JP2007103590A - Image pick-up device, focus detector and image pick-up system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image pick-up device, a focus detector and an image pick-up system, wherein it is possible to improve a responsivity at the time of low brightness upon obtaining photographing conditions (for example, a focus detection or range finding is performed). <P>SOLUTION: The image pick-up device 10 for picking up an image in a photographing optical system comprises a first pixel cell 11 containing a first photoelectrical converter 14 for generating electric charges in response to incident beams; and a second pixel cell 12 which contains an optical element 15 for focusing the incident beams and second photoelectrical converts 16, 17 for generating electric charges in response to beams focused by the optical element, and which has a larger cell size than the first pixel cell. The first pixel cell and the second pixel cell are two-dimensionally disposed on a substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image sensor capable of acquiring a captured image and acquiring a shooting condition (state) such as focus detection, a focus detection apparatus including the same, and an imaging system.

It has been proposed that pixel cells for captured images are two-dimensionally arranged on a substrate of an image sensor, and pixel cells for focus detection are arranged in a predetermined layout therein (for example, Patent Documents 1 and 2). See). Further, in Patent Document 1, the focus detection by the phase difference detection method is taken as an example, and the pixel cell is made the same size as the pixel cell for the photographed image. In Patent Document 2, the focus detection of the contrast detection method is taken as an example, and the pixel cell is made smaller in size than the pixel cell for the photographed image.
JP 2003-250080 A JP 2004-361611 A

However, in the imaging device described above, the size of the focus detection pixel cell is the same as that of the captured image pixel cell (or smaller than the captured image pixel cell), so that the focus detection responsiveness is reduced at low luminance. There was a problem. This problem is not limited to focus detection pixel cells, and can occur in the same manner when pixel cells for distance measurement, photometry, and the like are arranged.
An object of the present invention is to provide an imaging device, a focus detection device, and an imaging system that can improve responsiveness at low luminance when acquiring imaging conditions (for example, performing focus detection or distance measurement). .

  An imaging device according to the present invention includes a first pixel cell including a first photoelectric conversion unit that generates an electric charge according to incident light and an optical that collects incident light in the imaging device that captures an image by a photographing optical system. A second pixel cell including an element and a second photoelectric conversion unit that generates an electric charge according to light condensed by the optical element, and having a cell size larger than that of the first pixel cell. The first pixel cell and the second pixel cell are two-dimensionally arranged on the substrate.

Moreover, it is preferable that the cell size of the second pixel cell is an integer multiple of the first pixel cell.
The first and second pixel cells each include an optical element that collects incident light on the first and second photoelectric conversion units, and the optical element of the second pixel cell is the first pixel cell. The aperture size is preferably larger than the optical element of the pixel cell.

  An imaging element according to the present invention includes an optical element that collects incident light in an imaging element that captures an image by a photographing optical system, and a first photoelectric conversion that generates an electric charge according to the light collected by the optical element. A second pixel including a first pixel cell that includes a first pixel cell, an optical element that condenses incident light, and a second photoelectric conversion unit that generates a charge in accordance with the light collected by the optical element A first pixel cell and a second pixel cell are two-dimensionally arranged on a substrate, and an optical element of the second pixel cell is an optical element of the first pixel cell. The opening size is larger than that.

The optical element of the first pixel cell preferably has an aperture size smaller than 20 μm.
In addition, each of the second pixel cells includes a plurality of the second photoelectric conversion units, and each of the plurality of second photoelectric conversion units via the optical element of the second pixel cell, It is preferably substantially conjugate with the exit pupil of the photographing optical system.

In addition, it is preferable that two of the plurality of second photoelectric conversion units form a pair, and filters of different colors are arranged in each of the two second photoelectric conversion units forming the pair.
Further, it is preferable that a focus adjustment state of the photographing optical system is detected based on a photoelectric output obtained by the second pixel cell.
In addition, the optical element includes an optical element that collects incident light and a third photoelectric conversion unit that generates an electric charge according to the light collected by the optical element, and the cell size is different from that of the second pixel cell. It is preferable to further include a third pixel cell.

Moreover, it is preferable that the cell size of the third pixel cell is equal to that of the first pixel cell.
Further, it is preferable that a focus adjustment state of the photographing optical system is detected based on a photoelectric output obtained by the second pixel cell and the third pixel cell.
The focus detection apparatus of the present invention includes the above-described image sensor and detection means for performing focus detection based on the output of the second pixel cell.

A focus detection apparatus of the present invention includes the above-described imaging device, and a detection unit that performs focus detection based on at least one of the output of the second pixel cell and the output of the third pixel cell. is there.
An imaging system of the present invention includes the above-described focus detection device and a photographing optical system disposed on the object side of the imaging element, and the detection unit performs focus detection of the photographing optical system.

In addition, the captured image is displayed based on the output of the first pixel cell, and the display of the position of the second pixel cell is superimposed on the captured image as a region where the detection unit performs focus detection. Preferably means are provided.
In addition, an image signal at the position of the first pixel cell is generated based on the output of the first pixel cell, and an image signal at the position of the second pixel cell is generated by the second pixel cell. It is preferable that the image forming apparatus includes a generation unit configured to generate by interpolation processing based on the output of the surrounding first pixel cell.

  In addition, when generating the image signal at the position of the second pixel cell, the generating unit generates each color component of the image signal by the interpolation process, and the luminance component of the image signal is converted to the second pixel. It is preferable to generate based on the output of the cell.

  According to the present invention, it is possible to improve the responsiveness at the time of low luminance when acquiring photographing conditions (states) (for example, performing focus detection, distance measurement, photometry, etc.).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
Here, an image sensor that can acquire a captured image and acquire information related to focus detection will be described. Further, description will be given by taking focus detection by the phase difference detection method as an example. The information related to focus detection is one of various conditions (shooting conditions) when acquiring a shot image, and corresponds to the defocus amount of the shooting optical system arranged on the object side of the image sensor. When the photographing optical system is in focus (ideally defocus amount = 0), a clear subject image is formed on the image sensor.

  The image sensor 10 of the first embodiment includes a pixel cell 11 for a photographed image shown in FIG. 1A and a pixel cell 12 for focus detection shown in FIG. 1B, as shown in FIG. 1C. And arranged on a substrate. In FIG. 1C, each pixel cell 11 and 12 is hatched for easy understanding. FIGS. 1A to 1C are schematic views seen from the photographic optical system side. In addition to the pixel cells 11 and 12, the imaging element 10 is provided with a vertical scanning circuit, a horizontal scanning circuit, and the like (not shown).

In the present embodiment, each of the pixel cells 11 and 12 has a square shape. In addition, the focus detection pixel cell 12 has a larger cell size than the captured image pixel cell 11, and the four pixel cells 11 can be densely arranged in the size of one pixel cell 12. It is a size. That is, the cell size of the focus detection pixel cell 12 is four times the cell size of the captured image pixel cell 11. In this case, the length A ₁₂ on one side of the pixel cell ₁₂ is twice the length A ₁₁ on one side of the pixel cell 11.

On the substrate of the image sensor 10, the pixel cells 11 for captured images are two-dimensionally arranged almost densely, and focus detection pixel cells 12 are periodically embedded therein. The arrangement of the pixel cells 11 is a substantially square lattice.
The pixel cell 11 for a captured image (FIG. 1A) is provided with a circular microlens 13 and a rectangular photoelectric conversion unit 14. The microlens 13 is an optical element that collects incident light and guides it to the photoelectric conversion unit 14. The photoelectric conversion unit 14 is a photodiode that generates an electric charge according to the light collected by the microlens 13. Although not shown, any one of RGB color filters is disposed between the microlens 13 and the photoelectric conversion unit 14. The color filters of the plurality of pixel cells 11 have a predetermined RGB array (for example, a Bayer array).

  In the pixel cell 11, the power of the microlens 13 is set so that an output proportional to the size of the exit pupil of the photographing optical system (that is, the aperture diameter of the photographing optical system) can be obtained. For this purpose, it is necessary to guide the light beam from the entire exit pupil to the photoelectric conversion unit 14 regardless of the exit pupil size, and the exit pupil size when the aperture diameter is maximized (for example, F1.4). The power of the microlens 13 is set based on this.

