JP5675469B2 - Ranging system - Google Patents

Description

  The present invention relates to a ranging system having a solid-state imaging device that functions as a ranging sensor.

  2. Description of the Related Art Conventionally, as an application example of an image sensor, a method using a time-of-flight (TOF) method is known as a distance measuring method for measuring a distance to a distance measuring object in a non-contact manner. In the case of using the TOF method, a technique is known in which photoelectrons (negative charges) received by a photoelectric conversion element are distributed and then the distributed photoelectrons are read. In the following Non-Patent Documents 1 and 2, pulse light irradiation and irradiation stop are repeated at the same length (light emitting element drive duty is 50%), and light reception is performed in synchronization with pulse light irradiation and irradiation stop, It is described that the generated photoelectrons are distributed in two directions. The distance to the distance measuring object is measured using the photoelectrons distributed in these two directions. Patent Document 1 below describes that photoelectrons received by a photoelectric conversion element are distributed in four directions.

JP 2010-32425 A

Ryohei Miyagawa, Takeo Kanade “CCD-Based Range-Finding Sensor”, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 44, NO. 10, October 1997, p. 1648-1652 Ryohei Miyagawa, Takeo Kanade, ITE Technical Vol. 19, no. 65, PP37-41 (Nov. 1995)

  However, in the technologies described in Non-Patent Documents 1 and 2 and Patent Document 1, the distance from the photoelectron obtained by receiving the reflected light of the ambient light and the pulsed light to the object to be measured is measured. The distance measurement accuracy depends on the light emission intensity of the light source and the ambient light.

  Therefore, the present invention has been made in view of the conventional problems, and an object thereof is to provide a ranging system capable of acquiring highly reliable distance information that does not depend on the intensity of the light source or the ambient light. To do.

  In order to achieve the above object, the present invention is a distance measuring system, which irradiates irradiation light having a period in which light emission intensity is constant with respect to a distance measuring object, and the irradiation apparatus irradiated with the irradiation apparatus. The distance to the subject using the solid-state imaging device that receives the reflected light of the irradiation light in a light-receiving period predetermined with respect to the irradiation timing of the reflected light, and the number of photoelectrons obtained by light reception of the solid-state imaging device And the irradiation device irradiates the irradiation light at a first irradiation timing and a second irradiation timing for a predetermined time, and the solid-state imaging device is irradiated at the first irradiation timing. The reflected light of the irradiated light is received in a first light receiving period, and the reflected light of the irradiated light irradiated in the second irradiation timing is received in a second light receiving period, and the first irradiation timing or The light is received in a third light receiving period that is predetermined with respect to the second irradiation timing, and the calculation unit uses the number of photoelectrons obtained in the first light receiving period to the third light receiving period to perform the measurement. The distance to the distance object is calculated, and the first light receiving period and the second light receiving period are such that the reflected light reaches the solid-state imaging device after the intensity of the reflected light reaching the solid-state imaging device decreases. And the third light receiving period is a time during which the intensity of the reflected light reaching the solid-state imaging device is constant. To do.

  In order to achieve the above object, the present invention is a distance measuring system, which irradiates irradiation light having a period in which light emission intensity is constant with respect to a distance measuring object, and the irradiation apparatus irradiated with the irradiation apparatus. The distance to the subject using the solid-state imaging device that receives the reflected light of the irradiation light in a light-receiving period predetermined with respect to the irradiation timing of the reflected light, and the number of photoelectrons obtained by light reception of the solid-state imaging device And the irradiation device irradiates the irradiation light at a first irradiation timing and a second irradiation timing for a predetermined time, and the solid-state imaging device is irradiated at the first irradiation timing. The reflected light of the irradiated light is received in a first light receiving period, and the reflected light of the irradiated light irradiated in the second irradiation timing is received in a second light receiving period, and the first irradiation timing or The light is received in a third light receiving period that is predetermined with respect to the second irradiation timing, and the calculation unit uses the number of photoelectrons obtained in the first light receiving period to the third light receiving period to perform the measurement. The distance to the distance object is calculated, and the first light receiving period and the second light receiving period are such that the reflected light reaches the solid-state imaging device after the intensity of the reflected light reaching the solid-state imaging device decreases. Including the time until the end of, and is equal to or shorter than the predetermined time, and the third light receiving period is a time during which the reflected light does not reach the solid-state imaging device.

  The calculation unit obtains the intensity of the reflected light from the number of photoelectrons obtained in the first light receiving period and the number of photoelectrons obtained in the second light receiving period, and calculates the first light receiving period or the first light receiving period. From the number of photoelectrons obtained in two light receiving periods, the number of photoelectrons obtained in the third light receiving period, and the obtained intensity of the reflected light, the reflected light is irradiated The distance to the distance measuring object is calculated by obtaining time information indicating the time to reach the solid-state imaging device.

  The illumination light emitted by the irradiation device is pulsed light, and the first light receiving period and the second light receiving period include a timing after the predetermined time has elapsed after the reflected light reaches the solid-state imaging device. It is a period.

  The irradiation device irradiates the irradiation light alternately at the first irradiation timing and the second irradiation timing, and the first irradiation timing and the second irradiation timing, the first light receiving period, and the second light receiving light. The period arrives at a predetermined cycle, and the second irradiation timing is shifted in phase from the first irradiation timing by a certain period from the first irradiation timing, and the second light receiving period is half in phase with the first light receiving period. There is a period shift.

  The first irradiation timing, the second irradiation timing, and the first light receiving period to the third light receiving period are determined based on a predetermined distance measurement detection range.

  There are a plurality of predetermined ranging detection ranges, and the first irradiation timing and the second irradiation timing and the first light receiving period to the third light receiving period corresponding to the plurality of distance measuring detection ranges. And more than one is decided.

  The first irradiation timing and the second irradiation timing of the plurality of ranging detection ranges are out of phase with each other by twice a predetermined time, and the first light receiving period and the plurality of ranging detection ranges The second light receiving periods are not out of phase with each other.

  According to the present invention, an irradiation apparatus that irradiates irradiation light having a period in which the emission intensity is constant with respect to a distance measurement target, and the reflected light of the irradiation light irradiated by the irradiation apparatus, the irradiation timing of the reflected light A solid-state imaging device that receives light in a predetermined light-receiving period, and an arithmetic unit that measures a distance to a subject using the number of photoelectrons obtained by light reception of the solid-state imaging device, and the irradiation device Irradiates the irradiation light for a predetermined time at a first irradiation timing and a second irradiation timing, and the solid-state imaging device transmits the reflected light of the irradiation light irradiated at the first irradiation timing in a first light receiving period. The reflected light of the irradiation light received and irradiated at the second irradiation timing is received in a second light receiving period, respectively, and predetermined with respect to the first irradiation timing or the second irradiation timing. The light is received in a third light receiving period, and the calculation unit calculates a distance to the distance measuring object using the number of photoelectrons obtained in the first light receiving period to the third light receiving period, and The first light receiving period and the second light receiving period include a time from when the intensity of the reflected light reaching the solid-state imaging device decreases until the reflected light reaches the solid-state imaging device, and The third light receiving period is a time that is equal to or less than the predetermined time, and the third light receiving period is a time during which the intensity of the reflected light reaching the solid-state imaging device is constant. High distance information can be obtained.

  According to the present invention, an irradiation apparatus that irradiates irradiation light having a period in which the emission intensity is constant with respect to a distance measurement target, and the reflected light of the irradiation light irradiated by the irradiation apparatus, the irradiation timing of the reflected light A solid-state imaging device that receives light in a predetermined light-receiving period, and an arithmetic unit that measures a distance to a subject using the number of photoelectrons obtained by light reception of the solid-state imaging device, and the irradiation device Irradiates the irradiation light for a predetermined time at a first irradiation timing and a second irradiation timing, and the solid-state imaging device transmits the reflected light of the irradiation light irradiated at the first irradiation timing in a first light receiving period. The reflected light of the irradiation light received and irradiated at the second irradiation timing is received in a second light receiving period, respectively, and predetermined with respect to the first irradiation timing or the second irradiation timing. The light is received in a third light receiving period, and the calculation unit calculates a distance to the distance measuring object using the number of photoelectrons obtained in the first light receiving period to the third light receiving period, and The first light receiving period and the second light receiving period include a time from when the intensity of the reflected light reaching the solid-state imaging device decreases until the reflected light reaches the solid-state imaging device, and Since the third light-receiving period is a time during which the reflected light does not reach the solid-state imaging device, reliable distance information that does not depend on the intensity of irradiation light or ambient light is obtained. be able to.

