GB2497084A - Image sensor array comprising two diagonal blue filters and having shallow and deep photo detector regions. - Google Patents

Abstract

An image capture apparatus that includes an array of colour filters for green 114G, red 114B, and blue colours 114B arranged over an array of photoelectric conversion units (12, figure 3) , embedded in a substrate, in the manner of a primary colour Bayer pattern with the exception that a pair of blue colour filters B are arranged along a first diagonal of a sub array (figure 2B) whilst green (G figure 2B) and red colour filters (R, Figure 2B) are arranged along the second diagonal. A blue pixel comprises the blue colour filter 114B and a shallow photoelectric conversion unit, comprising a shallow doped region (< 1um) of a first conductivity type. The green and red pixels (14a, figure 6) comprise of a green and red colour filter respectively, and each posses a deep photoelectric conversion unit (figure 6), which comprise of a deep doped region (>1.5um) of a second conductivity type. A barrier means 66, 64 is disposed under the shallow photodiode to separate the depletion regions that extend from adjacent deep photodiodes. A method is disclosed for the full colour reconstruction of an image by interpolating blue pixel values, which are used for interpolating green pixel values (figure 11).

Description

COLOR IMAGE SENSOR, COLOR FILTER ARRAY and COLOR

RECONSTRUCTION METHOD

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject matter disclosed, generally relates to structures and methods for sampling color images on solid state image sensors and reconstructing the color images.

2. Background Information

Photographic equipment such as digital cameras and digital camcorders may contain electronic image sensors that capture light for processing into still or video images. Electronic image sensors typically contain millions of light capturing elements such as photodiodes.

The elements each receives light that passes through a color filter in a two-dimensional color filter array.

Figures lA and lB are illustrations showing prior-art color filter arrays according to the Bayer pattern in primary colors.

United States Patent 7,442,974 discloses a barrier region between adjacent photodiodes to prevent depletion region from one of the adjacent photodiodes from merging with a depletion region from the other one of the adjacent photodiodes.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present invention relates to a pixel array of an image sensor supported by a substrate of a first conductivity type, comprising a color filter array, said color filter array being a two-dimensional sub-array of two-by-two arrays of color filters where each two-by-two sub-array comprises a pair of blue color filters along a diagonal and a pair of a red color filter and a green color filter along the other diagonal. Each of the blue color filters transmits light to a shallow photodiode in the substrate whereas each of the red and green color filters transmits light to a deep photodiode in the substrate. The shallow photodiode comprises a shallow doped region of a second conductivity type. The shallow doped region is preferably less than l.Sum deep into the substrate, more preferably less than lum deep. The deep photodiode comprises a deep doped region of the second conductivity type. The deep doped region is more than 1.Sum deep into the substrate, preferably more than 2.Oum, and even more preferably more than 2.5um deep into the substrate. Either or both the shallow dope region and the deep doped region may be doped with phosphorus. The substrate may be a lightly doped epi layer of the first conductivity type doped with boron to a net doping concentration between 5el4/cm and 1e16/cm3. The substrate may have a thickness between 3um and 7um. The substrate may be on top of a heavily doped substrate of the first conductivity type doped to a doping concentration of at least lel9/cm.

In the first aspect, it is further desirable that a barrier means be disposed under the shallow photodiode and laterally between a deep photodiode and another deep photodiode, the barrier means being for preventing a depletion region that extends from the deep photodiode from merging with another depletion region that extends from the other deep photodiode. The barrier means is preferably a barrier region having the first conductivity type and doped to a higher doping concentration than the substrate. The doping concentration preferably peaks between 3e16/cm3 and 7e17/cm3.

In the first aspect, it is further desirable that a barrier region be disposed under the shallow photodiode and laterally between a deep photodiode and another deep photodiode, in the barrier region there being a neutral region that separates a depletion region that extends from the deep photodiode from another depletion region that extends from the other deep photodiode.

In a second aspect of the present invention, a barrier means is disposed under a shallow photodiode of a blue pixel. The shallow photodiode has a shallow doped region arranged to receive blue light from a blue color filter. The barrier means functions to keep a depletion region that extends from a deep photodiode of an adjacent pixel, arranged to detect a red (or green) light, on one lateral side of the blue pixel from merging with a depletion region that extends from another deep photodiode of another adjacent pixel, arranged to detect a red (or green) light, on another lateral side of the blue pixel.

