Design of integrated and autonomous conductivity–temperature–depth (CTD) sensors

Impedance characterization of interfaces is a basic technique for a large class of chemical and biological sensors. This technique is often used to model interfaces between ion-based and electron-based conductive materials by means of electric variables such as voltage, current and charge. Conductivity–temperature–depth (CTD) sensors are sophisticated devices used in the environmental monitoring field to understand the effects of climate changes on oceans and on marine organisms. They usually require impedance sensing as readout technique. High-accuracy CTD sensors are present on the market but they are bulky and power hungry. However, the downscale of modern CMOS technology allows shrinking very complex bioelectronic interfaces into millimeter square size systems, thus opening a large ground of applications. This paper will describe an IC architecture and the related design approach to implement an electrochemical impedance spectroscopy (EIS) technique for CTD sensing and will propose a general approach for sensing complex impedance with low power consumption and high precision. The presented system is designed to achieve 15-bit resolution and power consumption to ensure lifetime up to 1 year using button-size batteries in ocean environment.