  The first irradiation timing, the second irradiation timing, and the first light receiving period to the third light receiving period are determined based on a predetermined distance detection detection range, and a plurality of the distance detection detection ranges. Corresponding to the above, since a plurality of the first irradiation timing and the second irradiation timing and the first light receiving period to the third light receiving period are determined, the distance measurement detection range can be expanded.

  The first irradiation timing and the second irradiation timing of the plurality of ranging detection ranges are out of phase with each other by twice a predetermined time, and the first light receiving period and the plurality of ranging detection ranges Since the phases of the second light receiving periods are not shifted from each other, the distance measurement detection range can be expanded only by shifting the irradiation timing by a fixed time.

It is a figure which shows schematic structure of the ranging system which has a solid-state imaging device concerning embodiment. It is a figure which shows the structure of a solid-state imaging device. FIG. 3 is a plan view showing a part of a unit pixel 30 constituting the solid-state imaging device 28 shown in FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. FIG. 5 is a partial cross-sectional view taken along line VV in FIG. 3. FIG. 6A is an example of a potential diagram illustrating a movement state of photoelectrons by the photoelectric conversion element, the first transfer unit, the photoelectron holding unit, and the second transfer unit, and FIG. 6A is a potential diagram when photoelectrons are generated by the photoelectric conversion element. 6B and 6C show potential diagrams when the photoelectrons generated by the photoelectric conversion elements are transferred to the photoelectron holding unit, and FIG. 6D shows the photoelectrons holding unit 114 holding the photoelectrons. FIG. 6E shows a potential diagram when the photoelectrons held by the photoelectron holding unit are transferred to the floating diffusion layer. It is another example of the potential diagram which shows the movement state of the photoelectron by a photoelectric conversion element, a 1st transfer part, a photoelectron holding | maintenance part, and a 2nd transfer part. It is a figure which shows an example of the circuit structure of the light-receiving device shown in FIG. FIG. 9 is a circuit diagram when the unit pixel shown in FIG. 3 is configured using the light receiving device shown in FIG. 8. FIG. 9 is a diagram illustrating another example of the circuit configuration of the unit pixel in FIG. 8. It is a figure which shows the irradiation timing of the irradiation light in the distance measurement of this Embodiment, and the light reception timing of a solid-state imaging device. It is a time chart which shows the drive operation of a unit pixel. It is explanatory drawing of area S1 (the number of photoelectrons of a reflected light component) obtained in a 1st light reception period, and area S2 (number of photoelectrons of a reflected light component) obtained in a 2nd light reception period. It is a figure which shows the structure of a light emission part. It is a figure which shows the relationship between the voltage between drain-source of FET, and drain current. It is a figure which shows the irradiation timing of the irradiation light in the distance measurement of the modification 1, and the light reception timing of a solid-state imaging device. It is a figure which shows an example of the 1st irradiation timing and 2nd irradiation timing of the irradiation light which the irradiation apparatus in the modification 2 irradiates. It is a figure which shows the other example of the 1st irradiation timing of the irradiation light which the irradiation apparatus in the modification 2 irradiates, and a 2nd irradiation timing.

  A unit pixel, a solid-state imaging device having the unit pixel, and a distance measuring system having the unit pixel according to the present invention will be described below in detail with reference to the accompanying drawings with preferred embodiments.

  FIG. 1 is a diagram illustrating a schematic configuration of a distance measuring system 10 having a solid-state imaging device according to an embodiment. As shown in FIG. 1, the distance measuring system 10 includes an irradiation device 12, an imaging unit 14, a calculation unit 16, a control unit 18, and a power source 20.

  The power source 20 supplies a predetermined power source voltage to each part of the distance measuring system 10, and in FIG. 1, for the sake of simplicity, the display of the power source line from the power source 20 to each device is omitted.

  The irradiation device 12 irradiates the distance measurement target W with the pulsed light Lp, and the irradiation device 12 includes a light emitting unit 24 that outputs the pulsed light Lp under the control of the control unit 18. The light emitting unit 24 includes a capacitor and a light emitting element, and emits light when the charge held by the capacitor is supplied to the light emitting diode. Note that the control unit 18 and the arithmetic device 16 may be formed on a solid-state imaging device.

  The light emitting unit 24 emits infrared light. For example, infrared light having a wavelength of 870 nanometers (nm) can be irradiated with an output of 100 watts (W). The light emitting unit 24 outputs the pulsed light Lp with an output time (pulse width) of 100 (nanoseconds).

  Note that the light emitting unit 24 may have a plurality of light emitting points in a linear array shape, or may have a plurality of light emitting points arranged in a matrix. Other light emitting elements such as a laser diode and a light emitting diode (LED) may be used as the light emitting element.

  In the distance measuring system 10, the pulsed light Lp emitted from the irradiation device 12 is reflected by the distance measuring object W and enters the imaging unit 14. For convenience of explanation, the pulsed light Lp from the irradiation device 12 to the distance measuring object W is referred to as irradiation light Le, and the pulsed light Lp from the distance measuring object W to the imaging unit 14 is referred to as reflected light Lr.

  The imaging unit 14 includes a lens 26 and a solid-state imaging device 28. The reflected light Lr and the ambient light Ls that have passed through the lens 26 are collected on the solid-state imaging device 28 and received by the solid-state imaging device 28. The solid-state imaging device 28 has sensitivity to the pulsed light Lp and the environmental light Ls irradiated by the irradiation device 12. The computing unit 16 calculates the distance to the distance measuring object W based on the information on the number of photoelectrons captured by the solid-state imaging device 28 during the light receiving period.

  FIG. 2 is a diagram illustrating a configuration of the solid-state imaging device 28. The solid-state imaging device 28 includes a pixel array 32 in which unit pixels 30 are arranged in a matrix, a pixel driving circuit (light receiving device 100 driving unit) 34, a sample hold circuit 36, a horizontal selection circuit 38, and an output buffer 40. And an A / D converter 42.

  The power supply 20 applies a positive power supply voltage Vdd to the pixel array 32 and a reset voltage Vref. The pixel driving circuit 34 includes a gate driving circuit 44 and a vertical selection circuit 46. The gate driving circuit 44 generates (accumulates) photoelectrons in each unit pixel 30 of the pixel array 32 by outputting various gate driving signals. , Hold, transfer, discharge, etc. The vertical selection circuit 46 has a multiplexer (not shown), and selectively outputs a voltage signal (pixel signal) corresponding to the photoelectron held by the unit pixel 30 to the row to which the unit pixel 30 to be read belongs. Let The horizontal selection circuit 38 has another multiplexer (not shown), and selects a column to which the unit pixel 30 to be read belongs. The read pixel signal is held in the sample hold circuit 36 and then output through the horizontal selection circuit 38. Then, the data is output to the arithmetic unit 16 via the output buffer 40 and the A / D converter 42.

  FIG. 3 is a plan view showing an example of the unit pixel 30 constituting the solid-state imaging device 28 shown in FIG. The unit pixel 30 has a plurality of light receiving devices 100. In the present embodiment, the unit pixel 30 includes four light receiving devices 100 and is arranged in a matrix.

  The light receiving device 100 includes a photoelectric conversion element 104, three photoelectron sorting units 106, and one photoelectron discharge unit 108. Three photoelectron distribution units 106 are provided one by one symmetrically in the horizontal direction across the photoelectric conversion element 104, and one is provided above or below the photoelectric conversion element 104. The photoelectron distribution unit 106 is provided below or above the photoelectric conversion element 104 and is provided on the side where the photoelectron distribution unit 106 is not provided. The two light receiving devices 100 on the upper side of the unit pixel 30 are provided with the photoelectron distributing unit 106 on the upper side of the photoelectric conversion element 104 and with the photoelectron discharging unit 108 on the lower side. The lower two light receiving devices 100 of the unit pixel 30 are provided with a photoelectron distributing unit 106 below the photoelectric conversion element 104 and with a photoelectron discharging unit 108 on the upper side. By having such a configuration, the light receiving devices 100 of the unit pixels 30 adjacent to each other in the vertical direction share the diffusion layer 142 provided therebetween. Further, the light receiving devices 100 of the unit pixels 30 that are adjacent to each other in the horizontal direction share the floating diffusion layer 118 provided therebetween.

