement method

Abstract

[Problem] To provide a compact measurement device with which information related to an object, such as distance, may be obtained with high precision. [Solution] The measurement device includes: a light-emitting element array 111; a light-receiving element array 121; and a light-separating element 150 that includes a separating part 151 for separating light from the light-emitting element array into reference light to be guided to the light-receiving element array and irradiating light for irradiating an object via an optical system 130, in which signal light, which is a portion of the irradiating light that is reflected by the object and incident via the optical system, is guided to the light-receiving element array by the light-separating element via the separating part. Information related to the object is acquired by using a first time from a light emission instruction given to the light-emitting element array to reception of the reference light at the light-receiving element array and a second time from the light emission instruction to reception of the signal light at the light-receiving element array. The measurement device includes a reflecting means 152 that reflects reference light from the separating part back to the separating part, and the reference light from the reflecting means is guided to the light-receiving element array via the separating part.

Description

Measurement device, processing device, and measurement method

[0001] The present invention relates to a measurement device using a ToF (Time of Flight) method.

[0002] In the ToF method, the distance to an object is measured based on the time between irradiating the object with light and detecting the light reflected from the object. Patent Document 1 discloses a measurement device that has a detector that detects a portion of the light irradiated from a laser light source as reference light and a detector that detects signal light generated when the irradiated light is reflected from the object, and that improves distance measurement accuracy by using the cross-correlation between the reference light and the signal light.

[0003] JP 2014-174069 A

[0004] However, the measurement device of Patent Document 1 requires an optical system for detecting the reference light in addition to an optical system for receiving the signal light, which increases the size of the device.

[0005] The present invention provides a small-sized measurement device and a measurement method that can obtain information about an object, such as distance, with high accuracy.

[0006] A measurement device and a measurement method according to one aspect of the present invention include a light-emitting element array including a plurality of light-emitting elements, a light-receiving element array including a plurality of light-receiving elements, an optical system, and a separation unit that separates light from the light-emitting element array into illumination light that is irradiated onto an object via the optical system and reference light that is guided to the light-receiving element array, and a light separation element that guides signal light that is reflected from the object and enters via the optical system to the light-receiving element array via the separation unit. The measurement device and method further include processing means for acquiring information about the object using a first time period from an instruction to emit light to the light-emitting element array until the light-receiving element array receives the reference light and a second time period from the instruction to emit light until the light-receiving element array receives the signal light. The measurement device and the method further include reflecting means that reflects the reference light from the separation unit back to the separation unit, and guides the reference light from the reflecting means to the light-receiving element array via the separation unit. Note that a processing device that includes the above-described measurement device and performs processing using information about the object also constitutes another aspect of the present invention.

[0007] According to the present invention, it is possible to provide a small-sized measuring device and a measuring method that can obtain information about an object, such as distance, with high accuracy.

[0008] 8 is a block diagram showing the configuration of a distance measuring device according to the first embodiment. FIG. 9 is a diagram showing the configuration of a light source unit and a light source control unit according to the first embodiment. FIG. 10 is a diagram showing the configuration of a measurement unit according to the first embodiment. FIG. 11 is a diagram showing the configuration of a pixel of a light receiving element array according to the first embodiment. FIG. 12 is a diagram showing the configuration of a TDC array section of the measurement unit. FIG. 13 is a diagram showing the configuration of an oscillator in a TDC in the TDC array section. FIG. 14 is a diagram showing an output signal of a buffer in the TDC and an internal signal of an oscillator. FIG. 15 is a diagram showing changes in a SPAD cathode potential, a pixel output signal, a synchronization clock, a synchronization clock count value, an oscillation start / stop signal, an oscillator output, and an oscillation count value according to the first embodiment. FIG. 16 is an enlarged view of a portion of FIG. 11. FIG. 17 is a diagram showing a configuration of an oscillation adjustment voltage generation circuit according to the first embodiment. FIG. 18 is a diagram showing a beam splitter, a light emitting element array, a light receiving element array, and an imaging lens according to the first embodiment. FIG. 19 is a flowchart showing distance measuring processing according to the first embodiment. FIG. 19 is a diagram showing histograms of reference light and signal light according to the first embodiment. FIG. 19 is a diagram showing a beam splitter, a light emitting element array, a light receiving element array, and an imaging lens according to the second embodiment. FIG. 19 is a diagram showing histograms of reference light and signal light according to the second embodiment.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] 1 shows the configuration of a distance measuring device as a measurement device according to embodiment 1 of the present invention. Solid lines connecting components in the figure indicate signal exchange, dashed lines indicate irradiated light projected (irradiated) onto an object, and dashed lines indicate signal light that is reflected from the object.

[0011] The distance measuring device is composed of a light projection unit 110, a measurement unit 120, an imaging lens 130 as an optical system, an overall control unit 140 as a processing means, and a beam splitter 150 as a light separation element. The light projection unit 110 is composed of a light source unit 113 and a light source control unit 114, which include a light-emitting element array 111 in which a plurality of light-emitting elements are arranged in a two-dimensional array and a light-emitting element drive unit 112 that drives each light-emitting element.

[0012] The measurement unit 120 is composed of a light receiving element array 121 including a plurality of light receiving elements, a TDC (Time-to-Digital Converter) array section 122, a signal processing section 123, a measurement control section 124, and a row selection circuit 125. In the light receiving element array 121, the plurality of light emitting elements are two-dimensionally arranged to form a plurality of rows.

