Distance measuring device

Abstract

To provide a distance measuring device that can efficiently execute distance measurement using rays of light with different wavelengths.SOLUTION: A distance measuring device has a light source unit that can radiate light with a first wavelength and light with a second wavelength longer than the first wavelength at the same time, and calculates distance information based on the time from the start of distance measurement until when incidence of light on pixels of a light receiving section is detected. In a pixel array of the light receiving section, first pixels configured to receive the light with the first wavelength and second pixels configured to receive the light with the second wavelength are two-dimensionally arranged.SELECTED DRAWING: Figure 19

Description

Technical Field

[0001] The present invention relates to a distance measuring device.

Background Art

[0002] A ToF (Time-of-Flight) distance measuring method is known in which the distance to an object that reflects light is measured by measuring the time difference from when light is irradiated until the reflected light is detected. In particular, when performing ToF distance measurement outdoors, it is important to suppress the influence of ambient light.

[0003] Patent Document 1 discloses a configuration in which the influence of ambient light is suppressed by controlling the combination of the wavelength emitted by a light emitting diode and the pass band of a band pass filter of a light receiving device according to the temperature.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Patent Document 1, it is necessary to provide at least two sets of at least one of a light emitting unit and a filter, or to use a light emitting diode whose emission wavelength changes depending on temperature, resulting in a complicated and large-sized configuration. Therefore, it is disadvantageous in terms of cost and is not suitable for applications such as being incorporated into small electronic devices. Furthermore, since only one wavelength is actually used for distance measurement, for example, when light having a wavelength close to that of ambient light exists, the influence of ambient light cannot be suppressed.

[0006] One object of the present invention is to improve at least one of the problems of such conventional techniques and to provide a distance measuring device capable of efficiently performing distance measurement using lights of different wavelengths.

Means for Solving the Problem

[0007] The above object is achieved by a light source unit capable of simultaneously irradiating light of a first wavelength and light of a second wavelength longer than the first wavelength, a pixel array having pixels arranged two-dimensionally, a light receiving unit that detects the incidence of light on the pixels, where the pixel array includes a first pixel configured to receive light of the first wavelength and a second pixel configured to receive light of the second wavelength, measurement means for detecting the time from the start of distance measurement until the incidence of light on the pixels is detected and calculating distance information based on the detected time, and determination means for determining the pixel to be used for calculating the distance information among the first pixel and the second pixel. A distance measuring device, The determination means when a first operation mode is set in the distance measuring device, determines that it is raining, and when a second operation mode different from the first operation mode is set in the distance measuring device, determines to use a first pixel and a second pixel for calculating distance information. uses the first pixel for calculating the distance information when the weather is

Figure 1

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a distance measuring device capable of efficiently performing distance measurement using light of different wavelengths.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] 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. Also, 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 given the same reference numerals, and redundant descriptions are omitted.

[0011] 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.

[0012] ●(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 measuring 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 measuring 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.

[0013] 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.

[0014] 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 (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.

[0015] 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 addition, 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 multiple times.

[0016] The signal processing unit 123 generates a histogram of the measurement results obtained multiple times by the TDC array unit 122 and removes the noise components based on the histogram. Then, the signal processing unit 123 substitutes 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) to calculate the distance L of the subject. 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.

[0017] (Projection unit 110) Using Fig. 2, a configuration example of the projection unit 110 will be described. Fig. 2(a) is a side view showing a configuration example of the collimator lens array 220 constituting the light source unit 111, and Fig. 2(b) is a side view showing a configuration example of the light source array 210 constituting the light source unit 111.

[0018] The light source array 210 has a configuration in which light-emitting elements 211, which are vertical cavity surface emitting laser (VCSEL) elements for example, 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 for each light-emitting element 211 unit.

[0019] Note that elements other than VCSELs, such as edge-emitting laser elements and LEDs (light-emitting diodes), may be used for 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.

[0020] 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. The VCSEL can be fabricated by a semiconductor process 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, a GaAs-based semiconductor material can be used. In this case, the dielectric multilayer film forming the DBR (distributed Bragg reflector) mirror constituting the VCSEL can be formed by alternately and periodically laminating 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.

[0021] The VCSELs constituting 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 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.

[0022] 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.

[0023] FIG. 2(c) is a vertical cross-sectional view showing an arrangement example of the light source unit driving unit 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.

[0024] 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 in the range of ±45 degrees. Note that the projection lens 131 may be omitted by controlling the light emission direction with the collimator lens 221.

[0025] FIG. 3(a) shows an example of a light projection pattern by the projection unit 110 using the light source array 210 in which VCSEL elements are arranged in 3 rows and 3 columns. 310 is a plane at a predetermined distance directly facing the light-emitting surface of the projection unit 110. The nine light projection areas 311 indicate regions having a diameter approximately equal to the full width at half maximum (FWHM) of the light intensity distribution from each VCSEL element on the plane 310.

[0026] Since the emitted light of the VCSEL converted into parallel light by the collimator lens 221 is given a slight divergence angle by the projection lens 131, a finite region 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 constituting the light source array 210 are formed on the plane 310.

[0027] The light projection unit 110 of the present embodiment has a light source unit driving 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 driving unit 112, the relative positional relationship between the light emitting element 211 and the collimator lens 221 or the light projection lens 131 can be changed. There is no particular limitation on the method by which the light source unit driving 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 a mechanism used to drive an imaging element for shake correction, can be used.

