Cable Termination Resistance Calculation for FlexRay Networks
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Solution Overview
Problem
High-speed communication networks, such as those using FlexRay, face significant challenges due to reflections caused by impedance discontinuities, which existing termination methods fail to adequately address, leading to communication failures and excessive power dissipation in improper terminations.
Innovation Solution
A method for determining cable termination resistances involves assigning weights to cable lengths and calculating termination resistances for each cable end by multiplying the cable impedance with a constant and the sum of weights divided by the specific cable end's weight, ensuring all cable ends are terminated to minimize reflections and power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single resistor is used at each main cable end to match the cable's differential-mode characteristic impedance, then reflections are eliminated and signal fidelity is excellent, but power dissipation in the termination resistors becomes excessive
Solution Approach 1:
The patent applies different termination resistance values to different cable ends based on their local topology characteristics. Each cable end is analyzed individually, and its termination resistance is calculated based on the sum of weights of all cable ends divided by its own weight. This localized approach allows each cable end to be optimally terminated according to its specific position in the network, eliminating reflections while distributing power dissipation more efficiently across the network.
2Loss of energy
If conventional termination methods are applied to only two main cable ends, then power dissipation is reduced, but harmful reflections occur at improperly terminated cable ends
Solution Approach 1:
The patent changes the termination resistance parameter for each cable end based on its position and connectivity in the network topology. Instead of using a uniform termination resistance or terminating only two ends, the method calculates a specific termination resistance for each cable end by summing the weights of all cable ends and dividing by the individual cable end's weight. This parameter adaptation ensures all cable ends are properly terminated, eliminating reflections while maintaining reasonable power dissipation.
3Loss of energy
If RC termination is used to minimize power dissipation, then power consumption is reduced, but lowpass effects limit its use to lower data-rate applications
Solution Approach 1:
The patent uses a simplified resistive termination model that copies the essential function of complex termination networks. Instead of using RC circuits with their lowpass filtering effects, the method calculates equivalent resistive termination values for each cable end that achieve the same reflection elimination goal without the bandwidth-limiting capacitor elements. This allows high-speed communication while maintaining power efficiency.
Data Source
AI summary
The invention relates in general to a method for determining cable termination resistances in communication networks and a corresponding communication network, and is applicable especially to high-speed communication networks in automobiles, which uses dual-wire harnesses like FlexRay e.g. For this purpose a method for determining cable termination resistances in communication networks is proposed, where a termination resistance is assigned to at least a part of the cable ends of the network in accordance with the following steps determining for each cable end the cable length to any other cable end, assigning a weight value to each length where lengths with greater values are combined with higher weights than lengths with smaller values, for all cable ends: summing up the weights assigned to all lengths starting from a specific cable end and assigning this sum to the respective cable end as the weight of this cable end, determining the termination resistance of a specific cable end by multiplying the cable impedance Z with a constant of proportionality and the sum of the weights of all cable ends divided by the weight of the specific cable end.