JP7600861B2 - Imaging device - Google Patents

Description

The present invention relates to an imaging device.

Image sensors equipped with focus detection pixels that receive light beams that have passed through a partial area of the exit pupil of a photographing optical system are known (see, for example, Patent Document 1). There has long been a demand for improved accuracy in focus detection.

JP 2016-66051 A

According to a first aspect, an imaging device includes an imaging element having a focus state detection unit including a plurality of image plane phase difference detection units with different design pupil distances, the image plane phase difference detection units being arranged at different positions in a second direction intersecting the first direction as a detection direction, an imaging optical system that forms a subject image on an imaging surface of the imaging element, and an adder that generates a sum signal by adding detection signals output by two or more image plane phase difference detection units having a design pupil distance closest to an exit pupil distance of the imaging optical system, among a plurality of detection signals detected by the plurality of image plane phase difference detection units included in the focus state detection unit.

1 is a cross-sectional view illustrating a configuration of an imaging apparatus according to an embodiment. 4 is a diagram showing an example of a bundle of rays incident on an image surface phase difference detection unit from an imaging optical system. FIG. 2 is a plan view of the imaging element according to the embodiment, as viewed from the imaging surface side. FIG. 2 is a diagram showing an electric circuit included in a pixel. FIG. 4 is a diagram showing a state in which a light beam that has passed through an exit pupil is incident on an image surface phase difference detection unit. 4A and 4B are diagrams showing examples of the arrangement of image plane phase difference detection units in the focus state detection unit. 5A and 5B are diagrams showing examples of positions of focus state detection units on an image sensor. 11A and 11B are diagrams showing modified examples of the arrangement of an image plane phase difference detection unit in the focus state detection unit.

First Embodiment
FIG. 1 is a cross-sectional view that shows a schematic configuration of an image pickup device 1 according to a first embodiment and an image pickup optical system 2 that is attached to the image pickup device 1 when used.

The X, Y, and Z directions indicated by arrows in Fig. 1 are mutually orthogonal directions. Note that the X, Y, and Z directions indicated in the following figures are the same as the X, Y, and Z directions indicated in Fig. 1, respectively. The directions of the arrows are the +X, +Y, and +Z directions, respectively.
Hereinafter, a position in the X direction will be referred to as an X position, a position in the Y direction will be referred to as a Y position, and a position in the Z direction will be referred to as a Z position.

FIG. 1 is a cross-sectional view of an imaging device 1 and an imaging optical system 2 as viewed from the +X direction.
The imaging device 1 includes an imaging element 3 , an imaging control unit 4 , a lens driving unit 6 , a display unit 7 , an operation unit 8 , and a first communication unit 9 .
The imaging optical system 2 forms a subject image on an imaging surface 3s of the imaging element 3. The imaging optical system 2 includes an aperture 21 having an aperture 22, a front lens group 20a arranged closer to the subject than the aperture 21, a rear lens group 20b arranged closer to the imaging element 3 than the aperture 21, and a second communication unit 23. Each of the front lens group 20a and the rear lens group 20b may be composed of a plurality of lenses.

The aperture 21 may be an iridescent aperture, a light-blocking member having an opening with a specified diameter, or a lens that limits the effective diameter of the light beam passing through the imaging optical system 2 by the effective diameter of a specified lens. One of the front lens group 20a or the rear lens group 20b does not have to be provided.

The front lens group 20a or the rear lens group 20b, or at least one of the multiple lenses that make them up, may be a focus adjustment lens that is movable in the optical axis AX direction (Z direction) to adjust the focus of the imaging optical system 2.
In addition, the front lens group 20a or the front lens group 20a, or at least one of the multiple lenses that make them up, may be a variable magnification (zoom) lens that is movable in the optical axis AX direction (Z direction) to change the focal length of the imaging optical system 2.

At least a portion of the focal length of the imaging optical system 2, the aperture value (F-number), and the current position information of the lens that can move in the optical axis AX direction are transmitted from the second communication unit 23 of the imaging optical system 2 to the first communication unit 9 of the imaging device 1, and then transmitted to the imaging control unit 4.

The imaging element 3 captures an image of a subject and outputs a signal. The imaging control unit 4 controls each unit, such as the imaging element 3. The imaging control unit 4 performs image processing, etc. on the image signal output by the imaging element 3 to generate image data. The imaging control unit 4 records the image data on a recording medium (not shown) and performs processing such as displaying an image based on the image data on the display unit 7. The display unit 7 is a display device having a display member such as a liquid crystal panel.

The imaging control unit 4 further performs focus detection processing required for automatic focusing (AF) of the imaging optical system 2 using a known image plane phase difference detection method. Specifically, the imaging control unit 4 detects a phase difference, which is the amount of phase shift between at least a pair of focus detection signals output from the imaging element 3, as described below.

The imaging control unit 4 calculates the amount of deviation (defocus amount) between the imaging position of the subject in the imaging optical system 2 and the imaging surface 3s of the imaging element 3 based on the detected phase difference. Then, depending on the defocus amount, it calculates the amount of drive in the optical axis AX direction for focusing the focus adjustment lens described above in the imaging optical system 2. A signal corresponding to this drive amount is sent from the lens drive unit 6 via the first communication unit 9 and the second communication unit 23 to an actuator (not shown) in the imaging optical system 2, and the focus adjustment lens is moved in the optical axis AX direction, thereby automatically adjusting the focus.

Figure 2 is a cross-sectional view of the imaging device 1 and the imaging optical system 2 viewed from the -Y direction, and shows an example of a bundle of rays LRB passing through the imaging optical system 2 and entering one focus state detection unit FA on the imaging element 3.

