Imaging apparatus and method for controlling the same, program, and storage medium

Abstract

To provide an imaging apparatus that can prevent a reduction in the S / N performance of an output signal irrespective of brightness, and can reduce power consumption.SOLUTION: An imaging apparatus comprises: a pixel unit in which pixels each having a photoelectric conversion element are arranged in matrix; AD conversion units that are arranged in correspondence with pixel columns of the pixel unit and convert pixel signals obtained from the pixels into digital signals; an addition unit that adds pixel signals on different N columns (N is an integer of 2 or more); and a control unit that performs control to perform AD conversion of the pixel signals added by the addition unit by using the plurality of AD conversion units corresponding to the N columns, and after the lapse of predetermined time from the start of the AD conversion in a period of the AD conversion, switch the operation of some AD conversion units of the plurality of AD conversion units to an operation to reduce power consumption.SELECTED DRAWING: Figure 12A

Description

[Technical field]

[0001] The present invention relates to an imaging apparatus and a control method thereof. [Background technology]

[0002] 2. Description of the Related Art In recent years, imaging elements such as CMOS image sensors have come into widespread use in imaging devices such as digital still cameras and digital video cameras.

[0003] Recently, the image sensors used in many cases are ones that are equipped with analog-to-digital (AD) converters that perform AD conversion for each column of pixels arranged in a matrix, enabling high-speed signal readout.

[0004] Here, one known AD conversion method is to use a comparator arranged for each column to compare the pixel output voltage output from each pixel with a reference signal whose voltage changes over time, and count the time until the comparator output is inverted. This type of method is called the single slope method.

[0005] Patent Document 1 discloses a configuration for reducing power consumption by operating multiple AD converters and saving the power of the AD converters after the AD conversion is completed. However, under high luminance conditions, the power of the AD converters is not saved, so the effect of reducing power consumption is limited.

[0006] In Patent Document 2, power consumption is reduced by saving the power of the AD converter only when the phase difference signal is read out, but the S / N performance of the phase difference signal at low luminance is degraded. Also, power of the AD converter is not saved when the image signal is read out, so the effect of reducing power consumption is limited. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-159271 A [Patent Document 2] JP 2021-114676 A Summary of the Invention [Problem to be solved by the invention]

[0008] In the configurations of Patent Documents 1 and 2 described above, it has been difficult to reduce power consumption while suppressing degradation in the S / N performance of the output signal, regardless of the luminance.

[0009] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide an imaging device that can reduce power consumption while suppressing degradation in the S / N performance of the output signal regardless of brightness. [Means for solving the problem]

[0010] The imaging device of the present invention is characterized in that it comprises a pixel section in which pixels having photoelectric conversion elements are arranged in a matrix, AD conversion means arranged corresponding to each pixel column of the pixel section and converting pixel signals obtained from the pixels into digital signals, an addition means which adds pixel signals of N different columns (N is an integer of 2 or more), and a control means which AD converts the pixel signals added by the addition means using a plurality of AD conversion means corresponding to the N columns, and during the AD conversion period, after a predetermined time has elapsed from the start of the AD conversion, controls some of the plurality of AD conversion means to switch to an operation that reduces power consumption. Effect of the Invention

[0011] According to the present invention, it is possible to provide an imaging device that can reduce power consumption while suppressing degradation in the S / N performance of an output signal, regardless of luminance. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing the configuration of a digital camera as an embodiment of an imaging apparatus of the present invention. [Diagram 2] FIG. 2 is a diagram showing a pixel array of an imaging element. [Diagram 3] 1A and 1B are a plan view and a cross-sectional view of a pixel of an imaging element. [Figure 4] FIG. 2 is an explanatory diagram of a pixel structure of an image sensor. [Diagram 5] FIG. 4 is an explanatory diagram of pupil division according to an embodiment. [Figure 6] 5 is a graph showing the relationship between a defocus amount and an image shift amount in an embodiment. [Figure 7] 1 is a diagram illustrating an overall circuit configuration of an image sensor used in an image pickup apparatus. [Figure 8] FIG. 2 is an equivalent circuit diagram of the pixel section of an image sensor. [Figure 9] FIG. 2 is a diagram showing the configuration of a signal addition circuit of the image sensor. [Figure 10] FIG. 2 is a diagram showing the configuration of an AD conversion circuit of an image sensor. [Figure 11] 4 is a readout timing chart in a non-additive readout mode of the image sensor. [Figure 12A] 4 is a readout timing chart in an additive readout mode of the image sensor. [Figure 12B] 4 is a readout timing chart in an additive readout mode of the image sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0014] FIG. 1 is a diagram showing the configuration of a digital camera which is an embodiment of an imaging apparatus according to the present invention.

[0015] In Fig. 1, the first lens group 101 is disposed closest to the subject (front side) in the imaging optical system as an image forming optical system, and is held so as to be movable in the optical axis direction. The aperture 102 adjusts the light amount by adjusting the aperture diameter. The second lens group 103 moves in the optical axis direction together with the aperture 102, and performs magnification change (zoom) together with the first lens group 101 moving in the optical axis direction.

[0016] The third lens group (focus lens) 105 moves in the optical axis direction to adjust the focus. The optical low-pass filter 106 is an optical element for reducing false colors and moire in the captured image. The first lens group 101, the aperture 102, the second lens group 103, the third lens group 105, and the optical low-pass filter 106 configure an imaging optical system.

[0017] The zoom actuator 111 rotates a cam barrel (not shown) around the optical axis, and moves the first lens group 101 and the second lens group 103 in the optical axis direction by a cam provided on the cam barrel, thereby performing magnification change. The aperture actuator 112 drives a plurality of light-shielding blades (not shown) in opening and closing directions to adjust the amount of light of the aperture 102. The focus actuator 114 moves the third lens group 105 in the optical axis direction to perform focus adjustment.

