Asymmetry Reduction Module for CAN Bus Line Emission Control
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Solution Overview
Problem
Existing CAN and CAN FD bus systems face challenges in reducing line emissions due to increased bit rates, which are not adequately addressed by current methods.
Innovation Solution
A transmitting/receiving device with an asymmetry reduction module, featuring a polarity reversing diode and an adjusting circuit, is used to symmetrize the voltage curve on bus wires, reducing parasitic currents and line emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bit rate is increased in CAN FD compared to classic CAN, then the data transmission speed is improved, but the line emissions increase significantly
Solution Approach 1:
The patent applies asymmetry principle by intentionally introducing asymmetrical compensation currents through the asymmetry reduction module. The module detects asymmetrical voltage curves on the bus wires and generates compensating currents with opposite polarity to counterbalance the asymmetry, thereby reducing line emissions while maintaining high bit rates
Solution Approach 2:
The asymmetry reduction module acts as an intermediary between the transmitting stage and the bus wires. It monitors the voltage curves on CAN_H and CAN_L wires and injects compensating currents to symmetrize the overall bus signals, effectively mediating between the differential signaling and the emission requirements
2Reliability
If reverse polarity diodes are used in the transmitting stage to protect against voltage spikes, then the reliability is improved, but asymmetrical voltage curves are generated causing increased line emissions
Solution Approach 1:
The patent converts the harmful effect of reverse polarity diodes (which create asymmetrical voltage curves) into a beneficial solution. The asymmetry reduction module detects the asymmetry caused by these diodes and generates compensating currents that actively counterbalance the asymmetry, thereby converting the original problem into a solved issue while maintaining the protective function of the diodes
3Object-generated harmful factors
If the voltage curve asymmetry is reduced to meet emission limits, then the line emissions are reduced, but the device complexity increases due to additional circuitry
Solution Approach 1:
The asymmetry reduction module is merged with the existing transmitting/receiving device architecture. The module shares common components such as the bus wire connections, voltage detection circuits, and current injection paths with the differential signaling stage, thereby reducing overall device complexity while achieving emission reduction
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
The solution significantly reduces line emissions and improves electromagnetic compatibility (EMC) by minimizing asymmetrical voltage curves and parasitic currents, particularly at higher CAN FD bit rates.
Implementation Method 1
the asymmetry reduction module having a polarity reversing diode, whose cathode is connected to the cathode of a reverse polarity diode of the transmitting stage
Data Source
AI summary
A transmitting/receiving device for a bus system and a method for reducing an oscillation tendency in the transition between different bit states. The transmitting/receiving device has a transmitting stage for transmitting a transmission signal to a first bus wire of a bus of the bus system and for transmitting the transmission signal as an inverse signal to a second bus wire of the bus, and an asymmetry reduction module for reducing an asymmetry of bus signals arising in the bus wires. The asymmetry reduction module includes a polarity reversing diode, whose cathode is connected to the cathode of a reverse polarity diode of the transmitting stage. The asymmetry reduction module switches a potential of the cathode of the polarity reversing diode to a potential that is greater than or equal to a level of a recessive bus state.