A Generic Approach in the Development of Ultra-Low Power Interfaces for Sensing Microsystems (original) (raw)

Abstract

Miniaturized sensors have gained an increasing interest due to smaller sizes and reduced power consumption compared to their macroscopic counterparts. Their fabrication technologies are compatible with standard integrated circuits, allowing for the co-integration with intelligent electronics either by a System-on-Chip (SOC) or by a System-in-a-Package (SIP) approach. Microsystems obtained through co-integration can run with minute power and still present excellent performances. In this work, the design, characterization, and integration of sensing systems are assessed with a generic approach in order to obtain portable, simple, and power efficient solutions. A methodology of the instrumentation system design is proposed in order to push the maturity of the systems technology from the fundamental research to a pre-industrial stage. The proposed interfacing principle is based on the insertion of the sensor into triangular voltage oscillating circuits. The data captured by the sensor deforms the analog output of the oscillator and is extracted by mathematical methods. The methodology is applied for two applicative contexts: 1) liquid sensing, and 2) the detection of variable magnetic fields. The first system for liquid sensing consists in an interdigitated electrodes (IDE), the sensing device is investigated and modeled using finite elements tools. The interfacing approach consists in stimulating the device with a square current wave; this results in a triangular output voltage with a shape that embeds the liquid properties, i.e., both conductivity and permittivity. The second system is a detector of magnetic field variations, e.g., for abrupt variations of power line currents. The sensing element is a square planar inductor modeled similarly to the IDE. Being also based on a triangular voltage oscillating system, the interfacing method we built consists in varying the triangular signal frequency for each detected magnetic perturbation. Output characteristics are consequently defined to quantify the amount of magnetic perturbations captured by the inductor. The system has been successfully tested for the detection of arc faults on high-powered current lines. We demonstrate that integrating the interface in current CMOS technologies can lead to data acquisition in the µW regime.

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