  4 and 5 are cross-sectional views of the light receiving device 100 shown in FIG. 3. Specifically, FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3, and FIG. It is a V-arrow arrow partial sectional view.

  The unit pixel 30 includes four light receiving devices 100 arranged in a matrix. The light receiving device 100 includes a photoelectric conversion element 104 formed on a p-type (first conductivity type) semiconductor substrate 102, four photoelectron sorting units 106, and two photoelectron discharge units 108. The photoelectric conversion element 104 has a photogate 110 structure having an electrode (hereinafter referred to as a photogate 110) 110 formed on a p-type (first conductivity type) semiconductor substrate 102 via an insulator (not shown). doing. The photoelectric conversion element 104 is a photodiode that detects light and generates photoelectrons (negative charges) (converts the detected light into photoelectrons). A gate drive signal Sa for driving the photoelectric conversion element 104 is input from the gate drive circuit 44 to the photogate 110.

  The photoelectron distribution unit 106 includes a first transfer unit 112, a photoelectron holding unit 114, a second transfer unit 116, and a floating diffusion layer 118. The first transfer unit 112 is for transferring photoelectrons generated in the photoelectric conversion element 104 to the photoelectron holding unit 114, and is an electrode (first transfer) formed on the p-type semiconductor substrate 102 via the insulator. It has a MOS diode structure having (gate) 120 (see FIG. 4). A gate drive signal Sb for driving the first transfer unit 112 is input from the gate drive circuit 44 to the first transfer gate 120. The photoelectron holding part 114 is disposed on the opposite side of the photoelectric conversion element 104 with the first rolling part 112 interposed therebetween, and temporarily holds the photoelectrons generated by the photoelectric conversion element 104, and is a p-type semiconductor substrate. A MOS diode structure having an electrode (holding gate) 122 formed on the insulator 102 via the insulator is provided (see FIG. 4). A gate drive signal Sc for driving the photoelectron holding unit 114 from the gate drive circuit 44 is input to the holding gate 122.

  The second transfer unit 116 is disposed on the opposite side of the photoelectron holding unit 114 with respect to the first transfer unit 112, and transfers the photoelectrons held by the photoelectron holding unit 114. It has a MOS diode structure having an electrode (second transfer gate) 124 formed through the body (see FIG. 4). A gate drive signal Sd for driving the second transfer unit 116 is input from the gate drive circuit 44 to the second transfer gate 124. The floating diffusion layer 118 (FD; floating diffusion) 118 is arranged on the opposite side of the photoelectron holding unit 114 with the second transfer unit 116 interposed therebetween, and takes in photoelectrons transferred from the photoelectron holding unit 114 and converts them into a voltage. In this case, an n-type (second conductivity type) impurity is formed on the p-type semiconductor substrate 102.

  As shown in FIG. 4, a reset transistor 126 that resets the potential of the floating diffusion layer 118 to a reference potential is connected to the floating diffusion layer 118. The source of the reset transistor 126 is connected to the floating diffusion layer 118, the reset voltage Vref from the power supply 20 is applied to the drain, and the reset signal R is supplied to the gate from the gate drive circuit 44. When the high reset signal R is supplied to the gate of the reset transistor 126, the reset transistor is turned on, and the potential of the floating diffusion layer 118 is reset to the reference potential.

  The floating diffusion layer 118 is connected to a signal reading transistor 130 for reading a voltage signal corresponding to the photoelectrons held by the floating diffusion layer 118. A selection transistor 134 for selecting whether to output the voltage signal read by the signal reading transistor 130 to the signal reading line 132 is connected to the signal reading transistor 130. A power supply voltage Vdd from the power supply 20 is applied to the drain of the signal readout transistor 130, the gate is connected to the floating diffusion layer 118, and the source is connected to the drain of the selection transistor 134. When a high selection signal Ss is supplied from the vertical selection circuit 46 to the selection transistor 134, the selection transistor 134 is turned on, and a voltage corresponding to the photoelectron held in the floating diffusion layer 118 is read from the signal readout line 132. . A signal readout line 132 is connected to the source of the selection transistor 134.

  The photoelectron discharge unit 108 includes a third transfer unit 140 and a diffusion layer 142. The third transfer unit 140 is for transferring the photoelectrons generated by the photoelectric conversion element 104 to the diffusion layer 142, and is an electrode (third transfer gate) formed on the p-type semiconductor substrate 102 via the insulator. ) 144 has a MOS diode structure (see FIG. 5).

  The diffusion layer 142 is disposed on the opposite side of the photoelectric conversion element 104 with the third transfer unit 140 interposed therebetween, and the power supply voltage Vdd from the power supply 20 is applied to the diffusion layer 142. When the discharge signal Se is input from the gate driving circuit 44 to the third transfer gate 144, the photoelectrons generated by the photoelectric conversion element 104 are discharged from the diffusion layer 142 via the third transfer unit 140.

  FIG. 6 is a potential diagram showing the movement state of photoelectrons by the photoelectric conversion element 104, the first transfer unit 112, the photoelectron holding unit 114, and the second transfer unit 116.

  6A shows a potential diagram when photoelectrons are generated by the photoelectric conversion element 104, and FIGS. 6B and 6C show potentials when the photoelectrons generated by the photoelectric conversion element 104 are transferred to the photoelectron holding unit 114. FIG. 6D is a potential diagram when the photoelectron holding unit 114 holds photoelectrons, and FIG. 6E shows a case where the photoelectrons held by the photoelectron holding unit 114 are transferred to the floating diffusion layer 118. Is a potential diagram.

As shown in FIG. 6A, when a high gate drive signal Sa is input to the photogate 110, the potential position is lowered in the photoelectric conversion element 104, and the generated photoelectrons e ⁻ accumulate in the photoelectric conversion element 104. . Then, as shown in FIG. 6B, by inputting a high gate drive signal Sb to the first transfer gate 120, the photoelectrons e ⁻ generated by the photoelectric conversion element 104 are transferred to the photoelectron holding unit 114. At this time, the high gate drive signal Sc is input to the holding gate 122. Further, by inputting a low gate drive signal Sa to the photogate 110, the potential position of the photoelectric conversion element 104 is increased (see FIG. 6C), and the photoelectrons e ⁻ generated in the photoelectric conversion element 104 are photoelectrons. Then, the low gate drive signal Sb is input to the first transfer gate 120 and the photoelectrons generated by the photoelectric conversion element 104 are held in the photoelectron holding unit 114 as shown in FIG. 6D. By repeating the states of FIGS. 6A to 6C, the photoelectrons generated by the photoelectric conversion element 104 during a plurality of light receiving periods can be held in the photoelectron holding unit 114. Note that the light receiving period refers to a period (accumulation period) in which photoelectrons are generated and accumulated in accordance with received light.

Thereafter, as shown in FIG. 6E, by inputting the high gate drive signal Sd to the second transfer gate 124, the potential position of the second transfer unit 116 is lowered, and the low gate drive signal Sc is input to the holding gate 122. As a result, the potential position of the photoelectron holding unit 114 increases, and the photoelectrons e ⁻ held by the photoelectron holding unit 114 are transferred to the floating diffusion layer 118.

  Note that as shown in FIG. 7, even during light reception, a high gate drive signal Sb may be input to the first transfer gate 120 to simultaneously perform light reception and transfer of photoelectrons generated in the photoelectric conversion element 104.

  FIG. 8 is a diagram illustrating an example of a circuit configuration of the light receiving device 100. Photoelectrons held by the photoelectric conversion element 104 of the light receiving device 100 are transferred to the floating diffusion layer 118 of the photoelectron sorting units 106a, 106b, and 106c via the transfer paths 146a, 146b, and 146c. The transfer paths 146a, 146b, and 146c include the first transfer unit 112, the photoelectron holding unit 114, and the second transfer unit 116 of the photoelectron sorting units 106a, 106b, and 106c shown in FIGS. The source of one reset transistor 126 is connected to the floating diffusion layer 118 of the photoelectron distributors 106a, 106b, 106c, and the gate of one signal readout transistor 130 is connected.

  Before the photoelectrons held by the respective photoelectron holding units 114 of the photoelectron distributing units 106a, 106b, and 106c are transferred to the respective floating diffusion layers 118, the reset transistor 126 is turned on, whereby each floating diffusion layer 118 is set as a reference. The potential is reset, and the voltage (hereinafter, black level) of each floating diffusion layer 118 at that time is read out. Thereafter, the photoelectrons held by the photoelectron holding units 114 of the photoelectron sorting units 106a, 106b, and 106c are sequentially transferred to the floating diffusion layer 118. The photoelectrons transferred to each floating diffusion layer 118 are sequentially converted into a voltage signal (signal level) by the signal readout transistor 130 and read out from the signal readout line 132 through the selection transistor 134.

