Color pattern and pixel level binning for APS image sensor using 2×2 photodiode sharing scheme

• US 7,773,138 B2
• Filed: 09/12/2007
• Issued: 08/10/2010
• Est. Priority Date: 09/13/2006
• Status: Active Grant

• Current Assignee: Tower Semiconductor Limited
• Original Assignee: Tower Semiconductor Limited
• Inventors: Lahav, Assaf, Cohen, David
• Primary Examiner(s): Chan; Jason
• Assistant Examiner(s): Giles; Nicholas G
• Application Number:
  US11/854,501
• Publication Number:
  US 20080062290A1
• Time in Patent Office: 1,063 Days
• Field of Search: 348/273, 348/275, 348/276, 348/277, 348/280, 348/281
• US Class Current: 348/280
• CPC Class Codes: H01L 27/14621 Colour filter arrangements
• CPC Class Codes: H01L 27/14641 Electronic components shared by two or more pixel-elements, e.g. one amplifier shared by two pixel elements
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H04N 2209/046 Colour interpolation to calculate the missing colour values
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements
• CPC Class Codes: H04N 25/46 by combining or binning pixels
• CPC Class Codes: H04N 25/778 comprising amplifiers shared between a plurality of pixels, i.e. at least one part of the amplifier must be on the sensor array itself

Abstract

A color image sensor includes an array of pixels arranged in a plurality of pixel groups, each pixel group including a floating diffusion that is shared by four pixels disposed in a 2×2 arrangement. Each of said four pixels includes a photodetector and a color filter superposed over the photodetector, wherein a first pair of said four pixels include green color, and a second pair of said four pixels includes either red or blue color filters. A control circuit controls the pixel groups such that discrete image information is generated from each pixel in normal light situations, and such that summed image information is generated from each pixel group in low light situations by simultaneously connecting the green pixels to the floating diffusion during a first time period, and simultaneously connecting the red/blue pixels to said floating diffusion during a second time period.

Claims

1. A color image sensor comprising:

a sensor circuit including an array of photodetectors arranged in rows and columns; and

a color filter mosaic including individual filter elements that are superposed in one-to-one registry over said plurality of photodetectors, said mosaic being comprised of a first type of filter element having a first luminance transparency characteristic, a second type of filter element having a second transparency characteristic different from that of said first luminance transparency characteristic, and a third type of filter element having a third transparency characteristic different from that of said first and second luminance transparency characteristics,

wherein the filter elements are arranged in repeating patterns such that;

the first type of filter element is present over every other said photodetector in each row and column, whereby a first group of the first type of filter element forms a first diagonal line comprising only said first type of filter element, and

the second and third types of color filters are arranged in repeating patterns such that the second and third types of filter element are present over every fourth said photodetector in each row and column, whereby a second group of said second type of filter elements forms a second diagonal line comprising only said second type of filter element, and whereby a third group of said third type of filter elements forms a third diagonal line comprising only said third type of filter element,

wherein the sensor circuit further comprises;

a plurality of floating diffusions, each floating diffusion being coupled to a first photodetector by a first transfer gate, a second photodetector by a second transfer gate, a third photodetector by a third transfer gate, and a fourth photodetector by a fourth transfer gate, the first, second, third and fourth photodetectors being included in said array of photodetectors with the first and second photodetectors being disposed in a first row of the array, and the third and fourth photodetectors being disposed in a second row of the array, and

means for simultaneously transferring both a first charge present in the first photodetector and a second charge present in the fourth photodetector to said floating diffusion during a first time period, and for simultaneously transferring both a third charge present in the second photodetector and a fourth charge present in the third photodetector to said floating diffusion during a second time period.

2. The color image sensor according to claim 1, wherein the first type of color filters comprises green color filters, the second type of color filters comprises blue color filters, and the third type of color filters comprises red color filters.

3. The color image sensor according to claim 1,

wherein the first diagonal line is disposed between the second diagonal line and the third diagonal line,

wherein the second diagonal line is disposed between the first diagonal line and a fourth diagonal line comprising only said first type of filter element, and

wherein the third diagonal line is disposed between the first diagonal line and a fifth diagonal line comprising only said first type of filter element.

4. The color image sensor according to claim 1, wherein the sensor circuit comprises a complementary metal-oxide-silicon (CMOS) circuit, and wherein the photodetectors comprise photodiodes.

5. The color image sensor according to claim 1,

wherein both a first color filter superposed over the first photodetector and a second color filter superposed over the fourth photodetector comprise the first type of filter element, and

wherein both a third color filter superposed over the second photodetector and a fourth color filter superposed over the third photodetector comprise one of the second type and the third type of filter element.