  The pixel cell 12 for focus detection (FIG. 1B) is provided with a circular microlens 15 and two photoelectric conversion units 16 and 17 having a rectangular shape. The microlens 15 is an optical element that collects incident light and guides it to the photoelectric conversion units 16 and 17. The photoelectric conversion units 16 and 17 are photodiodes that generate charges in accordance with the light collected by the microlens 15, respectively. These two photoelectric conversion units 16 and 17 form a pair and are used for focus detection by the phase difference detection method using the microlens 15.

In addition, as can be seen from the cross-sectional view of FIG. 2, the pair of photoelectric conversion units 16 and 17 includes a surface p + layer 23 and an n layer 24 of the substrate 22, respectively. A gate insulating film 25 (SiO ₂ film) is formed on the surface of the substrate 22. Such a cross-sectional structure is similar to the above-described pixel cell 11 for a captured image. In the focus detection pixel cell 12, an infrared cut filter 21 is disposed between the pair of photoelectric conversion units 16 and 17 and the microlens 15 in order to remove infrared light unnecessary for focus detection. Is done. Incidentally, since the pair of photoelectric conversion units 16 and 17 are not provided with a color filter, light beams in the entire wavelength region of visible light are incident.

Further, in this pixel cell 12, in order to realize focus detection by the phase difference detection method, the pair of photoelectric conversion units 16 and 17 and the exit pupil of the photographing optical system are conjugated via the micro lens 15. . That is, the power of the microlens 15 is set so that the pair of photoelectric conversion units 16 and 17 can be projected onto the exit pupil of the photographing optical system.
Such a conjugate relationship is illustrated in FIG. In FIG. 3A, the exit pupil 18 is indicated by a thick dotted line. When the exit pupil 18 is viewed from the direction of the optical axis 19 of the photographing optical system (not shown), it is substantially circular as shown in FIG. The regions 8A and 8B in the exit pupil 18 are regions where the pair of photoelectric conversion units 16 and 17 are projected by the microlens 15 and have a substantially rectangular shape.

The regions 8A and 8B are arranged substantially symmetrically about the optical axis 19. Then, the light beam that has passed through the region 8 </ b> A of the exit pupil 18 enters one photoelectric conversion unit 16, and the light beam that has passed through the region 8 </ b> B enters the other photoelectric conversion unit 17. That is, the light beam passing through the exit pupil 18 can be divided into two and guided to the photoelectric conversion units 16 and 17 (pupil division method).
It should be noted that when focus detection is performed using the phase difference detection method, when the pair of regions 8A and 8B partially protrudes from the exit pupil 18, light beams guided to the pair of photoelectric conversion units 16 and 17 (light beams used for focus detection). As a result, the focus detection accuracy deteriorates. Accordingly, in the pixel cell 12 for focus detection, the microlens 15 is arranged so that the pair of regions 8A and 8B are accommodated in the exit pupil 18 regardless of the size of the exit pupil 18 (that is, the aperture diameter of the photographing optical system). The power is set. Therefore, the power of the microlens 15 is set based on the size of the exit pupil 18 when the aperture diameter is minimum (for example, F2.8 or F5.6).

Furthermore, in this embodiment, the microlenses 13 and 15 are circular (FIGS. 1A and 1B), and the respective opening sizes (diameters) are the lengths A ₁₁ and A of one side of the pixel cells 11 and 12, respectively. _It was configured to be equal to ₁₂ . Therefore, one side of the length A ₁₂ of the pixel cells 12 as described above by longer than one side of the length A ₁₁ of the pixel cells 11, a micro lens for capturing an image size of the opening of the micro-lens 15 for focus detection It can be larger than 13 opening sizes. The aperture area can be increased by increasing the aperture size, and many light beams can be incident on the pair of photoelectric conversion units 16 and 17 through the microlens 15.

  Further, the charge accumulated in the photoelectric conversion unit 14 of the pixel cell 11 for the captured image and the charge accumulated in the pair of photoelectric conversion units 16 and 17 of the pixel cell 12 for focus detection are, for example, FIG. It can be read out by the MOS type circuit configuration shown in FIG. FIG. 4 shows 4 × 4 pixels (that is, 12 pixel cells 11 and 1 pixel cell 12) of the pixel cell 11, and a readout circuit thereof.

  Since the focus detection pixel cell 12 includes the two photoelectric conversion units 16 and 17, the circuit portion of the pixel cell 12 corresponds to two pixel cells 11 for the captured image. Further, since the cell size of the pixel cell 12 corresponds to four times that of the pixel cell 11, the locations 30 (1), 30 (2) adjacent to the circuit portion of the pixel cell 12 and corresponding to two pixel cells 11. ) Becomes empty. These locations 30 (1) and 30 (2) may be dummy.

  The photoelectric conversion unit 14 of the captured image pixel cell 11 and the pair of photoelectric conversion units 16 and 17 of the focus detection pixel cell 12 are respectively a transfer switch MOS transistor 31 and a reset MOS transistor 32. The source follower amplifier MOS transistor 33 and the horizontal selection switch MOS transistor 34 are connected to the vertical output line V. The MOS transistors 31, 32, and 34 are connected to the vertical scanning circuit 41 through control lines R, P, and S, respectively. The vertical scanning circuit 41 controls on / off of the MOS transistors 31 and 33 and the like.

  Further, a load MOS transistor 35 is connected to one end of the vertical output line V, and a horizontal output line H is connected via an output storage capacitor 37 and a horizontal transfer MOS transistor 38. An output amplifier 43 is connected to one end of the horizontal output line H. Further, a horizontal scanning circuit 42 is connected to the MOS transistor 38. The MOS transistor 35 constitutes a source follower similar to the MOS transistor 33 and is connected to a control circuit (not shown) via a control line L. The horizontal scanning circuit 42 controls on / off of the MOS transistor 38.

  When accumulating charges in the photoelectric conversion units 14, 16, and 17, first, the control line L is set to high level to reset the vertical output line V, and then the control line L is set to low level. Next, the vertical scanning circuit 41 sets the control lines R and P to the high level to reset the photoelectric conversion units 14, 16 and 17, and then sets the control lines R and P to the low level. By this operation, the photoelectric conversion units 14, 16, and 17 are reset to a predetermined potential, and charge accumulation in the photoelectric conversion units 14, 16, and 17 is started.

  When reading the charges of the photoelectric conversion units 14, 16, and 17, first, the vertical scanning circuit 41 sets the control line P to the high level to turn on the MOS transistor 31, and the charges of the photoelectric conversion units 14, 16, and 17 are changed. Applied to the gate of the MOS transistor 33. Further, the control line S is set to the high level to turn on the MOS transistor 34, and the charge on the horizontal line is selected as a reading target. At this time, the MOS transistor 33 generates an amplified signal in accordance with the amount of charge applied to its gate, and outputs it to the output storage capacitor 37 via the vertical output line V.

Each output stored in the output storage capacitor 37 is transferred to the horizontal output line H via the MOS transistor 38 in response to a scanning timing signal from the horizontal scanning circuit 42 to the MOS transistor 38. Further, the signal is transferred to the output amplifier 43 through the horizontal output line H, and read out through the signal amplification in the output amplifier 43.
The output of the pixel cell 11 read out in this manner is caused by the electric charge accumulated in the photoelectric conversion unit 14, and is used for displaying a captured image in the imaging system including the imaging device 10 of the first embodiment. It is done. Further, the output of the pixel cell 12 is caused by the electric charges accumulated in the pair of photoelectric conversion units 16 and 17, and in the focus detection apparatus and the imaging system including the imaging device 10 of the first embodiment, the phase difference detection method is used. Used for focus detection.

  When performing phase difference detection type focus detection based on the output of the pixel cell 12, the first subject image is captured from the output related to one of the plurality of pixel cells 12 and the other photoelectric conversion unit 17. The second subject image is taken in from the output related to, and the positional phase difference between the two subject images (that is, the positional deviation amount in the arrangement direction of the pair of photoelectric conversion units 16 and 17) is obtained by, for example, correlation calculation. Then, by converting this phase difference into a defocus amount (that is, a positional deviation amount in the optical axis direction) of the photographing optical system, information related to focus detection is generated.