[0018] The focus driving circuit 126 drives the focus actuator 114 in response to a focus driving command from the camera CPU 121, and moves the third lens group 105 in the optical axis direction. The aperture driving circuit 128 drives the aperture actuator 112 in response to an aperture driving command from the camera CPU 121. The zoom driving circuit 129 drives the zoom actuator 111 in response to a zoom operation by the user.

[0019] In this embodiment, a case will be described in which the imaging optical system, the actuators 111, 112, 114, and the drive circuits 126, 128, 129 are provided integrally with the camera body 100 including the image sensor 107. However, an interchangeable lens having the imaging optical system, the actuators 111, 112, 114, and the drive circuits 126, 128, 129 may be configured to be detachable from the camera body 100.

[0020] The electronic flash 115 has a light-emitting element such as a xenon tube or an LED, and illuminates the subject. The electronic flash control circuit 122 controls the electronic flash 115 to be turned on in synchronization with the imaging operation. The AF auxiliary light emission unit 116 improves focus detection performance for dark or low-contrast subjects by projecting an image of a mask having a predetermined opening pattern onto the subject via a projection lens. The auxiliary light drive circuit 123 controls the AF auxiliary light emission unit 116 to be turned on in synchronization with the focus detection operation.

[0021] Camera CPU 121 is responsible for various controls in camera body 100. Camera CPU 121 has a calculation unit, ROM, RAM, an A / D converter, a D / A converter, a communication interface circuit, etc. Camera CPU 121 drives various circuits in camera body 100 according to a computer program stored in ROM, and also controls a series of operations such as AF, imaging, image processing, and recording.

[0022] The image sensor 107 is composed of a two-dimensional CMOS sensor including a plurality of pixels and its peripheral circuits, and is disposed on the imaging plane of the imaging optical system. The image sensor 107 photoelectrically converts the subject image formed by the imaging optical system. The image sensor drive circuit 124 controls the operation of the image sensor 107.

[0023] The shutter 108 has a focal plane shutter, and drives the focal plane shutter in response to a command from a shutter drive circuit built into the shutter 108 based on an instruction from the camera CPU 121. The shutter 108 blocks light from the image sensor 107 while reading out a signal from the image sensor 107. Also, while exposure is being performed, the focal plane shutter is opened to guide a shooting light beam to the image sensor 107.

[0024] The image processing unit 125 applies predetermined image processing to image data stored in the RAM in the camera CPU 121. The image processing applied by the image processing unit 125 includes, but is not limited to, so-called image processing such as white balance processing, color interpolation (demosaic) processing, and gamma correction processing, as well as signal format conversion processing and scaling processing. Furthermore, the image processing unit 125 determines the main subject based on posture information of the subject and position information of an object unique to the scene (hereinafter, unique object). The result of the determination processing may be used for other image processing, for example, white balance adjustment processing. The image processing unit 125 saves, in the RAM in the camera CPU 121, the joint positions of each subject of the processed image data, the position and size information of the unique object, the center of gravity of the subject determined to be the main subject, position information of the face and eyes, and the like.

[0025] The display 131 includes a display element such as an LCD, and displays information about the imaging mode of the camera body 100, a preview image before imaging, a confirmation image after imaging, an index of the focus detection individual area, and a focused image. In this embodiment, two types of display are used: an EVF (electronic viewfinder) and a rear display. The operation switch group 132 includes a main (power) switch, a release (photography trigger) switch, a zoom operation switch, an imaging mode selection switch, and the like, and is operated by the user. The flash memory 133 records captured images. The flash memory 133 is detachable from the camera body 100.

[0026] The subject detection unit 140 performs subject detection based on dictionary data generated by machine learning.

[0027] Dictionary data storage unit 141 stores dictionary data for each object. Object detection unit 140 estimates the position of the object in the image based on captured image data and dictionary data. Object detection unit 140 may estimate the object's position, size, reliability, etc., and output the estimated information. Object detection unit 140 may output other information.

[0028] The camera movement detection unit 142 detects panning and tilting operations performed by the user to hold the camera and bring the subject within the shooting range, along with unintentional camera shake by the user, etc. The camera movement detection unit 142 detects changes in the camera position in six axial directions using an acceleration sensor and an angular velocity sensor.

[0029] Next, the pixel array of the image sensor 107 will be described with reference to Fig. 2. Fig. 2 is a diagram showing the pixel array of the image sensor 107 in a range of 4 pixel rows x 4 pixel columns as viewed from the optical axis direction (z direction).

[0030] One pixel unit 200 includes four imaging pixels arranged in 2 rows x 2 rows. By arranging a large number of pixel units 200 on the image sensor 107, photoelectric conversion of a two-dimensional subject image can be performed. In one pixel unit 200, an imaging pixel (hereinafter, R pixel) 200R having a spectral sensitivity of R (red) is arranged at the upper left, and an imaging pixel (hereinafter, G pixel) 200G having a spectral sensitivity of G (green) is arranged at the upper right and lower left. Furthermore, an imaging pixel (hereinafter, B pixel) 200B having a spectral sensitivity of B (blue) is arranged at the lower right. Each imaging pixel is divided into two in the horizontal direction (x direction), and a first focus detection pixel 201 and a second focus detection pixel 202 that output a signal for detecting a focus state are formed.

[0031] In the image sensor 107 of this embodiment, the pixel pitch of the imaging pixels is 4 μm, and the number of imaging pixels N is 5575 horizontal columns (x)×3725 vertical rows (y)=approximately 20.75 million pixels. The pixel pitch PAF of the focus detection pixels is 2 μm, and the number of focus detection pixels NAF is 11150 horizontal columns×3725 vertical rows=approximately 41.5 million pixels. In this embodiment, a case will be described in which each imaging pixel is divided into two in the horizontal direction, but it may also be divided in the vertical direction.

