Distance image capturing device, and control method

Abstract

This distance image capturing device comprises a light source unit that emits light pulses into a measuring space, a plurality of pixels that are provided with photoelectric conversion elements that generate an electric charge corresponding to light incident from the measuring space and a plurality of charge accumulating units that accumulate the electric charge, and a pixel drive circuit that distributes and accumulates electric charge in each of the charge accumulating units at a predetermined timing synchronized with the emission of the light pulses, and, after accumulating the electric charge, outputs a voltage signal corresponding to the charge amount of the electric charge accumulated in each charge accumulating unit, wherein, after outputting the voltage signal corresponding to the charge amount of the electric charge accumulated in each charge accumulating unit, and before next distributing and accumulating the electric charge in each charge accumulating unit, the pixel drive circuit resets each charge accumulating unit to a predetermined voltage value, and varies the reset timing for each predetermined pixel among the plurality of pixels.

Description

Range image capturing device and control method

[0001] This application claims priority to Japanese Patent Application No. 2024-127955, filed on August 2, 2024, the contents of which are incorporated herein by reference.

[0002] Time-of-Flight (hereinafter referred to as "ToF") distance image sensors have been developed that utilize the known speed of light to measure the distance between a measuring device and an object based on the time of flight of light in space (measurement space) (see, for example, Patent Document 1). In a ToF distance image sensor, incident light is photoelectrically converted by a photoelectric conversion element, and the generated electric charges are distributed and stored in multiple charge storage units. Then, based on the ratio of the amount of electric charge accumulated in the multiple charge storage units, the delay time from the time a light pulse is irradiated to the time the light pulse reflected from the object returns is calculated, and the delay time and the speed of light are used to calculate the distance to the object. ToF distance image sensors that distribute electric charges among multiple charge storage units in this way are sometimes referred to as multi-tap ToF sensors.

[0003] Japanese Patent No. 4235729

[0004] In conventional multi-tap ToF sensors, the discharge of charges generated in a photoelectric conversion element (e.g., a photodiode (PD)) is performed by controlling a drain gate transistor connected to the photoelectric conversion element. The history of multiple charge accumulation units (floating diffusions (FD)) is erased (reset) by controlling a reset gate transistor connected to the charge accumulation units after reading out a voltage signal corresponding to the amount of charge accumulated in the multiple charge accumulation units.

[0005] Here, if there is a long time between resetting the charge storage unit after reading out a voltage signal from the charge storage unit and the next exposure, an offset (error) occurs in the charge storage unit due to dark current, etc. One possible method for reducing the offset is to reset the charge storage unit for the entire pixel before exposure. However, resetting the entire pixel simultaneously generates a large current, which raises concerns about fluctuations in the high-level voltage or low-level voltage. To suppress fluctuations in the high-level or low-level voltage, for example, it is necessary to reduce the resistance value of the wiring that supplies the voltage, which may increase the size of the control block.

[0006] The present invention has been made in consideration of the above-mentioned problems, and one of its objects is to provide a distance imaging device and a control method that can reduce offset caused by dark current in a ToF sensor without increasing the size of the control block.

[0007] A distance image capturing device according to one aspect of the present invention comprises a light source unit that irradiates a measurement space with a light pulse, a photoelectric conversion element that generates a charge in response to the light incident from the measurement space, and a plurality of pixels each having a plurality of charge accumulation units that accumulate the charge, and a pixel driving circuit that allocates and accumulates the charge in each of the charge accumulation units at a predetermined timing synchronized with the irradiation of the light pulse, and after accumulating the charge, outputs a voltage signal corresponding to the amount of charge accumulated in each of the charge accumulation units, wherein the pixel driving circuit, after outputting a voltage signal corresponding to the amount of charge accumulated in each of the charge accumulation units, resets each of the charge accumulation units to a predetermined voltage value before allocating and accumulating the charge in each of the charge accumulation units, and varies the timing of the reset for each of the plurality of pixels.

[0008] In addition, a distance image capturing device according to one aspect of the present invention comprises a light source unit that irradiates a measurement space with a light pulse, a photoelectric conversion element that generates a charge in accordance with the light incident from the measurement space, and a plurality of pixels each having a plurality of charge accumulation units that accumulate the charge, and a pixel driving circuit that allocates and accumulates the charge in each of the charge accumulation units at a predetermined timing synchronized with the irradiation of the light pulse, and after accumulating the charge, outputs a voltage signal corresponding to the amount of charge accumulated in each of the charge accumulation units, wherein the pixel driving circuit, after outputting a voltage signal corresponding to the amount of charge accumulated in each of the charge accumulation units, resets each of the charge accumulation units to a predetermined voltage value before allocating and accumulating the charge in each of the charge accumulation units, and varies the timing of the reset for each of the predetermined pixels among the plurality of pixels so that the periods from the start timing to the end timing of the reset for each of the predetermined pixels do not overlap.

[0009] In addition, a distance image capturing device according to one aspect of the present invention includes a light source unit that irradiates a measurement space with a light pulse, a photoelectric conversion element that generates a charge in accordance with the light incident from the measurement space, and a plurality of pixels each having a plurality of charge accumulation units that accumulate the charge, and a pixel driving circuit that allocates and accumulates the charge in each of the charge accumulation units at a predetermined timing synchronized with the irradiation of the light pulse, and after accumulating the charge, outputs a voltage signal corresponding to the amount of charge accumulated in each of the charge accumulation units, wherein the pixel driving circuit, after outputting the voltage signal corresponding to the amount of charge accumulated in each of the charge accumulation units, resets each of the charge accumulation units to a predetermined voltage value before allocating and accumulating the charge in each of the charge accumulation units, and differs the timing of the reset for each of the predetermined pixels among the plurality of pixels so that a portion of the period from the start timing to the end timing of the reset for each of the predetermined pixels overlaps, while differing the start timing and end timing of the reset for each of the predetermined pixels.

