WO2016027656A1 - 測距方法及び測距装置 - Google Patents
測距方法及び測距装置 Download PDFInfo
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- WO2016027656A1 WO2016027656A1 PCT/JP2015/072048 JP2015072048W WO2016027656A1 WO 2016027656 A1 WO2016027656 A1 WO 2016027656A1 JP 2015072048 W JP2015072048 W JP 2015072048W WO 2016027656 A1 WO2016027656 A1 WO 2016027656A1
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- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
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- G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
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- H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
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Definitions
- the present invention relates to a distance measuring method and a distance measuring apparatus.
- a distance measuring device including a TOF (Time-Of-Flight) type distance sensor is known (for example, see Patent Document 1).
- the distance sensor includes a light receiving layer, a photogate electrode for charge transfer, and a floating diffusion layer for extracting charge.
- the charge generated in the light receiving layer by the incidence of pulsed light is caused to flow into the floating diffusion layer by applying a pulse signal to the photogate electrode.
- the flowed-in charges are accumulated as signal charges in the floating diffusion layer.
- the charge accumulated in the floating diffusion layer is read out as an output corresponding to the accumulated charge amount. Based on this output, the distance to the object is calculated.
- the distance measuring apparatus as described in Patent Document 1, even if the driving signal of the light source is a square wave, the light intensity signal of the pulsed light emitted from the light source gradually increases in light intensity to a predetermined value. Is a trapezoidal wave having a rising period in which the light intensity is maintained at a predetermined value or more, and a falling period in which the light intensity falls below the predetermined value and gradually decreases.
- the distance measurement accuracy of the distance measuring device may deteriorate due to the fact that the light intensity signal of the pulsed light becomes a trapezoidal wave.
- a distance measuring method includes a light source that emits pulsed light toward an object, a charge generation region that generates charges in response to incidence of reflected light of the pulsed light on the object, and a charge generation region
- the charge is accumulated in the charge accumulation region over the second period, and is based on the amount of charge accumulated in the charge accumulation region over the first period and the amount of charge accumulated in the charge accumulation region over the second period.
- the distance to the calculated, when emitting pulsed light from the light source emits pulse light is the light intensity stabilization period previously set longer than the respective first and second periods in the extraction phase of the pulsed light from the light source.
- a distance measuring device includes a light source that emits pulsed light toward an object, a charge generation region that generates charges in response to incidence of reflected light of the pulsed light on the object, and a charge generation region
- a distance sensor having a charge accumulation region for accumulating the charge generated in step 1, wherein the charge generated in the charge generation region is sent to the charge accumulation region in a first period relative to a pulsed light emission period
- the charge is accumulated in the charge accumulation region over the first period, and the charge generated in the charge generation region is sent to the charge accumulation region in the second period that is different in timing from the first period and has the same width as the first period.
- a charge transfer unit that accumulates in the charge accumulation region over the second period, an amount of charge accumulated in the charge accumulation region over the first period, and an amount of charge accumulated in the charge accumulation region over the second period
- a distance calculation unit that calculates the distance to the object based on the light source, and a light source that emits preset pulse light whose light intensity stabilization period in the pulse light emission period is longer than each of the first and second periods
- pulsed light is emitted from the light source, and reflected light of the pulsed light from the object enters the distance sensor.
- charges are generated in response to the incident reflected light.
- the charges generated in the charge generation region are sent to the charge accumulation region in the first and second periods and accumulated in the charge accumulation region.
- the first and second periods have different timings and the same width.
- the distance to the object is determined based on the amount of charge accumulated over the first and second periods.
- the amount of charge generated in the charge generation region is compared to the case where it is a square wave. It decreases during the rising period and increases during the falling period. Therefore, for example, when the first period overlaps with the rising period and the second period overlaps with the falling period, the amount of charge accumulated in the charge accumulation region over the first period is smaller than when the first period is a square wave, The amount of charge accumulated in the charge accumulation region over two periods is increased as compared to the case of a square wave. Thus, the amount of charge used to determine the distance to the object changes due to the influence of the rising period and the falling period. As a result, ranging accuracy is lowered.
- the light intensity stabilization period in the emission period of the pulsed light is set longer than each of the first and second periods.
- the proportion of the amount of charge accumulated corresponding to the light intensity stabilization period increases, and corresponds to the rising period and the falling period.
- the proportion of the amount of charge accumulated becomes lower. Therefore, the influence of the rising period and the falling period on the distance measurement accuracy is reduced. As a result, ranging accuracy can be improved.
- the pulsed light When emitting pulsed light from the light source, the pulsed light may be emitted delayed with respect to the start timing of the first period. In this case, in the charge amount accumulated in the charge accumulation region over the second period, the proportion of the charge amount accumulated corresponding to the light intensity stabilization period of the pulsed light is further increased. As a result, distance measurement accuracy can be improved particularly at a short distance.
- the delay time of the pulsed light emission timing with respect to the start timing of the first period is set in advance to a time corresponding to the lower limit value of the linearity region of the distance measurement profile indicating the correlation between the actual distance and the distance obtained by the distance sensor. It may be. In this case, measurement can be performed under the condition that the distance 0 is offset to the distance of the lower limit value. For this reason, it becomes possible to improve ranging accuracy even for a distance range less than the lower limit.
- the distance sensor has a plurality of charge accumulation regions and a plurality of transfer electrodes that send charges generated in the charge generation regions to the plurality of charge accumulation regions, and transfer signals having different phases are respectively transmitted to the plurality of transfer electrodes. May be given. In this case, each time pulse light is emitted once, the generated charges are accumulated in different charge accumulation regions, and the distance to the object is obtained. For this reason, it can prevent that ranging accuracy falls by the time change of the distance to a target object.
