JP6366341B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus.

  2. Description of the Related Art In recent years, imaging apparatuses such as electronic cameras that can acquire not only light intensity distribution but also light incident direction and distance information are known. Japanese Patent Application Laid-Open No. 2004-228688 discloses a technique that enables pupil division type phase difference detection in an imaging apparatus. According to Patent Document 1, one pixel of an image sensor has two photodiodes (hereinafter referred to as divided pixels), and each photodiode receives light that has passed through different pupils of a photographing lens by one microlens. It is configured to In the imaging device having such divided pixels, the imaging surface phase difference AF can be performed by comparing the waveforms of the output signals from the two photodiodes. Moreover, a normal captured image can be obtained by adding the output signals from the two photodiodes.

Moreover, as a technique for measuring the distance to the object, for example, there is a time of flight (TOF) method. The time-of-flight method is a method of measuring a distance by projecting light onto an object, measuring the time until the light hits the object, is reflected, and returns. Although the flight speed of light is as high as 3 × 10 ⁸ m / sec, improvement in semiconductor miniaturization technology has made it possible to realize a device capable of detecting this.

  Patent Document 2 discloses a technology of a distance image sensor using a CMOS solid-state image sensor in which the time-of-flight method is applied to a solid-state image sensor. According to Patent Document 2, a unit pixel of an image sensor has two floating diffusions and two transfer switches for one photodiode. In synchronization with the pulse timing of the projection light, the two transfer switches are alternately opened and closed to distribute the charge generated by the reflected light from one photodiode to two floating diffusions. The distance to the subject can be estimated from the distributed charge distribution ratio.

JP 2001-124984 A JP 2004-294420 A

  By the way, the pupil division method phase difference detection method can increase the speed of AF (automatic focus adjustment) as compared with the contrast method using the contrast of the subject, but there are also conditions that are not good. For example, when the depth of field is deep or when sufficient light cannot be received due to a decrease in the amount of peripheral light such as the periphery of the image, it is difficult to obtain a pupil division phase difference and it is difficult to perform focus adjustment with high accuracy. . On the other hand, in the time-of-flight method, a distance image can be acquired in units of pixels. However, when the subject is at a long distance, the projection light does not reach and acquisition of distance information may be difficult.

  An object of the present invention is to provide an imaging apparatus capable of performing focus adjustment with high accuracy regardless of a position in an image and a subject.

An imaging device according to the present invention includes an imaging device having a plurality of pixels that perform photoelectric conversion, a light projecting unit that projects pulsed light onto a subject, and at least the image sensor without projecting pulsed light onto the light projecting unit. first and first read drive to read out a signal to drive the driving method in which the pixels of the first area corresponding to the pupil slicing phase difference detection method, by projecting pulsed light onto said light projecting portion, at least A control circuit for controlling to perform a second readout drive for reading out a signal by driving a pixel in the second region of the image sensor by a second drive method corresponding to a time-of-flight method ; comprising: the signal read from the imaging device by the reading drive, and an image processing circuit for generating a focus adjustment information by using the signals read from the imaging device by the second reading drive And

According to the present invention, focus adjustment can be performed with high accuracy regardless of the position in the pixel and the subject.

It is a figure which shows the structural example of an imaging device. It is a figure which shows the example of arrangement | positioning of the pixel of an image pick-up element. It is a conceptual diagram in which the light beam emitted from the exit pupil of the photographing lens enters the unit pixel. It is a circuit diagram which shows the structural example of the unit pixel which concerns on 1st Embodiment. It is a figure which shows the structural example of the unit pixel which concerns on 1st Embodiment. It is a figure for demonstrating the read-out circuit of an image pick-up element. It is a timing chart which shows the 1st drive method of an image sensor. It is a timing chart which shows the 2nd drive method of an image sensor. It is a timing chart which shows the 2nd drive method of an image sensor. It is a timing chart of projection light and reflected light. It is a figure which shows the example which switches the distance image acquisition method. It is a flowchart which shows the drive method of an imaging device. It is a figure which shows the example which switches the distance image acquisition method. It is a figure which shows the pixel arrangement example of the image pick-up element which concerns on 2nd Embodiment. It is a circuit diagram which shows the structural example of the unit pixel which concerns on 2nd Embodiment. It is a figure which shows the structural example of the unit pixel which concerns on 2nd Embodiment.

(First embodiment)
FIG. 1 is a block diagram illustrating a configuration example of an imaging apparatus 100 according to the first embodiment of the present invention. The light that has passed through the photographic lens 101 is imaged near the focal position of the photographic lens 101 by adjusting the exposure amount by the lens diaphragm 114. The microlens array 102 includes a plurality of microlenses 113, and is arranged in the vicinity of the focal position of the photographing lens 101 to divide light that has passed through different pupil regions of the photographing lens 101 for each pupil region. Exit. The image sensor 103 is a solid-state image sensor such as a CMOS image sensor or a CCD image sensor. The image pickup device 103 is arranged so that a plurality of pixels of the image pickup device 103 correspond to one microlens 113, thereby dividing the light emitted by the microlens 113 for each pupil region as division information. The light is received while being maintained and converted into an image signal that can be processed.

  An analog signal processing circuit (AFE) 104 performs correlated double sampling processing, signal amplification, reference level adjustment, A / D conversion processing, and the like on the image signal output from the image sensor 103. A digital signal processing circuit (DFE) 105 performs digital image processing such as reference level adjustment on the image signal output from the analog signal processing circuit 104.