  Specifically, by turning on the reset transistor 126, the potential of each floating diffusion layer 118 is reset, and the black level is read out. Thereafter, the photoelectrons held by the photoelectron holding unit 114 of the photoelectron sorting unit 106 a are transferred to the floating diffusion layer 118, and a voltage signal (signal level) corresponding to the transferred photoelectrons is read from the signal readout line 132. Next, by turning on the reset transistor 126, the potential of each floating diffusion layer 118 is reset, and the black level is read out. Thereafter, the photoelectrons held by the photoelectron holding unit 114 of the photoelectron distributing unit 106 b are transferred to the floating diffusion layer 118, and a voltage signal (signal level) corresponding to the transferred photoelectrons is read from the signal readout line 132. Finally, by turning on the reset transistor 126, the potential of each floating diffusion layer 118 is reset, and the black level is read out. Thereafter, the photoelectrons held by the photoelectron holding unit 114 of the photoelectron sorting unit 106 c are transferred to the floating diffusion layer 118, and a voltage signal (signal level) corresponding to the transferred photoelectrons is read from the signal readout line 132.

  As described above, the voltage signal corresponding to the photoelectrons held by the photoelectron holding units 114 of the photoelectron sorting units 106a, 106b, and 106c of the light receiving device 100 is read from the same signal readout line 132. In FIG. 8, the photoelectron discharge unit 108 is not shown.

  FIG. 9 is a circuit diagram when the unit pixel 30 shown in FIG. 3 is configured using the light receiving device 100 shown in FIG. The unit pixel 30 includes four light receiving devices 100. The light receiving device 100 includes one photoelectric conversion element 104, four photoelectron sorting units 106a, 106b, 106c, and two, as illustrated in FIG. And a photoelectron discharge unit 108. Each floating diffusion layer 118 of the photoelectron allocating units 106 a, 106 b, and 106 c of all the light receiving devices 100 is connected to the source of the reset transistor 126 and the gate of the signal readout transistor 130.

  By turning on the reset transistor 126, the potentials of the floating diffusion layers 118 of the photoelectron allocating units 106a, 106b, and 106c are reset, and the black level is read out. Thereafter, the photoelectrons held by the photoelectron holding unit 114 of each photoelectron sorting unit 106a of the unit pixel 30 are transferred to the floating diffusion layer 118 of each photoelectron sorting unit 106a, and a voltage signal (in accordance with the transferred photoelectrons) Signal level) is read out from the signal readout line 132. That is, a voltage signal corresponding to the number of photoelectrons obtained by adding (adding) the photoelectrons transferred to the floating diffusion layer 118 of the photoelectron sorting unit 106 a of each light receiving device 100 of the unit pixel 30 is read from the signal readout line 132.

  Next, by turning on the reset transistor 126, the potentials of the floating diffusion layers 118 of the photoelectron sorting units 106a, 106b, and 106c are reset, and the black level is read out. Thereafter, the photoelectrons held in the photoelectron holding unit 114 of each photoelectron sorting unit 106b of the unit pixel 30 are transferred to the floating diffusion layer 118 of each photoelectron sorting unit 106b, and a voltage signal (in accordance with the transferred photoelectrons) Signal level) is read out from the signal readout line 132. That is, a voltage signal corresponding to the number of photoelectrons obtained by adding the photoelectrons transferred to the floating diffusion layer 118 of the photoelectron sorting unit 106 b of each light receiving device 100 of the unit pixel 30 is read from the signal readout line 132.

  Finally, by turning on the reset transistor 126, the potentials of the floating diffusion layers 118 of the photoelectron sorting units 106a, 106b, and 106c are reset, and the black level is read out. Thereafter, the photoelectrons held by the photoelectron holding unit 114 of each photoelectron sorting unit 106c of the unit pixel 30 are transferred to the floating diffusion layer 118 of each photoelectron sorting unit 106c, and a voltage signal corresponding to the transferred photoelectron (( Signal level) is read out from the signal readout line 132. That is, a voltage signal corresponding to the number of photoelectrons obtained by adding the photoelectrons transferred to the floating diffusion layer 118 of the photoelectron sorting unit 106 c of each light receiving device 100 of the unit pixel 30 is read from the signal readout line 132. In this way, all voltage signals corresponding to the photoelectrons held by the photoelectron holding unit 114 of the light receiving device 100 of the unit pixel 30 are read out from the same signal readout line 132.

  As shown in FIG. 9, the photoelectron sorting unit 106c of the upper right light receiving device 100 and the photoelectron sorting unit 106b of the upper left light receiving device 100 share a floating diffusion layer 118, and the lower right light receiving device. The photoelectron distribution unit 106b of 100 and the photoelectron distribution 106c of the lower left light receiving device 100 share the floating diffusion layer 118 with each other.

  As shown in FIG. 10, the light receiving device 100 may include two signal readout lines 132a and 132b. In this case, for example, the voltage signal corresponding to the photoelectrons transferred to the floating diffusion layer 118 of the photoelectron sorting units 106a and 106b is transferred from the signal readout line 132a to the floating diffusion layer 118 of the photoelectron sorting unit 106c. The voltage signals corresponding to are read out from the signal readout line 132b. In the light receiving device 100 shown in FIG. 10, the sources of the reset transistors 126a, 126b, and 126c are connected to the floating diffusion layer 118 of the photoelectron distributing units 106a, 106b, and 106c, and the reset voltage Vref from the power supply 20 is applied to the drain. Is done. Further, reset signals R1, R2, and R3 are supplied to the gates of the reset transistors 126a, 126b, and 126c. In addition, the gates of the signal reading transistors 130a, 130b, and 130c are connected to the floating diffusion layer 118 of the photoelectron distributing units 106a, 106b, and 106c, and the gates of the selection transistors 134a, 134b, and 134c are selected. Signals Ss1, Ss2, and Ss3 are supplied. In short, the signal readout line 132 may be connected to the plurality of floating diffusion layers 118 of the light receiving device 100. As described above, the photoelectron held by the photoelectron holding unit 114 may be read out via the independent signal reading transistor 130 using the light receiving device 100 shown in FIG.

  As described above, in the above-described embodiment, the light receiving device 100 of the unit pixel 30 has the first transfer unit 112 for transferring the photoelectrons generated in the photoelectric conversion element 104 and the photoelectron holding for temporarily holding the photoelectrons. Unit 114, a second transfer unit 116 for transferring the photoelectrons held by the photoelectron holding unit 114, and a floating diffusion layer 118 for holding the transferred photoelectrons and converting the transferred photoelectrons into a voltage. Therefore, the photoelectrons generated by the photoelectric conversion element can be distributed and read out in a plurality of directions, and reset noise can be accurately removed.

  That is, since the photoelectrons generated in the photoelectric conversion element 104 distributed by the photoelectron distribution unit 106 are held in the photoelectron holding unit 114 of the photoelectron distribution unit 106, when it is desired to read out the photoelectrons held by the photoelectron holding unit 114 After resetting the potential of the floating diffusion layer 118 of the photoelectron distribution unit 106, the black level is read out. Thereafter, the photoelectrons held by the photoelectron holding unit 114 may be transferred to the floating diffusion layer 118 and a voltage signal corresponding to the photoelectrons may be read, so that the difference between the reset timing of the potential of the floating diffusion layer 118 and the read timing is sufficient. Can be minimized. Therefore, an accurate black level can be obtained and reset noise can be accurately removed.

  Since the unit pixel 30 includes a plurality of light receiving devices 100, it is possible to acquire a large number of photoelectrons during the light receiving period. Further, since the plurality of light receiving devices 100 of the unit pixel 30 share at least a part of the floating diffusion layer 118 of the plurality of light receiving devices 100, the unit pixel 30 is reduced and the chip area is reduced. As the cost decreases, the unit pixel 30 can be downsized to increase the resolution.