[0028] When the light source unit driving 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 light projection lens 131), it is possible to substantially translate the light projection area 311 in the plane 310. For example, by lighting the light source unit 111 multiple 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.

[0029] 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.

[0030] Therefore, by performing distance measurement in a state where the relative positions of the light source unit 111 and the light projection lens 131 are different, the density of the distance measurement points can be increased. Since the spatial resolution of the light 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.

[0031] In addition, the relative position between the light source unit 111 and the light projection lens 131 may be changed by moving the light projection lens 131 within a plane parallel to the substrate of the light source unit 111. When the light projection lens 131 includes a plurality of lenses, the entire light projection lens 131 may be moved, or only some of the lenses may be moved.

[0032] Furthermore, the light source unit driving unit 112 may be configured to move the light source unit 111 in a direction perpendicular to the substrate of the light source array 210 (the optical axis direction of the light projection lens 131). Thereby, the divergence angle and the light projection angle of the light can be controlled.

[0033] 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.

[0034] (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.

[0035] The measurement unit 120 has a configuration in which a light reception element substrate 510 including a light reception unit 121 in which pixels 511 are 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 reception element substrate 510 and the logic substrate 520 are electrically connected through a substrate connection 530. FIG. 4 shows the light reception element substrate 510 and the logic substrate 520 in a separated state for the sake of explanation.

[0036] 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 pixel 511, or one may be arranged for each pixel 511.

[0037] 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.

[0038] 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.

[0039] The pixel L has a configuration in which a second optical bandpass filter is provided on a light attenuation layer 903 made of a tungsten thin film with a film thickness of 30 nm and having a transmittance of about 45%. The second optical bandpass filter has a configuration in which the optical resonators 911 to 914 are stacked with the low refractive index layer 902 having a film thickness dL interposed therebetween. The second optical bandpass filter has the spectral characteristics shown in FIG. 6(a) and is an example of an optical element added to the light receiving element.

[0040] The pixel H has a structure in which a multilayer interference mirror 915, a film thickness adjustment layer 905 with a film thickness dE4 made of a low refractive index layer, and a first optical band-pass filter are provided on a transmittance layer 904 with a transmittance of about 100% composed of a low refractive index layer with a film thickness of 30 nm. 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).

[0041] The first optical band-pass filter has a structure in which an optical resonator 911 and an optical 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 Pass filter band ​ 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.

[0042] 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. In the low-sensitivity pixel L, the half-value width WL is narrowed so as to be able to handle a long ToF, and it is suppressed that noise light is measured before the reflected light arrives.

[0043] Also, the pixel L is configured to be less sensitive than the pixel H by providing a light attenuation layer 903. The light attenuation layer 903 is an example of an optical element for reducing the sensitivity of the pixel. Instead of the light attenuation layer 903, other optical elements such as a mask with different aperture amounts may be used to make the sensitivities of the pixel H and the pixel L different.

[0044] For example, by providing a mask with a smaller aperture amount than the mask provided for pixel H to pixel L, 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.

[0045] In this embodiment, instead of varying the configuration of the light-receiving element itself or the applied voltage, the sensitivity of the pixel is varied using an optical element added to the light-receiving element. 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 element can be suppressed.

[0046] 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 region (photoelectric conversion region) 1001 and an avalanche region 1002 that generates an avalanche current by signal charges generated by photoelectric conversion.

[0047] In addition, in order to prevent the light obliquely incident on the light-receiving region 1001 from reaching the light-receiving region 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 region 1004 is provided between the light-shielding wall 1003 and the light-receiving region 1001.

[0048] FIG. 8(a) is a diagram showing the potential distribution of the semiconductor region of the a-a' cross-section of FIG. 7. FIG. 8(b) is a diagram showing the potential distribution of the b-b' cross-section of FIG. 7. FIG. 8(c) is a diagram showing the potential distribution of the c-c'' cross-section of FIG. 7.

[0049] 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).

[0050] The signal charges that reach the avalanche region 1002 cause an 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 (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, and becomes a noise component. In addition, carriers are generated not only by incident light but also thermally. The avalanche current caused by thermally generated carriers is called dark count and becomes a noise component.

[0051] 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 combined region of the light-receiving region 1001 and the avalanche region 1002 in FIG. 7.

[0052] 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 such 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".

[0053] 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".

[0054] When the cathode potential Vc decreases, the reverse bias applied to the SPAD element 1401 decreases, and when the reverse bias becomes below 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, causing the cathode potential Vc to rise. The output (pixel output) of the inverter 1403 returns from "1" to "0", returning to the state before the arrival of photons. The signal output from the pixel 511 in this way is input to the TDC array unit 122 via a relay buffer (not shown).

[0055] (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. In the TDC array unit 122, a high-resolution TDC 1501 having a first measurement resolution and a low-resolution TDC 1502 having a second measurement resolution are each provided with half the number of pixels constituting one pixel row of the pixel array, and measure ToF for each pixel in one-pixel units. 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.

[0056] Here, the output signal of the high-sensitivity pixel H is input to the high-resolution TDC 1501, and the output signal of the low-sensitivity pixel L is input to the low-resolution TDC 1502, and it is driven by a relay buffer. That is, for the high-sensitivity pixel H, the time is measured with a higher measurement resolution than the low-sensitivity pixel L. In FIG. 10, the pixel outputs of odd numbers are the outputs of the pixel H, and the pixel outputs of even numbers are the outputs of the pixel L. The high-resolution TDC 1501 and the low-resolution TDC 1502 are alternately arranged to make the delay times in the relay buffer approximately equal.

