Split Pixel HDR Imaging With Overflow Capacitor Charge Transfer
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Solution Overview
Problem
Conventional high dynamic range (HDR) image sensors often experience lower resolution, sensitivity, and higher noise levels, which limits their performance in capturing images across varying light conditions.
Innovation Solution
Incorporating a split pixel design with high and low sensitivity photodiodes and an overflow capacitor, allowing charge to overflow from one photodiode into a storage capacitor, thereby increasing the dynamic range and signal-to-noise ratio of the imaging pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional HDR image sensors use alternate rows of pixels with different integration times, then dynamic range is improved, but resolution and sensitivity decrease while noise levels increase
Solution Approach 1:
Each pixel is divided into multiple photodiodes (e.g., first photodiode with longer integration time for high luminance, second photodiode with shorter integration time for low luminance). This segmentation allows different portions of the same pixel to capture different exposure levels simultaneously, resolving the contradiction between dynamic range and measurement precision by enabling both long and short exposure measurements within each pixel location.
Solution Approach 2:
Different photodiodes within the same pixel are assigned different integration times tailored to specific luminance conditions. The first photodiode is optimized for capturing high luminance scenes with longer integration, while the second photodiode captures low luminance scenes with shorter integration. This local quality differentiation within each pixel enables optimal measurement precision for varying luminance levels while maintaining extended dynamic range.
2Adaptability or versatility
If conventional HDR image sensors use alternate rows of pixels with different integration times, then dynamic range is improved, but noise levels increase
Solution Approach 1:
By segmenting each pixel into multiple photodiodes with different integration times, the system can select the appropriate photodiode output based on scene luminance. This avoids the need to combine data from alternate rows with different integration times, thereby reducing noise while maintaining dynamic range capability.
Solution Approach 2:
Each pixel independently determines which photodiode output to use based on the captured signal levels, selecting the measurement with optimal signal-to-noise ratio for the given luminance conditions. This self-service mechanism eliminates the need for complex inter-row data combination that introduces noise in conventional HDR sensors.
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 configuration enhances the dynamic range and signal-to-noise ratio of image sensors, improving their ability to capture images with better resolution and sensitivity across a wider range of light conditions.
Implementation Method 1
Typical image pixels contain a photodiode for generating charge in response to incident light
Data Source
AI summary
A high dynamic range imaging pixel may include first and second photodiodes that generate charge in response to incident light. The second photodiode may have a higher sensitivity than the first photodiode. When generated charge in the first photodiode exceeds a given charge level, the charge may overflow through a transistor to a capacitor. The overflow path from the first photodiode to the capacitor may optionally pass through the floating diffusion region. A transistor may be coupled between the first and second photodiodes. A gain select transistor may be coupled between the floating diffusion region and the capacitor. After sampling the overflow charge, the charge from both the first and second photodiodes may be sampled. In one arrangement, overflow charge may be transferred to a capacitor in a subsequent row.