The light beam LRB shown in FIG. 2 is refracted by the front lens group 20a, and then its diameter is restricted by the aperture 21. After passing through the aperture 22, the light beam LRB is refracted again by the rear lens group 20b, and enters the image side focus FP near the focus state detection unit FA of the image sensor 3. Here, the entrance side (+Z side) of the image sensor 3 is arranged so as to roughly coincide with the focusing point of the light beam LRB, i.e., the image side focus FP of the image sensor 2. In FIG. 2, the focus state detection unit FA of the image sensor 3 is arranged, as an example, at a position a distance X1 away from the optical axis AX of the image sensor 2 in the +X direction.

The exit pupil EP is a virtual image of the opening 22 of the diaphragm 21 formed by the rear lens group 20b as seen from the image-side focus FP. In other words, the exit pupil EP coincides with an XY plane that includes the intersection PCI between the optical axis AX and a line segment PRI, which is a linear extension of the optical path between the rear lens group 20b and the image sensor, of the principal ray LPR of the light beam LRB that passes through the intersection PC between the XY plane on which the diaphragm 21 is located and the optical axis AX. The intersection PCI can be said to be the center (center PCI) of the exit pupil EP.

In this specification, the distance in the Z direction from the exit pupil EP to the image-side focus FP is also referred to as the exit pupil distance LPD.
Also, as described above, the exit pupil EP is a virtual image of the opening 22 of the aperture 21 and is optically equivalent, so the light beam LRB passing through the opening 22 is also referred to as the light beam LRB passing through the exit pupil EP.

The exit pupil distance LPD of the imaging optical system 2, like the focal length and other information of the imaging optical system 2 described above, is transmitted from the second communication unit 23 of the imaging optical system 2 to the first communication unit 9 of the imaging device 1, and is then transmitted to the imaging control unit 4.

(Image sensor)
3 is a view of the imaging element 3 as viewed from the imaging surface 3s side, i.e., from the +Z side. The imaging element 3 has a semiconductor substrate 30 and a plurality of pixels 40 arranged in the X and Y directions on the semiconductor substrate 30. The arrangement of the pixels 40 in the X direction is also called a "row," and the arrangement of the pixels 40 in the Y direction is also called a "column." Although some of the pixels 40 are omitted in FIG. 2, a large number of pixels 40 may be arranged in each of the X and Y directions, for example, 1000 or more.

Each of the pixels 40 has a higher spectral sensitivity to one of three different wavelengths of light than to the other wavelengths. The pixels 40 marked with R (hereinafter also referred to as "R pixels") have a high spectral sensitivity to red light, the pixels 40 marked with G (hereinafter also referred to as "G pixels") have a high spectral sensitivity to green light, and the pixels 40 marked with B (hereinafter also referred to as "B pixels") have a high spectral sensitivity to blue light. These RGB pixels 40 are arranged in the imaging area in, for example, a Bayer array.
The above-mentioned spectral sensitivities of the R, G and B pixels are set, for example, by color filters (to be described later) provided in each pixel 40 .

A horizontal control unit 31H is provided at the left end of the effective imaging area IA, which is an area in which a plurality of pixels 40 are arranged, in FIG. 3, and a vertical control unit 31V is provided at the top end of the effective imaging area IA. The horizontal control unit 31H and the vertical control unit 31V are also referred to as the control unit 31, either together or individually.

A number of control lines 32 extend from the horizontal control unit 31H in the X direction, and each control line 32 is connected to a number of pixels 40 arranged in a row in the X direction among the number of pixels 40. A signal line 33 is connected to each of a number of pixels 40 arranged in a column in the Y direction among the number of pixels 40 in the imaging element 3.

Each of the pixels 40 generates a signal based on the amount of light incident thereon within a predetermined imaging period. The signal generated by the pixel 40 connected to one or more control lines 32 to which a predetermined control voltage is applied from the horizontal control unit 31H is read out by a predetermined readout unit 34 via a signal line 33 connected to the pixel 40. As an example, the signal output from each pixel 40 is an analog signal, and the readout unit 34 is an analog/digital converter that converts the analog signal into a digital signal (A/D conversion).
The signals from the pixels 40 that have been subjected to A/D conversion or the like by the readout unit 34 are output as output signals Sg from the output unit 36 of the imaging element 3 via the data lane 35 to the imaging control unit 4 .

Some of the pixels 40 are a first AF pixel P and a second AF pixel M for detecting a pair of detection signals used in the focus detection process required for AF of the imaging optical system 2 in the phase difference detection method described above. The first AF pixel P is a pixel 40 marked with the symbol P, and the second AF pixel M is a pixel 40 marked with the symbol M.

The first AF pixels P are arranged in a line in the X direction at a predetermined position in the Y direction. The first AF pixels P arranged in a line in the X direction at the same Y position are also called the first detection unit F1. The signal output from the first detection unit F1 is the first detection signal, which is one of the pair of detection signals described above.

The second AF pixels M are also arranged in a line in the X direction at a predetermined position in the Y direction different from the first detection unit F1. The second AF pixels M arranged in a line in the X direction at the same Y position are also referred to as the second detection unit F2. The signal output from the second detection unit F2 is the other second detection signal of the pair of detection signals described above.