  The unit pixel 30 includes the four light receiving devices 100 arranged in a matrix. The light receiving device 100 includes three photoelectron sorting units 106, and the three photoelectron sorting units 106 include the photoelectric conversion elements 104. Are provided one by one symmetrically in the horizontal direction, and one is provided above or below the photoelectric conversion element 104. The light receiving devices 100 adjacent to each other in the horizontal direction are provided therebetween. Since the floating diffusion layer 118 is shared, the unit pixel 30 is reduced, the chip area is reduced, the cost is reduced, and the unit pixel 30 can be reduced in size to increase the resolution.

  A solid-state imaging device 28 having a pixel array 32 in which unit pixels 30 are arranged one-dimensionally or two-dimensionally includes a signal readout transistor 130 for reading out the potentials of a plurality of floating diffusion layers 118 and a signal readout transistor 130. Signal readout lines 132 for reading out signals, and each potential of the floating diffusion layer 118 of the unit pixel 30 is read out through one signal readout transistor 130, so that the signal readout circuit can be shared, and the readout circuit The output variation due to the manufacturing variation can be suppressed, and the solid-state imaging device 28 can be downsized to increase the resolution.

  Next, the distance measuring method of the present embodiment will be described. FIG. 11 is a diagram illustrating the irradiation timing of the irradiation light Le and the light reception timing of the solid-state imaging device 28 in the distance measurement of the present embodiment. The irradiation device 12 irradiates the irradiation light Le alternately for a predetermined time at the first irradiation timing and the second irradiation timing. That is, the irradiation time in the first irradiation timing and the second irradiation timing is the same time. The second irradiation timing is shifted in phase from the first irradiation timing by a certain period (Δt) from the half cycle. In FIG. 11, the irradiation light Le has a period in which the emission intensity is constant. The first irradiation timing and the second irradiation timing arrive at a predetermined cycle.

  The light receiving device 100 of the solid-state imaging device 28 receives the reflected light Lr incident on the photoelectric conversion element 104 during the first light receiving period to the third light receiving period (the number of photoelectrons corresponding to the reflected light Lr incident on the photoelectric conversion element 104). Generated). The light receiving timings of the first light receiving period and the third light receiving period are light receiving periods predetermined with respect to the first irradiation timing, and the light receiving timings of the second light receiving period are predetermined with respect to the second irradiation timing. This is the light receiving period. The lengths of the first light receiving period to the third light receiving period are the same at time T, and the first light receiving period to the third light receiving period are the time equal to or shorter than the predetermined time during which the irradiation device 12 emits the irradiation light Le. The first light receiving period to the third light receiving period arrive at the predetermined period. The phase of the second light receiving period is shifted from the first light receiving period by a half cycle. In the third light receiving period, the intensity of the reflected light Lr of the irradiation light Le emitted at the first irradiation timing reaching the solid-state imaging device 28 is high. It is a fixed time. The first irradiation timing and the second irradiation timing and the first light receiving period to the third light receiving period are determined based on the distance measurement detection range. The distance measurement detection range is a distance range in which a distance can be measured (for example, a range from 5 m ahead to 20 m ahead).

  Since the light travels 30 cm in 1 nsec (nanosec), it takes 15 cm in one way considering the round trip. Therefore, when the light receiving period is 100 nsec, the distance measurement detection range is 15 (cm) × 100 (nsec). However, the measurement is performed by Δt (nsec) × 15 (cm) by setting the certain time (Δt). The distance detection range is shortened. Thus, the light receiving period and the set value of Δt are determined according to the distance measurement detection range and set by the control unit 18.

  In the first light receiving period and the second light receiving period, the time from when the intensity of the reflected light Lr reaching the solid-state imaging device 28 decreases until the reflected light Lr arrives at the solid-state imaging device 28 (the reflected light Lr Falling period). When the irradiation light Le is a complete rectangular wave pulse light, the timing at which the intensity of the reflected light Lr reaching the solid-state imaging device 28 decreases and the timing at which the arrival of the reflected light Lr at the solid-state imaging device 28 ends. Therefore, the first light receiving period and the second light receiving period are periods including a timing after a predetermined time has elapsed since the reflected light Lr reaches the solid-state imaging device 28, and the solid-state imaging device 28 of the reflected light Lr. This is a period including the timing when the arrival at is completed.

  The irradiation time of the irradiation device 12 (the predetermined time) is, for example, a period equal to or greater than the sum of the first light receiving period, the third light receiving period, and the non-light emitting period between the first light receiving period and the third light receiving period. It is set. By setting in this way, the distance derived by [first light receiving period−Δt] × light speed / 2 becomes the distance measurement detection range. More specifically, when the end timing of the emission time of the irradiation light Le and the first light receiving period are set to overlap for a certain period, the distance measurement detection range is shortened only during the overlapping period.

  FIG. 12 is a time chart showing the driving operation of the unit pixel 30. As shown in FIG. 12, one frame period for capturing one luminance image has an exposure period and a readout period. The exposure period causes the photoelectric conversion element 104 to perform exposure, and the readout period depends on the exposure period. This is a period for reading the obtained photoelectrons from the signal readout line 132.

  The exposure period is a period in which photoelectrons corresponding to the amount of incident light are generated in the photoelectric conversion element 104 by supplying a gate drive signal Sa to the photogate 110 of the photoelectric conversion element 104. The irradiation device 12 drives the light emitting unit 24 by supplying the light emission signal to the light emitting unit 24 during the exposure period, irradiates the irradiation light Le to the distance measuring object W, and supplies the gate driving signal Sa to the photogate 110. Then, the photoelectric conversion element 104 receives light.

  The irradiation device 12 drives the light emitting unit 24 to emit the irradiation light Le at the first irradiation timing and the second irradiation timing, and the gate drive circuit 44 receives light in the first light receiving period to the third light receiving period. A gate drive signal Sa is supplied to the photogate 110. During the exposure period of one frame period, the irradiation at the first irradiation timing and the second irradiation timing and the light reception in the first light receiving period to the third light receiving period are repeatedly performed a predetermined number of times (for example, 100 times). Photoelectrons generated during the period are transferred to the photoelectron holding unit 114 by the photoelectron sorting units 106a, 106b, and 106c.

  For example, the photoelectron number Qa generated in the photoelectric conversion element 104 in the first light receiving period is transferred to the photoelectron holding unit 114 of the photoelectron sorting unit 106a, and the photoelectron number Qb generated in the photoelectric conversion element 104 in the second light receiving period is The number of photoelectrons Qc transferred to the photoelectron holding unit 114 of the photoelectron sorting unit 106b and generated in the photoelectric conversion element 104 in the third light receiving period is transferred to the photoelectron holding unit 114 of the photoelectron sorting unit 106c. The optoelectronic distribution units 106a, 106b, and 106c are driven by the gate drive signal sent from the gate drive circuit 44 as described above.

  When the light receiving period ends and the reading period starts, the photoelectrons held by the photoelectron holding units 114 of the photoelectron sorting units 106a, 106b, and 106c are sequentially read from the signal read line 132.

  Note that photoelectrons generated by light incident on the photoelectric conversion element 104 during a period other than the first light receiving period to the third light receiving period are input to the third transfer gate 144 from the gate drive circuit 44, and the discharge signal Se is input. The light is discharged from the diffusion layer 142 via the third transfer unit 140.

  The calculation unit 16 outputs the voltage signal VQa corresponding to the number of photoelectrons Qa held by the photoelectron holding unit 114 of the photoelectron sorting unit 106a of each pixel read out via the signal readout line 132, and the photoelectron of the photoelectron sorting unit 106b. Using the voltage signal VQb corresponding to the number of photoelectrons Qb held by the holding unit 114 and the voltage signal VQc corresponding to the number of photoelectrons Qc held by the photoelectron holding unit 114 of the photoelectron sorting unit 106c, Calculate the distance.

  Specifically, the calculation unit 16 uses the reflected light Lr from the voltage signal VQa corresponding to the number of photoelectrons Qa obtained in the first light receiving period and the voltage signal VQb corresponding to the number of photoelectrons Qb obtained in the second light receiving period. Is obtained in the third light receiving period and the voltage signal VQa corresponding to the number of photoelectrons Qa obtained in the first light receiving period or the voltage signal VQb corresponding to the number of photoelectrons Qb obtained in the second light receiving period. From the voltage signal VQc corresponding to the number of photoelectrons Qc and the intensity of the obtained reflected light Lr, the reflected light Lr is applied to the solid-state imaging device 28 (unit pixel 30, light receiving device 100) after irradiating the irradiated light Le. The distance to the distance measurement target W is calculated by obtaining the time information ΔT indicating the time until it reaches. In the light receiving period in which the falling period of the reflected light Lr is received, the number of photoelectrons that can be obtained when the light reception start timing is later than the incident timing of the reflected light Lr to the solid-state imaging device 28 is reduced. VQa has a lower value due to the voltage signal VQb. That is, in the second light receiving period, the light receiving start timing is earlier than the first light receiving period by the predetermined time (Δt) with respect to the incident timing.

