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Recently, a novel recording system is strongly required for agile and precise recording of biosignals in various fields, such as medicine, neuroscience, BMI (brain machine interface), and so on. To enable such various biosignal recording, we have proposed an agile biosignal recording system with a newly designed analog front-end LSI chip having amplification, filtering, and A/D conversion functions. In this paper, we designed and evaluated a neural signal recording circuit and a portable front-end motherboard. The neural signal recording circuit chip and discrete ICs were mounted on the motherboard. We confirmed that our functional LNA (low noise amplifier) had variable gains and cutoff frequencies appropriate for various biosignals, and also confirmed that biosignal recording board system successfully measured a human electrocardiogram. C⃝ 2017 Wiley Periodicals, Inc. Electron Comm Jpn, 101(1): 47-54, 2018; Published online in Wiley Online Library (wileyonlinelibrary.com).

A Si neural probe is one of the most important tools for neuroscience because it can record neuronal activities in a brain densely. However, it would damage the brain during insertion. Therefore, it is necessary for the Si neural probe to reduce invasiveness to the brain. In this study, we proposed the lower invasive Si neural probe having both triangular shank and sharpened tip fabricated using Si anisotropic etching technique. From in vivo mouse brain insertion experiments, it was clearly indicated that the proposed Si neural probe had insertion force of 15 % compared to a Si probe with normal tip. The lower invasive Si neural prove becomes a versatile tool of neurophysiology and neuroscience.

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.