In Figure 2, for convenience of illustration, a G pixel G is included within the dashed frame indicating the first detection unit F1 and the second detection unit F2, but the first detection unit F1 and the second detection unit F2 do not have to include the G pixel G.
2, the first detection unit F1 and the second detection unit F2 are arranged from approximately the end on the -X side to approximately the end on the +X side of the effective imaging area IA, but the first detection unit F1 and the second detection unit F2 may be arranged in a part of the effective imaging area IA in the X direction. Also, the first detection unit F1 and the second detection unit F2 may be arranged in a plurality of discrete positions in the X direction of the effective imaging area IA.

A pair of one first detection unit F1 and one second detection unit F2 is also called an image plane phase difference detection unit FS. The image plane phase difference detection unit FS generates a pair of detection signals for detecting the phase difference between the phase of the intensity distribution in the X direction of the image of the imaging optical system 2 formed in the first detection unit F1 and the phase of the intensity distribution in the X direction of the image of the imaging optical system 2 formed in the second detection unit F2.

The X direction in which the first AF pixel P and the second AF pixel M are arranged side by side can be referred to as the detection direction or the first direction, and the Y direction can be referred to as the second direction.
The first AF pixel P and the second AF pixel M together or individually are also referred to as AF pixels.
On the other hand, among the plurality of pixels 40, the pixels other than the AF pixels (R pixels, G pixels, B pixels) are collectively or individually referred to as imaging pixels.

As an example, the first AF pixel P and the second AF pixel M are both arranged in a position where a B pixel would be arranged in the original Bayer array. However, the first AF pixel P and the second AF pixel M may both be arranged in a position where an R pixel would be arranged in the original Bayer array.

In FIG. 3, the distance in the Y direction between the first detection unit F1 and the second detection unit F2 is such that five pixels 40 are arranged therebetween, but the distance may be such that any odd number of pixels 40, such as three or seven, are arranged therebetween.

4 is a diagram showing an electric circuit included in a pixel 40. The pixel 40 includes a photoelectric conversion unit 41 and an amplifier circuit 42. The structure of the pixel 40 will be described later.
The photoelectric conversion unit 41 is composed of a photodiode or the like, and performs photoelectric conversion on incident light. When a transfer signal is input to the transfer unit TX, the charge generated by the photoelectric conversion in the photoelectric conversion unit 41 is transferred to the storage unit FD by the transfer unit TX. A predetermined voltage VDD is supplied from a power source to the amplification unit TA, and a signal corresponding to the charge transferred to the storage unit FD is amplified and output to the selection unit TS.

A control line 32 is connected to the selection unit TS. When a predetermined signal is input from the horizontal control unit 31 H to the control line 32 , the signal output from the selection unit TS is output to a signal line 33 .
A predetermined voltage VDD is supplied to the reset unit TR from a power supply, and when a reset signal is input to the reset unit at a predetermined timing, the reset unit becomes conductive and the storage unit FD is reset to the voltage VDD.

The transfer unit TX, the amplification unit TA, the selection unit TS, and the reset unit TR may be MOS transistors, and the electrical circuit that constitutes the pixel 40 may be similar to the electrical circuit included in the pixel of a conventional so-called four-transistor CMOS image sensor, for example.
The transfer signal and reset signal described above may be supplied from the horizontal control unit 31H via a control line extending in the X direction similar to the control line 32.

Hereinafter, the configuration of the pixel 40 including the first AF pixel P and the second AF pixel M will be described with reference to FIGS.
FIG. 5 is an enlarged view of the image plane phase difference detection unit FS (see FIG. 3) included in the focus state detection unit FA shown in FIG.
FIG. 5A is a diagram showing an XZ cross-sectional view of a pixel 40 (the G pixel G and the first AF pixel P) in the first detection unit F1 (see FIG. 3) included in the image surface phase difference detection unit FS.
FIG. 5B is a diagram showing an XZ cross-sectional view of the pixels 40 (the G pixel G and the second AF pixel M) in the second detection unit F2 (see FIG. 3) included in the image surface phase difference detection unit FS.

As shown in FIG. 5(a) and FIG. 5(b), the semiconductor substrate 30 is, for example, a stack of an upper substrate 30a on which a photoelectric conversion unit 41 such as a photodiode and an amplifier circuit 42 are formed, and a lower substrate 30b on which a wiring layer is formed. The upper substrate 30a and the lower substrate 30b may be electrically connected via bumps.

A transparent protective film 43 is formed on the upper substrate 30a (in the +Z direction), and the above-mentioned color filter 44 is formed above the protective film 43. A microlens 45 that focuses light to be captured on the photoelectric conversion unit 41 is formed above the color filter 44.
Light irradiated onto the pixel 40 from above (+Z direction) is refracted by the microlens 45 , and the wavelength range of the transmitted light is roughly selected by the color filter 44 , after which the light enters the photoelectric conversion unit 41 .

The color filter 44 arranged in the first AF pixel P and the second AF pixel M may be a color filter that preferentially transmits any one of the above-mentioned blue light, green light, or red light, or may be a color filter that preferentially transmits any two of the above-mentioned blue light, green light, and red light, or may be a filter that transmits the entire range of visible light or a filter that transmits infrared light.

The photoelectric conversion section 41 may be a photodiode formed in the upper substrate 30a, or may be a photoelectric conversion section made of an organic film formed above (on the +z side) the upper substrate 30a.
In addition, when the spectral sensitivity of the photoelectric conversion unit 41 itself differs between the multiple pixels 40, the color filter 44 may be omitted.

As shown in FIG. 5(a), the first AF pixel P has a first light-shielding portion 46P on the upper end (+Z end) of the photoelectric conversion unit 41 that blocks light incident on the +X side of the photoelectric conversion unit 41. Also, as shown in FIG. 5(b), the second AF pixel M has a second light-shielding portion 46M on the upper end (+Z end) of the photoelectric conversion unit 41 that blocks light incident on the -X side of the photoelectric conversion unit 41.

