Ranging devices and electronic equipment

Abstract

To provide a novel technique for achieving a light-receiving device having a wide dynamic range.SOLUTION: The light-receiving device has a pixel array. The pixel array includes a first pixel and a second pixel arranged in a two-dimensional array. The first pixel includes a first sensitivity and is provided with a first optical bandpass filter. The second pixel has a second sensitivity that is lower than the first sensitivity and is provided with a second optical bandpass filter. The half-width of the second optical bandpass filter is narrower than the half-width of the first optical bandpass filter.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention provides measurement range device and electronic devices 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 emitting light and detecting the reflected light. The accuracy of distance measurement with the ToF method depends on the accuracy of measuring the time difference. Therefore, in order to improve distance measurement accuracy, it is necessary to improve the accuracy of measuring the time difference.

[0003] One way to improve the accuracy of measuring the time difference is to shorten the delay time from when the reflected light is received until when it is detected. In Patent Document 1, a photodetector in which multiple light-receiving elements are arranged two-dimensionally uses SPADs (Single Photon Avalanche Diodes) as the light-receiving elements.

[0004] The SPAD generates avalanche current by operating the avalanche photodiode in Geiger mode. The time from the incidence of a photon to the generation of avalanche current is 10 -12 Because it is short, on the order of seconds, the timing of receiving reflected light 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] Japanese Patent Application Laid-Open No. 2014-081254 [Patent Document 2] Japanese Patent Application Publication No. 2019-190892 Summary of the Invention [Problem to be solved by the invention]

[0007] The two types of SPADs used in Patent Document 2 differ in physical structure and applied voltage, and therefore the SPAD characteristics, such as temporal response characteristics, differ depending on the type of SPAD. This results in differences in measurement time depending on the type of SPAD, which is disadvantageous in terms of distance measurement accuracy. Furthermore, when manufacturing SPADs with different physical structures within a single chip, the manufacturing process may become complicated and the SPAD characteristics may vary greatly.

[0008] The present invention has a wide dynamic range Distance measurement One of the objectives is to provide a new technology for realizing the device. [Means for solving the problem]

[0009] The object of the present invention is to provide a light receiving device having a pixel array in which first pixels each having a first optical bandpass filter and a first sensitivity and second pixels each having a second optical bandpass filter and a second sensitivity lower than the first sensitivity are arranged two-dimensionally. a first measuring means for measuring the time of flight of light corresponding to the output signal based on the output signal of the first pixel; and a second measuring means for measuring the time of flight of light corresponding to the output signal based on the output signal of the second pixel. The half width of the second optical bandpass filter is narrower than the half width of the first optical bandpass filter. The resolution of the first measurement means is higher than the resolution of the second measurement means. Characterized by Distance measurement This is achieved by the device. [Effects of the Invention]

[0010] According to the present invention, a wide dynamic range Distance measurement It is possible to provide a novel technique for realizing the device. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing an example of the functional configuration of a distance measuring device 100 using a light receiving device according to an embodiment. [Figure 2] FIG. 1 shows an example of the configuration of a light source unit 111. [Figure 3]FIG. 10 is a diagram showing an example of a light projection pattern of the light source unit 111. [Figure 4] FIG. 1 is an exploded perspective view showing a typical example of the implementation of the measurement unit 120. [Figure 5] FIG. 1 is a diagram illustrating an example of the configuration of a light receiving unit 121. [Figure 6] FIG. 5 is a diagram showing an example of the spectral characteristics of an optical bandpass filter provided in a pixel 511. [Figure 7] A vertical cross-sectional view showing an example of the configuration of a light receiving element of a pixel 511. [Figure 8] FIG. 8 is a diagram showing an example of potential distribution in the cross section of FIG. 7; [Figure 9] Circuit diagram showing a configuration example of a pixel 511 [Figure 10] FIG. 1 is a block diagram showing a configuration example of a TDC array unit 122. [Figure 11] Circuit diagram showing an example of the high-resolution TDC1501 [Figure 12] High-Resolution TDC1501 Operation Diagram [Figure 13] Timing chart for distance measurement operation [Figure 14] A timing chart showing an enlarged portion of Figure 13 [Figure 15] FIG. 1 is a diagram illustrating an example of the circuit configuration of a second oscillator 1512 included in a low-resolution TDC 1502. [Figure 16] A block diagram showing an example of the functional configuration of a first oscillation adjustment circuit 1541 and a second oscillation adjustment circuit 1542. [Figure 17] 1 is a flowchart illustrating an example of a distance measurement operation according to an embodiment. [Figure 18] A diagram showing an example of a histogram of distance measurement results DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below based on exemplary embodiments with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the claimed invention. Furthermore, although multiple features are described in the embodiments, not all of them are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0013] In this specification, the fact that the characteristics of the light-receiving elements are the same means that the physical configuration and bias voltage of the light-receiving elements are not intentionally changed. Therefore, differences in characteristics may exist due to unavoidable factors such as manufacturing variations.

