Photon transfer curve test time reduction

• US 20080243419A1
• Filed: 04/05/2007
• Published: 10/02/2008
• Est. Priority Date: 03/28/2007
• Status: Active Grant

• Current Assignee: United Microelectronics Corporation
• Original Assignee: Dialog Imaging Systems GmbH
• Inventors: D'Onofrio, Guiseppe, Nussbacher, Mark
• Granted Patent: US 8,363,042 B2
• Time in Patent Office: Days
• US Class Current: 702/117
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors

Abstract

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 m₁, a second plurality of pixel rows at a second intensity level t₂, and so forth up to an nth plurality of pixel rows illuminated at an nth intensity level m_n where m_n>m₂>m₁. 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.

Claims

1. A method for photon transfer curve (PTC) testing to determine pixel reliability in an image sensor device, comprising:

(a) providing a substrate and a sensor array having a plurality of pixels rows and columns formed thereon wherein each pixel is comprised of a charged photo gate at the base of a light column and a capacitor (storage node) for storing charge transferred from the photo gate, said substrate is linked to a test system;

(b) illuminating the sensor array with a uniform light source such that a first plurality of x₁ pixels in a first region are illuminated at a first light intensity level m₁ in a first step, a second plurality of x₂ pixels in a second region are illuminated at a second light intensity level m₂ 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 x₁, x₂, . . . x_n are integers, m_n>

m₂>

m₁, and the length of each step is a constant time “

t”

;

(c) transferring a residual charge in the photo gate to a capacitor for each pixel and subsequently sending residual charge information for each pixel to an image processor where an image for a first frame (F1) is generated, said image has a top and bottom and two sides;

(d) resetting the photo gate 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 (F2) in said image processor wherein illumination values for F1, F2, and (F2−

F1) may be calculated and a difference frame (F2−

F1) 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 F1 and F2 frames.

3. The method of claim 2 wherein the light intensity level m₁ for the first plurality of pixels produces a substantially black region in said images for the F1 and F2 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 t₁ 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 1 wherein x₁=x₂=x_n.

7. The method of claim 1 wherein one or more of the values x₂, . . . x_n are unequal to the value x₁.

8. 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.

9. 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.

10. The method of claim 9 wherein sending residual charge information for each pixel to an image processor in step (c) occurs through a frame grabber component of the test system.

11. The method of claim 8 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 substrate and a sensor array having a plurality of pixels rows and columns formed thereon wherein each pixel is comprised of a charged photo gate at the base of a light column and a capacitor (storage node) for storing charge transferred from the photo gate, said substrate is linked to a test system;

(b) illuminating the sensor array with a uniform light source such that a first plurality of x₁ pixel rows are illuminated at a first intensity level m₁ in a first step, a second plurality of x₂ pixel rows are illuminated at a second intensity level m₂ 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 x₁-x_n are integers, m_n>

m₂>

m₁, and all rows are illuminated for a constant time “

t”

;

(c) transferring a residual charge in the photo gate to a capacitor for each pixel and subsequently sending residual charge information for each pixel to an image processor where an image for a first frame (F1) is generated, said image has a top and bottom;

(d) resetting the photo gate 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 (F2) in said image processor wherein illumination values for F1, F2, and (F2−

F1) may be calculated and a difference frame (F2−

F1) 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 F1 and F2 frames and wherein the light intensity level m₁ for the first plurality of pixel rows produces a substantially black region in said images for the F1 and F2 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 m₁ 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 x₁=x₂=x_n.

17. The method of claim 12 wherein one or more of the values x₂, . . . x_n are unequal to the value x₁.

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 12 wherein sending residual charge information for each pixel to an image processor in step (c) occurs through a frame grabber component of the test system.

20. The method of claim 18 wherein the intelligent light source is synchronized with the image sensor device using HSYNC and VSYNC signals.