CAN Transceiver Dynamic Output Impedance Control
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Solution Overview
Problem
Existing CAN transceivers face challenges in efficiently controlling output impedance to minimize signal reflections and ringing on the CAN bus, particularly in networks with multiple nodes and varying bus topologies.
Innovation Solution
The proposed CAN transceiver incorporates an impedance control device connected to two bus terminals, which dynamically adjusts output impedance based on the length of time a logic zero state persists before transitioning to a logic one state. This adjustment follows two distinct schemes: one for longer durations and another for shorter durations, or no control, to optimize impedance matching and reduce signal disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If output impedance is controlled to minimize signal reflections, then signal quality improves, but device complexity increases due to dynamic impedance adjustment mechanisms
Solution Approach 1:
The patent implements dynamic output impedance control by adjusting the impedance value based on the detected duration of the logic zero state. The impedance control device switches between different impedance values (first impedance value for longer durations, second impedance value for shorter durations) to optimize signal quality in real-time, resolving the contradiction between maintaining simple device architecture and achieving dynamic signal optimization.
Solution Approach 2:
The patent changes the impedance parameter dynamically based on the detected time duration of logic zero states. By varying the impedance value according to the duration threshold, the system adapts to different transmission conditions and minimizes signal reflections without requiring complex hardware modifications, thus improving signal quality while managing device complexity.
2Object-affected harmful factors
If dynamic impedance control is implemented, then signal reflections and ringing are reduced, but the control mechanism becomes more complex
Solution Approach 1:
The patent employs a feedback mechanism where the signalling detector monitors the duration of logic zero states and provides this information to the impedance control device. The impedance control device then adjusts the output impedance based on this feedback, creating a closed-loop system that effectively reduces signal reflections and ringing while using a manageable control architecture.
Solution Approach 2:
The system performs self-adjustment by automatically detecting the duration of logic zero states and autonomously selecting appropriate impedance values without external intervention. This self-service capability allows the transceiver to compensate for signal reflections and ringing on its own, reducing harmful effects while minimizing the need for complex external control mechanisms.
3Device complexity
If impedance control is applied only for certain duration thresholds, then control complexity is reduced, but signal quality optimization is limited
Solution Approach 1:
The patent applies different impedance control strategies based on local conditions detected by the signalling detector. Instead of applying uniform control, the system selects different impedance values (first impedance value for durations exceeding the threshold, second impedance value for durations below the threshold) to optimize signal quality in specific operational contexts, achieving targeted optimization without excessive complexity.
Data Source
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AI summary
A Controller Area Network, CAN, transceiver comprising: two terminals for coupling to a CAN bus; a transmitter arrangement configured to transmit signalling on the bus based on transmit data, the transmitter arrangement configured to drive the bus to a dominant state or recessive state based on the transmit signal; an impedance control device; a signalling detector to determine the length of time the transmit data comprises a logic zero prior to a transition to a logic one state and: based on the length of time being longer than a predetermined threshold, provide for control of an output impedance by the impedance control device in accordance with a first scheme; and based on the length of time being shorter than said predetermined threshold, provide for one of: control of said output impedance in accordance with a second scheme; and no control of the output impedance by the impedance control device.