Photon transfer curve test time reduction
View Patent ↗An improved method for photon transfer curve (PTC) testing in an image sensor is described. A cost and time savings is achieved by reducing the number of frames necessary for measurements to two that are generated by illuminating a first plurality of pixel rows at a first intensity level m 1 , a second plurality of pixel rows at a second intensity level t 2 , and so forth up to an nth plurality of pixel rows illuminated at an nth intensity level m n where m n >m 2 >m 1 . The resulting image has “n” regions each with a different brightness. The highest intensity level essentially saturates the pixels in the nth region. In one example, a four row exposure and five intensity levels are employed in the illuminator sequence. An intelligent light source is pre-programmable with illumination intensity settings and is synchronized to the image sensor using HSYNC and VSYNC signals, for example.
1. A method for photon transfer curve (PTC) testing to determine pixel reliability in an image sensor device, comprising:
(a) providing a sensor array having a plurality of pixel rows and columns formed thereon wherein each pixel is in a charged state;
(b) illuminating the sensor array with a uniform light source such that a first plurality of x 1 pixels in a first region are illuminated at a first light intensity level m 1 in a first step, a second plurality of x 2 pixels in a second region are illuminated at a second light intensity level m 2 in a second step, and so forth up to an nth plurality of x n pixels in an nth region illuminated at a light intensity level m n in an nth step wherein x 1 , x 2 , . . . x n are integers, m n >m 2 >m 1 , and the length of each step is a constant time “t”, said illuminating the sensor array produces a result comprising:
(1) an intensity level m 1 in a first plurality of pixel rows, an intensity m 2 in a second plurality of pixel rows, and so forth up to an intensity level m n in an nth plurality of pixel rows; and
(2) a first transition pixel region with a variable intensity between the first plurality of pixel rows and the second plurality of pixel rows, a second transition pixel region with a variable intensity between the second plurality of pixel rows and a third plurality of pixel rows up to an (n−1)th transition pixel region with a variable intensity between an (n−1)th plurality of pixel rows and the nth plurality of pixel rows;
(c) sending residual charge information for each pixel in the “n” plurality of pixel rows to an image processor where an image for a first frame (F 1 ) is generated, said image has a top and bottom and two sides;
(d) resetting the plurality of pixel rows and columns to the same charged state as in step (a); and
(e) repeating steps (b)-(c) in succession to form an image having a top and bottom and two sides for a second frame (F 2 ) in said image processor wherein illumination values for F 1 , F 2 , and (F 2 -F 1 ) may be calculated and a difference frame (F 2 -F 1 ) determined.
2. The method of claim 1 wherein the light intensity level m n for the nth plurality of pixels essentially saturates said nth plurality of pixels to produce a white region in said images for the F 1 and F 2 frames.
3. The method of claim 2 wherein the light intensity level m 1 for the first plurality of pixels produces a substantially black region in said images for the F 1 and F 2 frames.
4. The method of claim 3 wherein the substantially black region is formed at the top of said images and the essentially white region is formed at the bottom of said images and the illuminations having light intensity levels between t 1 and t n produce successively brighter regions between the top and bottom of said images wherein the brightness increases as the light intensity level increases in magnitude.
5. The method of claim 1 wherein step (b) comprises a multiple “s” row exposure wherein “s” rows in each of the “n” pixel regions are illuminated to the same light intensity level.
6. The method of claim 5 wherein an illumination sequence that comprises the number of illumination steps, the number of pixels in each pixel region, and the number of “s” rows in each pixel region is preprogrammed into a light control element in said test system that controls the uniform light source.
7. The method of claim 6 wherein sending residual charge information for each pixel to an image processor in step (c) occurs through a frame grabber component of a PTC test system.
8. The method of claim 1 wherein x 1 =x 2 =x n .
9. The method of claim 1 wherein one or more of the values x 2 , . . . x n are unequal to the value x 1 .
10. The method of claim 1 wherein the uniform light source is an intelligent light source that is capable of being pre-programmed with illumination sequence settings and can be synchronized with said image sensor device.
11. The method of claim 10 wherein the intelligent light source is synchronized with the image sensor device using HSYNC and VSYNC signals.
12. A method for photon transfer curve testing to determine pixel reliability in an image sensor device, comprising:
(a) providing a sensor array having a plurality of pixels rows and columns formed thereon wherein each pixel is in a charged state;
(b) illuminating the sensor array with a uniform light source such that a first plurality of x 1 pixel rows are illuminated at a first intensity level m 1 in a first step, a second plurality of x 2 pixel rows are illuminated at a second intensity level m 2 in a second step, and so forth up to an nth plurality of x n pixel rows illuminated at an intensity level m n in an nth step wherein x 1 -x n are integers, and all rows are illuminated for a constant time “t”, said illuminating the sensor array produces a result comprising:
(1) an intensity level m 1 in a first plurality of pixel rows, an intensity m 2 in a second plurality of pixel rows, and so forth up to an intensity level m n in an nth plurality of pixel rows; and
(2) a first transition pixel region with a variable intensity between the first plurality of pixel rows and the second plurality of pixel rows, a second transition pixel region with a variable intensity between the second plurality of pixel rows and a third plurality of pixel rows up to an (n−1)th transition pixel region with a variable intensity between an (n−1)th plurality of pixel rows and the nth plurality of pixel rows;
(c) sending residual charge information for each pixel in said “n” plurality of pixel rows to an image processor where an image for a first frame (F 1 ) is generated, said image has a top and bottom;
(d) resetting the plurality of pixel rows and columns to the same charged state as in step (a);
(e) repeating steps (b)-(c) in succession to form an image having a top and bottom for a second frame (F 2 ) in said image processor wherein illumination values for F 1 , F 2 , and (F 2 -F 1 ) may be calculated and a difference frame (F 2 -F 1 ) determined.
13. The method of claim 12 wherein the light intensity level m n for the nth plurality of pixel rows essentially saturates said nth plurality of pixel rows to produce a white region in said images for the F 1 and F 2 frames and wherein the light intensity level m 1 for the first plurality of pixel rows produces a substantially black region in said images for the F 1 and F 2 frames.
14. The method of claim 13 wherein the substantially black region is formed at the top of said images and the essentially white region is formed at the bottom of said images and the illuminations having light intensity levels between m 1 and m n produce successively brighter regions between the top and bottom of said images wherein the brightness increases as the light intensity level increases in magnitude.
15. The method of claim 12 wherein step (b) comprises a multiple “s” row exposure wherein “s” rows in each of the “n” plurality of pixel rows are illuminated at the same light intensity level.
16. The method of claim 12 wherein x 1 =x 2 =x n .
17. The method of claim 12 wherein one or more of the values x 2 , . . . x n are unequal to the value x 1 .
18. The method of claim 15 wherein the uniform light source is an intelligent light source that is capable of being pre-programmed with illumination sequence settings and can be synchronized with said image sensor device.
19. The method of claim 18 wherein the intelligent light source is synchronized with the image sensor device using HSYNC and VSYNC signals.
20. The method of claim 12 wherein sending residual charge information for each pixel to an image processor in step (c) occurs through a frame grabber component of a PTC test system.