[0014] ●(First embodiment) 1 is a block diagram showing an example of the functional configuration of a distance measuring device using a 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 Converter) 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 a light receiving unit 133.

[0015] The overall control unit 140 controls the overall operation of the distance measuring device 100. The overall control unit 140 has, for example, a CPU, a ROM, and a RAM, and controls each unit of the distance measuring device 100 by loading a program stored in the ROM into the RAM and executing it on 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 period of time, pulsed light (pulsed light) is irradiated via a light-projecting lens 131. The pulsed light emitted from each light-emitting element irradiates a different space. A portion of the pulsed light irradiated from the light source unit 111 is reflected by the subject and enters the light-receiving unit 121 via a light-receiving lens 132. In this embodiment, the light-emitting element 211 that emits light is configured to optically correspond to a specific pixel among the plurality of pixels arranged in the light-receiving unit 121. Here, a pixel that optically corresponds to a certain light-emitting element 211 is a pixel that is positioned so as to detect the most reflected light of the light emitted from that light-emitting element 211.

[0017] The time from when the light source unit 111 emits light until the reflected light is incident on the light receiving unit 121 is measured as the time of flight ToF by the TDC array unit 122. Note that the time of flight ToF is measured multiple times to reduce the influence of noise components such as ambient light and dark counts, and noise from the TDC array unit 122 on the measurement results.

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

[0019] (Light projector unit 110) An example of the configuration of the light projection unit 110 will be described with reference to Fig. 2. Fig. 2(a) is a side view showing an example of the configuration of the collimator lens array 220 that constitutes the light source unit 111, and Fig. 2(b) is a side view showing an example of the configuration 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, such as vertical cavity surface emitting lasers (VCSELs), are arranged in a two-dimensional array. The light source array 210 is turned on and off under the control of a light source control unit 113. The light source control unit 113 can control the light source array 210 to be turned on and off for each light emitting element 211.

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

[0022] Although there are no particular limitations on the emission wavelength of the light-emitting element 211, a wavelength in the near-infrared band can suppress the effects of ambient light. VCSELs can be fabricated using semiconductor processes using materials used in edge-emitting lasers and surface-emitting lasers. 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 forming the DBR (distributed Bragg reflector) reflector of the VCSEL can be constructed 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 element combination and composition of the compound semiconductor.

[0023] The VCSELs that make up the VCSEL array are provided with electrodes 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 any 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 row by row, column by column, or rectangular area by rectangular area.

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

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

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

[0027] 3(a) shows a light projection pattern formed by three rows and three columns of light-emitting elements in light source array 210 on a plane at a predetermined distance directly facing the light-emitting surface of light-projecting unit 110. Nine light-projection areas 311 indicate regions on plane 310 within the intensity distribution of light from each light-emitting element, each having a diameter approximately equal to the full width at half maximum (FWHM).

[0028] The light emitted from the light emitting elements 211, converted into parallel light by the collimator lens 221, is given a slight divergence angle by the projection lens 131, and therefore forms a finite area on the irradiation surface (plane 310). When the positional relationship between the collimator lens array 220 and the light source array 210 is constant, a light projection area 311 equal to the number of light emitting elements 211 constituting the light source array 210 is formed on the plane 310.

[0029] The light projecting unit 110 of this 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 with the light source unit drive unit 112, it is possible to change the relative positional relationship between the light emitting element 211 and the collimator lens 221 or the light projecting lens 131. There are no particular limitations on the method by which the light source unit drive unit 112 drives the light source unit 111, and it is possible to use, for example, a mechanism that uses an electromagnetic induction system or a piezoelectric element, such as a mechanism used to drive an imaging element for image stabilization.

