Abstract
This paper introduces an ambient light rejection (ALR) circuit for the autonomous adaptation of a subretinal implant system. The sub-retinal implants, located beneath a bipolar cell layer, are known to have a significant advantage in spatial resolution by integrating more than a thousand pixels, compared to epi-retinal implants. However, challenges remain regarding current dispersion in high-density retinal implants, and ambient light induces pixel saturation. Thus, the technical issues of ambient light associated with a conventional image processing technique, which lead to high power consumption and area occupation, are still unresolved. Thus, it is necessary to develop a novel image-processing unit to handle ambient light, considering constraints related to power and area. In this paper, we present an ALR circuit as an image-processing unit for sub-retinal implants. We first introduced an ALR algorithm to reduce the ambient light in conventional retinal implants; next, we implemented the ALR algorithm as an application-specific integrated chip (ASIC). The ALR circuit was fabricated using a standard 0.35-μm CMOS process along with an image-sensor-based stimulator, a sensor pixel, and digital blocks. As experimental results, the ALR circuit occupies an area of 190 µm2, consumes a power of 3.2 mW and shows a maximum response time of 1.6 s at a light intensity of 20,000 lux. The proposed ALR circuit also has a pixel loss rate of 0.3%. The experimental results show that the ALR circuit leads to a sensor pixel (SP) being autonomously adjusted, depending on the light intensity.
Highlights
Retinal implants have great promise in restoring vision for the blind, who suffer from retinal diseases such as retinitis pigmentosa and age-related macular degeneration [1,2,3,4].The fundamental idea for retinal prosthetics is to electrically stimulate impaired retina cells using a microelectrode array and its driving circuitry [5,6,7,8,9]
To cancel out the ambient light, we developed a control circuit to adjust the integration time used for 3-Tr complementary metal-oxidesemiconductor (CMOS) image sensors, where the integration time facilitates sensing the light intensity
Results end of the integration time. It means that the integration time on sequence will be Figure 6 shows the micrograph of the proposed ambient light rejection (ALR) circuit, where we integrated a shorter than this sequence
Summary
The fundamental idea for retinal prosthetics is to electrically stimulate impaired retina cells using a microelectrode array and its driving circuitry [5,6,7,8,9] This retinal prosthesis can be classified into epi-retinal [5,6] and sub-retinal implants [7,8,9], based on the anatomical location. According to a clinical trial [11,12], the sub-retinal implant with 1500 stimulation pixels shows equal vision restoration compared with the epi-retinal implant with only 60 pixels This mainly arises from the interface between neighboring pixels during stimulation and a strong ambient light projected onto the subretinal chip
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