[0013] It is desirable to place a bandpass filter on the light receiving element array, which transmits light in a wavelength range that includes the wavelength of the light emitted from each light emitting element and reflects or absorbs light in other wavelength ranges.

[0014] The beam splitter 150 has a half mirror 151 as a separating section that transmits part of the incident light and reflects the rest, and a reflecting structure section 152 as a reflecting means.

[0015] Illumination light as pulsed light emitted from the plurality of light-emitting elements of the light-emitting element array 111 in the light source unit 113 is projected in different directions in space via the imaging lens 130. Signal light of the illumination light reflected by an object in space is received via the imaging lens 130 by a light-receiving element, among the plurality of light-receiving elements in the light-receiving element array 121, that corresponds to the light-emitting element that emitted light. In the light-receiving element array 121, the plurality of light-receiving elements are two-dimensionally arranged to form a plurality of rows.

[0016] The time of flight (ToF) is the time from when the light-emitting element emits light until the signal light is received by the light-receiving element. This time of flight is calculated using the measurement results from the TDC array unit 122. To reduce distance measurement errors due to noise components caused by ambient light and dark counts, noise within the measurement circuit, and delays in light emission from the light-emitting element after the light-emission command (start of time counting), the system repeatedly emits irradiated light and counts the time. The signal processing unit 123 then creates a histogram of the measurement results, removes noise components, and averages the measurement results. The light-emission delay time from the light-emission command varies due to individual differences and temperature characteristics of the light-emitting element driver unit 112, light-emitting element, light-receiving element, TDC array unit 122, and buffers in the signal transmission path. Therefore, a portion of the irradiated light actually emitted from the light-emitting element is detected as reference light, and the time of flight ToF is calculated by subtracting the light-emission delay time from the light-emission command time to the reference light detection time from the time from the light-emission command time to the signal light detection time.

[0017] By substituting the thus determined time of flight ToF into the following equation (1), the distance L to the object can be determined with high accuracy: In equation (1), c is the speed of light.

[0018] L=ToF×c / 2 (1) It should be noted that by using ToF, not only distance information (L) to an object but also information about the object including the shape of the object can be acquired.

[0019] 2 shows an example of the configuration of the light source unit 113 and light source control unit 114 that constitute the light projection unit 110. In the light-emitting element array 111, a plurality of VCSELs (Vertical Cavity Surface Emitting Lasers) are arranged in a two-dimensional array to form a plurality of rows on a substrate as light-emitting elements 201. The light-emitting element drive circuit 112 is configured to arrange row drive circuits 202 in a one-dimensional array.

[0020] The light-emitting element is not limited to a VCSEL, but is preferably one that can be integrated in a one-dimensional or two-dimensional array. Examples include an edge-emitting laser and an LED (light-emitting diode). When an edge-emitting laser is used as the light-emitting element instead of a VCSEL array, the light-emitting element array can be a laser bar array that is one-dimensionally arranged on a substrate, or a laser bar stack that is stacked to form a two-dimensional light-emitting element array. Furthermore, when an LED is used as the light-emitting element, a substrate can be used in which the LEDs are arranged in a two-dimensional array.

[0021] In the distance measuring device of this embodiment, the wavelength of light emitted by the light-emitting element is preferably in the near-infrared band to suppress the effects of ambient light. In this case, the VCSEL is fabricated using a semiconductor process with materials used in conventional edge-emitting lasers and surface-emitting lasers, and GaAs-based semiconductor materials can be used as the main material when emitting light with a wavelength in the near-infrared band. In this case, the dielectric multilayer film forming the DBR (distributed Bragg reflector) reflector constituting the VCSEL can be composed of two thin films made of materials with different refractive indices alternately and periodically stacked (GaAs / AlGaAs). The wavelength of the light emitted from the VCSEL can be changed by adjusting the elemental combination and composition of the compound semiconductor.

[0022] Each VCSEL constituting the VCSEL array is provided with an electrode for injecting current and holes into the active layer. The electrode is shared by multiple VCSELs in the row direction and connected to a row drive circuit 202 arranged in each row. By operating only a specific row drive circuit 202 among the light-emitting element drive circuits 112, current is injected only into multiple VCSELs (first light-emitting elements) belonging to a specific row (light-emitting element row), making it possible to cause the multiple VCSELs in the specific row to emit light simultaneously.

[0023] By switching the row drive circuit 202 in operation, it is possible to sequentially cause the VCSELs in multiple rows to emit light row by row.

[0024] 3 shows the configuration of the measurement unit 120. The measurement unit 120 includes a light-receiving element array 121 having a plurality of pixels 301 arranged in a two-dimensional array, a TDC array section 122, a signal processing section 123, and a measurement control section 124. The measurement unit 120 further includes a row selection circuit 125 for enabling only specific rows, row selection pulse wiring 303 for outputting an output signal of the row selection circuit 125 to the pixels 301, and a pixel output line 304 for outputting a pixel output signal from the pixel 301 to the TDC array section 122.

[0025] 4 shows the configuration of a pixel 301. The pixel 301 is composed of a SPAD (Single Photon Avalanche Diode) 401, which is a light-receiving element, a load transistor 402, an inverter 403, a pixel output circuit 404, a row selection pulse line 303, and a pixel output line 304. The SPAD 401 has a light-receiving region and an avalanche region.

