Image Sensor Self-Test Signal Chain During Streaming
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Solution Overview
Problem
Conventional image sensors used in safety-critical automotive applications require expensive and sophisticated test equipment to detect failures, which is not feasible for operational testing without disrupting data or frame rate, especially in systems like lane tracking and crash alert systems.
Innovation Solution
A method for testing an image sensor's signal chain during vertical blanking without disturbing regular image capture, using a test circuitry that can verify column address ranges and sequences, and alter test patterns for each frame to achieve comprehensive coverage over multiple frames, suitable for both column parallel and serial architectures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional test equipment is used to test image sensors, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The image sensor performs self-testing by utilizing its own internal circuitry (pixel array, readout circuitry, ADCs) to generate and process test signals. The sensor tests itself without requiring external precision test equipment, thereby reducing device complexity and cost while maintaining measurement precision through self-validation of the signal chain
Solution Approach 2:
The patent creates a virtual copy of the light signal generation process by using digital test patterns that simulate optical inputs. These digital test signals are injected into the signal chain to replace physical light injection, eliminating the need for sophisticated optical test equipment while maintaining test accuracy through mathematical modeling of expected sensor responses
2Reliability
If operational testing is performed during image capture, then reliability is improved, but productivity decreases due to data loss or frame rate disruption
Solution Approach 1:
The patent implements periodic testing by injecting test signals at specific intervals (e.g., during vertical blanking periods or at fixed frame rates) rather than continuously. This allows the sensor to alternate between normal image capture mode and test mode, ensuring reliability through regular self-validation while maintaining high productivity by minimizing interruptions to the data stream
Solution Approach 2:
The patent performs preliminary testing by validating the signal chain before full operational use or by preparing test patterns in advance during vertical blanking periods. This allows the sensor to verify its functionality proactively without disrupting the main imaging workflow, ensuring reliability is maintained while productivity is preserved through advance preparation
3Ease of operation
If test signals are injected during vertical blanking, then ease of operation is improved, but loss of time increases due to test duration
Solution Approach 1:
The patent utilizes the periodic vertical blanking intervals in the sensor's operating cycle to inject test signals. By synchronizing test operations with these natural periodic gaps in the imaging workflow, the system achieves ease of operation through straightforward integration into the existing timing structure while minimizing time loss since the tests occur during already-unused blanking periods
Solution Approach 2:
The patent dynamically adjusts test signal injection timing and duration based on the sensor's operational state and frame rate requirements. The test circuitry can adaptively select when to inject signals (during vertical blanking or other intervals) and how long to maintain test conditions, optimizing the balance between ease of operation and time efficiency according to real-time operational demands
Data Source
AI summary
An imager including a self test mode. The imager includes a pixel array for providing multiple pixel output signals via multiple columns; and a test switch for (a) receiving a test signal from a test generator and (b) disconnecting a pixel output signal from a column of the pixel array. The test switch provides the test signal to the column of the pixel array. The test signal includes a test voltage that replaces the pixel output signal. The test signal is digitized by an analog-to digital converter (ADC) and provided to a processor. The processor compares the digitized test signal to an expected pixel output signal. The processor also interpolates the output signal from a corresponding pixel using adjacent pixels, when the test switch disconnects the pixel output signal from the column of the pixel array.