- the distance sensor may have a transfer electrode that sends charges generated in the charge generation region to the charge storage region, and the transfer electrode may be supplied with a transfer signal that is intermittently phase-shifted at a predetermined timing. In this case, distance measurement is possible if there is at least one transfer electrode and one charge storage region. Thereby, a distance sensor can be reduced in size.
- FIG. 1 is an explanatory diagram showing the configuration of the distance measuring apparatus according to the present embodiment.
- FIG. 2 is a diagram for explaining a cross-sectional configuration of the distance image sensor.
- FIG. 3 is a schematic plan view of the distance image sensor.
- FIG. 4 is a configuration diagram of the distance sensor.
- FIG. 5 is a diagram showing a cross-sectional configuration along the line VV in FIG.
- FIG. 6 is a diagram showing a potential distribution in the vicinity of the second main surface of the semiconductor substrate along the line VV in FIG.
- FIG. 7 is a diagram for explaining deterioration in distance measurement accuracy in the distance measurement method according to the comparative example.
- FIG. 8 is a distance measurement profile showing the correlation between the distance obtained by the distance measurement method according to the comparative example and the actual distance.
- FIG. 8 is a distance measurement profile showing the correlation between the distance obtained by the distance measurement method according to the comparative example and the actual distance.
- FIG. 9 is an example of a timing chart of various signals in the distance measuring method according to the present embodiment.
- FIG. 10 is another example of a timing chart of various signals in the distance measuring method according to this embodiment.
- FIG. 11 is a flowchart showing a method for setting the light intensity stabilization period and the light emission delay time.
- FIG. 12 is an example of a distance measurement profile.
- FIG. 13 is a configuration diagram of a distance sensor according to a modification.
- FIG. 14 is a timing chart of various signals in the distance measuring method according to the modification.
- FIG. 1 is an explanatory diagram showing the configuration of the distance measuring apparatus according to the present embodiment.
- the distance measuring device 10 is a device that measures the distance d to the object OJ.
- the distance measuring device 10 includes a distance image sensor RS, a light source LS, a display DSP, and a control unit.
- the control unit includes a drive unit (light source drive unit) DRV, a control unit CONT, and a calculation unit (distance calculation unit) ART.
- the light source LS emits pulsed light Lp toward the object OJ.
- the light source LS is composed of, for example, a laser light irradiation device, an LED, or the like.
- the distance image sensor RS is a charge distribution type distance image sensor.
- the distance image sensor RS is disposed on the wiring board WB.
- the control unit includes a calculation circuit such as a CPU (Central Processing Unit), a memory such as a RAM (Random Access Memory) and a ROM (Read Only Memory), a power supply circuit, and It is configured by hardware such as a readout circuit including an A / D converter.
- This control unit may be partially or entirely configured by an integrated circuit such as ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array).
- the drive unit DRV applies the drive signal SD to the light source LS according to the control of the control unit CONT, and drives the light source LS so as to emit the pulsed light Lp toward the object OJ.
- the control unit CONT controls the drive unit DRV and outputs the first and second transfer signals S 1 and S 2 to the distance image sensor RS.
- the control unit CONT displays the calculation result of the calculation unit ART on the display DSP.
- the calculation unit ART reads the charge amounts Q 1 and Q 2 from the distance image sensor RS, respectively.
- the calculation unit ART calculates the distance d based on the read charge amounts Q 1 and Q 2 and outputs the calculation result to the control unit CONT. Details of the calculation method of the distance d will be described later with reference to FIG.
- the display DSP inputs the calculation result of the calculation unit ART from the control unit CONT and displays the calculation result.
- the pulse signal Lp is emitted from the light source LS by applying the drive signal SD to the light source LS.
- the pulsed light Lp emitted from the light source LS enters the object OJ
- reflected light Lr which is pulsed light
- the reflected light Lr emitted from the object OJ enters the charge generation region of the distance image sensor RS.
- the distance image sensor RS outputs the charge amounts Q 1 and Q 2 collected in synchronization with the first and second transfer signals S 1 and S 2 for each pixel.
- the output charge amounts Q 1 and Q 2 are input to the arithmetic unit ART in synchronization with the drive signal SD .
- the distance d is calculated for each pixel based on the input charge amounts Q 1 and Q 2 , and the calculation result is input to the control unit CONT.
- the calculation result input to the control unit CONT is transferred to the display DSP and displayed.
- FIG. 2 is a diagram for explaining a cross-sectional configuration of the distance image sensor.
- the distance image sensor RS is a surface incident type distance image sensor.
- the distance image sensor RS includes a semiconductor substrate 1 and a light shielding layer LI.
- the semiconductor substrate 1 has first and second main surfaces 1a and 1b facing each other.
- the second main surface 1b is a light incident surface.
- the distance image sensor RS is affixed to the wiring substrate WB via the adhesion region FL in a state where the first main surface 1a side of the semiconductor substrate 1 is opposed to the wiring substrate WB.
- the adhesion region FL has an insulating adhesive or filler.
- the light shielding layer LI is disposed in front of the second main surface 1 b of the semiconductor substrate 1.
- the reflected light Lr is incident on the distance image sensor RS from the second main surface 1b side of the semiconductor substrate 1.
- FIG. 3 is a schematic plan view of the distance image sensor.
- the light shielding layer LI is omitted.
