Patent Publication Number: US-11394903-B2

Title: Imaging apparatus, imaging system, and moving body

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The aspect of the embodiments relates to an imaging apparatus, an imaging system, and a moving body. 
     Description of the Related Art 
     A complementary metal-oxide-semiconductor (CMOS) sensor is known, which is obtained by providing pixels on a first chip, providing on a second chip an analog-digital conversion unit (an AD conversion unit) corresponding to one or more of the pixels, and bonding the first and second chips by Cu—Cu bonding. In Japanese Patent Application Laid-Open No. 2014-155175, the area of a portion covered by a single AD conversion unit corresponds to the area of a portion covered by a plurality of pixels. Thus, a plurality of pixels provided on a first chip and a single AD conversion unit provided on a second chip are connected together in association with each other. 
     Japanese Patent Application Laid-Open No. 2014-155175 discusses a reading order in  FIG. 10  (corresponding to FIG. 1 of Japanese Patent Application Laid-Open No. 2014-155175).  FIG. 10  illustrates a conceptual diagram of a reading method discussed in Japanese Patent Application Laid-Open No. 2014-155175. A thin-lined rectangle  10  represents a pixel. A thick-lined rectangle  11  represents a pixel block. A single pixel block  11  includes 4×4, i.e., a total of 16, pixels  10 .  FIG. 10  illustrates an example where nine pixel blocks  11  are disposed. In each pixel block  11 , with the pixel in the fourth row and the first column as a starting point, reading is started in the row direction. That is, reading is performed in the direction from the fourth row and the first column to the fourth row and the fourth column. Next, reading is sequentially performed from the third row and the first column to the third row and the fourth column, and from the second row and the first column to the second row and the fourth column. Then, the pixel in the first row and the fourth column is read last. 
     Further, Japanese Patent Application Laid-Open No. 2014-155175 also discusses a reading order in  FIG. 11A  (corresponding to FIG. 5 of Japanese Patent Application Laid-Open No. 2014-155175). In  FIG. 11A , the reading order of a pixel block  11  is different from the reading order of a pixel block  21 . In the pixel block  11 , a reading method similar to the reading method for the pixel block  11  in  FIG. 10  is executed. On the other hand, in the pixel block  21 , with the pixel in the fourth row and the fourth column as a starting point, reading is performed from the fourth row and the fourth column to the fourth row and the first column. Rows to be read are sequentially shifted in the direction of a smaller row number. Then, the pixel in the first row and the first column is read last. 
     In the case of the reading order in  FIG. 10 , the reading timings of pixels at the boundary between adjacent pixel blocks do not match each other. As a result of this, in the case of the reading order in  FIG. 10 , there is a possibility that discontinuity occurs in an image at the boundary between pixel blocks. On the other hand, according to the reading order in  FIG. 11A , the reading timings of pixels located at the boundary between adjacent pixel blocks are close to each other. This can reduce discontinuity that occurs at the boundary between pixel blocks. 
     Further, Japanese Patent Application Laid-Open No. 2014-155175 also discusses a reading order in  FIG. 11B  (corresponding to FIG. 6 of Japanese Patent Application Laid-Open No. 2014-155175). In a pixel block  31  in  FIG. 11B , with any of the four vertices (e.g., the first row and the first column, the first row and the fourth column, and the fourth row and the fourth column) of the pixel block  31  as a starting point, reading is performed in the row direction and then spirally shifts to the center of the pixel block  31 . Also in the case of  FIG. 11B , similar to the reading order in  FIG. 11A , the reading timings of pixels located at the boundary between adjacent pixel blocks are close to each other. This can reduce discontinuity that occurs at the boundary between pixel blocks. 
     In the reading order in  FIG. 10 , in the pixel block  11  at the top left, immediately after the pixel in the second row and the fourth column is read, the pixel in the first row and the first column is read. Similarly, in the pixel block  21  at the top left in  FIG. 11A , immediately after the pixel in the second row and the fourth column is read, the pixel in the first row and the first column is read. That is, in a case where reading shifts to an adjacent row, a pixel to be read next is away at a distance corresponding to the number of columns of the pixel block. 
