Switched CAN Bus Resistance for Ringing and Bit Rate Limits
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Solution Overview
Problem
In bus systems, particularly those using differential voltage signals like the CAN bus, oscillations or 'ringing' occur due to line inductances and input capacitances, limiting the maximum bit rate that can be transmitted, as they increase the time needed for a reliable signal state change, thus restricting the effective usable bit rate.
Innovation Solution
An attenuating device that dynamically controls the electrical resistance between bus lines using a semiconductor switch-based circuit, switching between low, moderate, and high resistance states to attenuate oscillations, ensuring even weaker bus subscribers can generate a differential voltage for error indication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the bus lines are connected with low resistance to attenuate oscillations, then the oscillation attenuation is improved, but the current consumption increases and weak bus subscribers cannot generate sufficient voltage difference
Solution Approach 1:
The patent applies dynamics by making the resistance value time-variable rather than fixed. The attenuating device switches between different resistance states (low resistance for oscillation attenuation, high resistance for normal operation) based on the signal edge detection, allowing the system to adapt its electrical characteristics dynamically to different operational conditions.
Solution Approach 2:
The patent implements periodic action by applying the low resistance state only during specific time periods following signal edges. The control circuit detects edges and activates the attenuating circuit temporarily, then returns to high resistance state, creating a periodic pattern of low-resistance intervals that attenuates oscillations without continuously consuming excess current.
2Power
If the resistance value is increased to allow weak bus subscribers to generate voltage difference, then the voltage generation capability is improved, but the oscillation attenuation capability is reduced
Solution Approach 1:
The patent resolves this contradiction by dynamically adjusting the resistance value based on operational needs. The control circuit switches between high resistance (for voltage generation) and low resistance (for oscillation attenuation) states, allowing the system to have both capabilities at different times rather than being constrained to a single fixed resistance value.
Solution Approach 2:
The patent applies preliminary action by detecting signal edges in advance and proactively switching to low resistance state before oscillations can develop. This preemptive approach allows the system to prevent oscillation problems before they occur, then return to high resistance state to allow normal voltage generation by weak subscribers.
3Object-affected harmful factors
If a fixed low resistance connection is used to attenuate oscillations, then the oscillation attenuation is improved, but the bit rate is limited due to extended signal transition times
Solution Approach 1:
The patent uses periodic action by applying low resistance only during brief intervals following signal edges when oscillations occur, rather than maintaining it continuously. This temporary attenuation approach allows the system to suppress oscillations during critical transition periods while maintaining high bit rate capability during normal data transmission when high resistance is restored.
Solution Approach 2:
The patent resolves the speed-attenuation contradiction by making the resistance dynamic rather than fixed. The system transitions to low resistance state only when needed for oscillation attenuation during edge transitions, then returns to high resistance state for normal high-speed operation, thereby achieving both oscillation suppression and high bit rate performance.
4Object-affected harmful factors
If the resistance value is dynamically controlled, then both oscillation attenuation and voltage generation are improved, but the device complexity increases
Solution Approach 1:
The patent applies self-service by implementing an automatic control mechanism that detects signal edges and autonomously switches the resistance state without external intervention. The control circuit monitors the bus lines itself and triggers the attenuating circuit based on detected edges, allowing the system to self-regulate its resistance characteristics based on operational conditions.
Solution Approach 2:
The patent uses feedback by having the control circuit continuously monitor the differential voltage signal on the bus lines and use this information to control the switching of the attenuating circuit. The edge detection mechanism provides feedback about signal transitions, which automatically triggers the appropriate resistance state changes without requiring external control signals.
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 effectively suppresses oscillations, allowing for a higher effective bit rate by dynamically managing resistance, enabling even weaker bus subscribers to generate a voltage difference, thereby improving the CAN bus's data transmission efficiency.
Implementation Method 1
The variable resistance value is particularly advantageously generated by the on-resistance (e.g., RDSon) of at least one semiconductor switch, preferably of at least two anti-serially switched semiconductor switches. By variably controlling this at least one semiconductor switch, different resistance values can be generated particularly easily
Data Source
AI summary
An attenuating device for a bus of a controller area network bus system based on differential voltage signals. The bus has first and second bus lines, having an attenuating circuit that provides a variable electrical resistance value between the first and second bus lines and that is operable in at least three circuit states. In a first circuit state, the first and second bus lines are connected via an attenuating resistor having a first resistance value. In a second circuit state, the first and second bus lines are connected via an attenuating resistor having a second resistance value. In a third circuit state, the first and second bus lines are connected via an attenuating resistor having a third resistance value. The first resistance value is lower than the second resistance value. The second resistance value is lower than the third resistance value.