- the semiconductor substrate 1 of the distance image sensor RS has an imaging region 1A composed of a plurality of distance sensors P (m, n) arranged in a two-dimensional manner. Each distance sensor P (m, n) outputs the above-described two charge amounts Q 1 and Q 2 . Therefore, a distance image of the object OJ can be obtained by forming an image of the reflected light Lr from the object OJ in the imaging region 1A.
- One distance sensor P (m, n) functions as one pixel.
- Two or more distance sensors P (m, n) may function as one pixel.
- FIG. 4 is a configuration diagram of the distance sensor.
- FIG. 5 is a diagram showing a cross-sectional configuration along the line VV in FIG. In FIG. 4, the light shielding layer LI is omitted.
- the distance image sensor RS includes the light shielding layer LI in front of the second main surface 1b which is a light incident surface.
- An opening LIa is formed in each of the regions corresponding to the distance sensors P (m, n) of the light shielding layer LI.
- the opening LIa has a rectangular shape. In the present embodiment, the opening LIa has a rectangular shape.
- the light enters the semiconductor substrate 1 through the opening LIa of the light shielding layer LI. Therefore, the light receiving region is defined in the semiconductor substrate 1 by the opening LIa.
- the light shielding layer LI is made of a metal such as aluminum, for example.
- the semiconductor substrate 1 includes a p-type first semiconductor region 3 and a p ⁇ -type second semiconductor region 5 having an impurity concentration lower than that of the first semiconductor region 3.
- the first semiconductor region 3 is located on the first main surface 1a side.
- the second semiconductor region 5 is located on the second main surface 1b side.
- the semiconductor substrate 1 is obtained, for example, by growing a p ⁇ type epitaxial layer having an impurity concentration lower than that of the semiconductor substrate on the p type semiconductor substrate.
- an insulating layer 7 is formed on the second main surface 1b (second semiconductor region 5) of the semiconductor substrate 1.
- Each distance sensor P (m, n) is a charge distribution type distance sensor.
- Each distance sensor P (m, n) includes a photogate electrode PG, first and second charge storage regions FD1 and FD2, and first and second transfer electrodes TX1 and TX2.
- the photogate electrode PG is disposed corresponding to the opening LIa.
- a region corresponding to the photogate electrode PG in the semiconductor substrate 1 (second semiconductor region 5) (a region located below the photogate electrode PG in FIG. 5) is the reflected light Lr of the pulsed light Lp from the object OJ. It functions as a charge generation region where charges are generated in response to incidence.
- the photogate electrode PG also corresponds to the shape of the opening LIa and has a rectangular shape in plan view. In the present embodiment, the photogate electrode PG has a rectangular shape like the opening LIa.
- the first and second charge accumulation regions FD1, FD2 are arranged with the photogate electrode PG interposed therebetween.
- the first and second charge accumulation regions FD1 and FD2 are disposed apart from the photogate electrode PG.
- the first and second charge accumulation regions FD1, FD2 have a rectangular shape in plan view.
- the first and second charge storage regions FD1, FD2 have a square shape in plan view, and have the same shape.
- the first and second charge accumulation regions FD1 and FD2 are n-type semiconductor regions formed in the second semiconductor region 5 and having a high impurity concentration.
- the first and second charge accumulation regions FD1 and FD2 accumulate charges generated in the charge generation region as signal charges.
- the first transfer electrode TX1 is disposed on the insulating layer 7 and between the first charge storage region FD1 and the photogate electrode PG.
- the first transfer electrode TX1 is disposed separately from the first charge storage region FD1 and the photogate electrode PG.
- the first transfer electrode TX1 sends charges generated in the charge generation region to the first charge accumulation region FD1 in the first period T 1 (see FIG. 7) according to the first transfer signal S 1 (see FIG. 7).
- the first period T 1 corresponds to the pulsed light Lp emitted period T T (see FIG. 7).
- the second transfer electrode TX2 is on the insulating layer 7 and is disposed between the second charge storage region FD2 and the photogate electrode PG.
- the second transfer electrode TX2 is disposed separately from the second charge accumulation region FD2 and the photogate electrode PG.
- Second transfer electrode TX2 is a charge generated in the charge generation region, according to the first transfer signals S 1 and the second transfer phase different signal S 2 (see FIG. 7), see the second period T 2 (FIG. 7 ) To the second charge storage region FD2.
- Second period T 2 are different in the first period T 1 and the timing, and the same width as the first period T 1.
- the control unit CONT outputs the first and second transfer signals S 1 and S 2 .
- the first and second transfer electrodes TX1 and TX2 apply the first and second transfer signals S 1 and S 2 output by the control unit CONT, thereby generating charges generated in the charge generation region in the first and second transfer electrodes.
- the two charge accumulation regions FD1 and FD2 are distributed and sent. Therefore, a part of the control part CONT and the first and second transfer electrodes TX1, TX2 function as a charge transfer part.
- the first and second transfer electrodes TX1, TX2 have a rectangular shape in plan view.
- the first and second transfer electrodes TX1, TX2 are rectangular and have the same shape.
- the long sides of the first and second transfer electrodes TX1, TX2 are shorter than the long sides of the photogate electrode PG.
- the insulating layer 7 is provided with a contact hole for exposing the surface of the second semiconductor region 5.
- a conductor 13 for connecting the first and second charge storage regions FD1, FD2 to the outside is disposed in the contact hole.
- the impurity concentration is high means that the impurity concentration is, for example, about 1 ⁇ 10 17 cm ⁇ 3 or more, and “+” is attached to the conductivity type.