     Incidentally, the remainder of reset may occur in a signal processing unit for processing a signal output from a pixel. That is, there is a possibility that the place which should be reset is not sufficiently reset. For example, there is a case where the reset potential of a clamp capacitor provided at the input of a comparator included in an AD conversion unit cannot reach a desired value. Due to this, a signal of a previously read pixel influences a signal of a pixel to be read next (crosstalk). In a case where the reading orders in  FIGS. 10 and 11A  are employed, and when intense light is incident on, for example, the pixel at the right end (the second row and the fourth column) of the pixel block, there is a possibility that an image is formed by irradiating the pixel at the left end (the first row and the first column), which is away from the right end column, with light having an amount of light greater than or equal to that of normal incident light. Even if crosstalk caused by the remainder of reset is very small, but if the right end column and the left end column are away from each other, the crosstalk is more conspicuous as an image than in a case where crosstalk occurs in adjacent pixels. 
     On the other hand, there is also an issue with the reading method in  FIG. 11B . That is, in the reading order in  FIG. 11B , there is a great difference between the time when the pixel at the left end of the first row of the pixel block  31  is read and the time when the pixel at the left end of the second row of the pixel block  31  is read. For example, in the example of  FIG. 11B , the pixel in the second row and the first column is read 11 pixels after the pixel in the first row and the first column is read. As a result of this, the difference between the reading timings of adjacent pixels becomes great, which increases the possibility that discontinuity occurs in an image. 
     As described above, if the reading orders in FIGS. 1 and 5 of Japanese Patent Application Laid-Open No. 2014-155175 (corresponding to  FIGS. 10 and 11A  of the present application) are used, there is a possibility of forming an image in which crosstalk resulting from the remainder of the reset of a signal processing unit such as an AD conversion unit is conspicuous. 
     Further, if the reading order in FIG. 6 of Japanese Patent Application Laid-Open No. 2014-155175 (corresponding to  FIG. 11B  of the present application) is used, the difference between the reading timings of adjacent pixels becomes great, and there is a possibility that an image of an object becomes discontinuous. 
     That is, according to an imaging apparatus discussed in Japanese Patent Application Laid-Open No. 2014-155175, an image with good quality cannot be formed. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the embodiments, an apparatus includes a pixel block including a plurality of pixels arranged in a matrix, a processing unit configured to process signals read from the plurality of pixels, and a reading unit configured to control a reading order of the plurality of pixels, wherein the reading unit reads in a first direction, a first pixel group including a part of the plurality of pixels, and after reading the first pixel group, reads in a second direction, which is opposite to the first direction, a second pixel group including a part of the plurality of pixels adjacent to the first pixel group. 
     Further features of the disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic diagrams illustrating an imaging apparatus according to a first exemplary embodiment. 
         FIGS. 2A and 2B  are schematic diagrams illustrating the imaging apparatus according to the first exemplary embodiment. 
         FIGS. 3A, 3B, and 3C  are schematic diagrams illustrating the imaging apparatus according to the first exemplary embodiment. 
         FIG. 4  is a schematic diagram illustrating the imaging apparatus according to the first exemplary embodiment. 
         FIG. 5  is a timing diagram of the imaging apparatus according to the first exemplary embodiment. 
         FIG. 6  is a schematic diagram illustrating the imaging apparatus according to the first exemplary embodiment. 
         FIGS. 7A and 7B  are schematic diagrams illustrating an imaging apparatus according to a second exemplary embodiment. 
         FIG. 8  is a diagram illustrating a configuration of an imaging system according to a third exemplary embodiment. 
         FIGS. 9A and 9B  are diagrams illustrating a configuration of a moving body according to a fourth exemplary embodiment. 
         FIG. 10  is a schematic diagram illustrating an imaging apparatus according to Japanese Patent Application Laid-Open No. 2014-155175. 
         FIGS. 11A and 11B  are schematic diagrams illustrating the imaging apparatus according to Japanese Patent Application Laid-Open No. 2014-155175. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIGS. 3A, 3B, and 3C  are schematic diagrams illustrating an imaging apparatus according to a first exemplary embodiment. A first chip  400  includes a plurality of pixel blocks  110 , each of which includes a plurality of pixels  100 . Further, a second chip  410  includes a plurality of signal processing units  115 . Each signal processing unit  115  includes an analog-digital conversion unit (an AD conversion unit) for converting an analog signal into a digital signal. The first chip  400  and the second chip  410  are laminated together, thereby forming a laminated-type imaging apparatus. In each pixel  100 , a single photoelectric conversion unit is provided, and a single microlens (not illustrated) is provided corresponding to the single photoelectric conversion unit. 
