Showing papers by "Takashi Tokuda published in 2003"
TL;DR: Experimental results showed that the newly designed pulse frequency modulation photosensor was sensitive over a dynamic range of input light of about 120 dB, and that photosensitivity could be varied from 0 dB to around -40 dB.
Abstract: A newly designed pulse frequency modulation photosensor for use in retinal prosthesis is proposed and demonstrated. The pixel converts the intensity of incident light into biphasic current pulses at frequencies suitable for the electrical stimulation of retinal neurons. Experimental results showed that the device was sensitive over a dynamic range of input light of about 120 dB, and that photosensitivity could be varied from 0 dB to around -40 dB.
40 citations
TL;DR: In this article, an arc plasma gun was used as a novel C source for the first time, which was confirmed to consist mainly of 12 C and to include very few microparticles.
25 citations
TL;DR: In this paper, the authors fabricated SiGe/Si free-standing micro-objects on a silicon-on-insulator (SOI) substrate using the SiO2 sacrificial layer.
Abstract: We fabricated SiGe/Si free-standing micro-objects on a silicon-on-insulator (SOI) substrate using the SiO2 sacrificial layer SiGe/Si strained films were grown by molecular beam epitaxy on SOI substrates The films were released from the substrate by selective etching of the SiO2 layer The released films rolled up due to the elastic strain in the SiGe layer Microtubes and microspirals with a diameter of about 40 μm were obtained
19 citations
TL;DR: In this article, an intra-ocular epi-retinal prosthesis device using a back-illuminated photosensor is proposed and demonstrated for the first time, based on a pulse frequency modulation, is fabricated on a transparent sapphire substrate.
Abstract: An intra-ocular epi-retinal prosthesis device using a back-illuminated photosensor is proposed and demonstrated for the first time. The photosensor, based on a pulse frequency modulation, is fabricated on a transparent sapphire substrate to detect the backside incident light. Experimental results show that the device is sensitive over a dynamic range of incident light of 30 dB.
17 citations
TL;DR: In this article, the effect of bending on the pulse-frequency-modulation (PFM)-based photosensor was studied. And the maximum frequency variation to bending is about +4% when extrapolated to the curvature of the human eye.
Abstract: In this work, we study the effect of bending on the pulse-frequency-modulation (PFM)-based photosensor. Based on the results of our study of strain on metal oxide semiconductor field-effect transistor (MOSFET) devices, we explain the behavior of the photosensor under compressive and tensile bending. We found that the maximum frequency variation to bending is about +4% when extrapolated to the curvature of the human eye. From this study we hope to minimize or eliminate the effect of bending on LSI circuits. Although this study specifically deals with the PFM photosensor circuit, any other LSI circuit subjected to strain can be treated similarly.
16 citations
TL;DR: In this article, the effect of lower growth temperature Ts on C incorporation to substitutional sites in Ge 1−x C x / Si (0 0 1) grown by molecular beam epitaxy was investigated.
Abstract: Effect of lower growth temperature Ts on C incorporation to substitutional sites in Ge 1−x C x / Si (0 0 1) grown by molecular beam epitaxy was investigated To enhance the non-equilibrium growth condition, the temperature Ts was lowered from 600°C down to 300°C The C incorporation into substitutional sites of GeC epilayers was very sensitive to Ts X-ray diffraction (XRD) measurement indicated that the substitutional C composition x increased with decrease in Ts from 600°C to 400°C At Ts⩽350°C, the estimation of x by the XRD analysis was impossible because of polycrystallization The Raman shift measurement enables to estimate x for Ts⩽350°C, as consequently larger x than that grown at Ts=400°C was verified The enhancement of non-equilibrium growth condition by decreasing Ts was important to increase x
9 citations
Journal Article•
1 citations
TL;DR: A pixel-level signal processing, which is to control on the stimulus waveform and the amount of the electrical injection charge, to replace photoreceptor cells in the retina is described.
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.
22 Oct 2003
TL;DR: In this paper, a 32/spl times/32-pixel PFM photosensor array chip is fabricated using 0.6 /spl mu/m CMOS technology and demonstrated the improved functions.
Abstract: This paper describes improvements in output waveform of pulse frequency modulation (PFM) photosensor to be effectively adapted for retinal prosthesis. A 32/spl times/32-pixel PFM photosensor array chip is fabricated using 0.6 /spl mu/m CMOS technology and demonstrated the improved functions. Also the output pulse pattern is displayed with 32/spl times/32-LED array to visualize the pulse output waveform. The next version of a PFM vision chip is designing for in vivo experiment, in which in-pixel image processing functions in pulse domain are employed.
20 Oct 2003
TL;DR: A CMOS intra-ocular retinal prosthesis device with continuous voltage monitoring of the stimulus electrodes with circuit characteristics discussed and an example of a device packaging for in-vitro experiments is reported.
Abstract: In this paper, we propose and demonstrate a CMOS intra-ocular retinal prosthesis device with continuous voltage monitoring of the stimulus electrodes. The retinal prosthesis device has 16 /spl times/ 16 current stimulus driver circuits and a 3 channel 16/spl times/16 switch matrix to monitor the voltages of the stimulus electrodes. In this paper, we discuss the circuit characteristics. We also report an example of a device packaging for in-vitro experiments.