A Fast Square Wave-based Electrochemical Impedance Spectroscopy for Impedance-based Biomedical Applications

This paper introduces a fast, high-accuracy methodology for conducting Electrochemical Impedance Spectroscopy (EIS) based on Fast Fourier Transform (FFT), in order to meet the requirements of portable, real-time biomedical impedance-based detections. Instead of using white noise-like wideband signals as in conventional FFT-based EIS, the proposed method uses a square wave as the sensor excitation signal. This approach achieves a fast EIS measurement, but no longer requires complex circuits like high-resolution DACs or frequency mixers for the signal generation. The conditions where the sensor behaves like a pseudo electronic Linear Time-Invariance (LTI) circuit are firstly identified by investigating its large-signal behavior, Cyclic Voltammetry (CV), which ensures the sensor shows no potential-amplitude dependence, hence also providing possibilities for other novel EIS circuitry. A circuit consisting of a control amplifier and a Trans-Impedance Amplifier (TIA) is designed and fabricated with 65 nm CMOS to implement this methodology for validating its on-chip feasibility. This work shortens the EIS measurement time by 91.7% in a frequency sweep range from 0.5 Hz to 500 Hz, with only 1.48% average Mean Absolute Percentage Error (MAPE), compared to a commercial chemical instrument AutoLab, which ensures this method is suitable for portable, real-time EIS biomedical detections and applications.