Ring Oscillator Circuits in Flexible aIGZO Technology for Biosignal Acquisition

Biosignal acquisition has escaped hospital or laboratory environments to invade daily activities. Usually, the type of biosignals to be measured determines the location of sensors: the wrist is not always the best place to measure, and a smartwatch is not always the best wearable to use. In this scenario, skin patches appear to help in the sensing of biosignals such as skin temperature (SKT), electrodermal activity (EDA), and blood volume pulse (BVP) among others. These patches should be built with flexible printed circuit boards (PCB) and, even, with flexible integrated circuits, to assure an easy adaptation to skin morphology. aIGZO (amorphous Indium Gallium Zinc Oxide) technology is a promising solution to explore new integration of analog-front-ends in biosignal acquisition and preprocessing. In this paper, different implementations of a ring oscillator (RO) as analog front-end to measure galvanic skin response (GSR) with aIGZO technology are analysed with regard to linearity, signal range, power consumption and area. The best result in terms of power consumption and range was the resistor load RO, with maximum power consumption of 0.198 mW and a frequency range of 151.13 kHz to 204.88 kHz for a voltage input range of 1.59 V to 3.3 V.