  The image processing circuit 106 performs correlation calculation, focus detection, predetermined image processing, defect correction, and the like, which will be described later, on the image signal output from the digital signal processing circuit 105. The memory circuit 107 and the recording circuit 108 are recording media such as a nonvolatile memory or a memory card that records and holds the image signal output from the image processing circuit 106.

  The control circuit 109 comprehensively drives and controls the entire imaging apparatus such as the photographing lens 101, the imaging element 103, the image processing circuit 106, the operation circuit 110, the display circuit 111, and the light emitting device 112. The operation circuit 110 inputs a signal from an operation unit provided in the imaging apparatus 100 and outputs a user command to the control circuit 109. The display circuit 111 displays an image after shooting, a live view image, various setting screens, and the like.

  The light emitting device 112 is a light projecting unit that projects pulsed light onto a subject in accordance with a signal PLIGHT (FIGS. 7 to 10) in synchronization with a command from the control circuit 109.

  Next, the relationship between the photographing lens 101, the microlens array 102, and the image sensor 103, the definition of pixels, and the principle of the pupil division method phase difference detection method will be described. 2 is a diagram of the image sensor 103 and the microlens 113 as seen from the direction of the optical axis Z in FIG. In the present embodiment, each microlens 113 forming the microlens array 102 is defined as one pixel and is referred to as a unit pixel 200. The unit pixel 200 is arranged so that a plurality of divided pixels 201 </ b> A and 201 </ b> B correspond to one microlens 113. In the present embodiment, the unit pixel 200 has two divided pixels 201A and 201B in the X-axis direction. The image sensor 103 has a plurality of unit pixels 200 arranged in a two-dimensional matrix, and FIG. 2 shows unit pixels 200 in 5 rows and 5 columns.

  FIG. 3 is a diagram of a state in which light emitted from the photographing lens 101 passes through one microlens 113 and is received by the unit pixel 200 as viewed from a direction perpendicular to the optical axis Z (Y-axis direction). . Light that has passed through the exit pupils 302 and 303 of the photographic lens 101 enters the unit pixel 200 with the optical axis Z as the center. The light beam passing through the pupil region 302 is received by the divided pixel 201 </ b> A through the microlens 113. The light beam passing through the pupil region 303 is received by the divided pixel 201 </ b> B through the microlens 113. Therefore, the divided pixels 201A and 201B receive light from different exit pupils 302 and 303 of the photographing lens 101, respectively.

  The image sensor 103 acquires signals from the divided pixels 201A of the plurality of unit pixels 200 arranged in the X-axis direction, and uses a subject image formed by these output signal groups as an A image. Similarly, the image sensor 103 acquires signals of the divided pixels 201B of the plurality of unit pixels 200 arranged in the X-axis direction, and uses a subject image formed by these output signal groups as a B image. The image processing circuit 106 performs a correlation operation on the A image and the B image, and detects an image shift amount (pupil division phase difference). Further, the image processing circuit 106 multiplies the image shift amount by a conversion coefficient determined by the focal position of the photographic lens 101 and the optical system of the photographic lens 101 to thereby obtain a focal position corresponding to an arbitrary subject position in the image. Is calculated. The control circuit 109 can perform pupil division phase difference AF (automatic focus adjustment) by controlling the focus of the photographing lens 101 based on the calculated focal position information. Further, the image processing circuit 106 can generate an A + B image signal by adding the A image signal and the B image signal, and use the A + B image signal for a normal captured image.

  FIG. 4 is a circuit diagram illustrating a configuration example of the unit pixel 200. The left half circuit in FIG. 4 corresponds to the divided pixel 201A, and the right half circuit in FIG. 4 corresponds to the divided pixel 201B. The unit pixel 200 includes photodiodes 401A and 401B. Two transfer switches 402A and 402C are connected to the photodiode 401A. Two transfer switches 402B and 402D are connected to the photodiode 401B. Floating diffusions 403A to 403D are connected to the transfer switches 402A to 402D, respectively. Reset switches 404A to 404D and source follower amplifiers 405A to 405D are connected to the floating diffusions 403A to 403D, respectively. Select switches 406A to 406D are connected to the source follower amplifiers 405A to 405D, respectively. The drains of the reset switches 404A and 404B and the source follower amplifiers 405A and 405B share a reference potential (VDD) 408. The drains of the reset switches 404C and 404D and the source follower amplifiers 405C and 405D share the reference potential 408.

  The photodiodes 401 </ b> A and 401 </ b> B are photoelectric conversion units that receive light that has passed through the same microlens 113 and generate charges corresponding to the amount of received light by photoelectric conversion. The transfer switch 402A transfers the charge generated in the photodiode 401A to the floating diffusion 403A. The transfer switch 402B transfers the charge generated in the photodiode 401B to the floating diffusion 403B. The transfer switch 402C transfers charges generated in the photodiode 401A to the floating diffusion 403C. The transfer switch 402D transfers charges generated in the photodiode 401B to the floating diffusion 403D. The transfer switches 402A to 402D are controlled by transfer pulse signals PTXA to PTXD, respectively.

  The floating diffusions 403A to 403D are charge-voltage converters that temporarily hold the charges transferred by the transfer switches 402A to 402D and convert the held charges into voltages. The reset switches 404A to 404D reset the potentials of the floating diffusions 403A to 403D to the reference potential 408, respectively. The reset switches 404A to 404D are controlled by a reset pulse signal PRES.

