Satoru Nishino

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

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.

Wide-range and precise tissue impedance analysis circuit with ultralow current source using gate-induced drain-leakage current

This paper presents a bioelectrical impedance analysis circuit with ultralow-current source using gate-induced drain-leakage (GIDL) current for biomedical applications. The proposed circuit consists of an ultralow-current reference circuit, a minimal voltage measurement block, a precise current source block, and a digital control logic circuit. The reference circuit generates pico-ampere-order currents based on GIDL current of an n-channel MOSFET. Fabricated in a 0.18μm 1P6M standard CMOS technology, the impedance analysis circuit occupies 0.27mm2 and can measure impedance range from 100Ω to 10MΩ. Experimental results shows that the fabricated current source using GIDL current generates a quite stable ultralow-current of 50pA, 100pA and 200pA, respectively. In addition, the proposed analysis circuit successfully measures the electrode-tissue interface impedance and tissue impedance by functional verification using monolayer and inhomogeneous agarose gel test setup phantom.