Active Pixel Sensor Logic Circuit for Star Tracker SEU Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Star tracker images are corrupted by single event upsets (SEU) caused by solar flares and cosmic radiation, leading to image integrity issues, particularly in missions near the sun, and existing technologies require complex post-processing to address these issues.
Innovation Solution
An active pixel sensor apparatus with an on-chip logic circuit that performs non-destructive readouts during integration time, detects discontinuities in the pixel signal, and modifies the signal to subtract the SEU contribution, allowing for on-the-fly rejection of SEU, thereby simplifying image processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-destructive readout is performed multiple times during integration time to detect SEU, then image integrity is improved, but device complexity increases
Solution Approach 1:
The patent performs preliminary non-destructive readouts during the integration time to detect SEU events before the final image is completed. By detecting discontinuities in the pixel signal early in the integration process, the system can identify and reject images affected by SEU, preventing corrupted data from being stored and processed later.
Solution Approach 2:
The patent implements a feedback mechanism where the logic circuit continuously monitors the pixel signal during integration time by performing multiple non-destructive readouts. When a discontinuity indicating SEU is detected, the system provides feedback to reject the current integration and initiate a new one, thereby maintaining image integrity through real-time monitoring and correction.
2Device complexity
If on-the-fly SEU rejection is implemented, then image processing complexity is reduced, but measurement precision requirements increase
Solution Approach 1:
The patent performs more readouts than strictly necessary for basic image capture by implementing multiple non-destructive readouts during integration time. This excessive sampling provides redundant measurements that enable reliable detection of SEU-induced discontinuities, allowing the system to reject corrupted images while maintaining simple downstream processing.
Solution Approach 2:
The patent changes the monitoring parameter from continuous signal level to discontinuity detection by comparing pixel signals across multiple non-destructive readouts. This parameter transformation converts the complex problem of SEU filtering into a simpler binary decision: either a discontinuity is detected (SEU present) or it is not (image valid), thereby reducing processing complexity.
3Reliability
If multiple non-destructive readouts are performed during integration time, then SEU detection capability is improved, but integration time is extended
Solution Approach 1:
The patent implements periodic non-destructive readouts at specific intervals during the integration time rather than continuous monitoring. This periodic sampling approach provides sufficient SEU detection capability by checking for discontinuities at critical points in the integration process, while avoiding the need for constant monitoring that would unnecessarily extend the total integration time.
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 effective on-the-fly processing and rejection of SEU, reducing image processing complexity and improving image integrity by distinguishing and removing SEU contributions from continuous light sources, resulting in enhanced image quality in high-radiation environments.
Implementation Method 1
The core of the pixels is formed by photodiodes accumulating charge generated by irradiated photons
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
The invention relates to an active-pixel-sensor (APS) apparatus for use in a star tracker device including an imager chip (10), said imager chip (10) comprising an array (13) of photo-diodes operating as optical pixels, and a logic circuit (14). The logic circuit is configured for reading out a pixel signal depending on an amount of light irradiated during a predetermined integration time (T) and resetting the optical pixel upon termination of the predetermined integration time (T) processing the pixel signals and to output the modified signals and for performing a non-destructive readout of the pixel signal during the integration time (T). In order to distinguish Single-Event-Upset (SEU) contributions to the signal from star signal contributions, it is proposed to further configure the logic circuit (14) to detect whether or not a discontinuity has occurred in the pixel signal during the integration time, and to modify the signal depending on the result of this detection.