Sensor module design improves automotive electrical integration, functionality (Part 1)

June 30, 2011 // By Torsten Herz, ZMDI
In order to improve fuel efficiency and reduce CO2 emissions, designers rely on an increasing number of sensors throughout the car. Reliability and space requirements call for higher integration and more intelligence in the sensors. The article describes how sensor modules drive integration and functionality in vehicle environments.

Thanks to state-of-the-art sensor-based control systems that provide precise real-time monitoring, automotive engines operate more efficiently and with lower environmental impact. One result of this improved performance is that the number of sensor applications in vehicles has realized double-digit growth over the past several years. The other result is a growing trend to add more sensor modules to vehicles. Such modules must be reliable and robust and operate with long-term stability and high precision under harsh physical, chemical, and electrical stress conditions.

Additionally, a set of built-in-diagnostic functions is required for automotive sensor modules to support the “maintenance-on-demand” policy of automotive OEMs as well as special failure-mode-operations required for safety-critical sensor applications like brake pressure sensing.

The chemical (i.e. media/humidity/corrosion resistance) and physical (shock; vibrations) robustness of sensor modules is mainly determined by the materials used, and the assembly and connection technologies. The electrical robustness (i.e. EMC) is determined by the application circuit, the chosen electric components (ICs, discrete parts), and the layout of the electrical connections, according to the application circuit.

This series will describe the latter aspect of the design of an automotive sensor module. The module incorporates a sensor signal conditioner ( ZSC31150) to enable the design of highly accurate sensor modules operating at temperatures of -40 to +150C and providing EMC performance and a set of on-chip-protection and diagnostic features addressing safety-critical applications at SIL2-level. By clever electrical design of the sensor module considering all EMC-related parameters (i.e. parasitic capacitances and inductances), high electrical robustness and built-in-diagnostic functionality can be achieved at optimized module cost, together with very high accuracy of the measured signal.

Because the mechanical design and the interconnection between a sensor system and the processing unit have a major influence on their electromagnetic behavior, it is essential to separate “embedded sensing functions” and “stand-alone-sensor modules”.

In case of embedded sensing functions (ESF) the sensor electronics are placed closed to the processing unit—in

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