JP6067993B2 - Single plate color image sensor - Google Patents

Description

  The present invention relates to a single-plate color image pickup device, and more particularly to a single-plate color image pickup device capable of suppressing color mixing and color moire.

  In order to capture a color image with one image sensor, a single-plate color image sensor in which each light receiving element on the image sensor is covered with a color filter having different spectral characteristics has been used.

  Color filters can be broadly divided into complementary color arrangements with priority on resolution and primary color arrangements with priority on color tone. In complementary color arrangements, there are already various arrangements such as field color difference sequential arrangements and in primary color arrangements such as Bayer arrangement. Proposed.

  FIGS. 6A and 6B are layout diagrams of color filters that have already been proposed, and show (a) a vertical stripe arrangement, (b) a triangle arrangement, and (c) an oblique arrangement.

  A color filter called a vertical stripe (three-color stripe) shown in FIG. 6A, in which three types of filters are sequentially arranged in the horizontal direction, is widely used because of its simple configuration, but the aspect ratio of the number of pixels is small. In the case where it is defined, it cannot be avoided that the horizontal resolution is reduced to 1/3.

  That is, in order to prevent a reduction in resolution in the horizontal direction, the number of light receiving elements in the horizontal direction may be set to be three times the number of light receiving elements in the vertical direction. It is necessary to make the element a vertically long rectangle having an aspect ratio of 3: 1.

  However, if the number of pixels is increased in order to capture a high-definition image, the light receiving element and the color filter become finer, making their manufacture difficult.

Therefore, proposals for avoiding the rectangular shape of the light receiving element have already been made (see, for example, Patent Document 1 and Patent Document 2).
That is, Patent Document 1 discloses a triangle (delta) arrangement of color filters shown in FIG.
Further, Patent Document 2 discloses a color filter having an oblique color arrangement as shown in FIG.

JP-A-7-104115 JP 2010-263228 A

  However, the array disclosed in Patent Document 1 captures a high-definition image in a situation where the aspect ratio of the screen is prescribed to a predetermined value (for example, 9 to 16) because the shape of each light receiving element is a square. For this purpose, it is necessary to make the vertical and horizontal lengths of each light receiving element 1/2 and 2/3 of the side length of one square pixel, respectively, and it is inevitable that the light receiving elements and the color filters are miniaturized. is there.

Also, in the arrangement disclosed in Patent Document 2, since the aperture shape of each light receiving element is a square, the number of pixels in the horizontal direction is set in a situation where the aspect ratio of the screen is limited to a predetermined value (for example, 9 to 16). It is impossible to make it 3 times.
Furthermore, the conventional vertical stripe and the triangle arrangement disclosed in Patent Document 1 have a problem that color mixing is likely to occur because a sufficient distance between adjacent light receiving elements cannot be secured.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a single-plate color imaging device capable of suppressing color mixing and color moiré while maintaining sensitivity.

A single plate color image pickup device according to the present invention includes a single plate color including an image pickup device having a plurality of light receiving elements and a color filter array that covers the light receiving elements formed of first, second, and third color filters. Each of the light receiving element and the color filter has a diamond shape in which a ratio of a horizontal diagonal length to a vertical diagonal length is 2 to 3, and the image pickup element has a gap between the diamond light receiving elements . The color filter array has a configuration in which the first color filter, the second color filter, and the third color filter are arranged in a zigzag manner in the horizontal direction without any gap.

  According to the above configuration, it is possible to suppress color mixing and color moiré while maintaining sensitivity.

  In the single-plate color image pickup device according to the present invention, the image pickup device has a two-pixel common readout structure, and the gates of the two light receiving devices covered with the same color filters adjacent in the vertical direction are closed at the same time. A readout unit is provided that reads out the combined charges.

  According to the above configuration, the sensitivity can be doubled.

In the single-plate color image pickup device according to the present invention, the first color filter is a red filter, the second color filter is a green filter, the third color filter is a blue filter, and the color filter array is the red filter. The green filter , the blue filter and the green filter are repeatedly arranged in the order of zigzag in the horizontal direction without gaps.

  According to the above configuration, not only the resolution with respect to green light, which greatly affects the resolution, but also the sensitivity can be increased.

In the single-plate color image pickup device according to the present invention, the image pickup device has a two-pixel common readout structure, and the two light receiving devices are simultaneously closed by closing the gates of the two light receiving devices covered with the green filters adjacent vertically and horizontally. A reading unit is provided that reads out the charge of the element.

  According to the above configuration, the sensitivity to green light can be increased although the resolution is slightly reduced.