The intensity I of the reflected light Lr can be obtained from the relational expression shown in Equation 1.
I≡ (VQb−VQa) / Δt Equation 1

  Since the second light receiving period receives a larger amount of reflected light Lr for a certain time (Δt) than the first light receiving period, the number of photoelectrons Qb obtained in the second light receiving period is the number of photoelectrons Qa obtained in the first light receiving period. Further, the number of photoelectrons increases by Δt × I. Therefore, the number of photoelectrons Qb = the number of photoelectrons Qa + ΔI × I, and the above formula 1 can be derived from this formula. The number of photoelectrons Qb and Qa can be equivalent to the voltage signals VQb and VQa.

  Of the number of photoelectrons generated by the photoelectric conversion element 104, the number of photoelectrons generated by the reflected light Lr is proportional to the product of the intensity of the incident reflected light Lr and the incident time of the reflected light Lr, and thus the photoelectrons generated by the reflected light Lr. The number can be expressed as an area obtained by integrating the intensity of the incident reflected light Lr and the incident time. Therefore, the photoelectron number Qra of the reflected light Lr component obtained in the first light receiving period can be represented by the area S1 shown in FIG. 11, and the photoelectron number Qrb of the reflected light Lr component obtained in the second light receiving period is It can be represented by an area S2 shown in FIG.

  FIG. 13 is an explanatory diagram of the area S1 (number of photoelectrons Qra) obtained in the first light receiving period and the area S2 (number of photoelectrons Qrb) obtained in the second light receiving period. The area S1 includes an area (number of photoelectrons) A and an area (number of photoelectrons) C, and the area A is obtained by multiplying the intensity I of the reflected light Lr and the time information ΔT. Therefore, the area S1 can be expressed by a relational expression of S1 = I × ΔT + C. The area C depends on the characteristics of the irradiation device 12 that irradiates the irradiation light Le (including the intensity I of the irradiation light Le) and the characteristics of the photoelectric conversion element 104. The time information ΔT is information indicating the time from when the irradiation light Le is irradiated until the reflected light Lr reaches the solid-state imaging device 28 (unit pixel 30, light receiving device 100). In addition, when the irradiation light Le is a complete rectangular wave pulse light, the area C is zero.

  The area S2 includes an area (number of photoelectrons) B and an area (number of photoelectrons) C. The area B is obtained by multiplying the intensity I of the reflected light Lr by time information ΔT, and the intensity I and Δt of the reflected light Lr. And the product of multiplying and. That is, the area B can be expressed as I × ΔT + I × Δt. Since the area S2 receives the reflected light Lr more than the area S1 by Δt, the area S2 can be obtained by the number of photoelectrons corresponding to Δt × I. Therefore, the area S2 can be expressed by S2 = I × ΔT + I × Δt + C. Note that the number of photoelectrons Qc of the reflected light Lr component obtained in the third light receiving period can be expressed by Qc = I × T.

From the photoelectron number Qrc and the photoelectron number Qra, the relational expression shown in Formula 2 is established.
(Qrc−Qra) / I = [(I × T) − (I × ΔT + C)] / I = T− (ΔT + C / I) Expression 2

From the photoelectron number Qrc and the photoelectron number Qrb, the relational expression shown in Formula 3 is established.
(Qrc−Qrb) / I = [(I × T) − (I × ΔT + I × Δt + C)] / I = T− (ΔT + Δt + C / I) Equation 3

  Since the area C is proportional to the intensity of the reflected light Lr, C / I can be regarded as a constant independent of the intensity, and C / I can be known in advance by measurement.

(Qrc−Qra) can be replaced by (Qc−Qa), and Qc and Qa can be equivalent to VQc and VQa.
ΔT = T− (VQc−VQa) / I−C / I Equation 4
Can be expressed as The reason why (Qrc-Qra) can be replaced with (Qc-Qa) is that the number of photoelectrons Qc obtained in the third light receiving period is the number of photoelectrons Qrc of the reflected light Lr component and the number of photoelectrons of the ambient light Ls component. The number of photoelectrons Qa obtained in the first light receiving period is the sum of the number of photoelectrons Qra of the reflected light Lr component and the number of photoelectrons of the ambient light Ls component, and the first light receiving period and the third light receiving time. Since both the lengths of the periods are time T, subtracting the photoelectron count Qa from the photoelectron count Qc removes the ambient light Ls component, resulting in (Qc−Qa) = (Qrc−Qra). It is.

(Qrc−Qrb) can be replaced by (Qc−Qb), and Qc and Qb can be equivalent to VQc and VQb. Therefore, ΔT can be calculated using Equation 3.
ΔT = T−Δt− (VQc−VQb) / I−C / I Equation 5
Can be expressed as The reason why (Qrc−Qrb) can be replaced with (Qc−Qb) is that the number of photoelectrons Qc obtained in the third light receiving period is the number of photoelectrons Qrc of the reflected light Lr component and the number of photoelectrons of the ambient light Ls component. The number of photoelectrons Qb obtained in the second light receiving period is the sum of the number of photoelectrons Qrb of the reflected light Lr component and the number of photoelectrons of the ambient light Ls component, and the second light receiving period and the third light receiving time. Since both the lengths of the periods are time T, subtracting the photoelectron count Qb from the photoelectron count Qc removes the ambient light Ls component, resulting in (Qc−Qb) = (Qrc−Qrb). It is.

  Therefore, the arithmetic unit 16 can calculate the time information ΔT from the time T of the third light receiving period, the constant C / I stored in advance, and the voltage signals VQc and VQa using Equation 4. In addition, the calculation unit 16 can calculate time information ΔT from the time T of the third light receiving period, the constant C / I stored in advance, Δt, and the voltage signals VQc and VQb using Equation 5. it can. The computing unit 16 may calculate the time information ΔT using either one of the mathematical formula 4 or the mathematical formula 5, but calculates the time information ΔT using the mathematical formula 4 and the mathematical formula 5, and calculates the calculated two time information. More accurate time information ΔT can be obtained by taking the average of ΔT. Note that the emission intensity I of Equation 4 and Equation 5 can be derived using Equation 1.

  Note that the third light receiving period is a time during which the intensity of the reflected light Lr of the irradiation light Le irradiated at the first irradiation timing is constant, but the reflected light Lr of the irradiation light Le irradiated at the second irradiation timing is constant. It may be a time when the intensity becomes constant. In this case, the third light receiving period may be a predetermined light receiving period with respect to the second irradiation timing.

  Here, as the distance from the solid-state imaging device 28 to the distance measurement target W is longer, the incident timing of the reflected light Lr to the solid-state imaging device 28 is delayed, and the time information ΔT is increased correspondingly, and conversely the solid-state imaging device 28. As the distance from the distance measurement target W is closer, the incident timing of the reflected light Lr to the solid-state imaging device 28 is earlier, and the time information ΔT is shortened accordingly. Accordingly, the calculation unit 16 can determine the distance to the distance measurement target W by determining the time information ΔT. Note that the calculation unit 16 applies the time information ΔT calculated by irradiating the reference distance measurement object that is a fixed distance away from the solid-state imaging device 28 as the initial value and receiving the reflected light Lr to the reference time. Even if it is stored as information ΔTs, the distance from the distance measurement object W to the distance measurement object W is obtained by receiving the reflected light Lr from the distance measurement object W, the time information ΔT, the reference time information ΔTs, and the fixed distance. Good. Specifically, the distance from the reference distance measurement object to the distance measurement object W is obtained from the difference between the obtained time information ΔT and the reference time information ΔTs, and the distance measurement object is obtained from the solid-state imaging device 28 from the obtained distance and the fixed distance. The distance to W may be obtained.

  Thus, since the distance of the distance measuring object W can be obtained using only the voltage signal corresponding to the photoelectrons corresponding to the incident reflected light Lr, the reliability does not depend on the intensity of the irradiation light Le or the environmental light Ls. High distance information can be obtained.