[0026] Light incident on the SPAD 401, i.e., photons, undergoes photoelectric conversion in its light-receiving region, generating electrons and holes. Positively charged holes are discharged via the anode electrode Vbd. Negatively charged electrons are transported as signal charges to the avalanche region by an electric field set in the light-receiving region so that the potential decreases toward the avalanche region. The signal charges that reach the avalanche region undergo avalanche breakdown due to the strong electric field in the avalanche region, generating an avalanche current.

[0027] When no avalanche current is flowing, the voltage of the anode electrode Vbd is set so that a reverse bias equal to or greater than the breakdown voltage is applied to the avalanche region of the SPAD 401. At this time, no current flows through the load transistor 402, so the cathode potential Vc is close to the power supply voltage Vdd, and the inverter output signal is "0."

[0028] When a photon strikes the SPAD 401 and an avalanche current is generated in the SPAD 401, the cathode potential Vc drops and the output of the inverter 403 is inverted. That is, the inverter output changes from "0" to "1." When the cathode potential Vc drops, the reverse bias applied to the SPAD 401 decreases, and when the reverse bias becomes equal to or lower than the breakdown voltage, the generation of the avalanche current stops.

[0029] Thereafter, when a hole current flows from the power supply voltage Vdd to the cathode potential Vc via the load transistor 402, the cathode potential Vc rises and the inverter output returns from "1" to "0", returning to the state before the arrival of the photon.

[0030] Furthermore, in a pixel 301 in which the row selection pulse wiring 303 is turned on, the output of the inverter 403 is controlled to be output from the pixel output circuit 404 to the pixel output line 304. In a pixel 301 in which the row selection pulse wiring 303 is turned off, the inverter output is controlled to be disconnected from the pixel output line 304. This makes it possible for the pixel 301 to detect only the light incident on the specific row (light receiving element row) selected by the row selection circuit 125.

[0031] In this way, pixel output signals corresponding to light detection in the plurality of pixels 301 belonging to the row selected by the row selection circuit 125 are output to the TDC array unit 122 as low-delay digital signals.

[0032] The TDC array unit 122 measures the time from when the light emitting element array 111 emits light until the pixel output signal changes from "0" to "1" as ToF.

[0033] 5 is a schematic diagram of the TDC array unit 122. The TDC array unit 122 is provided with TDCs 501 in a number twice the number of pixels 301 in the horizontal direction in the light receiving element array 121, and simultaneously measures pixel output signals from two rows of pixels 301. One of the two rows of pixels 301 is used as pixels that detect signal light from an object, and the other row of pixels 301 is used as pixels that detect reference light.

[0034] Each TDC 501 has an oscillator 511, an oscillation count circuit 521, and a synchronous clock count circuit 531. The count value in the synchronous clock count circuit 531 corresponds to the upper bits, the internal signal of the oscillator 511 corresponds to the lower bits, and the count value in the oscillation count circuit 521 corresponds to the intermediate bits therebetween. In other words, the pixel output signal is roughly measured by the synchronous clock count circuit 531, more precisely measured by the internal signal of the oscillator 511, and the intermediate bits are measured by the oscillation count circuit 521. Note that a configuration in which redundant bits are provided for each of the upper and intermediate bits may also be employed.

[0035] 6 shows a schematic configuration of the oscillator 511 of the TDC 501. The oscillator 511 has an oscillation start / stop signal generator 640, buffers 611 to 618, an oscillation switch 630, and a delay adjustment current source 620. The buffers 611 to 618 and the oscillation switch 630 are alternately connected in a loop of eight stages.

[0036] FIG. 7 shows the output signals of buffers 611 to 618 and the internal signal of oscillator 511 at reset, and the output signals of buffers 611 to 618 and the internal signal of oscillator 511 after a certain time has elapsed since oscillation switch 630 was turned on.

[0037] At the time of reset, the outputs of the buffers 611 to 617 are "0" and the output of the buffer 618 is "1". The delay time t ｂｕｆｆ After this time, the outputs of the buffers 612 to 618, which have input / output matching, do not change, and only the output of the buffer 611, which has input / output mismatch, changes from "0" to "1" (the signal advances by one stage). ｂｕｆｆ After the time has elapsed (2 x t ｂｕｆｆ After that, the outputs of the buffer 611 and the buffers 613 to 618, which have input / output matching, do not change, and only the output of the buffer 612, which has input / output mismatch, changes from "0" to "1." In this way, the delay time t ｂｕｆｆ The output of one buffer with mismatched input and output changes in sequence every 8×tｂｕｆｆ After that, the outputs of all the buffers 611 to 618 change (the signal goes around once), and 16×t ｂｕｆｆ After that, all the buffers change again (the signal goes around twice) and return to the original state. ｂｕｕｆ The same operation is repeated every time t ｂｕｆｆ The time measurement is performed at a time resolution of t ｂｕｆｆ is half the synchronous clock by the oscillation adjustment voltage generation circuit 541 described later. ７ It is adjusted to be.

[0038] The oscillator output, which is the output of the buffer 618, is input to an oscillation count circuit 521. The oscillation count circuit 521 counts the rising edges of the oscillator output, thereby achieving a time resolution of 16×t ｂｕｆｆ The time measurement is carried out.