6. A color image sensor comprising:

an array of photodetectors arranged in pixel groups on a substrate, each pixel group comprising;

a floating diffusion; and

first, second, third and fourth photodetectors respectively coupled to the floating diffusion by first, second, third and fourth transfer gates, wherein the first and second photodetectors are disposed in a first row of the array, the third and fourth photodetectors are disposed in a second row of the array, the first and third photodetectors disposed in a first column of the array, and the second and fourth photodetectors disposed in a second column of the array,

a color filter mosaic including individual filter elements that are superposed in one-to-one registry over said array of photodetectors, said mosaic being comprised of a first type of filter element having a first luminance transparency characteristic, a second type of filter element having a second transparency characteristic different from that of said first luminance transparency characteristic, and a third type of filter element having a third transparency characteristic different from that of said first and second luminance transparency characteristics, wherein both a first color filter superposed over said first photodetector of each pixel group and a second color filter superposed over the fourth photodetector of said each group comprise the first type of filter element, and wherein both a third color filter superposed over the second photodetector and a fourth color filter superposed over the third photodetector comprise one of the second type and the third type of filter element, and

means for simultaneously transferring both a first charge present in the first photodetector and a second charge present in the fourth photodetector of a selected pixel group to said floating diffusion during a first time period, and for simultaneously transferring both a third charge present in the second photodetector and a fourth charge present in the third photodetector of said selected pixel group to said floating diffusion during a second time period.

7. The color image sensor according to claim 6, wherein the first type of color filters comprises green color filters, the second type of color filters comprises blue color filters, and the third type of color filters comprises red color filters.

8. The color image sensor according to claim 6, wherein the third color filter superposed over the second photodetector and the fourth color filter superposed over the third photodetector comprise red color filters.

9. The color image sensor according to claim 6, wherein the third color filter is superposed over the second photodetector and the fourth color filter superposed over the third photodetector comprise blue color filters.

10. The color image sensor according to claim 6, wherein the sensor circuit comprises a complementary metal-oxide-silicon (CMOS) circuit, and wherein the photodetectors comprise photodiodes.

11. The color image sensor according to claim 10, wherein each pixel group further comprises:

a reset transistor coupled to said floating diffusion;

a source-follower circuit having a gate connected to the floating diffusion; and

a select transistor coupled to the source-follower circuit.

12. The image sensor according to claim 11, wherein said means for simultaneously transferring comprises:

means for actuating, during the first time period, the first and fourth transfer gates of said selected pixel group, thereby simultaneously transferring both a first charge present in the first photodetector and a second charge present in the fourth photodetector to said floating diffusion during said first time period, and

means for actuating, during the second time period, the second and third transfer gates of said selected pixel group, thereby simultaneously transferring both a third charge present in the second photodetector and a fourth charge present in the third photodetector to said floating diffusion during said second time period.

13. A color image sensor comprising:

an array of pixels arranged in a plurality of pixel groups, each pixel group including a floating diffusion and four pixels disposed in a 2×

2 arrangement, each of said four pixels including a photodetector, a transfer gate connected between said photodetector and said floating diffusion, and a color filter superposed over said photodetector, wherein a first pair of said four pixels include color filters of a first type having a first luminance transparency characteristic, and a second pair of said four pixels include color filters having one of a second type and a third type, the second type having a second luminance transparency characteristic different from that of said first luminance transparency characteristic, and the third type having a third transparency characteristic different from that of said first and second luminance transparency characteristics; and

means for determining an image signal strength received by said array of pixels;

means for generating discrete image information from each of said four pixels of a selected pixel group by sequentially connecting each of said four pixels to said floating diffusion of said selected pixel group when the determined image signal strength is above a predetermined minimum signal value; and

means for generating summed image information from said four pixels of the selected pixel group by simultaneously connecting the first pair of said four pixels to said floating diffusion during a first time period, and simultaneously connecting the second pair of said four pixels to said floating diffusion during a second time period different from the first time period when the determined image signal strength is below the predetermined minimum signal value.

14. The color image sensor according to claim 13, wherein the first type of color filters comprises green color filters, the second type of color filters comprises blue color filters, and the third type of color filters comprises red color filters.

15. The color image sensor according to claim 13, wherein the first pair of said four pixels includes green color filters and the second pair of said four pixels include red color filters.

16. The color image sensor according to claim 13, wherein the first pair of said four pixels includes green color filters and the second pair of said four pixels include blue color filters.

17. The color image sensor according to claim 13, wherein each pixel group further comprises:

a reset transistor coupled to said floating diffusion;

a source-follower circuit having a gate connected to the floating diffusion; and

a select transistor coupled to the source-follower circuit.

18. The image sensor according to claim 13, further comprising means for generating summed image information from a set of said pixel groups by simultaneously connecting all pixels of said set of said pixel groups having color filters of said first type during said first time period, simultaneously connecting all pixels of said set of said pixel groups having color filters of said second type during said first time period, and simultaneously connecting all pixels of said set of said pixel groups having color filters of said third type during a third time period.