- the impurity concentration is low means, for example, about 10 ⁇ 10 15 cm ⁇ 3 or less, and “ ⁇ ” is given to the conductivity type.
- the thickness / impurity concentration of each semiconductor region is as follows.
- First semiconductor region 3 thickness 10 to 1000 ⁇ m / impurity concentration 1 ⁇ 10 12 to 10 19 cm ⁇ 3
- Second semiconductor region 5 thickness 1 to 50 ⁇ m / impurity concentration 1 ⁇ 10 12 to 10 15 cm ⁇ 3
- First and second charge accumulation regions FD1, FD2 thickness 0.1 to 1 ⁇ m / impurity concentration 1 ⁇ 10 18 to 10 20 cm ⁇ 3
- a reference potential such as a ground potential is applied to the semiconductor substrate 1 (first and second semiconductor regions 3 and 5) via a back gate or a through electrode.
- the semiconductor substrate 1 is made of Si
- the insulating layer 7 is made of SiO 2
- photo gate electrode PG and the first and second transfer electrodes TX1, TX2 is made of polysilicon. These may be composed of other materials.
- the second transfer signal S 2 of the phase applied to the first transfer signals S 1 and the phase of the second transfer electrode TX2 applied to the first transfer electrode TX1, are 180 degrees.
- the light incident on each distance sensor P (m, n) is converted into electric charge in the semiconductor substrate 1 (second semiconductor region 5). Some of the charges generated in this way travel as signal charges in the direction of the first transfer electrode TX1 or the second transfer electrode TX2 according to the potential gradient.
- the potential gradient is formed by a voltage applied to the photogate electrode PG and the first and second transfer electrodes TX1 and TX2.
- n-type semiconductor includes a positively ionized donor and has a positive potential, and therefore attracts electrons.
- FIG. 6 is a diagram showing a potential distribution in the vicinity of the second main surface of the semiconductor substrate along the line VV in FIG.
- Figure 6 is a potential phi TX1 in the region immediately below the first transfer electrode TX1, the second transfer electrode potential region immediately below the TX2 phi TX2, the potential phi PG charge generation region immediately below the photogate electrode PG, the first potential phi FD1 charge storage regions FD1, and the potential phi FD2 of the second charge accumulation region FD2 is shown.
- the potential ⁇ PG in the region immediately below the photogate electrode PG is the potential ( ⁇ TX1 , ⁇ TX2 ) in the region immediately below the adjacent first and second transfer electrodes TX1 and TX2 when no bias is applied. Then, it is set higher than this reference potential.
- the potential ⁇ PG of this charge generation region is higher than the potentials ⁇ TX1 and ⁇ TX2 . For this reason, the potential distribution has a shape recessed downward in the drawing in the charge generation region.
- the charge accumulation operation will be described with reference to FIG.
- the first transfer signals S 1 of phase applied to the first transfer electrode TX1 is 0 degrees
- the first transfer electrode TX1 is given positive potential.
- the second transfer electrode TX2 is supplied with a reverse-phase potential, that is, a potential having a phase of 180 degrees (for example, a ground potential).
- a potential between the potential applied to the first transfer electrode TX1 and the potential applied to the second transfer electrode TX2 is applied to the photogate electrode PG.
- FIG. 6 (a) negative charge e generated in the charge generation region, the semiconductor potential phi TX1 directly under the first transfer electrode TX1 drops below the potential phi PG charge generation region As a result, it flows into the potential well of the first charge accumulation region FD1.
- the semiconductor potential phi TX2 directly below the second transfer electrode TX2 is not lowered, the second charge accumulation within the potential well region FD2, the charge does not flow into.
- charges are collected and accumulated in the potential well of the first charge accumulation region FD1.
- the potential is recessed in the positive direction.
- the second transfer electrode TX2 is given positive potential.
- the first transfer electrode TX1 is supplied with a reverse-phase potential, that is, a potential with a phase of 180 degrees (for example, a ground potential).
- a potential between the potential applied to the first transfer electrode TX1 and the potential applied to the second transfer electrode TX2 is applied to the photogate electrode PG.
- FIG. 6 (b) negative charge e generated in the charge generation region, the semiconductor potential phi TX2 directly below the second transfer electrode TX2 drops below the potential phi PG charge generation region As a result, it flows into the potential well of the second charge storage region FD2.
- FIG. 7 is a diagram for explaining the deterioration of ranging accuracy in the ranging method according to the comparative example. Specifically, FIG. 7A is a timing chart of various signals when the light intensity signal of the pulsed light emitted from the light source becomes an ideal square wave. FIG. 7B is a timing chart of various signals in an actual case. FIG. 7C is a diagram comparing the light intensity signals of reflected light when returning to the imaging region.
- the drive signal S D applied to the light source LS by the control unit CONT the drive signal S D applied to the light source LS by the control unit CONT
- the light intensity signal S Lp of the pulsed light Lp emitted from the light source LS and when returning to the imaging region 1A.
- the light intensity signal S Lr of the reflected light Lr, the first transfer signal S 1 applied to the first transfer electrode TX1, and the second transfer signal S 2 applied to the second transfer electrode TX2 are shown.
- the drive signal S D , the light intensity signals S Lp and S Lr , and the first and second transfer signals S 1 and S 2 are all pulses that are ideal square waves. Signal. All these signals are at a low level before the drive signal SD is applied to the light source LS.
- the drive signal SD is a pulse signal having a pulse width Tp.
- the pulse width Tp of the drive signal SD is a set value of the pulse width of the light intensity signal SLp .