Figure 6 is a diagram showing the state in which a light beam LRB that has passed through the exit pupil EP of the imaging optical system 2 is incident on the first AF pixel P and the second AF pixel M included in the image plane phase difference detection unit FS in the focus state detection unit FA of the image sensor 3, and shows an XZ cross section of the image sensor 3 viewed from the -Y direction.
In addition, in FIG. 6, the first AF pixel P and the second AF pixel M, which are arranged at the same X position in the image surface phase difference detection unit FS, i.e., arranged so as to overlap in the depth direction of the paper surface, are shown overlapping each other.

The distance in the Z direction between the vertex 45c of the microlens 45 and the first light shielding portion 46P or the second light shielding portion 46M is defined as a distance DML.
The first light-shielding portion 46P and the second light-shielding portion 46M are disposed at a Z position Z1 that is approximately conjugate (in an imaging relationship) with the exit pupil EP of the above-described imaging optical system 2 via the microlens 45. In other words, the first light-shielding portion 46P and the second light-shielding portion 46M are disposed at a Z position Z1 that is approximately conjugate with the aperture 21 of the above-described imaging optical system 2 via the microlens 45 and the rear lens group 20b (see FIG. 4).

For this reason, a large amount of light that has passed through the exit pupil EP on the +X side of the optical axis AX is incident on the photoelectric conversion unit 41 of the first AF pixel P. Also, a large amount of light that has passed through the exit pupil EP on the -X side of the optical axis AX is incident on the photoelectric conversion unit 41 of the second AF pixel M.
The photoelectric conversion unit 41 of the first AF pixel P can also be said to be a first light receiving unit that detects more light that has passed through the + side (one side) in the X direction of the exit pupil EP of the imaging optical system 2 than light that has passed through the - side (the other side) in the X direction of the exit pupil.
The photoelectric conversion unit 41 of the second AF pixel M can also be said to be a second light receiving unit that detects more light that has passed through the - side in the X direction of the exit pupil EP of the imaging optical system 2 (the other side mentioned above) than light that has passed through the + side in the X direction of the exit pupil (the one side mentioned above).

The focus state detection unit FA shown in Figures 2 and 6 is, as an example, located at the center of the image sensor 3 in the X direction and at a position a distance X1 away in the +X direction from the optical axis AX of the imaging optical system 2. Therefore, the light beam LRB enters the focus state detection unit FA from a direction centered on a direction slightly tilted in the -X direction from the +Z direction.

In response to this, in order to increase the light receiving efficiency of the photoelectric conversion unit 41, in each pixel 40 of the focus state detection unit FA, the center position in the X direction of the microlens 45 is shifted in the -X direction with respect to the center position in the X direction of the photoelectric conversion unit 41. In other words, the center position in the X direction of the photoelectric conversion unit 41 is shifted in the +X direction with respect to the center position in the X direction of the microlens 45.

For this reason, as shown in FIG. 5(a), the position of the -X side edge 46PE of the first light-shielding portion 46P in the first AF pixel P is shifted to the +X side by a distance XP from the vertex 45c of the microlens 45 (the point closest to the +Z side). Also, as shown in FIG. 5(b), the position of the +X side edge 46ME of the second light-shielding portion 46M in the second AF pixel M is shifted to the +X side by a distance XM from the vertex 45c of the microlens 45.

The vertex 45c of the microlens 45 is disposed at a distance X1 from the optical axis AX in the +X direction. The distance in the Z direction between the exit pupil EP and the vertex 45c of the microlens 45 is the exit pupil distance LPD. Therefore, the principal ray LPR of the light beam LRB that passes through the center PCI of the exit pupil EP and is incident on the vertex 45c of the microlens 45 of the first AF pixel P and the second AF pixel M advances in a direction inclined from the -Z direction toward the +X direction by an angle θ determined by the following equation (1).
tan(θ) = X1/LPD...(1)

That is, the principal ray LPR travels in a direction inclined by an angle θ with respect to both the optical axis AX parallel to the Z direction and the normal NL to the imaging surface 3s of the image sensor 3.
The principal ray LPR is refracted near the vertex 45c of the microlens 45, passes through the microlens 45, the color filter 44, and the protective film 43, and is blocked by the first light-shielding portion 46P or the second light-shielding portion 46M, or is incident on the photoelectric conversion portion 41.

The distance in the X direction from the vertex 45c of the microlens 45 to the principal ray LPR at the Z position Z1 where the first light shielding portion 46P or the second light shielding portion 46M is disposed is defined as a distance XC. From a geometrical optical viewpoint, the distance XC can be approximately calculated by the following formula (2).
XC = tan(θ)×DML/n...(2)

Here, the distance DML is the distance in the Z direction between the vertex 45c of the microlens 45 and the first light shielding portion 46P or the second light shielding portion 46M, as described above, and n is the refractive index of the lens material that constitutes the microlens 45.
Moreover, the following formula (3) can be derived from formulas (1) and (2).
XC = X1 x DML/(n x LPD)...(3)

At this time, if the distance XC is equal to the average value of the above-mentioned distances XP and XM, the amount of light incident on the photoelectric conversion unit 41 of the first AF pixel P and the amount of light incident on the photoelectric conversion unit 41 of the second AF pixel M can be made approximately equal. In other words, the amount of light that passes through the +X side of the exit pupil EP and enters the photoelectric conversion unit 41 without being blocked by the first light-shielding unit 46P of the first AF pixel P can be made approximately equal to the amount of light that passes through the -X side of the exit pupil EP and enters the photoelectric conversion unit 41 without being blocked by the second light-shielding unit 46M of the second AF pixel M. Therefore, the accuracy of the focus position detection of the image plane phase difference detection unit FS can be improved at this time.

