CAN Bus Reflection Attenuation Circuit for Open Ends and Star Points
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Solution Overview
Problem
Bus systems, particularly CAN bus systems, face limitations in data transfer due to reflections at open ends and branch points, which restrict data rates and flexibility, especially when termination is not possible, such as in trailers connected via a private CAN line, and require complex voltage regulation to maintain voltages within 0 V to 2 V.
Innovation Solution
A reflection attenuation device using a pair of electrical semiconductor components connected in parallel with a capacitor in series, which is robust against short circuits and common-mode interferences, allowing for symmetrical design and flexible cable harnesses, effectively suppressing high-frequency reflections and enabling higher data transfer rates without impairing communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two terminating resistors are used at the farthest user stations, then reflections are attenuated, but the system becomes inflexible when trailers are connected and data rates are limited
Solution Approach 1:
The patent introduces an intermediary component (the reflection attenuation device with capacitor and antiparallel diodes/transistors) at the star point to handle reflection attenuation, freeing the bus ends from termination requirements and enabling flexible trailer connections without compromising signal integrity
Solution Approach 2:
The patent extracts the termination function from the bus ends and concentrates it at the star point through the reflection attenuation device, allowing bus lines to remain open at ends while still achieving effective reflection suppression and enabling flexible system configurations
2Reliability
If Zener diode with operational amplifier is used to limit voltages to 0 V to 2 V, then voltage regulation is achieved, but the device complexity increases
Solution Approach 1:
The patent employs antiparallel diodes or transistors that automatically clamp voltages to the 0 V to 2 V range through their inherent electrical characteristics, eliminating the need for external operational amplifiers and complex control circuits while maintaining reliable voltage regulation
Solution Approach 2:
The patent replaces expensive and complex operational amplifier circuits with simple, inexpensive antiparallel diodes or transistors that provide the same voltage limiting function with fewer components and lower cost
3Productivity
If data bit rate is increased to achieve higher data transfer, then productivity improves, but reflections at high frequencies worsen communication
Solution Approach 1:
The patent converts the harmful high-frequency reflections into beneficial effects by using the reflection attenuation device to capture and dissipate reflection energy, thereby enabling higher data bit rates to be used productively without suffering from degradation due to reflections
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 allows for increased data rates in bus systems, enabling flexible use of CAN FD or its successors at higher data transfer rates than conventional CAN or CAN FD, while maintaining robustness and voltage regulation within 0 V to 2 V, thus improving communication efficiency.
Implementation Method 1
at least one capacitor, connected in series to the at least one pair of electrical semiconductor components connected in parallel, for attenuating reflections on a bus line of the bus
Data Source
AI summary
A reflection attenuation device for a bus of a bus system and a method for attenuating reflections during a data transfer in a bus system. The reflection attenuation device may close off a free end of bus lines of the bus in a transceiver device of a user station of the bus system. Alternatively, the reflection attenuation device may be connected to a branch point of the bus which is a star point or is used to connect a user station to the bus. Thus, bus users in a vehicle trailer are also connectable to the bus system of the vehicle, as needed. The reflection attenuation device includes at least one pair of electrical semiconductor components connected in parallel, and at least one capacitor that is connected in series to the pair of electrical semiconductor components connected in parallel, for attenuating reflections on a bus line of the bus.