A Fully Intraocular High-Density Self-Calibrating Epiretinal Prosthesis

Abstract

This paper presents a fully intraocular self-calibrating epiretinal prosthesis with 512 independent channels in 65 nm CMOS. A novel digital calibration technique matches the biphasic currents of each channel independently while the calibration circuitry is shared among every 4 channels. Dual-band telemetry for power and data with on-chip rectifier and clock recovery reduces the number of off-chip components. The rectifier utilizes unidirectional switches to prevent reverse conduction loss in the power transistors and achieves an efficiency > 80%. The data telemetry implements a phase-shift keying (PSK) modulation scheme and supports data rates up to 20 Mb/s. The system occupies an area of 4.5 ×3.1 mm². It features a pixel size of 0.0169 mm² and arbitrary waveform generation per channel. In vitro measurements performed on a Pt/Ir concentric bipolar electrode in phosphate buffered saline (PBS) are presented. A statistical measurement over 40 channels from 5 different chips shows a current mismatch with μ = 1.12 μA and σ = 0.53 μA. The chip is integrated with flexible MEMS origami coils and parylene substrate to provide a fully intraocular implant.

Silicon-Integrated High-Density Electrocortical Interfaces

“…To date, integration of 100-1600 channels has been achieved [84]- [86], [91]- [93]. In order to integrate such high channel counts, programmability of waveform parameters, individual connectivity to each channel, and/or charge balancing need to be compromised to some extent.…”

“…In order to integrate such high channel counts, programmability of waveform parameters, individual connectivity to each channel, and/or charge balancing need to be compromised to some extent. For example, groups of 4-8 electrodes in [91], [93]- [95] can share a single digital-to-analog converter for optimized, high density integration.…”

“…Instead of external capacitors, capacitive electrodes made with high-k dielectric coatings have been investigated for safe neural interfaces [88], [100], [101]. Several other techniques for better charge balancing have been demonstrated: 1) shorting electrodes to ground [102]; and 2) utilizing a discharging resistor [94], active current balancing by feedback control [103], [104], generating additional balancing current pulses by monitoring electrode voltages [105], and embedded DAC calibration [93], [106].…”

“…For devices implanted to a depth of a few centimeters, and that are on the order of millimeter-to-centimeter in diameter, near-or mid-field electromagnetic power transfer is generally considered to be the most efficient and practical method to power such devices. Near-field power transfer, which operates at frequencies up to approximately 100 MHz for typical implants, has been extensively used for cochlear implants [135], retinal prostheses [86], [93], and various research IMD systems [122], [136]- [139], and has been investigated and characterized to maximize its usage and power transfer efficiency for implants [140]- [145].…”

Design of a Customized Multipurpose Nano-Enabled Implantable System for In-Vivo Theranostics

“…Other interesting examples for close-loop systems are presented in [17,43,44]. Salam et al [43] developed an implantable drug delivery system for the treatment of refractory epilepsy.…”