Distance measuring device, measurement unit, and control method for distance measuring device

Abstract

To provide a distance measuring device that uses a light receiving device having pixels with different sensitivities, the distance measuring device capable of performing appropriate processing considering the difference in sensitivity between the pixels.SOLUTION: A distance measuring device uses a light receiving device in which first pixels having first sensitivity and second pixels having second sensitivity lower than the first sensitivity are two-dimensionally arranged. The distance measuring device has measuring means that measures the time from a predetermined time until the time when light is incident on the first pixels and second pixels, and calculation means that, based on the measured time, calculates distance information for the first pixels and the second pixels. In the measuring means, the time measurement resolution for the second pixels is lower than that for the first pixels.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a distance measuring device and a measurement unit. and a method for controlling a distance measuring device Regarding. [Background technology]

[0002] A known distance measurement method is the ToF (Time-of-Flight) method, which measures the distance to an object that reflects light by measuring the time difference between irradiating light and detecting the reflected light. The accuracy of distance measurement with the ToF method depends on the accuracy of the time difference measurement. Therefore, in order to improve the accuracy of distance measurement, it is necessary to improve the accuracy of the time difference measurement.

[0003] One method for improving the accuracy of measuring the time difference is to shorten the delay time from when the reflected light is received to when it is detected. In Patent Document 1, a photodetector has multiple light receiving elements arranged two-dimensionally, and SPADs (Single Photon Avalanche Diodes) are used as the light receiving elements.

[0004] The SPAD generates an avalanche current by operating an avalanche photodiode in Geiger mode. The time from the incidence of a photon to the generation of the avalanche current is 10 -12 Since the time is short, on the order of seconds, the timing at which the reflected light is received can be detected with high precision.

[0005] Furthermore, Patent Document 2 discloses a pixel array in which two types of light receiving elements (SPADs) with different sensitivities are arranged in order to expand the dynamic range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-081254 A [Patent Document 2] JP 2019-190892 A Summary of the Invention

Problems to be Solved by the Invention

[0007] Patent Document 2 discloses using different types of SPADs with different sensitivities, but neither discloses nor suggests considering sensitivity in the method of handling the output of the SPADs. For example, a highly sensitive SPAD is more susceptible to the influence of noise light than a less sensitive SPAD, but there is no disclosure or suggestion regarding considering the difference in characteristics due to such differences in sensitivity.

[0008] One object of the present invention is to provide a distance measuring device using a light receiving device having pixels with different sensitivities, capable of performing appropriate processing considering the difference in sensitivity of the pixels.

Means for Solving the Problems

[0009] The above object is achieved by a light receiving device in which a first pixel having a first sensitivity and a second pixel having a second sensitivity lower than the first sensitivity are two-dimensionally arranged, emitted by the light emitting device measuring means for measuring the time from a time until the time when light is incident on each of the first pixel and the second pixel, and calculating means for calculating distance information for each of the first pixel and the second pixel based on the measured time, The light emitting device has a plurality of light emitting elements arranged two-dimensionally, and each of the plurality of light emitting elements is configured to correspond to a specific pixel of the light receiving device. Among the plurality of light emitting elements, the light emission period of the light emitting element corresponding to the first pixel is shorter than the light emission period of the light emitting element corresponding to the second pixel. characterized in that the time measurement resolution for the second pixel in the measuring means is lower than the time measurement resolution for the first pixel.

Effects of the Invention

[0010] According to the present invention, it is possible to provide a distance measuring device and a measurement unit using a light receiving device having pixels with different sensitivities, capable of performing appropriate processing considering the difference in sensitivity of the pixels.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail based on its exemplary embodiments with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. In addition, although a plurality of features are described in the embodiments, not all of them are essential to the invention, and a plurality of features may be arbitrarily combined. Furthermore, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0013] In this specification, the fact that the characteristics of the light-receiving elements are the same indicates that the physical configurations and bias voltages of the light-receiving elements are not actively made different. Therefore, there may be differences in characteristics due to inevitable factors such as manufacturing variations.

[0014] ●(First Embodiment) FIG. 1 is a block diagram showing a functional configuration example of a distance measuring device using the light receiving device according to the present invention. The distance measuring device 100 includes a light projecting unit 110, a measurement unit 120, a light receiving lens 132, and an overall control unit 140. The light projecting unit 110 includes a light source unit 111 in which light emitting elements are arranged in a two-dimensional array, a light source unit driving unit 112, a light source control unit 113, and a light projecting lens 131. The measurement unit 120 includes a light receiving unit 121, a TDC (Time-to-Digital Convertor) array unit 122, a signal processing unit 123, and a measurement control unit 124. In this specification, the combination of the light receiving lens 132 and the light receiving unit 121 may be referred to as the light receiving unit 133.

[0015] The overall control unit 140 controls the operation of the entire distance measuring device 100. The overall control unit 140 has, for example, a CPU, a ROM, and a RAM, and controls each part of the distance measuring device 100 by reading a program stored in the ROM into the RAM and executing it with the CPU. At least a part of the overall control unit 140 may be realized by a dedicated hardware circuit.

[0016] By causing a plurality of light emitting elements 211 (FIG. 2(b)) arranged in the light source unit 111 to emit light for a short time, pulsed light (pulse light) is irradiated through the projection lens 131. The pulsed light emitted from each light emitting element irradiates different spaces. A part of the pulsed light irradiated from the light source unit 111 is reflected by the subject and enters the light receiving unit 121 through the light receiving lens 132. In the present embodiment, the light emitting element 211 that emits light and a specific pixel among the plurality of pixels arranged in the light receiving unit 121 are configured to be optically corresponding. Here, the pixel optically corresponding to a certain light emitting element 211 is a pixel in a positional relationship that most detects the reflected light of the light emitted from the light emitting element 211.

[0017] The time from the emission of light from the light source unit 111 until the reflected light enters the light receiving unit 121 is measured by the TDC array unit 122 as the time of flight ToF. In order to reduce the influence of noise components such as ambient light and dark count and the noise of the TDC array unit 122 on the measurement result, the time of flight ToF is measured a plurality of times.

[0018] The signal processing unit 123 generates a histogram of the measurement results obtained a plurality of times by the TDC array unit 122 and removes the noise components based on the histogram. Then, the signal processing unit 123 calculates the distance L of the subject by substituting the time of flight ToF obtained by, for example, averaging the measurement results from which the noise components have been removed into the following formula (1). L[m] = ToF[sec]*c[m / sec] / 2 ···(1) Note that c is the speed of light. In this way, the signal processing unit 123 calculates the distance information for each pixel.

[0019] (Light projection unit 110) Using FIG. 2, a configuration example of the light projection unit 110 will be described. FIG. 2(a) is a side view showing a configuration example of the collimator lens array 220 that constitutes the light source unit 111, and FIG. 2(b) is a side view showing a configuration example of the light source array 210 that constitutes the light source unit 111.

[0020] The light source array 210 has a configuration in which light emitting elements 211, which are, for example, vertical cavity surface emitting laser elements (VCSELs), are arranged in a two-dimensional array. The lighting and extinguishing of the light source array 210 are controlled by the light source control unit 113. The light source control unit 113 can control the lighting and extinguishing of the light source array 210 on a per light emitting element 211 basis.

[0021] Note that elements other than VCSELs, such as edge emitting laser elements and LEDs (light emitting diodes), may be used as the light emitting element 211. When an edge emitting laser element is used as the light emitting element 211, a laser bar in which the elements are arranged in a one-dimensional array on a substrate, or a laser bar stack in which laser bars are stacked to form a two-dimensional array configuration can be used as the light source array 210. Also, when an LED is used as the light emitting element 211, a light source array 210 in which LEDs are arranged in a two-dimensional array on a substrate can be used.