[0057] The high-resolution TDC1501 has a first oscillator 1511, a first oscillation counting circuit 1521, and a first synchronous clock counting circuit 1531. The low-resolution TDC1502 has a second oscillator 1512, a second oscillation counting circuit 1522, and a second synchronous clock counting circuit 1532. The first oscillation counting circuit 1521 and the second oscillation counting circuit 1522 are second counters that count changes in the output values of the corresponding oscillators. The first synchronous clock counting circuit 1531 and the second synchronous clock counting circuit 1532 are first counters that count synchronous clocks.

[0058] In the output values of each TDC, the count result of the synchronous clock counting circuit constitutes the upper bits, the internal signal of the oscillator constitutes the lower bits, and the count result of the oscillation counting circuit constitutes the middle bits. That is, it is configured to roughly measure with the synchronous clock counting circuit, finely measure with the internal signal of the oscillator, and measure the interval with the oscillation counting circuit. Note that redundant bits may be provided for each measurement bit.

[0059] FIG. 11 is a diagram schematically showing a configuration example of the first oscillator 1511 of the 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 in 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.

[0060] FIG. 12 shows the output signals of the buffers 1611 to 1617 and the inverter 1618 and the internal signal of the oscillator at the time of reset and the delay time t of one buffer stage after the oscillation switch 1630 is turned on. buffEach change is shown. The WI11 output to the WI18 output are the output signals of buffers 1611 to 1617 and inverter 1618, respectively.

[0061] At the time of reset, the outputs of buffers 1611 to 1617 are "0", and the output of inverter 1618 is "1". After the oscillation switch 1630 is turned on, after the delay time t of one buffer stage buff has elapsed, the outputs of buffers 1612 to 1617 and inverter 1618 whose input and output are in alignment do not change. On the other hand, the output of buffer 1611 whose input and output are not in alignment changes from "0" to "1" (the signal advances by one stage).

[0062] Furthermore, after t buff has elapsed (after 2×t buff ), the outputs of buffers 1611, 1613 to 1617 and inverter 1618 whose input and output are in alignment do not change. On the other hand, the output of buffer 1612 whose input and output are not in alignment changes from "0" to "1" (the signal advances by one more stage).

[0063] In this way, every time the delay time t of one buffer stage buff elapses, one output among buffers 1611 to 1617 and inverter 1618 whose input and output are not in alignment changes from "0" to "1" in order. Then, after 8×t buff has elapsed since the oscillation switch 1630 was turned on, the outputs of all buffers and inverters change to "1" (the signal makes one round). Furthermore, after 8×t buff has elapsed (after 16×t buff has elapsed), the outputs of all buffers and inverters change to "0" (the signal makes two rounds) and return to the original state.

[0064] After that, the output changes in the same way with a period of 16×t buuf . In this way, the time resolution of the high-resolution TDC1501 is equal to t buff . Also, the time resolution t buff is 2 of the period of the synchronization clock by the first oscillation adjustment circuit 1541 described later -7It is adjusted to be (1 / 128).

[0065] Also, the oscillator output, which is the output of the inverter 1618, is input to the first oscillation count circuit 1521. In the first oscillation count circuit 1521, by counting the rising edge of the oscillator output, 16×t buff The time is measured with a time resolution of.

[0066] 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.

[0067] The cathode potential Vc of the SPAD element 1401 is an analog voltage, and the upper side of the paper shows a higher voltage. The synchronization clock, the output of the oscillator start / stop signal generation circuit, and the oscillator output are digital signals, and the upper side of the paper indicates the on state and the lower side of the paper indicates the off state. The count values of the synchronization clock count circuit and the oscillator count circuit are digital values and are shown in decimal.

[0068] FIG. 14 is an enlarged view of the output of the oscillator start / stop signal generation circuit, the oscillator output, the count value of the oscillator count circuit, and the internal oscillator signal from time 1803 to time 1805 in FIG. 13. The internal oscillator signal is a digital value and is shown in decimal.

[0069] Using FIGS. 13 and 14, the operation of measuring the time from the light emission time 1801 of the light source unit 111 until the time 1803 when photons are incident on the SPAD element 1401 of the pixel and the pixel output signal changes from 0 to 1 with the high-resolution TDC 1501 will be described.

[0070] 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 synchronization clock supplied via the overall control unit 140. When the first synchronization clock count circuit 1531 is instructed to start measurement from the overall control unit 140 at time 1801 when the light emitting element 211 emits light, it starts counting the rising edges of the synchronization clock.

[0071] 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.

[0072] When the oscillation switch 1630 turns on, the oscillation operation starts, and a signal loop starts inside the oscillator as shown in FIG. 12. Every time 16×t buff has elapsed and the signal makes two rounds inside the oscillator after the oscillation switch 1630 turns on, a rising edge appears in the oscillator output, and the first oscillation count circuit 1521 measures the number. Also, at time 1803, the first synchronization clock count circuit 1531 stops counting and holds the count value.

[0073] After time 1803 when the first oscillator 1511 turns on, the timing at which the synchronization clock first rises is time 1805. In response to the rising of the synchronization 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.

[0074] The count result D of the synchronization clock count circuit Gclk is the time from time 1801 to time 1802 divided by 2 7 ×t buffbecomes the value measured in units. Also, the count result D of the oscillator count circuit ROclk is the time from time 1803 to time 1804 in 2 4 ×t buff units. Further, the internal oscillator signal D ROin is the time from time 1804 to time 1805 in t buff units. The high-resolution TDC1501 completes one measurement operation by performing the following processing on these values and outputting them to the signal processing unit 123.

