Ringing Suppression Circuit for CAN Bus Impedance Control
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Solution Overview
Problem
Current CAN bus networks face issues with ringing, which reduces maximum data rate due to reflections and impedance variations, especially with the advancement of protocols like CAN FD, making it challenging to maintain data integrity at higher speeds without costly network topology redesigns.
Innovation Solution
A ringing suppression circuit that lowers the impedance of the CAN bus by outputting a drive signal in response to dominant to recessive transitions, using a controller and transmitter to manage the impedance transition rates and phases, thereby mitigating reflections and maintaining data integrity at higher data rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the data rate is increased to support CAN FD protocol, then the productivity and communication speed are improved, but ringing and reflections occur on the bus which compromises signal integrity
Solution Approach 1:
The circuit applies preliminary anti-action by proactively lowering the impedance at the transmitting node before and during dominant bit transmission. This preemptive impedance reduction counteracts the reflections that would otherwise occur at impedance discontinuities, particularly at nodes far from termination resistors. The circuit monitors the bus state and applies counteracting drive signals to suppress ringing before it degrades signal integrity, enabling high-speed CAN FD operation without compromising reliability.
Solution Approach 2:
The circuit dynamically changes the impedance parameter of the transmitting node by controlling the output drive strength. When a dominant bit is detected, the circuit adjusts the impedance to a lower value to match the transmission line characteristics, thereby reducing reflections. This parameter adjustment is achieved through controlled drive signals that modify the effective output impedance of the transceiver, allowing the system to maintain signal integrity at higher data rates.
2Stability of the object's composition
If traditional termination with 120Ω resistors is used, then the impedance matching is improved, but nodes far from terminations cause reflections and ringing that limit maximum data rate
Solution Approach 1:
The circuit applies local quality by creating a localized impedance adjustment at the transmitting node, rather than requiring uniform impedance matching throughout the entire bus. The circuit modifies the electrical characteristics only at the specific node where transmission occurs, using controlled drive signals to lower the local impedance. This localized approach allows nodes at any position on the bus to maintain proper impedance matching during transmission, eliminating the limitation imposed by distance from termination resistors and enabling higher data rates.
3Reliability
If the bus cable length is limited to prevent ringing, then the reliability is improved, but the adaptability and network flexibility are reduced
Solution Approach 1:
The circuit applies preliminary action by proactively adjusting the impedance at the transmitting node before signal reflections can propagate and cause ringing. The circuit monitors bus conditions and applies corrective drive signals in advance, allowing the network to support longer cable lengths and greater topological flexibility without sacrificing data integrity. This preliminary intervention eliminates the need to constrain cable length to prevent ringing, thereby enhancing network adaptability.
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 ringing, allowing CAN bus networks to operate at higher data rates without significant network redesigns, ensuring data integrity and reducing the risk of glitches, while being compatible with existing topologies.
Implementation Method 1
lower an impedance of the bus... output a first drive signal to drive the bus to a low impedance state
Implementation Method 2
The transmitter may be coupled to the bus in anti-phase to the coupling of a transmitter of the bus transceiver to the bus... drive the bus in an opposite polarity
Data Source
AI summary
A circuit is provide comprising a first input coupled to a transmit data input of a bus transceiver; and a first output coupled to a bus. The circuit is configured to be coupled in parallel with the bus transceiver. The circuit is further configured to, in response to a dominant to recessive transition on the transmit data input, lower an impedance of the bus.