Image sensor for detecting flicker noise and method thereof

Abstract

An image sensor has improved functions so as to automatically eliminate a flicker noise. For the purpose, the image sensor includes a pixel array for capturing information about an image provided from the outside and having N pixel rows and M pixel columns for maximizing a feature of reacting to light, wherein M and N are integers, respectively, a flicker noise detective pixel unit containing X pixel rows, which has a form extended from the N pixel rows of the pixel array, and M pixel columns, wherein each pair of X pixel rows has an identical exposure time and X is an even number, and a flicker noise for controlling an exposure point for the flicker noise detective pixel unit and detecting the flicker noise by using outputs of the flicker noise detective pixel unit.

1. A method for detecting a flicker noise of an image sensor, comprising the steps of:
 (a) securing information about images of a first pair of pixel rows by differing exposure points of the first pair of pixel rows having a first exposure time and repeating the image information securing process as changing the exposure points of the first pair of pixel rows; 
 (b) capturing information about images of a second pair of pixel rows by differing exposure points of the second pair of pixel rows having a second exposure time and repeating the image information capturing process as changing the exposure points of the second pair of pixel rows; 
 (c) calculating an average value of the image information for each pixel row of the first and the second pairs of pixel rows in every image information detecting process; 
 (d) ciphering a maximum value and a minimum value among average values for said each pixel row obtained from the step (c); 
 (e) determining a first subtract value by subtracting the minimum value from the maximum value of one pixel row having the first exposure time, deciding a second subtract value by subtracting the minimum value from the maximum value of the other pixel row having the first exposure time, and outputting a smaller one of the first subtract value and the second subtract value as a first minimum subtract value; 
 (f) determining a third subtract value by subtracting the minimum value from the maximum value of one pixel row having the second exposure time, deciding a fourth subtract value by subtracting the minimum value from the maximum value of the other pixel row having the second exposure time, and outputting a smaller one of the third subtract value and the fourth subtract value as a second minimum subtract value; and 
 (g) deciding an exposure time corresponding to the flicker noise by comparing the first minimum subtract value and the second minimum subtract value. 
 
     
     
       2. The method as recited in  claim 1 , wherein, in the step (g), an exposure time having a larger one of the first minimum subtract value and the second minimum subtract value is determined as the flicker noise. 
     
     
       3. The method as recited in  claim 1 , wherein, in the step (g), a light source corresponding to an exposure time having a smaller one of the first minimum subtract value and the second minimum subtract value is decided as a real light source. 
     
     
       4. The method as recited in  claim 2 , wherein, in the step (g), a light source corresponding to an exposure time having a smaller one of the first minimum subtract value and the second minimum subtract value is decided as a real light source. 
     
     
       5. The method as recited in  claim 3 , wherein the first minimum subtract value and the second minimum subtract value are larger than a signal conversion minimum value for preventing an error operation due to minute variation of an external environment. 
     
     
       6. The method as recited in  claim 4 , wherein the first minimum subtract value and the second minimum subtract value are larger than a signal conversion minimum value for preventing an error operation due to minute variation of an external environment. 
     
     
       7. The method as recited in  claim 1 , wherein the image information for each pixel row is obtained at one exposure point to thereby cipher the average value. 
     
     
       8. The method as recited in  claim 1 , wherein one time of the image information detecting process corresponds to one frame. 
     
     
       9. A method for detecting a flicker noise of an image sensor, comprising the steps of:
 (a) securing information about an image of each of a first and a second pixel row by differing exposure points of the first and the second pixel rows having a first exposure time and repeating the image information securing process as changing the exposure points of the first and the second pixel rows; 
 (b) capturing information about an image of each of a third and a fourth pixel row by differing exposure points of the third and the fourth pixel rows having a second exposure time and repeating the image information capturing process as changing the exposure points of the third and the fourth pixel rows; 
 (c) calculating an average value of the image information for each of the first to the fourth pixel rows in every image information detecting process; 
 (d) ciphering a maximum value and a minimum value among average values for said each of the first to the fourth pixel rows obtained from the step (c); 
 (e) determining a first subtract value by subtracting the minimum value from the maximum value of the first pixel row, deciding a second subtract value by subtracting the minimum value from the maximum value of the second pixel row, and outputting a smaller one of the first subtract value and the second subtract value as a first minimum subtract value; 
 (f) determining a third subtract value by subtracting the minimum value from the maximum value of the third pixel row, deciding a fourth subtract value by subtracting the minimum value from the maximum value of the fourth pixel row, and outputting a smaller one of the third subtract value and the fourth subtract value as a second minimum subtract value; and 
 (g) deciding an exposure time corresponding to the flicker noise by comparing the first minimum subtract value and the second minimum subtract value. 
 