[0030] When the light source unit 111 is moved by the light source unit drive unit 112, for example, in a plane parallel to the substrate of the light source unit 111 (perpendicular to the optical axis of the projector lens 131), it is possible to move the light projection area 311 in a substantially parallel direction on the plane 310. For example, by turning on the light source unit 111 multiple times while moving the light source unit 111 in a plane parallel to the substrate of the light source unit 111, it is possible to artificially increase the spatial resolution of the light projection area.

[0031] 3(b) shows the spatial resolution of the light projection area 411 on the surface 410 when the light source unit 111, which has the same light source array 210 as in Fig. 3(a), is turned on four times at a constant cycle while moving the light source unit 111 once in a circle in a plane parallel to the substrate of the light source unit 111. A spatial resolution four times higher than that obtained when the light source unit 111 is not moved, as shown in Fig. 3(a).

[0032] Therefore, the density of distance measurement points can be increased by performing distance measurement with the relative positions of light source unit 111 and projection lens 131 changed. Because the spatial resolution of projection area 411 can be increased without separating the light beam, there is no risk of the measurable distance becoming shorter or the distance accuracy decreasing due to a decrease in the intensity of the reflected light.

[0033] The relative positions of the light source unit 111 and the projection lens 131 may be changed by moving the projection lens 131 in a plane parallel to the substrate of the light source unit 111. When the projection lens 131 has multiple lenses, the entire projection lens 131 may be moved, or only some 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 by the light source unit drive section 112. This makes it possible to control the divergence angle and projection angle of light.

[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 receiving timing and light receiving resolution of the light receiving unit 133.

[0036] (Measuring Unit 120) Next, the configuration of the measurement unit 120 will be described. Fig. 4 is an exploded perspective view that schematically shows an example of the implementation of the measurement unit 120. Fig. 4 shows a light receiving section 121, a TDC array section 122, a signal processing section 123, and a measurement control section 124. The light receiving section 121 and the TDC array section 122 constitute a light receiving device.

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

[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, for example, composed of a Cu-Cu connection, and one or more may be arranged in each column of the pixel 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. Further, 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. 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] Pixel L has a configuration in which a second optical bandpass filter is provided on top of a dimming layer 903 made of a 30-nm-thick tungsten thin film with a transmittance of approximately 45%. The second optical bandpass filter has a configuration in which optical resonators 911 to 914 are stacked with a low-refractive-index layer 902 with a thickness of dL sandwiched between them. The second optical bandpass filter has the spectral characteristics shown in FIG. 6(a) and is an example of an optical element added to a light-receiving element.

[0042] 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 of dE4, and a first optical bandpass 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 approximately 100%. The first optical bandpass filter is an example of an optical element added to a light receiving element, and has the spectral characteristics shown in Figure 6(b).

[0043] The first optical bandpass filter has a laminated structure in which optical resonators 911 to 913 are stacked with a low refractive index layer 902 having a thickness dL sandwiched therebetween. optics band Pass Filter The passbands of the first and second optical bandpass filters have essentially the same center wavelength, λcL = λcH in Fig. 6. The center wavelength can be the peak wavelength of the light emitted by the light source unit 111. On the other hand, the half width WL of the spectral characteristics of the second optical bandpass filter is narrower than the half width WH of the spectral characteristics of the first optical bandpass filter.

[0044] The half-value width WL is narrower than the half-value width WH because it is assumed that the low-sensitivity pixel L will primarily perform long-distance distance measurement, and the high-sensitivity pixel H will primarily perform short-distance distance measurement. The half-value width WL is narrowed in the low-sensitivity pixel L to accommodate a long ToF, thereby suppressing the measurement of noise light before the reflected light arrives.

[0045] Furthermore, pixel L is provided with a light-reducing layer 903, which makes it less sensitive than pixel H. The light-reducing layer 903 is an example of an optical element for reducing the sensitivity of a pixel. Note that instead of the light-reducing layer 903, other optical elements such as masks with different opening sizes may be used to make pixel H and pixel L different in sensitivity.

[0046] For example, by providing a mask in pixel L with a smaller opening than the mask provided in pixel H, the light receiving area of ​​the light receiving element in pixel L can be made narrower than the light receiving area of ​​the light receiving element in pixel H. It is not necessary to provide a mask in pixel H, in which case it is sufficient to provide a mask in pixel L with an opening ratio of less than 100%. The mask can be made of any material that can form a light-shielding film.