[0039] 8 shows the changes in the SPAD cathode potential Vc, pixel output signal, synchronous clock, synchronous clock count value, output of the oscillation start / stop signal generator 640 (oscillation start / stop signal), oscillator output, and count value (oscillation count value) in the oscillation count circuit 521 from the time when the light-emitting element 201 belonging to a specific row of the light-emitting element array 111 emits light until the SPAD 401 receives light and the counting operation of the TDC 501 ends. The SPAD cathode potential Vc is an analog voltage, and the upper side in the figure is shown as a high potential. The synchronous clock, oscillation start / stop signal, and oscillator output are digital signals, and the upper side in the figure is shown as on and the lower side is shown as off. The synchronous clock count value and oscillator count value are digital values ​​and are shown as decimal numbers.

[0040] 9 shows the oscillation start / stop signal, oscillator output, oscillator count value, and internal signal (oscillator internal signal) of oscillator 511 from time 803 to time 805 in Fig. 8. The oscillator internal signal is a digital value and is expressed as a decimal number.

[0041] Using Figures 8 and 9, we will explain the measurement operation (TDC operation) of the TDC 501 from time 801 when the light-emitting element 201 belonging to a specific row of the light-emitting element array 111 emits light to time 803 when the SPAD 401 in the pixel 301 receives light (photons).

[0042] At time 801, which coincides with the rising edge of the synchronous clock supplied via the overall control unit 140 shown in Fig. 1, a light emission signal indicating an instruction to emit light is output from the overall control unit 140 to the light source unit 113. The synchronous clock count circuit 531 shown in Fig. 5 starts counting the rising edges of the synchronous clock from the time the light emission signal is input.

[0043] At time 803, when a photon reflected by an object is received by the SPAD 401, the SPAD cathode potential Vc drops, and the pixel output signal changes from "0" to "1." In response to the pixel output signal becoming "1," the oscillation start / stop signal changes from "0" to "1," and the oscillation switch 630 turns on. When the oscillation switch 630 turns on, the oscillator 511 starts oscillating, and a loop of the oscillator internal signal begins, as shown in FIG. 9. Every time the oscillator internal signal makes two cycles, a rising edge appears in the oscillator output, and the oscillator count circuit 521 counts the number of rising edges. Also at time 803, the synchronous clock count circuit 531 stops counting and holds the count value at that time.

[0044] The timing at which the synchronous clock first rises after the oscillation switch 630 is turned on is time 805. In response to the rising edge of the synchronous clock, the oscillation start / stop signal becomes "0" and the oscillation switch 630 turns off. When the oscillation switch 630 turns off, the oscillator 511 stops oscillating and the internal signal of the oscillator is held as is. Furthermore, as the oscillation stops, the counting in the oscillation count circuit 521 also stops.

[0045] By doing so, the synchronous clock count value D Ｇｃｌｋ The time from time 801 to time 802 is divided into two ７ ×tｂｕｆｆ The oscillation count value D ＲＯｃｌｋ The time from time 803 to time 804 is 2 ４ ×t ｂｕｆｆ The value is counted every time the oscillator internal signal D ＲＯｉｎ The time from time 804 to time 805 is t ｂｕｆｆ The TDC 501 counts these count values ​​D Ｇｃｌｋ , D ＲＯｃｌｋ and oscillator internal signal D ＲＯｉｎ The following process is performed using the count value D ＴｏＦ to the signal processing unit 123, thereby completing one TDC operation.

[0046] First, the oscillation count value D ＲＯｃｌｋ and oscillator internal signal D ＲＯｉｎ are added together as shown in the following equation (2).

[0047] D ＲＯ =2 ４ ×D ＲＯｃｌｋ +D ＲＯｉｎ (2) D ＲＯ The time from time 804 to time 805 is t ｂｕｆｆ The time from time 802 to time 805 is the period of the synchronous clock, which is 2 ７ ×t ｂｕｆｆ Therefore, as shown in the following equation (3), ＲＯ Subtract and the result is D Ｇｃｌｋ This adds up the flight time of light (the time from time 801 to time 803) to t ｂｕｆｆ Count value D counted every ＴｏＦ is required.

[0048] D ＴｏＦ =2 ７ ×D Ｇｃｌｋ　 + (2 ７ -D ＲＯ ) = 2 ７ ×D Ｇｃｌｋ　 + (2 ７ -24 x D ＲＯｃｌｋ -DＲＯｉｎ ) (3) Delay time for one buffer stage t ｂｕｆｆ varies due to process factors such as transistor manufacturing errors, fluctuations in the voltage applied to the TDC 501, and temperature. For this reason, as shown in FIG. 5, the TDC array unit 122 is provided with an oscillation adjustment voltage generation circuit 541. As shown in FIG. 10, the oscillation adjustment voltage generation circuit 541 is composed of a dummy oscillator 1001, a 1 / 23 frequency divider 1002, and a phase comparator 1003. The dummy oscillator 1001 is the same oscillator as the oscillator 511 mounted in the TDC 501.

[0049] The output of the dummy oscillator 1001 is 1 / 2 ３ Input to frequency divider 1002. ３ The frequency divider 1002 divides the input clock frequency by 2. ３ The phase comparator 1003 outputs a clock signal having a clock frequency of 1 / 2 the synchronous clock. ３ The clock signal from the frequency divider 1002 is input to the phase comparator 1003. The frequency of the synchronous clock is 1 / 2 ３ The output voltage of the phase comparator 1003 is input to the delay adjustment current source 620 of the oscillator 511, and the oscillation frequency of the oscillator 511 is adjusted to 2 times the frequency of the synchronous clock. ３ It is adjusted to double.