  In order to ensure distance measurement accuracy, the irradiation device 12 needs to irradiate the irradiation light Le having a period in which the emission intensity is constant (see FIG. 11). Since the potential decreases with the discharge, the light emission intensity of the light emitting element also decreases. Therefore, in the present embodiment, as shown in FIG. 14, the light emitting section 24 is further provided with an FET (field effect transistor) 164 in addition to the capacitor 160 and the light emitting element 162, so that the light emission intensity is constant. Irradiation light Le having The light emitting element 162 is interposed between the capacitor 160 and the FET 164, and the source of the FET 164 is connected to the light emitting element 162 and the drain is connected to the capacitor 160.

  FIG. 15 is a diagram showing the relationship between the drain-source voltage of the FET 164 and the drain current, and shows the characteristics of the FET 164. As shown in FIG. 15, when the drain-source voltage becomes a certain value or more, the drain current becomes a substantially constant value regardless of the drain-source voltage. Therefore, even when the voltage of the capacitor 160 is reduced due to the discharge of the capacitor 160 shown in FIG. 14, the voltage between the drain and the source is reduced so that the current (drain current) flowing through the light emitting element 162 is constant. The voltage applied to the light emitting element 162 becomes substantially constant, and the light emission intensity of the light emitting element 162 can be kept constant. The irradiation device 12 causes the light emitting unit 24 to emit light by applying a high light emission signal to the gate of the FET 164.

  The embodiment may be modified as follows.

  (Modification 1) In the above-described embodiment, the third light receiving period is a time during which the intensity of the reflected light Lr of the irradiation light Le emitted at the first irradiation timing or the second irradiation timing is constant. 1, in the third light receiving period, a time during which the reflected light Lr of the irradiation light Le irradiated at the first irradiation timing and the second irradiation timing does not reach the solid-state imaging device 28, that is, the reflected light Lr is applied to the solid-state imaging device 28. It is the time when it is not incident.

  FIG. 16 is a diagram illustrating the irradiation timing of the irradiation light Le and the light reception timing of the solid-state imaging device 28 in the distance measurement of the first modification. As shown in FIG. 16, it can be seen that the third light receiving period is a time during which the reflected light Lr does not enter the solid-state imaging device 28. Thereby, the photoelectrons Qc obtained in the third light receiving period become photoelectrons corresponding to the ambient light Ls. Here, the irradiation time (the predetermined time) at the first irradiation timing and the second irradiation timing of the irradiation device 12 is set to be longer than the light reception period (first light reception period or second light reception period). By setting in this way, the distance derived by [first light receiving period−Δt] × light speed / 2 becomes the distance measurement detection range.

  The photoelectron number Qa is composed of the photoelectron number Qra of the reflected light Lr component and the photoelectron number of the ambient light Ls component. As described above, the number of photoelectrons Qra can be represented by the number of photoelectrons Qra = I × ΔT + C, and the number of photoelectrons of the ambient light Ls component of the number of photoelectrons Qa can be represented by the number of photoelectrons Qc. The photoelectron number Qb is composed of the photoelectron number Qrb of the reflected light Lr component and the photoelectron number of the ambient light Ls component. As described above, the number of photoelectrons Qrb can be expressed by the number of photoelectrons Qrb = I × ΔT + I × Δt + C. The number of photoelectrons of the ambient light Ls component with the number of photoelectrons Qb can be represented by the number of photoelectrons Qc. Here, since the lengths of the first light receiving period to the third light receiving period are the same at time T, the number of photoelectrons of the ambient light Ls component of the number of photoelectrons Qa obtained in the first light receiving period and the second light receiving period The number of photoelectrons of the ambient light Ls component with the number of photoelectrons Qb obtained in step 1 is the same as the number of photoelectrons Qc obtained in the third light receiving period.

Therefore, the relational expression shown in Expression 6 is established from the photoelectron number Qa and the photoelectron number Qc, and the relational expression shown in Expression 7 is established from the photoelectron number Qb and the photoelectron number Qc.
(Qa−Qc) / I = [(I × ΔT + C) + Qc−Qc] / I = ΔT + C / I Equation 6
(Qb−Qc) / I = [(I × ΔT + I × Δt + C) + Qc−Qc] / I = ΔT + Δt + C / I Equation 7
Since Qa and Qc can be equivalent to VQa and VQc, ΔT can be calculated using Equation 6:
ΔT = (VQa−VQc) I−C / I Expression 8
Can be expressed as In addition, since Qb and Qc can be equivalent to VQb and VQc, ΔT can be calculated using Equation 7.
ΔT = (VQb−VQc) / I−Δt−C / I Equation 9
Can be expressed as

  Therefore, the arithmetic unit 16 can calculate the time information ΔT from the voltage signals VQa and VQc and the constant C / I stored in advance using Expression 8. In addition, the calculation unit 16 can calculate time information ΔT from the voltage signals VQb and VQc, Δt, and a constant C / I stored in advance using Equation 9. The calculating unit 16 can calculate the time information ΔT using Expression 8 and Expression 9, and obtain the more accurate time information ΔT by taking the average of the two calculated time information ΔT. Note that the emission intensity I of Equation 8 and Equation 9 can be derived using Equation 1. The computing unit 16 obtains the distance from the obtained time information ΔT to the distance measuring object W.

  Thus, since the distance of the distance measuring object W can be obtained using only the voltage signal corresponding to the photoelectrons corresponding to the incident reflected light Lr, the reliability does not depend on the intensity of the irradiation light Le or the environmental light Ls. High distance information can be obtained.

  (Modification 2) In the above-described embodiment and Modification 1, there is one distance detection detection range, and based on the distance measurement detection range, the first irradiation timing and the second irradiation timing, and the first light receiving period to the first light receiving period. In the second modification, a plurality of ranging detection ranges are prepared, and a plurality of first and second irradiation timings and a plurality of first to third light receiving periods are provided. It is determined corresponding to the range detection range. For example, there are ranging detection ranges from 1 to 3, and a plurality of first and second irradiation timings and first to third light receiving periods are provided corresponding to the ranging detection ranges 1 to 3, respectively. ing. Thereby, the range which can measure distance can be expanded.

  Here, the first light receiving period and the second light receiving period of the plurality of distance measuring detection ranges 1 to 3 are not shifted from each other, and the first irradiation timing and the second irradiation of the plurality of distance measuring detection ranges 1 to 3 are set. The timing may be shifted in phase by twice the fixed time (Δt). In other words, the first light receiving periods of the distance measurement detection ranges are in phase with each other, the second light reception periods of the distance measurement detection ranges are in phase with each other, and the first irradiation timing of each distance measurement detection range is a fixed time (Δt ), And the phase of the second irradiation timing of each distance measurement detection range is delayed by twice the fixed time.

  FIG. 17 is a diagram illustrating an example of the first irradiation timing and the second irradiation timing of the irradiation light Le irradiated by the irradiation device 12 according to the second modification. As shown in FIG. 17, the first irradiation timing of the distance measurement detection range 2 is delayed by 2 × Δt from the second irradiation timing of the distance measurement detection range 1, and the first irradiation timing of the distance measurement detection range 3 is The phase is delayed by 2 × Δt from the first irradiation timing in the distance measurement detection range 2. Further, the second irradiation timing of the distance measurement detection range 2 is delayed in phase by 2 × Δt from the second irradiation timing of the distance measurement detection range 1, and the second irradiation timing of the distance measurement detection range 3 is the distance detection detection range. The phase is sent 2 × Δt from the second second irradiation timing.

  Note that the second irradiation timings of the distance measurement detection ranges 1 to 3 are timings in which the phases of the first irradiation timings of the distance measurement detection ranges 1 to 3 are delayed by Δt. Therefore, the irradiation device 12 irradiates the irradiation light Le at the first irradiation timing and the second irradiation timing in each distance measurement detection range if the irradiation timing is shifted by Δt each time the irradiation light Le is irradiated. In other words, even when there are a plurality of distance measurement detection ranges, the irradiation timing can be easily controlled.

  Moreover, the irradiation timing of each ranging detection range may overlap with the irradiation timing of other ranging detection ranges. For example, the first irradiation timing of a certain distance measurement detection range may overlap with the second irradiation timing of another distance measurement detection range irradiated immediately before, and the second irradiation timing of the certain distance detection detection range is It may overlap with the 1st irradiation timing of the other ranging detection range irradiated immediately after.