[0032] Fig. 3(a) shows one imaging pixel 200G (200R, 200B) as viewed from the light receiving surface side (+z direction) of the imaging element 107. Fig. 3(b) shows the aa cross section of the imaging pixel of Fig. 3(a) as viewed from the -y direction. As shown in Fig. 3(b), one imaging pixel is provided with one microlens 305 for collecting incident light.

[0033] Furthermore, the imaging pixel is provided with photoelectric conversion units (photoelectric conversion elements) 301, 302 that are divided into N parts in the x direction (divided into two parts in this embodiment). The photoelectric conversion units 301, 302 correspond to the first focus detection pixel 201 and the second focus detection pixel 202, respectively. The centers of gravity of the photoelectric conversion units 301, 302 are decentered on the -x side and +x side, respectively, with respect to the optical axis of the microlens 305.

[0034] R, G, and B color filters 306 are provided between the microlens 305 and the photoelectric conversion units 301 and 302 in each imaging pixel. Note that the spectral transmittance of the color filters may be changed for each photoelectric conversion unit, or the color filters may be omitted.

[0035] Light incident on the imaging pixel from the imaging optical system is collected by the microlens 305 , dispersed by the color filter 306 , and then photoelectrically converted by the photoelectric conversion units 301 and 302 .

[0036] Next, the relationship between the pixel structure shown in Fig. 3 and pupil division will be described with reference to Fig. 4. Fig. 4 shows the aa cross section of the imaging pixel shown in Fig. 3(a) viewed from the +y side, and also shows the exit pupil of the imaging optical system. In Fig. 4, the x-axis and y-axis directions of the imaging pixel are inverted with respect to Fig. 3(b) in order to correspond to the coordinate axes of the exit pupil.

[0037] A first pupil region 501, the center of gravity of which is decentered on the +x side of the exit pupil, is a region that is substantially conjugate with the light receiving surface of the photoelectric conversion unit 301 on the -x side of the imaging pixel by the microlens 305. The light flux that passes through the first pupil region 501 is received by the photoelectric conversion unit 301, i.e., the first focus detection pixel 201. A second pupil region 502, the center of gravity of which is decentered on the -X side of the exit pupil, is a region that is substantially conjugate with the light receiving surface of the photoelectric conversion unit 302 on the +x side of the imaging pixel by the microlens 305. The light flux that passes through the second pupil region 502 is received by the photoelectric conversion unit 302, i.e., the second focus detection pixel 202. The pupil region 500 indicates a pupil region that can receive light by the entire imaging pixel including all of the photoelectric conversion units 301, 302 (first and second focus detection pixels 201, 202).

[0038] FIG. 5 shows pupil division by the image sensor 107. A pair of light beams passing through the first pupil region 501 and the second pupil region 502, respectively, are incident on each pixel of the image sensor 107 at different angles and are received by the first and second focus detection pixels 201 and 202 divided into two. In this embodiment, output signals from the multiple first focus detection pixels 201 of the image sensor 107 are collected to generate a first focus detection signal, and output signals from the multiple second focus detection pixels 202 are collected to generate a second focus detection signal. In addition, in each of the multiple imaging pixels, the output signal from the first focus detection pixel 201 and the output signal from the second focus detection pixel 202 are added together to generate an imaging pixel signal. Then, the imaging pixel signals from the multiple imaging pixels are synthesized to generate an image with a resolution corresponding to the number of effective pixels N.

[0039] Next, the relationship between the defocus amount of the imaging optical system and the phase difference (image shift amount) between the first focus detection signal and the second focus detection signal acquired from the image sensor 107 will be described with reference to FIG.

[0040] The image sensor 107 is disposed on the imaging plane 600 in Fig. 6, and as described with reference to Figs. 4 and 5, the exit pupil of the imaging optical system is divided into a first pupil region 501 and a second pupil region 502. The defocus amount d is defined such that |d| is the distance (size) from the imaging position C of the light beam from the subject (801, 802) to the imaging plane 600, a front-focus state in which the imaging position C is on the subject side of the imaging plane 600 is represented by a negative sign (d<0), and a back-focus state in which the imaging position C is on the opposite side of the subject from the imaging plane 600 is represented by a positive sign (d>0). In a focused state in which the imaging position C is on the imaging plane 600, d=0. The imaging optical system is in a focused state (d=0) for the subject 801, and in a front-focus state (d<0) for the subject 802. The front focus state (d<0) and the back focus state (d>0) are collectively called the defocus state (|d|>0).

[0041] In the front focus state (d<0), the light beam from the subject 802 that passes through the first pupil region 501 (second pupil region 502) is once collected and then spreads to a width Γ1 (Γ2) centered on the center of gravity position G1 (G2) of the light beam, forming a blurred image on the imaging surface 600. This blurred image is received by each first focus detection pixel 201 (each second focus detection pixel 202) on the image sensor 107, and a first focus detection signal (second focus detection signal) is generated. In other words, the first focus detection signal (second focus detection signal) is a signal that represents an image of the subject 802 at the center of gravity position G1 (G2) of the light beam on the imaging surface 600, where the subject 802 is blurred by the blur width Γ1 (Γ2).

[0042] The blur width Γ1 (Γ2) of the subject image increases roughly in proportion to an increase in the magnitude |d| of the defocus amount d. Similarly, the magnitude |p| of the image shift amount p (= the difference G1-G2 between the center of gravity positions of the light beams) between the first focus detection signal and the second focus detection signal also increases roughly in proportion to an increase in the magnitude |d| of the defocus amount d. In the back-focus state (d>0), the direction of the image shift between the first focus detection signal and the second focus detection signal is opposite to that in the front-focus state, but the same is true.

