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

Abstract

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)mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> prototype is fabricated in a 130nm CMOS process. It consumes 10μA from a 1.2V supply.