Until the last few years, the primary in-vehicle communications system was the controller area network (CAN) bus, which facilitates transmission of control traffic between electronic or engine control units (ECUs) within the vehicle at maximum bus speeds up to 1 Mbps. To keep up with the significant increase in data, CAN has undergone protocol modifications to become CAN FD (Flexible Data Rate) with the maximum bit rate increased to 15 Mbps, using the same physical layer.
As requirements for data transfer become more advanced, many vehicle designs may use a combination of protocols alongside CAN such as LIN, FlexRay, SENT, and, more recently, Ethernet.
The local interconnect network or LIN bus was developed by the LIN consortium in 1999 as a lower cost alternative to the CAN bus for applications where the cost, versatility, and speed of CAN were overkill. These applications typically include communications between intelligent sensors and actuators, such as window controls, door locks, rain sensors, windshield wiper controls, and climate control, to name a few.
FlexRay came into being as cars got smarter and advanced electronic systems found their way into more automotive applications. Manufacturers found that the existing automotive serial standards, CAN and LIN, did not have the speed, reliability, or redundancy required to address X-by-wire applications, such as brake-by-wire or steer-by-wire. Today, these functions are dominated by mechanical and hydraulic systems. In the future, they will be replaced by a network of sensors and highly reliable electronics that will not only lower the cost of the automobile, but also significantly increase passenger safety due to intelligent electronic-based features, such as anticipatory braking, collision avoidance, and adaptive cruise control.
When sensor resolution is required, automotive designers are adopting single edge nibble transmission (SENT) protocol for low-cost, asynchronous, point-to-point transmission of data. While the SENT protocol was initially adopted for powertrain applications, it is a good solution for communications from a multitude of sensors at a lower cost point than CAN and LIN.
The addition of advanced driver-assistance systems (ADAS), smart safety systems, and human-to-machine subsystems that generate vast amounts of data to transport throughout a vehicle, has created a broader band data transfer requirement. Further requirements for greater software integration between vehicle subsystems are driving fundamental architectural changes; moving from simple ring networks to more complex topologies, including gateways connected to a backbone.
The next evolution is automotive Ethernet, and it stems from proven IT technology serving the need for both capacity and integration. Unlike non-automotive Ethernet, the automotive bus uses unshielded, single twisted-pair cabling designed for lower weight and cost. It uses PAM3 modulation to achieve high data rates and reliability. The first version of Ethernet for vehicle applications is known as BroadR-Reach and is being supplanted by IEEE versions known as 100BASE-T1 (P802.3bw) and 1000BASE-T1 (802.3bp).
There is no question that greater integration between subsystems is driving fundamental architectural changes that require new strategies as the industry moves from isolated systems to networked systems, including gateways connected to a backbone as shown in Figure 1. These increased speeds and associated complexity mean that automotive engineers must learn new tools and techniques and move to higher-performance test instrumentation. Additionally, it is vital for test and measurement suppliers to reduce the inherent complexity involved and shorten time to insight.
Automotive engineers often need to validate operation of a design on the bench, bringing up a design and characterizing it to make sure it is within specification. For this type of application, oscilloscopes are the go-to instrument. Automated amplitude and time measurements offer a quick way to check signal quality. With the advent of more complex systems, more advanced analysis tools are required such as eye diagrams, jitter profiles, and histograms to help with debug and troubleshooting.
For compliance testing, automated tests and procedures help ensure that designs adhere to standards. In many cases, automation means that engineers do not have to be experts in a particular standard to perform compliance tests.