Image Sensor Test Pattern Injection for Active Reliability Verification
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Solution Overview
Problem
Conventional image sensors lack a reliable method to verify the functionality of their components during both standby and active operation, making it difficult to detect failures that may occur during active use.
Innovation Solution
The integration of a test pattern injection system that allows for direct testing of photodiodes within a pixel array using a multiplexer and transistors, enabling on-the-fly verification of image sensor integrity by applying test signals and patterns to individual pixels, even during active operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional image sensors are provided with testing methods only during stand-by mode, then device complexity is kept simple, but reliability is reduced because failures during active operation cannot be detected
Solution Approach 1:
The pixel array is designed to perform both normal imaging operations and self-testing functions using the same hardware components. The photodiodes and circuitry serve dual purposes: capturing images during active operation and receiving test patterns for verification, eliminating the need for separate dedicated testing hardware and thus adding reliability without proportionally increasing device complexity
Solution Approach 2:
The image sensor performs self-diagnosis by generating and injecting test patterns into its own photodiodes through integrated circuitry. The sensor monitors its own functionality during both stand-by and active operation without requiring external testing equipment, enabling autonomous reliability verification while maintaining relatively simple device architecture
2Reliability
If test patterns are injected into individual photodiodes during active operation, then reliability is improved through continuous monitoring, but device complexity increases due to additional circuitry
Solution Approach 1:
The testing circuitry is merged with the normal pixel array circuitry. The same transistors, signal lines, and control logic that operate during normal imaging are repurposed to generate, route, and read test patterns. This integration allows real-time reliability monitoring during active operation while minimizing additional hardware complexity by reusing existing components
Solution Approach 2:
The system dynamically switches between normal imaging mode and self-testing mode using existing control circuitry. During active operation, the pixel array can transition to receiving test patterns without requiring permanent dedicated testing hardware, enabling real-time reliability verification while keeping the device architecture flexible and relatively simple
3Reliability
If conventional testing methods are used during stand-by mode only, then device complexity remains low, but loss of time occurs because failures are not detected until after active operation
Solution Approach 1:
The self-testing capability operates continuously during both stand-by and active operation modes, providing uninterrupted reliability monitoring. The pixel array can perform self-diagnosis at any time without interrupting normal device functionality, ensuring that failures are detected immediately when they occur rather than delayed until the next scheduled test or until failure manifests during active use
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 allows for continuous monitoring and verification of image sensor components, ensuring the quality of imaging data and enhancing vehicle safety systems by detecting potential issues in real-time, thereby preventing failures that could impact safety.
Implementation Method 1
Each image pixel may include a photodiode... The floating diffusion node may be set to a reset voltage while the column provides a selected test voltage that generates a test charge in the photodiode
Data Source
AI summary
An imaging system may include an image sensor having a pixel array. The pixel array may receive test signals from multiplexers located at the top or bottom of each column of the array. Test signals may be provided to each column based on a predefined test pattern. In some arrangements, pixel array photodiodes may receive test signals through an anti-blooming transistor while the anti-blooming transistor is on. In other arrangements, dark current of photodiodes in the pixel array may be modulated by voltages applied to the drain of an anti-blooming transistor while the anti-blooming transistor is off. In other arrangements, pixel array photodiodes may receive test signals through a reset transistor. Arbitrary test patterns may be applied to determine photodiode or floating diffusion node leakage and incorrect pixel control voltages. Arbitrary patterns may also be superimposed on light-based image data in the manner of a watermark.