Image Sensor Test Pixels for Continuous Fault Detection
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Solution Overview
Problem
Existing methods for testing image sensors in safety-critical applications like driver assistance systems in motor vehicles cannot perform tests during ongoing operation without disrupting regular image output, limiting their effectiveness in identifying errors and faults.
Innovation Solution
A method and device that allow testing of image sensors with test pixels interconnected to predefined voltage values, enabling the use of signal values from subsets of test pixels to identify errors and faults during regular operation, including brightness errors, row and column processing errors, and image shifts, while accounting for noise and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If testing is performed using existing methods during start-up or maintenance, then the image sensor can be tested for functional capability, but regular image output is interrupted and testing cannot occur during ongoing operation
Solution Approach 1:
The image sensor is segmented into regular pixels for image capture and test pixels for testing purposes. This segmentation allows the test pixels to be used for continuous testing while regular pixels maintain normal image output functionality, resolving the contradiction between testing reliability and operational continuity.
Solution Approach 2:
The test pixels are designed to serve multiple functions: they can be used for continuous testing during operation and their signal values can be differentiated from regular pixels through processing. This multi-functionality enables both continuous testing and uninterrupted regular image output, addressing the contradiction between reliability and productivity.
2Reliability
If test pixels are used for continuous testing during operation, then testing can occur without interrupting regular image output, but the complexity of processing signal values increases due to the need to distinguish test pixels from regular pixels
Solution Approach 1:
Test pixels are assigned specific spatial locations and interconnection patterns that differ from regular pixels. This local quality differentiation allows the processing unit to easily identify test pixels based on their position or interconnection characteristics, reducing the complexity of distinguishing them from regular pixels while enabling continuous testing.
Solution Approach 2:
The test pixels are interconnected with predefined voltage values that create distinct signal patterns, essentially creating a copy or reference pattern that is easily identifiable. This copying approach simplifies the processing complexity by providing a known reference signal that can be continuously monitored without complex analysis.
3Measurement precision
If subsets of test pixels are used for testing, then specific errors such as row processing errors, column processing errors, and block position deviations can be identified, but the complexity of analyzing multiple subsets increases
Solution Approach 1:
The test pixels are organized into distinct subsets based on their interconnection patterns (rows, columns, blocks). This segmentation allows specific error types to be isolated to particular subsets, enabling precise error detection while simplifying analysis by localizing problems to specific segments rather than requiring analysis of all test pixels simultaneously.
Solution Approach 2:
Instead of analyzing all test pixels uniformly, the method uses partial action by selecting specific subsets of test pixels for testing based on the type of error being detected. This approach reduces the complexity of analysis by focusing only on the relevant subsets needed for detecting specific error types, rather than processing the entire set of test pixels for every error category.
Data Source
AI summary
In a method for testing an image sensor having (i) regular pixels and test pixels, of which each is interconnected with one of two predefined voltage values, and (ii) a signal processing unit for providing digital signal values for output voltages of the pixels and test pixels, the following steps are performed: receiving digital signal values of the test pixels; and using the signal values of at least one proper or improper subset of the test pixels for testing the image sensor, all test pixels of the subset being interconnected with a first of the two voltage values. Using the test pixels for testing allows testing during ongoing operation, i.e., during reception of regular image signals.