Owing to productivity and cost concerns, actual CAN networks may be configured as joint-connector-based bus structures in usual automotive applications, which suffer from signal distortion caused by a transient voltage intensified by the larger impedance mismatch of a star-like topology. In this study, we propose a passive filter that alleviates signal distortion in a joint-connector-based CAN bus and supports a star-like topology in a high-speed CAN bus. In addition, the proposed filter enables lengthening of the stubs in the given propagation time owing to fast stabilization of the signals. The design objective of the proposed passive filter is to reduce the transient voltage and to relieve the impedance mismatch. To reduce the transient voltage, the driving current is reduced by inserting a resistor in series into each stub pair. To relieve the impedance mismatch in the transient region, the impedance of each stub pair is increased by adding a bead in series. Consequently, a passive filter consisting of a resistor and bead in series is proposed. A 5.6 Ω resistor and a bead with an impedance of 35 Ω, at 100 MHz were used for the performance test. The tested bus wire set included a main bus 7 m long and a joint connector with six stubs. All the stubs have the same length in each test, and two length conditions were tested. The settling time was reduced by approximately 60% using the proposed filter. The signal level at the dominant state was reduced by 10% to 1.87 V, which is allowable considering the typical margin between the input and the output levels. The settling time for the stubs 2 m long with the proposed filter is shorter than the settling time for the stubs 1 m long without the filter. The proposed filter has the effect of improving the reliability of communication in the same wiring dimension or, equivalently, lengthening the stubs with the same reliability. The increase in the length of stubs may allow shortening of the main bus, thereby facilitating more effective wiring designs.
Passive filter design supporting a starlike joint-connector-based topology in high-speed controller area networks
2013
11 Seiten, 8 Bilder, 18 Quellen
Article (Journal)
English
Automotive engineering | 2013
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