[0010] Furthermore, a control method for a distance imaging device according to one aspect of the present invention is a control method for a distance imaging device comprising: a light source unit that irradiates a measurement space with a light pulse; a plurality of pixels each having a photoelectric conversion element that generates a charge in accordance with the light incident from the measurement space; and a plurality of charge accumulation units that accumulate the charge; and a pixel drive circuit that allocates and accumulates the charge in each of the charge accumulation units at a predetermined timing synchronized with the irradiation of the light pulse, and after accumulating the charge, outputs a voltage signal in accordance with the amount of charge accumulated in each of the charge accumulation units, the control method including: a step of causing the pixel drive circuit to output a voltage signal in accordance with the amount of charge accumulated in each of the charge accumulation units; and a step of resetting each of the charge accumulation units to a predetermined voltage value after outputting the voltage signal in accordance with the amount of charge, before allocating and accumulating the charge in each of the charge accumulation units, and when resetting each of the charge accumulation units to the predetermined voltage value, the timing of the reset is varied for a predetermined pixel among the plurality of pixels.

[0011] According to the present invention, the offset caused by the dark current in the ToF sensor can be reduced without increasing the size of the control block.

[0012] 1 is a block diagram showing a schematic configuration of a range image pickup device according to a first embodiment; FIG. 2 is a block diagram showing a schematic configuration of a range image sensor according to the first embodiment; FIG. 3 is a circuit diagram showing an example of the configuration of a pixel of the range image sensor according to the first embodiment; FIG. 4 is a schematic diagram explaining the process from exposure to readout according to the first embodiment; FIG. 5 is a timing chart showing an example of timing when all pixels are simultaneously reset during global reset; FIG. 6 is a diagram showing an example of current waveforms of the power supply and ground when the drive signal RST is controlled simultaneously; FIG. 7 is a timing chart showing an example of global reset according to the first embodiment; FIG. 8 is a diagram showing an example of current waveforms of the power supply and ground during global reset according to the first embodiment; FIG. 9 is a timing chart showing an example of global reset according to a second embodiment; FIG. 10 is a timing chart showing an example of global reset according to a third embodiment; FIG. 11 is a timing chart showing an example of global reset according to a fourth embodiment; FIG. 12 is a timing chart showing an example of global reset according to a fifth embodiment.

[0013] Hereinafter, a distance imaging device according to an embodiment of the present invention will be described with reference to the drawings.

[0014] First Embodiment First, a first embodiment will be described. Fig. 1 is a block diagram showing the schematic configuration of a distance imaging device according to this embodiment. The distance imaging device 1 is configured as a distance image sensor (ToF sensor) that measures (range-finding) the distance to an object using the ToF method. The distance imaging device 1 includes, for example, a light source unit 2, a light receiving unit 3, and a distance image processing unit 4. Fig. 1 also shows a subject OB, which is an object (target) whose distance is to be measured by the distance imaging device 1.

[0015] The light source unit 2 irradiates a space to be measured (measurement space) with a light pulse PO under control of the distance image processing unit 4. The light source unit 2 is, for example, a surface-emitting semiconductor laser module such as a vertical cavity surface-emitting laser (VCSEL). The light source unit 2 includes a light source device 21 and a diffuser plate 22.

[0016] Light source device 21 is a light source that emits laser light in the near-infrared wavelength band (e.g., a wavelength band of 850 nm to 940 nm) that becomes the light pulse PO that is irradiated into the space to be measured. Light source device 21 is, for example, a semiconductor laser light-emitting element. Light source device 21 emits pulsed laser light in response to control from distance image processing unit 4.

[0017] The diffuser plate 22 is an optical component that diffuses the laser light in the near-infrared wavelength band emitted by the light source device 21 to the extent of the surface that irradiates the space to be measured. The pulsed laser light diffused by the diffuser plate 22 is emitted as a light pulse PO and irradiates the space to be measured.

[0018] When an object OB is present in a space to be measured for distance measurement in the distance image capturing device 1, the light receiving unit 3 receives reflected light RL of the light pulse PO that is emitted from the light source unit 2 and reflected by the object OB, and outputs a pixel signal corresponding to the received reflected light RL. The light receiving unit 3 includes a lens 31 and a distance image sensor 32.

[0019] The lens 31 is an optical lens that guides the incident reflected light RL to the range image sensor 32. The lens 31 emits the incident reflected light RL toward the range image sensor 32, causing the light to be received (incident) by pixels provided in the light receiving region of the range image sensor 32.

[0020] The range image sensor 32 is an imaging element used in the range image capturing device 1. The range image sensor 32 has a plurality of pixels in a two-dimensional light receiving area. Each pixel of the range image sensor 32 is provided with one photoelectric conversion element, a plurality of charge accumulation units corresponding to this one photoelectric conversion element, and components that distribute charge to each of the charge accumulation units. In other words, the pixel is an imaging element with a distribution configuration in which charge is distributed and stored in a plurality of charge accumulation units.

[0021] The range image sensor 32 distributes the charges generated by the photoelectric conversion elements to the respective charge accumulation sections in accordance with control from the timing control section 41. The range image sensor 32 also outputs pixel signals according to the amounts of charges distributed to the charge accumulation sections. The range image sensor 32 has a plurality of pixels arranged in a two-dimensional matrix, and outputs pixel signals for one frame corresponding to each pixel.

[0022] The distance image processing unit 4 controls the distance image capturing device 1 and calculates the distance to the subject OB. The distance image processing unit 4 includes a timing control unit 41, a distance calculation unit 42, and a measurement control unit 43.

[0023] The timing control unit 41 controls the timing of outputting various control signals required for measurement in accordance with the control of the measurement control unit 43. The various control signals here include, for example, a signal for controlling the irradiation of the light pulse PO, a signal for allocating and accumulating the reflected light RL in multiple charge accumulation units, and a signal for controlling the number of accumulations per frame. The number of accumulations is the number of times that the process of allocating and accumulating electric charge in multiple (e.g., four) charge accumulation units CS (see FIG. 3 ) is repeated. The exposure time is the product of the number of accumulations and the time duration (accumulation time duration) for accumulating electric charge in each charge accumulation unit per process of allocating and accumulating electric charge.

