Image Sensor Pixel With Dual Floating Diffusion For Wide Dynamic Range
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Solution Overview
Problem
Conventional image sensors have a narrow dynamic range, leading to poor expression of image colors when one of the red, green, or blue colors becomes saturated, and existing wide dynamic range (WDR) pixel solutions either limit sensitivity variation with light intensity or reduce the fill factor.
Innovation Solution
A pixel design incorporating a photo-electro conversion unit with two floating diffusion regions of different capacitances, allowing independent control of capacitors to adjust gain based on light intensity, thereby improving sensitivity while maintaining a high fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two PDs are installed in one pixel to achieve WDR operation, then the dynamic range is widened, but the fill factor is reduced
Solution Approach 1:
The invention segments the charge storage function by dividing the floating diffusion region into two distinct regions: a first floating diffusion region for storing first quantity of charges and a second floating diffusion region for storing second quantity of charges. This segmentation allows independent control of charge storage capacities, enabling WDR operation without requiring multiple photodiodes, thus maintaining a high fill factor.
Solution Approach 2:
The single photodiode serves multiple functions by transferring charges to two different floating diffusion regions with different capacitances. The first floating diffusion region handles low-light conditions with higher gain, while the second floating diffusion region handles high-light conditions with lower gain, making the single photodiode structure universal for both low-light and high-light scenarios.
2Adaptability or versatility
If additional capacitor is provided to change FD capacity for WDR operation, then overflow charges can be stored, but the device complexity increases
Solution Approach 1:
The invention merges the charge storage function into the existing floating diffusion regions, combining the roles of charge generation, storage, and readout into a unified structure. The first and second floating diffusion regions are integrated with the photodiode and transistor structure, eliminating the need for separate additional capacitors and reducing device complexity while achieving WDR capability.
3Adaptability or versatility
If irradiation time is adjusted for WDR operation, then the dynamic range is improved, but the sensitivity becomes constant regardless of light intensity variation
Solution Approach 1:
The invention applies local quality by creating two floating diffusion regions with different capacitance values in specific locations. The first floating diffusion region has a first capacitance value optimized for low-light conditions, while the second floating diffusion region has a second capacitance value optimized for high-light conditions. This local differentiation in capacitance allows the system to maintain optimal sensitivity across varying light intensities.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances sensitivity under low light conditions and reduces sensitivity under high light conditions, achieving WDR characteristics while increasing the fill factor and maintaining image quality across varying illumination levels.
Implementation Method 1
a photodiode PD to receive the light
Data Source
AI summary
Disclosed are a pixel, a pixel array, an image sensor including the pixel array and a method for operating the image sensor. The pixel includes a photo-electro conversion unit; a first capacitor for storing a first quantity of charges of the photo-electro conversion unit; a second capacitor for storing a second quantity of charges of the photo-electro conversion unit; and an output unit to output the first and second quantities of the charges.