[0043] In this way, the magnitude of the image shift amount between the first and second focus detection signals increases as the magnitude of the defocus amount increases. In this embodiment, focus detection is performed using an image plane phase difference detection method in which the defocus amount is calculated from the image shift amount between the first and second focus detection signals obtained using the image sensor 107.

[0044] [Overall configuration of the image sensor] FIG. 7 is a diagram showing an outline of the overall circuit configuration of an image sensor used in the image pickup apparatus of this embodiment.

[0045] The image sensor 107 includes a pixel array section 701 , an AD conversion section 711 , a vertical selection circuit 721 , a horizontal selection circuit 731 , an output section 741 , and a signal addition section 751 .

[0046] Pixels 702 (corresponding to any of pixels 200R, 200G, and 200B in FIG. 2) are arranged in a two-dimensional array in the pixel array section 701. When the output of a vertical selection circuit 721 is input to pixels arranged in a row direction via pixel drive pulse wiring 703, a pixel selection switch in a predetermined row is turned on, and an amplification transistor in the predetermined row is connected to a column output line 704.

[0047] It is possible to provide one column output line 704 for each pixel column, one for each set of pixel columns, or multiple column output lines 704 for each pixel column. The column output lines 704 are input to an AD conversion unit 711 via signal addition circuits 752 arranged every three columns.

[0048] The signal addition circuit 752 is connected to the AD conversion circuit unit 111 via AD input lines 753 whose number is an integer multiple of the number of input column output lines 704. The signal addition circuit 752 has a non-addition mode in which the voltages of the column output lines 704 are output to the AD input line 753 without being added and averaged, and an addition mode in which the signal addition circuit 752 outputs to the AD input line 753 a voltage obtained by averaging the voltages of adjacent or nearby column output lines.

[0049] The AD conversion unit 711 has AD conversion circuits 713 arranged in approximately the same number as the column output lines 704, and performs AD conversion on the voltage output from the signal addition circuit 752. The AD conversion unit 711 includes a reference signal generation circuit 712, an AD conversion circuit 713 arranged for each column output line, an AD counter 714, and a power-down signal generation circuit 761.

[0050] In the pixel signal readout operation, the output voltage of the pixel in the row selected by the vertical selection circuit 721 is converted into a digital signal by the AD conversion circuit 713, and the signals of the columns selected in sequence by the horizontal selection circuit 731 are output to the outside of the image sensor 107 via the output unit 741. By sequentially performing this pixel signal readout operation while changing the row selected by the vertical selection circuit 721, two-dimensional pixel signals can be read out from the image sensor 107.

[0051] [Pixel circuit] FIG. 8 is a diagram illustrating a schematic equivalent circuit of a pixel 702 of the image sensor 107. As shown in FIG.

[0052] The pixel 702 includes the first focus detection pixel (first photoelectric conversion element, hereinafter PDA) 201, the second focus detection pixel (second photoelectric conversion element, hereinafter PDB) 202, and a charge-voltage converter (hereinafter FD) 805 that converts signal charges into voltage. The pixel 702 also includes a transfer switch (hereinafter TXA) 803 for transferring the signal charges accumulated in the PDA 201 to the FD 805, and a transfer switch (hereinafter TXB) 804 for transferring the signal charges accumulated in the PDB 202 to the FD 805. The pixel 702 also includes a reset switch (hereinafter RES) 806 for discharging and resetting the signal charges of the PDA 201, the PDB 202, and the FD 805, and a selection switch (hereinafter SEL) 807 for selecting a pixel. The pixel 702 also includes an amplification transistor (hereinafter SF) 808 for outputting a signal voltage from the pixel, a column output line 704, and a constant voltage source 810. The gates of the TXA 803 , the TXB 804 , the RES 806 , and the SEL 807 are each connected to the pixel drive pulse wiring 703 .

[0053] In this embodiment, the signal charge accumulated in the photoelectric conversion unit is electrons, the photoelectric conversion unit is formed from an N-type semiconductor, and the signal charge is separated by a P-type semiconductor; however, the signal charge may be holes, the photoelectric conversion unit may be formed from a P-type semiconductor, and the signal charge may be separated by an N-type semiconductor.

[0054] [Signal summing circuit] FIG. 9 is a diagram illustrating a schematic configuration of the signal adding circuit.

[0055] The signal adding circuit 752 includes three coupling capacitors 802 and an adding switch 901 capable of connecting the AD input lines 753 of the coupling capacitors 802 on the AD conversion circuit 713 side to each other. Of the electrodes of the coupling capacitor 802, the electrode on the side where the adding switch 901 is provided is connected to the AD input line 753, and the electrode on the opposite side across the capacitor is connected to the column output line 704. Note that in this embodiment, the signal adding circuit 752 is configured to add signals from every third column, but the number of columns to be added is not limited to this, and it is possible to configure the signal adding circuit 752 to add signals from two or more columns (N columns or more: N is an integer equal to or greater than 2).

[0056] In the case of a non-additive readout mode, which will be described later, the addition switch 901 is off, and the voltages of the three column output lines 704 are output directly to the three AD input lines 753. In the case of an additive readout mode, which will also be described later, the addition switch 901 is on, and a voltage obtained by averaging the voltages of the three column output lines 704 is output to the three AD input lines 753.

[0057] [AD conversion section] FIG. 10 is a diagram showing a schematic diagram of AD conversion circuits 713 for three columns. The AD conversion method is a single slope AD conversion method, and the AD conversion circuit 713 includes a comparator 1001 and a latch unit 1002. A signal from the AD input line 753 and a reference signal are input to the input of the comparator 1001, and the output of the comparator 1001 is inverted when the high and low voltages of the two input signals are reversed. A count signal corresponding to the time elapsed from the start of AD conversion is input to the latch unit 1002, and the count signal at the timing when the output of the comparator 1001 is inverted (the timing when the voltage of the pixel signal and the voltage of the reference signal match) is held in the latch unit 1002. After the AD conversion is completed, the held signal is output to the output unit 741.