In a third aspect of the present invention, a barrier region is disposed under a shallow photodiode of a blue pixel. The shallow photodiode has a shallow doped region arranged to receive blue light from a blue color filter.

The barrier region includes a neutral region that separates a depletion region that extends from a deep photodiode of an adjacent pixel, arranged to detect a red (or green) light, on one lateral side of the blue pixel from a depletion region that extends from another deep photodiode of another adjacent pixel, arranged to detect a red (or green) light, on another lateral side of the blue pixel.

In a fourth aspect of the present invention, a pixel array of an Image sensor comprises a color filter array that is a two-dimensional array of two-by-two sub-arrays of color filters where each two-by-two sub-array comprises a pair of blue color filters along a diagonal and a pair of a red color filter and a green color filter along the other diagonal. A full-color image is reconstructed by a color interpolation method of this invention from a first image generated from the pixel array. Blue pixel values are interpolated for pixels that have no blue pixel values in the first image. Green pixel values are generated by interpolation for pixels that have no green pixel values in the first image, using at least the interpolated blue pixel values and green pixel values of the first image. Red pixel values are generated by interpolation for pixels that have no red pixel values in the first image, using at least the interpolated blue pixel values and red pixel values of the first image.

In the first to third aspeots, the barrier region has the first conductivity type and doped to a higher doping concentration than the substrate. The doping concentration preferably peaks between 3e16/cnt3 and 7 e 17/cm3.

In the first to third aspects, the first conductivity type may be p-type and the second conductivity type may be n-type.

In the first to third aspects, it is preferable that a portion of at least one of the deep photodiodes extends under the blue color filter.

In the first to third aspects, it is preferable that a portion of at least one of the deep photodiodes extends under the shallow doped region.

In the first to third aspects, it is preferable that at least one of the depletion regions extends under the blue color filter.

In the first to third aspects, it is preferable that at least one of the depletion regions extends under the shallow doped region.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1A and lB are illustrations showing prior-art color filter arrays according to the Bayer pattern in primary colors; Figures 2A and 2B are illustrations showing color filter arrays according to the present invention; Figure 3 shows an embodiment of an image sensor; Figure 4 shows an embodiment of an image capture system; Figure 5 shows a schematic of a color filter and a corresponding photodiode for each of four adjacent pixels in an embodiment of the pixel array; Figure 6 shows a vertical section (along the XX' line of Figure 10) of an embodiment of a green pixel; Figure 7 shows a vertical section (along the XX' line of Figure 10) of an embodiment of a blue pixel; Figure 8 is a plot of nen doping concentration along the vertical YY' line across the green pixel shown in Figure 6; Figure 9 is a plot of net doping concentration along the vertical ZZ' line across the blue pixel shown in Figure 7; Figure 11 shows a block diagram of a camera processor coupled to receive image data from the pixel array of the image sensor.

DETAILED DESCRIPTION

Disclosed is an image sensor pixel array supported by a substrate and a color image reconstruction method.

Figure 3 and Figure 4 describe an image sensor 10 and an image capture system 202, respectively.

Referring to the drawings more particularly by reference numbers, Figure 3 shows an embodiment of an image sensor 10 that comprises a pixel array 12, a row decoder 20, a light reader 16, and an ADC 24. The pixel array comprises a two dimensional array of a two-by-two group 15 of pixels, where each pixel has one or more photodetector(s) and a color filter that filters light before it reaches the photodetector. Bus 18 comprises column output signals lines that connect pixels by the column. The light reader 16 may be as described in US Patent 7,233,350 or as described in U.S. Patent Application 12/639,941. It has one or more capacitor(s) for sampling each column output signal in the bus 18.

Analog output signal(s) 26 from the light reader 16 is provided to ADO 24 for conversion into digital image data that are output onto bus 66. Row decoder 20 provides row signals in bus 22 for selecting pixels by the row, for resetting pixels by the row, and for transferring charges in pixels by the row. Color filter array 13 is a two-dimensional array of color filters that overlay photodetectors of the pixel array 12.

Figure 4 shows an embodiment of an image capture system 202 that includes the image sensor 10, a focus lens 204, a drive motor and circuit 218, a processor 212, an input device 206, a display 214, and a storage device 216.