In the imaging device 10 of the first embodiment, the aperture size of the focus detection microlens 15 is set to be used for a captured image in order to make the cell size of the pixel cell 12 for focus detection larger than the cell size of the pixel cell 11 for captured image. The opening size of the microlens 13 can be made larger, and the opening area can be increased accordingly.
Therefore, as compared with the case where the focus detection pixel cell 12 has the same cell size as that of the captured image pixel cell 11 (or a cell size smaller than the pixel cell 11), a large amount of light flux passes through a pair of microlenses 15. The light can enter the photoelectric conversion units 16 and 17. As a result, an output level necessary for focus detection can be secured in a normal charge accumulation time even at low luminance, and responsiveness at low luminance can be improved.

  Furthermore, in the image sensor 10 of the first embodiment, even when the cell size of the pixel cell 11 for photographed images is reduced (for example, when the pixel size is reduced to the wavelength order) as the number of pixels increases, the pixels for the photographed images are used. Compared with the microlens 13 of the cell 11, the aperture size of the microlens 15 of the focus detection pixel cell 12 can be ensured, and the influence of diffraction in the microlens 15 can be reduced.

  Here, in order to explain the relationship between the aperture size of the microlens 15 and the influence of diffraction on the microlens 15, diffraction simulations (FIGS. 5 to 9) were performed. The simulation condition assumes a circular exit pupil 18 corresponding to F2.8 (FIG. 5A), assumes an XY coordinate system with the optical axis 19 of the imaging optical system as the origin, and starts from the exit pupil 18. The distance to the microlens 15 is 100 mm, and the size of the rectangular photoelectric conversion unit 16 (FIG. 5B) conjugate to the exit pupil 18 is X = −2 to −12 mm, and Y = −10 to 10 mm. . This size is such that the photoelectric conversion unit 16 is projected in a substantially inscribed manner on the exit pupil 18 in an ideal case where there is no influence of diffraction as in the diffraction image 8C shown in FIG. is there. The wavelength was 500 nm.

  Further, when the microlens 15 is circular (see FIG. 1B) and the opening size (diameter) of the microlens 15 is 20 μm, 10 μm, 4 μm, and 2 μm, the results are shown in FIGS. FIGS. 6A to 9A are schematic shapes of a diffraction image 8C of the photoelectric conversion unit 16 by the microlens 15 having each opening size. FIG. 6B to FIG. 9B are intensity distributions at Y = 0 of each diffraction image 8C.

As shown in FIGS. 6A and 6B, when the aperture size (diameter) of the microlens 15 is 20 μm, the influence of diffraction is small, and most of the diffraction image 8C (about 96%) is F2. 8 within the exit pupil 18.
Further, as shown in FIGS. 7A and 7B, when the aperture size (diameter) of the microlens 15 is 10 μm, the influence of diffraction increases, and a part (base) of the diffraction image 8C is F2.8. It protrudes from the exit pupil 18. The portion included in the exit pupil 18 is about 92%.

Further, as shown in FIGS. 8A and 8B, when the aperture size (diameter) of the microlens 15 is 4 μm, the influence of diffraction is further increased, and the edge of the diffraction image 8C is staggered, and the diffraction image 8C Protrudes from the exit pupil 18 of F2.8. The portion included in the exit pupil 18 is about 81%.
Further, as shown in FIGS. 9A and 9B, when the aperture size (diameter) of the microlens 15 is 2 μm, the influence of diffraction further increases, and the diffraction image 8C spreads in a circular shape, and the diffraction image 8C. About half of the projection protrudes from the exit pupil 18 of F2.8. The portion included in the exit pupil 18 is about 60%.

  As can be seen from this simulation, when the aperture size (diameter) of the microlens 15 becomes 20 μm or less, the projection performance of the microlens 15 deteriorates, and the shape of the diffraction image 8C projected on the exit pupil 18 is affected by the influence of diffraction. The collapse starts, and a part of the diffraction image 8C starts to spread outside the exit pupil 18. As the aperture size of the microlens 15 becomes smaller, the influence of diffraction increases, and about half of the diffraction image 8C protrudes outside the exit pupil 18 at a diameter of 2 μm as shown in FIGS.

  That is, the influence of diffraction in the microlens 15 becomes prominent when the aperture size (diameter) is smaller than 20 μm. For this reason, when the aperture size (diameter) of the microlens 13 of the pixel cell 11 for captured images is smaller than 20 μm, the aperture size of the microlens 15 of the focus detection pixel cell 12 is smaller than that of the microlens 13. It is particularly effective to ensure a large value, and the influence of diffraction on the microlens 15 can be reliably reduced.

  If the influence of diffraction in the microlens 15 can be reduced, the portion included in the exit pupil 18 in the pair of regions 8A and 8B (FIG. 3) projected onto the exit pupil 18 by the microlens 15 is increased ( For example, FIG. 8 → FIG. 6), and the vignetting of the light beam used for focus detection can be suppressed. For this reason, the intensity distribution shapes of the two subject images described above can be substantially matched, and an error in computation (for example, correlation computation) when obtaining the positional phase difference between the two subject images can be reduced. Therefore, it is possible to avoid a situation in which the focus detection accuracy is lowered as the number of pixels increases.

  Furthermore, when the aperture size (diameter) of the microlens 15 is larger than 20 μm, the pair of photoelectric conversion units 16 and 17 can be accurately projected onto the exit pupil 18 by the microlens 15 (see FIG. 5A). In other words, the projection can be performed so that the pair of regions 8A and 8B can be accommodated in the exit pupil 18, and the light flux used for focus detection can be eliminated to maintain good focus detection accuracy.

  Further, in the image sensor 10 of the first embodiment, the cell size of the focus detection pixel cell 12 is set to four times the cell size of the captured image pixel cell 11 (see FIG. 1). Compared to the basic circuit configuration in the case where the image sensor is configured only from the pixel cells 11, it is not necessary to make a significant change. For this reason, even when the cell size of the focus detection pixel cell 12 is increased, the circuit configuration of the image sensor 10 is facilitated. Further, the microlens 15 can be easily manufactured. Further, no special change is required for the operation control of the image sensor 10.

(Second Embodiment)
Here, an imaging system 40 including the imaging device 10 (FIGS. 1 to 4) will be described with reference to FIGS. 10 to 12.
As shown in FIG. 10, the imaging system 40 according to the second embodiment includes a photographing optical system 41, an aperture 42, an imaging element 10, a signal processing unit 43, an AD conversion unit 44, a signal processing unit 45, a memory unit 46, and timing generation. A unit 47, a control unit 48, interfaces (IF) 49 and 50, and an operation unit 51 are provided.

The photographing optical system 41 includes a lens group that forms a subject image on the image pickup surface of the image pickup device 10 and includes a focusing lens. The diaphragm 42 adjusts the amount of light flux that passes through the photographing optical system 41. The image sensor 10 captures a subject image by the photographing optical system 41 and outputs a signal for a photographed image and a signal for focus detection.
The signal processing unit 43 includes a gain variable amplifier that amplifies the output of the image sensor 10 and a gain correction circuit that corrects the gain value. The AD converter 44 converts the signal (analog signal) after passing through the signal processor 43 into a digital signal. The signal processing unit 45 performs various corrections on the data output from the AD conversion unit 44. The memory unit 46 temporarily stores data after passing through the signal processing unit 45.

  The timing generator 47 outputs various timing signals to the image sensor 10, signal processors 43 and 45, and AD converter 44. The control unit 48 performs various calculations and overall control of the imaging system 40. The IF 49 performs data recording and reading with respect to the removable recording medium 9A. The recording medium 9A is, for example, a semiconductor memory. The IF 50 communicates with an external computer (not shown). The operation unit 51 outputs a command corresponding to an operation from the outside to the control unit 48.

An operation (FIG. 11) of the imaging system 40 of the second embodiment will be described.
First (step S1), after the main power supply is turned on, the control system power supply is turned on, and the imaging system circuit such as the AD converter 44 is turned on. Thereafter, the control unit 48 opens the aperture 42 in order to control the exposure amount. The output from the image sensor 10 is stored in the memory unit 46 after passing through the signal processing unit 43, the AD conversion unit 44, and the signal processing unit 45.