[0075] The count result D of the oscillator count circuit ROclk and the internal oscillator signal D ROin are added according to the following equation (2). D RO = 2 4 ×D ROclk + D ROin ···(2)

[0076] The D obtained by equation (2) RO is the time from time 1803 to time 1805 in t buff units. Also, since the time from time 1802 to time 1805 is equal to one cycle of the synchronous clock, 2 7 ×t buff . Therefore, by subtracting D RO from one cycle of the synchronous clock, the time from time 1802 to time 1803 is obtained. Adding this to D Gclk , which is the time from time 1801 to time 1802, gives the value D buff of the time from time 1801 to time 1803 measured in t ToF units (Equation (3)). D ToF = 2 7 ×D Gclk +(2 7 - D RO ) = 2 7 ×D Gclk +(2 7 - 24×D ROclk - D ROin )···(3)

[0077] 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. Further, 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 an adjustment voltage.

[0078] When compared with the high-resolution TDC 1501, the number of buffers and oscillation switches has decreased from seven to three. On the other hand, each of the buffers 2011 to 2013 and the inverter 2014 has a delay time t buff which is adjusted by a second oscillation adjustment circuit 1542 so as to be twice that of t buff of the high-resolution TDC 1501.

[0079] 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 made one bit less in the second oscillator 1512 than in the first oscillator 1511.

[0080] As described above, the low-sensitivity pixel L is mainly assumed to be used for long-distance distance measurement 。T The influence of the measurement resolution of oF on the accuracy of the distance measurement 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 the ToF is made lower than that of the high-resolution TDC 1501.

[0081] The delay time t buffFactors such as manufacturing errors in the manufacturing process of transistors, fluctuations in the voltage applied to the TDC circuit, and variations due to temperature cause variations. Therefore, the first oscillation adjustment circuit 1541 and the second oscillation adjustment circuit 1542 are provided for each of the eight TDCs.

[0082] 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.

[0083] 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.

[0084] The output of the dummy oscillator 2101 is input to the 1 / 2 3 frequency divider 2102. The 1 / 2 3 frequency divider 2102 outputs a clock signal with the frequency of the input clock signal reduced to 1 / 2 3 . The phase comparator 2103 receives the synchronization clock and the output of the 1 / 2 3 frequency divider 2102. The phase comparator 2103 compares the frequency of the synchronization clock with the frequency of the clock signal output by the 1 / 2 3 frequency divider 2102.

[0085] Then, when the frequency of the synchronization clock signal is higher, the phase comparator 2103 raises the output voltage, and when the frequency of the synchronization 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 oscillation frequency of the first oscillator 1511 becomes twice that of the synchronization clock. 3Adjust the delay so as to be doubled. The same applies to the second oscillation adjustment circuit 1542.

[0086] 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 changes in process / voltage / temperature, it is possible to suppress variations in the oscillation frequency of the oscillator due to changes in process / voltage / temperature.

[0087] 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.

[0088] (Distance measurement sequence) FIG. 17 is a flowchart regarding 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 included in the signal processing unit 123. 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.

[0089] 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.

[0090] 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 distance measurement range has elapsed since the light emission, S2204 is executed.

[0091] In S2204, the signal processing unit 123 adds the measurement result obtained in S2203 to the histogram for each pixel. For pixels for which no measurement result has been obtained, the signal processing unit 123 does not add the measurement result to the histogram.

[0092] 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 measurements N total If the signal processing unit 123 determines that the value of the measurement count counter i is greater than the number of measurements N total it executes S2207, and if it determines that the value of the measurement count counter i is not greater than the number of measurements N total it executes 2202.

[0093] In S2207, the signal processing unit 123 removes the count results that are considered noise components based on the histograms of the individual pixels, and executes S2208. In S2208, the signal processing unit 123 averages the measurement results that remained without being removed in S2207 in the histograms of the individual pixels, outputs the average value as the measured ToF, and ends one ranging sequence.

[0094] (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.

[0095] FIG. 18(a) is a diagram showing an example of a histogram of the N total TDC measurement results 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.

[0096] Since the measurement results included in section 2302 form a frequency peak, they are considered to be the correct measurement results of the time from emission to reception. On the other hand, since the measurement results included in section 2304 have an irregular and sparse distribution, they are considered to be noise light such as ambient light randomly generated, 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 ranging result.

[0097] Similar to Fig. 18(a), Fig. 18(b) shows an example of a histogram of the TDC measurement results for the high-sensitivity pixel H, total for N times. 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 during the measurement shown in Fig. 18(a). The noise light included in section 2304 causes the N total TDC measurements to be completed, and the TDC measurement results for the reflected light from the subject are not obtained.

[0098] Fig. 18(c) shows an example of a histogram of the TDC measurement results for the low-sensitivity pixel L obtained in the same environment as Fig. 18(b), total for N times. Since the sensitivity is lower than that of the high-sensitivity pixel H, the number of TDC measurements performed for the noise light decreases. As a result, the number of measurement results included in section 2302 increases, and similar to Fig. 18(a), the average value of the measurement results included in section 2302 can be calculated as the ranging result. In this way, the low-sensitivity pixel L has higher tolerance to situations with high ambient light noise than the high-sensitivity pixel H.

[0099] 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 ranged is at a long distance. This is because when the object is at a long distance, the period from emission until the reflected light returns (i.e., the period during which the noise light is detected) becomes longer.

