CN-122002148-A - Image sensor with high dynamic range lateral overflow integrated capacitor and split pixel with light emitting diode flicker mitigation

Abstract

An image sensor having a lateral overflow integrating capacitor LOFIC for high dynamic range HDR and split pixels for light emitting diode LED flicker mitigation is disclosed herein. The pixel array is made up of a plurality of pixel cells, each comprising a pixel photodiode area having at least a large photosensor LPD and a small photosensor SPD, wherein the LPD comprises a lateral overflow integration capacitor LOFIC. A method of generating an HDR image includes exposing a large photosensor LPD of a pixel cell for a first duration, exposing a small photosensor SPD of the pixel cell for a second duration, and combining the resulting readouts into a combined pixel readout CPR. This CPR is then used in combination with the generated LED flicker mapped LFM bits and the resulting readout from the SPD to generate a final corrected pixel readout that mitigates LED flicker in the resulting HDR image.

Inventors

• R. Kakarra
• SONG YUJUN
• HUANG ZHONGYANG

Assignees

• 豪威科技股份有限公司

Dates

Publication Date

20260508

Application Date

20250829

Priority Date

20241106

Claims (19)

1. 1. A pixel array for a complementary metal oxide semiconductor image sensor, comprising: a plurality of pixel units formed in a semiconductor substrate, each pixel unit comprising: A pixel photodiode region having at least a large photosensitive element and a small photosensitive element, wherein the large photosensitive element has a size larger than the small photosensitive element, and wherein the large photosensitive element comprises a lateral overflow integrating capacitor, and A pixel transistor region disposed adjacent to the pixel photodiode region; Wherein the large photosensitive element is exposed for a first duration during each exposure and the small photosensitive element is exposed for a second duration during each exposure; Wherein the first duration and the second duration are at least partially simultaneous; wherein for each exposure: The large photosensor produces a high conversion gain readout, a low conversion gain readout, and a lateral overflow integration capacitor readout, an The small photosensitive element produces a short exposure readout; and wherein the high conversion gain readout, the low conversion gain readout, the lateral overflow integration capacitor readout, and the short exposure readout are combined into a combined pixel readout.
2. 2. The pixel array of claim 1, wherein the first duration is less than the second duration, and wherein the large photosensitive element and the small photosensitive element begin their respective exposures simultaneously.
3. 3. The pixel array of claim 2, wherein the first duration is less than 5ms and the second duration is greater than or equal to 11ms.
4. 4. The pixel array of claim 1, wherein the first duration is greater than the second duration, and wherein the large photosensitive element begins its exposure before the small photosensitive element begins its exposure.
5. 5. The pixel array of claim 4, wherein the first duration is greater than or equal to 11ms and the second duration is less than 5ms.
6. 6. The pixel array of claim 1, wherein the pixel cells are arranged in a split diode tiled arrangement, wherein the arrangement comprises: Multiple large photosensitive elements A plurality of small photosensitive elements, wherein the plurality of large photosensitive elements and the plurality of small photosensitive elements are each arranged in rows and columns, wherein the plurality of large photosensitive elements are configured adjacent to each other, and wherein the plurality of small photosensitive elements are embedded between adjacent large photosensitive elements such that the large photosensitive elements and the small photosensitive elements are embedded to share a common boundary with each other.
7. 7. The pixel array of claim 6, wherein the plurality of large photosensors and the plurality of small photosensors each include two green photodiodes, one blue photodiode, and one red photodiode, and wherein the plurality of large photosensors and the plurality of small photosensors alternate colors by their respective rows and columns.
8. 8. The pixel array of claim 1, wherein the combined pixel readout is a high dynamic range image.
9. 9. The pixel array of claim 1, wherein the high conversion gain readout, the low conversion gain readout, the lateral overflow integration capacitor readout, and the short exposure readout are combined into a combined pixel readout by: shifting the short exposure readout; Determining a first absolute difference between the high conversion gain readout and the short exposure readout; determining a second absolute difference between the low conversion gain readout and the short exposure readout; determining a third absolute difference between the lateral overflow integrated capacitor readout and the short exposure readout; Assigning a weight for each absolute difference calculated; Selecting a maximum weight calculated for each absolute difference; Generating a flicker pixel map Corrected pixel readouts are output based on the combined pixel readouts, the scintillation pixel map, and the small photosensor readouts.
10. 10. A method of generating a high dynamic range image, comprising: exposing a large photosensitive element of a pixel cell for a first duration, wherein the large photosensitive element comprises a laterally overflowing integrated capacitor, and wherein the large photosensitive element produces a high conversion gain readout, a low conversion gain readout, and a laterally overflowing integrated capacitor readout; Exposing a small photosensitive element of the pixel cell to light for a second duration, wherein the large photosensitive element is larger than the small photosensitive element, and wherein the small photosensitive element produces a short exposure readout, and wherein the first duration is at least partially simultaneous with the second duration, and The high conversion gain readout, the low conversion gain readout, the lateral overflow integration capacitor readout, and the short exposure readout are combined into a combined pixel readout.
11. 11. The method as recited in claim 10, further comprising: shifting the short exposure readout; Determining a first absolute difference between the high conversion gain readout and the short exposure readout; determining a second absolute difference between the low conversion gain readout and the short exposure readout; determining a third absolute difference between the lateral overflow integrated capacitor readout and the short exposure readout; Assigning a weight for each absolute difference calculated; Selecting a maximum weight calculated for each absolute difference; Generating a flicker pixel map Corrected pixel readouts are output based on the combined pixel readouts, the scintillation pixel map, and the small photosensor readouts.
12. 12. The method of claim 11, wherein the corrected pixel readout is calculated by equation c= (CPR x W) +s x (1-W).
13. 13. The method of claim 10, wherein the first duration is less than the second duration, and wherein the large photosensitive element and the small photosensitive element begin their respective exposures simultaneously.
14. 14. The method of claim 13, wherein the first duration is less than 5ms and the second duration is greater than or equal to 11ms.
15. 15. The method of claim 10, wherein the first duration is greater than the second duration, and wherein the large photosensitive element begins its exposure before the small photosensitive element begins its exposure.
16. 16. The method of claim 15, wherein the first duration is greater than or equal to 11ms and the second duration is less than 5ms.
17. 17. The method of claim 10, wherein the pixel cells are arranged in a split diode tiled arrangement, wherein the arrangement comprises: Multiple large photosensitive elements A plurality of small photosensitive elements, wherein the plurality of large photosensitive elements and the plurality of small photosensitive elements are each arranged in rows and columns, wherein the plurality of large photosensitive elements are configured adjacent to each other, and wherein the plurality of small photosensitive elements are embedded between adjacent large photosensitive elements such that the large photosensitive elements and the small photosensitive elements are embedded to share a common boundary with each other.
18. 18. The method of claim 17, wherein the plurality of large photosensitive elements and the plurality of small photosensitive elements each include two green photodiodes, one blue photodiode, and one red photodiode, and wherein the plurality of large photosensitive elements and the plurality of small photosensitive elements alternate colors by their respective rows and columns.
19. 19. The method of claim 10, wherein the combined pixel readout is a high dynamic range image.