Conversely, once the distances X1, DML, XP, and XM, which are quantities related to the configuration of the image plane phase difference detection unit FS, and the refractive index n, are determined, the value of the exit pupil distance LPD suitable for that focus state detection unit FA can be found. Hereinafter, the exit pupil distance LPD suitable for a given image plane phase difference detection unit FS is also referred to as the design pupil distance DPD of the image plane phase difference detection unit FS.

As an example, the designed pupil distance DPD can be obtained by transforming equation (3) by substituting the above-mentioned condition XC = (XP + XM) / 2 and replacing the exit pupil distance LPD with the designed pupil distance DPD, as given by the following equation (4).
DPD = X1 x DML/{n x (XP+XM)/2}...(4)

To improve the accuracy of focus position detection by the image plane phase difference detection unit FS, it is desirable to match its design pupil distance DPD with the exit pupil distance LPD of the imaging optical system 2. However, the exit pupil distance LPD differs depending on the imaging optical system 2, and if the imaging optical system 2 is a zoom lens, the exit pupil distance LPD also varies with zooming. For this reason, it is difficult to always match the design pupil distance DPD of one image plane phase difference detection unit FS with the exit pupil distance LPD of the imaging optical system 2.

Therefore, in the image sensor 3 of the first embodiment, as shown in FIG. 7, a single focus state detection unit FA is provided with multiple image plane phase difference detection units FS (FSA to FSE) each with a different design pupil distance DPD. Each of the image plane phase difference detection units FSA to FSE includes a first detection unit F1 (F1A to F1E) and a second detection unit F2 (F2A to F2E).

The first AF pixels P included in each of these first detection units F1A to F1E have mutually different distances XP, as an example, which are described above. The second AF pixels M included in each of these second detection units F2A to F2E have mutually different distances XM, as an example, which are described above. As a result, the designed pupil distances DPD of the image plane phase difference detection units FSA to FSE have different values.

In the imaging device 1 of the first embodiment, the imaging control unit 4 selects an image plane phase difference detection unit FS having a design pupil distance DPD close to the exit pupil distance LPD of the imaging optical system 2 from the image plane phase difference detection units FSA to FSE, and detects the focal position using a detection signal from the selected image plane phase difference detection unit FS. This makes it possible to detect the focal position with high accuracy even when the attached imaging optical system 2 is replaced or when the imaging optical system 2 is zoomed.

The number of image plane phase difference detection units FSA to FSE provided in one focus state detection unit FA is not limited to the above-mentioned five, and may be any number m (m is a natural number equal to or greater than 2). The exit pupil distance LPD of each of the image plane phase difference detection units FSA to FSE may be any length between about 10 mm and about 150 mm, for example. As a further example, it may be any length between about 0.6 times the diagonal length of the effective imaging area IA of the image sensor 3 and about 5 times the length.

The exit pupil distances LPD of the multiple image plane phase difference detection units FSA to FSE may be set so that they increase at approximately equal intervals between the minimum and maximum values. Alternatively, the inclination angle θ of the principal ray LPR incident on the first AF pixel P and the second AF pixel M from the exit pupil EP at each exit pupil distance LPD with respect to the normal line NL shown in FIG. 6 may be set so that it increases at approximately equal intervals between the minimum and maximum values.

In the first AF pixels P included in each of the first detection units F1A to F1E, instead of or in addition to the distance XP described above, the values of the distance DML described above may be different from each other. Also, in the second AF pixels M included in each of the second detection units F2A to F2E, instead of or in addition to the distance XM described above, the values of the distance DML described above may be different from each other.

In addition, the exit pupil distance LPD of each of the multiple image plane phase difference detection units FSA to FSE may monotonically increase or decrease according to the respective Y positions, or may change randomly regardless of the respective Y positions.

In FIG. 7, to avoid complicating the drawing, the imaging pixels (G pixels G, B pixels B, and R pixels R) arranged between the first detection units F1A-F1E and the second detection units F2A-F2E in the Y direction are omitted. However, within one focus state detection unit FA, for example, three or more imaging pixels may be arranged between the first detection units F1A-F1E and the second detection units F2A-F2E in the Y direction.

The distance in the Y direction between the first detection units F1A-F1E and the second detection units F2A-F2E in one image surface phase difference detection unit FSA-FSE can be referred to as a first distance P1. Also, the distance in the Y direction between each of the multiple image surface phase difference detection units FSA-FSE can be referred to as a second distance P2. The second distance P2 may be longer than the first distance P1.
Conversely, the second distance P2 may be shorter than the first distance P1.

However, when using the imaging device 1 to capture an image, for example, under low illuminance conditions, the amount of light in the light beam LRB from the subject decreases, which reduces the S/N ratio of the detection signal obtained from one of the image plane phase difference detection units FSA to FSE. In this case, there is a risk that the accuracy of the detection of the focal position by the image plane phase difference detection units FSA to FSE will decrease.

In the imaging device 1 and imaging element 3 of the embodiment, some of the detection signals detected by the focus state detection units FA arranged at different positions in the Y direction are added together to generate a sum signal, and the sum signal is used as the detection signal to improve the accuracy of detecting the focus position.