[0100] In this embodiment, by using the high-sensitivity pixel H and the low-sensitivity pixel L, stable distance measurement with the influence of noise light suppressed is possible even when the amount of noise light is large 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, the variation between the distance measurement results obtained with the high-sensitivity pixel H and the distance measurement results obtained with the low-sensitivity pixel L is small, and an accurate distance measurement result can be obtained.

[0101] (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).

[0102] 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 high-sensitivity pixel H can perform distance measurement four times more frequently than the low-sensitivity pixel L. Since the probability that the number of distance measurement results to be averaged is higher than that of the low-sensitivity pixel L and the measurement of 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.

[0103] When the object to be distance-measured is far away, the ToF becomes long, 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 perform the next emission 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 performs the next emission before the reflected light is detected. As a result, 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 between the emission and the arrival of the reflected light can be suppressed. Thus, accurate time measurement with the high-sensitivity pixel H is possible even in an environment with a large amount of noise light.

[0104] The signal processing unit 123 applies offset correction based on the measurement results obtained for the adjacent low-sensitivity pixels L to the measurement results obtained for the high-sensitivity pixels H. The offset correction is to add a constant multiple of the emission period (measurement period) 2602 of the high-sensitivity pixels H to the measurement result 2611 for the high-sensitivity pixels H based on the measurement result 2711 for the adjacent low-sensitivity pixels L.

[0105] Since the measurement result for the low-sensitivity pixel L adjacent to the high-sensitivity pixel H is 2711, for the high-sensitivity pixel H as well, the time until the reflected light of the emitted light arrives is likely to be a value 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 for the high-sensitivity pixel H. Therefore, in the offset correction, the signal processing unit 123 adds a time that is twice the emission period 2602 to the measurement result 2611 of the high-sensitivity pixel H.

[0106] 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 the vertical direction.

[0107] Further, 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.

[0108] According to this embodiment, by using light-receiving elements with different sensitivities, a light-receiving device with a wide dynamic range can be realized. Further, the sensitivities of the light-receiving elements are made different by 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 manufacture and suppression of variations in characteristics. Also, for low-sensitivity pixels, by making the resolution of time measurement lower than that of high-sensitivity pixels, it is possible to efficiently reduce the circuit scale and power consumption while suppressing a decrease in ranging accuracy.

[0109] ●(Second Embodiment) Next, a second embodiment of the present invention will be described. The ranging device according to this embodiment uses pulsed light of a plurality of wavelengths for ranging. FIG. 19 is a diagram showing a configuration example of the light projecting unit 110 according to this embodiment, and the same reference numerals as those in FIG. 2 are given to the components common to the first embodiment. FIG. 19(a) is a side view showing a configuration example of the collimator lens array 2820 constituting the light source unit 111, and FIG. 19(b) is a side view showing a configuration example of the light source array 2810 constituting the light source unit 111.

[0110] In this embodiment, the light source array 2810 includes a first light-emitting element 2811 that emits light of a first wavelength and a second light-emitting element 2812 that emits light of a second wavelength longer than the first wavelength. Therefore, the light source unit 111 can simultaneously irradiate light of the first wavelength and light of the second wavelength. Note that one type of light-emitting element whose emission wavelength can be switched between the first wavelength and the second wavelength may be used. In this case, the following description may be read with the light-emitting element controlled to emit the first wavelength as the first light-emitting element and the light-emitting element controlled to emit the second wavelength as the second light-emitting element. Here, the first wavelength and the second wavelength are the center wavelengths of the emitted light.

[0111] Here, it is assumed that both the first light-emitting element 2811 and the second light-emitting element 2812 are VCSELs and are two-dimensionally arranged so as to be alternately arranged in the row direction and the column direction. Also, the center wavelength λ1 of the first light-emitting element 2811 is 850 nm, and the center wavelength λ2 of the second light-emitting element 2812 is 940 nm. However, these center wavelengths λ1 and λ2 are merely examples. Also, three or more types of light-emitting elements having different emission wavelengths may be used.

[0112] As shown in FIG. 19(a), in the collimator lens array 2820, a first collimator lens 2821 corresponding to the first light-emitting element 2811 and a second collimator lens 2822 corresponding to the second light-emitting element 2812 are two-dimensionally arranged. Therefore, the arrangement of the first collimator lens 2821 and the second collimator lens 2822 corresponds to the arrangement of the first light-emitting element 2811 and the second light-emitting element 2812 in the light source array 2810. The first collimator lens 2821 and the second collimator lens 2822 may have a shape and / or material suitable for the wavelengths λ1 and λ2. Also, the first collimator lens 2821 and the second collimator lens 2822 may be the same if there is no problem in performance.

[0113] FIG. 19(c) is a vertical cross-sectional view showing an arrangement example of the light source unit driving unit 112, the light source unit 111, and the projection lens 131. In the present embodiment, the configuration is the same as that of the first embodiment except that there are two types of light-emitting elements and collimator lenses.

[0114] FIG. 20 is a diagram showing an example of a light projection pattern by the light projection unit 110 according to the present embodiment, similar to FIG. 3(a). Among the light source arrays 2810, a light projection pattern formed on a plane at a predetermined distance facing the light emitting surface of the light projection unit 110 by light emitting elements in 3 rows and 3 columns is shown. 2910 is. Among the nine light projection areas, the light projection area 2911 is a light projection area by the first light emitting element 2811, and the light projection area 2912 is a light projection area by the second light emitting element 2812. The light projection area indicates a region in the plane 2910 having a diameter approximately equal to the full width at half maximum (FWHM) among the light intensity distributions from the individual light emitting elements.

