Solid state imaging device and driving method thereof

1. A solid state imaging device, comprising:

a solid state imaging element including a plurality of photoelectric conversion elements arranged in a matrix, the solid state imaging element including pixels grouped into pixel mixture unit areas, each of which includes q pixels (q is a natural number equal to or greater than 2) in the first direction of the solid state imaging element and p pixels (p is a natural number equal to or greater than 2) in the second direction that crosses the first direction;

pixel addition means for performing a first-field pixel addition process of adding together electric charges of a plurality of pixels included in the plurality of pixel mixture unit areas and a second-field pixel addition process of adding together the electric charges of the plurality of pixels included in the plurality of pixel mixture unit areas based on a combination of the pixel mixture unit areas which is different from that of the first-field pixel addition process; and

output means for alternately outputting signals of the electric charges obtained in the first-field pixel addition process and second-field pixel addition process as signals for interlaced scanning.

2. The solid state imaging device of claim 1 , wherein the pixel mixture unit areas overlap one another in the first and second directions to constitute an arrangement which has a two-dimensional repetition.

3. The solid state imaging device of claim 2 , wherein:

the number of pixels in the first direction in each of the pixel mixture unit areas, q, satisfies the relationship of q=4m+1 (m is a natural number), and the number of pixels in the second direction in each of the pixel mixture unit areas, p, satisfies the relationship of p=4n+1 (n is a natural number); and

the pixel mixture unit areas overlap one another by (q+1)/2 pixels in the first direction and by (p+1)/2 pixels in the second direction.

4. The solid state imaging device of claim 2 , wherein:

the number of pixels in the first direction in each of the pixel mixture unit areas, q, satisfies the relationship of q=4m−1 (m is a natural number), and the number of pixels in the second direction in each of the pixel mixture unit areas, p, satisfies the relationship of p=4n−1 (n is a natural number); and

the pixel mixture unit areas repeatedly overlap one another alternately by (q−1)/2 pixels and (q+3)/2 pixels in the first direction and alternately by (p−1)/2 pixels and (p+3)/2 pixels in the second direction.

5. The solid state imaging device of claim 2 , wherein:

electric charges of a plurality of pixels included in one pixel mixture unit area are added together in the first direction; and

the electric charges of the pixels which are added together respectively in the plurality of pixel mixture unit areas and transferred in the first direction are added together in the second direction.

6. The solid state imaging device of claim 2 , wherein:

the pixel addition means performs a plurality of line processes on two of the pixel mixture unit areas which are adjacent in the first direction wherein electric charges of the plurality of pixels included in the two pixel mixture unit areas are added together; and

in at least one of the plurality of line processes, two of the pixel mixture unit areas which are shifted in the second direction by one or more pixels are processed.

7. The solid state imaging device of claim 6 , wherein the centroid position of a first region formed by two of the pixel mixture unit areas which are processed in one of the line processes is on a line that extends in the first direction and passes over the median point between the centroid position of a second region formed by two of the pixel mixture unit areas which are processed in another one of the line processes and the centroid position of a third region formed by two of the pixel mixture unit areas which is processed at the same time with the second region and is placed adjacent to the second region in the second direction.

8. The solid state imaging device of claim 1 , wherein the solid state imaging element includes a color filter provided over front faces of the photoelectric conversion elements.

9. The solid state imaging device of claim 8 , wherein:

a color filter arrangement of the solid state imaging element is a combination of Bayer arrangements of 2 rows×2 columns;

the pixel addition means includes a first-direction transfer stage for adding together electric charges of the plurality of pixels in the first direction in each of the pixel mixture unit areas and a second-direction transfer stage for adding together the electric charges obtained by the addition in the first-direction transfer stage in the second direction; and

the electric charges obtained by the addition in the second-direction transfer stage are pixel signals for complementary color filter arrangement display.

10. The solid state imaging device of claim 8 , wherein a color filter arrangement of the solid state imaging element is a combination of four colors, cyan, yellow, green and magenta, arranged in 2 rows×2 columns.

11. The solid state imaging device of claim 1 , wherein the pixel addition means includes a first-direction transfer stage and a second-direction transfer stage, the first-direction transfer stage including a plurality of CCDs which transfer the electric charges of the pixels in the first direction, the second-direction transfer stage including a plurality of CCDs which transfer the electric charges transferred from the first-direction transfer stage in the second direction.

12. The solid state imaging device of claim 11 , wherein:

the second-direction transfer stage alternately includes a storage region which includes a first gate and retains an electric charge and a barrier region which includes a second gate and functions as a barrier against transfer of electric charges; and

the first gate and the second gate are electrically separated to receive separate biases.

13. A method for driving a solid state imaging device which includes a solid state imaging element including a plurality of photoelectric conversion elements arranged in a matrix, the solid state imaging element including pixels grouped into pixel mixture unit areas, each of which includes q pixels (q is a natural number equal to or greater than 2) in the first direction of the solid state imaging element and p pixels (p is a natural number equal to or greater than 2) in the second direction that crosses the first direction, the method comprising the steps of:

(a) adding together electric charges of pixels included in each of the pixel mixture unit areas and transferring the added electric charges in the first direction;

(b) adding together electric charges of pixels from a plurality of pixel mixture unit areas while the electric charges added and transferred in the first direction at step (a) are transferred in the second direction; and

(c) alternately outputting signals which relates to the electric charges added together at step (b) in first and second fields as signals for interlaced scanning.

14. The method of claim 13 , wherein the pixel mixture unit areas overlap one another in the first and second directions to constitute a two-dimensional repetition arrangement.

15. The method of claim 13 , wherein:

at step (a), electric charges of pixels included in one pixel mixture unit area are added together in the first direction; and

at step (b), the electric charges added together in the first direction at step (a) are added together in the second direction.

16. The method of claim 15 wherein, at step (b), a line process of adding together in the second direction electric charges of pixels of two pixel mixture unit areas which are adjacent in the first direction is performed over a plurality of stages.

17. The method of claim 13 , wherein the solid state imaging element includes a color filter provided over front faces of the photoelectric conversion elements.

18. The method of claim 17 , wherein:

a color filter arrangement of the solid state imaging element is a combination of Bayer arrangements of 2 rows×2 columns; and

at step (b), electric charges of pixels having different colors in each of the pixel mixture unit areas are added together to generate a pixel signal for a complementary color filter arrangement.

19. The method of claim 17 , wherein a color filter arrangement of the solid state imaging element is a combination of four colors, cyan, yellow, green and magenta, arranged in 2 rows×2 columns.

20. The method of claim 13 , wherein:

step (a) uses a first-direction transfer stage including a plurality of CCDs which transfer the electric charges of the pixels in the first direction; and

step (b) uses a second-direction transfer stage including a plurality of CCDs which transfer the electric charges transferred from the first-direction transfer stage in the second direction.