Pixel Array Figures 2A and 2B are illustrations showing color filter arrays according to the present invention; Figure 2A shows a color filter array 13 according to the present invention. Image output from the pixel array 12 begins at the bottom and progresses to the top, in the direction indicated by the "Vertical Scan" arrow. The color filter array is organized as a two-dimensional array of color filters of Green (G), Red (F), and Blue (B) colors. More particularly, the color filter array 13 is organized as a two-dimensional array of a two-by-two unit 13a (encircled in dashed line) that consists of a pair of Blue (B) color filters disposed along one diagonal and a pair of a Red (R) color filter and a Green (G) color filter disposed along the other diagonal.

Figure 2B shows oolor filter array 13' as an alternate embodiment of color filter array according to the present invention. This color filter array 13' is rotated 45 degrees with respect to the color filter array 13, and thus is rotated 45 degrees with respect to the vertical scan direction. More particularly, the color filter array 13' is organized as a two-dimensional array of a two-by-two unit 13a' (encircled in dashed line) that is 45-degree rotated with respect to the two-by-two unit 13a.

Figure 5 is a schematic of four pixels in the two-by-two pixel group 15, showing a color filter and a photodetector for each of the four pixels. A pair of blue color filters 114B, a red color filter ll4R and a green color filter 114G are arranged in the order according to the two-by-two unit 13a shown in Figure 2A. On the upper right, green pixel 14a has a green color filter 1140 that filters light for photodetector bOa. On the lower right, blue pixel 14b has a blue color filter 114B that filters light for its photodetector 10Gb. Likewise, on the upper left, another blue pixel 14d has a blue color filter ll4B that filters light for its photodetector bOb. On the lower left, red pixel l4c has a red color filter 114k that filters light for photodetector lOOc.

Green Pixel Figure 6 describes the green pixel 14a. The red pixel l4c is similarly constructed except the gl2red color filter 114k replaces the green color filter 114G.

Figure 6 shows a vertical section of an embodiment of a green pixel 14a that includes a photodiode bOa formed in a lightly doped semiconductor substrate 56, which is of a first conductivity type, e.g. p-type and typically doped with boron. This can be seen as a vertical section along the cut line XX' of Figure 10. The substrate 56 further preferably has a net doping concentration between 5el4/cm3 and 5e15/cm. Typically, the dopant impurity is boron. The substrate 56 is preferably a p-epi layer on a heavily doped p-substrate (not shown) having net doping concentration in excess of 1e19/cm3. Photodiode lOOa comprises deep doped region 54c of a second conductivity type, preferably n-type and typically doped with phosphorus. Photodiode bOa further comprises a shallow doped region 54a, also of the second conductivity type, disposed vertically above the deep doped region 54c and under a surface first region 63, of the first conductivity type. The surface first region 63 prevents depletion region that extends from the shallow doped region 54a from reaching the top interface of the substrate 56. The photodiode bOa further comprises a mezzanine doped region 54b of the second conductivity type. Together, the shallow doped region 54a, the mezzanine doped region 54b and the deep doped region 54c are electrically mutually connected and are as a whole electrically connected to a sensing node 111 (a source/drain diffusion of the second conductivity type for transfer switch 117) via a transfer switch 117 that when turned ON transfers charges between the photodiode lOOa and the sensing node 111. The transfer switch 111 has a gate 58. The mezzanine doped region 54b is not necessary if the bottom of the shallow doped region 54a meets the to of the deep doped region 54c. The phctodiode lOOa has a connection region 55 of the second conductivity type to electrically connect the shallow doped region 54a to the transfer switch 117 during the transfer of charges. The doped regions 54a, 54b, 54c may have a peak doping concentration between lel6/cm and 3e18/cm3, and preferably between 5el6/cm and 1e18/cm3.

The doped regions 54b, 540 more preferably has a peak doping concentration between 3e16/cm3 and 7e17/cm3 Phosphorus may be a dopant impurity. The bottom of the deep doped region 54c may reach between l.Sum to 4um into the substrate 56, and preferably between 2.5um to 3.Sum.

A reset transistor 112 and an output transistor 116 are drawn schematically in Figure 6. The reset transistor 112 resets the sensing node 111 to a predetermined voltage. The output transistor 116 buffers a voltage signal on the sensing node 111 to an electrical signal line (OUT(m) mentioned above) connected to a source/drain node of the output transistor 116. Routing wires 83 and via 85 are part of interconnect layers that connect among transistors in the pixel array 12 and between the transistors and the row decoder 20 and the readout circuit light reader 16.