     
     
       10. The method as recited in  claim 9 , wherein, in the step (g), an exposure time having a larger one of the first minimum subtract value and the second minimum subtract value is determined as the flicker noise. 
     
     
       11. The method as recited in  claim 9 , wherein, in the step (g), a light source corresponding to an exposure time having a smaller one of the first minimum subtract value and the second minimum subtract value is decided as a real light source. 
     
     
       12. The method as recited in  claim 10 , wherein, in the step (g), a light source corresponding to an exposure time having a smaller one of the first minimum subtract value and the second minimum subtract value is decided as a real light source. 
     
     
       13. The method as recited in  claim 11 , wherein the first minimum subtract value and the second minimum subtract value are larger than a signal conversion minimum value for preventing an error operation due to minute variation of an external environment. 
     
     
       14. The method as recited in  claim 12 , wherein the first minimum subtract value and the second minimum subtract value are larger than a signal conversion minimum value for preventing an error operation due to minute variation of an external environment. 
     
     
       15. The method as recited in  claim 9 , wherein the image information for each of the first to the fourth pixel rows is obtained at one exposure point to thereby cipher the average value. 
     
     
       16. The method as recited in  claim 9 , wherein one time of the image information detecting process corresponds to one frame. 
     
     
       17. The method as recited in  claim 16 , wherein the step of detecting information about an image of each of two pixel rows by differing exposure points of the two pixel rows and repeating the image information detecting process is performed for 4 frames. 
     
     
       18. An image sensor comprising:
 a pixel array for capturing information about an image provided from the outside and having N pixel rows and M pixel columns for maximizing a feature of reacting to light, wherein M and N are integers, respectively; 
 a flicker noise detective pixel unit containing X pixel rows, which has a form extended from the N pixel rows of the pixel array, and M pixel columns, wherein each pair of X pixel rows has an identical exposure time and X is an even number; and 
 a flicker noise detecting block for controlling an exposure point for the flicker noise detective pixel unit and detecting the flicker noise by using outputs of the flicker noise detective pixel unit, 
 wherein the flicker noise detective pixel unit secures the image information during one frame by making one pair of rows have different exposure points from each other, captures the image information during a next frame by differing the exposure points of the rows and performs its operation by varying the exposure points of the rows during a plurality of frames. 
 
     
     
       19. An image sensor comprising:
 a flicker noise detective pixel block including a plurality of pixel rows;   a flicker noise detecting block configured to detect a flicker noise by providing exposure time starting points to the plurality of pixel rows during a first frame and by changing at least one of the exposure time starting points in the plurality of pixel rows during a second frame; and   wherein values of the exposure time starting points are determined with reference to start times of a corresponding one of the first frame or the second frame.   
     
     
       20. The image sensor of claim 19, wherein the plurality of pixel rows includes a first pair of pixel rows; and
 wherein the flicker noise detecting block is further configured to provide exposure time starting points for a first exposure time to the first pair of pixel rows to detect a flicker of a first light source.   
     
     
       21. The image sensor of claim 20, wherein the flicker noise detecting block is further configured to provide different exposure time starting points to each row of the first pair of pixel rows during the first frame. 
     
     
       22. The image sensor of claim 20, wherein the plurality of pixel rows includes a second pair of pixel rows; and
 wherein the flicker noise detecting block is further configured to provide exposure time starting points for a second exposure time to the second pair of pixel rows to detect a flicker of a second light source.   
     