[0024] The distance calculation unit 42 outputs distance information obtained by calculating the distance to the object OB based on the pixel signals output from the distance image sensor 32. The distance calculation unit 42 calculates the delay time from when the light pulse PO is emitted until when the reflected light RL is received based on the amount of charge accumulated in the multiple charge accumulation units. The distance calculation unit 42 calculates the distance to the object OB according to the calculated delay time.

[0025] The measurement control unit 43 controls the timing control unit 41. For example, the measurement control unit 43 sets the number of accumulations and accumulation time for one frame, and controls the timing control unit 41 so that imaging is performed according to the set contents.

[0026] With this configuration, in the distance image capturing device 1, the light source unit 2 irradiates a light pulse PO in the near-infrared wavelength band onto the subject OB, and the light receiving unit 3 receives the reflected light RL reflected by the subject OB, and the distance image processing unit 4 outputs distance information measuring the distance to the subject OB.

[0027] Note that while Figure 1 shows a distance image capturing device 1 configured such that the distance image processing unit 4 is provided inside the distance image capturing device 1, the distance image processing unit 4 may also be a component provided outside the distance image capturing device 1.

[0028] Here, the configuration of the distance image sensor 32 used as an imaging element in the distance image capturing device 1 will be described with reference to Fig. 2. Fig. 2 is a block diagram showing a schematic configuration of the imaging element (distance image sensor 32) used in the distance image capturing device 1 according to this embodiment.

[0029] 2 , the distance image sensor 32 includes, for example, a light receiving area 320 in which a plurality of pixels 321 are arranged, and a pixel drive circuit 322. The pixel drive circuit 322 also includes a vertical scanning circuit 323 having a distribution operation, a horizontal scanning circuit 324, a pixel signal processing circuit 325, and a control circuit 326.

[0030] The light receiving area 320 is an area in which a plurality of pixels 321 are arranged, and FIG. 2 shows an example in which the pixels are arranged in a two-dimensional matrix of 8 rows and 8 columns. The pixels 321 accumulate electric charges corresponding to the amount of light received. The control circuit 326 comprehensively controls the range image sensor 32. The control circuit 326 controls the operation of the components of the range image sensor 32 in accordance with instructions from, for example, the timing control unit 41 of the range image processing unit 4. Note that the components of the range image sensor 32 may be directly controlled by the timing control unit 41, in which case the control circuit 326 may be omitted.

[0031] The vertical scanning circuit 323 is a circuit that controls the pixels 321 arranged in the light receiving region 320 for each row in accordance with control from the control circuit 326. The vertical scanning circuit 323 outputs a voltage signal corresponding to the amount of charge accumulated in each charge accumulation section CS of the pixels 321 to the pixel signal processing circuit 325. In this case, the vertical scanning circuit 323 distributes and accumulates the charge converted by the photoelectric conversion element in each charge accumulation section of the pixels 321.

[0032] The pixel signal processing circuit 325 is a circuit that performs predetermined signal processing (e.g., noise suppression processing, A / D conversion processing, etc.) on the voltage signals output from the pixels 321 in each column to the corresponding vertical signal lines in accordance with control from the control circuit 326.

[0033] Horizontal scanning circuit 324 is a circuit that sequentially outputs signals output from pixel signal processing circuit 325 to horizontal signal lines in accordance with control from control circuit 326. As a result, pixel signals corresponding to the amount of charge accumulated for one frame are sequentially output to distance image processing unit 4 via the horizontal signal lines.

[0034] In the following description, it is assumed that the pixel signal processing circuit 325 performs A / D conversion processing and the pixel signals are digital signals.

[0035] Next, the configuration of the pixel 321 arranged in the light receiving region 320 provided in the range image sensor 32 will be described with reference to Fig. 3. Fig. 3 is a circuit diagram showing an example of the configuration of the pixel 321 arranged in the light receiving region 320 of the range image sensor 32 according to this embodiment. Fig. 3 shows an example of the configuration of one pixel 321 out of the multiple pixels 321 arranged in the light receiving region 320. Here, the pixel 321 shows an example of a four-tap configuration equipped with four pixel signal readout units.

[0036] The pixel 321 includes one photoelectric conversion element PD, a drain gate transistor GD, and four pixel signal readout units RU that output voltage signals from corresponding output terminals O. Each pixel signal readout unit RU includes a gate transistor G, a floating diffusion FD, a charge storage capacitance C, a reset gate transistor RT, a source follower gate transistor SF, and a select gate transistor SL. In each pixel signal readout unit RU, the floating diffusion FD and the charge storage capacitance C form a charge storage unit CS.

[0037] 3, the four pixel signal readout units RU are distinguished from one another by adding the numbers "1," "2," "3," or "4" after the reference numeral "RU" of each unit. Similarly, the components of each of the four pixel signal readout units RU are distinguished from one another by adding the number representing each pixel signal readout unit RU after the reference numeral.

[0038] 3, the pixel signal readout unit RU1, which outputs a voltage signal from the output terminal O1, includes a readout gate transistor G1, a floating diffusion FD1, a charge storage capacitance C1, a reset gate transistor RT1, a source follower gate transistor SF1, and a select gate transistor SL1. In the pixel signal readout unit RU1, the floating diffusion FD1 and the charge storage capacitance C1 form a charge storage unit CS1. The pixel signal readout units RU2 to RU4 have a similar configuration.

[0039] The photoelectric conversion element PD is a buried photodiode that photoelectrically converts incident light to generate electric charges and accumulates the generated electric charges. The photoelectric conversion element PD may have any structure. For example, the photoelectric conversion element PD may be a PN photodiode having a structure in which a P-type semiconductor and an N-type semiconductor are joined together, or a PIN photodiode having a structure in which an I-type semiconductor is sandwiched between a P-type semiconductor and an N-type semiconductor. Furthermore, the photoelectric conversion element PD is not limited to a photodiode, and may be, for example, a photogate-type photoelectric conversion element.

