Differential TOF Pixel HDR Imaging via Dual Polyfinger Segmentation
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Solution Overview
Problem
Existing HDR imaging techniques face challenges in capturing both high dynamic range images and depth images accurately, often resulting in motion artifacts and increased pixel size and complexity due to the use of multiple photodiodes.
Innovation Solution
A time-of-flight (TOF) camera with a differential TOF pixel configuration, featuring two polysilicon gates (polyfingers) controlled by complementary clock signals, allows for the generation of HDR images by comparing charges collected at each polyfinger and selecting appropriate data for inclusion in the image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple photodiodes are used to capture different exposure levels simultaneously, then HDR imaging capability is improved, but pixel size and device complexity increase
Solution Approach 1:
The integration period is divided into multiple exposure intervals with different durations. Each polyfinger collects charge during a specific interval, segmenting the temporal dimension rather than using multiple photodiodes simultaneously. This allows HDR capture without increasing pixel area or structural complexity.
Solution Approach 2:
The patent transitions from spatial multiplexing (multiple photodiodes side-by-side) to temporal multiplexing (single photodiode collecting charge over different time intervals). By adding the time dimension to the imaging process, the system achieves HDR capability without increasing pixel density or device complexity.
2Adaptability or versatility
If multiple photodiodes are used for HDR imaging, then high light and low light data collection is improved, but motion artifacts increase due to time-sequential capture
Solution Approach 1:
Multiple exposure intervals are merged into a single integration period, with all polyfingers collecting charge simultaneously during their respective intervals. This temporal merging within a unified exposure window eliminates the motion artifacts associated with sequential time-based HDR capture while maintaining the ability to capture both high and low light data.
3Illumination intensity
If longer exposure time is used to capture low light data, then low light performance is improved, but saturation occurs in high light regions
Solution Approach 1:
The integration period is segmented into multiple exposure intervals of different durations. Shorter intervals prevent saturation in high light regions, while longer intervals capture sufficient signal in low light regions. Each polyfinger is assigned to a specific interval, allowing simultaneous optimization for both bright and dark areas without compromise.
Solution Approach 2:
The exposure time parameter is varied across different intervals and polyfingers. By changing the integration time parameter from one interval to another, the system adapts to different light conditions within the same scene, preventing saturation while maintaining sensitivity.
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 effectively avoids motion artifacts and reduces pixel size and complexity by allowing high light and low light data to be collected during the same integration period, while also enabling accurate depth imaging.
Implementation Method 1
charge carriers generated during the drive intervals by a radiation pulse reflected from the object of measurement
Data Source
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AI summary
One example provides a method of generating a high dynamic range image via a differential TOF pixel comprising an array of pixels each having a first charge collection point and a second charge collection point, the first charge collection point and the second charge collection point being independently controllable to integrate current during an integration period, the method comprising, during the integration period, controlling the first charge collection point for a first exposure time and controlling the second charge collection point for a second exposure time, and for each pixel comparing a charge collected at the first charge collection point and a charge collected at the second charge collection point to a threshold to select one for inclusion in the HDR image.