  According to the single-plate color image sensor according to the present invention, it is possible to suppress the occurrence of color mixing and color moire while maintaining the sensitivity.

It is a schematic diagram of a color filter array applied to the image sensor according to the present invention. It is a figure for demonstrating the horizontal scanning method of the image pick-up element comprised with the color filter and light receiving element of the diamond arrangement | sequence which concern on this invention. It is a block diagram of the modification 1 of the diamond arrangement | sequence which concerns on this invention. It is a block diagram of the modification 2 of the diamond arrangement | sequence which concerns on this invention. It is a block diagram of the modification 3 of the diamond arrangement | sequence which concerns on this invention. It is a figure which shows the conventional stripe arrangement | sequence (a), a triangle arrangement | sequence (b), and a diagonal arrangement | positioning.

The single-plate color imaging device according to the present invention includes an imaging device having a plurality of light receiving elements, and a color filter array that includes first, second, and third color filters and covers the light receiving elements.
Each of the light receiving element and the color filter has a diamond shape in which the ratio of the diagonal length in the horizontal direction to the diagonal length in the vertical direction is 2 to 3.

In addition, the imaging element has a configuration in which diamond-shaped imaging elements are arranged on the wafer without any gap.
Further, the color filter array has a configuration in which the first, second, and third color filters are arranged in a zigzag manner in the horizontal direction without a gap.

  First, the reason why each of the light receiving element and the color filter is formed in a diamond shape in which the ratio of the diagonal length in the horizontal direction to the diagonal length in the vertical direction is 2 to 3.

The requirements for determining the shape of the light receiving element and the color filter are as follows.
(1) When the aspect ratio of the imaging screen is defined to a predetermined value (for example, 9 to 16), in order to maximize the opening of the light receiving element, the vertical length of the light receiving element and the color filter is set to one side. The length is equal to the vertical length of the pixel having the length “a”.
(2) to arrange the equator three kinds of color filters in one pixel, to one light-receiving element and the area of the color filter and (a ^2/3).
(3) To prevent color mixing, the distance between adjacent light receiving elements is increased as much as possible.
(4) In order to suppress the occurrence of color moiré, the shape of the light receiving element is a shape having no horizontal and vertical sides.
(5) A shape in which the light receiving elements can be arranged on the wafer without any gap.

  A shape that satisfies all the above five requirements is a diamond (parallelogram) shape having a diagonal length of "a" in the vertical direction.

  When the horizontal diagonal length of the diamond shape is b, [Equation 1] must be satisfied in order to satisfy the requirement (2).

したがって、［数２］が成立する。

Therefore, [Equation 2] holds.

That is, a shape that satisfies all the above five requirements is a diamond shape in which the ratio of the diagonal length in the horizontal direction to the diagonal length in the vertical direction is 2 to 3, for example, if a = 4.7 μm (micrometer), then b = 3. 1 μm.
FIG. 1 is a schematic diagram of a color filter array in which the first color filter is a green filter, the second color filter is a blue filter, and the third color filter is a red filter.

  That is, the color filter array according to the present invention has a configuration in which R, G, and B three kinds of diamond-shaped color filters are arranged in a zigzag manner in the horizontal direction so that the sides are in contact with each other in the order of R, G, and B.

  The distance between adjacent light receiving elements can be evaluated by the inscribed circle of the light receiving element, and it can be considered that the distance between adjacent light receiving elements increases as the radius of the inscribed circle increases.

That is, the radius of an inscribed circle when the diamond shaped according to the light receiving element of the present invention the radius r _D.
Further, assuming that the radius of the inscribed circle in the stripe arrangement and the triangle arrangement shown in FIG. 6 is r _S and r _T , each radius can be calculated by [Equation 3].
In addition, since the diagonal arrangement cannot make the number of pixels in the horizontal direction triple, it is not considered.

From the above examination results, it can be seen that the diamond arrangement according to the present invention has the largest distance between adjacent light receiving elements and is effective in preventing color mixing.
FIG. 2 is a diagram for explaining a horizontal scanning method of an image pickup element constituted by a diamond-array color filter and a light receiving element according to the present invention. When the zigzag is scanned as indicated by a one-dot chain line L, FIG. The color pattern B is used alternately.

In other words, when attention is paid to green (G), scanning is performed in the horizontal direction at a position vertically shifted by half a pixel (a / 2), and the following advantages are produced.
(1) In the stripe arrangement conventionally used, since the pixel centers are in a straight line in the horizontal direction, color moiré is likely to occur when a subject having a regular arrangement (for example, a distant view of a building) is imaged. According to the diamond arrangement according to the above, since the horizontal lines are scanned in a zigzag manner, the generation of color moire can be suppressed.

