Jun Deguchi

Three-Dimensionally Stacked Analog Retinal Prosthesis Chip

As blind patients with an intact optic nerve and damaged photoreceptor cells increase in number in recent years, there has been a growing interest in visual prostheses by electrically stimulating their retinas. Previous clinical studies indicated that blind patients perceive a controlled electrical current applied to a small area of the retina via electrodes as a spot of light. We propose a novel implantable device, so-called three-dimensionally (3D) stacked retinal prosthesis, which is composed of a photodetector, an image processor, electrical current generator circuits, and an electrode array on one chip. The spice simulation showed that our designed analog circuits for 3D stacked retinal prosthesis chip could output desirable electrical current with variable pulse width by controlling bias voltages.

Development of a High Speed Vision System for Mobile Robots

In order to achieve human-like quick eye movements and image processing for intelligent mobile robots, a high speed vision system is developed. The vision system is composed of a binocular camera head and high speed image sensors. The camera head is originally designed to mount neuromorphic vision chips fabricated using three-dimensional integration technology. The prototype of the neuromorphic vision chip has three layers: (1) photoreceptor layer, (2) horizontal and bipolar cell layer, and (3) ganglion cell layer. An image sensor is separately developed, which corresponds to the photoreceptor layer of the layered vision chip. The image sensors are tentatively mounted on the camera head, since the resolution of the prototype of the layered vision chip is not sufficient at this stage. The camera head has an azimuth DOF for each eye and a common elevation DOF. The weight of the camera head is strictly limited, since it is mounted on a mobile robot. In order to satisfy both demands for the quick movements and light weight, the camera head is designed based upon a simple parallel mechanism. The total performance of the vision system is examined in this work. Saccadic eye movement and frequency response are experimentally reviewed

Evaluation of Electrical Stimulus Current Applied to Retina Cells for Retinal Prosthesis

We have proposed a novel multilayer stacked retinal prosthesis chip based on three-dimensional integration technology. Implantable stimulus electrode arrays in polyimide flexible cables were fabricated for the electrical stimulation of the retina. To evaluate optimal retinal stimulus current, electrically evoked potential (EEP) was recorded in animal experiments using Japanese white rabbits. The EEP waveform was compared with visually evoked potential (VEP) waveform. The amplitude of the recorded EEP increased with stimulus current. The EEP waveform shows a similar behavior to the VEP waveform, indicating that the electrical stimulation of the retina can be exploited for the blind to perceive incident light to the retina.

Quantitative Derivation and Evaluation of Wire Length Distribution in Three-Dimensional Integrated Circuits Using Simulated Quenching

Three-dimensional (3D) integration is the most promising technology to improve IC performance by stacking some active device layers and connecting them using vertical interconnections. In this paper, in order to quantitatively evaluate the benefits of 3D IC, wire length distributions in 3D ICs are derived by adapting the simulated quenching algorithm for 3D placement and routing of specific benchmark circuits. By evaluating the wire length distribution, we can confirm that the total wire length is reduced by 26.0 and 41.3% with three and five active layers, respectively. Similarly, 38.1 and 52.0% reduction in the longest wire length with three and five active layers can be achieved.

Low-Power and High-Sensitivity Magnetoresistive Random Access Memory Sensing Scheme with Body-Biased Preamplifier

In this paper, we describe a new magnetoresistive random access memory (MRAM) sensing scheme with a body-biased preamplifier for low-power and high-sensitivity operation. The proposed new MRAM sense amplifier consists of a current sense preamplifier with a body biasing differential pair of a common-gate amplifier and a voltage sense amplifier. The preamplifier controls bitline voltage appropriately and amplifies the difference in bitline current as current-mode sense amplifier. The new sense amplifier enhances sensitivity, and the body-biased preamplifier enables low-voltage operation. To evaluate the proposed circuit, the modeling of magnetic tunnel junction (MTJ) resistance characteristics was performed with a VHDL-AMS description, and the proposed circuit was simulated with a mixed signal circuit simulator. From the simulation result, it is confirmed that the proposed sensing scheme results in a 1.57 times faster access time than a conventional scheme, and that the power of the sense amplifier is lower than that of the conventional amplifier at the same speed.

Evaluation of Electrical Stimulus Current to Retina Cells for Retinal Prosthesis

Dept. of Bioengineering and Robotics, Graduate School of Eng., Tohoku University. 6-6-01 Aza Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Phone: +81-22-795-6906 E-mail: sdlab@sd.mech.tohoku.ac.jp Biofunctional Science, Tohoku University Biomedical Engineering Research Organization 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan Ophthtalmology, Tohoku University School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan

Vision Chip with Electrical Fovea Motion

A foveated vision of a human visual processing system is known to reduce the amount of information passed to subsequent processing layers significantly and lends itself to fast image processing and pattern recognition tasks. In order to realize such a vision chip based on the foveated vision processing system, we propose two concepts: the receptive field and the refractory period. Our vision chip can focus the fovea on a target electrically using these concepts.