  The source follower amplifiers 405A to 405D are source follower circuits each having a MOS transistor, and amplify the voltage based on the charges held in the floating diffusions 403A to 403D and output them as pixel signals. The select switches 406A to 406D output the pixel signals amplified by the source follower amplifiers 405A to 405D to the vertical output lines 407A to 407D, respectively. The vertical output lines 407A to 407D are shared by a plurality of unit pixels 200 in the same column. The select switches 406A to 406D are controlled by a select pulse signal PSEL.

  FIG. 5 is a layout diagram illustrating a configuration example of the unit pixel 200. As described with reference to FIG. 4, the photodiode 401A has two transfer switches 402A and 402C at both ends thereof. The photodiode 401B has two transfer switches 402B and 402D at both ends thereof. The charge of the photodiode 401A can be transferred by either of the transfer switches 402A and 402C. The charge of the photodiode 401B can be transferred by either of the transfer switches 402B and 402D. Floating diffusions 403A to 403D are connected to the transfer switches 402A to 402D, respectively.

  FIG. 6 is a diagram illustrating a configuration example of the image sensor 103. The image sensor 103 has a plurality of unit pixels 200 arranged in a matrix. In FIG. 6, a total of 12 unit pixels 200 in 4 rows and 3 columns are illustrated, but in actuality, they are configured by millions or tens of millions of unit pixels 200. The unit pixels 200 are arranged according to a Bayer array, and generally provided with red (R), green (G), and blue (B) color filters, respectively. Here, for the purpose of increasing the light receiving efficiency of infrared light and reflected light used as projection light, the unit pixel 200 formed with an infrared filter or a transparent filter may be arranged. The vertical shift register 601 selects and drives a row of unit pixels 200 via a signal line 602 connected to each unit pixel 200 of each row. The signals converted by the floating diffusions 603A to 603D of the unit pixel 200 are input to the column circuit 603 through the vertical output lines 407A to 407D, respectively.

  Next, a configuration example of the column circuit 603 will be described. A reference voltage 611 is input to the operational amplifier 610. A clamp capacitor 608 and a feedback capacitor 609 are connected to the other input terminal of the operational amplifier 610. A switch 612 for short-circuiting both ends of the feedback capacitor 609 is controlled by a reset signal PC0R. Capacitors 613 and 614 hold a voltage. The switches 615 and 616 are switches for writing the output voltage of the operational amplifier 610 to the capacitors 613 and 614, respectively. The switch 615 is controlled by the signal PTS, and the switch 616 is controlled by the signal PTN. The switches 617 and 618 are switches for inputting a signal from the horizontal shift register 604 and outputting a signal to the output amplifier 607 via the horizontal output lines 605 and 606, respectively. The signal processed by the column circuit 603 is transferred by the horizontal shift register 604 to the output amplifier 607 through the horizontal output lines 605 and 606. The switch 617 is controlled by the signal PHS of the horizontal shift register 604, and the switch 618 is controlled by the signal PHN of the horizontal shift register 604. The output amplifier 607 outputs the difference between the voltage of the horizontal output line 605 and the voltage of the horizontal output line 606.

  FIG. 7 is a timing chart illustrating a first driving method of the imaging apparatus. The first driving method is a driving method for pixel signal readout in the normal imaging mode or pixel signal readout in the pupil division type phase difference detection mode. The charges generated in the two photodiodes 401A and 401B are read out to the floating diffusions 403A and 403B, respectively.

  First, the period HBLK will be described. At time t0, the signal PRES is set to high level, the reset switches 404A to 404D are turned on, and the floating diffusions 403A and 403B are reset. At time t1, the signals PTXA and PTXB are set to the high level, the transfer switches 402A and 402B are turned on, and the photodiodes 401A and 401B are also reset. At time t2, the signals PTXA and PTXB are set to low level, the transfer switches 402A and 402B are turned off, and charge accumulation in the photodiodes 401A and 401B is started. Here, the transfer switches that are turned on / off for resetting are not limited to the transfer switches 402A and 402B used for charge transfer after charge accumulation, and transfer switches 402C and 402D based on signals PTXC and PTXD may be used.

  At the time t3 after the start of accumulation, the signal PSEL is set to the high level, the select switches 406A and 406B are turned on, and the source follower amplifiers 405A and 405B are set in the operating state. At time t4, the signal PRES is set to low level, the reset switches 404A to 404D are turned off, and the reset of the floating diffusions 403A and 403B is released. The output voltages of the source follower amplifiers 405A and 405B at this time are read out as reset signal levels (noise components) to the vertical output lines 407A and 407B, respectively, and input to the column circuit 603. At time t5, the signal PC0R is set to low level, the switch 612 is turned off, and the reset of the operational amplifier 610 is released. At time t6, the signal PTN is set to high level, the switch 616 is turned on, and writing of the output signal of the operational amplifier 610 to the capacitor 614 is started. At time t7, the signal PTN is set to low level, the switch 616 is turned off, and writing of the output signal of the operational amplifier 610 to the capacitor 614 is completed. A reset signal level is written in the capacitor 614.