[0058] In addition, a power-down control signal is input to the comparator 1001 and the latch unit 1002, and when the power-down control signal is at a high level, the comparator 1001 and the latch unit 1002 are turned off (power supply is stopped) or the amount of current is reduced. This makes it possible to suppress the power consumption of the comparator and the latch unit when AD operation is not performed.

[0059] [First read mode: non-additive read mode] Next, the drive timing in the non-additive readout mode, which is the first readout mode of pixel signals, will be described with reference to Fig. 11. In the non-additive readout mode, a signal with high resolution can be obtained.

[0060] In FIG. 11, t501 to t515 indicate each timing (time). Also, φSEL indicates the control signal of SEL807. When φSEL is at the HIGH level, SEL807 turns on, and when it is at the LOW level, SEL807 turns off. The same applies to other switches.

[0061] The "VAD input line" in FIG. 11 shows the change state of the voltage of the AD input line 753, and the "V reference signal" shows the change state of the voltage of the reference signal. Note that in the non-additive readout mode, one column output line 704 corresponds to one AD input line 753, and there is no position dependency in the signal addition circuit 752. Also, the reference signals a to c (see FIG. 10) in the non-additive readout mode use the same signal for each column. Therefore, the "VAD input line", which is the voltage of the AD input line 753, and the "V reference signal", which is the reference signal voltage, are each explained using one in FIG. 11.

[0062] Pixel signal readout consists of N signal readout, N+A signal readout, and N+A+B signal readout. The N signal is a signal corresponding to the voltage of FD805 before transferring the charges accumulated in PDA201 and PDB202. The N+A signal is a signal corresponding to the voltage of FD805 after transferring the charges accumulated in PDA201. Further, the N+A+B signal is a signal corresponding to the voltage of FD805 after transferring the charges accumulated in PDA201 and PDB202. Hereinafter, the operation of signal readout will be described according to the timing chart of FIG. 11.

[0063] <N signal readout (time t501 to time t506)> At time t501, turn on SEL807 to connect SF808 and the column output line 704. Further, at times t501 and t502, turn RES806 on / off to set FD805 to the reset voltage before charge transfer. The VAD input line, which is the voltage of the AD input line 753, becomes a voltage (reset signal) corresponding to the FD reset voltage.

[0064] After the AD input line 753 is stabilized, at time t503, the AD counter 714 is driven to increment the count value at regular intervals. At the same time, the reference signal generation circuit 712 outputs a reference signal (from time t503 to time t505) so that the change amount (slope) of the voltage of the reference signal with respect to time or the count value is constant. In this embodiment, this period (from time t503 to time t505) is referred to as the N conversion period. Note that in this embodiment, since electrons are accumulated in the photoelectric conversion unit (hereinafter, PD), the reference signal is decreased from a high voltage. However, when holes are accumulated in the PD, the reference signal may be increased from a low voltage.

[0065] At time t504, when the voltage of the V reference signal and the VAD input line become the same, the output of the comparator 1001 is inverted, and the count value of the AD counter 714 is held in the latch unit 1002 as the N signal. In this embodiment, the AD counter 714 is configured as a common circuit, and the count value is transmitted to the latch of each column. However, the AD counter may be arranged in each column, and the time until the comparator 1001 is inverted may be counted by transmitting a clock signal.

[0066] <N+A signal readout (from time t506 to time t511)> Subsequently, at times t506 and t507, TXA803 is turned on / off to transfer the charge accumulated in the PDA201 to the FD805. The voltage of the FD805 drops by a voltage amount (ΔVFD) approximately proportional to the number of transferred charges, and the voltage of the VAD input line, which is the voltage of the AD input line 753, also drops by a voltage amount approximately proportional to ΔVFD. That is, the voltage drop amount ΔVAD input line of the AD input line 753 becomes a voltage approximately proportional to the amount of light incident on the PDA201.

[0067] Thereafter, similar to the N conversion period, the AD counter 714 is driven so that the count value is incremented every fixed time, and the reference signal generation circuit 712 outputs a reference signal so that the slope of the reference signal is constant (from time t508 to time t510). In the present embodiment, this period (from time t508 to time t510) is referred to as the N+A conversion period. The N+A conversion period is set longer than the N conversion period.

[0068] At time t509, when the V reference signal and the VAD input line have the same voltage, the output of the comparator 1001 is inverted, and the count value of the AD counter 714 is held in the latch section 1002 as the N+A signal.

[0069] <N+A+B signal readout (from time t511 to time t515)> Subsequently, at times t511 and t512, TXB804 is turned on / off to transfer the charge accumulated in PDB201 to FD805. The voltages of FD805 and the AD input line 753 each drop by a voltage approximately proportional to the number of transferred charges. Similar to the N+A signal, ΔVAD input line, which is the voltage drop amount of the AD input line 753, becomes a voltage approximately proportional to the amount of light incident on PDB202.

[0070] Thereafter, similar to the N+A conversion period, the AD counter 714 is driven so that the count value is incremented every fixed time, and the reference signal generation circuit 712 outputs a reference signal so that the slope of the reference signal is constant (from time t513 to time t515). In the present embodiment, this period (from time t513 to t515) is referred to as the N+A+B conversion period. In the present embodiment, the N+A+B conversion period is set to the same time as the N+A conversion period, but the N+A+B conversion period may be set longer than the N+A conversion period.

[0071] At time t514, when the V reference signal and the VAD input line have the same voltage, the output of the comparator 1001 is inverted, and the count value of the AD counter 714 is held in the latch section 1002 as the N+A+B signal.

