CAN Bus Transceiver Bit Symmetry Compensation
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Solution Overview
Problem
The CAN bus system experiences faulty transmissions due to poor bit symmetry, which is exacerbated at higher bit rates, leading to communication failures when the bit symmetry requirements are not met.
Innovation Solution
A user station with a transceiver that includes a transmission signal processing device configured to set a predetermined bit symmetry by shortening the dominant phase and lengthening the recessive phase of bits, ensuring exclusive and collision-free access to the bus, thereby improving transmission quality and preventing faulty transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the bit rate is increased to improve data transmission speed, then the productivity is improved, but the bit symmetry deteriorates leading to faulty transmissions
Solution Approach 1:
The transmission signal processing device performs preliminary action by pre-adjusting the bit symmetry parameters before data transmission begins. It calculates the optimal bit symmetry values based on the selected bit rate and applies compensation factors to ensure that even at high bit rates, the bit symmetry remains within acceptable ranges, preventing faulty transmissions before they occur
Solution Approach 2:
The invention dynamically changes transmission parameters (bit symmetry values, compensation factors) based on the operating bit rate. When the bit rate is increased to improve productivity, the system automatically adjusts the bit symmetry parameters to compensate for the degradation, thereby maintaining transmission quality across different data rates
2Stability of the object's composition
If the dominant phase is lengthened to improve signal stability, then the stability is improved, but the recessive phase becomes too short causing bit asymmetry
Solution Approach 1:
The invention intentionally introduces asymmetric compensation factors to balance the overall bit symmetry. By applying different compensation values to the dominant and recessive phases, it counteracts the natural asymmetry caused by bus delays and capacitances, ensuring that the total bit duration remains symmetric even when individual phases have different characteristics
Solution Approach 2:
The transmission signal processing device dynamically adjusts the bit phase durations based on real-time conditions and selected bit rates. Rather than using fixed phase lengths, the system continuously optimizes the dominant and recessive phase durations to maintain bit symmetry across varying operating conditions, ensuring both stability and precision
3Reliability
If the switching time from dominant to recessive state is increased to improve signal reliability, then the reliability is improved, but the recessive bit duration becomes too short at high bit rates
Solution Approach 1:
The system performs preliminary calculation of the required recessive bit duration based on the selected bit rate and bus characteristics. Before transmission, it determines the appropriate compensation factor to apply to the switching time, ensuring that even at high bit rates where time is critical, the recessive bit duration remains sufficient for reliable detection
Solution Approach 2:
The invention changes the switching time parameter dynamically based on the operating bit rate. At higher bit rates where the recessive bit duration becomes critically short, the system adjusts the switching time parameter to optimize the balance between signal reliability and time constraints, preventing transmission errors
Data Source
AI summary
A user station for a bus system and a method for improving the transmission quality in a bus system are provided. The user station includes a transceiver for transmitting or receiving a message to/from at least one additional user station of the bus system via the bus system. In the bus system, exclusive, collision-free access to a bus of the bus system by a user station is at least temporarily ensured. The transceiver includes a transmission signal processing device for transmission signal processing of a transmission signal to be transmitted by the transceiver. The transmission signal processing device is configured for setting a predetermined bit symmetry of bits of the transmission signal by generating an internal transmission signal for the message. In the internal transmission signal, the dominant phase of the bits is shortened and the recessive phase of the bits is lengthened.