  Next, at time t8, the signals PTXA and PTXB are set to high level, the transfer switches 402A and 402B are turned on, and the charges accumulated in the photodiodes 401A and 401B are transferred to the floating diffusions 403A and 403B, respectively. At time t10, the signals PTXA and PTXB are set to the low level, the transfer switches 402A and 402B are turned off, and the above transfer ends. Then, the optical signal levels (light component + noise component) corresponding to the potential fluctuations of the floating diffusions 403A and 403B are read out to the vertical output lines 407A and 407B and input to the column circuit 603, respectively. At time t13, the signal PTS is set to high level, the switch 615 is turned on, and writing of the output voltage of the operational amplifier 610 to the capacitor 613 is started. At time t14, the signal PTS is set to low level, the switch 615 is turned off, and writing of the output voltage of the operational amplifier 610 to the capacitor 613 is completed. An optical signal level is written in the capacitor 613. Note that when signals are written to the capacitors 613 and 614, the operational amplifier 610 performs amplification of an inversion gain according to the ratio of the clamp capacitor 608 and the feedback capacitor 609, and outputs a voltage.

  Thereafter, at time t15, the signal PRES is set to the high level, the reset switches 404A to 404D are turned on, and the floating diffusions 403A and 403B are reset.

  Next, the period HSR will be described. From time t16 to t17, the switches 617 and 618 of each column are sequentially turned on by the pulses of the signals PHS and PHN, and the signals held in the capacitors 613 and 614 of each column are sequentially output to the horizontal output lines 605 and 606. The The output amplifier 607 outputs a difference signal (light component) between the signals of the horizontal output lines 605 and 606.

  Thereafter, when the imaging apparatus is driven in the normal imaging mode, the image processing circuit 106 adds the signals of the photodiodes 401A and 401B to generate a captured image. On the other hand, in the pupil division method phase difference detection mode, the image processing circuit 106 performs a correlation operation on the A image and the B image, and acquires a defocus amount (a defocus amount). In this case, the image processing circuit 106 adds the signals of the A image and the B image in the normal imaging mode after acquiring the defocus amount. Here, a combination of signals PTXA and PTXB is used, but a combination of signals PTXA and PTXD or a combination of signals PTXB and PTXC can also be used.

  FIG. 8 is a timing chart illustrating a second driving method of the imaging apparatus. The second driving method is a pixel signal reading driving method in the light travel time ranging mode. The charge generated in one photodiode 401A is read out to different floating diffusions 403A and 403C.

  First, the period HBLK will be described. At time t0, the signal PRES is set to high level, the reset switches 404A to 404D are turned on, and the floating diffusions 403A and 403C are reset. At time t1, the signals PTXA and PTXC are set to the high level, the transfer switches 402A and 402C are turned on, and the photodiode 401A is also reset. At time t2, the signals PTXA and PTXC are set to low level, the transfer switches 402A and 402C are turned off, and charge accumulation of the photodiode 401A is started.

  At the time t3 after the start of accumulation, the signal PSEL is set to the high level, the select switches 406A and 406C are turned on, and the source follower amplifiers 405A and 405C are set in the operating state. At time t4, the signal PRES is set to the low level, the reset switches 404A to 404D are turned off, and the reset of the floating diffusions 403A and 403C is released. The output signals of the source follower amplifiers 405A and 405C at this time are read out as reset signal levels (noise components) to the vertical output lines 407A and 407C, respectively, and input to the column circuit 603. At time t5, the signal PC0R is set to low level, the switch 612 is turned off, and the reset of the operational amplifier 610 is released. At time t6, the signal PTN is set to high level, the switch 616 is turned on, and writing of the output signal of the operational amplifier 610 to the capacitor 614 is started. At time t7, the signal PTN is set to low level, the switch 616 is turned off, and writing of the output signal of the operational amplifier 610 to the capacitor 614 is completed. A reset signal level is written in the capacitor 614.

  Next, at time t8, the signal PTXA is set to the high level, the transfer switch 402A is turned on, and the photoelectric charge accumulated in the photodiode 401A is started to be transferred to the floating diffusion 403A. Thereafter, at time t9, the signal PLIGHT is set to the high level, and the light emitting device 112 starts to project infrared rays. At time t10, the signal PTXA is set to the low level and the signal PTXC is set to the high level, the transfer switch 402A is turned off, and the transfer switch 402C is turned on. Thereby, the transfer of the charge accumulated in the photodiode 401A to the floating diffusion 403C is started. At time t11, the signal PLIGHT is set to a low level, and the light emitting device 112 ends the infrared light projection. At time t12, the signal PTXC is set to low level, the transfer switch 402C is turned off, and the transfer ends.

  Optical signal levels (light component + noise component) corresponding to the potential fluctuation of the floating diffusions 403A and 403C are read out to the vertical output lines 407A and 407C, respectively, and input to the column circuit 603. At time t13, the signal PTS is set to high level, the switch 415 is turned on, and writing of the output signal of the operational amplifier 610 to the capacitor 613 is started. At time t14, the signal PTS is set to low level, the switch 415 is turned off, and writing of the output signal of the operational amplifier 610 to the capacitor 613 is completed. An optical signal level is written in the capacitor 613. Note that when signals are written to the capacitors 613 and 614, the operational amplifier 610 amplifies with an inversion gain corresponding to the ratio of the clamp capacitor 608 and the feedback capacitor 609, and outputs a signal.

  Thereafter, at time t15, the signal PRES is set to the high level, the reset switches 404A to 404D are turned on, and the floating diffusions 403A and 403C are reset.

  Next, the period HSR will be described. From time t16 to t17, the switches 617 and 618 of each column are sequentially turned on by the pulses of the signals PHS and PHN, and the signals held in the capacitors 613 and 614 of each column are sequentially output to the horizontal output lines 605 and 606. The The output amplifier 607 outputs a difference signal (light component) between the signals of the horizontal output lines 605 and 606. Thereafter, the image processing circuit 106 calculates the delay time of the reflected light with respect to the projection light based on the ratio of the read signals as described later, and calculates the distance to the subject.