- the pulse width of the light intensity signal S Lp is equal to the pulse width Tp of the drive signal SD as set.
- the drive signal SD is set to the high level during the pulse width Tp and then set to the low level.
- the light intensity signal S Lp rises simultaneously with the start of application of the drive signal SD , and has a level corresponding to the light intensity of the pulsed light Lp.
- the light intensity signal S Lp falls after the pulse width Tp and becomes low level.
- the first and second transfer signals S 1 and S 2 are applied to the first and second transfer electrodes TX1 and TX2 in opposite phases in synchronization with the emission of the pulsed light Lp.
- the first transfer signals S 1 are synchronized with a phase difference of 0 in the light intensity signal S Lp, is applied during the pulse width Tp to the first transfer electrode TX1, are during this time a high level.
- Second transfer signal S 2 is synchronized with a phase difference of 180 degrees on the light intensity signal S Lp, is applied during the pulse width Tp to the second transfer electrode TX2, are during this time a high level.
- the periods during which the first and second transfer signals S 1 and S 2 are at the high level are the first and second periods T 1 and T 2 , respectively.
- the first and second periods T 1 and T 2 have different timings and the same width. In this case, the widths of the first and second periods T 1 and T 2 are equal to the pulse width Tp of the drive signal SD , respectively.
- the light intensity signal S Lr rises at the same time as the reflected light Lr returns to the imaging region 1A, and has a level corresponding to the light intensity of the reflected light Lr.
- the light intensity signal S Lr falls after the pulse width Tp and becomes low level.
- the pulse width of the light intensity signal S Lr is equal to the pulse width Tp of the drive signal SD .
- the phase difference Td between the light intensity signal S Lp and the light intensity signal S Lr is the flight time of light.
- the phase difference Td corresponds to the distance d from the distance image sensor RS to the object OJ.
- the charge generated in the charge generation region in response to the incidence of the reflected light Lr is accumulated in the first charge in the first period T 1 in which the first transfer signal S 1 is at a high level with respect to the emission period T T of the pulsed light Lp. by being sent to the region FD1, it is accumulated over a first period T 1 in the first charge storage region FD1.
- the emission period T T of the pulsed light Lp is a period in which the light intensity signal S Lp is not at a low level. In this case, the width of the emission period T T is equal to the pulse width Tp of the drive signal S D.
- the charge amount Q 1 accumulated in the first charge storage region FD1 is a charge amount among the light intensity signal S Lr of the first period T 1 and the first transfer signal S 1 is stored in the overlap period.
- the charge amount Q 2 to which is accumulated in the second charge storage region FD2 is a charge amount of the second period T 2 of the out optical intensity signal S Lr and the second transfer signal S 2 is stored in the overlap period.
- Range of measurable distances d in this case is different by the first and second period T 1, T 2 each having a width, a phase difference Td equal to or less than the first and second period T 1, T 2 each width It is a range. That is, the distance d at which the phase difference Td becomes equal to the width of each of the first and second periods T 1 and T 2 is the maximum value of the measurable distance d. Therefore, the distance measurement range which is the width of the distance range to be measured can be set by the widths of the first and second periods T 1 and T 2 . Note that “measurable” theoretically means that the distance d can be calculated by the above equation (1).
- the light intensity signals S Lp and S Lr are trapezoidal waves.
- Light intensity signal S Lp, S Lr are each gradually increased in a rising period T R reaches a predetermined value, the light intensity stabilization period T S maintains a predetermined value or more, below the predetermined value in the falling period T F Decrease gradually.
- the emission period T T of the pulsed light Lp is longer than the pulse width Tp of the drive signal SD .
- the light intensity stabilization period T S is not only a period in which the light intensity signals S Lp and S Lr are constant, but a period in which the light intensity signals S Lp and S Lr fall within 5% of the maximum value, for example. .
- Light intensity signal S Lp if S Lr has a light intensity stabilization period T S of the period in which a constant period except the rising period T R and the falling period T F from the extraction phase T T of the pulsed light Lp light strength is stable period T S.
- the extraction phase T T of the pulsed light Lp is equal to the sum of the pulse width Tp of the width and the drive signal S D falling period T F.
- FIG. 8 is a distance measurement profile showing a correlation between the actual distance and the distance obtained by the distance measurement method according to the comparative example.
- the horizontal axis indicates the actual distance d
- the vertical axis indicates the distance (calculated distance) d cal obtained by the distance measuring method according to the comparative example.
- Pulse light Lp obtained by setting the pulse width Tp of the drive signal SD to 30 ns was used for measurement.
- the range of the horizontal axis and the vertical axis is a range that can be measured when the widths of the first and second periods T 1 and T 2 are set to 30 ns, which is the same as the pulse width Tp of the drive signal SD .
- a straight line B is a straight line having an inclination of 1 passing through the origin.
- the ranging profile is divided into a linearity area A line and non-linearity areas A short and A long .
- the linearity area A line is an area where the actual distance d and the calculated distance d cal are substantially equal (equivalent), and the error (
- the linearity region A line is a region where the error is several percent or less, for example. In the linearity area A line , since the error is small as described above, the distance measurement accuracy is high. In the linearity area A line , the measurement data is generally arranged on the straight line B.
- the non-linearity areas A short , A long are areas other than the linearity area A line , and areas where the actual distance d and the calculated distance d cal are not equivalent are adjacent to at least the linearity area A line. It is an area to include. That is, the non-linearity regions A short and A long may include a region where the actual distance d and the calculated distance d cal are equivalent to a region that is not adjacent to the linearity region A line . The region where the actual distance d is not equal to the calculated distance d cal is a region where the error exceeds the allowable limit, for example, a region where the error exceeds several percent.
