CAN Node DTO Circuit for Stuck Dominant Fault Isolation
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Solution Overview
Problem
Controller Area Network (CAN) systems face issues with 'stuck dominant' faults, which can block the entire network due to physical constraints and limited flexibility in topologies, especially in environments like airplanes, where different branches have varying resistances and signal integrity is compromised by non-standard termination resistances.
Innovation Solution
The implementation of an RXD dominant time out (DTO) circuit in each CAN node, which detects a dominant state and overrides it to a recessive state after a predetermined time, preventing network blocking and allowing for robust fault detection and diagnostics, enabling proper termination of CAN branches with matched impedance resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-standard termination resistances are used to accommodate varying branch resistances in star/stub topologies, then adaptability to different physical configurations is improved, but signal integrity deteriorates due to reflections and impedance mismatches
Solution Approach 1:
The patent changes the electrical parameters of the termination resistors to match the characteristic impedance of each branch (e.g., 120 ohms for star topology, 60 ohms for stub topology). This parameter adjustment resolves the impedance mismatch problem while maintaining adaptability to different physical configurations. Each branch is terminated with a resistor value specifically calculated for its topology type, eliminating reflections and signal integrity issues.
2Object-affected harmful factors
If standard termination resistors are used in star/stub topologies, then signal integrity is improved through proper impedance matching, but adaptability to varying branch resistances deteriorates
Solution Approach 1:
The patent applies different termination resistor values to different branches based on their specific topology and characteristic impedance. Instead of using a uniform termination value, each branch is terminated locally with the appropriate resistance (120 ohms for star, 60 ohms for stub). This local quality approach maintains signal integrity for each branch while accommodating varying physical configurations and resistance requirements.
3Device complexity
If bus topology is used to simplify network design, then device complexity is reduced, but reliability deteriorates due to stuck dominant faults blocking the entire network
Solution Approach 1:
The patent segments the bus topology into electrically isolated branches using high-value resistors (e.g., 10k ohms) connected to each node. This segmentation prevents a stuck dominant fault on one branch from affecting other branches, as the isolating resistors block fault propagation. The physical bus topology is maintained for simplicity, but electrically it behaves as segmented independent channels, improving reliability while preserving design simplicity.
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 prevents network blocking by CAN nodes with 'stuck dominant' faults, enhances signal integrity, and allows for flexible configuration of CAN branches, improving the robustness and reliability of CAN networks by enabling proper termination and fault detection without requiring redundant link layer controllers.
Implementation Method 1
a differential comparator that compares a voltage differential between a CANH and a CANL
Implementation Method 2
These bus lines have two states: a 'recessive' state, and a 'dominant' state, which is determined by a voltage differential between the CANH and the CANL. The CANH and the CANL are driven by a transmission driver circuit.
Implementation Method 3
allowing for flexible configuration of CAN branches, improving the robustness and reliability of CAN networks by enabling proper termination
Data Source
AI summary
A controller area network (CAN) node comprises an internal high differential bus line (CANH) and an internal low differential bus line (CANL). The CAN node further comprises a receiver (RXD) comparator coupled to both the internal CANH and the internal CANL that outputs an internal RXD signal. The CAN node further comprises an RXD dominant time out (DTO) circuit. The RXD DTO circuit includes: a) an RXD dominant transition detector coupled to an output of the RXD comparator; b) a timer triggered by the RXD dominant transition detector detecting a dominant RXD transition; c) an RXD dominant timer comparator that is coupled to an output of the timer which compares an output of the timer to a selected value; d) an internal RXD dominant signal is changed to an RXD DTO recessive signal after a selected time interval has lapsed and can include a fault output to signal this fault condition.