Sensor Interface Circuit Self-Testing for Common Cause Fault Detection
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Solution Overview
Problem
Existing sensor interface circuits in safety-critical applications, such as automotive systems, face challenges in detecting common cause faults and electromagnetic compatibility (EMC) issues when using sensors with different manufacturing technologies, leading to unreliable data and potential safety risks.
Innovation Solution
A sensor interface circuit with at least two sensor inputs and front-end circuits, featuring a test circuit that applies a test input intermittently to evaluate the correct functionality by comparing sensor signal acquisitions and test results, thereby increasing safety integrity without significantly increasing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two separate analog front-ends are used for reading out two sensors, then redundancy is provided for safety critical applications, but the device complexity increases and common cause faults cannot be detected
Solution Approach 1:
The patent combines the test signal generation and injection functionality into the existing analog front-end circuitry. The test circuit uses the same operational amplifiers, filters, and ADCs that are already present for sensor signal processing, thereby providing redundancy testing without adding significant circuit complexity. The test signal is injected through the existing differential input structure, merging test and operational functions.
Solution Approach 2:
The analog front-end circuitry performs self-testing by generating internal test signals and processing them through its own signal path. The operational amplifiers, filters, and ADCs test themselves by processing test signals that mimic real sensor outputs, enabling the system to detect faults in its own components without requiring separate external test equipment.
2Reliability
If sensors with different manufacturing technologies are used, then diversity is achieved to reduce common cause faults, but electromagnetic compatibility issues and signal distortion occur due to longer electrical connections
Solution Approach 1:
The patent introduces an intermediary test signal that is generated and processed entirely within the analog front-end circuitry on the same chip. This eliminates the need for long external electrical connections between separate sensor chips and interface chips. The test signal acts as an intermediary that allows fault detection without requiring physical separation of sensor and interface functions.
Solution Approach 2:
The test signal generation and processing is nested within the existing analog front-end circuit structure. The test functionality is embedded inside the operational amplifiers, filters, and ADCs that are already present for sensor signal processing. This nesting allows the test functions to utilize the same signal path and components without requiring external connections.
3Ease of manufacture
If the same design is used for both analog front-ends, then design consistency is maintained, but common cause faults like design weaknesses and fabrication process weaknesses cannot be detected
Solution Approach 1:
The patent implements feedback by comparing the outputs of two identical analog front-ends processing the same test signal. The processing device compares the test results from both front-ends and can identify discrepancies that indicate faults. This feedback mechanism allows detection of common cause faults while maintaining design consistency, as the comparison reveals deviations from expected behavior.
Solution Approach 2:
The patent introduces asymmetry in the testing approach by independently testing each analog front-end with test signals and comparing their responses. Although the front-end designs are symmetric and identical, the testing process creates asymmetry by separately evaluating each channel's performance and comparing results, enabling detection of faults that would affect both channels equally.
Data Source
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AI summary
A sensor interface circuit (100) comprising: at least two sensor inputs (111, 112) and at least two front-end circuits (121, 122) to obtain sensor signal acquisitions from the at least two sensor inputs; a test circuit (131, 132) configured to test correct functionality of at least part of one of the front end circuits (121, 122) by applying a test input to the front end circuit under test, by reading a test output of the front end circuit, and by comparing the test output with an expected result thus obtaining at least one test result, wherein the test input is applied intermittently between sensor signal acquisitions; a processing device (140) configured for comparing the sensor signal acquisitions from the different sensor inputs and for combining the comparison with the at least one test result in order to evaluate correct functionality of the sensor interface circuit.