  FIG. 9 is a timing chart illustrating another example of the second driving method of the imaging apparatus. In addition to the photodiode 401A, the photodiode 401B is also used and read simultaneously.

  First, the period HBLK will be described. At time t0, the signal PRES is set to high level, the reset switches 404A to 404D are turned on, and the floating diffusions 403A to 403D are reset. At time t1, the signals PTXA to PTXD are set to the high level, the transfer switches 402A to 402D are turned on, and the photodiodes 401A and 401B are also reset. At time t2, the signals PTXA to PTXD are set to low level, the transfer switches 402A to 402D are turned off, and charge accumulation of the photodiodes 401A and 401B is started.

  After the start of accumulation, at time t3, the signal PSEL is set to the high level, the select switches 406A to 406 are turned on, and the source follower amplifiers 405A to 405D are set in the operating state. At time t4, the signal PRES is set to low level, the reset switches 404A to 404D are turned off, and the reset of the floating diffusions 403A to 403D is released. The output signals of the source follower amplifiers 405A to 405D at this time are read out as reset signal levels (noise components) to the vertical output lines 407A to 407D and input to the column circuit 603. At time t5, the signal PC0R is set to low level, the switch 612 is turned off, and the reset of the operational amplifier 610 is released. At time t6, the signal PTN is set to high level, the switch 616 is turned on, and writing of the output signal of the operational amplifier 610 to the capacitor 614 is started. At time t7, the signal PTN is set to low level, the switch 616 is turned off, and writing of the output signal of the operational amplifier 610 to the capacitor 614 is completed. A reset signal level is written in the capacitor 614.

  Next, at time t8, the signals PTXA and PTXB are set to the high level, the transfer switches 402A and 402B are turned on, and the charges accumulated in the photodiodes 401A and 401B are started to be transferred to the floating diffusions 403A and 403B, respectively. Thereafter, at time t9, the signal PLIGHT is set to the high level, and the light emitting device 112 starts the infrared light projection. At time t10, the signals PTXA and PTXB are set to the low level, and at the same time, the signals PTXC and PTXD are set to the high level. The transfer switches 402A and 402B are turned off, the transfer switches 402C and 402D are turned on, and the charges accumulated in the photodiodes 401A and 401B are started to be transferred to the floating diffusions 403C and 403D, respectively. At time t11, the signal PLIGHT is set to a low level, and the light emitting device 112 ends the light projection. At time t12, the signals PTXC and PTXD are set to the low level, the transfer switches 402C and 402D are turned off, and the above transfer ends.

  The output signals of the source follower amplifiers 405A to 405D are read as optical signal levels (light component + noise component) on the vertical output lines 607A to 607D, respectively, and input to the column circuit 403. At time t13, the signal PTS is set to high level, the switch 615 is turned on, and writing of the output signal of the operational amplifier 610 to the capacitor 613 is started. At time t14, the signal PTS is set to low level, the switch 615 is turned off, and writing of the output signal of the operational amplifier 610 to the capacitor 613 is completed. An optical signal level is written in the capacitor 613. Note that when signals are written to the capacitors 613 and 614, the operational amplifier 610 amplifies with an inversion gain corresponding to the ratio of the clamp capacitor 608 and the feedback capacitor 609, and outputs a signal.

  Thereafter, at time t15, the signal PRES is set to the high level, the reset switches 404A to 404D are turned on, and the floating diffusions 403A to 403D are reset.

  Next, the period HSR will be described. From time t16 to t17, the switches 617 and 618 of each column are sequentially turned on by the pulses of the signals PHS and PHN, and the signals held in the capacitors 613 and 614 of each column are sequentially output to the horizontal output lines 605 and 606. The The output amplifier 607 outputs a difference signal (light component) between the signals of the horizontal output lines 605 and 606.

  FIG. 10 shows a part of the timing chart of FIG. 8 (FIG. 9), and is a diagram for explaining the principle of distance measurement by the optical travel time method. At time t8, the transfer switch 402A (and 402B) by the signal PTXA (and PTXB) is turned on. At time t10, the transfer switch 402A (and 402B) by the signal PTXA (and PTXB) is turned off, and at the same time, the transfer switch 402C (and 402D) by the signal PTXC (and PTXD) is turned on. At time t12, the transfer switch 402C (and 402D) by the signal PTXC (and PTXD) is turned off. Here, the on-periods of the transfer switch 402A (and 402B) and the transfer switch 402C (and 402D) are equal, and the light emitting device 112 projects pulsed light by the signal PLIGHT at times t9 and t11 in the respective on-periods. The pulsed light is reflected by the subject, and the imaging device receives the reflected light.

  If the distance from the imaging device to the subject is zero, the reflected light is received at the same timing as the signal PLIGHT, and the pixel signal transferred by the signal PTXA (and PTXB) and the pixel signal transferred by the signal PTXC (and PTXD). Are output as equal signals. However, when the distance from the imaging device to the subject is not zero, the reflected light is received with a delay of (t9a-t9) as shown in FIG. As a result, the pixel signal transferred by the signal PTXA (and PTXB) is a reflected light signal received during the period (t10-t9a), and the pixel signal transferred by the signal PTXC (and PTXD) is (t11a The signal of the reflected light received during the period of -t10). Both are biased. The image processing circuit 106 can estimate the delay time of the reflected light with respect to the projection light based on the ratio of these pixel signals, and can calculate the distance to the subject from the product of the delay time and the speed of light.