[0047] In this embodiment, the sensitivity of the pixels is changed by using optical elements added to the light receiving elements, rather than changing the configuration or applied voltage of the light receiving elements themselves. Therefore, the configuration and applied voltage of the light receiving elements can be the same for pixel H and pixel L. This makes it easy to manufacture the light receiving element array, and also makes it possible to suppress variations in the characteristics of the light receiving elements.

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

[0049] In addition, a light-shielding wall 1003 is provided between the adjacent pixels to prevent light that is obliquely incident on the light-receiving region 1001 from reaching the light-receiving region 1001 of an adjacent pixel. The light-shielding wall 1003 is made of metal, and an insulating region 1004 is provided between the light-shielding wall 1003 and the light-receiving region 1001.

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

[0051] 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 via the anode electrode Vbd. The negatively charged electrons are transported as signal charges to the avalanche region 1002 by an electric field set so that the potential decreases toward the avalanche region 1002, as shown in Figures 8(a), 8(b), and 8(c).

[0052] The signal charge that reaches the avalanche region 1002 causes avalanche breakdown due to the strong electric field in the avalanche region 1002, generating an avalanche current. This phenomenon occurs not only with signal light (reflected light from the light source unit 111) but also with incident ambient light, which is noise light, and becomes a noise component. Furthermore, carriers are not only generated by incident light, but also thermally. Avalanche current caused by thermally generated carriers is called dark count and becomes a noise component.

[0053] 9 is an equivalent circuit diagram of a pixel 511. The pixel 511 has 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 combined area of ​​the light receiving region 1001 and the avalanche region 1002 in FIG.

[0054] When a pixel selection switch 1404 is turned on by an externally supplied control signal, the output signal of the inverter 1403 is output to a 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 greater than the breakdown voltage is applied to the SPAD element 1401. At this time, no current flows through the load transistor 1402, so the cathode potential Vc is close to the power supply voltage Vdd, and the pixel output signal is "0."

[0055] When an avalanche current occurs in the SPAD element 1401 due to the arrival of a photon, 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 decreases, the reverse bias applied to the SPAD element 1401 decreases, and when the reverse bias becomes equal to or lower than the breakdown voltage, the generation of the avalanche current stops. Thereafter, a hole current flows from the power supply voltage Vdd via the load transistor 1402, causing the cathode potential Vc to rise, and the output (pixel output) of the inverter 1403 returns from "1" to "0," returning to the state before the arrival of the photon. 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 section 122) The TDC array section 122 measures the time from when the light source unit 111 emits light to when the output signal of the pixel 511 changes from "0" to "1" as ToF. 10 is a diagram schematically illustrating an example of the configuration of the TDC array unit 122. The TDC array unit 122 includes a high-resolution TDC 1501 having a first measurement resolution and a low-resolution TDC 1502 having a second measurement resolution, each of which corresponds to half the number of pixels constituting one pixel row of the pixel array, and measures the ToF for each pixel on a pixel-by-pixel basis. The second measurement resolution is lower than the first measurement resolution. A synchronization clock is supplied from, for example, the overall control unit 140.

[0058] Here, the relay buffer drives the output signals of the high-sensitivity pixels H so that they are input to the high-resolution TDC 1501, and the output signals of the low-sensitivity pixels L so that they are input to the low-resolution TDC 1502. In other words, the high-sensitivity pixels H measure time at a higher measurement resolution than the low-sensitivity pixels L. In FIG. 10, odd-numbered pixel outputs are the outputs of pixels H, and even-numbered pixel outputs are the outputs of pixels L. To make the delay times in the relay buffers roughly equal, the high-resolution TDC 1501 and low-resolution TDC 1502 are arranged alternately.

[0059] The high-resolution TDC 1501 has a first oscillator 1511, a first oscillation count circuit 1521, and a first synchronous clock count circuit 1531. The low-resolution TDC 1502 has 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 changes in the output value of the corresponding oscillator. The first synchronous clock count circuit 1531 and the second synchronous clock count circuit 1532 are first counters that count synchronous clocks.

[0060] In each TDC output value, 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 intermediate bits. In other words, the synchronous clock count circuit measures roughly, the internal signal of the oscillator measures finely, and the oscillation count circuit measures the interval between them. Note that each measurement bit may have a redundant bit.

