A Squarewave-Based Multi-Frequency Impedance Analyzer Based on the Heterodyne Architecture

Abstract

This paper presents a custom chip in 180 nm TSMC CMOS process for fast multi-frequency impedance measurements on biological samples. It uses square waveforms for the excitation of the sample and demodulation to drastically reduce the required power consumption of the chip. Impedance inaccuracies given by the harmonics of square waves are avoided using a mixed-signal heterodyne structure with a proper selection of the excitation and demodulation frequencies. The system allows the simultaneous measurement of the impedance at two frequencies and of the DC current. The chip dissipates only 6 mW, including the delta-sigma analog-to-digital converter, and operates up to a frequency of 12 MHz.