High Dynamic Range Image Sensor Pixel Array
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Solution Overview
Problem
Semiconductor imaging devices face challenges in achieving a large dynamic range, which is essential for accurately reading and processing photocurrents from photons, especially in ultraviolet and infrared applications, where the existing designs often result in saturation and limited detection capabilities.
Innovation Solution
The proposed imaging device incorporates a pixelated array of semiconductor detector elements with in-pixel integrated circuits, including a comparator, readout decoder block, and address arbitration control block, which provides timestamps for pixels exceeding a threshold voltage using an off-pixel time-to-digital converter, preventing saturation and allowing for efficient readout of accumulated charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional active pixel sensor designs are used, then device complexity is reduced, but dynamic range is limited due to saturation
Solution Approach 1:
The pixel array is divided into multiple readout regions, with each region having independent readout circuitry. This segmentation allows different regions to operate at different integration times, enabling high dynamic range imaging without requiring complex per-pixel circuitry for each pixel.
Solution Approach 2:
The patent implements variable integration times for different regions of the pixel array. The integration time can be dynamically adjusted for each region based on the expected signal intensity, allowing the system to adapt to varying light conditions and achieve high dynamic range without saturation.
2Measurement precision
If integration time is increased to detect low photocurrents, then measurement precision for low signals is improved, but saturation occurs for high photocurrents
Solution Approach 1:
Different regions of the pixel array are assigned different integration times based on their expected signal characteristics. Regions expecting low signals use longer integration times for high precision, while regions expecting high signals use shorter integration times to avoid saturation. This local optimization resolves the contradiction between detection precision and saturation prevention.
Solution Approach 2:
The patent uses multiple readout regions with different integration times, effectively applying partial action to different parts of the scene. Each region is optimized for its specific signal level, allowing the system to capture both very low and very high photocurrents without either detection failure or saturation.
3Reliability
If multiple readout regions with different integration times are used, then dynamic range is enhanced, but device complexity increases
Solution Approach 1:
Each readout region is designed with multi-functional circuitry that can operate in different modes (different integration times) without requiring completely separate hardware for each function. The readout circuitry serves multiple purposes: short integration for high signal regions, long integration for low signal regions, and can be reconfigured as needed, reducing overall device complexity while maintaining high dynamic range 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 solution enhances the dynamic range of imaging devices by preventing saturation, enabling accurate readout of both high and low photocurrents, and allowing for the reconstruction of charge profiles, making it suitable for applications requiring high dynamic range, such as hyperspectral imaging.
Implementation Method 1
When a photon with sufficient energy is incident upon, and absorbed in the structure, an electron-hole pair is created
Data Source
AI summary
An imaging device in accordance with the present disclosure comprises of a pixelated array of semiconductor detector elements, each of the pixels in the array having an in-pixel integrated circuit, the integrated circuit having a comparator, a readout decoder block, and an address arbitration control block. The readout decoder block reads out the integrated signals of the pixels. The address arbitration control block determines the pixel address of the pixels charging beyond a threshold voltage, the threshold exceedance determined by the comparator. The addressed pixels are provided a timestamp for each of the pixels integrating beyond the threshold voltage, the timestamp provided by an off-pixel time-to-digital converter (TDC), the value of the timestamp corresponding with the accumulated charge of the pixel.