[0040] In pixel 321, the photoelectric conversion element PD photoelectrically converts the incident light to generate electric charges, which are then distributed to each of the four charge storage sections CS, and voltage signals corresponding to the amount of electric charge distributed are output to the pixel signal processing circuit 325.

[0041] The gate transistor G1 is controlled to be turned on by a drive signal TX1 at the timing when charge is distributed to the charge storage unit CS1. The gate transistor G2 is controlled to be turned on by a drive signal TX2 at the timing when charge is distributed to the charge storage unit CS2. The gate transistor G3 is controlled to be turned on by a drive signal TX3 at the timing when charge is distributed to the charge storage unit CS3. The gate transistor G4 is controlled to be turned on by a drive signal TX4 at the timing when charge is distributed to the charge storage unit CS4. In other words, by controlling each of the gate transistors G1 to G4, the timing when charge is distributed to each of the charge storage units CS1 to CS4 and the storage time are controlled.

[0042] The pixel driving circuit 322 sequentially drives the driving signals TX1, TX2, TX3, and TX4 to sequentially switch on the gate transistors G1, G2, G3, and G4, and distributes and accumulates the electric charge generated in the photoelectric conversion element PD in the charge storage units CS1, CS2, CS3, and CS4, in that order.

[0043] Furthermore, when the pixel driving circuit 322 repeatedly accumulates charge in each of the charge accumulation units CS1 to CS4, after the accumulation (distribution) of charge in the charge accumulation unit CS4 is completed, the pixel driving circuit 322 controls the driving signal RSTD to turn on the drain gate transistor GD provided on the discharge path that discharges charge from the photoelectric conversion element PD.

[0044] As a result, before the accumulation cycle for the charge accumulation unit CS1 is started, the drain gate transistor GD discards the charge generated in the photoelectric conversion element PD after the accumulation cycle for the previous charge accumulation unit CS4 (i.e., resets the photoelectric conversion element PD).

[0045] The pixel driving circuit 322 controls the reset gate transistor RT and the selection gate transistor SL using driving signals RST and SEL, respectively, converts the charges stored in the charge storage section CS into a voltage signal using the source follower gate transistor SF, and outputs the converted voltage signal from the output terminal O.

[0046] The reset gate transistor RT is controlled to be turned on by the pixel drive circuit 322 controlling the drive signal RST at the timing when the charge storage unit CS is reset to a predetermined reset voltage value (for example, the voltage value of the power supply VRD).

[0047] The configuration of the pixels arranged in the range image sensor 32 is not limited to the four-tap configuration having four pixel signal readout units RU as shown in Fig. 3, but may be any pixel having a configuration having a plurality of pixel signal readout units RU. In other words, the number of pixel signal readout units PU (charge accumulation units CS) provided in the pixels arranged in the range image sensor 32 may be, for example, three or five or more.

[0048] 3 shows an example in which the charge storage unit CS is configured by a floating diffusion FD and a charge storage capacitance C. However, the charge storage unit CS only needs to be configured by at least a floating diffusion FD, and the pixel 321 may not have a charge storage capacitance C.

[0049] Furthermore, in the pixel 321 having the configuration shown in FIG. 3, an example of a configuration including a drain gate transistor GD is shown, but if there is no need to discard the charge accumulated (remaining) in the photoelectric conversion element PD, the pixel 321 may have a configuration not including a drain gate transistor GD.

[0050] Next, the occurrence of an offset due to dark current and the process of reducing the offset in the process from exposure to readout in the pixel 321 will be described with reference to Fig. 4. Fig. 4 is a schematic diagram for explaining the process from exposure to readout according to this embodiment.

[0051] In Figure 4, the horizontal axis represents the passage of time. Period TA represents the period during which exposure (the operation of distributing charge to the charge storage unit CS) is performed, and period TB represents the period until the next exposure. During period TB, a voltage signal corresponding to the amount of charge stored in the charge storage unit CS is read (READ). For comparison, (A) shows the conventional process, and (B) shows the process according to this embodiment.

[0052] In the conventional process shown in (A), during the exposure period TA(1), the photoelectric conversion element PD photoelectrically converts incident light to generate electric charges, which are then distributed and stored in each of the four charge storage units CS. After the exposure period ends, during the period TB(1), a voltage signal corresponding to the amount of electric charge stored in the charge storage unit CS is read out (READ) row by row from the plurality of pixels 321 arranged in a matrix. The period TB(1) continues until the next exposure period TA(2).

[0053] Here, after reading out (READ) the voltage signal according to the amount of charge, the charge storage unit CS is reset once, but if there is a long time until the next exposure, an offset (offset of the FD potential) occurs in the charge storage unit CS due to dark current, etc. If the next exposure is performed while the offset is occurring, it may affect the amount of charge stored in the charge storage unit CS, resulting in a decrease in distance measurement accuracy.

[0054] In addition, the calculation of the distance D for one pixel in the case of four taps (a pixel using four charge storage units CS) can be expressed by equation 2 when the signal amount (amount of charge) Qn of one gate of the pixel is expressed by equation 1, and it can be seen that dark current affects the measurement of the distance D.

[0055]

[0056]

[0057] ΔQ BackLight Ideally, they are the same (the difference in fluctuations is small), so they are 0. DarkCurrent Ideally, the slope of ΔQ would be the same over time, so it would be 0. However, the FD dark current generally varies widely, so it is not ideal and differences occur. DarkCurrentdoes not become 0. As shown in Equation 2, ΔQ DarkCurrent is proportional to the time t, so the smaller the time t, the smaller ΔQ DarkCurrent In other words, the shorter the time t, the better.

[0058] Therefore, in this embodiment, as shown in (B), after reading (READ) a voltage signal corresponding to the charge amount during period TB(1), the charge storage unit CS of the entire pixel is reset immediately before the next exposure (period TA(2)). This reset of the entire pixel performed before exposure is called a global reset (GR). By performing a global reset immediately before exposure (period TA(2)), the offset of the charge storage unit CS is eliminated at the time of the global reset. Even if an offset gradually occurs in the charge storage unit CS after that due to dark current or the like, the offset that occurred over a relatively long period after reading (READ) the voltage signal during period TB(1) has been canceled, so the offset caused by dark current can be reduced for the next exposure (period TA(2)). This prevents a decrease in distance measurement accuracy.