[0115] FIG. 21 is a vertical cross-sectional view schematically showing a configuration example of the light receiving unit 121 of the distance measuring device 100 in the present embodiment. In the present embodiment, the light receiving unit 121 includes a first pixel 3011 having a passband with a center wavelength λ1 and a second pixel 3012 having a passband with a center wavelength λ2. The arrangement of the first pixel 3011 and the second pixel 3012 in the light receiving unit 121 corresponds to the arrangement of the first light emitting element 2811 and the second light emitting element 2812 in the light source array 2810. Therefore, in the present embodiment, the first pixel 3011 and the second pixel 3012 are two-dimensionally arranged so as to be alternately arranged in the row direction and the column direction.

[0116] As described with reference to FIG. 7, 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 passbands of the first pixel 3011 and the second pixel 3012 can be realized by an optical bandpass filter using a multilayer film buffer mirror as described with reference to FIG. 5(b). Therefore, an optical bandpass filter having a center wavelength of the passband of λ1 is provided for the first pixel 3011, and an optical bandpass filter having a center wavelength of the passband of λ2 is provided for the second pixel 3012. In the present embodiment, it is not necessary to actively make the half-value widths of the first optical bandpass filter and the second optical bandpass filter different. Further, the structures of the first pixel 3011 and the second pixel 3012 may both be the structure of pixel H.

[0117] FIG. 22 is a diagram schematically showing distance measurement using light of two types of wavelengths with the light source array 2810 and the light receiving unit 121 in the distance measurement device 100 according to the present embodiment. For convenience, in FIG. 22, it is described that the light from the light source array 2810 passes through the object and enters the light receiving unit 121. However, actually, the light from the light source array 2810 is reflected by the object and enters the light receiving unit 121. Also, the description of the light projecting lens 131 and the light receiving lens 132 is omitted.

[0118] The light beam 3111 having a center wavelength λ1 emitted from the first light emitting element 2811 is reflected by the object, and a part of the reflected light 3121 passes through the first band-pass filter 3021 and enters the light receiving region 1001 (FIG. 7) of the first pixel 3011. Further, the light beam 3112 having a center wavelength λ2 emitted from the second light emitting element 2812 is reflected by the object, and a part of the reflected light 3122 passes through the second band-pass filter 3022 and enters the light receiving region 1001 of the second pixel 3012.

[0119] Next, in the distance measurement operation of the distance measurement device 100 of the present embodiment having the light source unit 111 and the light receiving unit 121 having the above-described configuration, how the TDC array unit 122 uses the outputs of the first pixel 3011 and the second pixel 3012 will be described.

[0120] First, the difference in relative characteristics due to the difference in wavelengths of λ1 (850 nm) and λ2 (940 nm) will be described. The light of 850 nm has a relatively short penetration length into Si among near-infrared light, and the probability of being photoelectrically converted in the light receiving region 1001 is high. That is, the light receiving sensitivity is high.

[0121] On the other hand, since the sunlight spectrum of the light of 940 nm is relatively small, the probability of being included in the ambient light is low, it is hardly affected by noise light, and it is suitable when the intensity of the ambient light is high. On the contrary, since the light of 940 nm is highly absorbed by moisture, the signal-to-noise ratio is likely to decrease in an environment with high humidity such as during rain.

[0122] Due to such differences in characteristics, when the ambient light intensity is low (e.g., indoors) or in an environment with high humidity such as during rainy days, it is easier to obtain high-precision ranging results by measuring distance with light of a shorter wavelength λ1 (850 nm). On the other hand, when the ambient light intensity is high (e.g., on sunny days), it is easier to obtain high-precision ranging results by measuring distance with light of a longer wavelength λ2 (940 nm). Therefore, when it is considered that the influence of ambient light is significant, it can be determined to measure distance using the second pixel 3012, and when it does not meet such conditions, to measure distance using the first pixel 3011.

[0123] However, if only one type of pixel is used, the spatial resolution of the distance information will decrease. Therefore, when the spatial resolution of the distance information is prioritized over the ranging accuracy, ranging may be performed using both the first pixel 3011 and the second pixel 3012.

[0124] The information (indoors / outdoors, ambient light intensity, humidity, weather, etc.) required for these determinations can be obtained from the device using the ranging device. Of course, sensors for detecting this information in the ranging device, communication circuits for obtaining this information from external devices, etc. may be provided. Also, this information may be detected from an image taken of the range including the range to be measured. Further, the captured image may be transmitted to an external device to obtain information from the external device. Alternatively, the own position information may be provided to the external device to obtain this information. Also, the user may be allowed to input this information.

[0125] The flowchart shown in FIG. 23 can be executed, for example, by the overall control unit 140. When the overall control unit 140 determines the wavelength of the light (type of pixel) to be used for measurement, it notifies the measurement unit 120. The measurement control unit 124 controls the TDC array unit 122 and the signal processing unit 123 so as to obtain distance information based on the measurement results obtained by the TDC array unit 122 for the pixel based on the notification among the outputs of the first pixel 3011 and the second pixel 3012 of the light receiving unit 121.

[0126] Regarding the light emission control of the light source unit 111 and the drive control of the light source unit drive unit 112 during distance measurement, for example, it is assumed that the light source control unit 113 performs them according to predetermined settings. Also, the operations of the TDC array unit 122 and the operations of the signal processing unit 123 during distance measurement are as described in the first embodiment.