     The pixel blocks  110  and the signal processing units  115  correspond to each other on a one-to-one basis. That is, the configuration is such that not all the pixels disposed on the first chip  400  are processed by a single signal processing unit, but the pixels are divided into a plurality of pixel blocks, and each pixel block is processed by a single signal processing unit. Consequently, it is possible to perform AD conversion in parallel. This can speed up processing. Further, as compared with a case where both a plurality of pixel blocks and a plurality of signal processing units are provided on a single substrate, it is not necessary to place wiring between each pixel block and a signal processing unit corresponding to the pixel block near another pixel block or another signal processing unit. Thus, it is possible to reduce crosstalk between pixel blocks. 
     A pair of a pixel block  110  and a signal processing unit  115  corresponding to each other is provided such that the pixel block  110  and the signal processing unit  115  overlap each other in a plan view. This placement shortens a channel electrically connecting an output line from the pixel block  110  and the signal processing unit  115 . Thus, it is possible to reduce wiring capacity. 
       FIG. 1A  illustrates the reading order of the pixel blocks  110 . With the first row and the first column as a starting point, reading is started in the row direction. If the reading reaches the first row and the fourth column, reading is performed from the second row and the fourth column in the row direction and in a direction opposite to that of the reading of the first row. Such reading is sequentially performed to the fourth row and the first column. That is, the plurality of pixels disposed in the first row (a first pixel group) are read in a first direction. Further, the plurality of pixels disposed in the second row (a second pixel group) are read in a second direction, which is opposite to the first direction. Further, the plurality of pixels disposed in the third row (a third pixel group) are read in the first direction again. 
     Each signal processing unit  115  successively processes signals of pixels. The levels of the signals, however, differ from pixel to pixel according to the amount of light with which each pixel is irradiated. After the signal processing unit  115  performs signal processing on a certain pixel, and if the reset of the signal processing unit  115 , which is performed while a signal of a next pixel is processed, is not complete, the signal level of the previous pixel influences the signal processing result of the next pixel (crosstalk). At this time, if the reading order of the pixels is set as illustrated in  FIG. 1A , a pixel adjacent to a previous pixel is read, and therefore, crosstalk resulting from the remainder of the reset of the signal processing unit  115  continuously appears in the adjacent pixel. Consequently, even if crosstalk occurs, it is possible to make the crosstalk inconspicuous as an image. 
     Further, the reading method in  FIG. 1A  is capable of acquiring an image with higher quality than a reading method discussed in Japanese Patent Application Laid-Open No. 2014-155175. Referring to  FIG. 11B , time for 11 pixels is required from the end of the reading of a pixel in the first row and the first column to the reading of a pixel in the second row and the first column. In contrast, in  FIG. 1A , a maximum of time for seven pixels is required from the reading of a certain pixel to the reading of a pixel adjacent to the certain pixel. For example, time for seven pixels is only required from the end of the reading of the pixel in the first row and the first column to the end of the reading of the pixel in the second row and the first column. Thus, in one embodiment, the reading method in  FIG. 1A  requires about two thirds of the time of the reading method in  FIG. 11B . Thus, when a high-speed object is imaged, it is possible to reduce the discontinuity of an image. 
     Further, the reading in  FIG. 1A  can be achieved using a simpler selection circuit than in the reading in  FIG. 11B . For example, in  FIG. 1A , reading in the row direction can be achieved by general shift registers and decoders, and reading in the column direction can be achieved by shift registers having a reverse running function and decoders having a function for switching between counting up and counting down. 
     Although reading is performed in the direction of the ascending order of row numbers in  FIG. 1A , reading may be performed in the direction of the descending order of row numbers. Alternatively, as illustrated in  FIG. 1B , reading may be performed in the direction of the ascending order of column numbers. Further, although reading is performed in the direction of the ascending order of column numbers in  FIG. 1B , reading may be performed in the direction of the descending order of column numbers. 