[0072] From the difference between the N signal and the N+A signal thus obtained, a signal A corresponding to the amount of signal charge accumulated in the PDA 201 can be obtained. Also, from the difference between the N+A signal and the N+A+B signal, a signal B corresponding to the amount of signal charge accumulated in the PDB 202 can be obtained. The difference calculation may be performed within the AD conversion unit 711, or may be performed after output from the image sensor 107. A phase difference signal can be obtained by using each of the signals A and B, and an image signal can be obtained by adding together the signals A and B.

[0073] [Second readout mode: additive readout mode] Next, the driving timing in the additive readout mode, which is the second readout mode of pixel signals, will be described with reference to Figures 12A and 12B. Explanations of parts similar to those in the non-additive readout mode will be omitted, and only parts specific to the additive readout mode will be described. The additive readout mode reduces resolution, but can improve the signal-to-noise ratio of signals while suppressing power consumption compared to the non-additive readout mode.

[0074] Fig. 12A is a timing chart when the amount of received light is small and the amount of charge accumulated in the PDA 201 and the PDB 202 is small in the additive readout mode, and Fig. 12B is a timing chart when the amount of charge accumulated in the PDA 201 and the PDB 202 is large.

[0075] When the amount of received light is small, the signal S / N is more susceptible to the effect of readout dark random noise (DRN) than when the amount of received light is large, so reducing the DRN is effective in improving the signal S / N. On the other hand, when the amount of received light is large, the signal S / N is limited by the optical shot noise, so the signal S / N does not change significantly even if the DRN increases.

[0076] In the addition mode, the reference signals a, b, and c (see FIG. 10) are generated so that the start timing of the voltage drop (time change of voltage) is different. Specifically, as shown by times t603a, t603b, and t603c, the voltage drop starts in the order of reference signal a, reference signal b, and reference signal c. This is done to shift the inversion timing of the comparator 1001, which will be described later. Alternatively, the inversion timing may be shifted by other methods, such as shifting the reset voltage level of the comparator 1001 or shifting the start timing of operation.

[0077] In the addition mode, the addition switch 901 in the signal addition circuit 752 is turned on, and the voltage obtained by averaging the voltages of the column output lines 704 is input to the three comparators.

[0078] During the N conversion period, the comparators 1001(a), 1001(b), and 1001(c) (see FIG. 10) are input with the averaged signal of the output voltages of the three pixels and the reference signal. Since the reference signals a, b, and c are shifted in time, the inversion timings of the comparators 1001(a), 1001(b), and 1001(c) are different from each other, as shown by times t604a, t604b, and t604c. The count values ​​of the AD counter 714 at each timing are stored as N signal a, N signal b, and N signal c in the respective latch units 1002(a), 1002(b), and 1002(c) (see FIG. 10).

[0079] During the N+A conversion period and the N+A+B period, the AD conversion unit 713(b) and the AD conversion unit 713(c) are powered down by the power-down control signal 2, and power consumption is suppressed (reduced). Also, as in the N conversion period, time-shifted reference signals are input to the comparators 1001(a), 1001(b), and 1001(c). Therefore, when the amount of received light is small, the outputs of the comparators 1001(a), 1001(b), and 1001(c) are inverted at times t609a to t609c and times t615a to t615c, respectively, as shown in FIG. 12A, and the N+A signal a, N+A signal b, N+A signal c, N+A+B signal a, N+A+B signal b, and N+A+B signal c are acquired. If the amount of received light is small, after these signals are obtained, AD conversion units 713(b) and 713(c) are powered down, so that a signal with a good S / N ratio can be obtained even if the amount of received light is small.

[0080] On the other hand, when the amount of received light is large, the timing at which the voltage of the AD input line 753 and the voltage of the reference signal are inverted occurs after the timing at which the power-down control signal 2 is turned on (time t610, time t616). Therefore, as shown in Fig. 12B, the comparators 1001(b) and 1001(c) that are powered down by the power-down control signal 2 do not invert, and only the comparator 1001(a) is inverted (time t609a, time t615a). As a result, only the N+A signal a and the N+A+B signal a are acquired.

[0081] We will now explain how to calculate, from the signals thus acquired, a signal A3pix corresponding to the amount of signal charge accumulated in PDA201 for three pixels, and a signal B3pix corresponding to the amount of signal charge accumulated in PDB202 for three pixels.

[0082] The signal A3pix is ​​calculated by adding the value obtained by subtracting the N signal from the N+A signal only for the AD converters where the N+A signal is acquired, and then multiplying the result by a value α obtained by dividing 3 by the number of A signals acquired. That is, the formula is as follows.

[0083] Signal A3pix={([N+A signal a]-[N signal a])+([N+A signal b]-[N signal b]) +([N+A signal c]-[N signal c])}×α …Equation (1) α=3÷(N+A signal acquisition number) …Formula (2) Similarly, for the signal B3pix, only for the AD converters where the N+A+B signal is acquired, the value obtained by subtracting the N+A signal from the N+A+B signal is added, and then the result is multiplied by β, which is the value obtained by dividing 3 by the number of A+B signals acquired. That is, the following formula is obtained.

[0084] Signal B3pix = {([N+A+B signal a] - [N+A signal a]) +([N+A+B signal b]-[N+A signal b]) +([N+A+B signal c]-[N+A signal c])}×β …Equation (3) β=3÷(N+A+B signal acquisition number)...Formula (4) [About phase detection AF signal accuracy] Here, the accuracy of phase-difference AF will be described.

[0085] In phase-difference AF, the amount of image shift between signal A and signal B (hereafter referred to as phase-difference signals) is calculated (hereafter referred to as correlation calculation), and the amount of image shift is multiplied by a conversion coefficient to calculate the amount of focus shift (hereafter referred to as defocus amount). At this time, signals A and B used in the correlation calculation may each be used by adding together signals from multiple pixels. Therefore, the accuracy of the defocus amount calculation in phase-difference AF increases as the S / N ratio of the added phase-difference signals increases.