[0127] Therefore, hereinafter, only the operation of determining the wavelength of the light used for distance measurement will be described. Note that this determination operation can be executed, for example, when starting distance measurement. For example, at the start of the distance measurement sequence described with reference to FIG. 17, the wavelength used for distance measurement is determined, and during one distance measurement sequence (measurement for the set number N total ), the determined wavelength is not changed. The operation of determining the wavelength of the light may be executed at other timings.

[0128] In S3211, the overall control unit 140 determines whether the operation mode set in the distance measurement device 100 is the high-resolution mode or the high-precision mode. The operation mode can be set by the user, for example, and the set value is stored in the ROM of the overall control unit 140. Note that the operation mode may be set from an external device such as an electronic device including the distance measurement device 100. The high-resolution mode is an operation mode that prioritizes the spatial resolution of distance measurement, and the high-precision mode is an operation mode that prioritizes distance measurement accuracy.

[0129] When the high-resolution mode is set, the overall control unit 140 executes S3212. In S3212, the overall control unit 140 determines to use both of the two wavelengths λ1 (850 nm) and λ2 (940 nm), and ends the wavelength determination process.

[0130] On the other hand, when the high-precision mode is set, the overall control unit 140 executes S3213. In S3213, the overall control unit 140 determines whether the distance measurement environment is indoors or outdoors. The overall control unit 140 can make the determination based on, for example, the output of a sensor that detects the type of ambient light included in the distance measurement device 100 or an external device, or the result of analyzing an image of the distance measurement environment by the signal processing unit 123. Other methods may be used for the determination.

[0131] If it is determined that the ranging environment is indoor, the overall control unit 140 executes S3214; if it is determined that the environment is outdoor, the overall control unit 140 executes S3215. In S3214, the overall control unit 140 determines to use the wavelength λ1 (850 nm) that enables high-sensitivity measurement, and ends the wavelength determination process.

[0132] In S3215, the overall control unit 140 determines whether it is daytime (morning or noon) or nighttime based on, for example, the date and time obtained from the built-in clock or an external device. For example, the overall control unit 140 stores in the ROM approximate sunrise and sunset times for each week, and can determine whether it is daytime or nighttime based on the obtained date and time. If the position information of the ranging device can be obtained, the position information may be considered.

[0133] If it is determined that it is daytime, the overall control unit 140 executes S3216; if it is determined that it is nighttime, the overall control unit 140 executes S3219. In S3216, the overall control unit 140 determines whether the current weather is rainy or not rainy. Here, it is assumed that the user makes the selection, but the overall control unit 140 may make the determination by using the output of the barometric pressure sensor and / or the humidity sensor, or by obtaining it from an external device.

[0134] If the weather is not selected by the user, or if the overall control unit 140 cannot make a determination, the overall control unit 140 executes S3217. In S3217, the overall control unit 140 determines to use both of the two wavelengths λ1 (850 nm) and λ2 (940 nm), and ends the wavelength determination process. Note that, unlike the case of the high-resolution mode, the signal processing unit 123 is controlled to evaluate the results measured using both wavelengths and select one that is determined to have good ranging accuracy.

[0135] If the user designates "not rainy" in S3216, or if the overall control unit 140 determines that it is not rainy, the overall control unit 140 executes S3218. In S3218, the overall control unit 140 determines to use λ2 (940 nm) which has strong environmental light resistance, and ends the wavelength determination process.

[0136] When the user designates rain using S3216, or when the overall control unit 140 determines that it is raining, the overall control unit 140 executes S3219. In S3219, the overall control unit 140 determines to use λ1 (850 nm), which is less likely to be absorbed by water than 940 nm, and ends the wavelength determination process.

[0137] Note that the determination conditions in the wavelength determination process described here are examples, and other determination conditions may be used, or a combination of multiple conditions may be used for determination. Also, the determination conditions may be changed according to the emission wavelength.

[0138] Also, since it is conceivable that the ranging environment includes a mixture of indoor and outdoor areas, basically, ranging is performed using both wavelengths, and based on the evaluation of the ranging results, the measurement results using one wavelength are selected for each partial region of the ranging range. The evaluation of the ranging results can be performed using known methods. As an example, one or more of the following can be used as an indicator of high ranging accuracy: the peak frequency of the histogram is high, there are not two or more peaks above a certain level, and the half-width of the frequency group including the peak frequency is narrow (the base of the peak is narrow).

[0139] According to this embodiment, it is possible to perform ranging using light of a plurality of wavelengths using a set of light source units and projection lenses and one light receiving unit, which is advantageous for miniaturization and cost reduction of the ranging device. Also, by performing ranging using light of a plurality of wavelengths in parallel and using the one determined to have good accuracy, an appropriate ranging result can be obtained according to changes in the situation. Also, when the spatial resolution of ranging is required, all the ranging results using light of a plurality of wavelengths can be used. In this case, the ranging accuracy can also be improved by correcting the ranging results obtained using wavelengths with an unfavorable signal-to-noise ratio based on the ranging results obtained using other wavelengths as necessary.

[0140] (Modification example) In this embodiment, for the sake of easy explanation and understanding, the pixels of the light receiving unit 121 are all configured as the high-sensitivity pixels H in the first embodiment. However, similar to the first embodiment, it is also possible to use high-sensitivity pixels H and low-sensitivity pixels L. Specifically, high-sensitivity pixels H and low-sensitivity pixels L having a first band-pass filter for passing the wavelength λ1, and high-sensitivity pixels H and low-sensitivity pixels L having a second band-pass filter for passing the wavelength λ2 can be provided in the light receiving unit 121. Also in this case, the half-value width of the band-pass filter provided for the low-sensitivity pixel L can be made narrower than the half-value width of the band-pass filter provided for the high-sensitivity pixel H.

