Design of an LSI Chip for a Bio-machine Interface in 0.18 µm CMOS Technology


Akiyoshi Shimada, Masaya Yamaguchi*, Nobuhiko Nakano*, and Keiichi Torimitsu
Materials Science Laboratory, *Keio University

 Brain-machine interfaces that link the brain and the external world have been developed in the neuroscience and medical fields. Most of these interfaces are designed for one-way communication; however we have developed an interface that makes two-way communication possible through a microelectrode array (MEA)[1]. The electrical stimulation of the brain and neural activity measurement are important in relation to this communication, as is the interpretation of information in the brain. Furthermore, an unwired and miniaturized device is desirable in terms of reducing the stress induced when the device is worn on the body. In this study, we have developed 16-ch preamplifiers with multi-channel stimulation circuits on a 2.5 mm × 1.4 mm LSI chip using a 0.18 µm CMOS process [2].
 Figure 1 shows the three main components of this LSI chip: a stimulation block, a measurement block and a mode change block. The stimulation block can produce a 16 ch 4-bit parallel arbitrary waveform by combining 10 µs-wide pluses for electrical stimulation. The measurement block has 16 ch pre-amplifiers, and a multiplexer to combine 16 ch neural signals into one signal at a sampling rate of 40 kS/s. The mode change block switches between the stimulation and measurement blocks when it receives a control signal generated by the stimulation block. Figure 2 shows the neural activity of dissociated rat cortical neurons on the MEA with and without stimulation. A few tens of milliseconds after applying three stimulation pulses to one electrode, neural activity was observed with a different electrode.
 We will unwire the input and output between this LSI chip and the external unit to improve the portability of the device as a brain-machine interface.

[1] A. Shimada et al., SFN 2008, Washington, D.C. U.S.A. (Nov. 2008).
[2] M. Yamaguchi et al., Jpn. J. Appl. Phys. Accepted.

Fig. 1. Circuit diagram of LSI chip designed as
brain-machine interface.
Fig. 2. Neural activity evoked by 3 stimulation

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