CAN Bus Recessive Level Driving for EMI Immunity
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Solution Overview
Problem
Current bus communication systems in automotive applications face challenges in providing improved immunity against electro-magnetic interference (EMI) while maintaining high data rates and robustness, especially in sophisticated lighting systems.
Innovation Solution
A method involving a master-slave communication architecture over a CAN FD bus, where the bus is actively driven to a recessive level during message transmission, and end-to-end data protection mechanisms are implemented using CRC and error checking to enhance EMI robustness and symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CAN bus communication is used in sophisticated lighting systems, then basic communication functionality is achieved, but immunity against electro-magnetic interference is insufficient
Solution Approach 1:
The patent applies asymmetry by actively driving the CAN bus to a recessive level during message transmission, creating an asymmetric communication mode that provides improved EMI immunity. This asymmetric driving approach breaks the conventional symmetric dominant/recessive state transitions and establishes a more robust communication protocol for automotive lighting systems
Solution Approach 2:
The patent changes the communication parameter by actively setting the bus to a recessive level during transmission, rather than relying on passive impedance matching. This parameter change in the communication protocol enhances the system's ability to reject electro-magnetic interference while maintaining high data rates
2Measurement precision
If high data rate communication is implemented in distributed lighting systems, then control precision is improved, but energy dissipation increases
Solution Approach 1:
The patent implements periodic action by using structured message transmission with defined dominant and recessive levels. Messages are transmitted in periodic frames with specific timing, allowing for efficient energy utilization while maintaining high data rates for precise control of distributed LED elements
Solution Approach 2:
The patent optimizes energy dissipation by changing the communication parameter to actively drive the bus to a recessive level during transmission. This parameter change reduces the energy required for maintaining communication integrity in high-data-rate applications compared to conventional dominant-state continuous driving
3Reliability
If active recessive level driving is implemented during message transmission, then EMI immunity is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing a transceiver circuit that can operate in multiple modes (conventional CAN and active recessive driving). The same hardware infrastructure supports both standard communication and the enhanced EMI-immune mode, reducing the need for additional dedicated components while improving reliability
Data Source
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AI summary
A method of operating a CAN bus comprises coupling a first device (10) and second devices (201, ..., 20n) to the CAN bus (30) via respective CAN transceiver circuits. The method comprises configuring the first device as a communication master device to transmit first messages carrying operation data message portions indicative of operations for implementation by the second devices, and second messages addressed to the second devices, the second messages conveying identifiers identifying respective ones of the second devices to which the second messages are addressed requesting respective reactions towards the first device within respective expected reaction intervals. The method comprises configuring the second devices as communication slave devices to receive the first messages transmitted from the first device, read respective operation data message portions in said operation data message portions and implement respective operations as a function of the respective operation data message portions read, and to receive the second messages transmitted from the first device and react thereon within said respective expected reaction intervals by transmitting reaction messages towards the first device. The method comprises configuring said respective CAN transceiver circuits to set the CAN bus to a recessive level during transmission of said messages via the CAN bus by the respective first device or second device.