Figure 8 shows an exemplary vertical net doping profile through the vertical cut line YY' of Figure 6.

The net doping concentration begins at the top surface of the substrate 56 (depth of Oum) at lel8/cmi of the first type (e.g. p-type) in the surface first region 63. At a depth of approximately 0.lsum (the junction depth), the net doping concentration switches to the second type (e.g. n-type) and remains so until approximately 3.l5um, where it switches back to the first type arid converges to the substrate's doping concentration.

Referring to Figure 6 again, a green color filter 1140 is disposed above the substrate 56 to transmit green light, which has wavelengths in air between SOOnm and 600nm, through upper light guide 130 and lower light guide 116 to reach the photodiode llOa. The green color filter 1140 (as well as other color filters ll4B and 114R) may comprise a dye, such as an organic or organometallic colorant, that absorbs light outsides the abovementioned wavelength range of the green light more than the green lights. The upper 130 and lower 116 light guides may comprise a silicon nitride. The upper 130 and lower 116 light guides use total internal reflection at their lateral boundaries to prevent lateral exit of light rays. The lower light guide 116 is preferably embedded in an insulating film (e.g. an intermetal dielectric and/or a interlayer dielectric, either or both comprising a silicon oxide) Referring to Figure 6 again, the doped regions 54b, 54c are flanked on both left and right sides by barrier regions 64, 66. These barrier regions 64, 66 are of the first conductivity type, and have peak doping concentrations that are above that of the substrate 56, preferably peaking between 3e16/cm3 and 7e17/cn3. The barrier regions 64, 66 are located vertically below blue color filters 114B that are laterally adjacent to the green color filter 114G of the present green pixel 14a.

The barrier regions 64, 66 function to prevent depletion region(s) that extend from the doped regions 54b, 54c of the present photodiode lOOa from merging with depletion region(s) that extend from other photodiodes. As shown in Figure 6, outer boundary 71b of a depletion region that extends from within the deep doped region 54c at inner boundary 73a is kept apart from another outer boundary 71a (of a depletion region of a photodiode of another green pixel outside the page to the left of the blue pixel on the left) by a neutral region (marked "xxx") in the barrier region 64 on the left. Likewise, on the right side of the photodiode lOOa, an outer boundary 7lc of a depletion region that extends from inner boundary 73b within the doped region 54c is kept apart from outer boundary 71d (of a depletion region of a photodiode of the blue pixel on the right) by a neutral region (marked "xxx") within the barrier region 64 on the right.

It is noted that the depletion regions that extend from the photodiode lOOa extend to vertically below the adjacent blue color filters 114B at a depth within the range of depth of the deep doped region 54c. This is particularly beneficial for green light (and red light as well, for red pixel, which is similarly constructed as the green pixel except red color filter ll4R is used in lieu of the green color filter ll4G), which penetrates deep into the substrate and radiates out from bottom of the lower light guide 114 in the shape of an inverted funnel.

Blue Pixel Figure 7 shows a vertical section of an embodiment of a blue pixel l4d (or 14b) as the neighbor to the right of the green pixel 14a shown in Figure 6. This can be seen as a vertical section along the cut line XX' of Figure 10.

The blue pixel 14d has a shallow photodiode lOOd that comprises a shallow doped region 54d under a surface first region 63 (like the one in the green pixel 14a) Incident light from above the blue pixel 14d is filtered by the blue color filter 114B, continues through upper and lower 116 light guides, and enters the shallow doped region 54d after passing through the surface first region 63.

Under the photodiode lOOd is a slab of barrier region 66, already discussed above in connection with the green pixel 14a. This barrier region 66 belong to the first conductivity type (e.g. p-type), and can be formed by doping the substrate 56 to a higher doping concentration, such as between 3e16/cm3 and 7e17/cm3. The barrier region 66 maintains a neutral region (marked with "uuu" and "vvv") to maintain separation of a depletion region that extends from the shallow doped region 54d of the present photodiode lOOd of the present blue pixel l4d from the depletion regions that extend from the deep doped regions 54o of the neighboring green pixels (or red pixels) . As shown in Figure 7, the outer boundaries 75, 71c, 71d of these three different depletion regions are maintained separate in the barrier region 66.