Specifically, signals generated by multiple first AF pixels P at the same X position but different Y positions within multiple image plane phase difference detection units FSA-FSE within one focus state detection unit FA are added together. Similarly, signals generated by multiple second AF pixels M at the same X position but different Y positions within multiple image plane phase difference detection units FSA-FSE within one focus state detection unit FA are added together.

As one example, the addition of multiple detection signals is performed by so-called source follower addition. That is, signals generated by multiple first AF pixels P included in different focus state detection units FA and located at the same X position are outputted approximately simultaneously to a signal line 33 connected to those first AF pixels P. Similarly, signals generated by multiple second AF pixels M included in different focus state detection units FA and located at the same X position are outputted approximately simultaneously to a signal line 33 connected to those second AF pixels M. These added signals on the signal line 33 are then read out by a readout unit 34.

The horizontal control unit 31H sends a control signal via a control line 32 to the first AF pixel P or the second AF pixel M, whose signals are added together, and causes the signals from these pixels to be output to a signal line 33 substantially simultaneously.
In this case, the signal line 33 and the readout unit 34 constitute an adder that adds at least two of the multiple detection signals to generate an added signal.

The addition of the multiple detection signals may be performed by other configurations. For example, the output section 36 of the image sensor 3 may be provided with a memory for temporarily storing the digital signals output from the predetermined AF pixels (P, M) via the data lane 35, and an adder circuit for adding the signals from the predetermined multiple AF pixels, and the multiple detection signals may be added by this adder circuit.
In this case, the adder circuit provided in the output section 36 of the image sensor 3 constitutes an adder section that adds at least two of the multiple detection signals to generate a sum signal.

These memories and summing circuits may be provided as summing circuit section 5 in imaging control section 4, rather than in imaging element 3. In this case, the summing section that adds at least two of the multiple detection signals to generate a summed signal is included in imaging control section 4.

As an example, the sum signal is generated by adding detection signals from image plane phase difference detection units FS whose designed pupil distance DPD is closest to the exit pupil distance LPD of the imaging optical system 2 from the first to the kth closest (k is a natural number equal to or less than m). As an example, the exit pupil distance LPD of the imaging optical system 2 is 100 mm, and the designed pupil distances DPD of the multiple image plane phase difference detection units FSA to FSE are 50 mm, 70 mm, 90 mm, 110 mm, and 130 mm, respectively. In this case, as an example, the summation unit adds detection signals from two (k=2) image plane phase difference detection units FS whose designed pupil distances DPD are 90 mm and 110 mm.

As described above, in order to improve the accuracy of the focus position detection by the image plane phase difference detection unit FS, it is desirable to match its design pupil distance DPD with the exit pupil distance LPD of the imaging optical system 2. For this reason, if a sum signal is generated by adding detection signals from an image plane phase difference detection unit FS having a design pupil distance DPD that is significantly different from the exit pupil distance LPD of the imaging optical system 2, there is a risk that the accuracy of the focus position detection will decrease.

Therefore, when generating the sum signal, the number of detection signals to be added may be changed based on the amount of light in the light beam LRB, i.e., the magnitude of the detection signal from the image plane phase difference detection unit FS. In other words, when the amount of light incident on the imaging element 3 is small and the intensity of the imaging signal output by the imaging element 3 is small, the adder may add more detection signals than when the intensity of the imaging signal is large. Here, the imaging signal output by the imaging element 3 may be a detection signal output by an AF pixel, or may be an image formation signal output by an imaging pixel (G pixel G, B pixel B, R pixel R).

The impact on the accuracy of focus position detection due to the mismatch between the exit pupil distance LPD of the imaging optical system 2 and the designed pupil distance DPD of the image plane phase difference detection unit FS is greater as the aperture value (F-number) of the imaging optical system 2 increases. Therefore, when generating the sum signal, the adder may add more detection signals when the aperture value of the imaging optical system 2 is small than when the aperture value of the imaging optical system 2 is large.

Incidentally, the impact on the accuracy of focus position detection due to the mismatch between the exit pupil distance LPD of the imaging optical system 2 and the designed pupil distance DPD of the image plane phase difference detection unit FS also depends on the position of the focus state detection unit FA in the image sensor 3. That is, when the focus state detection unit FA is located near the center of the detection direction (X direction) of the effective imaging area IA, that is, close to the detection direction from the optical axis AX of the imaging optical system 2, the impact is small, but when the focus state detection unit FA is away from the optical axis AX in the detection direction, the impact is large.

Therefore, when generating the sum signal, the adder may add more detection signals when the position of the focus state detection unit FA in the detection direction (X direction) is close to the center of the image sensor 3 than when the position of the focus state detection unit FA in the first direction is far from the center of the image sensor 3.

Figure 8 shows some examples of the positions of the focus state detection units FA (FA1 to FA6) on the image sensor 3. For example, in the focus state detection units FA1 and FA2 whose X-direction distance from the X-direction center CL of the effective imaging area IA on the imaging surface 3s of the image sensor 3 is less than distance D1, all of the detection signals from the m image surface phase difference detection units FS may be added together.

On the other hand, the adder may add k1 detection signals for focus state detection units FA5 and FA6 whose X-direction distance from the center CL is equal to or greater than distance D2, and may add k2 detection signals for focus state detection units FA3 and FA4 whose X-direction distance from the center CL is equal to or greater than distance D1 and less than distance D2. Here, k1 and K2 are both natural numbers, and 1≦k1<k2<m.

