CAN Transceiver Circuit With Adjustable Impedance to Suppress Ringing
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Solution Overview
Problem
Current CAN bus networks face limitations in data rate due to ringing and reflections caused by unterminated stub lines and impedance mismatches, especially with the introduction of higher data rates like those in CAN FD protocols, which can corrupt data and require costly topology redesigns to maintain signal integrity.
Innovation Solution
A transceiver circuit with dynamically adjustable push and pull resistances and an edge detector to control driver impedance and differential driver voltage, allowing independent adjustment of impedance and voltage to suppress ringing and maintain signal quality across existing network topologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If higher data rates are implemented in CAN bus networks, then data transmission speed is improved, but signal integrity deteriorates due to ringing and reflections
Solution Approach 1:
The patent implements dynamically adjustable push and pull resistances that can be modified in real-time based on detected bus conditions. The resistances transition between different states (e.g., from initial termination values to adjusted values) to adapt to varying data rates and network conditions, thereby maintaining signal integrity at higher speeds without requiring fixed topology constraints
Solution Approach 2:
The invention changes the resistance parameters of the push and pull resistors during operation. By adjusting these resistance values in response to detected ringing or reflections, the system optimizes impedance matching and damping characteristics dynamically, allowing higher data rates to be achieved while suppressing signal degradation
2Device complexity
If existing CAN bus network topology is maintained, then device complexity is reduced, but signal quality deteriorates at higher data rates due to reflections
Solution Approach 1:
The patent extracts the impedance control function from the fixed network topology and relocates it to the transceiver circuitry. By implementing adjustable push and pull resistances within the transceiver, the system compensates for topology-induced reflections without requiring changes to the physical network structure, thus maintaining simplicity while improving signal quality
Solution Approach 2:
The adjustable resistances act as intermediary elements between the fixed network topology and the high-speed signal transmission. These resistors provide dynamic impedance matching that mediates the conflict between the static topology and the high-speed requirements, enabling higher data rates without topology modification
3Reliability
If push and pull resistances are made dynamically adjustable, then signal integrity is improved, but device complexity increases
Solution Approach 1:
The transceiver circuit is designed with multi-functional resistive elements that serve both as termination resistors and as dynamically adjustable impedance control elements. This universal design allows the same hardware components to perform multiple functions (signal transmission, termination, and adaptive impedance matching) without requiring separate dedicated circuits for each function
Solution Approach 2:
The transceiver incorporates automatic detection and adjustment mechanisms that monitor bus conditions and self-regulate the push and pull resistance values without external intervention. The system detects ringing or impedance mismatches and automatically adjusts its resistance parameters to correct the issue, reducing the need for complex external control systems
Data Source
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AI summary
The present application relates to a circuit (300) and a transceiver comprising the circuit (300). The circuit (300) comprises two bus line terminals (301, 302) for coupling to a bus and a bridge circuit comprising two legs. Each leg comprises an adjustable pull resistance (315, 325) and an adjustable push resistance (310, 320) connected in series with a respective one of the two bus line terminals (301, 302). The adjustable pull resistances (315, 325) and the adjustable push resistances (310, 320) of the bridge circuit enable to independently adjust a driver impedance and to independently adjust a differential driver voltage on the bus. The circuit may further comprise an edge detector is coupled to a transmit data input and configured to detect a transition on the transmit data input and to adjust the impedances of the adjustable pull resistances (315, 325) and the adjustable push resistances (310, 320) in response to the detected transition.