[0022] Note that there is no particular limitation on the emission wavelength of the light emitting element 211, but if the wavelength is in the near infrared band, the influence of ambient light can be suppressed. VCSELs can be fabricated by semiconductor processes using materials used in edge emitting lasers and surface emitting lasers. When configured to emit laser light with a wavelength in the near infrared band, GaAs-based semiconductor materials can be used. In this case, the dielectric multilayer film that forms the DBR (distributed Bragg reflector) mirror constituting the VCSEL can be formed by alternately and periodically stacking two thin films made of materials with different refractive indices (GaAs / AlGaAs). The wavelength of the light emitted by the VCSEL can be changed by adjusting the elemental combination and composition of the compound semiconductor.

[0023] In the VCSELs that make up the VCSEL array, electrodes are provided for injecting current and holes into the active layer. By controlling the timing of injecting current and holes into the active layer, it is possible to emit arbitrary pulsed light or modulated light. The light source control unit 113 can drive the light emitting elements 211 individually, or drive the light source array 210 in units of rows, columns, or rectangular regions.

[0024] In addition, the collimator lens array 220 has a configuration in which a plurality of collimator lenses 221 are arranged in a two-dimensional array such that each collimator lens 221 corresponds to one light emitting element 211. The light beam emitted from the light emitting element 211 is converted into a parallel light beam by the corresponding collimator lens 221.

[0025] FIG. 2(c) is a vertical cross-sectional view showing an arrangement example of the light source unit driving section 112, the light source unit 111, and the projection lens 131. The projection lens 131 is an optical system for adjusting the projection range of the parallel light emitted from the light source unit 111 (light source array 210). In FIG. 2(c), the projection lens 131 is a concave lens, but it may be a convex lens, an aspherical lens, or an optical system composed of a plurality of lenses.

[0026] In this embodiment, as an example, it is assumed that the projection lens 131 is configured such that light is irradiated from the projection unit 110 within a range of ±45 degrees. Note that the projection lens 131 may be omitted by controlling the light emission direction by the collimator lens 221.

[0027] FIG. 3(a) shows a projection pattern formed on a plane at a predetermined distance where the light emitting elements in 3 rows and 3 columns of the light source array 210 face the light emitting surface of the projection unit 110. The nine projection areas 311 indicate regions in the plane 310 having a diameter approximately equal to the full width at half maximum (FWHM) of the light intensity distribution from each light emitting element.

[0028] Since the light emitted from the light-emitting element 211, which has been converted into parallel light by the collimator lens 221, is given a slight divergence angle by the projection lens 131, a finite area is formed on the irradiation surface (plane 310). When the positional relationship between the collimator lens array 220 and the light source array 210 is constant, the same number of light projection areas 311 as the number of light-emitting elements 211 that make up the light source array 210 are formed on the plane 310.

[0029] The light projection unit 110 of the present embodiment has a light source unit drive unit 112 that can move the light source unit 111 within the same plane. By moving the position of the light source unit 111 by the light source unit drive unit 112, the relative positional relationship between the light-emitting element 211 and the collimator lens 221 or the projection lens 131 can be changed. There is no particular limitation on the method by which the light source unit drive unit 112 drives the light source unit 111, but for example, a mechanism using an electromagnetic induction method or a mechanism using a piezoelectric element, such as the mechanism used to drive an imaging element for shake correction, can be used.

[0030] When the light source unit drive unit 112 moves the light source unit 111, for example, within a plane parallel to the substrate of the light source unit 111 (perpendicular to the optical axis of the projection lens 131), it is possible to substantially translate the light projection area 311 on the plane 310. For example, by lighting the light source unit 111 a plurality of times while moving the light source unit 111 within a plane parallel to the substrate of the light source unit 111, the spatial resolution of the light projection area can be pseudo-increased.

[0031] Fig. 3(b) shows the spatial resolution of the light projection area 411 on the plane 410 when the light source unit 111 having the same light source array 210 as in Fig. 3(a) is rotationally moved once in a circular shape within a plane parallel to the substrate of the light source unit 111 and the light source unit 111 is lit four times at regular intervals. A spatial resolution four times that of the case where the light source unit 111 is not moved, shown in Fig. 3(a), is obtained.

[0032] Therefore, by performing distance measurement with different relative positions between the light source unit 111 and the projection lens 131, the density of the distance measurement points can be increased. Since the spatial resolution of the projection area 411 can be increased without separating the light beam, the measurable distance does not become shorter, and the distance accuracy does not decrease due to a decrease in the intensity of the reflected light.

[0033] Note that the relative position between the light source unit 111 and the projection lens 131 may be changed by moving the projection lens 131 within a plane parallel to the substrate of the light source unit 111. When the projection lens 131 has a plurality of lenses, the entire projection lens 131 may be moved, or only a part of the lenses may be moved.

[0034] Furthermore, the light source unit 111 may be configured to be movable in a direction perpendicular to the substrate of the light source array 210 (the optical axis direction of the projection lens 131) by the light source unit driving unit 112. Thereby, the divergence angle and the projection angle of the light can be controlled.

[0035] The light source control unit 113 controls the light emission of the light source unit 111 (light source array 210) according to the light reception timing and the light reception resolution of the light reception unit 133.

[0036] (Measurement unit 120) Next, the configuration of the measurement unit 120 will be described. FIG. 4 is an exploded perspective view schematically showing an implementation example of the measurement unit 120. In FIG. 4, the light reception unit 121, the TDC array unit 122, the signal processing unit 123, and the measurement control unit 124 are shown. The light reception unit 121 and the TDC array unit 122 constitute a light reception device.

[0037] The measurement unit 120 has a configuration in which a light-receiving element substrate 510 including a light-receiving unit 121 with pixels 511 arranged in a two-dimensional array and a logic substrate 520 including a TDC array unit 122, a signal processing unit 123, and a measurement control unit 124 are stacked. The light-receiving element substrate 510 and the logic substrate 520 are electrically connected through an inter-substrate connection 530. FIG. 4 shows, for the sake of explanation, the light-receiving element substrate 510 and the logic substrate 520 in a separated state.

[0038] Note that the functional blocks mounted on each substrate are not limited to the illustrated examples. A configuration in which three or more substrates are stacked may be used, or all the functional blocks may be mounted on a single substrate. The inter-substrate connection 530 is composed of, for example, a Cu-Cu connection, and one or more may be arranged in each column of the pixels 511, or one may be arranged for each pixel 511.

[0039] The light-receiving unit 121 has a pixel array in which the pixels 511 are arranged in a two-dimensional array. In the present embodiment, it is assumed that the light-receiving elements included in the pixels 511 are avalanche photodiodes (APDs) or SPAD elements. Also, as shown in FIG. 5(a), pixels H (first pixels) having a first sensitivity and pixels L (second pixels) having a second sensitivity lower than the first sensitivity are alternately arranged in the row direction and the column direction. By arranging the pixels H and the pixels L adjacent to each other, offset correction of the pixels H based on the measurement results of the pixels L becomes possible. In this specification, the pixels H may also be referred to as high-sensitivity pixels H, and the pixels L may be referred to as low-sensitivity pixels L.

[0040] FIG. 5(b) is a vertical cross-sectional view showing a structural example of the pixels H and the pixels L. Here, let the resonance wavelength be λc, the refractive index of the high refractive index layer 901 be nH, and the refractive index of the low refractive index layer 902 be nL (<nH). The optical resonators 911 to 914 are multilayer interference mirrors having a high refractive index layer 901 with a film thickness dH = 0.25λc / nH and a low refractive index layer 902 with a film thickness dL = 0.25λc / nL. It is a configuration in which the low refractive index layer 902 with a film thickness dE1 (~dE4) = m1 (~m4) × 0.5λc / nL (m1 to m4 are natural numbers) is sandwiched from both sides by the high refractive index layer 901.

