With the development of automotive electronic systems, the demand for low-cost, high-reliability sensor systems has become increasingly important. Although many challenges need to be overcome to meet these needs, advances in interconnect architectures and mixed signal processes have greatly enhanced intelligence, reduced costs, and improved reliability. Moreover, more advanced technologies are also coming out.
At present, most sensor systems are based on an architecture, that is, an analog signal chain from the sensor to the system's main electronic control unit (ECU). In extremely noisy automotive environments, maintaining the signal integrity of these systems is a challenge.
One solution is to use simple special techniques (such as pulse width modulation (PWM) or variable pulse width) to transmit signals digitally on different physical layers. However, these methods have several disadvantages. In general, each signal requires a separate line, and the information is usually output unidirectionally from the sensor to the main ECU. Therefore, it is impossible to use this sensor subsystem for two-way communication and diagnosis.
Another solution is to use the CAN bus to pass the signal back to the main ECU. However, this method usually requires a microcontroller and supporting circuits, which will add considerable cost.
Figure 1: LIN-based sensor system architecture.
There are currently two technological trends driving the development of automotive sensor systems: regional interconnect network (LIN) protocols and advances in mixed-signal semiconductor process technology.
Although LIN initially aimed at body electronic components, it has been creatively applied to new areas, such as sensor interfaces. Several characteristics of LIN make it suitable as the physical layer and protocol of the sensor subsystem. This is a low-cost, bidirectional single-wire physical layer implementation method, reducing the need for signal lines and their harnesses. If the module contains more than one sensor, it can highlight the advantages of this method, and all outputs can be realized on a single LIN bus through multiplexing.
LIN-based sensor system architecture
The LIN protocol is based on a master-slave architecture. In this architecture, all bus communication is controlled and scheduled by the master node. This feature provides a guaranteed delay time for signal transmission and makes the system predictable, which is absolutely necessary for most sensor signals. The LIN bus architecture can be extended to 16 nodes and does not require an arbitration mechanism because all bus communications are scheduled by the master node.
The slave nodes are self-synchronizing and can use on-chip RC oscillators instead of crystal oscillators or ceramic resonators, thus greatly reducing costs at the system level. The protocol is very simple and has been standardized, suitable for asynchronous serial interface (UART / SCI). In addition, the cost of silicon implementation is quite low, even with the mixed signal process commonly used in sensor signal interface ICs. Through standardization, the LIN-based sensor subsystem can reduce costs and improve reliability.
The continuous development of mixed-signal semiconductor processes has made integration more and more important, especially in terms of digital integration and analog precision. There are currently several processes suitable for automotive sensor applications, such as linear BiCMOS, high-voltage CMOS, and silicon-on-insulator (SOI). Each process has its advantages and disadvantages, which should be selected according to the sensor type and application requirements.
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