Ringing Suppression in a Controller Area Network With Flexible Data Rate Using Frequency-Selective Impedance Matching and Temporal Impedance Switching

An inherent impedance mismatch in a controller area network with flexible data rate (CAN-FD) network gives rise to signal distortion called ringing. Ringing is one of the main causes of communication errors and performance degradation. In this paper, a ringing suppression system is proposed, which alleviates the impedance mismatch at two mismatch locations: the unterminated CAN nodes and the divergence points of bus lines. At the unterminated CAN nodes, a temporal impedance switching circuit, including a matching resistor and a limiting diode, is added. The circuit is controlled to only engage right after a dominant-to-recessive transition when ringing likely occurs. At the divergence points, a frequency-selective impedance matching circuit is inserted. The circuit consists of a resistor, a capacitor, and an inductor connected in parallel, which is also designed to activate only during state transitions with the dependency of their impedance on frequency. Thus, the side effects on CAN-FD operations can be prevented. The performance of the ringing suppression system is verified by experiments. The experimental results demonstrate that the proposed system reduces ringing to a level lower than the input threshold for recessive bit detection in diverse bus configurations and supports more reliable CAN-FD communication.