     After the last pixel in a pixel block is read, i.e., when a single frame ends, in one embodiment, the signal processing unit  115  is sufficiently reset and then the reading of a next frame is started. This is because, according to the reading orders in  FIGS. 1A and 1B , a pixel to be read last in a first frame is not adjacent to a pixel to be read first in a second frame, and therefore, the influence of the remainder of reset is great. To sufficiently reset the signal processing unit  115 , the period in which a reset signal is applied may be lengthened. Specifically, regarding the reset period of a clamp capacitor provided at the input of a comparator, a first period may be set for a pixel to be read last, and a second period may be set for a pixel other than the pixel to be read last. Then, the first period may be longer than the second period. Alternatively, the number of times the reset signal is input after a pixel to be read last is read may be greater than the number of times the reset signal is input after a pixel other than the pixel to be read last is read. 
     As described above, based on the imaging apparatus according to the present exemplary embodiment, it is possible to prevent crosstalk due to the remainder of the reset of a signal processing unit from being conspicuous as an image as compared with Japanese Patent Application Laid-Open No. 2014-155175. Further, it is possible to reduce the discontinuity of an object resulting from an increase in the difference between the reading timings of adjacent pixels. Consequently, it is possible to provide an imaging apparatus capable of forming an image with better quality than an imaging apparatus discussed in Japanese Patent Application Laid-Open No. 2014-155175. 
     (Relationship Between Operation of Imaging Apparatus and Crosstalk) 
     Next, with reference to  FIG. 4 , the relationship between the operation of the imaging apparatus in  FIGS. 1A and 1B  and crosstalk is described in further detail. Each pixel block  110  includes signal lines  120  to  123  and switches  130  to  133  in addition to the pixels  100 . The imaging apparatus includes a vertical reading unit (vertical scanning unit)  140 , a horizontal reading unit (horizontal scanning unit)  150 , and a ramp generator  160 . Using control signals TX 1 - 1  to TX 4 - 4 , the vertical reading unit  140  controls the accumulation times of the pixels in the rows disposed in the pixel block  110 . Further, using control signals SEL 1  to SEL 4 , the vertical reading unit  140  successively selects the rows of the pixel block  110 . Further, the signal processing unit  115  includes capacitors  200  and  210 , switches  220  and  230 , a comparator  240 , and a counter  250 , thereby forming an AD conversion unit. To one input node of the comparator  240 , the ramp generator  160  is connected via the capacitor  200 , and a ramp signal (a comparison signal) is input. Further, to the other input node of the comparator  240 , the signal lines  120  to  123  are connected via the capacitor  210 . The capacitor  210  clamps a pixel reset level and therefore is also referred to as a “clamp capacitor”. To one node of the capacitor  210 , analog signals are input through the signal lines  120  to  123 . Further, to the other node of the capacitor  210 , a signal at a reset level is input by CRES reaching a high level. Using control signals CSEL 1  to CSEL 4 , the horizontal reading unit  150  selects the signal lines  120  to  123  to connect to the signal processing unit  115 , thereby successively selecting the columns of the pixel block  110 . 
     Next, with reference to  FIG. 5 , the operation will be described using an example of the operation waveforms of the imaging apparatus in  FIG. 4 . From a time t 0  to a time t 11 , the control signal SEL 1  is at a high level, the control signals SEL 2 , SEL 3 , and SEL 4  are at low levels (the control signals SEL 3  and SEL 4  are not illustrated), and the top row of the pixel block  110  is in a selected state. From the time t 0  to a time t 8 , the control signal CSEL 1  is at a high level. From the time t 8  to a time t 9 , the control signal CSEL 2  is at a high level. From the time t 9  to a time t 10 , the control signal CSEL 3  is at a high level. From the time t 10  to the time t 11 , the control signal CSEL 4  is at a high level. Consequently, the first to fourth columns of the pixel block  110  are successively selected. 
     From the time t 11  to a time t 15 , the control signal SEL 2  is at a high level, the control signals SEL 1 , SEL 3 , and SEL 4  are at low levels (the control signals SEL 3  and SEL 4  are not illustrated), and the second row from the top of the pixel block  110  is in a selected state. From the time t 11  to a time t 12 , the control signal CSEL 4  is at a high level. From the time t 12  to a time t 13 , the control signal CSEL 3  is at a high level. From the time t 13  to a time t 14 , the control signal CSEL 2  is at a high level. From the time t 14  to the time t 15 , the control signal CSEL 1  is at a high level. Consequently, the fourth to first columns of the pixel block  110  are successively selected this time. 