  When the focus adjustment (steps S2 to S4) is started, the phase difference detection method is firstly performed using the data corresponding to the output of the focus detection pixel cell 12 among the data stored in the memory unit 46. Focus detection is performed (step S2). That is, for example, the positional phase difference between the two subject images described above is obtained by a well-known correlation calculation, and the defocus amount of the photographing optical system 41 is calculated.

  Next (step S3), it is determined based on this defocus amount whether or not the photographing optical system 41 is in focus. If it is not yet in focus (step S3 is No), based on the defocus amount. The focusing lens of the photographing optical system 41 is driven and moved toward the in-focus position (step S4). Thereafter, the process returns to step S2, and the focus adjustment (steps S2 to S4) is repeated until the defocus amount becomes zero.

If it is determined that the photographing optical system 41 is in focus (Yes in Step S3), the process proceeds to Step S5, and when it is detected that the release button of the operation unit 51 is pressed, the photographing operation is executed. (Step S6). That is, the output from the image sensor 10 is stored in the memory unit 46 via the AD conversion unit 44 or the like.
Next, the control unit 48 generates an image signal by using data corresponding to the output of the pixel cell 11 for the photographed image among the data stored in the memory unit 46 by the photographing operation of Step S6 (Step S7). ). An image signal at the position of the pixel cell 11 of the image sensor 10 is generated based on the data of the pixel cell 11. The image signal at the position of the focus detection pixel cell 12 is generated by interpolation processing based on the data of the pixel cells 11 around the pixel cell 12.

An example of image signal generation will be described. Here, it is assumed that the RGB array of the color filters of the plurality of pixel cells 11 is a Bayer array as shown in FIG. In this case, an image signal for one pixel at the position of the pixel cell 11 is obtained from the outputs of four adjacent pixel cells 11 (for example, G11a, B11, R11, G11b) by the following equations (1) to (4). Can be generated according to
In the expressions (1) to (4), the output of each pixel cell 11 is I (G11a), I (B11), I (R11), I (G11b). Equation (1) is the luminance component Iy11 of the image signal. Expressions (2) to (4) are the green component Ig11, red component Ir11, and blue component Ib11 of the image signal, respectively. k1 to k3 are predetermined coefficients.

Iy11 = k1 × [I (G11a) + I (G11b)] + k2 × I (R11) + k3 × I (B11) (1)
Ig11 = [I (G11a) + I (G11b)] / Iy11 (2)
Ir11 = I (R11) / Iy11 (3)
Ib11 = I (B11) / Iy11 (4)
Furthermore, an image signal for one pixel at the position of the pixel cell 12 can be generated by the following interpolation process. First, assuming that the four pixel cells 11 (G22a, B22, R22, G22b) shown in FIG. 12B are arranged at the position of the pixel cell 12, the pixel cells 11 in four directions around the pixel cell 12 are arranged. (G12a, G21a, G23a, G32a,...) Are substituted into the following equations (5) to (8) to output the pixel cell 11 (G22a, B22, R22, G22b) in FIG. The data corresponding to is obtained. Calculations of equations (5) to (8) correspond to averaging processing.

I (G22a) = [I (G12a) + I (G21a) + I (G23a) + I (G32a)] / 4 (5)
I (G22b) = [I (G12b) + I (G21b) + I (G23b) + I (G32b)] / 4 (6)
I (R22) = [I (R12) + I (R21) + I (R23) + I (R32)] / 4 (7)
I (B22) = [I (B12) + I (B21) + I (B23) + I (B32)] / 4 (8)
Then, using the results of the expressions (5) to (8), an image signal for one pixel at the position of the pixel cell 12 can be generated according to the following expressions (9) to (12). Equation (9) is the luminance component Iy22 of the image signal. Expressions (10) to (12) are the green component Ig22, red component Ir22, and blue component Ib22 of the image signal, respectively.

Iy22 = k1 * [I (G22a) + I (G22b)] + k2 * I (R22) + k3 * I (B22) (9)
Ig22 = [I (G22a) + I (G22b)] / Iy22 (10)
Ir22 = I (R22) / Iy22 (11)
Ib22 = I (B22) / Iy22 (12)
When the generation of the image signal (the process of step S7 in FIG. 11) is completed in this way, these data are also written in the memory unit 46. Then, for the next photographing operation, the process returns to the process of step S2 and the processes such as focus detection are repeated. On the other hand, the image signals (luminance component, green component, red component, blue component) stored in the memory unit 46 are recorded on the recording medium 9A through the IF 49 under the control of the control unit 48. Further, the image signal may be processed by being output to an external computer or the like via the IF 50.

  As described above, in the imaging system 40 of the second embodiment, focus detection of the imaging optical system 41 is performed based on the output of the pixel cell 12 for focus detection provided in the imaging device 10 (step S2 in FIG. 11). Therefore, it is possible to adjust the focus of the photographing optical system 41 with good responsiveness and accuracy even at low luminance. As a result, it is possible to obtain a focused image quickly even at low luminance.

Furthermore, in the imaging system 40 of the second embodiment, color filters are provided in the pair of photoelectric conversion units 16 and 17 of the pixel cell 12 in order to generate an image signal at the position of the focus detection pixel cell 12 by interpolation processing. Even if it is not, a good captured image can be obtained.
(Modification 1)
Here, a modified example of the generation of the image signal at the position of the pixel cell 12 will be described.

  When the outputs of the four pixel cells 11 (G22a, B22, R22, G22b) shown in FIG. 12B are obtained by interpolation processing, the pixel cells 11 (G11a, G12a, G13a, G21a) in the eight directions around the pixel cell 12 are obtained. , G23a, G31a, G32a, G33a, etc.) may be used to perform averaging processing similar to the above equations (5) to (8). Furthermore, weighting according to the relative position between the pixel cell 12 and the surrounding pixel cell 11 may be performed during the averaging process. By performing such processing, the accuracy of the interpolation processing is improved.

  Further, when the luminance component Iy22 is generated from the image signal at the position of the pixel cell 12, the output of the pixel cell 12 is not the output of the four pixel cells 11 (G22a, B22, R22, G22b) obtained by the interpolation process. Output may be used. For example, if the outputs of the pair of photoelectric conversion units 16 and 17 of the pixel cell 12 are I (W22a) and I (W22b) (FIG. 12C), and these are substituted into the following equation (13), the luminance Component Iy22 can be produced. k4 is a predetermined coefficient.

Iy22 = k4 × [I (W22a) + I (W22b)] (13)
In this case, the color components Ig22, Ir22, and Ib22 of the image signal are obtained by the above formulas (10) to (12) and the luminance component Iy22 (formula (13)) obtained from the output of the pixel cell 12 by interpolation processing. It is generated by substituting the outputs of the four pixel cells 11 (G22a, B22, R22, G22b).

Thus, by generating the luminance component Iy22 of the image signal at the position of the pixel cell 12 based on the output of the pixel cell 12, the accuracy in generating the luminance component Iy22 and the color components Ig22, Ir22, and Ib22 is improved. improves.
(Third embodiment)
Here, the digital still camera 60 of FIG. 13 will be described as a specific example of the imaging system 40 including the imaging device 10 (FIGS. 1 to 4).

The digital still camera 60 includes an interchangeable lens 61 and a camera body 62 and is coupled by a mount unit 63.
The interchangeable lens 61 is provided with a photographing optical system (64, 65), a diaphragm 66, driving units 67, 68, and a lens CPU 69. The photographing optical system (64, 65) includes a lens 65 for focusing. The drive unit 67 drives the lens 65 for focusing. The drive unit 68 drives the diaphragm 66. The lens CPU 69 controls the operation of the drive units 67 and 68.

  The camera body 62 is provided with the imaging device 10, a focus detection unit 71, a body CPU 72, a liquid crystal display element 73, an eyepiece lens 74, and a liquid crystal driving unit 75. The image sensor 10 is disposed on the planned imaging plane of the photographing optical system (64, 65) of the interchangeable lens 61. The focus detection unit 71 performs focus detection of the imaging optical system (64, 65) based on the output of the pixel cell 12 of the image sensor 10. The body CPU 72 performs overall operation control of the digital still camera 60. The liquid crystal display element 73 and the eyepiece lens 74 constitute a liquid crystal viewfinder. The liquid crystal driving unit 75 drives the liquid crystal display element 73 in accordance with an instruction from the body CPU 72.

