CAN Bus Driver Slew Rate Control for Ringing Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CAN bus ringing occurs during transitions from a dominant to a recessive state, causing signal corruption and communication failures, especially at higher baud rates and network sizes, due to impedance mismatching and high-frequency signal reflections.
Innovation Solution
Implementing a method that includes impedance matching using an operational transconductance amplifier (OTA) or a back-to-back connected transistor pair, coupled to the CAN bus only during and shortly after the driver transitions from a dominant to a recessive state, and controlling the CAN bus driver slew rate by successively disabling current sources or opening resistive switches to reduce high-frequency signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance matching is continuously applied to suppress CAN bus ringing, then signal reflection is reduced, but DC power loss increases due to continuous current flow
Solution Approach 1:
The patent applies periodic action by enabling impedance matching only during specific time intervals when ringing is detected or anticipated (during dominant-to-recessive transitions), rather than continuously. The circuit monitors bus conditions and activates the impedance matching network temporarily to suppress ringing, then disables it to conserve power, creating a periodic on-demand operation mode.
Solution Approach 2:
The patent implements local quality by applying impedance matching selectively at specific locations and times - only at the transceiver output stage during critical transition periods when ringing occurs, rather than globally across the entire bus system continuously. This localized application reduces power consumption while maintaining signal integrity where needed.
2Reliability
If slew rate control is applied to reduce high frequency signals, then ringing is suppressed, but communication speed is reduced
Solution Approach 1:
The patent applies dynamics by making the slew rate adjustable and time-dependent rather than fixed. The circuit dynamically changes the slew rate based on the operational phase - using higher slew rates during stable periods for fast communication, and applying controlled slew rate limiting only during transitions when ringing occurs, optimizing both speed and reliability.
Solution Approach 2:
The patent uses periodic action by applying slew rate control intermittently only during dominant-to-recessive transitions rather than continuously. The control mechanism activates slew rate limiting temporarily during critical transition windows, then releases it during stable states to maintain high communication speeds, creating a periodic modulation of the slew rate characteristic.
3Reliability
If impedance matching unit is continuously connected to CAN bus, then signal reflections are minimized, but device complexity and power consumption increase
Solution Approach 1:
The patent implements dynamics by using a switchable impedance matching unit that can transition between connected and disconnected states. The circuit includes control logic that dynamically connects the impedance matching network to the bus only when needed (during dominant-to-recessive transitions), and disconnects it during other periods, reducing both complexity and power consumption while maintaining effectiveness.
Solution Approach 2:
The patent applies the extraction principle by removing the impedance matching unit from continuous operation and extracting it as a separate, selectively activated component. The matching unit is taken out of the always-on circuitry and instead activated only during specific transition periods, reducing its impact on overall device complexity and power consumption while maintaining its beneficial effects when needed.
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 CAN bus ringing by minimizing signal reflections and maintaining communication integrity at higher data rates without altering the bus differential impedance, thus preventing driver overload and reducing DC power loss.
Implementation Method 1
matching impedance of the CAN bus with an impedance matching unit
Implementation Method 2
controlling CAN bus driver slew rate so as to reduce high frequency signals on the CAN bus
Data Source
AI summary
CAN bus drive slew rate control is used to suppress ringing using bus impedance matching that is only activated during and shortly after the bus driver unit transitions from driving the bus “dominant” to “recessive”. In one embodiment a bus impedance matching unit is a differential input and differential output operational trans-conductance amplifier (OTA). The differential OTA absorbs or provides the ringing current based on bus differential voltage. In another embodiment a bus impedance matching unit is a back-to-back connected RON regulated transistor pair together with a gate control related circuit. Where the total RON is equal to the CAN bus characteristic impedance.