[0041] The pixel L has a configuration in which a second optical band - pass filter is provided on a light - attenuation layer 903 made of a tungsten thin film with a film thickness of 30 nm and a transmittance of about 45%. The second optical band - pass filter has a configuration in which a light resonator 911 to a light resonator 914 are stacked with a low - refractive - index layer 902 having a film thickness dL interposed therebetween. The second optical band - pass filter has the spectral characteristics shown in Fig. 6(a) and is an example of an optical element added to the light - receiving element.

[0042] The pixel H has a configuration in which a multilayer interference mirror 915, a film - thickness adjustment layer 905 made of a low - refractive - index layer with a film thickness dE4, and a first optical band - pass filter are provided on a transmittance layer 904 made of a low - refractive - index layer with a film thickness of 30 nm and a transmittance of about 100%. The first optical band - pass filter is an example of an optical element added to the light - receiving element and has the spectral characteristics shown in Fig. 6(b).

[0043] The first optical band - pass filter has a configuration in which a light resonator 911 to a light resonator 913 are stacked with a low - refractive - index layer 902 having a film thickness dL interposed therebetween. The first optical band - pass filter and the second Optical band Pass filter pass bands basically have the same center wavelength, and in Fig. 6, λcL = λcH. The center wavelength can be the peak wavelength of the light irradiated by the light - source unit 111. On the other hand, the half - value width WL of the spectral characteristics of the second optical band - pass filter is narrower than the half - value width WH of the spectral characteristics of the first optical band - pass filter.

[0044] The reason for making the half - value width WL narrower than the half - value width WH is that it is assumed that the low - sensitivity pixel L mainly performs long - distance distance measurement and the high - sensitivity pixel H mainly performs short - distance distance measurement. For the low - sensitivity pixel L, in order to be able to handle a long ToF, the half - value width WL is narrowed to suppress the measurement of noise light before the reflected light arrives.

[0045] Further, a light attenuation layer 903 is provided in pixel L, and it is configured to be less sensitive than pixel H. The light attenuation layer 903 is an example of an optical element for reducing the sensitivity of the pixel. Note that, instead of the light attenuation layer 903, other optical elements such as a mask with a different aperture amount may be used to make the sensitivities of pixel H and pixel L different.

[0046] For example, by providing pixel L with a mask having a smaller aperture amount than the mask provided in pixel H, the light-receiving area of the light-receiving element of pixel L can be made narrower than the light-receiving area of the light-receiving element of pixel H. It is not necessary to provide a mask for pixel H. In this case, a mask with an aperture ratio of less than 100% may be provided for pixel L. The mask can be formed of any material capable of forming a light-shielding film.

[0047] In this embodiment, instead of varying the configuration of the light-receiving element itself or the applied voltage, the sensitivities of the pixels are varied using optical elements added to the light-receiving elements. Therefore, the configuration of the light-receiving element and the applied voltage can be made common between pixel H and pixel L. Accordingly, the manufacturing of the light-receiving element array is easy, and variations in the characteristics of the light-receiving elements can be suppressed.

[0048] FIG. 7 is a cross-sectional view including the semiconductor layer of the light-receiving element, which is common to pixel H and pixel L. 1005 is the semiconductor layer of the light-receiving element substrate 510, 1006 is the wiring layer of the light-receiving element substrate 510, and 1007 is the wiring layer of the logic substrate 520. The wiring layers of the light-receiving element substrate 510 and the logic substrate 520 are joined so as to face each other. The semiconductor layer 1005 of the light-receiving element substrate 510 includes a light-receiving area (photoelectric conversion area) 1001 and an avalanche area 1002 that generates an avalanche current by signal charges generated by photoelectric conversion.

[0049] Further, in order to prevent light obliquely incident on the light-receiving area 1001 from reaching the light-receiving area 1001 of an adjacent pixel, a light-shielding wall 1003 is provided between adjacent pixels. The light-shielding wall 1003 is formed of metal, and an insulator area 1004 is provided between the light-shielding wall 1003 and the light-receiving area 1001.

[0050] FIG. 8(a) is a diagram showing the potential distribution of the semiconductor region of the a-a' cross section in FIG. 7. FIG. 8(b) is a diagram showing the potential distribution of the b-b' cross section in FIG. 7. FIG. 8(c) is a diagram showing the potential distribution of the c-c' cross section in FIG. 7.

[0051] The light incident on the semiconductor layer 1005 of the light receiving element substrate 510 is photoelectrically converted in the light receiving region 1001, generating electrons and holes. The positively charged holes are discharged through the anode electrode Vbd. The negatively charged electrons are transported as signal charges to the avalanche region 1002 by an electric field set such that the potential decreases toward the avalanche region 1002 as shown in FIGS. 8(a), 8(b), and 8(c).

[0052] The signal charges reaching the avalanche region 1002 cause avalanche breakdown by the strong electric field in the avalanche region 1002, generating an avalanche current. This phenomenon occurs not only with the signal light (the reflected light of the light irradiated by the light source unit 111) but also with the incidence of ambient light which is noise light, becoming a noise component. Also, carriers are generated not only by the incident light but also thermally. The avalanche current caused by the thermally generated carriers is called dark count and becomes a noise component.

[0053] FIG. 9 is an equivalent circuit diagram of the pixel 511. The pixel 511 includes a SPAD element 1401, a load transistor 1402, an inverter 1403, a pixel selection switch 1404, and a pixel output line 1405. The SPAD element 1401 corresponds to the region combining the light receiving region 1001 and the avalanche region 1002 in FIG. 7.

[0054] When the pixel selection switch 1404 is turned on by a control signal supplied from the outside, the output signal of the inverter 1403 is output to the pixel output line 1405 as a pixel output signal. When no avalanche current is flowing, the voltage of the anode electrode Vbd is set so that a reverse bias equal to or higher than the breakdown voltage is applied to the SPAD element 1401. At this time, since no current flows through the load transistor 1402, the cathode potential Vc is a voltage close to the power supply voltage Vdd, and the pixel output signal is "0".

[0055] When an avalanche current is generated in the SPAD element 1401 due to the arrival of photons, the cathode potential Vc drops, and the output of the inverter 1403 is inverted. That is, the pixel output signal changes from "0" to "1".

[0056] When the cathode potential Vc drops, the reverse bias applied to the SPAD element 1401 decreases, and when the reverse bias becomes lower than the breakdown voltage, the generation of the avalanche current stops. Thereafter, a hole current flows from the power supply voltage Vdd through the load transistor 1402, so that the cathode potential Vc rises, the output (pixel output) of the inverter 1403 returns from "1" to "0", and the state before the arrival of photons is restored. The signal output from the pixel 511 in this way is input to the TDC array unit 122 via a relay buffer (not shown).

[0057] (TDC array unit 122) The TDC array unit 122 measures the time from the time when the light source unit 111 emits light to the time when the output signal of the pixel 511 changes from "0" to "1" as ToF. FIG. 10 is a diagram schematically showing a configuration example of the TDC array unit 122. The TDC array unit 122 is provided with a high-resolution TDC 1501 having a first measurement resolution and a low-resolution TDC 1502 having a second measurement resolution, each with half the number of pixels constituting one pixel row of the pixel array, and measures ToF for each pixel in units of one pixel. The second measurement resolution is lower than the first measurement resolution. Also, the synchronization clock is supplied, for example, from the overall control unit 140.

[0058] Here, the output signal of the high-sensitivity pixel H is input to the high-resolution TDC1501, and the output signal of the low-sensitivity pixel L is input to the low-resolution TDC1502, and they are driven by a relay buffer. That is, for the high-sensitivity pixel H, time is measured with a higher measurement resolution than that of the low-sensitivity pixel L. In FIG. 10, the odd-numbered pixel outputs are the outputs of the pixel H, and the even-numbered pixel outputs are the outputs of the pixel L. In order to make the delay times in the relay buffer approximately equal, the high-resolution TDC1501 and the low-resolution TDC1502 are arranged alternately.