[0059] Next, a control method for global resetting, which resets all pixels, will be described. If all pixels are reset simultaneously during global resetting, a large current will be generated, which may cause fluctuations in the power supply voltage. Therefore, the range image capturing device 1 according to this embodiment shifts the reset timing for each row to different values. This will be described in detail below.

[0060] First, as a comparison with this embodiment, an example in which all pixels are reset simultaneously during global reset will be described with reference to FIGS.

[0061] 5 is a timing chart showing an example of timing when all pixels are reset simultaneously during global reset. This diagram shows the waveform of the drive signal RST in the period between exposures (for example, period TB(1) in FIG. 4). Since pixel control is performed row by row, the drive signal RST is also controlled row by row. RST[j ＳＴＲ ] is the driving signal RST of the first row, RST[j ＳＴＲ+1] is the driving signal RST, RST[j ＥＮＤ ] indicates the drive signal RST of the last row. When the drive signal RST is High, the reset gate transistor RT is turned on, and the charge storage section CS is reset.

[0062] The pixel drive circuit 322 reads out (READ) a voltage signal corresponding to the amount of charge accumulated in the charge storage unit CS, row by row, and controls the drive signal RST to reset each row after reading. Furthermore, the pixel drive circuit 322 performs a global reset (GR) after reading the last row. Here, the pixel drive circuit 322 simultaneously controls and resets the drive signal RST for all rows (all pixels), so that the rising and falling timings of the drive signal RST are the same for all rows (all pixels).

[0063] FIG. 6 is a diagram showing an example of the current waveforms of the power supply and ground when the drive signal RST is controlled simultaneously. This FIG. 6 shows the relationship between the control timing of the drive signal RST and the changes in the current waveforms of the power supply (VDD) and ground (VSS). When the rising edges of the drive signal RST are synchronized across all rows (all pixels), a large current flows to the power supply (VDD), resulting in voltage fluctuations (voltage drops). Furthermore, when the falling edges of the drive signal RST are synchronized across all rows (all pixels), a large current flows to the ground (VSS), resulting in voltage fluctuations (voltage drops). In order to reduce the voltage fluctuations when a large current flows, it is necessary to reduce the wiring resistance of the power supply and ground, which increases the size of the control block. This method of simultaneously resetting all pixels is a commonly used conventional global reset method. The method of simultaneously resetting all pixels described with reference to FIGS. 5 and 6 is a commonly used conventional global reset method.

[0064] Next, an example in which the depth image capture device 1 according to this embodiment shifts the reset timing for each row when performing a global reset will be described with reference to Figures 7 and 8. Note that, while "global reset" generally refers to the simultaneous resetting of all pixels as described above, the method of this embodiment in which all pixels are reset by slightly shifting the reset timing for each row is also similar in that all pixels are reset collectively, and so will be described as "global reset" in a broader sense.

[0065] 7 is a timing chart showing an example of a global reset according to this embodiment. Similar to FIG. 5, this diagram shows the waveform of the drive signal RST in the period between exposures (e.g., period TB(1) in FIG. 4).

[0066] 5, the pixel drive circuit 322 reads out (READ) a voltage signal corresponding to the amount of charge accumulated in the charge accumulation unit CS for each row in turn, and controls the drive signal RST to reset each row after reading. Furthermore, the pixel drive circuit 322 performs a global reset (GR) after reading out the last row, but unlike the example shown in FIG. 5, the timing of the reset differs for each row.

[0067] For example, the pixel drive circuit 322 varies the rising timing (reset start timing) and falling timing (reset end timing) of the drive signal RST for each row. As an example, the pixel drive circuit 322 falls the drive signal RST for one row and then rises the drive signal RST for the next row, thereby shifting the reset timing for each row so that the pulse widths of the drive signals RST for each row (the period from the reset start timing to the reset end timing) do not overlap.

[0068] 8 shows an example of the current waveforms of the power supply and ground during global reset according to this embodiment. By shifting the rising and falling edges of the drive signal RST for each row, the changes in the drive signal RST are dispersed over time, thereby suppressing the peaks of the current flowing through the power supply (VDD) and ground (VSS). This makes it possible to suppress voltage fluctuations (voltage drops) without widening the wiring width of the circuit.

[0069] As described above, the distance image capture device 1 according to this embodiment includes a light source unit 2 that irradiates a space to be measured (measurement space) with a light pulse PO, pixels 321 each including a photoelectric conversion element PD that generates charge in response to light (e.g., reflected light RL) incident from the space to be measured and a plurality of charge accumulation units CS that accumulate the charge, and a pixel drive circuit 322 that allocates and accumulates charge in each of the charge accumulation units CS at a predetermined timing synchronized with the irradiation of the light pulse PO, and then outputs a voltage signal corresponding to the amount of charge accumulated in each of the charge accumulation units CS. After outputting a voltage signal corresponding to the amount of charge accumulated in each of the charge accumulation units CS, the pixel drive circuit 322 resets each of the charge accumulation units CS to a predetermined voltage value (e.g., global reset) before allocating and accumulating the charge in each of the charge accumulation units CS next (before the next exposure), and varies the timing of the reset for each of the plurality of pixels 321 (e.g., for each row).

[0070] As a result, the distance imaging device 1 can reduce offsets caused by dark current in the charge storage units CS by reading out voltage signals corresponding to the amount of charge stored in each charge storage unit CS and then performing a global reset immediately before exposure. Furthermore, when performing a global reset, the distance imaging device 1 can vary the timing of the reset for each specified pixel (e.g., each row), thereby suppressing peaks in current flowing to the power supply and ground and reducing voltage fluctuations (voltage drops). Therefore, the distance imaging device 1 can reduce offsets caused by dark current in the ToF sensor without increasing the size of the control block.

