Design and evaluation of area-efficient and wide-range impedance analysis circuit for multichannel high-quality brain signal recording system

Abstract

To enable chronic and stable neural recording, we have been developing an implantable multichannel neural recording system with impedance analysis functions. One of the important things for high-quality neural signal recording is to maintain well interfaces between recording electrodes and tissues. We have proposed an impedance analysis circuit with a very small circuit area, which is implemented in a multichannel neural recording and stimulating system. In this paper, we focused on the design of an impedance analysis circuit configuration and the evaluation of a minimal voltage measurement unit. The proposed circuit has a very small circuit area of 0.23 mm2 designed with 0.18 µm CMOS technology and can measure interface impedances between recording electrodes and tissues in ultrawide ranges from 100 Ω to 10 MΩ. In addition, we also successfully acquired interface impedances using the proposed circuit in agarose gel experiments.