[0059] The high-resolution TDC1501 includes a first oscillator 1511, a first oscillation count circuit 1521, and a first synchronous clock count circuit 1531. The low-resolution TDC1502 includes a second oscillator 1512, a second oscillation count circuit 1522, and a second synchronous clock count circuit 1532. The first oscillation count circuit 1521 and the second oscillation count circuit 1522 are second counters that count the changes in the output values of the corresponding oscillators. The first synchronous clock count circuit 1531 and the second synchronous clock count circuit 1532 are first counters that count the synchronous clocks.

[0060] In the output values of the respective TDCs, the count result of the synchronous clock count circuit constitutes the upper bits, the internal signal of the oscillator constitutes the lower bits, and the count result of the oscillation count circuit constitutes the middle bits. That is, it is configured such that the synchronous clock count circuit roughly measures, the internal signal of the oscillator measures finely, and the oscillation count circuit measures the interval therebetween. Note that redundant bits may be provided for each measurement bit.

[0061] FIG. 11 is a diagram schematically showing a configuration example of a first oscillator 1511 of a high-resolution TDC1501. The first oscillator 1511 includes an oscillation start / stop signal generation circuit 1640, buffers 1611 to 1617, an inverter 1618, an oscillation switch 1630, and a delay adjustment current source 1620. Further, the buffers 1611 to 1617 and the inverter 1618 as delay elements are alternately connected in series and in a ring shape with the oscillation switch 1630. The delay adjustment current source 1620 is provided for each of the buffers 1611 to 1617 and the inverter 1618, and adjusts the delay time of the corresponding buffer or inverter according to the adjustment voltage.

[0062] FIG. 12 shows changes in the output signals of the buffers 1611 to 1617 and the inverter 1618 and the internal signals of the oscillator at the time of reset and after the oscillation switch 1630 is turned on for each delay time t of one buffer stage. WI11 output to WI18 output are the output signals of the buffers 1611 to 1617 and the inverter 1618, respectively. buff At the time of reset, the outputs of the buffers 1611 to 1617 are “0” and the output of the inverter 1618 is “1”. After the oscillation switch 1630 is turned on, after the elapse of the delay time t of one buffer stage, the outputs of the buffers 1612 to 1617 and the inverter 1618 for which input / output matching is achieved do not change. On the other hand, the output of the buffer 1611 for which input / output matching is not achieved changes from “0” to “1” (the signal advances by one stage).

[0063] At the time of reset, the outputs of the buffers 1611 to 1617 are “0” and the output of the inverter 1618 is “1”. After the oscillation switch 1630 is turned on, after the elapse of the delay time t of one buffer stage, the outputs of the buffers 1612 to 1617 and the inverter 1618 for which input / output matching is achieved do not change. On the other hand, the output of the buffer 1611 for which input / output matching is not achieved changes from “0” to “1” (the signal advances by one stage). buff After the elapse of the delay time t of one buffer stage, the outputs of the buffers 1612 to 1617 and the inverter 1618 for which input / output matching is achieved do not change. On the other hand, the output of the buffer 1611 for which input / output matching is not achieved changes from “0” to “1” (the signal advances by one stage).

[0064] Furthermore, after the elapse of t buff (after 2×t buff ), the outputs of the buffers 1611, 1613 to 1617 and the inverter 1618 for which input / output matching is achieved do not change. On the other hand, the output of the buffer 1612 for which input / output matching is not achieved changes from “0” to “1” (the signal advances by one more stage).

[0065] In this way, for each delay time t of one buffer stage buffAs time elapses, among the buffers 1611 to 1617 and the inverter 1618, one output that is not input-output matched changes from "0" to "1" in sequence. Then, after 8×t buff has elapsed since the oscillation switch 1630 turned on, the outputs of all the buffers and the inverter change to "1" (the signal makes one round). Further, after 8×t buff has elapsed (after 16×t buff has elapsed), the outputs of all the buffers and the inverter change to "0" (the signal makes two rounds) and return to the original state.

[0066] After that, the output changes in the same way with a period of 16×t buuf . Thus, the time resolution of the high-resolution TDC 1501 is equal to t buff . Also, the time resolution t buff is adjusted by the first oscillation adjustment circuit 1541 described later to be 2 -7 (1 / 128) of the period of the synchronization clock.

[0067] Also, the oscillator output, which is the output of the inverter 1618, is input to the first oscillation count circuit 1521. The first oscillation count circuit 1521 measures time with a time resolution of 16×t buff by counting the rising edge of the oscillator output.

[0068] FIG. 13 is a timing chart until the time measurement from the light emission until the reflected light is detected by the SPAD element 1401 is completed. It shows the changes in the cathode potential Vc of the SPAD element 1401, the pixel output signal, the synchronization clock, the count value of the synchronization clock count circuit, the output of the oscillator start / stop signal generation circuit, the oscillator output, and the count value of the oscillation count circuit.

[0069] The cathode potential Vc of the SPAD element 1401 is an analog voltage, with the upper side of the paper showing a higher voltage. The synchronous clock, oscillator start / stop signal generation circuit output, and oscillator output are digital signals, with the upper side of the paper indicating the on state and the lower side indicating the off state. The count values of the synchronous clock count circuit and the oscillator count circuit are digital values, shown in decimal.

[0070] FIG. 14 is an enlarged view of the oscillator start / stop signal generation circuit output, oscillator output, count value of the oscillator count circuit, and internal oscillator signal from time 1803 to time 1805 in FIG. 13. The internal oscillator signal is a digital value, shown in decimal.

[0071] Using FIGS. 13 and 14, the operation of measuring, by the high-resolution TDC 1501, the time from the light emission time 1801 of the light source unit 111 to the time 1803 when photons enter the SPAD element 1401 of the pixel and the pixel output signal changes from 0 to 1 will be described.

[0072] The light source control unit 113 drives the light source unit 111 so that the light emitting element 211 emits light at time 1801 synchronized with the rising edge of the synchronous clock supplied via the overall control unit 140. When the first synchronous clock count circuit 1531 is instructed by the overall control unit 140 to start measurement at the time 1801 when the light emitting element 211 emits light, it starts counting the rising edges of the synchronous clock.

[0073] When the reflected light of the light irradiated at time 1801 enters the pixel at time 1803, the cathode potential Vc of the SPAD element 1401 drops, and the pixel output signal changes from "0" to "1". When the pixel output signal becomes "1", the output of the oscillation start / stop signal generation circuit 1640 changes from "0" to "1", and the oscillation switch 1630 turns on.

[0074] When the oscillation switch 1630 turns on, the oscillation operation starts, and a signal loop starts inside the oscillator as shown in FIG. 12. After the oscillation switch 1630 turns on, 16 × t buffEach time the signal makes two rounds in the oscillator after the passage of time, a rising edge appears in the oscillator output, and the first oscillation count circuit 1521 measures the number. Also, at time 1803, the first synchronous clock count circuit 1531 stops counting and holds the count value.

[0075] After time 1803 when the first oscillator 1511 is turned on, the timing at which the synchronous clock first rises is time 1805. In response to the rising edge of the synchronous clock at time 1805, the output of the oscillation start / stop signal generation circuit 1640 becomes "0", and the oscillation switch 1630 turns off. At the timing when the oscillation switch 1630 becomes "0", the oscillation of the first oscillator 1511 ends, and the internal signal of the oscillation circuit is held as it is. Also, since the oscillation ends, the counting of the first oscillation count circuit 1521 also stops.

