CAN Bus Balancing Resistor Bypass for Signal Integrity
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Solution Overview
Problem
High data rate transmission in CAN bus systems leads to signal distortion and unacceptable signal attenuation due to reflections and ringing, which existing solutions like ferrite beads and negative impedance fail to adequately address at higher speeds.
Innovation Solution
Incorporating switch means with Schottky diodes or transistors in parallel with balancing resistors to provide a bypass path for signals during transmission, ensuring correct characteristic wave impedance and reducing attenuation in star-like or double star topologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ferrite beads are used to approximate wave impedance at junction points, then signal distortion is reduced at low and medium data rates, but signal attenuation becomes insurmountable at high data rates up to 5 Mbit/s
Solution Approach 1:
The invention changes the electrical parameters at the junction point by introducing a negative impedance that compensates for the positive impedance of the cable branches. This parameter adjustment allows the system to maintain proper signal levels at high data rates by actively counteracting signal attenuation rather than passively approximating wave impedance.
Solution Approach 2:
The invention transitions from a static impedance approximation approach to a dynamic compensation approach. The negative impedance device actively adjusts to counteract signal attenuation in real-time, enabling the system to handle high data rates where static ferrite bead solutions fail.
2Adaptability or versatility
If a star-shaped topology is implemented to improve cable harness layout, then signal independence from cable branch length is achieved, but signal distortion due to reflections and ringing occurs at high data rates
Solution Approach 1:
The invention introduces a negative impedance device as an intermediary element at the center of the star-shaped topology. This intermediary actively compensates for the harmful reflections and ringing caused by the star topology, allowing the flexible cable layout to be maintained while correcting the signal quality issues at high data rates.
3Loss of energy
If negative impedance is used at the center of a star-shaped network to reduce attenuation, then signal amplitude is enhanced, but device complexity increases
Solution Approach 1:
The negative impedance device is designed to automatically compensate for signal attenuation without requiring external control or complex adaptation circuits. The device self-regulates to provide the necessary impedance compensation, reducing overall system complexity while maintaining signal amplitude enhancement.
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 minimizes signal distortion and attenuation, maintaining signal integrity across all ports even with varying line lengths, and reduces peak power losses during bus arbitration, achieving robust and efficient data transmission.
Implementation Method 1
Said switch means may be adapted to provide a bypass path for signals when said CAN is active or in transmitting mode. Said switches may comprise Schottky diodes or a pair of transistors located in parallel and each connected to each line of said pair of communication lines.
Implementation Method 2
Approximation of the wave impedance is accomplished by implementing proper ferrite beads with frequency dependent attenuation at the junction points.
Implementation Method 3
DE-B-12 95 662 proposes the use of a negative impedance at the centre of a star-shaped network for reducing attenuation.
Data Source
Figure 1
Figure 2a~2b
Figure 2c
AI summary
A CAN arrangement comprising at least one CAN, said CAN having a pair of communication lines, each adapted for communication/connection with one or more further CANs, via respective lines of a common connection line pair, and including first and second balancing resistor located between each of said pair of CAN communication lines and said respective common connection lines, and further including switch means located in parallel with said balancing resistor adapted to provide a by-pass path of signals away from said resistor.