[0071] For example, the pixel drive circuit 322 varies the start timing and end timing of the global reset for each predetermined pixel (for example, for each row) among the plurality of pixels.

[0072] This allows the distance image capturing device 1 to distribute the start and end timings of the global reset over time for each predetermined pixel (for example, for each row), thereby suppressing voltage fluctuations (voltage drops) during the global reset.

[0073] As an example, the pixel drive circuit 322 varies the timing of the global reset for each predetermined pixel (for example, for each row) among the plurality of pixels so that the periods from the start timing to the end timing of the reset do not overlap.

[0074] As a result, the range image pickup device 1 can suppress voltage fluctuations (voltage drops) because the global reset periods for each predetermined pixel (for example, each row) do not overlap.

[0075] Furthermore, a control method for the distance imaging device according to this embodiment includes a distance imaging device 1 including: a light source unit 2 that irradiates a space to be measured (measurement space) with a light pulse PO; a pixel 321 that includes a photoelectric conversion element PD that generates charges according to light (for example, reflected light RL) incident from the space to be measured and a plurality of charge accumulation units CS that accumulate the charges; and a pixel drive circuit 322 that distributes and accumulates the charges in each of the charge accumulation units CS at a predetermined timing synchronized with the irradiation of the light pulse PO, and then outputs a voltage signal according to the amount of charge accumulated in each of the charge accumulation units CS. The control method includes the steps of: causing the pixel driving circuit 322 to output a voltage signal corresponding to the amount of charge accumulated in each of the charge storage units CS; and, after outputting the voltage signal corresponding to the amount of charge, resetting (e.g., globally resetting) each of the charge storage units CS to a predetermined voltage value before distributing and storing the charge in each of the charge storage units CS (before the next exposure), wherein, when globally resetting each of the charge storage units CS to the predetermined voltage value, the timing of resetting is varied for each predetermined pixel (e.g., row) among the plurality of pixels 321.

[0076] As a result, the control method in the distance imaging device 1 reads out a voltage signal corresponding to the amount of charge accumulated in each charge accumulation unit CS, and then performs a global reset immediately before exposure, thereby reducing offset caused by dark current in the charge accumulation unit CS. Furthermore, the control method in the distance imaging device 1 varies the timing of the reset for each predetermined pixel (e.g., each row) when performing the global reset, thereby suppressing peaks in current flowing to the power supply and ground and reducing voltage fluctuations (voltage drops). Therefore, the control method in the distance imaging device 1 can reduce offset caused by dark current in the ToF sensor without increasing the size of the control block.

[0077] Second Embodiment Next, a second embodiment will be described. In the first embodiment, an example was described in which the timing of resetting each row is shifted so that the pulse widths of the drive signals RST for each row (the period from the start timing to the end timing of resetting) do not overlap when performing a global reset. In this embodiment, however, another example of controlling the global reset will be described.

[0078] If the rising and falling timings of the drive signal RST are different, the peak of the current flowing to the power supply and ground can be suppressed, so the pulse widths of the drive signals RST for each row may partially overlap.

[0079] 9 is a timing chart showing an example of a global reset according to this embodiment. Similar to FIGS. 5 and 7, this diagram shows the waveform of the drive signal RST in the period between exposures (e.g., period TB(1) in FIG. 4).

[0080] 5 and 7, the pixel drive circuit 322 reads out (READ) a voltage signal corresponding to the amount of charge accumulated in the charge accumulation unit CS, row by row, and controls the drive signal RST to reset each row after reading. After reading out the last row, the pixel drive circuit 322 also varies the timing of the global reset (GR) for each row, similar to the example shown in FIG. 7, but differs in that the reset pulse widths are partially overlapped.

[0081] For example, after the pixel drive circuit 322 raises the drive signal RST for one row, it raises the drive signal RST for the next row before it falls. That is, the pixel drive circuit 322 shifts the rising timing of the drive signal RST for each row without waiting for the falling timing of the drive signal RST for the previous row. Furthermore, after the pixel drive circuit 322 raises the drive signal RST for each row, it shifts the falling timing so that they do not coincide with each other.

[0082] In this way, the pixel drive circuit 322 makes the global reset start and end timings different for each predetermined pixel (for example, for each row) while partially overlapping the periods from the start timing to the end timing of the global reset.

[0083] As a result, the distance imaging device 1 can temporally distribute the start and end timings of the global reset for each predetermined pixel (e.g., for each row), thereby suppressing voltage fluctuations (voltage drops) during the global reset. Furthermore, by overlapping a portion of the period from the start timing to the end timing of the global reset for each predetermined pixel (e.g., for each row), the distance imaging device 1 can lengthen the reset period compared to the global reset control according to the first embodiment shown in Fig. 7 , thereby more reliably resetting the charge storage unit CS. Furthermore, compared to Fig. 7 , the timing (end timing) at which the reset of all rows is confirmed can be shortened, thereby shortening the dark current accumulation time and more effectively eliminating offsets.

[0084] In addition, in the examples of global reset according to the first and second embodiments shown in Figures 7 and 9, the pixel drive circuit 322 outputs a voltage signal corresponding to the amount of charge accumulated in each charge storage unit CS for each predetermined pixel (for example, for each row), and starts a global reset after outputting a voltage signal corresponding to the amount of charge of all pixels (i.e., after reading out a voltage signal corresponding to the amount of charge accumulated in each charge storage unit CS of all pixels).

[0085] This allows the range image pickup device 1 to perform a global reset after reliably reading out information on the amount of charge from all pixels.

[0086] Third Embodiment Next, a third embodiment will be described. In the first and second embodiments, a global reset is started after voltage signals corresponding to the amounts of charge of all pixels are output (i.e., after voltage signals corresponding to the amounts of charge accumulated in the charge storage units CS of all pixels are read out). However, a global reset may be started in order from rows where readout has been completed before readout from all pixels is completed.