[0050] In this way, since the oscillation frequency of the oscillator 511 is determined based on the frequency of the synchronous clock, it is preferable to generate the synchronous clock based on the output (clock) from an external IC that can output a constant frequency regardless of the above-mentioned process factors, voltage fluctuations, and temperature, thereby suppressing the frequency variations of the synchronous clock due to the above-mentioned process factors, applied voltage, and temperature.

[0051] For example, by inputting a clock having a frequency of 160 MHz from an external IC as a synchronous clock to the oscillator 511, the oscillation frequency becomes 1.28 GHz, which is eight times the synchronous clock frequency. ｂｕｆｆ becomes 48.8 ps.

[0052] [Optical Paths of Reference Light and Signal Light] Figure 11(A) schematically shows the beam splitter 150, light-emitting element array 111, light-receiving element array 121, and imaging lens 130. The light-emitting element array 111 and the light-receiving element array 121 are in a conjugate relationship via the half mirror 151 of the beam splitter 150 (they are optically conjugate with each other with respect to the half mirror 151), and each light-emitting element and each light-receiving element are also in a one-to-one conjugate relationship, thereby corresponding to each other. The row numbers in the light-emitting element array 111 are assigned in ascending order from the smaller Yv side to the larger Y side in Figure 11(A), and the row numbers in the light-receiving element array 121 are assigned in ascending order from the smaller Y side to the larger Y side in the same figure. Light-emitting elements and light-receiving elements with the same row number are in a conjugate relationship.

[0053] 11A is merely an example, and other numbers of rows may be used. Furthermore, the configuration is not limited to a one-to-one conjugate relationship between the light-emitting element array 111 and the light-receiving element array 121. The number of light-receiving elements may be n×n times the number of light-emitting elements, and one light-emitting element may be conjugately connected to n×n light-receiving elements.

[0054] 11B shows the optical path of light emitted from a light-emitting element (first light-emitting element) in row number 1 of the light-emitting element array 111. Light 1110 emitted from the light-emitting element is split into irradiation light 1111 that is reflected by a half mirror 151 of the beam splitter 150 and irradiated onto an object, and reference light 1112 that passes through the half mirror 151 and travels toward a reflective structure portion 152 of the beam splitter 150.

[0055] 11C shows the optical path of reference light 1113 reflected by the reflective structure 152 back to the half mirror 151. FIG. 11D shows the optical path of signal light 1114 reflected back from an object illuminated with irradiation light. The signal light 1114 from the object is incident on a light receiving element (first light receiving element) that is conjugate with the light emitting element that emitted the light. Meanwhile, the reference light 1113 reflected by the half mirror 151 is incident on a light receiving element (second light receiving element) in a row adjacent to the row of light receiving elements that are conjugate with the light emitting element that emitted the light.

[0056] The surface of the reflective structure 152 is provided with a structure that has a higher reflectance for light in a predetermined wavelength range, including the wavelength of light from the light-emitting element, than for light in other wavelength ranges, thereby transmitting and / or absorbing light in other wavelength ranges. This surface structure may be a structure in which dielectrics with different refractive indices are stacked, or a structure using an absorbing material such as metal. The reflective structure 152 has a triangular periodic structure with a period twice the spacing between the light-emitting elements in the row direction, and has the same shape in the depth direction perpendicular to the plane of the drawing. The reflective structure 152 may also be a semi-cylindrical periodic structure with the above period.

[0057] The reflective structure 152 having such a shape shifts the reflected reference light 1113 by one row relative to the incident reference light 1112 and returns it to the half mirror 151. Then, the reference light 1113 reflected by the half mirror 151 is incident on a light receiving element in a row adjacent to the row of light receiving elements that is conjugate with the light emitting element that emitted the light 1110. The row of light receiving elements that receives the reference light 1113 is the row that corresponds to the row that has a different Yv coordinate from the light emitting element that emitted the light, out of the two rows corresponding to the period of the reflective structure 152.

[0058] In the distance measurement process described below, distance measurement errors due to deviations in the light emission timing of the light-emitting element relative to the light emission instruction are reduced by subtracting the time from the output of the light emission instruction signal to the reception of the reference light 1113 from the time from the output of the light emission instruction signal to the reception of the signal light 1114. Note that although the light emitted from the light-emitting element in row number 1 has been described here, the same applies to the light emitted from the light-emitting elements in other row numbers.

[0059] 12 shows the distance measurement process (measurement method) executed by the overall control unit 140 via the light source control unit 114 and the measurement control unit 124. The overall control unit 140, the light source control unit 114, and the measurement control unit 124 may be configured as a single computer such as a CPU, or may be configured as separate computers.

[0060] First, in step 1201, the overall control unit 140 resets a row counter j to 1.

[0061] Next, in step 1202, the overall control unit 140 causes the row selection circuit 125 to select the row of pixels 301 corresponding to row counter j and its adjacent row via the measurement control unit 124. As a result, settings are made so that pixel output signals from the pixels 301 in the row that receive signal light and the pixels 301 in the adjacent row that receive reference light are output to the TDC array unit 122 via pixel output lines 304.