  FIG. 18 is a diagram illustrating another example of the first irradiation timing and the second irradiation timing of the irradiation light Le irradiated by the irradiation device 12 according to the second modification. As shown in FIG. 18, each irradiation timing (first to sixth irradiation timings) is out of phase by a certain time (Δt), and a certain irradiation timing and the irradiation timing immediately before or immediately after the irradiation timing. Thus, the range detection range is determined. For example, the distance measurement detection range 1 is determined by the first irradiation timing and the second irradiation timing, and the distance measurement detection range 2 is determined by the second irradiation timing and the third irradiation timing. The distance measurement detection range 3 is determined by the timing and the fourth irradiation timing, and the distance detection detection range 4 is determined by the fourth irradiation timing and the fifth irradiation timing. The fifth irradiation timing and the sixth irradiation time. The distance measurement detection range 5 is determined by the timing.

  The second irradiation timing is the second irradiation timing when viewed from the distance measurement detection range 1, but is the first irradiation timing when viewed from the distance measurement detection range 2. Similarly, the third irradiation timing is the second irradiation timing when viewed from the distance measurement detection range 2, but is the first irradiation timing when viewed from the distance measurement detection range 3. Similarly, the fourth and subsequent irradiation timings are the second irradiation timing when viewed from one distance measurement detection range, and the first irradiation timing when viewed from the other distance detection detection range.

  As described above, by overlapping the irradiation timings of the distance measurement detection ranges, the range in which the distance can be measured can be expanded without increasing the number of irradiation timings, and the ranging accuracy can be improved.

  The timing shown in FIGS. 17 and 18 describes the irradiation timing of one cycle in the exposure period within one frame period of the unit pixel 30 shown in FIG. 12, and light reception and photoelectron holding are repeated a plurality of times. After that, the signal is read out, and then the next frame is acquired at a timing delayed by 2 × Δt.

  (Modification 3) In the above embodiment and Modifications 1 and 2, the unit pixel 30 includes the four light receiving devices 100. However, the unit pixel 30 includes a plurality of unit pixels 30 such as two, three, and five. The light receiving device 100 may be included, or only one light receiving device 100 may be included. Further, although the light receiving device 100 has the three photoelectron sorting units 106, it may have only one photoelectron sorting unit 106. When the unit pixel 30 includes only one light receiving device 100 and the light receiving device 100 includes only one photoelectron distributing unit 106, the unit pixels 30 may be acquired in different frames. The unit pixels 30 that receive light may be different in the third light receiving period. For example, the unit pixel 30 that receives light in the first light receiving period is the first pixel, the unit pixel 30 that receives light in the second light receiving period is the second pixel, and the unit pixel 30 that receives light in the third light receiving period is the third pixel, The distance to the distance measuring object W is calculated using the number of photoelectrons obtained from the first pixel to the third pixel.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Ranging system 12 ... Irradiation device 14 ... Imaging part 16 ... Calculation part 18 ... Control part 20 ... Power supply 22 ... 2nd power supply 28 ... Solid-state imaging device 30 ... Unit pixel 32 ... Pixel array 34 ... Pixel drive circuit 44 ... Gate Drive circuit 100... Light receiving device 102... P-type semiconductor substrate 104... Photoelectric conversion element 106... Photoelectron distribution unit 108 .. Photoelectron discharge unit 110 ... Photogate 112 ... First transfer unit 114 ... Photoelectron holding unit 116 ... Second transfer unit 118 ... floating diffusion layer 120 ... first transfer gate 122 ... hold gate 124 ... second transfer gate 126 ... reset transistor 130 ... signal read transistor 132 ... signal read line 134 ... select transistor 140 ... third transfer section 142 ... diffusion Layer 144 ... Third transfer gate 160 ... Capacitor 162 ... Light emitting element 164 ... FET

Claims (8)

An irradiation device that irradiates irradiation light having a period in which the emission intensity is constant with respect to the distance measurement target;
A solid-state imaging device that receives the reflected light of the irradiation light irradiated by the irradiation device in a light receiving period that is predetermined with respect to the irradiation timing of the reflected light;
An arithmetic unit that measures the distance to the distance measurement object using the number of photoelectrons obtained by light reception of the solid-state imaging device;
With
The irradiation apparatus irradiates the irradiation light for a predetermined time at a first irradiation timing and a second irradiation timing,
The solid-state imaging device receives the reflected light of the irradiation light irradiated at the first irradiation timing in a first light receiving period, and secondly reflects the reflected light of the irradiation light irradiated at the second irradiation timing. Receiving light in each light receiving period, and receiving light in a third light receiving period that is predetermined with respect to the first irradiation timing or the second irradiation timing
The calculation unit obtains the intensity of the reflected light from the number of photoelectrons obtained in the first light receiving period and the number of photoelectrons obtained in the second light receiving period, and calculates the first light receiving period or the first light receiving period. From the number of photoelectrons obtained in two light receiving periods, the number of photoelectrons obtained in the third light receiving period, and the obtained intensity of the reflected light, the reflected light is irradiated By calculating time information indicating the time to reach the solid-state imaging device, the distance to the distance measurement target is calculated,
The first light receiving period and the second light receiving period include a time from when the intensity of the reflected light reaching the solid-state imaging device decreases until the reflected light reaches the solid-state imaging device, And a time equal to or shorter than the predetermined time,
The third light receiving period is a time during which the intensity of the reflected light reaching the solid-state imaging device is constant. An irradiation device that irradiates irradiation light having a period in which the emission intensity is constant with respect to the distance measurement target;
A solid-state imaging device that receives the reflected light of the irradiation light irradiated by the irradiation device in a light receiving period that is predetermined with respect to the irradiation timing of the reflected light;
An arithmetic unit that measures the distance to the distance measurement object using the number of photoelectrons obtained by light reception of the solid-state imaging device;
With
The irradiation apparatus irradiates the irradiation light for a predetermined time at a first irradiation timing and a second irradiation timing,
The solid-state imaging device receives the reflected light of the irradiation light irradiated at the first irradiation timing in a first light receiving period, and secondly reflects the reflected light of the irradiation light irradiated at the second irradiation timing. Receiving light in each light receiving period, and receiving light in a third light receiving period that is predetermined with respect to the first irradiation timing or the second irradiation timing
The calculation unit calculates a distance to the distance measurement target using the number of photoelectrons obtained in the first light receiving period to the third light receiving period,
The first light receiving period and the second light receiving period include a time from when the intensity of the reflected light reaching the solid-state imaging device decreases until the reflected light reaches the solid-state imaging device, And a time equal to or shorter than the predetermined time,
The third light receiving period is a time during which the reflected light does not reach the solid-state imaging device. The ranging system according to claim 2 ,
The calculation unit obtains the intensity of the reflected light from the number of photoelectrons obtained in the first light receiving period and the number of photoelectrons obtained in the second light receiving period, and calculates the first light receiving period or the first light receiving period. From the number of photoelectrons obtained in two light receiving periods, the number of photoelectrons obtained in the third light receiving period, and the obtained intensity of the reflected light, the reflected light is irradiated A distance measuring system characterized in that a distance to the distance measuring object is calculated by obtaining time information indicating a time required to reach the solid-state imaging device. It is a ranging system given in any 1 paragraph of Claims 1-3,
The illumination light irradiated by the irradiation device is pulsed light,
The first light receiving period and the second light receiving period are periods including a timing after the predetermined time has elapsed after the reflected light reaches the solid-state imaging device. A ranging system according to any one of claims 1 to 4,
The irradiation device alternately irradiates the irradiation light at the first irradiation timing and the second irradiation timing,
The first irradiation timing and the second irradiation timing, the first light receiving period and the second light receiving period arrive at a predetermined cycle,
The second irradiation timing has a phase shifted from the first irradiation timing by a certain period from a half cycle,
The distance measuring system, wherein the second light receiving period is shifted in phase by a half period from the first light receiving period. The ranging system according to any one of claims 1 to 5,
The first irradiation timing, the second irradiation timing, and the first light receiving period to the third light receiving period are determined based on a predetermined distance detection detection range. . The ranging system according to claim 6,
Having a plurality of predetermined distance detection ranges;
A plurality of the first irradiation timing and the second irradiation timing and a plurality of the first light receiving period to the third light receiving period are determined corresponding to the plurality of distance measuring detection ranges. system. The ranging system according to claim 7, wherein
The first irradiation timing and the second irradiation timing of the plurality of ranging detection ranges are out of phase with each other by twice a certain time,
The ranging system, wherein the first light receiving period and the second light receiving period of the plurality of ranging detection ranges are not out of phase with each other.

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