The body CPU 72 and the lens CPU 69 are connected to various information (lens characteristics information such as an open F value, focus adjustment information for lens driving, and information for aperture control via an electrical contact 76 provided on the mount 63. ).
In the digital still camera 60 of the third embodiment, when the focus detection unit 71 performs focus detection of the imaging optical system (64, 65) based on the output of the pixel cell 12 of the image sensor 10, the focus detection unit 71 performs imaging for the body CPU 72. A defocus amount representing the focus adjustment state of the optical system (64, 65) is output. The body CPU 72 determines whether or not the photographing optical system (64, 65) is in an in-focus state based on the defocus amount. If the in-focus state is not in focus, the lens CPU 69 drives the lens according to the defocus amount. Output information.

The lens CPU 69 controls the drive unit 67 based on the lens drive information, and moves the focusing lens 65 toward the in-focus position.
Further, the body CPU 72 generates an image signal based on the output of the pixel cell 11 of the image sensor 10, outputs this image signal to the liquid crystal drive unit 75, and displays a photographed image on the liquid crystal display element 73 of the liquid crystal viewfinder. Let At this time, it is preferable to perform an interpolation process similar to the above to generate and display an image signal at the position of the focus detection pixel cell 12.

  As described above, in the digital still camera 60 according to the third embodiment, the focus detection of the imaging optical system (64, 65) of the interchangeable lens 61 is performed based on the output of the focus detection pixel cell 12 of the image sensor 10. Therefore, it is possible to adjust the focus of the photographing optical system (64, 65) with good responsiveness and accuracy even at low luminance. As a result, it is possible to obtain a focused image quickly even at low luminance.

(Fourth embodiment)
Here, an example of an image sensor having two types of pixel cells for focus detection will be described with reference to FIGS.
The image sensor 80 of the fourth embodiment is provided with a pixel cell 81 shown in FIG. 14A in addition to the pixel cells 11 and 12 shown in FIGS. In other words, the imaging element 80 is provided with the pixel cell 11 for a captured image and two types of pixel cells 12 and 81 for focus detection. The configuration and operation of the pixel cells 11 and 12 shown in FIGS. 1A and 1B are the same as described above, and a description thereof is omitted here.

FIG. 14B shows a layout of the pixel cells 11, 12, 81. On the substrate of the image sensor 80, the pixel cells 11 for captured images are two-dimensionally arranged almost densely (square lattice shape), and one pixel cell 12 for focus detection is periodically embedded therein, The other pixel cells 81 for focus detection are arranged almost densely in a predetermined area.
The pixel cell 81 shown in FIG. 14A has a square shape like the pixel cells 11 and 12. The pixel cell 81 has a cell size different from that of the focus detection pixel cell 12 and is the same as the pixel cell 11 for captured image. The length A ₈₁ on one side of the pixel cell 81 is equal to the length A ₁₁ on one side of the pixel cell 11. In other words, the newly provided focus detection pixel cell 81 is smaller than the focus detection pixel cell 12 described above. In the following description, the small pixel cell 81 and the large pixel cell 12 are referred to as necessary.

A small pixel cell 81 is provided with a circular microlens 82 and two rectangular photoelectric conversion units 83 and 84. The microlens 82 is an optical element that collects incident light and guides the incident light to the photoelectric conversion units 83 and 84, and the opening size (diameter) thereof is equal to the length A ₈₁ of one side of the pixel cell 81. The photoelectric conversion units 83 and 84 are photodiodes that generate charges in accordance with the light collected by the microlens 82, respectively. These two photoelectric conversion units 83 and 84 form a pair and are used for phase difference detection type focus detection using the microlens 82. For this reason, the pair of photoelectric conversion units 83 and 84 are arranged in a conjugate manner with the exit pupil of the photographing optical system (not shown) via the microlens 82 (see FIG. 3).

The cross-sectional structure of the pixel cell 81 (FIG. 15) is the same as the cross-sectional structure of the pixel cell 12 (FIG. 2), and the photoelectric conversion units 83 and 84 are formed on the surface p + layer 23 and the n layer 24 of the substrate 22. The gate insulating film 25 is formed on the surface of the substrate 22, and the infrared cut filter 21 is disposed between the photoelectric conversion units 83 and 84 and the microlens 82.
Further, in the pixel cell 81, a pair of photoelectric conversion portions 83 and 84 are formed with the floating diffusion (FD) portion 2 A of the P-type well of the substrate 22 interposed therebetween. Then, in order to read out the charges accumulated in the pair of photoelectric conversion units 83 and 84 individually (or by adding) through the FD unit 2A, the transfer switch MOS transistors 85, 86 is provided. The MOS transistors 85 and 86 are connected to a vertical scanning circuit (not shown) via control lines P ′ and P ″ shown in FIG.

  Therefore, the charges accumulated in the pair of photoelectric conversion units 83 and 84 can be transferred individually (or added) to the FD unit 2A in accordance with on / off of the MOS transistors 85 and 86 by the vertical scanning circuit. it can. For example, when one of the MOS transistors 85 is selectively turned on, only the charge of the photoelectric conversion unit 83 corresponding to the MOS transistor 85 is selectively transferred to the FD unit 2A. If both MOS transistors 85 and 86 are simultaneously turned on, the charges of the pair of photoelectric conversion units 83 and 84 are simultaneously transferred to the FD unit 2A and added there.

  Further, the FD portion 2A is connected to the control line R ′ via the reset MOS transistor 87, and is connected to the control line S ′ and the vertical via the source follower amplifier MOS transistor 88 and the horizontal selection MOS transistor 89. Connected to the output line V. For this reason, the charge transferred to the FD unit 2A is amplified via the MOS transistor 88 and transferred to the vertical output line V via the MOS transistor 89.

  The circuit configuration shown in FIG. 16 corresponds to one small pixel cell 81, and this pixel cell 81 has the same cell size as the pixel cell 11 for a captured image. For this reason, when the circuit portion of the pixel cell 81 is incorporated in the circuit configuration of FIG. Note that the control lines P ′, P ″, R ′, and S ′ in FIG. 16 are provided in common or independently with the control lines P, R, and S in FIG. 4, respectively.

  Since the image sensor 80 of the fourth embodiment has two types of pixel cells 12 and 81 for focus detection, the two types of pixel cells 12 and 81 are selectively used according to various shooting conditions, and a focus suitable for the shooting conditions. Detection can be performed. For example, when it is desired to ensure the focus detection response at low luminance, it is preferable to use the output of the large pixel cell 12. Further, when it is desired to increase the accuracy of focus detection at high luminance, it is preferable to use the output of the small pixel cell 81. Since the small pixel cell 81 has a fine detection pitch, it is suitable for a fine subject.

  Further, in the image sensor 80 of the fourth embodiment, the cell size of the large pixel cell 12 is four times the cell size of the captured image pixel cell 11 and the cell size of the small pixel cell 81 is the cell size of the pixel cell 11. Therefore, it is not necessary to make a significant change compared to the basic circuit configuration in the case where the image sensor is configured only from the pixel cell 11 for the captured image. For this reason, the circuit configuration of the image sensor 80 is facilitated. Further, the microlenses 15 and 82 can be easily manufactured.

(Fifth embodiment)
Here, the operation of the imaging system (see FIGS. 10 and 13) including the imaging device 80 of the fourth embodiment will be described with reference to the flowchart of FIG. The operation procedure shown in FIG. 17 is provided with steps S11 to S13 instead of step S2 in FIG. Here, focus adjustment (steps S11 to S13, S3, S4) will be described.

  In step S11, it is determined based on the output of a photometric sensor (not shown) provided in the imaging system whether or not the luminance of the subject is smaller than a predetermined value. If the luminance is smaller than the predetermined value (step S11 is Yes), focus detection is performed using the output of the large pixel cell 12 with high low luminance performance (step S13). On the other hand, when the luminance is equal to or higher than the predetermined value (No in step S11), focus detection is performed using the output of the small pixel cell 81 with high focus detection accuracy (step S12).

Therefore, in the imaging system of the fifth embodiment, focus adjustment can be performed with good responsiveness at low luminance, and focus adjustment can be performed with high accuracy at high luminance. Moreover, such proper use can be performed automatically.
At high luminance, focus detection may be performed using both the pixel cells 12 and 81 having two large and small cell sizes.

