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.
Highlights
Retinal implants offer great promise for restoring vision to patients who suffer from retinal diseases such as retina pigmentosa and age-related macular degeneration
It has been reported that the subretinal implant can provide high pixel density of up to 1600 pixels [8], on a limited silicon chip area [9]; this is possible because the stimulator in the subretinal device does not need a high-resolution current-steering digital-to-analog converter (DAC)
The high-resolution DAC and the digital controller occupy a large area in a single-pixel stimulator (SPStim); the area becomes dominant with high-voltage CMOS
Summary
Retinal implants offer great promise for restoring vision to patients who suffer from retinal diseases such as retina pigmentosa and age-related macular degeneration. According to the anatomical position, retinal prostheses can be classified as epiretinal [1,2], subretinal [3,4,5], or suprachoroidal [6,7]. It has been reported that the subretinal implant can provide high pixel density of up to 1600 pixels [8], on a limited silicon chip area [9]; this is possible because the stimulator in the subretinal device does not need a high-resolution current-steering digital-to-analog converter (DAC). Its own local digital controller, which are employed to generate various biphasic current pulses for epiretinal and suprachoroidal prosthetics. The high-resolution DAC and the digital controller occupy a large area in a single-pixel stimulator (SPStim); the area becomes dominant with high-voltage CMOS (complementary metal-oxide semiconductor) process technology [2]. The prosthetic chip and cable, which works to deliver a power and a command
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