[0061] 11 is a diagram schematically illustrating an example configuration of the first oscillator 1511 of the high-resolution TDC 1501. 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. The buffers 1611 to 1617 and the inverter 1618, which serve as delay elements, are connected alternately 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 an adjustment voltage.

[0062] FIG. 12 shows the relationship between the output signals of the buffers 1611 to 1617 and the inverter 1618 and the internal signal of the oscillator, and the delay time t buff The WI11 output to WI18 output are the output signals of buffers 1611 to 1617 and inverter 1618, respectively.

[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, the delay time t buff After this time has elapsed, the outputs of buffers 1612 to 1617 and inverter 1618, which have matched inputs and outputs, do not change. On the other hand, the output of buffer 1611, which does not have matched inputs and outputs, changes from "0" to "1" (the signal advances by one stage).

[0064] Furthermore, buff After the time has elapsed (2×t buff After this, the outputs of the buffers 1611, 1613 to 1617 and inverter 1618, whose inputs and outputs are matched, do not change. On the other hand, the output of the buffer 1612, whose inputs and outputs are not matched, changes from "0" to "1" (the signal advances by another stage).

[0065] In this way, the delay time of one buffer stage t buffEach time t passes, one output of the buffers 1611 to 1617 and the inverter 1618 that does not have input / output matching changes from "0" to "1" in order. Then, after the oscillation switch 1630 is turned on, buff After this time, the output of all buffers and inverters changes to "1" (the signal goes around once). buff After elapsed (16 × t buff After this time has elapsed, the outputs of all buffers and inverters change to "0" (the signal goes around twice) and return to their original state.

[0066] After that, 16×t buuf The output changes in the same manner with a period of t buff Also, the time resolution t buff is adjusted by the first oscillation adjustment circuit 1541 (described later) to 2 times the period of the synchronous clock. -7 It is adjusted to be (1 / 128).

[0067] The oscillator output, which is the output of the inverter 1618, is input to a first oscillation count circuit 1521. The first oscillation count circuit 1521 counts the rising edges of the oscillator output, thereby calculating 16×t buff Measure time with a time resolution of .

[0068] 13 is a timing chart showing the time measurement from when light is emitted until reflected light is detected by the SPAD element 1401. It shows changes in the cathode potential Vc of the SPAD element 1401, the pixel output signal, the synchronous clock, the count value of the synchronous 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 page indicating a higher voltage. The synchronous clock, oscillator start / stop signal generation circuit output, and oscillator output are digital signals, with the upper side indicating the on state and the lower side indicating the off state. The count values ​​of the synchronous clock count circuit and oscillator count circuit are digital values ​​and are shown in decimal.

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

[0071] 13 and 14, the operation of measuring the time from the light emission time 1801 of the light source unit 111 to the time 1803 when a photon enters 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 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 is turned on, the oscillation operation starts, and a signal loop starts inside the oscillator as shown in Fig. 12. After the oscillation switch 1630 is turned on, 16 × t buffAfter time 1801 has elapsed and the signal makes two cycles in the oscillator, a rising edge appears in the oscillator output and the first oscillation count circuit 1521 counts the number of rising edges. Also, at time 1803, the first synchronous clock count circuit 1531 stops counting and holds the count value.

[0075] After the first oscillator 1511 is turned on at time 1803, the first rising edge of the synchronous clock is at 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. 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 is. Furthermore, because 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 The time from time 1801 to time 1802 is 2 7 ×t buff The count result of the oscillator count circuit is D ROclk The time from time 1803 to time 1804 is 2 4 ×t buff Furthermore, the oscillator internal signal D ROin The time from time 1804 to time 1805 is t buff The high-resolution TDC 1501 performs the following processing on these values ​​and outputs them to the signal processing unit 123, thereby completing one measurement operation.

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

[0078] D obtained from equation (2) ROThe time from time 1803 to time 1805 is t buff The time from time 1802 to time 1805 is equal to one cycle of the synchronous clock, so 2 7 ×t buff Therefore, from one cycle of the synchronous clock, D RO By subtracting , the time from time 1802 to time 1803 is obtained. This is called D Gclk Adding these, the time from time 1801 to time 1803 is t buff The value measured in units of D 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] 15 is a diagram schematically illustrating an example of the circuit configuration of the 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 in a ring shape, alternately with an oscillation switch 2030. 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 TDC1501, the number of buffers and oscillation switches has been reduced from seven to three. On the other hand, the buffers 2011 to 2013 and the inverter 2014 each have a delay time t buff However, the high-resolution TDC1501 buff The second oscillation adjusting circuit 1542 adjusts the frequency to twice the frequency of the first oscillation.