(Modification 2)
Here, an example will be described in which two types of focus detection pixel cells 12 and 81 (FIG. 14) having different cell sizes are switched according to manual settings, various camera settings, characteristics of an interchangeable lens, and the like.
When switching according to the focus adjustment mode, a small pixel cell 81 is selected with priority given to focus detection accuracy during one-shot AF (mode in which the lens is locked after focusing), and continuous AF (after focusing) is selected. It is conceivable that the large pixel cell 12 is selected with priority given to responsiveness in the mode in which the lens is driven by following the back and forth movement of the subject without locking the lens.

When switching according to the still image / moving image shooting mode, the small pixel cell 81 is selected with priority given to the focus detection accuracy in the still image shooting mode (still image shooting mode), and the moving image shooting mode (video It is conceivable to select the large pixel cell 12 in order to give priority to responsiveness in the image capturing mode).
When switching according to the shooting mode of single shooting / continuous shooting, a small pixel cell 81 is selected with priority given to focus detection accuracy in the single shooting mode (mode for shooting images one by one), and the continuous shooting mode is selected. It is conceivable that the large pixel cell 12 is selected with priority given to responsiveness in the case of (a mode in which images are continuously captured).

  When switching according to the portrait / sports shooting mode, the small pixel cell 81 is prioritized with focus detection accuracy in the portrait shooting mode (shooting mode suitable for shooting a stationary subject). It is conceivable to select the large pixel cell 12 with priority given to responsiveness in the sports shooting mode (shooting mode suitable for shooting a moving subject).

When switching according to the aperture value at the time of shooting, a small pixel cell 81 is selected with priority on focus detection accuracy when the aperture value is brighter than a predetermined value, and a large size with priority on responsiveness when darker than the predetermined value. It is conceivable to select the pixel cell 12.
When switching according to the photographing magnification, when the photographing magnification is smaller than a predetermined value, the small pixel cell 81 is selected with priority on focus detection accuracy, and when larger than the predetermined value, the large pixel cell is given priority on responsiveness. It is conceivable to select 12.

When switching according to the open F value of the attached interchangeable lens, when the open F value is brighter than the predetermined value, the small pixel cell 81 is selected giving priority to the focus detection accuracy, and when it is darker than the predetermined value, responsiveness is selected. It is conceivable to select the large pixel cell 12 with priority given to.
When switching according to the focal length of the attached interchangeable lens, priority is given to focus detection accuracy when the focal length is shorter than a predetermined value, and small pixel cells 81 are selected, and priority is given to response when the focal length is longer than the predetermined value. Then, it is conceivable to select a large pixel cell 12.

When switching according to non-use / use of the strobe, the small pixel cell 81 is selected with priority given to the focus detection accuracy when shooting without using the strobe, and responsiveness when shooting using the strobe. It is conceivable to select the large pixel cell 12 with priority given to.
When switching between using / not using a tripod, the small pixel cell 81 is selected with priority given to focus detection accuracy when shooting with the camera fixed to a tripod, etc., and the camera is not fixed to the tripod. It is conceivable to select the large pixel cell 12 with priority given to responsiveness when hand-held.

(Modification 3)
Here, a modified example of the layout of each pixel cell in the image sensor 10 (FIG. 1C) and the image sensor 80 (FIG. 14B) will be described.
As shown in FIG. 18, the pixel cells 11 for photographed images may be arranged almost densely, and the focus detection pixel cells 12 may be shifted in every other row in a staggered manner. In the case of such a layout, even if the size of the pattern of the subject image (for example, a linear pattern) is approximately the same as the arrangement pitches D1 and D2 of the pixel cells 12, focus detection can be performed regardless of the position.

As shown in FIG. 19, the pixel cells 11 for photographed images may be arranged almost densely, and the pixel cells 12 for focus detection may be arranged almost densely in a predetermined region therein. In the case of such a layout, even if the size of the pattern of the subject image (for example, a dot pattern) is approximately the same as the arrangement pitch D1 of the pixel cells 12, focus detection can be performed regardless of the position.
As shown in FIG. 20, the pixel cells 11 for photographed images are arranged almost densely, the pixel cells 12 for focus detection are arranged almost densely in a predetermined area, and are shifted by a half pitch for each row. May be. In this case, even if the size of the pattern of the subject image (for example, a linear pattern or a dot pattern) is approximately the same as the arrangement pitches D3 and D1 of the pixel cells 12, focus detection can be performed regardless of the position.

As shown in FIG. 21, a pixel cell 26 having a cell size different from that of the pixel cell 12 is provided for focus detection, and the length A ₂₆ of one side of the pixel cell 26 is set to the length of one side of the pixel cell 11 for a photographed image. It may be 2.5 times A ₁₁ . The cell size of the pixel cell 26 is 6.25 times that of the pixel cell 11. In FIG. 21, the pixel cells 11 for captured images are arranged substantially densely, and the pixel cells 26 are arranged substantially densely in a predetermined region therein. As described above, the cell size of the focus detection pixel cell is not limited to an integer multiple of the captured image pixel cell 11 and can be freely set. When the effect of mitigating the influence of diffraction is insufficient, a desired effect can be obtained by appropriately adjusting the ratio of the cell sizes of the focus detection pixel cell and the captured image pixel cell 11. it can.

As shown in FIG. 22, provided with different pixel cells 27 of the aspect ratio for the focus detection in the horizontal direction of one side of the length A ₂₇ of one side of the pixel cells 11 for photographing the image length A ₁₁ of the pixel cells 27 The vertical length A ₂₈ may be equal to the length A ₁₁ of the pixel cell 11. The cell size of the pixel cell 27 is twice that of the pixel cell 11. Since the vertical length A _{27 of the} focus detection pixel cell 27 is equal to that of the captured image pixel cell 11, the image quality can be maintained even when interpolation processing is performed when generating the image signal. Further, it is not necessary to change the circuit configuration by arranging the pixel cell 27.

As shown in FIG. 23, two types of pixel cells 12 and 81 for focus detection (see FIG. 14) are arranged almost densely in a predetermined region in which the pixel cells 11 for captured images are arranged almost densely. The large pixel cells 12 may be arranged in a staggered manner by shifting every other column (see FIG. 18), and the small pixel cells 81 may be disposed substantially densely therebetween.
As shown in FIG. 24, the pixel cells 12 for focus detection may be arranged in a line frame shape while the pixel cells 11 for captured images are arranged almost densely. In this case, a captured image is displayed on the screen of the liquid crystal viewfinder of the imaging system based on the output of the pixel cell 11, and the position of the pixel cell 12 is superimposed on the captured image as a focus detection area (focus frame). It is preferable to display. The focus frame display is performed by, for example, fixed data. Thus, since the position of the pixel cell 12 is displayed as the focus frame, it is not necessary to generate an image signal at the position of the pixel cell 12 by interpolation processing from the output of the surrounding pixel cells 11 or the like.

(Modification 4)
Here, a modified example of the photoelectric conversion unit of the pixel cell for focus detection will be described.
As in the pixel cell 90 for focus detection shown in FIG. 25, four photoelectric conversion units 91 to 94 may be provided. In this case, any two of the four photoelectric conversion units 91 to 94 can be selectively combined to form a pair of photoelectric conversion units that can be used for phase difference detection type focus detection. In the focus detection by the phase difference detection method, the positional phase difference between the two subject images (that is, the positional deviation amount in the arrangement direction of the pair of photoelectric conversion units) is obtained by, for example, correlation calculation. For this reason, the focus detection in a different direction can be performed according to the arrangement direction of the selected pair of photoelectric conversion units.

  For example, when performing horizontal focus detection in the figure, the outputs of the photoelectric conversion units 91 and 93 or the outputs of the photoelectric conversion units 92 and 94 are used. Further, the addition output of the photoelectric conversion units 91 and 92 and the addition output of the photoelectric conversion units 93 and 94 may be used. When performing vertical focus detection, the outputs of the photoelectric conversion units 91 and 92 or the outputs of the photoelectric conversion units 93 and 94 are used. Further, the addition output of the photoelectric conversion units 91 and 93 and the addition output of the photoelectric conversion units 92 and 94 may be used. In the case of focus detection in the upward and diagonal direction, each output of the photoelectric conversion units 91 and 94 is used. In the case of focus detection in the upward and diagonal direction, the outputs of the photoelectric conversion units 92 and 93 are used. In this manner, multidirectional focus detection can be performed with one type of pixel cell 90.

