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Proceedings Paper

System implementation of a CMOS vision chip for visual recovery
Author(s): Akihiro Uehara; David C. Ng; Tetsuo Furumiya; Keiichi Isakari; Keiichiro Kagawa; Takashi Tokuda; Jun Ohta; Masahiro Nunoshita
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Paper Abstract

We have developed a CMOS vision chip, an image sensor with pixel-level signal processing, to replace photoreceptor cells in the retina. In this paper, we describe a pixel-level signal processing, which is to control on the stimulus waveform and the amount of the electrical injection charge. Our CMOS vision chip is an array of a pixel, which consists of a photo detector, a pulse shaper, and a current stimulus circuit. The photo detector circuit generates a pulse frequency modulated (PFM) pulse, which frequency is proportional to the intensity of the incoming light. The PFM photo detector is also modified to restrict the maximum frequency of PFM pulse signal for safety neural stimulation. The PFM pulse signal should be converted into suitable waveform for efficient neural stimulation. We have employed a pulse shaper to generate one stimulus pulse from one PFM pulse. The pulse parameters (i.e., pulse duration, polarity, etc) of the output pulse signal are controlled by the external signal. For the electrical neural stimulus, the stimulus intensity is given by the amount of the electrical injection charge. The amount of the injection charge should be enough to evoke a phosphene but should be low to avoid the damage of the retinal tissue caused by the excess charge injection. In our prototyped CMOS vision chip, the stimulus current amplitude is used to control the amount of charge. The 6-bit binary-weighted digital-to-analog converter (DAC) with 2μA resolution is used to control the stimulus current amplitude.

Paper Details

Date Published: 16 May 2003
PDF: 8 pages
Proc. SPIE 5017, Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications IV, (16 May 2003); doi: 10.1117/12.476789
Show Author Affiliations
Akihiro Uehara, Nara Institute of Science and Technology (Japan)
Nidek Vision Institute (Japan)
David C. Ng, Nara Institute of Science and Technology (Japan)
Tetsuo Furumiya, Nara Institute of Science and Technology (Japan)
Keiichi Isakari, Nara Institute of Science and Technology (Japan)
Keiichiro Kagawa, Nara Institute of Science and Technology (Japan)
Takashi Tokuda, Nara Institute of Science and Technology (Japan)
Jun Ohta, Nara Institute of Science and Technology (Japan)
Masahiro Nunoshita, Nara Institute of Science and Technology (Japan)


Published in SPIE Proceedings Vol. 5017:
Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications IV
Nitin Sampat; Ricardo J. Motta; Morley M. Blouke; Nitin Sampat; Ricardo J. Motta, Editor(s)

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