Advanced techniques for directly interfacing resistive sensors to digital systems

Abstract

This chapter reviews advanced techniques for the direct connection of resistive sensors to digital systems without using any analogue circuit, such as an amplifier or an analogue-to-digital converter, in the signal path. The sensor electronic interfaces proposed herein rely on the following operating principle: the digital system measures through an embedded digital timer the charging/ discharging time of an RC circuit formed by the resistive sensor and a known capacitor. The chapter first explains how resistive sensors with a single, differential or bridge topology can be directly measured using a low-cost microcontroller. The uncertainty sources involved in the measurement (such as the mismatch of the internal resistances, quantisation and trigger noise) and the performance in some applications are reported. Next, the chapter deals with the direct connection of resistive sensor arrays to field-programmable gate arrays, where different resistances of the array are measured in parallel through a set of timers running simultaneously. The new uncertainty sources (mainly, crosstalk) and the applications are also reported. Although the proposed sensor interfaces are quite simple in terms of operating principle, their linearity and resolution are quite remarkable provided that the design rules indicated along this chapter are followed.