CMOS-Based Multifrequency Impedance Analyzer for Biomedical Applications

In this paper, we present a monolithic microsystem, which can perform bioimpedance analysis and electroimpedance tomography measurements as well as record electrocardiogram signals. In contrast to a full analog lock-in 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 10 kHz to 10 MHz in 1 kHz steps. The circuit ensures a CMRR of 81 dB@10 kHz, which increases to 84 dB@10 MHz. The measured equivalent input noise power spectral density is en = 2.57 nV/√Hz at 10 kHz in the worst case, close to the 1/f corner frequency. It decreases until en = 1.8 nV/√Hz at 1 MHz and en = 1.9 nV/√Hz at 10 MHz. 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.