- the non-linearity area A short is located on a shorter distance side than the linearity area A line .
- the non-linearity area A long is located on the longer distance side than the linearity area A line .
- the measurement data is arranged at a position shifted from the straight line B.
- the above error is large, so the distance measurement accuracy is low. This is because in the non-linearity region A short , the influence of the charge amount q 2 on the charge amount Q 2 becomes large. Further, in the non-linearity region A long , the influence of the charge amount q 1 on the charge amount Q 1 becomes large.
- FIG. 9 is an example of a timing chart of various signals in the distance measuring method according to the present embodiment.
- the pulse width Tp of the drive signal SD is longer than the widths of the first and second periods T 1 and T 2 by the extension time Tx. Long preset. Thus, it is preset larger than a width of the first and second period T 1, T 2 the width of each of the light intensity stabilization period T S of the pulsed light Lp emitted from the light source LS. Similar to the comparative example, the first and second periods T 1 and T 2 have different timings and the same width.
- FIG. 10 is another example of a timing chart of various signals in the distance measuring method according to the present embodiment.
- the pulse width Tp of the drive signal SD is longer than the widths of the first and second periods T 1 and T 2.
- the drive signal S D is set in advance so as to be applied with a delay of emission delay time (delay time) Ty than the application of the first transfer signals S 1 .
- the charge amount Q 2 to which is accumulated in the second charge accumulation region FD2 the proportion of the charge is further increased, which is accumulated in correspondence with the light intensity stabilization period T S of the pulsed light Lp. Therefore, the influence of the charge quantity q 2 that increases from the ideal case due to the influence of the falling period TF is further reduced on the charge quantity Q 2 . As a result, the influence of the falling period TF of the light intensity signal SLp on the short-range ranging accuracy is reduced. As a result, it becomes possible to improve the accuracy of ranging particularly at a short distance. When the distance d is calculated, it is necessary to offset the distance corresponding to the light emission delay time Ty.
- FIG. 11 a method for setting the light intensity stabilization period T S and the light emission delay time Ty advance.
- FIG. 11 is a flowchart showing a method for setting the light intensity stabilization period and the light emission delay time.
- FIG. 12 is an example of a distance measurement profile.
- step S01 various measurement conditions are set similarly to the distance measuring method according to the comparative example.
- the distance measurement range is set by setting each width of the first and second periods T 1 and T 2 to a value T 0 corresponding to the distance range to be measured.
- the pulse width Tp of the drive signal SD is also T0.
- the light emission delay time Ty is set to zero.
- the offset d ofs of the light emission delay time Ty with respect to the calculated distance d cal is set to 0 in accordance with the light emission delay time Ty.
- a distance measurement profile indicating the relationship between the calculated distance d cal and the actual distance d is created (step S02). As shown in FIG. 12, the ranging profile is divided into a linearity area A line and non-linearity areas A short , A long .
- the distance range d line of the linearity area A line and its lower limit value d short are confirmed, and the corresponding time range T line and its lower limit value T short are calculated (step S03).
- the lower limit d short of the linearity area A line corresponds to the value of the distance range of the non-linearity area A short .
- the measurement conditions are reset (step S04). Specifically, the pulse width Tp of the drive signal SD is T0 + (T0 ⁇ T line ).
- the light emission delay time Ty is Tshort .
- the offset d ofs of the light emission delay time Ty with respect to the calculated distance d cal is set as d short .
- the widths of the first and second periods T 1 and T 2 are not changed.
- a distance measurement profile is created again (step S05).
- the distance range d line linearity region A line, and the lower limit value d short linearity region A line is equal to or within the desired range is determined.
- the wider the distance range d line the wider the distance range that can be measured with high accuracy.
- the smaller the lower limit value d short the shorter the minimum distance that can be measured with high accuracy.
- step S06 the process ends. Thereby, the lower limit value T short of the time range T line is set in advance as the light emission delay time Ty. Further, as the light intensity stabilization period T S, the time range T line corresponding to the linearity region A line is set in advance. Incidentally, by the light intensity stabilization period T S is set in advance, inevitably pulse width Tp and the extension time Tx is set in advance. If NO in step S06, the process proceeds to step S03, and the processes in steps S03 to S06 are repeated.
- the light intensity stabilization period T S is set in advance longer, the ratio of rising period T R and the falling period T F is relatively reduced in the extraction phase T T of the pulsed light Lp, rising period T R and The influence of the falling period TF can be reduced. As a result, the ratio of the linearity area A line having high distance measurement accuracy to the entire distance measurement range increases, and the distance measurement accuracy is improved.
- the pulse light intensity stabilization period T S is the first and second period T 1 in the extraction phase T T of Lp, T 2 longer preset pulse light than the respective A drive unit DRV that drives the light source LS to emit Lp is provided.
- the charge amounts Q 1 and Q 2 accumulated in the first and second charge accumulation regions FD1 and FD2 over the first and second periods T 1 and T 2 respectively correspond to the light intensity stabilization period T S.
- the proportion of the amount of charge accumulated Te becomes high, the ratio of rising period T R and the amount of charge accumulated in correspondence with the falling period T F is lowered. Therefore, the effect on the charge amount to Q 1 charge amount q 1 decreases from the ideal case due to the effects of rising period T R becomes smaller.
- the influence of the charge amount q 2 that increases from the ideal case due to the influence of the falling period TF on the charge amount Q 2 is reduced.