[0087] 10 is a timing chart showing an example of a global reset according to this embodiment. Similar to FIGS. 5, 7, and 9, this diagram shows the waveform of the drive signal RST in the period between exposures (e.g., period TB(1) in FIG. 4).

[0088] 5, 7, and 9, the pixel drive circuit 322 reads out (READ) a voltage signal corresponding to the amount of charge accumulated in the charge accumulation unit CS for each row in turn, and controls the drive signal RST to reset each row after reading. Furthermore, after reading out of the last row is completed, the pixel drive circuit 322 varies the timing of the global reset (GR) for each row, as in the example shown in FIG. 7, but differs in that the reset starts before reading out from all pixels is completed.

[0089] The pixel drive circuit 322 sequentially reads out (READ) a voltage signal corresponding to the amount of charge accumulated in the charge storage unit CS for each row, and controls the drive signal RST to reset each row after reading. For example, after resetting the readout period of the first row, the pixel drive circuit 322 starts a global reset by raising the drive signal RST for the first row, even if readout of the last row has not yet been completed. Furthermore, after resetting the readout period of the second row, the pixel drive circuit 322 starts a global reset by raising the drive signal RST for the second row later than the rising timing of the drive signal RST for the first row, even if readout of the last row has not yet been completed.

[0090] That is, even if the readout of the last row is not yet complete, the pixel drive circuit 322 starts the global reset by raising the drive signal RST for each row from which readout has been completed. After the readout of the last row is completed, the pixel drive circuit 322 ends the global reset by lowering the drive signal RST for each row from the first row to the last row.

[0091] In this way, the pixel drive circuit 322 outputs a voltage signal corresponding to the amount of charge accumulated in each charge storage unit CS for each predetermined pixel (e.g., for each row), and starts a global reset after outputting a voltage signal for each predetermined pixel (e.g., for each row) even if output of voltage signals corresponding to the amount of charge for all pixels has not been completed.The pixel drive circuit 322 then ends the global reset for each predetermined pixel (e.g., for each row) before allocating and storing the charge in each charge storage unit CS.

[0092] As a result, the range imaging device 1 can temporally distribute the start and end timings of the global reset for each predetermined pixel (for example, for each row), thereby suppressing voltage fluctuations (voltage drops) during the global reset. Furthermore, the range imaging device 1 can set a longer reset period compared to the global reset control according to the second embodiment shown in Fig. 9, thereby enabling the reset to be performed more reliably. Furthermore, compared to Fig. 7, the timing at which the reset of all rows is confirmed (end timing) can be shortened, thereby shortening the dark current accumulation time and further eliminating offsets.

[0093] Fourth Embodiment Next, a fourth embodiment will be described. In the global reset described in the first to third embodiments, the pixel drive circuit 322 reads out (READ) a voltage signal corresponding to the amount of charge accumulated in the charge accumulation unit CS for each row, controls the drive signal RST after reading out each row to perform a reset (first reset), and then performs a global reset (second reset). This allows the distance image capture device 1 to reset the dark current generated in the charge accumulation unit CS after reading out before performing the next exposure.

[0094] Here, the pixel driving circuit 322 may control the reset (first reset) performed for each row and the global reset (second reset) as one continuous reset.

[0095] 11 is a timing chart showing an example of a global reset according to this embodiment. Similar to FIGS. 5, 7, 9, and 10, this diagram shows the waveform of the drive signal RST in the period between exposures (e.g., period TB(1) in FIG. 4).

[0096] As shown in this figure, the pixel drive circuit 322 controls each row as one continuous reset from the start timing of the reset after readout (first reset) to the end timing of the global reset (second reset).

[0097] Even in this way, the distance image capturing device 1 can distribute the timing of the rise and fall of the drive signal RST over time for each specified pixel (for example, for each row), thereby suppressing voltage fluctuations (voltage drops) when performing a global reset.

[0098] Fifth Embodiment Next, a fifth embodiment will be described. In the first to fourth embodiments, the pixel drive circuit 322 suppresses voltage fluctuations (voltage drops) by varying the timing of the global reset for each row, but this is not limited to every row. For example, when varying the timing of the global reset for each predetermined pixel, the pixel drive circuit 322 may vary the timing of the global reset for each of several rows.

[0099] 12A and 12B are timing charts showing an example of global reset according to this embodiment. Fig. 12A shows an example of the global reset according to this embodiment, in which the timing of the global reset is changed for each row shown in Fig. 7. On the other hand, Fig. 12B shows an example of the global reset according to this embodiment, in which the timing of the global reset is changed for every four rows.

[0100] When the timing of the global reset is varied every four rows, the current flowing to the power supply and ground at the rising and falling edges of the drive signal RST is larger than when controlling every row, but the current can be made smaller than when controlling all pixels simultaneously. As long as the number of rows controlled collectively is within the range of voltage fluctuation, the control can be simplified and the time required for the global reset can be shortened.

[0101] When the pixel driving circuit 322 varies the timing of the global reset for each predetermined pixel, the pixel driving circuit 322 may vary the timing of the global reset for each column depending on the specifications of the distance image sensor 32. Furthermore, the pixel driving circuit 322 may vary the timing of the global reset for each group of a predetermined number of pixels, not limited to rows or columns.

[0102] Note that all or part of the distance image processing unit 4 in the distance image capturing device 1 in the above-described embodiment may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program may be loaded and executed by a computer system. Note that the term "computer system" as used herein includes hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. Furthermore, the term "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within a computer system that serves as a server or client. Furthermore, the program may be for implementing part of the above-described functions, or may be capable of implementing the above-described functions in combination with a program already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA.

