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Proceedings Paper

A 16 x 16-pixel retinal-prosthesis vision chip with in-pixel digital image processing in a frequency domain by use of a pulse-frequency-modulation photosensor
Author(s): Keiichiro Kagawa; Tetsuo Furumiya; David Cheong Ng; Akihiro Uehara; Jun Ohta; Masahiro Nunoshita
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Paper Abstract

We are exploring the application of pulse-frequency-modulation (PFM) photosensor to retinal prosthesis for the blind because behavior of PFM photosensors is similar to retinal ganglion cells, from which visual data are transmitted from the retina toward the brain. We have developed retinal-prosthesis vision chips that reshape the output pulses of the PFM photosensor to biphasic current pulses suitable for electric stimulation of retinal cells. In this paper, we introduce image-processing functions to the pixel circuits. We have designed a 16x16-pixel retinal-prosthesis vision chip with several kinds of in-pixel digital image processing such as edge enhancement, edge detection, and low-pass filtering. This chip is a prototype demonstrator of the retinal prosthesis vision chip applicable to in-vitro experiments. By utilizing the feature of PFM photosensor, we propose a new scheme to implement the above image processing in a frequency domain by digital circuitry. Intensity of incident light is converted to a 1-bit data stream by a PFM photosensor, and then image processing is executed by a 1-bit image processor based on joint and annihilation of pulses. The retinal prosthesis vision chip is composed of four blocks: a pixels array block, a row-parallel stimulation current amplifiers array block, a decoder block, and a base current generators block. All blocks except PFM photosensors and stimulation current amplifiers are embodied as digital circuitry. This fact contributes to robustness against noises and fluctuation of power lines. With our vision chip, we can control photosensitivity and intensity and durations of stimulus biphasic currents, which are necessary for retinal prosthesis vision chip. The designed dynamic range is more than 100 dB. The amplitude of the stimulus current is given by a base current, which is common for all pixels, multiplied by a value in an amplitude memory of pixel. Base currents of the negative and positive pulses are common for the all pixels, and they are set in a linear manner. Otherwise, the value in the amplitude memory of the pixel is presented in an exponential manner to cover the wide range. The stimulus currents are put out column by column by scanning. The pixel size is 240um x 240um. Each pixel has a bonding pad on which stimulus electrode is to be formed. We will show the experimental results of the test chip.

Paper Details

Date Published: 7 June 2004
PDF: 8 pages
Proc. SPIE 5301, Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications V, (7 June 2004); doi: 10.1117/12.526693
Show Author Affiliations
Keiichiro Kagawa, Nara Institute of Science and Technology (Japan)
Tetsuo Furumiya, Nara Institute of Science and Technology (Japan)
David Cheong Ng, Nara Institute of Science and Technology (Japan)
Akihiro Uehara, 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. 5301:
Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications V
Nitin Sampat; Morley M. Blouke; Ricardo J. Motta, Editor(s)

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