Fully Integrated Light-Sensing Stimulator Design for Subretinal Implants

Abstract

This paper presents a fully integrated photodiode-based low-power and low-mismatch stimulator for a subretinal prosthesis. It is known that a subretinal prosthesis achieves 1600-pixel stimulators on a limited single-chip area that is implanted beneath the bipolar cell layer. However, the high-density pixels cause high power dissipation during stimulation and high fabrication costs because of special process technologies such as the complementary metal-oxide semiconductor CMOS image sensor process. In addition, the many residual charges arising from the high-density pixel stimulation have deleterious effects, such as tissue damage and electrode corrosion, on the retina tissue. In this work, we adopted a switched-capacitor current mirror technique for the single-pixel stimulator (SPStim) that enables low power consumption and low mismatch in the subretinal device. The customized P+/N-well photodiode used to sense the incident light in the SPStim also reduces the fabrication cost. The 64-pixel stimulators are fabricated in a standard 0.35-μm CMOS process along with a global digital controller, which occupies a chip area of 4.3 × 3.2 mm2 and are ex-vivo demonstrated using a dissected pig eyeball. According to measured results, the SPStim accomplishes a maximum biphasic pulse amplitude of 143 μA, which dissipates an average power of 167 μW in a stimulation period of 5 ms, and an average mismatch of 1.12 % between the cathodic and anodic pulses.

High-PSRR Wide-Range Supply-Independent CMOS Voltage Reference for Retinal Prosthetic Systems

“…The output of the LDO provides a positive supply voltage to 64 pixels stimulator circuit which requires maximum current of 10 mA. This requirement is based on our previous work which can be found in [10]. In the experimental setup to evaluate the line-transient responses of LDO, a 100 Ω resistor was chosen as a load for the LDO output terminal so that the load current is larger than 10 mA.…”

“…The command data modulated on the RF carrier are recovered using the demodulator and sent to the global digital controller that decodes the demodulated data in order to activate the stimulator array. Here, a single-pixel stimulator, which is composed of a photosensor, current amplifier, and pulse shaper [10], generates a biphasic current pulse, which is delivered to the bipolar cells through a microelectrode. Back telemetry is utilized to observe the operating status of the implanted device.…”

“…Here, a single-pixel stimulator, which is composed of a photosensor, current amplifier, and pulse shaper [10], generates a biphasic current pulse, which is delivered to the bipolar cells through a microelectrode. Back telemetry is utilized to observe the operating status of the implanted device.…”

Graphene Oxide–Based Nanomaterials: An Insight into Retinal Prosthesis

“…This is especially applicable in patients with blindness due to photoreceptor necrosis, where electrodes can be implanted in the retina to effectively stimulate bipolar or ganglion cells and subsequently enhance visual signal transmission. A retinal prosthesis chip is comprised of three structural units: a photodiode array, a photosensor with current amplifiers, and a biphasic circuit [38]. The power is mainly supplied by photovoltaic batteries, which convert incident light into electrical energy.…”

Micro/Nano Technologies for High-Density Retinal Implant

“…There is a long-lasting effort to increase the resolution and visual acuity of retinal implant [6,18,19]. Previous simulation has shown that a super-high density of 600–1000 stimulus electrodes (pixels) is required to help blind people with face recognition and reading large text in newspapers [20].…”