[0103] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0104] DESCRIPTION OF SYMBOLS 1...Distance image capturing device 2...Light source section 21...Light source device 22...Diffuser 3...Light receiving section 31...Lens 32...Distance image sensor 320...Light receiving area 321...Pixel 322...Pixel driving circuit 323...Vertical scanning circuit 324...Horizontal scanning circuit 325...Pixel signal processing circuit 326...Control circuit 4...Distance image processing section 41...Timing control section 42...Distance calculation section 43...Measurement control section CS...Charge accumulation section PO...Light pulse RL...Reflected light OB...Object

Claims

1. A distance imaging device comprising: a light source unit that irradiates a measurement space with a light pulse; a plurality of pixels each having a photoelectric conversion element that generates an electric charge in accordance with the light incident from the measurement space and a plurality of charge accumulation units that accumulate the electric charge; and a pixel drive circuit that allocates and accumulates the electric charge in each of the charge accumulation units at a predetermined timing synchronized with the irradiation of the light pulse, and after accumulating the electric charge, outputs a voltage signal corresponding to the amount of the electric charge accumulated in each of the charge accumulation units, wherein the pixel drive circuit outputs a voltage signal corresponding to the amount of the electric charge accumulated in each of the charge accumulation units, and then resets each of the charge accumulation units to a predetermined voltage value before allocating and accumulating the electric charge in each of the charge accumulation units, and varies the timing of the reset for each of predetermined pixels among the plurality of pixels.

2. The distance imaging device according to claim 1, wherein the pixel drive circuit varies the start timing and end timing of the reset for each predetermined pixel.

3. The distance imaging device according to claim 2, wherein the pixel driving circuit varies the timing of the resetting for each predetermined pixel so that the periods from the start timing to the end timing of the resetting for each predetermined pixel do not overlap.

4. The distance imaging device according to claim 2, wherein the pixel driving circuit makes the start timing and end timing of the reset different for each predetermined pixel while overlapping a portion of the period from the start timing to the end timing of the reset.

5. A distance imaging device comprising: a light source unit that irradiates a measurement space with a light pulse; a plurality of pixels each having a photoelectric conversion element that generates an electric charge according to the light incident from the measurement space and a plurality of charge accumulation units that accumulate the electric charge; and a pixel drive circuit that allocates and accumulates the electric charge in each of the charge accumulation units at a predetermined timing synchronized with the irradiation of the light pulse, and after accumulating the electric charge, outputs a voltage signal according to the amount of the electric charge accumulated in each of the charge accumulation units, wherein the pixel drive circuit, after outputting a voltage signal according to the amount of the electric charge accumulated in each of the charge accumulation units, resets each of the charge accumulation units to a predetermined voltage value before allocating and accumulating the electric charge in each of the charge accumulation units, and varies the timing of the reset for each of the predetermined pixels among the plurality of pixels so that the periods from the start timing to the end timing of the reset for each of the predetermined pixels do not overlap.

6. A distance imaging device comprising: a light source unit that irradiates a measurement space with a light pulse; a plurality of pixels each having a photoelectric conversion element that generates an electric charge in accordance with the light incident from the measurement space and a plurality of charge accumulation units that accumulate the electric charge; and a pixel drive circuit that allocates and accumulates the electric charge in each of the charge accumulation units at a predetermined timing synchronized with the irradiation of the light pulse, and after accumulating the electric charge, outputs a voltage signal corresponding to the amount of the electric charge accumulated in each of the charge accumulation units, wherein the pixel drive circuit outputs a voltage signal corresponding to the amount of the electric charge accumulated in each of the charge accumulation units, and then resets each of the charge accumulation units to a predetermined voltage value before allocating and accumulating the electric charge in each of the charge accumulation units, and varies the timing of the reset for each of the predetermined pixels among the plurality of pixels so that the period from the start timing to the end timing of the reset for each of the predetermined pixels overlaps, while making the start timing and end timing of the reset different.

7. A distance imaging device as described in claim 3 or claim 4, wherein the pixel driving circuit outputs a voltage signal corresponding to the amount of charge stored in each of the charge storage sections for each predetermined pixel among the plurality of pixels, and starts the resetting after outputting a voltage signal corresponding to the amount of charge for all pixels.

8. The distance imaging device of claim 4, wherein the pixel driving circuit outputs a voltage signal corresponding to the amount of charge stored in each of the charge storage sections for each of a predetermined number of pixels among the plurality of pixels, starts the resetting after outputting a voltage signal corresponding to the amount of charge for each of the predetermined pixels even if output of a voltage signal corresponding to the amount of charge for all of the pixels has not been completed, and then ends the resetting for each of the predetermined pixels before allocating and storing the charge in each of the charge storage sections.

9. The distance imaging device according to claim 1, wherein the pixel driving circuit performs the reset as a second reset after a first reset that is performed for each predetermined pixel at the end when a voltage signal corresponding to the amount of charge stored in each of the charge storage sections is output for each predetermined pixel among the plurality of pixels.

10. The distance imaging device according to claim 9, wherein the pixel drive circuit controls the first reset and the second reset as one continuous reset from the start timing of the first reset to the end timing of the second reset.

11. The distance imaging device according to claim 1, wherein the plurality of pixels are arranged in a matrix, and the pixel drive circuit varies the timing of resetting the plurality of pixels for each row.

12. The distance imaging device according to claim 1, wherein the plurality of pixels are arranged in a matrix, and the pixel drive circuit varies the reset timing for each of a plurality of rows of the plurality of pixels.

13. A control method for a distance imaging device comprising: a light source unit that irradiates a measurement space with a light pulse; a plurality of pixels each having a photoelectric conversion element that generates an electric charge according to the light incident from the measurement space; and a plurality of charge accumulation units that accumulate the electric charge; and a pixel drive circuit that allocates and accumulates the electric charge in each of the charge accumulation units at a predetermined timing synchronized with the irradiation of the light pulse, and after accumulating the electric charge, outputs a voltage signal according to the amount of the electric charge accumulated in each of the charge accumulation units, the control method comprising: a step in which the pixel drive circuit outputs a voltage signal according to the amount of electric charge accumulated in each of the charge accumulation units; and a step in which, after outputting the voltage signal according to the amount of electric charge, resets each of the charge accumulation units to a predetermined voltage value before allocating and accumulating the electric charge in each of the charge accumulation units, and when resetting each of the charge accumulation units to the predetermined voltage value, the reset timing is varied for predetermined pixels among the plurality of pixels.

Images