[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 oscillator internal signal of the second oscillator 1512 can be made one bit less than that of the first oscillator 1511.

[0082] As mentioned above, the low sensitivity pixel L is primarily intended for use in long-distance distance measurement. 。T The impact of the ToF measurement resolution on the accuracy of distance measurement results is greater for short distances than for long distances. Therefore, the low-resolution TDC1502, which measures the ToF of the low-sensitivity pixel L, prioritizes reducing the circuit size and power consumption, and has a lower ToF measurement resolution than the high-resolution TDC1501.

[0083] Delay time t buff The oscillation frequency varies depending on factors such as manufacturing errors in the transistors, fluctuations in the voltage applied to the TDC circuit, and temperature. For this reason, a first oscillation adjustment circuit 1541 and a second oscillation adjustment circuit 1542 are provided for every eight TDCs.

[0084] 16 is a block diagram showing an example of the functional configuration 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 following description will focus on the first oscillation adjustment circuit 1541. The first oscillation adjustment circuit 1541 is a 1 / 2 oscillation adjustment circuit including a dummy oscillator 2101 and a dummy oscillator 2102. 3 It has a (1 / 8) frequency divider 2102 and a phase comparator 2103 .

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

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

[0087] The phase comparator 2103 increases the output voltage when the frequency of the synchronous clock signal is higher, and decreases the output voltage when the frequency of the synchronous clock is lower. 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 oscillation frequency of the first oscillator 1511 is adjusted to 2 times the frequency of the synchronous clock. 3 The delay is adjusted so that the delay is doubled. The same applies to the second oscillation adjustment circuit 1542.

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

[0089] For example, by inputting a 160MHz clock signal as the synchronous clock signal, the oscillation frequency becomes 1.28GHz, which is eight times the synchronous clock frequency, for both the high-resolution TDC1501 and the low-resolution TDC1502. The delay time t buff is 48.8ps for the high-resolution TDC1501 and 97.7ps for the low-resolution TDC1502.

[0090] (ranging sequence) FIG. 17 is a flowchart showing an example of a distance measurement operation in this embodiment. In S2201, the overall control unit 140 resets the histogram circuit and measurement counter i of the signal processing unit 123. In addition, 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 that is caused to emit light in S2202 is input to the TDC array unit 122.

[0091] In S2202, the overall control unit 140 causes some of the light emitting elements 211 that make up 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 a time corresponding to a predetermined maximum distance measurement range has elapsed since the light emission, S2204 is executed.

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

[0094] In S2205, the signal processing unit 123 adds 1 to the value of the measurement number counter i. In S2206, the signal processing unit 123 counts the value of the measurement number counter i until it reaches a preset number N total The signal processing unit 123 determines whether the value of the measurement number counter i is greater than the set number N total If it is determined that the value of the measurement number counter i is greater than the set number N, S2207 is performed. total If it is not determined to be greater, 2202 is executed.

[0095] In S2207, the signal processing unit 123 removes the counting results that appear to be noise components based on the histogram of each pixel, and then executes S2208. In S2208, the signal processing unit 123 averages the measurement results that were not removed in S2207 in the histogram of each pixel, and outputs the average value as the measured ToF, thereby completing one ranging sequence.

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

[0097] FIG. 18(a) shows the N total 1 is a diagram showing an example of a histogram of TDC measurement results. The horizontal axis represents the TDC measurement results (time), and the vertical axis represents frequency. Note that the bin width of the TDC measurement results is set for convenience.

[0098] The measurement results included in section 2302 form a frequency peak and are therefore considered to be correct measurements of the time from light emission to light reception. On the other hand, the measurement results included in section 2304 are irregularly and sparsely distributed and are therefore considered to be noise light such as randomly occurring ambient light, or noise components due to dark counts. Therefore, the measurement results included in section 2304 are removed, and the average 2303 of only the measurement results included in section 2302 is used as the distance measurement result.

[0099] In FIG. 18(b), similarly to FIG. 18(a), N total 18(a) shows an example of a histogram of the TDC measurement results obtained in a situation where there is more ambient light than during the measurement shown in FIG. 18(a). The subject is the same as in FIG. 18(a), but the histogram shows an example of the TDC measurement results obtained in a situation where there is more ambient light than during the measurement shown in FIG. 18(a). total The TDC measurement has already been completed, and the TDC measurement results for the reflected light from the subject have not been obtained.