  As described above, the imaging element 103 in FIG. 6 is driven according to the timing chart shown in FIGS. 7 and 8 (FIG. 9), so that the first driving method and the optical flight time of the pupil division type phase difference detection method are obtained. It can be driven by two driving methods of the second driving method.

  In the pupil division type phase difference detection method, it may be difficult to detect the phase difference due to various optical conditions. For example, in shooting with the aperture fully open, the output of the pixels around the image sensor 103 is reduced due to a decrease in the amount of peripheral light. Furthermore, the incident angle of light is large, and the A and B images are also affected by the difference in incident angle, making accurate correlation calculation difficult. That is, an area in the image in which phase difference detection is difficult occurs. In view of the above problems, a driving method for switching the driving method of the image sensor depending on the region in the image will be described below.

  FIG. 11 is a diagram illustrating an example of a switching position for switching the driving method of the image sensor in the image. In the image sensor 103, the number of pixels in the X-axis direction is H, the number of pixels in the Y-axis direction is V, and the coordinates of the upper left pixel are (X, Y) = (0, 0). In the region 1101 of X = 0 to X1-1 and the region 1103 of X = X2 to H-1, driving is performed by the second driving method of the time-of-flight method, and in the region 1102 of X = X1 to X2-1, the pupil is driven. It drives by the 1st drive method of a division system phase difference detection method. A region 1102 is a central region of the image sensor 103. Regions 1101 and 1103 are peripheral regions of the image sensor 103.

  FIG. 12 is a flowchart illustrating a method for driving the imaging apparatus. In step S1201, the control circuit 109 performs mode setting such as still image shooting or moving image shooting, and shooting condition settings such as sensitivity and aperture value in accordance with a signal from the operation circuit 110 based on a user operation. .

  In step S1202, the control circuit 109 determines whether to acquire a normal captured image or to perform focus detection. When focus detection is performed, the process proceeds to step S1205. If a captured image is to be acquired, the process advances to step S1203.

  In step S1203, the image sensor 103 reads an image signal by the first driving method (normal imaging mode) under the control of the control circuit 109. Thereafter, in step S1204, the image processing circuit 106 performs predetermined image processing on the image signal read in step S1203, and outputs the image signal to the memory circuit 107, the recording circuit 108, and the display circuit 111.

  In step S1205, under the control of the control circuit 109, the image sensor 103 reads the signal of the area 1102 by the first driving method in FIG. Note that only pixel data corresponding to the area 1102 may be used when signals of all pixels are read out by the first driving method and a focus detection signal is generated in a later step. However, it is more preferable to read the signal of only the area 1102 by skip reading because the signal can be read at high speed. Here, skip reading refers to reading only signals in a desired column to the output amplifier 607 under the control of the horizontal shift register 604. By reading out only the signals in the desired column, the signal readout time can be shortened. The pixel signal of only the region 1102 is read by the first driving method, and the signal of the pixel of only the regions 1101 and 1103 is read by the second driving method in step S1206 described later. Thereby, although the pixel signal is read twice by two kinds of driving methods per frame, a pixel signal can be obtained in a time equivalent to a normal reading time of one frame.

  Subsequently, in step S <b> 1206, the image sensor 103 reads out the signals of the areas 1101 and 1103 by the second driving method of FIG. 8 or 9 in order to acquire a focus detection signal under the control of the control circuit 109. Note that, as in step S1205, all pixel signals may be read by the second driving method, and only the pixel data corresponding to the regions 1101 and 1103 may be used when focus detection is performed in a subsequent step. However, it is more preferable to read out the signals of only the areas 1101 and 1103 by skip reading because the signals can be read out at high speed. Further, according to the timing chart shown in FIG. 9, it is more preferable to read out signals from both the photodiodes 401A and 401B because a larger signal amount can be obtained.

  In step S1207, the image processing circuit 106 performs predetermined image processing on the image signal read in steps S1205 and S1206, and outputs the image signal to the memory circuit 107, the recording circuit 108, and the display circuit 111. To do. That is, in the areas 1101 and 1103 in FIG. 11, the focus adjustment information is generated using the data read by the second driving method. In a region 1102, focus adjustment information is generated using data read by the first driving method.

  Note that the region switching unit may generate the focus adjustment information by both the first driving method and the second driving method. For example, in FIG. 11, focus adjustment information is generated by the first and second driving methods in the region of X = X1−α to X1 + α and the region of X = X2−α to X2 + α. And the pixel signal of the area | region of X = X1 + (alpha) -X2- (alpha) is read by the 1st drive method. And the pixel signal of the area | region of X = 0-X1- (alpha) and X = X2 + (alpha) -H-1 is read by the 2nd drive method. That is, the pixel signal is read out by the second driving method in the region X = 0 to X1 + α and the region X = X2−α to H−1, and the first driving method in the region X = X1−α to X2 + α. To read out the pixel signal. In this case, the area read by the first driving method and the area read by the second driving method partially overlap each other.

  In step S <b> 1207, if the image processing circuit 106 generates focus adjustment information from the pixel signals of the respective areas, the focus adjustment information can be acquired by overlapping the vicinity of the area where the driving method is switched, and the focus adjustment is performed with higher accuracy. be able to.

  In step S1208, the control circuit 109 determines whether or not the photographing has been completed, and if continued, the process proceeds to step S1209. On the other hand, if it is finished, the series of operations is finished.

