Characterization and verification of Gigabit ethernet-based bus systems in vehicles

In this article, the complete analog front-end (AFE) of the high-speed Ethernet transmission systems (100BASE-T1 and 1000BASE-T1) are characterized. These bus systems consist of transceiver chip, low pass filter (LPF), common mode choke (CMC), DC block capacitor, common mode termination (CMT) and the transmission channel (unshielded-or shielded twisted pair, UTP/STP). The high-frequency models of the mentioned components are essential for design and simulation of high-speed bus systems. For this purpose, new simulation models are proposed in this article. In order to measure the appropriate CMC for 100BASE-T1 FR4 substrate was used as test-fixture. Due to the frequency range of 1000BASE-T1, high-frequency substrate, i.e. RO4350B was selected. The common-mode (CM) and differential-mode (DM) impedance of the choke are measured. Furthermore, to describe the general characteristics of the choke, the measurements of mixed mode S-parameters are made. The LPFs are fabricated using mentioned substrates. The filter attenuation is measured considering the signal frequency. In the next step, the impedance and mixed-mode S parameters of CMC and LPF were simulated using the suggested equivalent circuit models. The agreement between measurement and simulation results confirmed the validity of the proposed models. On this basis, the suggested models could be adapted and used for further research in the field of Multi-Gig data transmission. As the last step, a comparison between UTP and STP cable based on laboratory-level measurements is performed in two steps. First, the mixed-mode S-parameters of the mentioned cables are determined. Second, the shielding attenuation is examined according to the wire injection method. From the author's' point of view, this paper is the first detailed investigation of the analog front-end of the automotive Ethernet communication system.