[0141] By providing high-sensitivity pixels H and low-sensitivity pixels L for each type of band-pass filter, the dynamic range of the light receiving unit 121 can be expanded for each wavelength of light used for distance measurement. When providing pixels with different sensitivities, by performing emission control according to the HDR driving method described above, the influence of noise light can be further reduced.

[0142] Also, depending on the distance measurement environment, measurement may be performed only for one of the high-sensitivity pixel H and the low-sensitivity pixel L, or only the distance measurement result obtained for one of them may be used. For example, in an environment where the shorter wavelength λ1 (850 nm) is used, measurement may be performed only for the low-sensitivity pixel L, or measurement may be performed with the high-sensitivity pixel H and the low-sensitivity pixel L, and only the measurement result obtained for the low-sensitivity pixel L may be used.

[0143] Also, in an environment where λ2 (940 nm) is used, measurement may be performed only for the high-sensitivity pixel H, or measurement may be performed with the high-sensitivity pixel H and the low-sensitivity pixel L, and only the measurement result obtained for the high-sensitivity pixel H may be used. When measurement is performed only with one of the high-sensitivity pixel H and the low-sensitivity pixel L, power consumption can be suppressed. Also, by using the distance measurement result obtained for a pixel with a sensitivity more suitable for the environment, high measurement accuracy can be realized by an easy method.

[0144] (Other Embodiments) The above-described distance measuring device 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.

[0145] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiment to a system or device via a network or a storage medium, and causing one or more processors in a computer of the system or device to read and execute the program. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

[0146] The present invention is not limited to the contents of the above-described embodiment, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, claims are attached to disclose the scope of the invention.

Explanation of Reference Numerals

[0147] 100... Distance measuring device, 110... Light projecting unit, 111... Light source unit, 120... Measuring 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 source unit capable of simultaneously irradiating light of a first wavelength and light of a second wavelength longer than the first wavelength; A light receiving unit having a pixel array in which pixels are two-dimensionally arranged and detecting the incidence of light to the pixels, where the pixel array includes a first pixel configured to receive light of the first wavelength and a second pixel configured to receive light of the second wavelength; Measuring means for detecting the time from the start of distance measurement until the incidence of light to the pixels is detected and calculating distance information based on the detected time; A distance measuring device having determination means for determining a pixel to be used for calculating the distance information among the first pixel and the second pixel, where The determination means When a first operation mode is set in the distance measuring device, determines to use the first pixel for calculating the distance information when it is rainy weather and use the second pixel when it is other than rainy weather, When a second operation mode different from the first operation mode is set in the distance measuring device, determines to use the first pixel and the second pixel for calculating the distance information. The distance measuring device is characterized by this.

2. The determination means determines a pixel to be used for calculating the distance information based on weather information acquired from an external device when a first operation mode is set in the distance measuring device. The distance measuring device according to claim 1 is characterized by this.

3. The measuring means calculates the distance information based on the time when the incidence of light is detected for the pixel determined by the determination means. The distance measuring device according to claim 1 is characterized by this.

4. The second operation mode is an operation mode for performing distance measurement with a higher resolution than the first operation mode. The distance measuring device according to claim 1 is characterized by this.

5. When a first operation mode is set in the distance measuring device, the determination means determines to use the second pixel for calculating the distance information when it meets a predetermined condition where the influence of ambient light is considered to be large, and determines to use the first pixel for calculating the distance information when it does not meet the condition. The distance measuring device according to claim 4 is characterized by this.

6. The condition where the influence of ambient light is considered to be large is outdoor and other than rainy weather. The distance measuring device according to claim 5 is characterized by this.

7. The distance measuring device according to claim 1 or 2, wherein the measuring means calculates the distance information based on one of the time when light incidence is detected for the first pixel and the time when light incidence is detected for the second pixel.

8. The distance measuring device according to claim 7, wherein the measuring means selects one of the time when light incidence is detected for the first pixel and the time when light incidence is detected for the second pixel based on the histogram of the time when light incidence is detected for the first pixel and the histogram of the time when light incidence is detected for the second pixel, and uses the selected time for calculating the distance information.

9. The distance measuring device according to any one of claims 1 to 8, wherein the light source unit has a light source array in which a first light emitting element that irradiates light of the first wavelength and a second light emitting element that irradiates light of the second wavelength are two-dimensionally arranged.

10. The distance measuring device according to claim 9, wherein the arrangement of the first pixel and the second pixel in the pixel array corresponds to the arrangement of the first light emitting element and the second light emitting element in the light source array.

11. The distance measuring device according to any one of claims 1 to 10, wherein a first optical band-pass filter that allows light of the first wavelength to pass through is provided for the first pixel, and a second optical band-pass filter that allows light of the second wavelength to pass through is provided for the second pixel.

12. The distance measuring device according to any one of claims 1 to 11, wherein each of the first pixel and the second pixel includes a high-sensitivity pixel having a first sensitivity and a low-sensitivity pixel having a sensitivity lower than the first sensitivity.

13. An electronic device, comprising: the distance measuring device according to any one of claims 1 to 12; processing means for executing a predetermined process using the distance information obtained by the distance measuring device; and characterized by having the above.

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