  Furthermore, like the pixel cell 100 for focus detection shown in FIG. 26, six photoelectric conversion units 101 to 106 may be provided, and any one of RGB color filters may be provided for each. In this case, the two photoelectric conversion units 101 and 104 arranged along the focus detection direction (lateral direction in the figure) have the same R color component, the photoelectric conversion units 102 and 105 have the same G color component, and the photoelectric conversion units 103 and 104. Reference numeral 106 denotes the same B color component.

  When performing focus detection by the phase difference detection method using the pixel cell 100, the addition output of the three photoelectric conversion units 101 to 103 arranged along the direction perpendicular to the focus detection direction is obtained, and the photoelectric conversion unit 104 is obtained. ˜106 are obtained, and the positional phase difference between the two subject images (here, the amount of positional deviation in the horizontal direction in the figure) is obtained from these two addition outputs by, for example, correlation calculation.

  Further, when generating an image signal at the position of the pixel cell 100, the addition output (R color component) of the two photoelectric conversion units 101 and 104 arranged along the focus detection direction is obtained, and the photoelectric conversion unit 102 is also obtained. , 105 and the addition output (B color component) of the photoelectric conversion units 103 and 106 are obtained. Then, these three addition outputs may be substituted into the equations (9) to (12) instead of the respective color components (equations (5) to (8)) obtained by the interpolation processing described above.

  Similarly, like the pixel cell 110 for focus detection shown in FIG. 27, six photoelectric conversion units 111 to 116 are arranged along the focus detection direction (horizontal direction in the figure), and any one of RGB is respectively arranged. Two color filters may be provided. In this case, the two photoelectric conversion units 113 and 114 that are symmetrical with respect to the center of the pixel cell 110 have the same R color component, the photoelectric conversion units 112 and 115 have the same G color component, and the photoelectric conversion units 111 and 116 have the same B color. Let it be a color component.

When performing focus detection by the phase difference detection method using the pixel cell 110, the addition outputs of the three photoelectric conversion units 111 to 113 arranged along the focus detection direction are obtained, and the photoelectric conversion units 114 to 116 are also detected. The addition output is obtained, and the positional phase difference (here, the amount of positional deviation in the horizontal direction in the figure) of the two subject images is obtained from these two addition outputs by, for example, correlation calculation.
Further, when generating the image signal at the position of the pixel cell 110, the addition output (R color component) of the two photoelectric conversion units 113 and 114 symmetrical to the center of the pixel cell 110 is obtained and the photoelectric conversion is performed. The addition output (G color component) of the units 112 and 115 is obtained, and the addition output (B color component) of the photoelectric conversion units 111 and 116 is further obtained. Then, these three addition outputs may be substituted into the equations (9) to (12) instead of the respective color components (equations (5) to (8)) obtained by the interpolation processing described above.

Therefore, when generating an image signal at the position of the pixel cell 100 (or the pixel cell 110), it is not necessary to interpolate from the output of the pixel cell 11 for the captured image around the pixel cell 100 (or the pixel cell 110). Even if the pixel cells 100 (or the pixel cells 110) are arranged almost densely in a large area, the image quality does not deteriorate.
Further, when focus detection is performed using the pixel cell 100 (or the pixel cell 110), focus detection may be performed for each color component without adding the output of each color component of RGB. In this way, accurate focus detection can be performed even when the photographic optical system has chromatic aberration. In addition, focus detection can be performed on a subject having a color change even at the same brightness. Further, a color component used for focus detection may be selected manually or automatically, and focus detection may be performed using the output of the selected color component. In this way, it is possible to selectively perform focus detection for a subject of a specific color.

  Furthermore, when focus detection is performed using the pixel cell 110 of FIG. 27, the color component used for focus detection may be changed according to the open F value of the attached interchangeable lens. For example, the B color component photoelectric conversion units 111 and 116 located on the outer side take in the light beam that has passed outside the exit pupil of the photographing optical system, so that a lens with a brighter open F value than a predetermined value is mounted or high. It is preferably used when focus detection accuracy is required. Since the photoelectric conversion units 113 and 114 for the R color component located inside capture the light beam that has passed near the center of the exit pupil, the defocus amount becomes large when a lens with an open F value that is darker than a predetermined value is attached. It is preferably used when a lens (a lens with a long focal length) is attached.

  In the above example, the pair of photoelectric conversion units 16, 17, 91 to 94,... Of the pixel cell for focus detection are each rectangular, but the present invention is not limited to this. For example, as in the pixel cell 120 illustrated in FIG. 28, it is conceivable that the pair of photoelectric conversion units 121 and 122 are each substantially semicircular, and the two are combined into a substantially circular shape. In this case, the light beam inside the exit pupil (predetermined F value) of the photographing optical system can be taken into the photoelectric conversion units 121 and 122 without waste and used for focus detection. This is advantageous in terms of securing the amount of light at the time of focus detection. The size of the photoelectric conversion units 121 and 122 is irrelevant to securing the light amount.

(Modification 5)
Here, a modified example of the microlenses 13, 15,... Of the pixel cell will be described.
In the above example, the example in which the aperture size (diameter) of the microlenses 13 and 15 is equal to the lengths A ₁₁ and A 12 of one side of the pixel cells 11 and ₁₂ has been described, but the present invention is not limited to this. The opening size of the microlens may be smaller than the length of one side of the pixel cell. In this case, even if the pixel cell for the captured image and the pixel cell for focus detection have the same cell size, the aperture size of the micro lens in the pixel cell for focus detection is set to be smaller than the aperture size of the micro lens in the pixel cell for captured image. By increasing the size, the same effect as described above can be obtained.

  In the above example, the microlens has a circular shape inscribed in the square pixel cell, but the present invention is not limited to this. For example, as shown in FIGS. 29 (a) and 29 (b), a circular four-direction portion (hatched portion) larger than the pixel cell is cut off, and a square central portion is cut out and formed into the same shape as the pixel cell. A microlens may be used. It can be applied to microlenses for photographed images and focus detection. In this case, the opening size of the microlens corresponds to the length of one side of the square shape. In this way, the light beam incident on the image sensor can be used for shooting, focus detection, and the like without waste.

  Further, in the focus detection pixel cell 27 having a different aspect ratio as shown in FIG. 22, a circular portion in two vertical directions (hatching portions) larger than the pixel cell 27 is hatched as shown in FIG. 29C. A microlens that is cut off one by one and cut out at a rectangular central portion and shaped into the same shape as the pixel cell 27 may be used. Even in this case, the light beam incident on the image sensor can be used for focus detection without waste.

In the above example, the microlens is used as an optical element that condenses incident light to the pixel cell and guides it to the photoelectric conversion unit. However, the present invention is not limited to this. Instead of the microlens, a gradient index optical element or a reflective optical element may be used. However, since the microlens is easy to manufacture, it is advantageous in terms of cost.
Furthermore, in the above example, an optical element such as a microlens is provided in the pixel cell for a captured image, but the present invention can be applied to a case where this is omitted.

(Modification 6)
Here, other modified examples will be described.
In the above example, the square pixel cells are arranged in a square lattice shape, but the present invention is not limited to this. The present invention can also be applied when the pixel cell is rectangular or hexagonal. When the pixel cell has a hexagonal shape, it can be considered that the pixel cells are arranged in a two-dimensional honeycomb shape with a half-pitch shift for each row. The focus detection pixel cell may be replaced with a plurality of adjacent captured image pixel cells.

In the above example, the phase detection pixel cell for focus detection is described as an example, but the present invention is not limited to this. In addition, the present invention can be applied to a case where a pixel cell for focus detection using a contrast detection method is provided. In the case of the contrast detection method, the number of photoelectric conversion units in the pixel cell may be one, but the outputs of two or more photoelectric conversion units may be added.
Furthermore, in the above-described example, the example of the image sensor including the pixel cell for the captured image and the pixel cell for focus detection has been described, but the present invention is not limited to this. The present invention can also be applied to a case where a pixel cell for distance measurement, photometry, light adjustment, or the like is disposed instead of the pixel cell for focus detection (or in combination with the pixel cell for focus detection). Even in the case of a pixel cell for distance measurement, photometry, dimming, etc., the responsiveness at low luminance can be improved by making the cell size larger than the pixel cell for the photographed image.