[0062] Next, in step 1203, the overall control unit 140 causes the measurement control unit 124 to reset the histogram circuits arranged in the signal processing unit 123, the number of which is the same as the TDCs. The overall control unit 140 also resets the measurement number counter i to 0.

[0063] Next, in step 1204, the overall control unit 140 outputs a light emission instruction signal to the light source control unit 114 to cause the light emitting elements belonging to the row corresponding to row counter j to emit light via the row drive circuit 202 of that row. Here, the overall control unit 140 outputs the light emission instruction signal and simultaneously causes the TDCs 501 of the corresponding row and its adjacent row in the TDC array unit 122 to start TDC operation via the measurement control unit 124.

[0064] Next, in step 1205, the overall control unit 140 determines whether the time from the output of the light emission command signal is equal to or less than Tmax, which is the time corresponding to the longest distance measurement distance, and if Tmax is exceeded, performs the processing of step 1209, which will be described later. If the time from the output of the light emission command signal is equal to or less than Tmax, the overall control unit 140 waits in step 1206 until the pixel output signal becomes "1".

[0065] During this waiting period, the signal light reflected by the object and returned is incident on and received by the light receiving element that is conjugate with the light emitting element that emitted the light. When this light reception causes the pixel output signal to become "1," in step 1207, the TDC 501 measures the time from when the light emitting element emitted light to when the light receiving element received the light.

[0066] Thereafter, in step 1208, the measurement results (TDC results) by the TDC 501 are stored in a histogram, and the process returns to the standby state. In the process from light emission in step 1204 to step 1209 (step 1216 indicated by the dashed line in the figure), each light-receiving element, TDC 501, and histogram circuit individually performs measurement and histogram calculation operations in response to changes in pixel output due to light reception.

[0067] On the other hand, in step 1209, the overall control unit 140 increments the measurement number counter i by one.

[0068] Next, in step 1210, the overall control unit 140 determines whether the value of the measurement number counter i has reached a predetermined number N ｔｏｔａｌ It is determined whether the value of the measurement counter i is greater than a predetermined number N ｔｏｔａｌ If it is smaller, the determination in step 1205 is performed again a predetermined number of times N ｔｏｔａｌ If it is greater, the process proceeds to step 1211 .

[0069] In step 1211, the overall control unit 140 causes the signal processing unit 123 to perform histogram processing via the measurement control unit 124 to calculate, from the histogram of the TDC result, a reference light time (first time) from the light emission instruction to the detection of the reference light and a signal light time (second time) from the light emission instruction to the detection of the signal light. In the histogram processing, the intensity of the signal light, the intensity of the ambient light, etc. are also calculated.

[0070] Next, in step 1212, the overall control unit 140 calculates (obtains) the ToF by subtracting the reference light time from the signal light time obtained in step 1211. Details of this subtraction process will be described later.

[0071] Next, in step 1213, the overall control unit 140 causes the measurement control unit 124 to calculate and acquire distance information by substituting the ToF calculated in step 1222 into equation (1). The processing from step 1202 to step 1213 completes distance measurement using one row of light-emitting / light-receiving elements.

[0072] Next, in step 1214, the overall control unit 140 increments the row counter j by one.

[0073] Next, in step 1215, the overall control unit 140 determines whether the row counter j is greater than a predetermined number of rows Nrow (for example, Nrow=8 as shown in FIG. 11A), and if it is less than the predetermined number of times Nrow, it performs the process of step 1204 again to measure the distance on the next row. When the row counter j reaches the predetermined number of rows Nrow and distance measurements on all rows are completed, the measurement process ends.

[0074] By the above-described distance measurement process, distance measurement results in a two-dimensional array form similar to image information can be obtained.

[0075] FIG. 13 shows the predetermined number of times N ｔｏｔａｌ 12 shows examples of a reference light histogram 1301 and a signal light histogram 1302 obtained by storing the TDC results for the reference light and the signal light in a histogram circuit. Time 1303 indicates the time when an emission instruction signal is output from the overall control unit 140. Time 1304 from time 1303 to the peak time of the reference light histogram 1301 is the reference light time from when the emission instruction signal is output until the light-emitting element actually emits light. Furthermore, time 1303 from time 1303 to the peak time of the signal light histogram 1302 is the signal light time 1305 from when the emission instruction signal is output until the signal light from the object is received. By subtracting the reference light time 1304 from the signal light time 1305 in step 1212 of FIG. 12 , highly accurate ToF, i.e., distance information to the object, can be obtained regardless of variations in the emission delay time of the light-emitting element from the emission instruction.

[0076] As described above, in this embodiment, the light-emitting elements in the light-emitting element array 111 are caused to emit light at different times for each row. The beam splitter 150 is also provided with a reflective structure 152 for guiding the reference light to a light-receiving element in a row different from the light-receiving element (light-receiving element that receives the signal light) in the light-receiving element array 121 in a row corresponding to the row of the light-emitting element that emitted light. As a result, the signal light and the reference light can be received by the light-receiving element in the row corresponding to the row of the light-emitting element that emitted light and the light-receiving element in the adjacent row, respectively. This enables highly accurate distance measurement to be performed in a compact distance measuring device, with the effect of light emission delays of the light-emitting elements reduced.