     Next, the reading of a signal of a single pixel and the processing operation of the signal processing unit  115  will be described. At the time t 0 , the pixel  100  in the first row and the first column of the pixel block  110  is selected and connected to the signal processing unit  115 . CRES reaches a high level, whereby the switch  230  enters an on state, and one input node CIN of the comparator  240  is reset to a reset level. Simultaneously, the switch  220  also enters an on state, and the other input node of the comparator  240  is also reset to a reset level. 
     By the time t 1 , the reset is completed, and the pixel reset level of an output from the pixel  100  is also clamped. That is, at the time t 1 , the input node CIN, which is one node of the capacitor  210 , is at the reset level of the comparator  240 , and the other node of the capacitor  210  is at the reset level of the pixel  100  in the first row and the first column of the pixel block  110 . At this time, the node on the comparator  240  side of the capacitor  200  is at the reset level of the comparator  240 , and the node on the other side of the capacitor  200  is at the reference level of RAMP. 
     At the time t 1 , CRES is turned off, and the reset of the comparator  240  and the clamping of the pixel reset level are ended. From a time t 2  to a time t 3 , RAMP is sloped down, the counter  250  measures the time taken until the output of the comparator  240  is inverted, and a digital value corresponding to the measured time (t 3 −t 2 ) is obtained as the AD conversion value of the pixel reset level. At a time t 4 , the control signal TX 1 - 1  reaches a high level, thereby turning on a transfer transistor provided in the pixel  100 . Consequently, the photoelectric conversion unit transfers a signal charge to a floating diffusion, and the pixel  100  outputs a signal level. The reset level transitions to the signal level, whereby the potential of the input node CIN also decreases according to the signal level. The signal level differs from pixel to pixel according to the amount of light with which each pixel is irradiated. 
     From a time t 6  to a time t 7 , RAMP is sloped down again, the counter  250  measures the time taken until the output of the comparator  240  is inverted, and a digital value corresponding to the measured time (t 7 −t 6 ) is obtained as the AD conversion value of the pixel signal level. The difference between the AD conversion value of the pixel signal level and the AD conversion value of the pixel reset level is taken, thereby obtaining a final AD conversion result. 
     At the time t 8 , to read a next pixel, the reset of the comparator  240  and the clamping of the pixel reset level are started again. At this time, if the operation of resetting the comparator  240  performed with CRES at a high level is not complete, the lower the potential of the input node CIN from a time t 5  to the time t 8 , the lower the reset level of the input node CIN when the next pixel is read. Consequently, there is a possibility that the operating point of the comparator  240  fluctuates due to the signal level of the previous pixel, and crosstalk from the previous reading pixel to the next reading pixel occurs. In the present exemplary embodiment, adjacent pixels are continuously read, and therefore, crosstalk is prevented from being conspicuous as an image as compared with Japanese Patent Application Laid-Open No. 2014-155175. 
       FIG. 6  is a variation of the imaging apparatus in  FIG. 4 . Driving lines for the control signals TX 1 - 1  to TX 4 - 4  illustrated in  FIG. 4  are omitted.  FIGS. 4 and 6  are different from each other in the following respect. In  FIG. 4 , after rows are selected, columns are selected. In contrast, in  FIG. 6 , after columns are selected, rows are selected. Specifically, in  FIG. 6 , signal lines  120  to  123  are shared by the pixels  100  in the row direction. In this case, columns are selected using pixel control lines CSEL 1  to CSEL 4 , and rows are selected using switches  130  to  133 . Further, in  FIG. 6 , a sample holding unit including a switch  260  and a capacitor  270 , and a buffer  280  are included. The capacitor  270  is occasionally referred to as a “sample holding capacitor”. In a case where such a sample holding unit is included, the capacitor  270  holds the signal level of a certain pixel, and while AD conversion is performed on the signal level in the state, the pixel block  110  can start reading the reset level of a next pixel. This enables a high-speed operation. That is, parts of the reading of the previous pixel and the reading of the next pixel are overlapped, thereby enabling high-speed processing. In this case, however, the overlapping of operations increases the risk of crosstalk from the previous pixel to the next pixel. For example, the timing when the output of the comparator  240  is inverted changes according to the signal level of the previous pixel. This changes interference with the reset level of the next pixel. Further, the capacitor  270 , which is used for sample holding, also causes crosstalk. The initial value of the reset level of a pixel  100  to be written to the capacitor  270  is the signal level of a previous pixel. Thus, if the writing is not complete, crosstalk occurs. As described above, it is possible to speed up processing, but the risk of crosstalk increases at the same time. In such a configuration, particularly, it is important to prevent crosstalk from appearing in pixels placed far from each other and becoming conspicuous as an image. The method for reading pixel signals described in the present exemplary embodiment works more effectively. 