[0086] Here, the S / N ratios for the signals of three pixels in the non-additive reading mode and the additive reading mode are compared in the case of low illuminance where the influence of dark random noise (DRN) on the S / N ratio of the phase difference signal is large.

[0087] <Non-additive read mode> If the noise generated in one pixel unit is σpix and the noise generated in one AD conversion unit is σADC, the readout noise in the signal per pixel and per AD converter in the non-additive readout mode is expressed by the following equation.

[0088] σ(non-additive, 1 signal) = (σpix 2 +σADC 2 ) 1 / 2 …Formula (5) The total read noise of the three pixel signals is expressed by the following equation, since there is no correlation between the individual noises.

[0089] σ(non-additive, 3 pixels) = (3σpix 2 +3σADC 2 ) 1 / 2 ...Formula (6) <Additive read mode> In the additive readout mode, the voltage at the input of the AD conversion circuit is the average of the voltages for three pixels. Also, the pixel noise at the input of the AD conversion circuit is uncorrelated with each other, so it can be expressed by the following equation.

[0090] (3×σpix 2 ) 1 / 2 / 3 = 1 / (3 1 / 2 )×σpix Therefore, the read noise in the signal per AD converter is expressed by the following equation.

[0091] σ(addition, 1 pixel) = (1 / 3×σpix 2 +σADC 2 ) 1 / 2 …Formula (7) Furthermore, in the additive readout mode described above, the reference signals are shifted in time, so the timing at which the comparators in each AD converter invert also differs. When the inversion timings of the AD converters are separated sufficiently to the extent that the correlation of pixel noise can be considered to be eliminated, the total readout noise of the signals for three pixels is expressed by the following equation:

[0092] σ(addition, 3 pixels) = (σpix 2 +3σADC 2 ) 1 / 2 ...Formula (8) From equations (6) and (8), under low illuminance conditions where the amount of received light is small, the dark random noise (DRN) in the additive readout mode is lower than the DRN in the non-additive readout mode.

[0093] On the other hand, under high illuminance where the influence of DRN is small and the amount of received light is large, it is possible to power down some of the AD conversion circuits without using them, rather than using all of them, thereby suppressing power consumption. In addition, it is desirable to set the timing for turning on the power-down switch to the timing when the value of σ (sum, 3 pixels) becomes the same as the optical shot noise. In other words, it is desirable to turn on the power-down switch at a timing delayed from the start timing of AD conversion by a time equivalent to the time required to AD convert the pixel signal obtained with the amount of received light where the level of dark random noise is equal to the level of optical shot noise. Therefore, it is desirable to delay the timing for turning on the power-down switch later when reading out at a high sensitivity (high ISO sensitivity) with a large analog gain, compared to when reading out at a low sensitivity (low ISO sensitivity).

[0094] In addition, in this embodiment, a configuration has been described in which two of the three AD converters are powered down simultaneously, but the AD converters may be powered down stepwise one by one. Also, when there is a margin for power consumption, the power-down signal does not need to be turned on for both the N+A signal readout and the N+A+B signal readout.

[0095] Depending on the time required to restore the powered-down AD converter, the power-down switch may not be turned on when reading out the N+A signal, and may be turned on only when reading out the N+A+B signal. This configuration is more effective when the readout time per row is longer than the sum of the N signal readout, N+A signal readout, and N+A+B signal readout, such as when the readout time per row is combined with other readout modes.

[0096] As described above, according to the above embodiment, it is possible to reduce power consumption while suppressing degradation in the S / N performance of the output signal, regardless of the incident luminance.

[0097] The disclosure of this specification includes the following imaging apparatus, a control method thereof, a program, and a storage medium.

[0098] (Item 1) a pixel section in which pixels having photoelectric conversion elements are arranged in a matrix; an AD conversion unit arranged corresponding to each pixel column of the pixel unit and configured to convert a pixel signal obtained from the pixel into a digital signal; an adding means for adding pixel signals of N different columns (N is an integer of 2 or more); a control means for performing AD conversion on the pixel signals added by the adding means, using a plurality of AD converting means corresponding to the N columns, and controlling, during the AD conversion period, a portion of the plurality of AD converting means to switch to an operation that reduces power consumption after a predetermined time has elapsed since the start of the AD conversion; An imaging device comprising:

[0099] (Item 2) The imaging device described in item 1, wherein the AD conversion means has a comparison means for comparing the pixel signal with a reference signal whose value changes with respect to time at a predetermined slope, and a counting means for counting the time until the voltage of the pixel signal and the voltage of the reference signal match, and the control means reduces power supply to the comparison means and the counting means in the operation of reducing power consumption.

[0100] (Item 3) 3. The imaging device according to item 2, wherein the control means stops supplying power to the comparison means and the counting means during the operation of reducing power consumption.

[0101] (Item 4) 4. The imaging device according to any one of items 1 to 3, wherein the control means sets the predetermined time based on a level of dark random noise and a level of optical shot noise in the pixel signal.

[0102] (Item 5) The imaging device according to item 4, wherein the control means sets the predetermined time to a time equivalent to the time required for AD conversion of pixel signals obtained at an amount of received light at which the level of dark random noise and the level of optical shot noise are equivalent.

[0103] (Item 6) 6. The imaging device according to item 4 or 5, wherein the control means sets the predetermined time to a longer time as the ISO sensitivity increases.

[0104] (Item 7) 3. The imaging device according to item 2, wherein the control means controls the plurality of AD conversion means so that the timings at which the voltages of the pixel signals and the voltages of the reference signals match are different from each other.

[0105] (Item 8) 3. The imaging device according to item 2, wherein the control means causes the start timing of the operation of the comparison means to differ by a fixed time in the plurality of AD conversion means.