Note that if there are multiple focus state detection units FA (FA1 to FA6) within the effective imaging area IA, the adder may determine a method for adding detection signals from all focus state detection units FA according to the position of the selected focus state detection unit FA in the detection direction (X direction). In other words, when the position of the selected focus state detection unit FA in the X direction is close to the center of the image sensor 3, the adder may add more detection signals from the image plane phase difference detection unit FS in the multiple focus state detection units FA compared to when it is farther from the center of the image sensor 3.

Which of the multiple focus state detection units FA to select may be input by the user through the operation unit 8, or may be determined by the imaging control unit 4 based on the image output from the imaging element 3.

In the above, one focus state detection unit FA is described as including multiple image plane phase difference detection units FS each having a different design pupil distance DPD, but one focus state detection unit FA may also include image plane phase difference detection units FS having the same design pupil distance DPD. In this case, the adder may add detection signals from image plane phase difference detection units FS having the same design pupil distance DPD.

As an example of such a focus state detection section FA, a plurality of focus state detection sections FA shown in FIG. 7 may be arranged closely to each other in the Y direction at the same X position.
Alternatively, a plurality of image plane phase difference detection units FS having the same design pupil distance DPD may be arranged in close proximity to each other in the Y direction as a group, and a group of image plane phase difference detection units FS having a different design pupil distance DPD may be arranged at a position relatively distant from the group in the Y direction.

Depending on the imaging device 1, the size of the effective imaging area IA on the imaging element 3 may be changeable. For example, the size of the effective imaging area IA may be switchable between a so-called 35 mm full frame size and a smaller size. Changing the effective imaging area IA may change the optimal detection conditions of the image plane phase difference detection unit FS. Therefore, the adder may change the number of detection signals to be added depending on the size of the effective imaging area IA of the imaging element 3.

(Modification of Arrangement of Image Plane Phase Difference Detection Unit)
FIG. 9 is a diagram showing a modified example of the arrangement of the image plane phase difference detection section FS in the focus state detection section FA.
In the first embodiment described above, in the focus state detection unit FA, the first AF pixel P and the second AF pixel M, which are AF pixels, are both arranged at positions where the B pixel B (or the R pixel R) should be arranged in the original Bayer array. For this reason, the X positions of the AF pixels are arranged at intervals of two pixels 40.

In the modified arrangement shown in FIG. 9, the AF pixels are arranged at the B pixel B position of the original Bayer array in the image plane phase difference detection units FSA, FSC, and FSE that are odd-numbered in the Y direction, and are arranged at the R pixel R position in the image plane phase difference detection units FSBs and FSDs that are even-numbered in the Y direction. Therefore, inside the focus state detection unit FA, the X positions of the AF pixels are arranged at intervals of one pixel 40.

Therefore, in the arrangement of this modified example, the sampling density by the first AF pixel P and the second AF pixel M, which are AF pixels for the image formed by the imaging optical system 2, is improved, making it possible to perform image plane phase difference detection with higher accuracy.

Note that the example in Figure 9 is just one example, and the AF pixel may be arranged at the position of the R pixel R in the original Bayer array in the image plane phase difference detection units FSA, FSC, and FSE that are odd-numbered in the Y direction, and may be arranged at the position of the B pixel B in the image plane phase difference detection units FSBs and FSDs that are even-numbered in the Y direction.

In the above embodiments and modifications, for example, as described above, when the adder section is configured by the signal line 33 and the readout section 34, or when the adder section is configured by an adder circuit provided in the output section 36 of the image sensor 3, the image sensor 3 can also be said to be an imaging device. The adder circuit may be provided stacked on the imaging section of the image sensor 3.

(Effects of the embodiment and modified examples)
According to the above-described embodiment, the following advantageous effects can be obtained.
(1) The imaging device 1 in each of the above embodiments has an imaging element 3 having a focus state detection unit FA that has a first direction (X direction) as a detection direction and includes a plurality of image plane phase difference detection units FS each having a different design pupil distance DPD, the image plane phase difference detection units FS being arranged at different positions in a second direction (Y direction) that intersects the first direction, and an adder unit (reader unit 34, etc., or imaging control unit 4) that generates a sum signal by adding at least two of the plurality of detection signals detected by the plurality of image plane phase difference detection units FS included in the focus state detection unit FA.
With this configuration, it is possible to improve the accuracy of detecting the focal position of an object even in low-illumination conditions.

(2) The image surface phase difference detection unit FS may include a first detection unit F1 in which a plurality of first light receiving units (photoelectric conversion units 41 of the first AF pixel P) are arranged in the first direction, and the first detection unit F2 in which a plurality of second light receiving units (photoelectric conversion units 41 of the second AF pixel M) are arranged in the first direction, and the second ...
With this configuration, it is possible to further improve the accuracy of detecting the focal position of an object even under low illuminance conditions.

(3) When the amount of light incident on the image sensor 3 is small and the intensity of the image signal output by the image sensor 3 is small, the adder may add more detection signals than when the intensity of the image signal is large. In this case, when the amount of light incident on the image sensor 3 is small and the intensity of the image signal output by the image sensor 3 is small, the S/N ratio of the detection signal can be improved by adding more detection signals, thereby enabling highly accurate focus position detection. On the other hand, when the amount of light incident on the image sensor 3 is large and the intensity of the image signal output by the image sensor 3 is large, the detection signal with the highest detection accuracy, i.e., the detection signal from the image plane phase difference detection unit FS whose designed pupil distance DPD is closest to the exit pupil distance LPD of the imaging optical system 2, is preferentially used to enable highly accurate focus position detection.

