Variable-Resistance CAN Bus Damping for Ringing Suppression
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Solution Overview
Problem
Oscillations or 'ringing' in bus systems, such as the CAN bus, limit the maximum bit rate due to increased time for reliably detectable signal states, necessitating improved damping methods to enhance the effectively usable bit rate.
Innovation Solution
A damping device with a control circuit that selectively controls the electrical resistance between bus lines using semiconductor switches, particularly field-effect transistors, to manage oscillations and ensure weak bus participants can generate a voltage difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the bus lines are connected with low impedance to dampen oscillations, then oscillation damping is improved, but current consumption increases for all bus participants
Solution Approach 1:
The damping impedance is made dynamic rather than static. The circuit uses switching elements to change the impedance state based on signal conditions: during signal edges, the damping circuit activates to provide low impedance for oscillation suppression; during steady states, the damping circuit deactivates to maintain normal high impedance operation. This dynamic adaptation resolves the contradiction by providing low impedance only when oscillation damping is actually needed.
Solution Approach 2:
The impedance parameter is changed based on operating conditions. The damping circuit alters the electrical impedance between bus lines from high (normal operation) to low (oscillation suppression) depending on the detected signal state. This parameter change allows the system to optimize for oscillation damping during transitions while maintaining energy efficiency during stable operation.
2Stability of the object's composition
If the damping circuit uses very low resistance to suppress oscillations, then oscillation damping is improved, but weak bus participants cannot generate sufficient voltage difference
Solution Approach 1:
The damping circuit's resistance is dynamically adjusted based on the signal state. During dominant-to-recessive transitions when oscillations occur, the damping circuit activates with low resistance to suppress ringing. During error flag generation by weak participants, the damping circuit remains inactive with high resistance, allowing sufficient voltage difference to be generated. This temporal separation of damping and signal generation functions resolves the contradiction.
Solution Approach 2:
The damping circuit is activated in advance during the transition period when oscillations are most likely to occur, rather than being continuously active. The control circuit detects the edge condition and enables damping only during the critical transition window, allowing weak participants to freely generate error flags during steady states without interference from the damping circuit.
3Stability of the object's composition
If continuous low impedance connection is used for oscillation damping, then oscillation damping is improved, but signal transmission speed is reduced
Solution Approach 1:
The damping circuit operates periodically rather than continuously, activating only during signal transitions when oscillations occur and deactivating during steady states. This periodic operation allows fast signal transmission during most of the time while providing oscillation damping only during the brief transition periods when it is actually needed, thus resolving the speed-damping contradiction.
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
Effectively suppresses oscillations, allowing faster signal transitions and enabling even weak bus participants to indicate errors, thus enhancing the bus system's bit rate capacity.
Implementation Method 1
The variable resistance value is generated particularly advantageously by the on-resistance (e.g., RDSon) of at least one semiconductor switch, preferably by at least two semiconductor switches connected in anti-series
Implementation Method 2
The damping circuit (44) has a first terminal (32) for a first bus line (6) of the bus and a second terminal (34) for a second bus line (8). The damping circuit also has a control terminal (36) for connection to a control device (20)
Data Source
Figure 1~2
Figure 3
Figure 4A~4C
AI summary
The invention relates to an attenuating device (30) for a bus (10) of a bus system (2) based on differential voltage signals, in particular a controller area network bus system, wherein the bus has a first bus line (6) and a second bus line (8), having an attenuating circuit (44) that provides a variable electrical resistance value between the first bus line (6) and the second bus line (8) and that is operable in at least three circuit states, wherein in a first circuit state the first bus line (6) and the second bus line (8) are connected to a first resistance value via an attenuating resistor (50, 52), wherein in a second circuit state the first bus line (6) and the second bus line (8) are connected to a second resistance value via an attenuating resistor (50, 52), and wherein in a third circuit state the first bus line (6) and the second bus line (8) are connected to a third resistance value via an attenuating resistor (50, 52), the first resistance value being lower than the second resistance value, and the second resistance value being lower than the third resistance value.