The other barrier region 64, mentioned above in connection with the green pixel l4a, is shown in Figure 7 to maintain a neutral region (marked "xxx") that keep depletion regions extending from green pixels (or red pixels) from its left and right sides from merging together. Maintaining separation of depletion regions that extend from different photodiodes avoids capacitive coupling through the substrate between the photodiodes.

It is also noted that the deep doped regions 54c of the two neighboring green pixels (or red pixels) may extend below the photodiode lOOd and/or the blue color filter ll4B. The depletion regions that emanate from these deep doped regions 54c even more so overlap with the blue photodiode lOCd and/or the blue color filter ll4B. This arrangement has a benefit of retrieving the carrier (e.g. electron, where the substrate 56 is p-type) back into the green (or red) photodiode lOCa (or 10Cc) where the carrier is generated by green (or red) light that reaches the substrate's top surface at the green (or red) pixel at an obtuse angle and subseguently makes some lateral travel within the substrate 56 before generating the carrier.

Figure 9 is a graph that plots an exemplary net doping concentration profile in the substrate 56 through the vertical cut line ZZ' that slices through the surface first region 63, the shallow doped region 54d, the barrier regions 64, 66 and the substrate 56. As in Figure 8, which plots an exemplary vertical net doping concentration profile for the green (or red) pixel, Figure 9 starts with a surface doping concentration of the first type (e.g. p-type, where substrate 56 is p-type) at 1e18/cm3, then falls rapidly till depth of approximately 0.lSum (the junction depth) where the net doping concentration switches sign to the second type (e.g. n-type, where the substrate 56 is p-type) . From here till approximately 0.7um deep into the substrate 56 is the range of the shallow doped region 54d, doped to peak concentration of approximately 3e17/cmt Deeper than 0.7um, the net doping concentration switches sign back to the first type (e.g. p-type, where substrate 56 is p-type) . The net doping concentration climbs to a peak at approximately l.Sum depth in the substrate 56, corresponding to the slab of shallow barrier region 66, then continues to climb to the next peak at approximately 2.3um depth in the substrate 56, corresponding to the deeper barrier region 64. In general, either or both peaks can have net doping concentration between 3e161cm3 and 7e17/cm3.

Plan View Figure 10 shows a plan view of five blue pixels, two green pixels and two red pixels in a 3-by-3 array. The center pixel is a blue pixel. The four pixels in the four corners are also blue pixels. The two pixels to the left and right (in the plane of the drawing) of the center pixel are green pixels. The two pixels above and below (in the plane of the drawing) the center pixel are red pixels. A barrier region 64 is collocated with each blue pixel. A deep doped region 54c is centered within each green pixel and extends to overlap with adjacent blue pixels. Likewise, a deep doped region 54c is centered within each red pixel and extends to overlap with adjacent blue pixels. The barrier region 64 of the center blue pixel is located between the pair of deep doped regions 54c of the two green pixels, as well as between the pair of deep doped regions 54c of the two red pixels.

Additionally, between each pair of diagonally adjacent green pixel and red pixel is disposed a barrier region 68. The barrier region 68 functions like the barrier region 64 to prevent merger of depletion regions that extend from different deep dope regions of different pixels. Whereas the barrier region 64 provides separation of depletion regions of green (or red) pixels separated by a blue pixel, the barrier region 68 provides separation of a depletion region of a red pixel from that of an adjacent green pixel across a midpoint between a pair of mutually adjacent blue pixels that are both adjacent to the red pixel. The barrier region 68, like the barrier region 64, is of the first conductivity type (e.g. p-type if the substrate 56 is p-type) and has peak doping concentration between 3e16/cm3 and 7e17/cm3.

An advantage of barrier region 64 under the shallow doped region of the blue pixel compared with the barrier region disclosed in US 7,442,974 is that in the present invention the depletion regions that extend from the deep photodiodes of the adjacent green and red pixels are allowed to expand into the blue pixel in the depth of the substrate to capture the carrier generated by deep penetrating green or red light rays that make substantial horizontal travel beyond the respective green and red pixels.

The embodiment above is the best mode.

Other Embodiments Tn an alternative embodiment, the barrier regon 64 is not deployed. As a result, a depletion region may connect one deep photodiode to another photodiode across a blue pixel, resulting in some capacitive coupling between these two photodiodes. Nevertheless, this arrangement still retains the benefit of the depletion region surrounding the deep photodiode to take the shape of an inverted funnel, facilitating collection of charges generated by light that, while penetrating beyond 2um into the substrate, make substantial lateral travel.