[0077] The light receiving elements that receive the reference light do not necessarily have to belong to an adjacent row to the light receiving elements that receive the signal light, that is, the reflective structure 152 only needs to reflect the reference light so that the reference light is guided to a light receiving element that is different from the light receiving elements that receive the signal light.

[0078] Furthermore, in the light-emitting element array, it is not necessary to sequentially emit light from the light-emitting elements in each row, but the light-emitting elements may be sequentially emitted from every two or more rows. In other words, it is sufficient to sequentially emit light from the light-emitting elements in every predetermined number of rows.

[0079] 14A schematically shows the beam splitter 150, light-emitting element array 111, light-receiving element array 121, and imaging lens 130 in Example 2. In this example, the light-emitting element array 111 and the light-receiving element array 121 are in a conjugate relationship via the half mirror 151 of the beam splitter 150, and each light-emitting element and each light-receiving element are also in a one-to-one conjugate relationship. The row numbers in the light-emitting element array 111 and the light-receiving element array 121 are the same as those described in FIG. 11A.

[0080] In this example, the reflecting structure 152′ provided on the beam splitter 150 differs from the reflecting structure 152 in Example 1. As described with reference to FIGS. 11B and 11C , the reflecting structure 152 in Example 1 had a structure that reflected the reference light 1112 (1113) incident on the reflecting structure 152 from the half mirror 151 so as to shift the light by one row. In contrast, the reflecting structure 152′ in Example 2 has a structure that does not shift the reference light by one row. The reflecting structure 152′ has a structure that transmits, absorbs, or both on its surface so that the reflectance for light in a predetermined wavelength range, including the wavelength of the light from the light-emitting element, is lower than the reflectance for light in other wavelength ranges. This surface structure may be a laminated structure of dielectrics with different refractive indices, or a structure using an absorptive material such as a metal.

[0081] As shown in FIG. 14B, light 1410 emitted from a light-emitting element (first light-receiving element) in row number 1 of the light-emitting element array 111 is separated into illumination light 1411 reflected by a half mirror 151 and reference light 1412 transmitted through the half mirror 151. The reference light 1412 is incident on a reflecting structure 152′. As shown in FIG. 14C, the reference light 1413 reflected by the reflecting structure 152′ is incident on the half mirror 151 along the same optical path as the reference light 1412 incident on the reflecting structure 152′, and is reflected by the half mirror 151 toward the light-receiving element array 121. As a result, as can be seen from FIGS. 14C and 14D, the reference light 1413 is incident on a light-receiving element (first light-receiving element) that is conjugate with the light-emitting element that emitted the light. In other words, the reference light 1413 is incident on the same light-receiving element as the light-receiving element onto which signal light 1414 from the object is incident.

[0082] 12 , the overall control unit 140 causes the row selection circuit 125 to select only the row of pixels 301 corresponding to row counter j via the measurement control unit 124. This causes settings to be made so that pixel output signals from the pixels 301 in the row that receives the signal light and the reference light are output to the TDC array unit 122 via the pixel output line 304.

[0083] FIG. 15 shows the predetermined number of times N ｔｏｔａｌ15 shows an example of a reference light / signal light histogram obtained by storing the TDC results of 1000 sigma in a histogram circuit. Time 1503 indicates the time when a light emission instruction signal is output from the overall control unit 140. In Example 1 ( FIG. 13 ), the reference light histogram 1301 and the signal light histogram 1302 were obtained using TDC results obtained from the pixels 301 in the row conjugate to the row of the light-emitting element that emitted light and the adjacent row. In contrast, in this example, the reference light / signal light histogram 1500, in which the reference light histogram and the signal light histogram are combined, is obtained using only the TDC results obtained from the pixels 301 in the row conjugate to the row of the light-emitting element that emitted light.

[0084] Reference light / signal light histogram 1500 includes two peaks. Peak 1501, which is the shorter peak from time 1503, is the reference light peak, and peak 1502, which is the longer peak from time 1503, is the signal light peak. Time 1504 from time 1503 to the reference light peak 1501 is the reference light time from when the light emission command signal is output until the light emitting element actually emits light. Furthermore, the time from time 1503 to the signal light peak 1502 is signal light time 1505 from when the light emission command signal is output until the signal light from the object is received. By subtracting reference light time 1504 from signal light time 1505 in step 1212 of FIG. 12 , highly accurate ToF, i.e., distance information to the object, can be obtained regardless of variations in the light emission delay time of the light emitting element from the light emission command.

[0085] As described above, in this embodiment, the light-emitting elements in the light-emitting element array 111 are caused to emit light at different times for each row. The beam splitter 150 is also provided with a reflective structure 152' for guiding the reference light to the light-receiving elements in the light-receiving element array 121 in a row corresponding to the row of the light-emitting element that emitted light. As a result, the signal light and the reference light can be received with a time lag by the light-receiving elements in the light-receiving element array 121 in a row corresponding to the row of the light-emitting element that emitted light. This enables highly accurate distance measurement to be performed in a compact distance measuring device, with reduced influence of delays in light emission of the light-emitting elements.

[0086] In the above embodiments, the reflective structures 152, 152' serving as reflective means are integrally provided on the beam splitter 150. However, similar reflective means may be provided separately from the beam splitter. In this case, the reflective means may be disposed in contact with or close to the beam splitter, thereby making it possible to reduce the size of the distance measuring device.

