Dual Charge-Accumulation Photoelectric Conversion Element for Wide Dynamic Range
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Solution Overview
Problem
Conventional solid-state image sensors struggle to capture fast-moving targets with high sensitivity and wide dynamic range, especially in applications like in-vehicle and monitoring cameras, due to limitations in dynamic range and response speed.
Innovation Solution
A photoelectric conversion element with a principal layer of one conductivity type and surface-buried regions of another type, featuring dual charge-accumulation regions for signal charge transfer, allowing for alternating exposure periods to enhance sensitivity and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single accumulation region is used, then the structure is simple, but the dynamic range is limited
Solution Approach 1:
The accumulation region is divided into two separate accumulation regions with different capacities. The first accumulation region has a smaller capacity for capturing bright portions, while the second accumulation region has a larger capacity for capturing dark portions. This segmentation allows the image sensor to handle a wider dynamic range by storing different signal charge quantities in different regions.
Solution Approach 2:
The patent introduces a temporal dimension by alternately transferring signal charges to different accumulation regions during different periods within a frame. This time-division multiplexing approach allows the system to effectively utilize multiple accumulation capacities without requiring all regions to be active simultaneously, thus expanding the dynamic range while managing structural complexity.
2Measurement precision
If the accumulation period is extended to increase sensitivity, then the response speed decreases
Solution Approach 1:
The patent implements periodic alternation between two accumulation modes: a first accumulation period for transferring signal charges to the first accumulation region, and a second accumulation period for transferring signal charges to the second accumulation region. This periodic switching allows the system to achieve high sensitivity during each accumulation period while maintaining high response speed through the alternating pattern, effectively capturing fast-moving targets without motion distortion.
Solution Approach 2:
The system dynamically switches between different accumulation configurations based on the imaging requirements. By alternately activating different accumulation regions and adjusting the transfer timing, the system can adaptively optimize between sensitivity and response speed for different scene conditions, particularly for capturing fast-moving targets.
3Speed
If signal charges are transferred frequently to maintain high-speed response, then the sensitivity decreases
Solution Approach 1:
By segmenting the accumulation function into two separate regions, the system can accumulate signal charges for longer periods in each region during its designated accumulation period, thereby maintaining high sensitivity. The frequent transfers are distributed across different regions rather than continuously transferring to a single region, which preserves sensitivity while maintaining response speed.
Solution Approach 2:
The system performs preliminary accumulation of signal charges in the respective accumulation regions during dedicated accumulation periods before readout. This preliminary action allows sufficient charge accumulation time for high sensitivity while the alternating pattern ensures that the overall system maintains high response speed by preparing charges in advance in different regions.
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 enables high-sensitivity, wide dynamic range, and high-speed response, reducing motion distortion in imaging fast-moving targets, suitable for applications with varying illumination conditions.
Implementation Method 1
a surface-buried region of a second conductivity type, selectively buried in an upper portion of the principal layer so as to implement a photodiode with the principal layer
Data Source
AI summary
The present invention provides a photoelectric conversion element and a solid-state image sensor, having a simple structure, a wide dynamic range, a high speed and a high sensibility, which includes a principal layer of a first conductivity type, a surface-buried region of a second conductivity type, selectively buried in an upper portion of the principal layer so as to implements a photodiode with the principal layer, a first charge-accumulation region of the second conductivity type, buried in the upper portion of the principal layer configured to accumulate first signal charges transferred from the surface-buried region, generated by the photodiode, and a second charge-accumulation region of the second conductivity type, buried in the principal layer configured to accumulate second signal charges transferred from the surface-buried region, generated by the photodiode, wherein a process including a first period, in which the first signal charges are transferred from the surface-buried region to the first charge-accumulation region, and a second period shorter than the first period, in which the second signal charges are transferred from the surface-buried region to the second charge-accumulation region is repeated multiple times in one frame period.