Dr. Akihiro Uehara Profile

Dr. Akihiro Uehara

at NIDEK Co Ltd

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Author

Publications (5)

Proceedings Article | 7 March 2006 Paper

Flexible and extensible retinal prosthesis based on multi-chip architecture

Akihiro Uehara, Yasuo Terasawa, Takashi Tokuda, Keiichiro Kagawa, Masahiro Nunoshita, Jun Ohta

Proceedings Volume 6138, 61380R (2006) https://doi.org/10.1117/12.646202

KEYWORDS: Electrodes, Analog electronics, Packaging, Epoxies, Circuit switching, Switches, CMOS technology, Iridium, Silicon, Digital electronics

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Proceedings Article | 7 June 2004 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

Keiichiro Kagawa, Tetsuo Furumiya, David Ng, Akihiro Uehara, Jun Ohta, Masahiro Nunoshita

Proceedings Volume 5301, (2004) https://doi.org/10.1117/12.526693

KEYWORDS: Digital image processing, Digital electronics, Image processing, Digital electronic circuits, Amplifiers, Sensors, Cameras, Imaging systems, Digital photography, Electronic imaging

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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.

Proceedings Article | 19 November 2003 Paper

Pulse-frequency-modulation vision chip with frequency range control as a retinal prosthesis device

Tetsuo Furumiya, Akihiro Uehara, Keiichi Isakari, Norikatsu Yoshida, Keiichiro Kagawa, Jun Ohta, Masahiro Nunoshita

Proceedings Volume 4829, (2003) https://doi.org/10.1117/12.527528

KEYWORDS: Retina, Transistors, Control systems, Frequency modulation, Visualization, Modulation, Power supplies, Photodiodes, Filtering (signal processing), Optical fabrication

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Proceedings Article | 16 May 2003 Paper

System implementation of a CMOS vision chip for visual recovery

Akihiro Uehara, David Ng, Tetsuo Furumiya, Keiichi Isakari, Keiichiro Kagawa, Takashi Tokuda, Jun Ohta, Masahiro Nunoshita

Proceedings Volume 5017, (2003) https://doi.org/10.1117/12.476789

KEYWORDS: Sensors, Retina, Signal processing, Neurons, Visualization, Prototyping, Capacitors, Tissues, Electrodes, Signal detection

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Proceedings Article | 24 May 2000 Paper

Pulsed vision chip with inhibitory interconnections

Jun Ohta, Akihiro Uehara, Takashi Tokuda, Masahiro Nunoshita

Proceedings Volume 4089, (2000) https://doi.org/10.1117/12.386868

KEYWORDS: Image processing, Photodiodes, Analog electronics, Modulation, Frequency modulation, Logic, Transistors, Power supplies, Digital electronics, Very large scale integration

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