[0100] FIG. 18(c) shows the N obtained for the low-sensitivity pixel L under the same environment as FIG. 18(b). total18(a) is a diagram showing an example of a histogram of TDC measurement results. Because the low-sensitivity pixel L has lower sensitivity than the high-sensitivity pixel H, the number of times TDC measurement is performed for noise light decreases. As a result, the number of measurement results included in section 2302 increases, and the average value of the measurement results included in section 2302 can be calculated as the distance measurement result, as in FIG. 18(a). In this way, the low-sensitivity pixel L is more tolerant than the high-sensitivity pixel H to situations with high ambient light noise.

[0101] Note that we have described situations that can occur in environments with a lot of noise light. However, the same problem can also occur when the object being measured is at a long distance. This is because when an object is at a long distance, the period from when light is emitted until the reflected light returns (i.e., the period during which noise light is detected) becomes longer.

[0102] In this embodiment, by using the high-sensitivity pixel H and the low-sensitivity pixel L, stable distance measurement is possible with the influence of noise light suppressed, even when there is a large amount of noise light or when measuring the distance to a distant object. Furthermore, 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, there is little variation between the distance measurement results obtained with the high-sensitivity pixel H and the low-sensitivity pixel L, and accurate distance measurement results can be obtained.

[0103] (HDR driving method) Next, we will explain HDR driving of the high-sensitivity pixel H and the low-sensitivity pixel L using Figures 18(d) and 18(e). Figure 18(d) shows an example of a histogram of the measurement results of the high-sensitivity pixel H, and Figure 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 Figure 18(d).

[0104] The light emitting element 211 corresponding to the high-sensitivity pixel H has a light emission period of 2602, and the light emitting element 211 corresponding to the low-sensitivity pixel L has a light emission period of 2702. The light emission period 2702 is four times the light emission period 2602. Therefore, it is possible to measure the distance four times more times for the high-sensitivity pixel H than for the low-sensitivity pixel L within the same time period. Because there is a high probability that the number of distance measurement results to be averaged will be greater than that for the low-sensitivity pixel L, and because measurements for the high-sensitivity pixel H are performed by the high-resolution TDC 1501, the distance measurement accuracy of the space corresponding to the high-sensitivity pixel H is higher than the distance measurement accuracy of the space corresponding to the low-sensitivity pixel L.

[0105] When the object to be measured is far away, the ToF becomes longer, increasing the possibility of measuring noise light. The light-emitting element 211 corresponding to the low-sensitivity pixel L, which has a large noise light suppression effect, does not emit light again until it detects reflected light. On the other hand, the light-emitting element 211 corresponding to the high-sensitivity pixel H, which has a small noise light suppression effect, emits light again before detecting reflected light. This shortens the time from the start of measurement by the TDC to the detection of reflected light, reducing the possibility of measuring noise light between emission and the arrival of reflected light, enabling accurate time measurement with the high-sensitivity pixel H even in an environment with a large amount of noise light.

[0106] The signal processing unit 123 applies offset correction based on the measurement results obtained for the adjacent low-sensitivity pixel L to the measurement results obtained for the high-sensitivity pixel H. The offset correction is performed by adding a constant multiple of the light emission period (measurement period) 2602 of the high-sensitivity pixel H to the measurement results 2611 for the high-sensitivity pixel H based on the measurement results 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 it takes for the reflected light of emitted light to arrive at 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 more than twice but less than three times the light emission period 2602 for the high-sensitivity pixel H. Therefore, in the offset correction, the signal processing unit 123 adds a time twice the light emission period 2602 to the measurement result 2611 for the high-sensitivity pixel H.

[0108] The offset correction amount may be determined based on 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 measurement results obtained for four or two low-sensitivity pixels L adjacent to the high-sensitivity pixel H in the horizontal and / or vertical directions.

[0109] Alternatively, an imaging unit may be provided that captures an image of the projection range of the light projection unit 110, and the captured image may be used to identify low-sensitivity pixels L used to determine the offset correction amount. For example, the signal processing unit 123 may identify, based on the captured image, one or more adjacent low-sensitivity pixels L that are thought to be measuring the distance to the same subject as the high-sensitivity pixel H to be corrected. Then, the signal processing unit 123 may use the measurement results obtained for the identified low-sensitivity pixels L to determine the offset correction amount (or a coefficient to be multiplied by the light emission cycle of the high-sensitivity pixel H).

