Adjustable-Impedance CAN Transmitter for Reflection Suppression
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Solution Overview
Problem
Current CAN bus networks face limitations in data rate due to signal reflections and ringing, especially with the introduction of higher data rates like those in CAN FD, which can corrupt communication and require costly topology redesigns to maintain signal integrity.
Innovation Solution
A transceiver circuit with dynamically adjustable impedance and voltage properties, using an impedance bridge with controllable push and pull resistors, is implemented to suppress signal reflections and ringing, allowing for higher data rates without topology changes.
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 reflections and ringing increase causing communication corruption
Solution Approach 1:
The patent applies dynamics by making the transmitter impedance adjustable rather than fixed. The impedance can be dynamically changed between a first value (matched to termination resistance) and a second value (mismatched), allowing the system to adapt to different operating conditions and suppress reflections at higher data rates while maintaining compatibility with standard termination configurations
Solution Approach 2:
The patent changes the impedance parameter of the transmitter to resolve the contradiction. By varying the impedance between matched and mismatched states, the system can suppress signal reflections and ringing that occur at higher data rates, thereby maintaining signal integrity while enabling faster transmission speeds
2Reliability
If termination resistance is adjusted to suppress reflections, then signal integrity is improved, but device complexity increases
Solution Approach 1:
Rather than physically adjusting termination resistance, the patent changes the transmitter impedance parameter electronically. This is achieved through a circuit configuration with adjustable resistors that can switch between different impedance states, providing the needed reflection suppression without requiring complex physical adjustments to the termination network
Solution Approach 2:
The patent replaces what would traditionally require mechanical or physical adjustments to the termination network with an electronic impedance control mechanism. The transmitter circuit uses electronically controllable resistors to adjust impedance, substituting a simple electronic control system for what would otherwise require complex physical reconfiguration of the termination resistance
3Ease of operation
If impedance is fixed to match termination resistance, then ease of operation is improved, but ability to suppress reflections at high data rates deteriorates
Solution Approach 1:
The patent makes the impedance dynamic rather than fixed. The transmitter can operate with a simple fixed impedance configuration for ease of deployment, but when needed, the impedance can be dynamically adjusted to suppress reflections. This maintains ease of operation while adding the capability to handle high data rate scenarios
Solution Approach 2:
The transmitter circuit is designed to perform multiple functions: it can operate with standard fixed impedance for normal operations, and switch to adjustable impedance modes when reflection suppression is needed. This multi-functionality allows the same device to maintain ease of operation while also providing advanced reflection suppression capabilities when required
Data Source
AI summary
The present application relates to a circuit and a transceiver comprising the circuit. The circuit comprises two bus line terminals for coupling to a bus and a bridge circuit comprising two legs. Each leg comprises an adjustable pull resistance and an adjustable push resistance connected in series with a respective one of the two bus line terminals. The adjustable pull resistances and the adjustable push resistances 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 and the adjustable push resistances in response to the detected transition.