Image Sensor Pixel Dynamic Charge Integration for Wide Dynamic Range
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Solution Overview
Problem
Current image sensors have a narrow dynamic range, leading to poor expression of image colors under high illumination, and existing wide dynamic range (WDR) pixel solutions either maintain constant sensitivity across light intensities, darken images under low illumination, or reduce fill factor.
Innovation Solution
The solution involves setting different charge integration sections for high and low light intensities, with a shared charge conversion and storage unit, allowing for adjustable charge integration time and increased storage capacitance to widen the dynamic range under high illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charge integration time is extended to improve sensitivity under low illumination, then sensitivity is improved, but saturation occurs under high illumination causing loss of dynamic range
Solution Approach 1:
The patent implements dynamic charge integration time control by using a transfer switch to selectively connect the photodiode to either the floating diffusion region or the additional capacitor based on light intensity. Under high illumination, charges are transferred to the additional capacitor allowing longer effective integration; under low illumination, charges remain in the floating diffusion region for maximum sensitivity. This dynamic switching resolves the contradiction between sensitivity and dynamic range adaptability.
Solution Approach 2:
The patent changes the storage capacitance parameter dynamically by providing an additional capacitor that can be connected to the floating diffusion region through a transfer switch. The capacitance value is adjusted based on light intensity conditions: under high illumination, the additional capacitor is connected to increase storage capacity and prevent saturation; under low illumination, the additional capacitor is disconnected to maintain optimal sensitivity. This parameter change enables the system to adapt to varying light conditions.
2Adaptability or versatility
If an additional capacitor is provided to increase storage capacitance under high illumination, then dynamic range is improved, but fill factor is reduced
Solution Approach 1:
The additional capacitor serves multiple functions: it acts as overflow storage for high-intensity illumination to extend dynamic range, and can be integrated into the pixel layout in a space-efficient manner. The capacitor shares the pixel area with other components, and its switching mechanism allows the same physical structure to serve different purposes under different lighting conditions, thereby minimizing the impact on fill factor while achieving WDR functionality.
3Adaptability or versatility
If multiple PDs are installed in one pixel to individually detect different light intensities, then dynamic range is improved, but device complexity increases
Solution Approach 1:
The patent merges the functionality of multiple photodetectors into a single photodiode structure by using a transfer switch to redirect charges to either the floating diffusion region or an additional capacitor. This combining approach achieves the dynamic range extension of dual-PD systems while maintaining a simpler single-PD structure, thereby reducing device complexity while preserving WDR capability.
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
This approach enables the image sensor to detect light across a broader range of intensities, from low to high, by shortening charge integration time and increasing storage capacitance, thereby enhancing image quality under varying illumination conditions.
Implementation Method 1
a charge conversion unit PD, which detects light and converts the light into charges
Data Source
Figure 1~2
Figure 3a~3b(h)
Figure 4(a)~5a(e)
AI summary
present invention is according to pixel, pixel array, etc., comprising, at least one pixel according to one embodiment includes the steps of starting a charge integration in a charge conversion unit; transferring charges integrated in the charge conversion unit during a first integration section to a charge storage unit; reading out a signal level during the first integration section; transferring charges integrated in the charge conversion unit during a second integration section following the first integration section to the charge storage unit; reading out a signal level during the second integration section at a same time of transferring the charges integrated in the charge conversion unit during the second integration section to the charge storage unit; and calculating a light intensity by using the signal levels of the first and second integration sections.