     
       23. The image sensor of claim 22, wherein the flicker noise detecting block is further configured to provide different exposure time starting points to each row of the second pair of pixel rows during the first frame. 
     
     
       24. The image sensor of claim 22, wherein the first light source includes a frequency of 50 Hz and the second light source includes a frequency of 60 Hz. 
     
     
       25. The image sensor of claim 22, further comprising a pixel array configured to have an exposure time adjusted according to a detection of the flicker of the first light source or the flicker of the second light source. 
     
     
       26. A method for detecting flicker in an image sensor, the method comprising:
 providing exposure time starting points to a plurality of pixel rows during a first frame;   changing at least one of the exposure time starting points in the plurality of pixel rows during a second frame; and   wherein values of the exposure time starting points are determined with reference to start times of a corresponding one of the first frame or the second frame.   
     
     
       27. The method of claim 26, further comprising providing exposure time starting points for a first exposure time to a first pair of pixel rows to detect a flicker of a first light source. 
     
     
       28. The method of claim 27, further comprising providing different exposure time starting points to each row of the first pair of pixel rows during the first frame. 
     
     
       29. The method of claim 27, further comprising providing exposure time starting points for a second exposure time to a second pair of pixel rows to detect a flicker of a second light source. 
     
     
       30. The method of claim 29, further comprising providing different exposure time starting points to each row of the second pair of pixel rows during the first frame. 
     
     
       31. The method of claim 29, wherein the first light source includes a frequency of 50 Hz and the second light source includes a frequency of 60 Hz. 
     
     
       32. The method of claim 29, further comprising:
 detecting one of the flicker of the first light source or the flicker of the second light source; and   adjusting an exposure time of a pixel array according to said detecting one of the flicker of the first light source or the flicker of the second light source.   
     
     
       33. A method for detecting flicker in an image sensor, the method comprising:
 changing at least one of a plurality of exposure time starting points in a corresponding plurality of pixel rows between a first frame and a second frame;   capturing image information from the plurality of pixel rows during the first frame and the second frame;   detecting a flicker of a light source according to the image information from the plurality of pixel rows during the first frame and the second frame; and   wherein values of the plurality of exposure time starting points are determined with reference to start times of a corresponding one of the first frame or the second frame.   
     
     
       34. The method of claim 33, further comprising:
 changing at least one of the plurality of exposure time starting points for a first exposure time for a first pair of pixel rows between the first frame and the second frame;   capturing image information from each of the first pair of pixel rows during the first frame and the second frame; and   detecting a flicker of a first light source according to the image information from each of the first pair of pixel rows during the first frame and the second frame.   
     
     
       35. The method of claim 34, further comprising applying different exposure time starting points to the first pair of rows during the first frame. 
     
     
       36. The method of claim 34, further comprising:
 changing at least one of the plurality of exposure time starting points of a second exposure time for a second pair of pixel rows between the first frame and the second frame;   capturing image information from the second pair of pixel rows during the first frame and the second frame; and   detecting a flicker of a second light source according to the image information from the second pair of pixel rows during the first frame and the second frame.   
     
     
       37. The method of claim 36, further comprising applying different exposure time starting points to the second pair of rows during the first frame. 
     
     
       38. The method of claim 36, further comprising adjusting an exposure time of a pixel array according to said detecting a flicker of a first light source and said detecting a flicker of a second light source. 
     
     
       39. An image sensor comprising:
 a flicker noise detective pixel unit including a plurality of pixel rows; and   a flicker noise detection controller configured to provide:
 a first exposure point for a first pixel row of the plurality of pixel rows during a first frame; 
 a second exposure point for a second pixel row of the plurality of pixel rows during the first frame; 
 a third exposure point for the first pixel row of the plurality of pixel rows during a second frame; and 
 a fourth exposure point for the second pixel row of the plurality of pixel rows during the second frame; 
   wherein the first exposure point is different from the third exposure point and the second exposure point is different from the fourth exposure point;   wherein values of the first exposure point and the second exposure point are determined with reference to a start time of the first frame; and   wherein values of the third exposure point and the fourth exposure point are determined with reference to a start time of the second frame.