- the influence of the rising period T R and the falling period T F of the light intensity signal S Lp is reduced relative to the distance measuring accuracy, it is possible to improve the distance measurement accuracy.
- the pulse width Tp of the drive signal SD is set to the same length as the widths of the first and second periods T 1 and T 2 , the phase difference It is possible to measure the distance from Td to 0, which is the width of each of the first and second periods T 1 and T 2 .
- the pulse width T p of the drive signal S D is set to the same length as the first and second period T 1, T 2 each having a width, in fact, the rise time T R and the falling period T F the effect, the width of the light intensity stabilization period T S is reduced.
- the pulse width T p of the drive signal S D is intentionally set long in advance, and the width of the light intensity stabilization period T S is intentionally set long, the light intensity stabilization period T S The effect of the decrease in the width can be compensated.
- the pulsed light Lp when emitting pulsed light Lp from the light source LS, the pulsed light Lp is emitted delayed in emission delay time Ty to the start timing of the first period T 1.
- the charge amount Q 2 to which is accumulated over the second period T 2 in the second charge storage region FD2 the ratio of the amount of charge accumulated in correspondence with the light intensity stabilization period T S is enhanced. As a result, distance measurement accuracy can be improved particularly at a short distance.
- the measurement shows the correlation between the distance d cal determined by actual distance d and the distance sensor P (m, n) It is previously set to the lower limit value T short corresponding to the lower limit value d short linearity region a line of distance profiles. In this case, the measurement can be performed under the condition that the distance 0 is offset to the lower limit value d short . For this reason, it becomes possible to improve ranging accuracy even for a distance range less than the lower limit d short .
- the distance sensor P (m, n) includes the first and second charge accumulation regions FD1 and FD2, and the first and second charge accumulation regions FD1 and FD2 that send charges generated in the charge generation region to the first and second charge accumulation regions FD1 and FD2.
- First and second transfer signals S 1 and S 2 are applied to the first and second transfer electrodes TX1 and TX2, respectively.
- the first and second transfer signals S 1 and S 2 are 180 degrees out of phase.
- FIG. 13 is a configuration diagram of a distance sensor according to a modification.
- the light shielding layer LI is omitted.
- the distance sensor P (m, n) according to the modification includes a photogate electrode PG, a first charge accumulation region FD1, and a first transfer electrode TX1.
- the distance sensor P (m, n) according to the present modification is different from the above-described embodiment in that it does not include the second charge accumulation region FD2 and the second transfer electrode TX2.
- the photogate electrode PG has a rectangular ring shape in plan view.
- the photogate electrode PG has a square ring shape in plan view.
- the outer edge of the photogate electrode PG coincides with the outer edge of the distance sensor P (m, n).
- a first charge accumulation region FD1 is formed inside the square ring presented by the photogate electrode PG.
- the first charge accumulation region FD1 has a rectangular shape in plan view.
- the first charge accumulation region FD1 has a square shape in plan view.
- the first charge accumulation region FD1 is located approximately at the center of the distance sensor P (m, n) in plan view.
- a first transfer electrode TX1 is formed between the photogate electrode PG and the first charge storage region FD1.
- the first transfer electrode TX1 has a rectangular ring shape in plan view.
- the first charge accumulation region FD1 has a square ring shape in plan view.
- FIG. 14 is a timing chart of various signals in the distance measuring method according to the modification.
- the first transfer signals S 1 applied to the first transfer electrode TX1 is given intermittently phase shifted at a predetermined timing.
- the first transfer signals S 1 is given 180 degree phase shift at the timing of 180 degrees.
- the first transfer signal S 1 is synchronized with the drive signal SD at a timing of 0 degree, and has a phase difference of 180 degrees with respect to the drive signal SD at a timing of 180 degrees.
- the charge amount Q 1 accumulated in the first charge accumulation region FD1 at the timing of 0 degrees and the charge amount Q 2 accumulated in the first charge accumulation region FD1 at the timing of 180 degrees are read in order. .
- the distance d is calculated based on these charge amounts Q 1 and Q 2 .
- the distance sensor P (m, n) includes the first transfer electrode TX1 that sends the charge generated in the charge generation region to the first charge accumulation region FD1.
- the first transfer electrode TX1, the first transfer signal S 1 is given to intermittently 180 degree phase shift is given at a timing of 180 degrees.
- the distance can be measured, so that the distance sensor P (m, n) can be reduced in size.
- the present invention is not limited to the above embodiment.
- the extension time Tx and the light emission delay time Ty are set while creating the distance measurement profile.
- the present invention is not limited to this. If there is known information about the signal waveform of the light intensity signal S Lp of the pulsed light Lp when emitted from the light source LS, the extension time Tx and the light emission delay time Ty may be set based on this. For example, if the width of the light intensity stabilization period T S is known, the difference between the width of each of the first and second periods T 1 and T 2 and the width of the light intensity stabilization period T S is set as the extension time Tx. Can do.
- the width of the rise time T R of the light intensity signal S Lp is known, presumed width of the light intensity stabilization period T S the value obtained by subtracting the width of the drive signal S rising period from the pulse width Tp of D T R it can. Based on the width of the inferred light intensity stabilization period T S, it is possible to set the extension time Tx as well.
- the light emission delay time Ty is a negative value.
- Region close to the maximum value of the measurable distance range by the above formula (1), for example, the non-linearity region A long, are greatly affected by rising period T R of the light intensity signal S Lp. That is, in this region, the influence of the charge amount q 1 that decreases from the ideal case on the charge amount Q 1 is large.