     (Other Variations) 
       FIGS. 2A and 2B  illustrate variations of the reading method in  FIGS. 1A and 1B . In  FIGS. 2A and 2B , the configuration is such that the reading orders of pixels  100  are line-symmetric between adjacent pixel blocks  110 . In other words, a pixel group disposed in the first row of a first pixel block (a first pixel group) and a pixel group disposed in the first row of a second pixel block (a first pixel group) are placed opposed to each other. Further, the direction in which the first pixel group of the first pixel block is read (a first direction) and the direction in which the first pixel group of the second pixel block is read (a first direction) are opposite to each other. Consequently, it is possible to match the reading timings of pixels between adjacent pixel blocks  110  and reduce the discontinuity of an image spanning the pixel blocks  110 . 
     Further, as illustrated in  FIGS. 4 and 6 , the present exemplary embodiment has been described taking a slope-type AD converter as an example. The AD converter, however, is not limited to the slope type. For example, the ramp generator  160  and the capacitor  200  may be replaced with a binary weight capacitor group, thereby forming a successive approximation-type AD converter. 
     Further, as illustrated in  FIGS. 1A, 1B, 2A, and 2B , the present exemplary embodiment has been described on the premise that the plurality of pixel blocks  110  are included. Alternatively, a pixel array in which a plurality of pixels are arranged in a matrix may be considered as a single pixel block, and the above reading method may be employed for the pixel array. 
     Additionally, as illustrated in  FIGS. 3A, 3B, and 3C , in the present exemplary embodiment, a laminated-type imaging apparatus has been described which includes the pixel blocks  110  on the first chip  400  and the signal processing units  115  on the second chip  410 . The disclosure according to the present exemplary embodiment, however, can also be applied to an imaging apparatus that is not of a laminated-type. 
       FIGS. 7A and 7B  are schematic diagrams illustrating pixel blocks  110  according to a second exemplary embodiment. As illustrated in  FIGS. 7A and 7B , pixels  100  each include a first photoelectric conversion unit  300  and a second photoelectric conversion unit  310  for phase detection, corresponding to a single microlens. In  FIG. 7A , the first photoelectric conversion unit  300  and the second photoelectric conversion unit  310  are divided in the row direction (the horizontal direction). An image in the row direction obtained from the first photoelectric conversion unit  300  and an image in the row direction obtained from the second photoelectric conversion unit  310  are compared with each other, thereby detecting the phase difference between the images. At this time, if the reading times of pixels  100  placed in the row direction are greatly different from each other, there is a possibility that images used for phase detection becomes discontinuous. In response, in a case where each pixel  100  includes the photoelectric conversion units  300  and  310  divided in the row direction as in  FIG. 7A , a method for reading the pixels in the row direction and sequentially shifting the reading in the column direction is used. In this case, for example, using the imaging apparatus in  FIG. 4 , rows are selected, and reading is performed successively in the order of columns. 
     On the other hand, in a case where each pixel  100  includes the photoelectric conversion units  300  and  310  divided in the column direction (the vertical direction) as in  FIG. 7B , a form for scanning the pixels in the column direction and sequentially shifting the scanning in the row direction is used. In this case, for example, using the imaging apparatus in  FIG. 6 , columns are selected, and reading is performed successively in the order of rows. 
     Further, signals of the first photoelectric conversion unit  300  and the second photoelectric conversion unit  310  may not be used for phase detection. Instead, it is also possible to normally acquire an image, together with phase detection, by adding up the signals of the first photoelectric conversion unit  300  and the second photoelectric conversion unit  310 . 