(4) When the aperture value (F-number) of the imaging optical system 2 is small, the adder may add more detection signals than when the aperture value of the imaging optical system 2 is large. When the aperture value (F-number) of the imaging optical system 2 is small, the impact on the accuracy of focus position detection due to the mismatch between the exit pupil distance LPD of the imaging optical system 2 and the design pupil distance DPD of the image plane phase difference detection unit FS is small. Therefore, when the aperture value of the imaging optical system 2 is small, the improvement in focus position detection accuracy due to the improvement in the detection signal S/N by adding up many detection signals is greater than the decrease in focus position detection accuracy due to the mismatch between the exit pupil distance LPD and the design pupil distance DPD. This allows for highly accurate focus position detection.

(5) The image sensor 3 has a plurality of focus state detection units FA, and the adder may add more detection signals when the position of the focus state detection unit FA in the first direction is close to the center of the image sensor 3 than when the position of the focus state detection unit FA in the first direction is far from the center of the image sensor 3. When the position of the focus state detection unit FA in the first direction is close to the center of the image sensor 3, the impact on the accuracy of the focus position detection due to the mismatch between the exit pupil distance LPD of the imaging optical system 2 and the design pupil distance DPD of the image plane phase difference detection unit FS is small. When the position of the focus state detection unit FA in the first direction is close to the center of the image sensor 3, the improvement in the accuracy of the focus position detection due to the improvement in the detection signal S/N by adding up many detection signals is greater than the decrease in the accuracy of the focus position detection due to the mismatch between the exit pupil distance LPD and the design pupil distance DPD. This allows for highly accurate focus position detection.

Although various embodiments and modifications have been described above, the present invention is not limited to these. Furthermore, each embodiment and modification may be applied alone or in combination. Other aspects that are conceivable within the technical scope of the present invention are also included within the scope of the present invention.

1: Imaging device, 2: Imaging optical system, 3: Imaging element, 4: Imaging control unit, 6: Lens driving unit, 7: Display unit, 8: Operation unit, 30: Semiconductor substrate, 31: Control unit, 40: Pixel, P: First AF pixel, M: Second AF pixel, F1: First detection unit, F2: Second detection unit, FS: Image surface phase difference detection unit, 32: Control line, 33: Signal line, 34: Readout unit, 36: Output unit, 41: Photoelectric conversion unit, 42: Amplification circuit, 44: Color filter, 45: Microlens, 46P: First light shielding unit, 46M: Second light shielding unit

Claims (10)

an image sensor having a focus state detection unit including a plurality of image plane phase difference detection units each having a different design pupil distance, the image sensor having a first direction as a detection direction and arranged at different positions in a second direction intersecting the first direction;
an imaging optical system that forms a subject image on an imaging surface of the imaging element;
an adder that generates a sum signal by adding together detection signals output from two or more image surface phase difference detection units having a design pupil distance closest to an exit pupil distance of the imaging optical system, among a plurality of detection signals detected by a plurality of the image surface phase difference detection units included in the focus state detection unit;
An imaging device comprising: 2. The imaging device according to claim 1,
The image surface phase difference detection unit
a first detection unit in which a plurality of first light receiving units are arranged in the first direction, the first light receiving units detecting a larger amount of light that has passed through one side of an exit pupil of an imaging optical system in the first direction than a larger amount of light that has passed through another side of the exit pupil opposite to the one side;
a second detection unit including a plurality of second light receiving units arranged in the first direction, the second light receiving units detecting a greater amount of light that has passed through the other side of the exit pupil in the first direction than light that has passed through the one side of the exit pupil;
13. An imaging device comprising: 3. The imaging device according to claim 2,
The adding unit is
adding up detection signals output from two or more image surface phase difference detection units having a design pupil distance closest to an exit pupil distance of the imaging optical system, among a plurality of detection signals from the first detection units included in the plurality of image surface phase difference detection units ;
adding together detection signals output from two or more image surface phase difference detection units having a design pupil distance closest to an exit pupil distance of the imaging optical system, among a plurality of detection signals from the second detection units included in the plurality of image surface phase difference detection units ;
Imaging device. 4. The imaging device according to claim 2,
the second detection unit is disposed at a first distance in the second direction from the first detection unit,
The plurality of image surface phase difference detection units are arranged in the second direction at a second distance that is longer than the first distance.
Imaging device. 5. The imaging device according to claim 1,
An imaging device, wherein when an amount of light incident on the imaging element is small and the intensity of the imaging signal output by the imaging element is small, the adder adds up more of the detection signals than when the intensity of the imaging signal is high. 6. The imaging device according to claim 1,
The adder adds up a larger number of the detection signals when the aperture value of the imaging optical system is small, compared to when the aperture value of the imaging optical system is large. 7. The imaging device according to claim 1,
The imaging element includes a plurality of focus state detection units,
An imaging device, wherein the adder adds more of the detection signals when the position of the focus state detection unit in the first direction is close to the center of the imaging element compared to when the position of the focus state detection unit in the first direction is far from the center of the imaging element. The imaging device according to any one of claims 1 to 7,
The imaging element includes a plurality of focus state detection units,
an image pickup device, wherein the adder adds more of the detection signals from the image plane phase difference detection unit in the plurality of focus state detection units when the position in the first direction of the selected focus state detection unit from the plurality of focus state detection units is close to the center of the image sensor, compared to when the position in the first direction of the selected focus state detection unit is far from the center of the image sensor. 9. The imaging device according to claim 1,
The adder selects the plurality of detection signals to be added in accordance with an exit pupil distance of an imaging optical system. 10. The imaging device according to claim 1,
The adder changes the number of the detection signals to be added in accordance with a size of an effective imaging area of the imaging element.

Images