  In step S1209, the image processing circuit 106 performs focus detection based on the focus adjustment information obtained in step S1207, and calculates a lens driving amount. Next, in step S1210, the control circuit 109 performs focus driving by driving the photographing lens 101 by the lens driving amount described above. That is, focus adjustment is performed. Then, it returns to step S1201 and repeats said operation | movement.

  As described above, in step S <b> 1205, the control circuit 109 reads a pixel signal in the first region 1102 of the image sensor 103 without projecting pulsed light onto the light emitting device 112. In step S <b> 1206, the control circuit 109 projects pulsed light on the light emitting device 112, and reads the pixel signals of the second regions 1101 and 1103 of the image sensor 103. In step S <b> 1209, the image processing circuit 106 detects the focus of the subject based on the pixel signals of the first area 1102 and the second areas 1101 and 1103 of the image sensor 103. In step S1210, the control circuit 109 performs focus adjustment by driving the photographing lens 101 according to the distance calculated by the image processing circuit 106.

  FIG. 13 is a diagram illustrating another example of a switching position for switching the driving method of the image sensor in the image. In FIG. 11, since the influence of the peripheral light amount drop is larger in the long side direction of the image, the region is divided only by the columns, but there is a peripheral light drop although the short side direction is not as large as the long side direction. Therefore, as shown in FIG. 13, the driving method of the image sensor may be switched also in the row direction. In the image sensor 103, an area 1302 of coordinates (X, Y) = (X1, Y1) to (X2-1, Y2-1) is a focus detection signal by the first driving method of the pupil division type phase difference detection method. In other regions 1301, the focus detection signal is acquired by the second driving method of the time-of-flight method. Note that the area 1102 and the areas 1101 and 1103 may be uniquely determined, but may be changed according to the imaging conditions such as the pupil distance of the imaging lens 101 or the aperture value at the time of imaging.

  As described above, the focus adjustment can be performed with high accuracy regardless of the position in the image by switching the driving method of the image sensor depending on the region in the image. The configuration of the image sensor 103 is not limited to the configuration shown in the present embodiment as long as it can drive both the pupil division type phase difference detection method and the time-of-flight method. In the present embodiment, the signal is read out by dividing the region driven by the pupil division method phase difference detection method and the region driven by the optical flight time method, but the reading method is not limited to this. .

(Second Embodiment)
A second embodiment of the present invention will be described. In the second embodiment of the present invention, in the image sensor 103, an area driven by the first driving method (pupil division method phase difference detection method) and an area driven by the second driving method (light time-of-flight method). The feature is to change the configuration. That is, the image sensor 103 is formed with a configuration suitable for the driving method of each region.

  14 is a diagram of the image sensor 103 and the microlens 113 as seen from the direction of the optical axis Z in FIG. One microlens 113 is defined as one pixel, and this is defined as a unit pixel. Each unit pixel is expressed as (X, Y) with addresses of X coordinate and Y coordinate. Here, the unit pixels 200 in the central area arranged in three columns of X = 1, 2, and 3 are arranged so that a plurality of divided pixels 201A and 201B correspond to one microlens 113. . In the present embodiment, two divided pixels 201A and 201B are arranged in the X-axis direction. Further, the unit pixels 1402 in the peripheral area arranged at X = 0 and 4 are arranged so that one pixel corresponds to one microlens 113. In the present embodiment, the unit pixel 200 composed of two divided pixels 201A and 201B is used for the pupil division method phase difference detection method, and the unit pixel 1402 is used for the time-of-flight method. Note that the configuration of the unit pixel 200 is the same as the configuration described in FIGS. 4 and 5.

  FIG. 15 is a circuit diagram showing a configuration example of the unit pixel 1402 of FIG. The unit pixel 1402 has one photodiode 1501. Two transfer switches 1502A and 1502C are connected to the photodiode 1501. Floating diffusions 1503A and 1503C are connected to the transfer switches 1502A and 1502C, respectively. A reset switch 1504A and a source follower amplifier 1505A are connected to the floating diffusion 1503A. A reset switch 1504C and a source follower amplifier 1505C are connected to the floating diffusion 1503C. Select switches 1506A and 1506C are connected to the source follower amplifiers 1505A and 1505C, respectively. The drains of the reset switches 1504A and 1504C and the source follower amplifiers 1505A and 1505C share the reference potential 1508.

  The photodiode 1501 is a photoelectric conversion unit that receives light that has passed through the microlens 113 and generates charges according to the amount of light received through photoelectric conversion. The transfer switch 1502A transfers the charge generated in the photodiode 1501 to the floating diffusion 1503A. The transfer switch 1502C transfers the charge generated in the photodiode 1501 to the floating diffusion 1503C. Transfer switches 1502A and 1502C are controlled by transfer pulse signals PTXA and PTXC, respectively. The floating diffusions 1503A and 1503C are charge-voltage converters that temporarily hold the charge transferred from the photodiode 1501 and convert the held charge into a voltage signal.

  The reset switches 1504A and 1504C reset the potentials of the floating diffusions 1503A and 1503C to the reference potential 1508, respectively. The reset switches 1504A and 1504C are controlled by a reset pulse signal PRES. The source follower amplifier 1505A is a source follower circuit having a MOS transistor, amplifies the voltage based on the charge held in the floating diffusion 1503A, and outputs it as a pixel signal. The source follower amplifier 1505C is a source follower circuit having a MOS transistor, amplifies the voltage based on the charge held in the floating diffusion 1503C, and outputs it as a pixel signal.

