Sensors Go Systematic （1）

Published:2011/7/28 2:10:00 Author:Amy From:SeekIC

By Helmuth Lemme

Under the increasing time and cost pressures imposed on developing instrumentation devices, building preamplifiers for sensors is increasingly coming to be seen as an irksome secondary task. They must be exactly matched to the sensor output signals, which are usually weak, and if a different type of sensor is used, the entire job has to be done all over again. A far more user-friendly approach is to employ sensors whose signals have been preconditioned to remove distortion factors (such as temperature dependence, offsets and the like) and give them a standardized output format, such as 0-1OV or -1—20 mA. This makes it easy to swap sensors.

Fitting the sensor components and measurement electronics into the same package has been common practice for a long time already. In order to further reduce costs, the present trend is increasingly heading in the direction of integrating both of these elements onto a single silicon chip. This requires finding ways to construct the actual sensor element in silicon. In many cases, this has already been successfully accomplished. For temperature sensors, it is especially easy. For pressure sensors, in which the membrane often already consists of a silicon structure bearing piezoresistive tracks, the solution is also simple. Even if such a sensor system may appear to be expensive at first glance, overall costs are reduced thanks to savings realized in development effort.

Another reason for integration is failure prevention. Human lives can depend on the reliable operation of sensors, such as in the case of ABS and ESP systems in cars. In the automotive area, a special challenge is provided by the extreme range of tempera­ture variations, which extends from below -20 CC to the engine temperature of+125 rC. As has been shown by experience, fail­ures of soldered joints are much more common than internal fail­ures of ICs. Efforts to achieve increased levels of integration are thus primarily driven by considerations of safety and security. The cost savings that arise at the same time (assuming large-scale mass production) are a welcome side effect. Another bene­fit is increased interference immunity. If sensor signals must pass through long cables before they are amplified, as was the case in the past, interference will be coupled in. With everything on the same chip, this hazard is eliminated.

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