CMOS-Based Multifrequency Impedance Analyzer for Biomedical Applications

In this paper we present a monolithic microsystem, which can perform Bio-Impedance Analysis (BIA), and electro impedance tomography (EIT) measurements as well as record electrocardiogram (ECG) signals. In contrast to a full analog lockin approach, a mixed analog/digital solution is adopted. The proposed solution has been designed, implemented and tested using a commercial 0.35-μm CMOS technology. The tuning range of the signal generator and the detector is from 10kHz to 10MHz in 1kHz steps. The circuit ensures a CMRR of 81dB@10kHz, which increases to 84dB@10MHz. The measured equivalent input noise power spectral density is en=2.57nV/√Hz at 10kHz in the worst case, close to the 1/f corner frequency. It decreases until en=1.8nV/√Hz at 1MHz and en=1.9nV/√Hz at 10MHz. Measurements of a reference RC network performed with the proposed monolithic solution and compared with a Keysight E4980A Precision LCR Meter shows a maximal relative error of 0.8% over the whole operating frequency range.