[0087] The distance measuring device (measurement device) described in the above embodiments can be included in a processing device that performs processing using distance information (information about an object) obtained from the distance measuring device, and is installed in various devices, including imaging devices such as cameras, electronic devices such as smartphones, and mobile devices such as automobiles. For example, in imaging devices and electronic devices, the processing device can perform focus control (AF) using distance data or generate a distance map within the angle of view, as described above. In mobile devices, the processing device can also form part of an ECU (Electronic Control Unit) that measures the distance to a leading vehicle, controls braking and steering by detecting obstacles, and issues warnings.

[0088] The present invention can also be realized by a process in which a program that realizes one or more 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., an ASIC) that realizes one or more functions.

[0089] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention.

Claims

1. A measuring device comprising: a light-emitting element array including a plurality of light-emitting elements; a light-receiving element array including a plurality of light-receiving elements; an optical system; a light separation element having a separation section which separates light from the light-emitting element array into illumination light which is irradiated onto an object via the optical system and reference light which is guided to the light-receiving element array, and which guides signal light of the illumination light which is reflected by the object and enters via the optical system to the light-receiving element array via the separation section; and processing means which acquires information about the object using a first time from an instruction to emit light to the light-emitting element array to the reception of the reference light at the light-receiving element array and a second time from the instruction to emit light to the reception of the signal light at the light-receiving element array, wherein the measuring device has a reflection means which reflects the reference light from the separation section back to the separation section, and is characterized in that the reference light from the reflection means is guided to the light-receiving element array via the separation section.

2. The measuring device according to claim 1, wherein said reflecting means is integrally provided on said light separating element.

3. The measurement device described in claim 1 or 2, characterized in that the reference light reflected by the object from the irradiation light from a first light-emitting element in the light-emitting element array is guided via the separation section to a first light-receiving element corresponding to the first light-emitting element in the light-receiving element array, and the reflecting means reflects the reference light from the first light-emitting element so that the reference light is guided via the separation section to a second light-receiving element different from the first light-receiving element in the light-receiving element array.

4. The measurement device described in claim 3, characterized in that in the light-emitting element array and the light-receiving element array, the multiple light-emitting elements and the multiple light-receiving elements are two-dimensionally arranged to form multiple light-emitting element rows and multiple light-receiving element rows, respectively, and in the light-emitting element array, simultaneous emission of the multiple first light-emitting elements belonging to the same light-emitting element row is performed sequentially for each predetermined number of light-emitting element rows, and the reflection means reflects the reference light from the multiple first light-emitting elements so that the reference light is guided via the separation section to the multiple second light-receiving elements belonging to a light-receiving element row different from the light-receiving element row corresponding to the light-emitting element row to which the multiple first light-emitting elements belong in the light-receiving element array.

5. A measuring device according to claim 3 or 4, characterized in that said reflecting means has a structure for shifting said reference light reflected by said reflecting means with respect to said reference light incident on said reflecting means.

6. The measurement device described in claim 1 or 2, characterized in that the reference light reflected by the object from the irradiation light from a first light-emitting element in the light-emitting element array is guided via the separation section to a first light-receiving element corresponding to the first light-emitting element in the light-receiving element array, and the reflecting means reflects the reference light from the first light-emitting element so that the reference light is guided to the first light-receiving element via the separation section.

7. The measurement device described in claim 6, characterized in that in the light-emitting element array and the light-receiving element array, the multiple light-emitting elements and the multiple light-receiving elements are two-dimensionally arranged to form multiple light-emitting element rows and multiple light-receiving element rows, respectively, and in the light-emitting element array, simultaneous emission of the multiple first light-emitting elements belonging to the same light-emitting element row is performed sequentially for every predetermined number of light-emitting element rows, and the reflection means reflects the reference light from the multiple first light-emitting elements so that the reference light is guided via the separation section to the multiple second light-receiving elements belonging to the light-receiving element row corresponding to the light-emitting element row to which the multiple first light-emitting elements belong in the light-receiving element array.

8. A measuring device as described in any one of claims 1 to 7, characterized in that each light-emitting element in the light-emitting element array and each light-receiving element in the light-receiving element array are associated with each other by being arranged in optically conjugate positions with respect to the separation section.

9. A measuring device as described in any one of claims 1 to 8, characterized in that the reflecting means has a structure that at least one of transmits and absorbs light in a wavelength range different from the wavelength range including the wavelength of the reference light.

10. A measuring device as described in any one of claims 1 to 9, characterized in that the processing means acquires distance information as information relating to the object using a time of flight obtained by subtracting the first time from the second time.

11. A processing device comprising the measuring device according to any one of claims 1 to 10, and performing processing using information about the object.

12. A measurement method comprising: a light-emitting element array including a plurality of light-emitting elements; a light-receiving element array including a plurality of light-receiving elements; an optical system; and a light separation element having a separation section that separates light from the light-emitting element array into illumination light that is irradiated onto an object via the optical system and reference light that is guided to the light-receiving element array, and that guides signal light from the illumination light that is reflected by the object and enters via the optical system to the light-receiving element array via the separation section; providing a reflection means that reflects the reference light from the separation section back to the separation section, and guiding the reference light from the reflection means to the light-receiving element array via the separation section; and acquiring information about the object using a first time from an instruction to emit light to the light-emitting element array to the reception of the reference light at the light-receiving element array and a second time from the instruction to emit light to the reception of the signal light at the light-receiving element array.

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