A High Resolution Interface for Kelvin Impedance Sensing

Impedance sensing, together with impedance spectroscopy is a powerful tool detecting charge and mass transfer phenomena at complex interfaces between materials. It is widely used in electrochemical interfaces characterization and biosensing techniques. Recently, it has been proposed as a reliable readout technique to probe biomolecular interactions on modified electrodes in enzyme biosensors, DNA biosensors and immunosensors. Unfortunately, the requirements of impedance characterization accuracy, precision and dynamic range demanded by some specific application is usually accomplished by using cumbersome laboratory instrumentation. In this paper we present a fully integrated standalone, high precision, low power, 4-core impedance sensing interface to be implemented in the fast-growing application field of the ubiquitous sensing. The interface is based on a fully digital approach based on a ΔΣ demodulation that is able to achieve 15 bit of resolution, 150 ppm of temperature accuracy and dynamic ranges varying from 86 dB to 95 dB according to the impedance configuration. The 4-core chip has been implemented in 0.35 μm CMOS technology and occupies an area of 9 mm ².