(2) Similarly, in the conventional triangle arrangement, the side of the pixel is vertical and horizontal, but the side of the building is often vertical and horizontal, so the edge of the subject is placed on the light receiving element (in-phase). Although the difference between when it is not and when it is not (out phase) is significant, in the diamond arrangement according to the present invention, the sides of the light receiving element are slanted, so that the difference between the in phase and the out phase can be reduced.

  Note that several variations of the diamond arrangement according to the present invention are possible.

[Modification 1]
FIG. 3 is a block diagram of Modification Example 1 of the diamond arrangement according to the present invention. In an image sensor having a two-pixel common readout structure, the gates of two light receiving elements covered with the same color filters adjacent to each other at the top and bottom are closed simultaneously. And a reading unit that reads out the charges of the two light receiving elements together.
Here, the two-pixel common readout structure is a structure in which two light receiving elements are connected to one readout circuit via a gate and the light receiving element to be read can be selected by switching the gate in order to reduce the readout circuit. Say.

In a light receiving element having a two-pixel common readout structure, it is a normal usage method that one gate is turned on and the other gate is turned off and one light receiving element is connected to a readout circuit.
In this embodiment, the two gates are turned on at the same time, and the charges of the two light receiving elements are used so as to be summed by the gate capacitance of the signal reading floating diffusion (FD).
As a result, although the resolution is halved, the sensitivity can be improved twice.

It is also possible to add the outputs of a plurality of light receiving elements in software without connecting them in hardware.
In this case, the addition target can be changed by software, and flexible processing can be performed according to the application. However, when the output signals of the two light receiving elements are electrically added, the relative ratio of improvement in sensitivity to noise (S / N ratio improvement rate) remains (square root of 2) = 1.4 times.

[Modification 2]
FIG. 4 is a configuration diagram of a second modification of the diamond arrangement according to the present invention, in which a green filter is doubled as a red or blue filter, and two adjacent light receiving elements are connected in hardware. With this configuration, it is possible to increase the number of green pixels that greatly affects the resolution of the image, and it is possible to improve the resolution of the image as compared with the case where the number of pixels of the three primary colors is the same.

[Modification 3]
FIG. 5 is a block diagram of a third modification of the diamond arrangement according to the present invention, wherein the green filter is doubled to the red or blue filter, the image pickup element has a two-pixel common readout structure, and the right and left adjacent green light receiving elements. A reading unit for adding and reading the charges of the element is provided.

  With this configuration, when the gates of the green light receiving elements are simultaneously turned on, not only the spatial sampling intervals of R, G, and B can be made the same, but also the sensitivity to green is improved and the sensitivity of the entire image is improved. be able to.

  ADVANTAGE OF THE INVENTION According to this invention, the single plate color image pick-up element which can suppress generation | occurrence | production of color mixing and color moire while maintaining a sensitivity is provided, and it is industrially useful.

Claims (4)

A single-plate color image pickup device comprising: an image pickup device having a plurality of light receiving elements; and a color filter array covering the light receiving elements formed of first, second and third color filters,
Each of the light receiving element and the color filter has a diamond shape in which a ratio of a horizontal diagonal length to a vertical diagonal length is 2 to 3,
The imaging element has a configuration in which the diamond-shaped light receiving elements are arranged without gaps,
A single-plate color imaging device in which the color filter array has a configuration in which the first color filter, the second color filter, and the third color filter are arranged in a zigzag manner in the horizontal direction without gaps. The imaging device has a two-pixel common readout structure;
2. The single-plate color imaging device according to claim 1, further comprising: a reading unit that simultaneously reads the charges of the two light receiving elements by simultaneously closing the gates of the two light receiving elements covered by the same color filter adjacent in the vertical direction. The first color filter is a red filter, the second color filter is a green filter, and the third color filter is a blue filter,
2. The single-plate color image pickup device according to claim 1, wherein the color filter array has a configuration in which the red filter, the green filter, the blue filter, and the green filter are repeatedly arranged in a zigzag manner in the horizontal direction without gaps. The imaging device has a two-pixel common readout structure;
4. The single-plate color imaging device according to claim 3, further comprising: a reading unit that simultaneously reads out the charges of the two light receiving elements by simultaneously closing the gates of the two light receiving elements covered with the green filters adjacent to each other vertically or horizontally.

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