Know-How: Automotive Ethernet explained: features and test needs

Automotive electronics in today’s vehicles are increasingly complex. With more sensors, controls, and interfaces all using higher bandwidth, faster data throughput and more reliable networks are required. The weight of the cables and harnesses in the vehicle is also of concern to manufacturers.

Ethernet has already proven to be a secure transfer medium that can handle large amounts of data and reduce weight by 30% over the traditional CAN/LIN harnesses. The advantages of Ethernet – multi-point connections, higher bandwidth, and low latency – are attractive to automotive manufacturers. However, traditional Ethernet is too noisy and interference-sensitive to be used in automobiles.

Automotive Ethernet is a physical layer standard designed for use in automotive connectivity applications. IEEE standardized the technology with 802.3bw (100BASE-T1), later expanded to 802.3bp (1000BASE-T1). The transport layers are defined by AVNU and TSN Consortiums as well as Open Alliance Consortium. In the near future autonomous vehicles will require higher bandwidths, hence Automotive Ethernet is expected to grow to hundreds of Gigabit per second , e.g. 100Gb/s, 400Gb/s, etc.

The Automotive Ethernet cable is a single unshielded copper twisted pair making it low-weight and low-cost to manufacture. The single twisted pair is a fundamental difference between standard Ethernet and Automotive Ethernet. Unlike standard Ethernet, with a dedicated transmit-and-receive path, Automotive Ethernet, has a single twisted pair being used for both transmit and receive operations at the same time. This implies that both ends of the link employ a hybrid transceiver that is capable to distinguish what it is sent from what it is received. Automotive Ethernet has a shorter cable length due to the harsh environment of the vehicle. Impedance tolerances and loss are a big deal in the vehicle environment, and they are controlled very tightly. As for the connector, RJ45 is the classic, standard interface for home and office Ethernet. The connector type for Automotive Ethernet is not defined – meaning that you are free to use whatever connector you prefer. This can be an issue in form fitting standard test requirements and does require some custom cabling and fixtures.

Testing of Automotive Ethernet Devices

In automotive applications Advanced Driver Assistance Systems (ADAS) and autonomous vehicles (AV) use lots of sensors, controls and interfaces with higher bandwidth requirements. Automotive Ethernet provides a single universal medium for communication that allows different components to coexist on the same switched network. Whenever a Device Under Test (DUT) is equipped with Automotive Ethernet, PC control of the DUT requires a Media Converter that “translates” Ethernet to BASE-T1 protocol, i.e. standard Ethernet to Automotive Ethernet.