[0076] Count result D of the synchronous clock count circuit Gclk is the value measured in units of 2 7 ×t buff for the time from time 1801 to time 1802. Also, the count result D of the oscillator count circuit ROclk is the value measured in units of 2 4 ×t buff for the time from time 1803 to time 1804. Further, the internal signal D of the oscillator ROin is the value measured in units of t buff for the time from time 1804 to time 1805. The high-resolution TDC 1501 completes one measurement operation by performing the following processing on these values and outputting them to the signal processing unit 123.

[0077] The count result D of the oscillator count circuit ROclk and the internal signal D of the oscillator ROin are added according to the following formula (2). D RO = 2 4 × D ROclk + D ROin ···(2)

[0078] D obtained by formula (2) ROis the value measured in units of t from time 18:03 to time 18:05. Also, since the time from time 18:02 to time 18:05 is equal to one cycle of the synchronization clock, 2 buff ×t 7 is obtained. Therefore, by subtracting D buff from one cycle of the synchronization clock, the time from time 18:02 to time 18:03 can be obtained. Adding this to D RO , which is the time from time 18:01 to time 18:02, gives the value D Gclk measured in units of t for the time from time 18:01 to time 18:03 (Equation (3)). buff ToF ToF is obtained (Equation (3)). D ToF =2 7 ×D Gclk +(2 7 -D RO ) =2 7 ×D Gclk +(2 7 -24×D ROclk -D ROin )···(3)

[0079] FIG. 15 is a diagram schematically showing a circuit configuration example of a second oscillator 1512 included in the low-resolution TDC 1502. In the second oscillator 1512, buffers 2011 to 2013 and an inverter 2014 are connected in series and in a ring shape alternately with an oscillation switch 2030. Also, a delay adjustment current source 2020 is provided for each of the buffers 2011 to 2013 and the inverter 2014, and adjusts the delay time of the corresponding buffer or inverter according to the adjustment voltage.

[0080] Compared with the high-resolution TDC 1501, the number of buffers and oscillation switches has decreased from seven to three. On the other hand, the delay time t buff of each of the buffers 2011 to 2013 and the inverter 2014 is adjusted by a second oscillation adjustment circuit 1542 so as to be twice the t buff of the high-resolution TDC 1501.

[0081] As a result, the count period of the second oscillation count circuit 1522 becomes equal to the count period of the first oscillation count circuit 1521. Therefore, the number of output bits of the second oscillation count circuit 1522 is equal to the number of output bits of the first oscillation count circuit 1521. On the other hand, the number of bits of the internal signal of the oscillator can be one bit less in the second oscillator 1512 than in the first oscillator 1511.

[0082] As described above, the low-sensitivity pixel L is mainly assumed to be used for long-distance ranging. 。T The influence of the measurement resolution of oF on the accuracy of the ranging result is greater for short distances than for long distances. Therefore, in the low-resolution TDC 1502 that measures the ToF of the low-sensitivity pixel L, priority is given to reducing the circuit scale and power consumption, and the measurement resolution of ToF is made lower than that of the high-resolution TDC 1501.

[0083] Delay time t buff varies due to factors such as manufacturing errors in the manufacturing process of transistors, fluctuations in the voltage applied to the TDC circuit, and temperature. Therefore, the first oscillation adjustment circuit 1541 and the second oscillation adjustment circuit 1542 are provided for every eight TDCs.

[0084] FIG. 16 is a block diagram showing a functional configuration example of the first oscillation adjustment circuit 1541 and the second oscillation adjustment circuit 1542. Since the first oscillation adjustment circuit 1541 and the second oscillation adjustment circuit 1542 have the same configuration, the first oscillation adjustment circuit 1541 will be described below. The first oscillation adjustment circuit 1541 includes a dummy oscillator 2101 and a 1 / 2 3 (1 / 8) frequency divider 2102, and a phase comparator 2103.

[0085] The dummy oscillator 2101 is an oscillator having the same configuration as the oscillator of the connected TDC. Therefore, the dummy oscillator 2101 of the first oscillation adjustment circuit 1541 has the same configuration as the first oscillator 1511. The dummy oscillator 2101 of the second oscillation adjustment circuit 1542 has the same configuration as the second oscillator 1512.

[0086] The output of the dummy oscillator 2101 is 1 / 23 It is input to the frequency divider 2102. 1 / 2 3 The frequency divider 2102 divides the frequency of the input clock signal by 1 / 2 3 and outputs a clock signal. The phase comparator 2103 receives the synchronous clock and 1 / 2 3 the output of the frequency divider 2102. The phase comparator 2103 compares the frequency of the synchronous clock with the frequency of the clock signal output by the frequency divider 2102. 3

[0087] Then, when the frequency of the synchronous clock signal is higher, the phase comparator 2103 raises the output voltage, and when the frequency of the synchronous clock is lower, the phase comparator 2103 lowers the output voltage. The output of the phase comparator 2103 is input as an adjustment voltage to the delay adjustment current source 1620 of the first oscillator 1511, and the delay is adjusted so that the oscillation frequency of the first oscillator 1511 becomes twice that of the synchronous clock. The same applies to the second oscillation adjustment circuit 1542. 3

[0088] In this way, the oscillation frequency of the oscillator is determined based on the synchronous clock frequency. Therefore, by generating a synchronous clock signal using an external IC that can output a constant frequency regardless of process / voltage / temperature changes, it is possible to suppress variations in the oscillation frequency of the oscillator due to process / voltage / temperature changes.

[0089] For example, by inputting a 160 MHz clock signal as the synchronous clock signal, the oscillation frequency becomes 1.28 GHz, which is 8 times the synchronous clock frequency, in both the high-resolution TDC 1501 and the low-resolution TDC 1502. The delay time t for one buffer stage, which is the time resolution of the TDC buff is 48.8 ps for the high-resolution TDC 1501 and 97.7 ps for the low-resolution TDC 1502.

[0090] (Distance measurement sequence) FIG. 17 is a flowchart relating to an example of the distance measurement operation in the present embodiment. In S2201, the overall control unit 140 resets the histogram circuit and the measurement counter i that the signal processing unit 123 has. Also, in S2202, the overall control unit 140 changes the connection of a relay buffer (not shown) so that the output of the pixel 511 optically corresponding to the light emitting element 211 to be emitted is input to the TDC array unit 122.

[0091] In S2202, the overall control unit 140 causes a part of the light emitting elements 211 constituting the light source array 210 of the light source unit 111 to emit light. At the same time, the overall control unit 140 instructs the TDC array unit 122 to start measurement.

[0092] When the high-resolution TDC 1501 and the low-resolution TDC 1502 of the TDC array unit 122 detect that the output of the corresponding pixel 511 has changed from "0" to "1", they output the measurement result to the signal processing unit 123. When the time corresponding to the predetermined maximum measurement range has elapsed since the light emission, S2204 is executed.

[0093] In S2204, the signal processing unit 123 adds the measurement result obtained in S2203 to the histogram for each pixel. The signal processing unit 123 does not add the measurement result to the histogram for pixels for which no measurement result has been obtained.

[0094] In S2205, the signal processing unit 123 adds 1 to the value of the measurement count counter i. In S2206, the signal processing unit 123 determines whether the value of the measurement count counter i is greater than a preset number of settings N total If it is determined that the value of the measurement count counter i is greater than the number of settings N total then S2207 is executed, and if it is determined that the value of the measurement count counter i is not greater than the number of settings N total then 2202 is executed.

[0095] In S2207, the signal processing unit 123 removes the count result considered to be a noise component based on the histogram of each pixel and executes S2208. In S2208, the signal processing unit 123 averages the measurement results that remained without being removed in S2207 in the histogram of each pixel, outputs the average value as the measured ToF, and ends one ranging sequence.

[0096] (Noise light suppression effect by using pixels with different sensitivities) Here, after explaining the noise component removal process in S2207 and the averaging in S2208, the noise light reduction effect by pixels H and L with different sensitivities will be described.