Description

Image sensor with high dynamic range lateral overflow integrated capacitor and split pixel with light emitting diode flicker mitigation Technical Field The present disclosure relates generally to image sensors, and more particularly, but not exclusively, to image sensors that mitigate the effect of Light Emitting Diode (LED) flickering in images, such as High Dynamic Range (HDR) image sensors. Background CMOS Image Sensors (CIS) have become ubiquitous. The CMOS image sensor is widely used in digital still cameras, cellular telephones, security cameras, and medical, automotive, and other applications. Typical image sensors operate in response to image light reflected from an external scene being incident on the image sensor. An image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of incident image light and generate image charge upon absorption of the image light. The image charge of each of the pixels may be measured as an output voltage of each photosensitive element, which varies according to the incident image light. In other words, the amount of image charge generated is proportional to the intensity of the image light, which is used to generate a digital image (i.e., image data) representing an external scene. A typical image sensor operates as follows. Image light from an external scene is incident on the image sensor. The image sensor includes a plurality of photosensitive elements such that each photosensitive element absorbs a portion of incident image light. Photosensitive elements (e.g., photodiodes) included in an image sensor each generate image charges upon absorbing image light. The amount of image charge generated is proportional to the intensity of the image light. The generated image charge may be used to generate an image representing an external scene. Integrated Circuit (IC) technology for image sensors is continually improving, particularly for higher resolution and lower power consumption. Such improvements generally involve scaling device geometries to achieve lower fabrication costs, higher device integration density, higher speed, and better performance. As miniaturization of image sensors progresses, however, defects within the image sensor architecture become more apparent and can degrade the image quality of the image. For example, excessive current leakage within a particular area of an image sensor may cause high dark current, sensor noise, white pixel defects, and so forth. These defects can significantly degrade image quality from the image sensor, which can lead to reduced yields and increased production costs. High Dynamic Range (HDR) image sensors may present other challenges. For example, some HDR image sensor layouts are not space efficient and are difficult to miniaturize to smaller pitches to achieve higher resolution. Thus, there remains a need for systems and methods for improving HDR. Disclosure of Invention In one aspect, the disclosure relates to a pixel array for a CMOS image sensor comprising a plurality of pixel cells formed in a semiconductor substrate, each pixel cell comprising a pixel photodiode region having at least a Large Photosensor (LPD) and a Small Photosensor (SPD), wherein the LPD is larger in size than the SPD, and wherein the LPD comprises a lateral overflow integration capacitor (LOFIC), and a pixel transistor region disposed adjacent to the pixel photodiode region, wherein the LPD is exposed for a first duration during each exposure and the SPD is exposed for a second duration during each exposure, wherein the first duration is at least partially simultaneous with the second duration, wherein for each exposure the LPD produces a High Conversion Gain (HCG) readout, a Low Conversion Gain (LCG) readout, and a LOFIC readout, and the SPD produces a short exposure (S) readout, and wherein the HCG readout, the LCG readout, the LOG readout, and the CPR readout are combined as a group of pixel readouts. In another aspect, the present disclosure is directed to a method of generating a High Dynamic Range (HDR) image comprising exposing a large photosensitive element (LPD) of a pixel cell for a first duration, wherein the LPD comprises a lateral overflow integration capacitor (LOFIC), and wherein the LPD generates a High Conversion Gain (HCG) readout, a Low Conversion Gain (LCG) readout, and a LOFIC readout, exposing a small photosensitive element (SPD) of the pixel cell for a second duration, wherein the LPD is greater than the SPD, and wherein the SPD generates a short exposure (S) readout, and wherein the first duration and second duration are at least partially simultaneous, and combining the HCG readout, the LCG readout, the LOFIC readout, and the S readout into a Combined Pixel Readout (CPR). Drawings Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the