Sensors with digital or frequency output

Abstract

Most sensors are based on elements of which one of the parameters (resistivity, dielectric constant, Hall voltage, signal frequency, etc.) shows a small change in response to one or more measurands. To apply sensors is a system, an intimate knowledge of the working of the sensor element is usually necessary. The new age of sensors has come about with the development of planar silicon (and GaAs) technology, permitting the integration of sensor elements and signal conditioning circuitry on one chip. This approach might eventually lead to a family of sensors with a microprocessor-compatible output as shown in Fig. 1, which can easily be applied in bus-organized data-acquisition systems [1, 2]. An intermediate and necessary step to reach this ambitious goal is the design of sensors with a digital or frequency output. In this paper the most important techniques and structures are reviewed.