  The select switch 1506A outputs the pixel signal amplified by the source follower amplifier 1505A to the vertical output line 1507A. The select switch 1506C outputs the pixel signal amplified by the source follower amplifier 1505C to the vertical output line 1507C. The vertical output lines 1507A and 1507C are shared by a plurality of unit pixels 1402 in the same column. Select switches 1506A and 1506C are controlled by a select pulse signal PSEL.

  FIG. 16 is a diagram illustrating a layout example of the unit pixel 1402. As described in FIG. 15, the photo die auto 1501 has two transfer switches 1502A and 1502C connected to both ends thereof. The charge of the photodiode 1501 can be transferred by either of the transfer switches 1502A and 1502C. Floating diffusions 1503A and 1503C are connected to the transfer switches 1502A and 1502C, respectively.

  As described above, each unit pixel 200 in the central region has a plurality of photodiodes 401A and 401B, and each unit pixel 1402 in the peripheral region has one photodiode 1501. Using the imaging device 103 having such a configuration, a focus detection signal can be obtained with high accuracy regardless of the position in the image by a driving method similar to the driving method described in the first embodiment. Note that the circuit layout of the image sensor 103 can be improved by configuring the image sensor 103 according to the driving method for acquiring the distance image as in the present embodiment.

  In the first embodiment and the second embodiment, a focus detection signal by the pupil division type phase difference detection method of the first driving method is acquired in the central region of the image, and the second signal is acquired in the peripheral region of the image. A method of acquiring a focus detection signal by the time-of-flight method of driving method has been described. However, there is a case where the projection light does not reach the peripheral area of the image, and it is difficult to obtain the focus detection signal by the time-of-flight method in the peripheral area of the image. Further, there is a case where large defocus is caused in the center region of the image, the phase difference is small, and the pupil division type phase difference detection method is difficult. In that case, in the region in the image, the center region 1102 or 1302 performs the time-of-flight method by the second driving method, and the peripheral region 1101, 1103 or 1301 performs the pupil division method phase difference detection method by the first driving method. And a focus detection signal may be acquired.

  As described above, it is possible to acquire a distance image with high accuracy by selecting a method for acquiring a focus detection signal according to a region in an image according to a shooting condition.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

DESCRIPTION OF SYMBOLS 100 Imaging device, 101 Shooting lens, 103 Imaging element, 106 Image processing circuit, 109 Control circuit, 112 Light-emitting device

Claims (13)

An image sensor having a plurality of pixels that perform photoelectric conversion;
A light projecting unit that projects pulsed light onto the subject;
Without projecting pulsed light to the light projecting unit, a to read out at least a first signal by driving a driving method corresponding pixels of the first area in the pupil slicing phase difference detection method of the imaging device A first read drive, and a pulse light is projected onto the light projecting unit, and at least the pixels in the second region of the image sensor are driven by a second drive method corresponding to the time-of-flight method to read out a signal . A control circuit that controls to perform read drive of
An image processing circuit for generating a focus adjustment information by using the signals read from the imaging device by the first read drive, and a signal read from the imaging device by the second reading drive,
An imaging device comprising: Furthermore, it has a photographic lens for imaging light on the image sensor,
The imaging apparatus according to claim 1, wherein the control circuit drives the photographing lens in accordance with the focus adjustment information . An image sensor having a plurality of pixels that perform photoelectric conversion;
A light projecting unit that projects pulsed light onto the subject;
First, at least the pixels in the first region of the image sensor are driven by the first driving method corresponding to the pupil division type phase difference detection method and the signal is read without projecting the pulsed light onto the light projecting unit. Read-out driving and second readout in which pulse light is projected onto the light projecting unit, and at least pixels in the second region of the image sensor are driven by a second driving method corresponding to the time-of-flight method to read out signals. A control circuit that controls to perform driving,
A defocus amount of a subject image is detected using a signal read from the image sensor by the first readout drive, and the subject is detected using a signal read from the image sensor by the second readout drive. An image processing circuit for calculating the distance to
An imaging device comprising: Furthermore, it has a photographic lens for imaging light on the image sensor,
The control circuit controls the photographing lens according to a defocus amount of the subject image detected by the image processing circuit or a distance to the subject calculated by the optical time-of-flight method calculated by the image processing circuit. The imaging apparatus according to claim 3, wherein the imaging apparatus is driven. The first region is a central region of the image sensor,
The second region, the imaging apparatus according to any one of claims 1-4, characterized in that the peripheral area of the imaging element. The first region is a peripheral region of the image sensor,
The second region, the imaging apparatus according to any one of claims 1-4, characterized in that the central region of the imaging element. It said first region and said second region, the imaging apparatus according to any one of claims 1 to 6, wherein the overlapping part with each other. It said first region and said second region, the imaging apparatus according to any one of claims 1 to 7, characterized in that can be changed according to the photographing conditions. The imaging conditions, the imaging apparatus according to claim 8, characterized in that it comprises a pupil distance or the aperture value of the photographic lens. The imaging device according to claim 1, wherein each of the plurality of pixels includes a plurality of photoelectric conversion units. The imaging device according to claim 10, wherein each of the plurality of pixels includes a microlens. Each pixel in the first region has a plurality of photoelectric conversion units,
Wherein each of the pixels of the second region, the imaging apparatus according to any one of claims 1-6, characterized in that it comprises a single photoelectric conversion unit. The imaging device according to claim 12, wherein each pixel of the first region and the second region has a microlens.

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