- the light emission delay time Ty By setting the light emission delay time Ty to a negative value, the influence of the charge amount q 1 on the charge amount Q 1 is reduced, and the ranging accuracy in this region can be improved.
- the distance sensors P (m, n) are two-dimensionally arranged, but may be line sensors arranged one-dimensionally.
- a two-dimensional image can also be obtained by rotating the line sensor or scanning with two line sensors.
- the distance image sensor RS is not limited to the surface incident type distance image sensor.
- the distance image sensor RS may be a back-illuminated distance image sensor.
- the charge generation region in which charge is generated in response to incident light may be configured by a photodiode (for example, an embedded photodiode).
- the p-type and n-type conductivity types in the distance image sensor RS according to the present embodiment may be switched so as to be opposite to those described above.
- the present invention can be used for a distance measuring method and a distance measuring apparatus.
- 10 ... distance measuring device, A line ... linearity region, d ... distance, the lower limit of d short ... linearity region, FD1 ... first charge storage region, FD2 ... second charge accumulation region, P ... distance sensor, PG ... photogate Electrode, S 1 ... first transfer signal, S 2 ... second transfer signal, T 1 ... first period, T 2 ... second period, TX1 ... first transfer electrode (charge transfer unit), TX2 ... second transfer electrode (Charge transfer unit), LS ... light source, CONT ... control unit (charge transfer unit), DRV ... drive unit (light source drive unit), ART ... calculation unit (distance calculation unit), OJ ... object, Lp ... pulse light, Lr ... reflected light, T S ... light intensity stabilization period, T T ... pulse light emission period, Ty ... light emission delay time (delay time), Q 1 , Q 2 ... charge amount.
Abstract
Description
第一半導体領域3:厚さ10~1000μm/不純物濃度1×1012~1019cm-3
第二半導体領域5:厚さ1~50μm/不純物濃度1×1012~1015cm-3
第一及び第二電荷蓄積領域FD1,FD2:厚さ0.1~1μm/不純物濃度1×1018~1020cm-3
距離d=(c/2)×(Tp×Q2/(Q1+Q2))・・・(1)
Claims (6)
- 対象物に向けてパルス光を出射する光源と、前記対象物での前記パルス光の反射光の入射に応じて電荷が発生する電荷発生領域と前記電荷発生領域で発生した電荷を蓄積する電荷蓄積領域とを有する距離センサと、を用いた測距方法であって、
前記電荷発生領域に発生した電荷を、前記パルス光の出射期間に対する第一期間において前記電荷蓄積領域に送ることにより、前記第一期間にわたり前記電荷蓄積領域に蓄積し、
前記電荷発生領域に発生した電荷を、前記第一期間とタイミングが異なり、かつ、前記第一期間と同じ幅である第二期間において前記電荷蓄積領域に送ることにより、前記第二期間にわたり前記電荷蓄積領域に蓄積し、
前記第一期間にわたり前記電荷蓄積領域に蓄積された電荷量と、前記第二期間にわたり前記電荷蓄積領域に蓄積された電荷量と、に基づいて前記対象物までの距離を演算し、
前記光源から前記パルス光を出射する際に、前記光源から前記パルス光の出射期間における光強度安定期間が前記第一及び第二期間それぞれよりも長く予め設定されたパルス光を出射する、測距方法。 - 前記光源から前記パルス光を出射する際に、前記第一期間の開始タイミングに遅延して前記パルス光を出射する、請求項1記載の測距方法。
- 前記第一期間の開始タイミングに対する前記パルス光の出射タイミングの遅延時間は、実際の距離と前記距離センサにより求めた距離との相関関係を示す測距プロファイルのリニアリティ領域の下限値に対応する時間に予め設定された、請求項2記載の測距方法。
- 前記距離センサは、複数の前記電荷蓄積領域と、前記電荷発生領域で発生した電荷を複数の前記電荷蓄積領域に送る複数の転送電極と、を有し、
複数の前記転送電極には、異なる位相の転送信号がそれぞれ与えられる、請求項1~3のいずれか一項に記載の測距方法。 - 前記距離センサは、前記電荷発生領域で発生した電荷を前記電荷蓄積領域に送る転送電極を有し、
前記転送電極には、所定のタイミングで間欠的に位相シフトが与えられた転送信号が与えられる、請求項1~3のいずれか一項に記載の測距方法。 - 対象物に向けてパルス光を出射する光源と、前記対象物での前記パルス光の反射光の入射に応じて電荷が発生する電荷発生領域と前記電荷発生領域で発生した電荷を蓄積する電荷蓄積領域とを有する距離センサと、を備える測距装置であって、
前記電荷発生領域に発生した電荷を、前記パルス光の出射期間に対する第一期間において前記電荷蓄積領域に送ることにより、前記第一期間にわたり前記電荷蓄積領域に蓄積させ、前記電荷発生領域に発生した電荷を、前記第一期間とタイミングが異なり、かつ、前記第一期間と同じ幅である第二期間において前記電荷蓄積領域に送ることにより、前記第二期間にわたり前記電荷蓄積領域に蓄積させる電荷転送部と、
前記第一期間にわたり前記電荷蓄積領域に蓄積された電荷量と、前記第二期間にわたり前記電荷蓄積領域に蓄積された電荷量と、に基づいて前記対象物までの距離を演算する距離演算部と、
前記パルス光の出射期間における光強度安定期間が前記第一及び第二期間それぞれよりも長く予め設定されたパルス光を出射するように前記光源を駆動する光源駆動部と、を備える測距装置。
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