CAN Bus Transceiver Current Limiting for Interference Immunity
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Solution Overview
Problem
CAN bus systems face challenges in maintaining interference immunity and signal symmetrization, particularly during transitions between conventional CAN-HS and CAN-FD operations, due to fixedly configured transceivers that fail to meet direct power injection (DPI) test criteria, leading to potential communication interference.
Innovation Solution
A user station for the CAN bus system featuring a transmitter unit with a switching unit that temporarily disables current limiting functions when detecting HF signal components, ensuring minimal phase shift between CAN_H and CAN_L signals, and an edge controller for symmetrizing switching edges, allowing for high immunity to injected interferences without common mode chokes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a CAN transceiver is configured with fixed parameters to comply with functional demands, then reliability is improved, but adaptability deteriorates when transitioning between CAN-HS and CAN-FD operations
Solution Approach 1:
The patent applies dynamics by making the current limiting function switchable rather than fixed. The switching unit dynamically activates or deactivates the current limiting function based on operational mode (CAN-HS or CAN-FD) and detected signal conditions, allowing the transceiver to adapt its characteristics while maintaining reliability in each specific mode
2Manufacturing precision
If current limiting function is activated to control signal levels, then manufacturing precision is improved, but signal shift increases causing DPI test failures
Solution Approach 1:
The patent applies partial action by selectively applying current limiting only when necessary. The switching unit partially activates the current limiting function based on detected signal conditions and operational mode, rather than continuously applying it, thus achieving sufficient signal level control without excessive current limiting that would cause signal shifts
Solution Approach 2:
The patent changes the operational parameters of the current limiting function by switching it on or off based on detected HF signal components and operational mode. This parameter change allows optimization of signal level control for each specific operating condition while maintaining DPI test compliance
3Reliability
If signal symmetrization is enforced to meet DPI test criteria, then reliability is improved, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent merges the current limiting function control with the existing operational mode switching. The switching unit integrates multiple control functions (current limiting activation, HF signal detection response) into a single control mechanism that operates based on the detected operational mode, thereby achieving signal symmetrization without proportionally increasing device complexity
Data Source
AI summary
A user station for a bus system and a method for reducing line-related emissions in a bus system as described. The user station includes a transmitter unit for sending a message to another user station of the bus system via the bus system, an exclusive, collision-free access of a user station to a bus of the bus system being at least temporarily provided, and a switching unit for switching off a current limiting function of the transmitter unit when an HF signal component on the message sent by the transmitter unit is detected and a method for measuring the interference immunity in the area of electromagnetic compatibility is carried out for the transmitter unit.