Failsafe Image Sensor Real-Time Pixel Path Integrity
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Solution Overview
Problem
Conventional image sensors in safety-critical applications, such as automotive systems, face challenges in detecting pixel errors and defects in real-time without losing data or frame rate, leading to latency and potential failure in detecting relevant objects.
Innovation Solution
The implementation of a column-parallel analog-to-digital converter (ADC) architecture that allows for complete testing of the signal path from each pixel during real-time image processing, using a fail-safe test mode that interchanges the order of sampling and conversion phases, and employs a digital-to-analog converter to validate the analog and digital data paths without interrupting normal operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional image sensors perform self-tests using precision equipment to detect pixel errors, then reliability is improved, but the system complexity and cost increase significantly
Solution Approach 1:
The image sensor performs self-diagnosis by incorporating dedicated test pixels and test circuits within the sensor array itself. The sensor uses its own hardware resources (test pixels, test readout circuits, test ADC paths) to automatically detect pixel defects without requiring external precision equipment, thereby reducing system complexity while maintaining reliability
Solution Approach 2:
The patent creates a simplified copy of the signal path for testing purposes by routing test signals through duplicate test circuits parallel to the main signal path. This allows the sensor to replicate and monitor the functionality of critical components (pixel circuit, ADC path, data output) without needing complex external test equipment
2Reliability
If a majority vote camera system is used to detect pixel errors, then reliability is improved through redundancy, but detection latency increases significantly
Solution Approach 1:
The sensor performs continuous real-time monitoring of each pixel's signal path during normal operation by routing test signals through dedicated test circuits. This preliminary detection action occurs continuously rather than periodically, allowing pixel errors to be identified immediately when they occur, eliminating the latency associated with post-event analysis in majority vote systems
Solution Approach 2:
The patent implements a feedback mechanism where the test circuits continuously monitor the signal path and provide real-time status information about pixel functionality. When a pixel defect is detected, the system immediately generates error signals that can trigger corrective actions, creating a closed-loop feedback system that eliminates detection delays
3Speed
If real-time validation of pixel output circuits is implemented, then detection speed is improved, but the device complexity increases
Solution Approach 1:
The patent divides the sensor array into functional segments by incorporating dedicated test pixels interspersed within the main pixel array. These test pixels are organized in specific patterns (e.g., every Nth pixel) and are independently controllable through separate test readout circuits, allowing modular testing of different regions without affecting the entire sensor system
Solution Approach 2:
The test circuits are designed to serve multiple functions: they can test individual pixels, detect signal path failures, validate ADC conversion, and monitor data output integrity. By making the test infrastructure multi-functional, the patent reduces overall system complexity compared to having separate dedicated test equipment for each function
4Reliability
If complete testing of the signal path is performed during real-time image processing, then reliability is improved, but data loss and frame rate reduction occur
Solution Approach 1:
The patent segments the testing operation from the main image processing by using separate test pixels and test readout circuits that operate independently. This allows test signals to be routed through dedicated paths without interfering with the main signal path, enabling parallel execution of testing and image capture operations without frame rate loss
Solution Approach 2:
The test circuits are designed to operate continuously during normal sensor operation by utilizing idle time slots or parallel processing channels. The real-time validation is performed as a continuous background process that does not interrupt the main image acquisition and processing pipeline, maintaining continuous productivity while ensuring ongoing reliability
Data Source
AI summary
A method of testing analog and digital paths of a pixel in a row of an imager, includes the following steps: (a) injecting first and second charges into the analog path of the pixel, wherein the first charge is in response to a light exposure, and the second charge is in response to a built-in test; (b) sampling the first and second charges to form an image signal level and a test signal level, respectively; and (c) converting, by an analog-to-digital converter (ADC), the image signal level and the test signal level to form image data end test data, respectively. The method then validates the image data based on the test data.