     Further, in the present exemplary embodiment, the signals of the first photoelectric conversion unit  300  and the second photoelectric conversion unit  310  are successively read. If, however, the signal processing unit  115  includes a signal processing unit for the first photoelectric conversion unit  300  and a signal processing unit for the second photoelectric conversion unit  310 , it is possible to simultaneously read both signals in parallel. Consequently, it is possible to ensure the simultaneity of phase detection images and perform processing by further reducing the influence of the discontinuity of both images. 
     Further, the present exemplary embodiment has been described using an example where all the pixels  100  have a two-pixel configuration for phase detection. The two-pixel configuration, however, is not limited to all the pixels. Alternatively, the configuration may be employed in which pixels for phase detection are discretely placed. 
     Based on the imaging apparatus according to the present exemplary embodiment, it is possible to prevent crosstalk resulting from the remainder of the reset of a signal processing unit from being conspicuous as an image as compared with Japanese Patent Application Laid-Open No. 2014-155175. Further, it is possible to reduce the discontinuity of an object resulting from an increase in the difference between the reading timings of adjacent pixels. Consequently, it is possible to provide an imaging apparatus capable of forming an image with better quality than the imaging apparatus discussed in Japanese Patent Application Laid-Open No. 2014-155175. 
       FIG. 8  is a block diagram illustrating the configuration of an imaging system  500  according to a third exemplary embodiment. The imaging system  500  according to the present exemplary embodiment includes an imaging apparatus  2000 , to which the configuration of either of the above imaging apparatuses is applied. Specific examples of the imaging system  500  include a digital still camera, a digital camcorder, and a monitoring camera. The imaging system  500  includes the imaging apparatus  2000 , a lens  5020 , a diaphragm  504 , and a barrier  506 , which protects the lens  5020 . The imaging system  500  includes a signal processing unit  5080 , which processes an output signal output from the imaging apparatus  2000 . The signal processing unit  5080  performs a signal processing operation for performing various types of correction and compression on an input signal as necessary and outputting the resulting signal. The signal processing unit  5080  may have the function of performing an AD conversion process on a signal output from the imaging apparatus  2000 . The imaging system  500  further includes a buffer memory unit  510 , which temporarily stores image data, and an external interface unit (external I/F unit)  512 , which is used to communicate with an external computer. Further, the imaging system  500  includes a recording medium  514  such as a semiconductor memory to or from which captured data is recorded or read, and a recording medium control interface unit (recording medium control I/F unit)  516 , which is used to record or read captured data to or from the recording medium  514 . 
     Further, the imaging system  500  includes an entirety control/calculation unit  518 , which performs various calculations and also controls the entirety of the digital still camera, and a timing generation unit  520 , which outputs various timing signals to the imaging apparatus  2000  and the signal processing unit  5080 . The imaging apparatus  2000  outputs an image signal to the signal processing unit  5080 . The signal processing unit  5080  performs predetermined signal processing on the image signal output from the imaging apparatus  2000  and outputs image data. Further, the signal processing unit  5080  generates an image using the image signal. 
     An imaging system is configured using the imaging apparatus according to each of the above exemplary embodiments, whereby it is possible to achieve an imaging system capable of acquiring an image with better quality. 
     With reference to  FIGS. 9A and 9B , an imaging system and a moving body according to a fourth exemplary embodiment are described. In the present exemplary embodiment, an example of an imaging system regarding an in-vehicle camera is illustrated.  FIGS. 9A and 9B  illustrate examples of a vehicle system and an imaging system mounted on the vehicle system. An imaging system  701  includes an imaging apparatus  702 , an image pre-processing unit  715 , an integrated circuit  703 , and an optical system  714 . The optical system  714  forms an optical image of an object on the imaging apparatus  702 . The imaging apparatus  702  converts the optical image of the object formed by the optical system  714  into an electric signal. The imaging apparatus  702  is the imaging apparatus according to any of the above exemplary embodiments. The image pre-processing unit  715  performs predetermined signal processing on the signal output from the imaging apparatus  702 . In the imaging system  701 , at least two sets of the optical system  714 , the imaging apparatus  702 , and the image pre-processing unit  715  are provided so that outputs from the image pre-processing units  715  in the respective sets are input to the integrated circuit  703 . 