As an image sensor having a pixel cell for distance measurement, for example, when the object to be measured is irradiated with pulse-modulated laser light or the like, the reflected light from the object to be measured is detected for each pixel cell. One can be considered (International Publication No. 97/01111). In order to measure the distance to the object to be measured, the round trip time of light is measured for each pixel cell, and this is converted into a distance.
A special metering or dimming filter (such as a visual sensitivity filter) is placed in the photometric pixel cell that measures the subject brightness or the dimming pixel cell that detects the strobe light reflected from the subject. In addition, a special circuit configuration that can monitor the amount of accumulated charge in a non-destructive manner in real time is added. When such a special circuit configuration is added to the pixel cell for photometry or dimming, the pixel cell for photometry or dimming is made larger than the pixel cell for photographed image, so The chip area can be increased, which is advantageous in terms of circuit layout.

In the above example, pixel cells for captured images are arranged two-dimensionally, and pixel cells for acquiring imaging conditions (focus detection, distance measurement, photometry, dimming, etc.) are arranged therein. However, the present invention is not limited to this. A pixel cell for a photographed image may be arranged one-dimensionally, and a pixel cell for obtaining a photographing condition may be arranged therein.
Furthermore, in the above example, the MOS type imaging device (see FIG. 4 of the circuit configuration) has been described as an example, but the present invention is not limited to this. In addition, the present invention can be applied to a CCD type image pickup device.

  In the above example, a digital still camera (see FIG. 13) has been described as a specific example of the imaging system, but the present invention is not limited to this. In addition, the present invention can be applied to the case where the above-described imaging device is incorporated in an imaging system such as a digital microscope or a surveillance camera.

It is a figure which shows the structure of the image pick-up element 10 of 1st Embodiment. 2 is a diagram showing a cross-sectional structure of a pixel cell 12. FIG. 3 is a diagram for explaining a conjugate relationship between a pair of photoelectric conversion units 16 and 17 and an exit pupil 18. FIG. 1 is a diagram illustrating a circuit configuration of an image sensor 10. It is a figure explaining the conditions of a diffraction simulation. It is a figure explaining the result of diffraction simulation (when opening size of micro lens 15 is 20 micrometers). It is a figure explaining the result of diffraction simulation (when opening size of micro lens 15 is 10 micrometers). It is a figure explaining the result of diffraction simulation (when opening size of micro lens 15 is 4 micrometers). It is a figure explaining the result of diffraction simulation (when opening size of micro lens 15 is 2 micrometers). It is a block diagram which shows the structure of the imaging system 40 of 2nd Embodiment. 3 is a flowchart showing an operation procedure of the imaging system 40. FIG. 4 is a diagram for explaining generation of an image signal in the image sensor 10. It is the schematic which shows the structure of the digital still camera 60 of 3rd Embodiment. It is a figure which shows the structure of the image pick-up element 80 of 4th Embodiment. 2 is a diagram showing a cross-sectional structure of a pixel cell 81. FIG. 2 is a diagram illustrating a circuit configuration of a pixel cell 81. FIG. It is a flowchart which shows the operation | movement procedure of the imaging system of 5th Embodiment. It is a figure which shows the modification of the layout of a pixel cell. It is a figure which shows the modification of the layout of a pixel cell. It is a figure which shows the modification of the layout of a pixel cell. It is a figure which shows the modification of the layout of a pixel cell. It is a figure which shows the modification of the layout of a pixel cell. It is a figure which shows the modification of the layout of a pixel cell. It is a figure which shows the modification of the layout of a pixel cell. It is a figure which shows the modification of the photoelectric conversion part of the pixel cell for focus detection. It is a figure which shows the modification of the photoelectric conversion part of the pixel cell for focus detection. It is a figure which shows the modification of the photoelectric conversion part of the pixel cell for focus detection. It is a figure which shows the modification of the photoelectric conversion part of the pixel cell for focus detection. It is a figure which shows the modification of a micro lens.

Explanation of symbols

10,80 Image sensor; 11,12,26,27,81,90,100,110,120 Pixel cell; 13,15,82 Microlens; 14,16,17,83,84,91-94,101 106,111-116,121,122 photoelectric conversion part; 18 exit pupil;
40 imaging system; 41, 64, 65 photographing optical system; 60 digital still camera

Claims (17)

In an image sensor that captures an image by an imaging optical system,
A first pixel cell including a first photoelectric conversion unit that generates a charge in response to incident light;
An optical element that condenses incident light, and a second photoelectric conversion unit that generates an electric charge according to the light condensed by the optical element, and has a cell size larger than that of the first pixel cell. Two pixel cells,
An image sensor, wherein the first pixel cell and the second pixel cell are two-dimensionally arranged on a substrate. The imaging device according to claim 1,
The image sensor, wherein the second pixel cell has an integer multiple of the first pixel cell. The imaging device according to claim 1,
The first and second pixel cells include optical elements that collect incident light on the first and second photoelectric conversion units, respectively.
The optical element of the second pixel cell has an aperture size larger than that of the optical element of the first pixel cell. In an image sensor that captures an image by an imaging optical system,
A first pixel cell including an optical element that collects incident light, and a first photoelectric conversion unit that generates an electric charge according to the light collected by the optical element;
A second pixel cell including an optical element that condenses incident light, and a second photoelectric conversion unit that generates an electric charge according to the light collected by the optical element;
Two-dimensionally arranging the first pixel cell and the second pixel cell on a substrate;
The optical element of the second pixel cell has an aperture size larger than that of the optical element of the first pixel cell. In the imaging device according to any one of claims 1 to 4,
The optical element of the first pixel cell has an aperture size smaller than 20 μm. In the imaging device according to any one of claims 1 to 5,
Each of the second pixel cells includes a plurality of the second photoelectric conversion units,
Each of the plurality of second photoelectric conversion units is substantially conjugate with an exit pupil of the photographing optical system via an optical element of the second pixel cell. The image sensor according to claim 6, wherein
Two of the plurality of second photoelectric conversion units form a pair,
The two second photoelectric conversion units forming the pair are each provided with a filter of a different color. The imaging device according to any one of claims 1 to 7,
An imaging element, wherein a focus adjustment state of the photographing optical system is detected based on a photoelectric output obtained by the second pixel cell. The imaging device according to any one of claims 1 to 8,
An optical element that condenses incident light; and a third photoelectric conversion unit that generates an electric charge according to the light condensed by the optical element, and has a third cell size different from that of the second pixel cell. An image sensor, further comprising: a pixel cell. The imaging device according to claim 9,
The image sensor according to claim 3, wherein the third pixel cell has a cell size equal to that of the first pixel cell. In the imaging device according to claim 9 or 10,
An imaging element that detects a focus adjustment state of the photographing optical system based on photoelectric outputs obtained by the second pixel cell and the third pixel cell. The image sensor according to claim 8,
A focus detection apparatus comprising: a detection unit that performs focus detection based on an output of the second pixel cell. An image sensor according to claim 11,
A focus detection apparatus comprising: a detection unit that performs focus detection based on at least one of an output of the second pixel cell and an output of the third pixel cell. The focus detection apparatus according to claim 12 or 13,
A photographing optical system disposed on the object side of the image sensor;
The detection unit performs focus detection of the photographing optical system. The imaging system according to claim 14, wherein
Display means for displaying a photographed image based on the output of the first pixel cell and displaying the position of the second pixel cell superimposed on the photographed image as a region where the detection means performs focus detection. An imaging system characterized by comprising. The imaging system according to claim 14, wherein
An image signal at the position of the first pixel cell is generated based on the output of the first pixel cell, and an image signal at the position of the second pixel cell is generated around the second pixel cell. An imaging system comprising: generating means for generating by interpolation processing based on the output of the first pixel cell. The imaging system according to claim 16, wherein
When generating the image signal at the position of the second pixel cell, the generation unit generates each color component of the image signal by the interpolation process, and the luminance component of the image signal is calculated by the second pixel cell. An imaging system characterized by being generated based on an output.

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