[0110] According to this embodiment, a light receiving device with a wide dynamic range can be realized by using light receiving elements with different sensitivities. Furthermore, the sensitivity of the light receiving elements is varied depending on the optical elements added to the light receiving elements. This allows light receiving elements with the same configuration to be used, which is advantageous from the viewpoints of ease of manufacturing and suppression of characteristic variations. Furthermore, by setting the time measurement resolution of low-sensitivity pixels lower than that of high-sensitivity pixels, it is possible to efficiently reduce circuit size and power consumption while suppressing degradation of distance measurement accuracy.

[0111] (Other embodiments) The distance measuring device described above can be implemented in any electronic device having a 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 consoles, robots, drones, vehicles, etc. These are merely examples, and the distance measuring device according to the present invention can also be implemented in other electronic devices.

[0112] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0113] The present invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Therefore, the following claims are appended to clarify the scope of the invention. [Explanation of symbols]

[0114] 100... distance measuring device, 110... light projection unit, 111... light source unit, 120... measurement unit, 122... TDC array unit, 123... signal processing unit, 124... measurement control unit, 131... light projection lens, 140... overall control unit,

Claims

1. a light receiving device having a pixel array in which first pixels each having a first sensitivity and each having a first optical bandpass filter and second pixels each having a second sensitivity lower than the first sensitivity are arranged two-dimensionally; a first measuring means for measuring a time of flight of light corresponding to an output signal of the first pixel based on the output signal; a second measurement means for measuring a time of flight of light corresponding to an output signal of the second pixel based on the output signal of the second pixel, a half width of the second optical bandpass filter is narrower than a half width of the first optical bandpass filter; A distance measuring device, characterized in that the resolution of the first measuring means is higher than the resolution of the second measuring means.

2. 2. The distance measuring device according to claim 1, wherein a light-receiving element of the second pixel is provided with a light-reducing means or a mask as an optical element.

3. 3. The distance measuring device according to claim 1, wherein the light receiving elements of the first pixel and the second pixel are avalanche photodiodes.

4. 4. The distance measuring device according to claim 1, wherein the center wavelengths of the pass bands of the first optical band pass filter and the second optical band pass filter are equal to each other.

5. 5. The distance measuring device according to claim 1, wherein the first pixels and the second pixels are arranged alternately.

6. A ranging device as described in any one of claims 1 to 5, characterized in that it further has a calculation means for calculating distance information for each of the first pixel and the second pixel based on the flight times measured by the first measurement means and the second measurement means, respectively.

7. A ranging device as described in Claim 6, characterized in that the flight time measured by the first measuring means and the second measuring means is the time from when the light emitting device emits light to when light is incident on each of the first pixel and the second pixel.

8. the light-emitting device has a plurality of light-emitting elements arranged two-dimensionally, 8. The distance measuring device according to claim 7, wherein each of the plurality of light emitting elements is configured to correspond to a specific pixel of the light receiving device.

9. 9. The distance measuring device according to claim 8, wherein the light emitting element corresponding to the first pixel among the plurality of light emitting elements has a light emitting period shorter than the light emitting element corresponding to the second pixel.

10. A light receiving device having a pixel array in which first pixels each having a first sensitivity and a second pixel each having a second sensitivity and a second optical band pass filter are arranged two-dimensionally; a light-emitting device in which a plurality of light-emitting elements including a light-emitting element corresponding to the first pixel and a light-emitting element corresponding to the second pixel are two-dimensionally arranged; a calculation means for calculating distance information for each of the first pixel and the second pixel based on the time from a predetermined time to the time when light is incident on each of the first pixel and the second pixel, a half width of the second optical bandpass filter is narrower than a half width of the first optical bandpass filter; A distance measuring device, wherein a light emitting period of a light emitting element corresponding to said first pixel is shorter than a light emitting period of a light emitting element corresponding to said second pixel.

11. 11. The distance measuring device according to claim 10, wherein the time measured for the first pixel is corrected based on the time measured for the second pixel adjacent to the first pixel.

12. A distance measuring device according to any one of claims 6 to 11; a processing means for executing a predetermined process using distance information obtained by the distance measuring device; An electronic device comprising:

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