     The integrated circuit  703  is an integrated circuit for an imaging system and includes an image processing unit  704 , which includes a memory  705 , an optical distance measurement unit  706 , a parallax calculation unit  707 , an object recognition unit  708 , and an abnormality detection unit  709 . The image processing unit  704  performs a development process or image processing such as defect correction on an output signal from each image pre-processing unit  715 . The memory  705  primarily stores a captured image or stores the position of a defect of a captured pixel. The optical distance measurement unit  706  focuses on an object or measures the distance from the object. The parallax calculation unit  707  calculates a parallax (the phase difference between parallax images) from a plurality of pieces of image data acquired by the plurality of imaging apparatuses  702 . The object recognition unit  708  recognizes an object such as a car, a road, a sign, or a person. If detecting an abnormality of the imaging apparatuses  702 , the abnormality detection unit  709  informs a main control unit  713  of the abnormality. 
     The integrated circuit  703  may be achieved by hardware designed exclusively for the integrated circuit  703 , or achieved by a software module, or achieved by the combination of these. Alternatively, the integrated circuit  703  may be achieved by a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), or achieved by the combination of these. 
     The main control unit  713  performs overall control of the operations of the imaging system  701 , a vehicle sensor  710 , and a control unit  720 . It is also possible to employ a method in which the main control unit  713  is not included, and the imaging system  701 , the vehicle sensor  710 , and the control unit  720  individually include communication interfaces, and each transmit and receive a control signal via a communication network (e.g., the Controller Area Network (CAN) standard). 
     The integrated circuit  703  has the function of transmitting a control signal or a setting value to each imaging apparatus  702  by receiving a control signal from the main control unit  713  or by a control unit of the integrated circuit  703 . For example, the integrated circuit  703  transmits a setting for driving a voltage switch  13  in the imaging apparatus  702  in a pulsed manner, or a setting for switching the voltage switch  13  in each frame. 
     The imaging system  701  is connected to the vehicle sensor  710  and can detect the running states, such as the speed, the yaw rate, and the steering angle, of a vehicle in which the imaging system  701  is provided, the environment outside the vehicle, and the states of another vehicle and an obstacle. The vehicle sensor  710  is also a distance information acquisition unit for acquiring, from parallax images, information regarding the distance from a target object. Further, the imaging system  701  is connected to a driving assistance control unit  711 , which performs various types of driving assistance such as automatic steering, automatic cruising, and a collision prevention function. Particularly, regarding a collision determination function, based on the detection result of the imaging system  701  or the vehicle sensor  710 , a collision determination unit estimates collision with another vehicle or an obstacle or determines the presence or absence of collision with another vehicle or an obstacle. Consequently, in a case where collision is estimated, avoidance control is performed. Further, when collision occurs, a safety device is started. 
     Further, the imaging system  701  is also connected to an alarm device  712 , which gives an alarm to a driver based on the determination result of the collision determination unit. For example, as the determination result of the collision determination unit, if there is a high possibility of collision, the main control unit  713  applies a brake, returns the gas pedal, or suppresses the engine output, thereby controlling the vehicle to avoid collision and reduce damage. The alarm device  712  warns a user by setting off an alarm such as a sound, displaying alarm information on a screen of a display unit of an automotive navigation system or a meter panel, or imparting a vibration to a seat belt or the steering. 
     In the present exemplary embodiment, the imaging system  701  images the periphery, such as the front or the rear, of the vehicle.  FIG. 9B  illustrates an example of the placement of the imaging system  701  in a case where the imaging system  701  captures the front direction of the vehicle. 
     Further, in the present exemplary embodiment, control for preventing a vehicle from colliding with another vehicle has been described. Alternatively, the present exemplary embodiment is also applicable to control for automatically driving a vehicle by following another vehicle, or control for automatically driving a vehicle so as to stay in a lane. Further, the imaging system  701  can be applied not only to a vehicle such as an automobile but also to a moving body (a moving apparatus) such as a vessel, an aircraft, or an industrial robot. Additionally, the imaging system  701  can be applied not only to a moving body but also to a device widely using object recognition, such as an intelligent transportation system (ITS). 
     Other Exemplary Embodiments 
     While the exemplary embodiments have been described, the disclosure is not limited to these exemplary embodiments, and can be changed and modified in various manners. Further, the exemplary embodiments are applicable to each other. 
     While the disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2017-192056, filed Sep. 29, 2017, which is hereby incorporated by reference herein in its entirety.