In another embodiment, the abovementioned arrangement among the blue pixel and the neighboring green pixels is employed in a pixel array covered by a color filter array arranged according to the Bayer pattern as shown in Figure 1A or lB. In particular, in this embodiment, the blue pixel has a shallow photodiode lOOd as described above that comprises a shallow doped region 54d as described above and under the shallow doped region is disposed a barrier region 64. A green pixel bOa on a lateral side of the blue pixel lOOd and another green pixel bOa on an opposite lateral side of the blue pixel lOOd both have deep doped regions 54c from which depletion regions extend into the barrier region 64 but are prevented from merging by a neutral region in the barrier region 64.

More generally, an alternative embodiment has a blue pixel that includes a blue color filter and a shallow photodiode lOOd, with a barrier region 64 disposed underneath. The blue pixel is adjacent to a second pixel arranged to detect a red light and/or a green light. For example, the second pixel may have a green or a red or a yellow color filter. The second pixel may even be a white pixel, i.e. light from the entire visible light spectrum is permitted to reach a photodetector of the second pixel.

The second pixel has a deep photodiode lOOa that includes the deep doped region 54c. On a opposite side of the blue pixel is a third pixel that also employs a deep photodiode in the substrate, the deep photodiode may or may not reach the same depth as that of the second pixel but is deeper than the shallow photodiode lOOd of the blue pixel. The barrier region 64 has a neutral region that separates depletion regions that extend from the deep photodiodes of the second and third pixels into the barrier region 64.

Pixel Operations An output signal line OUT(m) 124 (not shown) connected to source of transistor 116 is part of bus 18 and may be sampled by the light reader 16. U.S. Patent Application 12/639,941 shows various methods of the sequence of operating switches in such a circuit and sampling the column output signal. Alternatively, the switches may be operated and the column output signal sampled according to conventional correlated double sampling for pinned photodiode.

The photodetectors, transfer switch 117 (or ll7c) reset switch 112 and output transistor 116 may be operated in accordance with any method shown in U.S. Patent Application 12/639,941. In particular, to begin integrating charge on the photodetector, an output signal transmitted by the output transistor 116 onto column signal line OUT(m) 124 is sampled by a light reader when the reset switch 112 and the transfer switch 117 are both in triode region; an output signal is subsequently sampled again when the reset switch 112 is turned off while the transfer switch 117 remains in triode region; an output signal is finally sampled again after the transfer switch 117 switches off; and, a signed-weighted sum among these three sample signals is formed to provide a noise signal. At the end of the charge integration, an output signal from output transistor 116 is sampled on column signal line OUT(m) 124 when the reset switch 112 is in triode region while the transfer switch is non-conducting; the reset switch 112 is subsequently switched off and an output signal on column signal line OUT(m) 124 sampled; an output signal on line OUT(m) 124 is sampled again when the transfer switch 117 is in triode region; and, a signed-weighted sum among these three sampled signals is formed to provide a light response signal. The noise signal is subtracted from the light response signal to provide a de-noised light response output signal.

Alternatively, the photodiode lOOd (and/or lOOb) and the transfer switch 117, the reset switch 112 and the output transistor 116 of the blue pixel may be operated in accordance with correlated double sampling method for a pinned photodiode pixel to sample signals from the blue pixel. To begin a charge integration: (i) turn on the transfer switch 117 and the reset switch 112 and completely deplete photodiode lOUd, (ii) switch off the transfer switch 117 and the reset switch 112. To end a charge integration: (A) turn the reset switch 112 on and off, thus resetting the sensing node 111, (B) transmit buffered and level-shifted reset output signal from the output transistor 116 to the light reader 16, (C) the light reader samples the output signal, (D) turn on the transfer switch 117 and charges from the photodiode lOOd (or lOOb) are transferred to the sensing node 111, (E) the light reader samples an output signal from the output transistor 116, and (F) a difference is taken between the two sampled output signals.

Reconstruction of Full-Color Image The image data captured from the pixel array 12 has one color for each pixel. The image is referred to as a mosaic image. In an embodiment that employs the color filter array of Figure 2A or 2B, essentially, 50% of the pixels are blue, 25% are red, and the other 25% are green.

