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Session: Eye
Session starts: Thursday 26 January, 14:30
Presentation starts: 15:15
Room: Room 558

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Yihan Ouyang (TU Delft)
Dante Gabriel Muratore (TU Delft)

Abstract:
Retinal prostheses have been proposed recently as a promising method to restore partial visual sensation in patients with degenerative diseases by stimulating the remaining healthy neurons in the retina [1-2]. However, current devices do not provide sufficient results for patients to become fully independent. A fundamental problem is that current stimulation strategies fail to respect the different retinal cell types that encode different scene information. Instead, they activate cells indistinctively, sending a scrambled message to the brain. An artificial retina proposed in [3] is under development and aims at restoring vision with more precise control of natural neural codes in the retina. This work focuses on an implantable chip that is clinically viable, fully wireless and has bi-directional capabilities when interfacing with neurons. It operates in three modes: cell calibration (to record the spontaneous activity and learn which cells and cell types are available to the device), dictionary calibration (to learn individual cell responses to the stimulation parameters), and runtime (to stimulate available cells optimally based on a cell-type specific dictionary). The envisioned chip consists of three major building blocks: 1) recording channels that can capture spike activities over a massively parallel microelectrode array; 2) stimulation channels that can activate neurons with single-cell resolution; 3) wireless power and data circuits. A proof-of-concept chip for the wireless power and data system has been fabricated in CMOS BCD 0.18-µm process. The full-custom chip occupies an area of 1.15-mm2. Compared to other state-of-the-art literature [1-2], this work features a high-speed data uplink capable of 20 Mbps for closed-loop neuromodulation based on the dictionary approach described in [3]. For the power downlink, a high-frequency carrier signal (40.68-MHz) in the ISM band is chosen to minimize the area consumed by the passive components. Also, this work uses a 200 kbps ASK-PPM downlink modulation that can provide a self-synchronized clock and data to solve the inaccurate synchronization problem in conventional approaches. In addition, some overshoot/undershoot reduction approaches are proposed to enhance the load transient response of the capacitor-less voltage regulator. The experimental results of the wireless chip will be presented during the conference. A fully integrated design of the wireless retina implant system will be further explored in future work. 1. M. Monge et al., "A Fully Intraocular High-Density Self-Calibrating Epiretinal Prosthesis," in IEEE Transactions on Biomedical Circuits and Systems, vol. 7, no. 6, pp. 747-760, Dec. 2013. 2. A. Akinin et al., "An Optically Addressed Nanowire-Based Retinal Prosthesis With Wireless Stimulation Waveform Control and Charge Telemetering," in IEEE Journal of Solid-State Circuits, vol. 56, no. 11, pp. 3263-3273, Nov. 2021. 3. Muratore, D.G., & Chichilnisky, E.J. (2020). Artificial Retina: A Future Cellular-Resolution Brain-Machine Interface.