[0106] (Item 9) 3. The imaging device according to item 2, wherein the control means causes start timings of the time change of the reference signal input to the plurality of AD conversion means to differ by a fixed time.

[0107] (Item 10) 10. The imaging device according to any one of items 1 to 9, wherein the pixel has a plurality of photoelectric conversion elements that receive light beams that pass through different pupil regions of an imaging optical system.

[0108] (Item 11) The imaging device described in item 10, characterized in that the control means sequentially reads out a reset signal from the pixel, reads out signals from some of the photoelectric conversion elements of the plurality of photoelectric conversion elements, and reads out signals from all of the plurality of photoelectric conversion elements, and the control means controls some of the plurality of AD conversion means to switch to an operation that reduces power consumption when reading out signals from the some of the photoelectric conversion elements.

[0109] (Item 12) The imaging device described in item 11, characterized in that the control means controls some of the plurality of AD conversion means to switch to an operation that reduces power consumption when reading out signals from all of the photoelectric conversion elements.

[0110] (Item 13) A method for controlling an imaging device including a pixel section in which pixels having photoelectric conversion elements are arranged in a matrix, AD conversion means arranged corresponding to each pixel column of the pixel section and converting pixel signals obtained from the pixels into digital signals, and addition means for adding pixel signals of N different columns (N is an integer of 2 or more), comprising: a control step of: converting the pixel signals added by the adding means into analog-to-digital conversion using a plurality of AD conversion means corresponding to the N columns; and controlling, during the AD conversion period, some of the plurality of AD conversion means to switch to an operation that reduces power consumption after a predetermined time has elapsed from the start of the AD conversion.

[0111] (Item 14) Item 14. A program for causing a computer to execute the control method according to item 13.

[0112] (Item 15) A computer-readable storage medium storing a program for causing a computer to execute the control method according to item 13.

[0113] (Other embodiments) The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0114] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0115] 100: camera body, 105: focus lens, 107: imaging element, 121: camera CPU, 125: image processing circuit, 201: first photoelectric conversion unit, 202: second photoelectric conversion unit

Claims

1. a pixel section in which pixels having photoelectric conversion elements are arranged in a matrix; an AD conversion unit arranged corresponding to each pixel column of the pixel unit and configured to convert a pixel signal obtained from the pixel into a digital signal; an adding means for adding pixel signals of N different columns (N is an integer of 2 or more); a control means for performing AD conversion on the pixel signals added by the adding means, using a plurality of AD conversion means corresponding to the N columns, and controlling, during the AD conversion period, a portion of the plurality of AD conversion means to switch to an operation that reduces power consumption after a predetermined time has elapsed since the start of the AD conversion; An imaging device comprising:

2. 2. The imaging device according to claim 1, wherein the AD conversion means includes a comparison means for comparing the pixel signal with a reference signal whose value changes with respect to time at a predetermined gradient, and a counting means for counting the time until a voltage of the pixel signal and a voltage of the reference signal match, and the control means reduces power supply to the comparison means and the counting means in the operation for reducing power consumption.

3. 3. The imaging apparatus according to claim 2, wherein the control means stops supplying power to the comparison means and the counting means in the operation for reducing power consumption.

4. 2. The image pickup apparatus according to claim 1, wherein the control means sets the predetermined time based on a level of dark random noise and a level of optical shot noise in the pixel signal.

5. 5. The imaging device according to claim 4, wherein the control means sets the predetermined time to a time equivalent to the time required for AD conversion of a pixel signal obtained with an amount of received light at which a level of dark random noise and a level of optical shot noise are equivalent.

6. 5. The image pickup apparatus according to claim 4, wherein the control means sets the predetermined time to a longer time as the ISO sensitivity increases.

7. 3. The imaging apparatus according to claim 2, wherein the control means controls the plurality of AD conversion means so that the timings at which the voltages of the pixel signals and the voltages of the reference signals match are different from one another.

8. 3. The image pickup apparatus according to claim 2, wherein the control means causes the start timings of the operations of the comparison means to differ by a fixed time in the plurality of AD conversion means.

9. 3. The imaging apparatus according to claim 2, wherein the control means causes start timings of the time change of the reference signal input to the plurality of AD conversion means to differ by a fixed time.

10. 2. The image pickup apparatus according to claim 1, wherein the pixel has a plurality of photoelectric conversion elements each receiving a light beam passing through a different pupil region of an image forming optical system.

11. The imaging device described in claim 10, characterized in that the control means sequentially reads out a reset signal from the pixel, reads out signals from a portion of the plurality of photoelectric conversion elements, and reads out signals from all of the plurality of photoelectric conversion elements, and the control means controls a portion of the plurality of AD conversion means to switch to an operation that reduces power consumption when reading out signals from the portion of the photoelectric conversion elements.

12. 12. The imaging apparatus according to claim 11, wherein the control means controls some of the plurality of AD conversion means to switch to an operation that reduces power consumption when reading out signals from all of the photoelectric conversion elements.

13. A method for controlling an imaging device including a pixel section in which pixels having photoelectric conversion elements are arranged in a matrix, AD conversion means arranged corresponding to each pixel column of the pixel section and converting pixel signals obtained from the pixels into digital signals, and addition means for adding pixel signals of N different columns (N is an integer of 2 or more), comprising: A control method for an imaging device, comprising a control step of: A-D converting the pixel signals added by the adding means using a plurality of A-D conversion means corresponding to the N columns; and controlling, during the A-D conversion period, some of the plurality of A-D conversion means to switch to an operation that reduces power consumption after a predetermined time has elapsed from the start of the A-D conversion.

14. A program for causing a computer to execute the control method according to claim 13.

15. A computer-readable storage medium storing a program for causing a computer to execute the control method according to claim 13.

Images