[0097] FIG. 18(a) is a diagram showing an example of a histogram of N total measurement results of the TDC in the high-sensitivity pixel H. The horizontal axis is the TDC measurement result (time), and the vertical axis is the frequency. Note that the bin width of the TDC measurement result is set for convenience.

[0098] Since the measurement results included in the section 2302 form a frequency peak, they are considered to be the correct measurement results of the time from light emission to light reception. On the other hand, since the measurement results included in the section 2304 have an irregular and sparse distribution, they are considered to be noise light such as ambient light generated randomly or noise components due to dark counts. Therefore, the measurement results included in the section 2304 are removed, and the average 2303 of only the measurement results included in the section 2302 is used as the ranging result.

[0099] Similar to FIG. 18(a), FIG. 18(b) is a diagram showing an example of a histogram of N total measurement results of the TDC in the high-sensitivity pixel H. The subject is the same as in FIG. 18(a), but it shows an example of a histogram of the TDC measurement results obtained in a situation with more ambient light than at the time of measurement shown in FIG. 18(a). The noise light included in the section 2304 has completed N total TDC measurements, and the TDC measurement results for the reflected light from the subject are not obtained.

[0100] FIG. 18(c) shows N obtained for the low-sensitivity pixel L in the same environment as FIG. 18(b). totalIt is a diagram showing an example of a histogram of the TDC measurement results of the cycles. Since the sensitivity is lower than that of the high-sensitivity pixel H, the number of times the TDC measurement is performed for the noise light decreases. As a result, the number of measurement results included in the section 2302 increases, and similar to FIG. 18(a), the average value of the measurement results included in the section 2302 can be calculated as the distance measurement result. In this way, the low-sensitivity pixel L has higher resistance to the situation where the ambient light noise is large than the high-sensitivity pixel H.

[0101] Here, the situation that can occur in an environment with a lot of noise light has been described. However, the same problem can also occur when the object to be distance-measured exists at a long distance. This is because when the object exists at a long distance, the period from the emission of light until the reflected light returns (that is, the period during which the noise light is detected) becomes long.

[0102] In the present embodiment, by using the high-sensitivity pixel H and the low-sensitivity pixel L, stable distance measurement with the influence of the noise light suppressed is possible even when the amount of the noise light is large or when measuring a distant object. Further, the configuration of the light-receiving element (SPAD) (light-receiving area and thickness of the light-receiving portion) and the voltage applied to the light-receiving element are common to the high-sensitivity pixel H and the low-sensitivity pixel L. Therefore, the variation between the distance measurement result obtained by the high-sensitivity pixel H and the distance measurement result obtained by the low-sensitivity pixel L is small, and an accurate distance measurement result can be obtained.

[0103] (HDR driving method) Next, the HDR driving of the high-sensitivity pixel H and the low-sensitivity pixel L will be described with reference to FIGS. 18(d) and 18(e). FIG. 18(d) shows an example of a histogram of the measurement results of the high-sensitivity pixel H, and FIG. 18(e) shows an example of a histogram of the measurement results of the low-sensitivity pixel L adjacent to the high-sensitivity pixel H in FIG. 18(d).

[0104] The emission period of the light-emitting element 211 corresponding to the high-sensitivity pixel H is 2602, and the emission period of the light-emitting element 211 corresponding to the low-sensitivity pixel L is 2702. The emission period 2702 is four times the emission period 2602. Therefore, within the same time, the distance measurement can be performed four times more frequently for the high-sensitivity pixel H than for the low-sensitivity pixel L. Since the probability that the number of averaged distance measurement results is larger than that of the low-sensitivity pixel L is high, and the measurement for the high-sensitivity pixel H is performed by the high-resolution TDC1501, the distance measurement accuracy of the space corresponding to the high-sensitivity pixel H is higher than that of the space corresponding to the low-sensitivity pixel L.

[0105] When the object to be distance-measured is far away, the ToF becomes longer, so the possibility of measuring noise light increases. The light-emitting element 211 corresponding to the low-sensitivity pixel L with a large noise light suppression effect does not emit the next light until the reflected light is detected. On the other hand, the light-emitting element 211 corresponding to the high-sensitivity pixel H with a small noise light suppression effect emits the next light before detecting the reflected light. Thereby, the time from the start of measurement by the TDC to the detection of the reflected light can be shortened, and the possibility of measuring noise light during the period from the emission of light to the arrival of the reflected light can be suppressed, enabling accurate time measurement with the high-sensitivity pixel H even in an environment with large noise light.

[0106] The signal processing unit 123 applies offset correction based on the measurement result obtained for the adjacent low-sensitivity pixel L to the measurement result obtained for the high-sensitivity pixel H. The offset correction is to add a constant multiple of the emission period (measurement period) 2602 of the high-sensitivity pixel H to the measurement result 2611 for the high-sensitivity pixel H based on the measurement result 2711 for the adjacent low-sensitivity pixel L.

[0107] Since the measurement result for the low-sensitivity pixel L adjacent to the high-sensitivity pixel H is 2711, it is highly likely that the time until the reflected light of the emitted light arrives for the high-sensitivity pixel H is also close to the measurement result 2711. In the examples of FIGS. 18(d) and 18(e), the measurement result 2711 for the low-sensitivity pixel L is greater than twice and less than three times the emission period 2602 of the high-sensitivity pixel H. Therefore, in offset correction, the signal processing unit 123 adds twice the emission period 2602 to the measurement result 2611 of the high-sensitivity pixel H.

[0108] Note that the offset correction amount may be determined based on the measurement results obtained for two or more low-sensitivity pixels L adjacent to the high-sensitivity pixel H to be corrected. For example, the offset correction amount may be determined based on the measurement results obtained for four or two low-sensitivity pixels L adjacent in the horizontal direction and / or vertical direction.

[0109] In addition, an imaging unit that images the light projection range of the light projection unit 110 may be provided, and the low-sensitivity pixel L used for determining the offset correction amount may be specified using the captured image. For example, the signal processing unit 123 specifies one or more adjacent low-sensitivity pixels L that are considered to be measuring the same subject as the high-sensitivity pixel H to be corrected based on the captured image. Then, the signal processing unit 123 may determine the offset correction amount (or the coefficient to be multiplied by the emission period of the high-sensitivity pixel H) using the measurement results obtained for the specified low-sensitivity pixels L.

[0110] According to the present embodiment, by using light receiving elements with different sensitivities, a light receiving device with a wide dynamic range can be realized. In addition, the sensitivity of the light receiving elements is made different by the optical elements added to the light receiving elements. Therefore, light receiving elements with the same configuration can be used, which is advantageous from the viewpoints of ease of manufacturing and suppression of variations in characteristics. Also, for the low-sensitivity pixels, by reducing the resolution of time measurement compared to the high-sensitivity pixels, it is possible to efficiently reduce the circuit scale and power consumption while suppressing a decrease in ranging accuracy.

[0111] ●(Second Embodiment) Next, a second embodiment of the present invention will be described. This embodiment can be realized with the same configuration as the first embodiment except for the configuration of the TDC array unit 122. Therefore, the configuration of the TDC array unit 122 in this embodiment will be mainly described.

[0112] FIG. 19 is a block diagram schematically showing a functional configuration example of the TDC array unit 122 in this embodiment. Also in this embodiment, in the TDC array unit 122, a high-resolution TDC 2801 and a low-resolution TDC 2802 are provided, each with half the number of pixels constituting one pixel row of the pixel array, and the ToF is measured for each pixel in units of one pixel. The high-resolution TDC 2801 has a higher time resolution for measurement than the low-resolution TDC 2802. Also, the synchronization clock is supplied, for example, from the overall control unit 140.

