A 10μA on-chip electrochemical impedance spectroscopy system for wearables/implantables

This work proposes a new time-domain integration method to realize Electrochemical Impedance Spectroscopy (EIS). Unlike traditional EIS systems which use a quadrature sinusoid stimulus, we propose a low-frequency, low-amplitude sinusoid stimulus, which is realized through a sinusoid DAC without the need for analog filter. The error caused by harmonic generation can be suppressed through integration in detection. The response current is sensed by a switched capacitor integrator with control synchronized with sinusoid DAC. The integration output is sampled and digitized by an 8-bit SAR ADC. The (1×1.1)mm² prototype is fabricated in a 130nm CMOS process. It consumes 10μA from a 1.2V supply.

I. Introduction

There is an increasing demand for biofilm monitoring for wearables and implantables. Electrochemical Impedance Spectroscopy (EIS) is a popular method of quantitative and qualitative monitoring of biofilm. [1]. The electrical property of an EIS sensor interface can be modeled as a complex impedance shown in Fig. 1(a). When biofilm forms on a sensor, the complex impedance is modified [2]. A small amplitude and variable frequency sinusoid is applied between sensor electrodes. By comparing the amplitude and phase difference between the input signal and its response current, the impedance, thus biofilm formation information is acquired [3].