This mosaic image will be interpolated to a reconstructed full-color image where each pixel has all three colors, viz, red, green, and blue.

The reconstruction of the full-color image can be performed using any of the known techniques for Bayer image color interpolation (or demosaicking) by interchanging the roles of green and blue colors. For example, a blue pixel value is interpolated for each image pixel of the mosaic image that does not have a blue pixel value by interpolating from the blue pixel values of the blue image pixels of the mosaic image. Any method for interpolating green pixel values for a mosaic image of the Bayer pattern type may be employed to interpolate blue pixel values for the mosaic image of the color filter pattern of Figure 2A and 2B.

In this example, interpolated green pixel value for the blue image pixels may be computed by interpolation from at least the blue pixel values of the blue image pixels of the mosaic image, the interpolated blue pixel values of the green image pixels of the mosaic image, and the green pixel values of the green image pixels of the mosaic image. For example, the green pixel value of the green image pixel is subtracted from the interpolated blue pixel value of the green image pixel to form a blue chroma signal B-G, and subsequently an interpolated blue chroma signal S is computed for the blue image pixels by interpolation from the blue chroma signal B-El, then finally the interpolated green pixel value for the blue image pixel is found by subtracting the interpolated blue chroma signal S from the blue pixel value of the blue image pixel.

In a similar manner, interpolated red pixel values for the blue image pixels may be computed by interpolation from at least the blue pixel values of the blue image pixels of the mosaic image, the interpolated blue pixel values of the red image pixels of the mosaic image, and the red pixel values of the red image pixels of the mosaic image. For example, the red pixel value of the red image pixel is subtracted from the interpolated blue pixel value of the red image pixel to form a blue-red difference signal B-R. The blue-red difference signal B-B. is interpolated to the blue image pixel to form an interpolated blue-red difference signal Q. Finally, the interpolated red pixel value for the blue image pixel is found by subtracting the interpolated blue-red difference signal Q from the blue pixel value of the blue image pixel.

In a similar manner, interpolated green pixel values for the red image pixels may be computed by interpolation from at least the interpolated blue pixel values of the green image pixels and the red image pixels, and the green pixel values of the green image pixels of the mosaic image. For example, the blue-green difference signal B-C is interpolated from the green image pixels to the red image pixels to form an interpolated blue-green difference signal T. Subseguently, the interpolated green pixel value for the red image pixel is found by subtracting this interpolated blue-green difference signal T from the interpolated blue pixel value of the red image pixel.

In a similar manner, interpolated red pixel values for the green image pixels may be computed by interpolation from at least the interpolated blue pixel values of the green image pixels and the red image pixels, and the red pixel values of the red image pixels of the mosaic image. For example, the blue-red difference signal B-R is interpolated from the red image pixels to the green image pixel to form an interpolated blue-red difference signal P. Subseguently, the interpolated red pixel value for the green pixel is found by subtracting the interpolated blue-red difference signal P from the interpolated blue pixel value of the green pixel.

Alternatively, interpolated red pixel values for the green image pixels may be computed by interpolation from at least the red pixel values of the red image pixels, the interpolated green pixel values generated for the red image pixels, and the green pixel values of the green image pixels. For example, the interpolated green pixel values generated for the red image pixels are first subtracted from the red pixel values of the red image pixels to form a red-green difference signal R-G over the red image pixels. This red-green difference signal R-G is then interpolated to the green pixels to form an interpolated red-green difference signal U. Finally, the interpolated red pixel value for the green image pixel is formed by adding the green pixel value of the green image pixel to the interpolated red-green difference signal U at the green image pixel.

The reconstruction of the image data from the pixel array 12 may be performed in a demosaicking unit 222 of a processor 212 located on a separate semiconductor substrate than substrate 56. The image data from the pixel array 12 is transferred across a bus 66 into a buffer 220 on the separate semiconductor substrate via an input port 240 of the processor 212. A buffer 220 receives the image data and subseguently provides the image data to the demosaicking unit 222. The demosaicking unit 222 is a circuit that performs computation on the image data.

The full-color image thus reconstructed is processed through a color correction unit 224, an image compression unit 226 and eventually stored in a storage device 216.

The demosaicking unit may perform the color interpolation under control of computer instructions, which may be stored in a non-volatile memory 228. The non-volatile memory 228 may be an on-chip flash memory.

Closing While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.