[0113] In this embodiment, the configuration corresponding to the first oscillator 1511 in the first embodiment is composed of a first oscillator 2811 and a first encoding circuit 2821. Also, the configuration corresponding to the second oscillator 1512 in the first embodiment is composed of a second oscillator 2812 and a second encoding circuit 2822.

[0114] The first oscillation counting circuit 2831 and the second oscillation counting circuit 2832 have the same configuration as the components with the same name in the first embodiment. Also, the first synchronization clock counting circuit 2841 and the second synchronization clock counting circuit 2842 have the same configuration as the components with the same name in the first embodiment.

[0115] FIG. 20 is a circuit diagram showing a configuration example of the first oscillator 2811 and the first encoding circuit 2821 of the high-resolution TDC 2801. The first oscillator 2811 includes a start signal generation circuit 2930, a signal synthesis circuit 2940, and eight buffers 2911 to 2918 connected in series. The first encoding circuit 2821 includes a stop signal generation circuit 2960 and eight flip-flop circuits 2951 to 2958 each taking the output of a different buffer as an input. The first encoding circuit 2821 functions as a holding circuit for holding the internal signal of the first oscillator 2811.

[0116] The start signal generation circuit 2930 generates a short pulse in response to the pixel output changing from "0" to "1". The signal synthesis circuit 2940 receives the output of the start signal generation circuit 2930 and the output of the final-stage buffer 2918, and outputs "1" if either one of them is "1".

[0117] FIG. 21, similar to FIG. 12, shows the changes of the output signals of the buffers 2911 to 2918 and the internal signal of the oscillator for each delay time t of one buffer stage from the reset time. buff The WS11 output to WS18 output are the output signals of the buffers 2911 to 2918 respectively.

[0118] At the time of reset, the outputs of all the buffers 2911 to 2918 are "0". When the start signal generation circuit 2930 outputs a short pulse in response to the pixel output changing from "0" to "1", after the delay time t of one buffer stage, the output of the buffer 2911 becomes "1". The outputs of the other buffers 2912 to 2918 remain "0". buff After that, the output of the buffer 2912 becomes "1" and the output of the buffer 2911 returns to "0". The outputs of the other buffers 2913 to 2918 remain "0".

[0119] Furthermore, when t buff elapses (after 2×t buff ), the output of the buffer 2912 becomes "1" and the output of the buffer 2911 returns to "0". The outputs of the other buffers 2913 to 2918 remain "0".

[0120] In this way, every time the delay time t of one buffer stage elapses, the buffer that outputs "1" changes in order. After 8×t buff elapses after the first oscillator 2811 starts to move, the final-stage buffer 2918 outputs "1". When t buff further elapses, it returns to the buffer 2911 that outputs "1". In this way, each of the buffers 2911 to 2918 outputs "1" with a period of 8×t buff . buff

[0121] ​Flip-flop circuits 2951 to 2958 that receive the outputs of buffers 2911 to 2918 receive the signals shown in the WS11 output to WS18 output in accordance with the elapsed time since a short pulse is output from the start signal generation circuit 2930 and time measurement is started. The stop signal generation circuit 2960 outputs a signal so as to hold the input signal at the rising edge of the synchronous clock in each of the flip-flop circuits 2951 to 2958. As a result, the internal signal of the oscillator at the time of stop is held in the flip-flop circuits 2951 to 2958.

[0122] Therefore, in the high-resolution TDC 2801, time measurement is performed with t buff as the time resolution. The t buff of the high-resolution TDC 2801 is adjusted by the first oscillation adjustment circuit 2851 provided for each of the eight TDCS so as to be 2 -6 (1 / 64) of the period of the synchronous clock.

[0123] FIG. 22 is a circuit diagram showing a configuration example of the second oscillator 2812 and the second encoding circuit 2822 of the low-resolution TDC 2802. The second oscillator 2812 includes a start signal generation circuit 3130, a signal synthesis circuit 3140, and four buffers 3111 to 3114 connected in series. The second encoding circuit 2822 includes a stop signal generation circuit 2960 and four flip-flop circuits 3151 to 3154 each of which receives the output of a different buffer. The second encoding circuit 2822 functions as a holding circuit for holding the internal signal of the second oscillator 2812.

[0124] The second oscillator 2812 of the low-resolution TDC 2802 has a configuration in which the number of buffer stages is half that of the first oscillator 2811 of the high-resolution TDC 2801. The t buff of the low-resolution TDC 2802 is adjusted by the second oscillation adjustment circuit 2852 provided for each of the eight TDCS so as to be 2 -5 (1 / 32) of the period of the synchronous clock.

[0125] Although the configurations of the high-resolution TDC2801 and the low-resolution TDC2802 are different, their operations are the same as those in the first embodiment. Therefore, also in this embodiment, the same effects as those in the first embodiment can be achieved.

[0126] ●(Third Embodiment) Next, a third embodiment of the present invention will be described. This embodiment can be realized with the same configuration as the first embodiment except for the configuration of the TDC array unit 122. Therefore, the configuration of the TDC array unit 122 in this embodiment will be mainly described.

[0127] FIG. 23 is a block diagram schematically showing a functional configuration example of the TDC array unit 122 in this embodiment. Also in this embodiment, in the TDC array unit 122, a high-resolution TDC3201 and a low-resolution TDC3202 are provided, each with half the number of pixels constituting one pixel row of the pixel array, and ToF is measured for each pixel in units of one pixel. The high-resolution TDC3201 has a higher time resolution for measurement than the low-resolution TDC3202. Also, the synchronization clock is supplied, for example, from the overall control unit 140.

[0128] The high-resolution TDC3201 includes an oscillator 3211, an oscillation encoding circuit 3221, an oscillation counting circuit 3231, a first delay circuit 3261, a second delay circuit 3262, a delay encoding circuit 3263, and a synchronization clock counting circuit 3241. Since the low-resolution TDC3202 has substantially the same configuration as the low-resolution TDC2802 in the second embodiment, the description thereof will be omitted. The oscillator 3211 corresponds to the second oscillator 2812, the oscillation counting circuit 3231 corresponds to the second oscillation counting circuit 2832, and the oscillation encoding circuit 3221 corresponds to the second encoding circuit 2822, respectively.

[0129] FIG. 24 shows a configuration example of the oscillator 3211, the oscillation encoding circuit 32 21 , the first delay circuit 3261, the second delay circuit 3262, and the delay encoding circuit 3263 of the high-resolution TDC3201. The oscillator 3211 and the oscillation encoding circuit 32 21It has the same configuration as the low-resolution TDC3202. Therefore, the oscillation adjustment voltage is also the same voltage, and the time resolution of the internal signal of the oscillator is the same for the high-resolution TDC3201 and the low-resolution TDC3202.

[0130] The high-resolution TDC3201 realizes measurement with a time resolution higher than that of the internal signal of the oscillator by performing a so-called Vernier operation using the first delay circuit 3261, the second delay circuit 3262, and the delay encoding circuit 3263.

[0131] The first delay circuit 3261 has eight buffers 3371 to 3378 connected in series. Similarly, the second delay circuit 3262 has eight buffers 3381 to 3388 connected in series. The delay time t of one stage of the buffer in the first delay circuit 3261 buff_slow is adjusted to be shorter than the delay time t of one stage of the buffer in the second delay circuit buff_fast And the encoding circuit 3263 detects the number of buffer stages passed until the signal of the second delay circuit 3262 catches up with the signal of the first delay circuit 3261.

[0132] Every time the signal of the second delay circuit 3262 passes through one buffer stage, the signal approaches the signal of the first delay circuit 3261 by t buff_fast - t buff_slow Therefore, measurement can be performed with t buff_fast - t buff_slow as the time resolution.

[0133] Also, the delay start signal generation circuit 3332 outputs a delay start signal at the timing when any of the outputs of the buffers 3311 to 3314 of the oscillator 3211 changes from "0" to "1". Further, the delay stop signal generation circuit 3333 outputs a delay stop signal at the rising timing of the synchronous clock.

[0134] For example, the oscillation adjustment circuit 3251 adjusts the delay time t of one stage of the buffers 3311 to 3314 of the oscillator 3211 buff to be 2 of the period of the synchronous clock -5Adjust so that it becomes (1 / 32). Also, the buffer 33 of the first delay circuit 3261 is adjusted by the first delay adjustment circuit 3271 7 The delay time t for one stage from 1 to 3378 buff_slow to 2 of the period of the synchronization clock -3 / 5 (1 / 40). Further, the buffer 3381 to 3388 of the second delay circuit 3262 is adjusted by the second delay adjustment circuit 3272 so that the delay time t for one stage buff_fast to 2 of the period of the synchronization clock -3 / 6 (1 / 48).

[0135] Assuming that the frequency of the synchronization clock is 160 MHz, t buff is 195.3 ps, t buff_slow is 156.3 ps, t buff_fast is 130.2 ps. In this case, the time resolution of the high-resolution TDC 3201 is 26.0 ps, and the time resolution of the low-resolution TDC 3202 is 195.3 ps.

[0136] In this embodiment, the time resolutions of the high-resolution TDC and the low-resolution TDC can be made significantly different. Other effects are common to the first embodiment.

[0137] (Other embodiments) The distance measuring device described above can be implemented in any electronic device having processing means for executing predetermined processing using distance information. Such electronic devices include imaging devices, computer devices (personal computers, tablet computers, media players, PDAs, etc.), mobile phones, smartphones, game machines, robots, drones, vehicles, and the like. These are examples, and the distance measuring device according to the present invention can also be implemented in other electronic devices.

[0138] The present invention can also be realized by supplying a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and causing one or more processors in a computer of the system or apparatus to read and execute the program. It can also be realized by a circuit (for example, an ASIC) that implements one or more functions.

[0139] The present invention is not limited to the contents of the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the claims are appended to disclose the scope of the invention.

Explanation of Reference Numerals

[0140] 100... distance measuring device, 110... light projecting unit, 111... light source unit, 120... measurement unit, 122... TDC array unit, 123... signal processing unit, 124... measurement control unit, 131... light projecting lens, 140... overall control unit

Claims

1. A light receiving device in which a first pixel having a first sensitivity and a second pixel having a second sensitivity lower than the first sensitivity are two-dimensionally arranged, Measuring means for measuring the time from the time when the light emitting device emits light to the time when light is incident on each of the first pixel and the second pixel, Calculating means for calculating distance information for each of the first pixel and the second pixel based on the measured time, which has, wherein the light emitting device has a plurality of light emitting elements two-dimensionally arranged, each of the plurality of light emitting elements is configured to correspond to a specific pixel of the light receiving device, among the plurality of light emitting elements, the emission period of the light emitting element corresponding to the first pixel is shorter than the emission period of the light emitting element corresponding to the second pixel, A distance measuring device, wherein the measurement resolution of the time for the second pixel in the measuring means is lower than the measurement resolution of the time for the first pixel.

2. The distance measuring device according to claim 1, wherein the measuring means includes a first TDC (Time-to-Digital Convertor) that measures the time with a first measurement resolution for the first pixel and a second TDC that measures the time with a second measurement resolution for the second pixel.

3. The first TDC and the second TDC are, a first counter that counts a synchronous clock, an oscillator whose output value changes at a period shorter than the period of the synchronous clock, and a second counter that counts the change in the output value of the oscillator, and the first counter starts counting from the time when the light emitting device emits light, from the time when the light emitting device emits light to the time when light is incident on each of the first pixel and the second pixel, the time obtained by the second counter and the oscillator, from the time when light incidence is detected at the corresponding pixel until the synchronous clock next rises, and the time obtained from the value of the first counter at the time when light incidence is detected at the corresponding pixel, The distance measuring device according to claim 2, characterized in that.

4. Furthermore, it has a holding circuit for holding the internal signal of the oscillator, from the time when the light emitting device emits light to the time when light is incident on each of the first pixel and the second pixel, The time from when light incidence is detected at the corresponding pixel, obtained by the second counter and the holding circuit, until the synchronous clock next rises, and is obtained from the value of the first counter at the time when light incidence is detected at the corresponding pixel, The distance measuring device according to claim 3, characterized in that.

5. The first TDC and the second TDC have an oscillator using a plurality of delay elements connected in a ring shape, and the number of the plurality of delay elements of the oscillator of the second TDC is less than the number of the plurality of delay elements of the oscillator of the first TDC. The distance measuring device according to any one of claims 2 to 4, characterized in that.

6. The distance measuring device according to claim 5, characterized in that the delay time by the plurality of delay elements of the oscillator of the second TDC is equal to the delay time by the plurality of delay elements of the oscillator of the first TDC.

7. The oscillators of the first TDC and the second TDC have the same configuration, The first TDC includes a first delay circuit that uses a delay element with a first delay time with the output of the oscillator as an input, and a second delay circuit that uses a delay element with a second delay time shorter than the first delay time with the synchronous clock as an input, The second TDC determines the time from when the light emitting device emits light to when light enters the second pixel as the time from when light incidence is detected at the corresponding pixel, obtained by the second counter and the holding circuit, until the synchronous clock next rises, and is obtained from the value of the first counter at the time when light incidence is detected at the corresponding pixel, The first TDC determines the time from when the light emitting device emits light to when light enters the first pixel as the time from when light incidence is detected at the corresponding pixel, obtained by the second counter and the holding circuit, until the synchronous clock next rises, and the value of the first counter at the time when light incidence is detected at the corresponding pixel, and is obtained from the time obtained based on the signals held by the first delay circuit and the second delay circuit, The distance measuring device according to claim 4, characterized in that.

8. The ranging device according to any one of claims 2 to 7, wherein the first measurement resolution and the second measurement resolution are based on the period of a synchronization clock input to the first TDC and the second TDC.

9. The ranging device according to any one of claims 1 to 8, wherein the time measured for the first pixel is corrected based on the time measured for the second pixel adjacent to the first pixel.

10. A ranging device according to any one of claims 1 to 9, processing means for executing predetermined processing using the distance information obtained by the ranging device, An electronic device characterized by comprising:

11. A light receiving device in which a first pixel having a first sensitivity and a second pixel having a second sensitivity lower than the first sensitivity are two-dimensionally arranged, measurement means for measuring the time from the time when the light emitting device emits light to the time when light is incident on each of the first pixel and the second pixel, comprising the light emitting device having a plurality of light emitting elements two-dimensionally arranged, each of the plurality of light emitting elements being configured to correspond to a specific pixel of the light receiving device, among the plurality of light emitting elements, the emission period of the light emitting element corresponding to the first pixel is shorter than the emission period of the light emitting element corresponding to the second pixel, A measurement unit characterized in that the measurement resolution of the time for the second pixel in the measurement means is lower than the measurement resolution of the time for the first pixel.

12. A control method executed by a ranging device having a light receiving device in which a first pixel having a first sensitivity and a second pixel having a second sensitivity lower than the first sensitivity are two-dimensionally arranged, a measurement step of measuring the time from the time when the light emitting device emits light to the time when light is incident on each of the first pixel and the second pixel, a calculation step of calculating distance information for each of the first pixel and the second pixel based on the measured time, the light emitting device having a plurality of light emitting elements two-dimensionally arranged, each of the plurality of light emitting elements being configured to correspond to a specific pixel of the light receiving device, among the plurality of light emitting elements, the emission period of the light emitting element corresponding to the first pixel is shorter than the emission period of the light emitting element corresponding to the second pixel, A control method for a distance measuring device, characterized in that a time measurement resolution for the second pixel in the measurement process is lower than a time measurement resolution for the first pixel.

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