A Highly-Scalable Poisson-Coded Retinal Optogenetic Stimulator With Fully-Analog ED-Based Adaptive Spike Detection and Closed-Loop Calibration

We present a fully implantable, inductively powered optogenetic stimulator that enhances stimulation efficacy and pathway specificity while maximizing energy efficiency and channel-count scalability. By leveraging opsins’ photon integration properties with raster scanning and Poisson-coded stimulation, we achieve a uniform power profile and reduce wiring complexity, enabling a scalable system that supports more stimulation channels without compromising safety or functionality, improving prosthetic vision resolution. We also employed a compact and power-efficient (0.026 $mm^{2}$ and 1.02 $\mu$W overhead) SNR-boosted ADC-less spike detection circuit to adapt each LED's light intensity based on real-time feedback from RGC spiking cells. This closed-loop adaptivity adjusts stimulation to opsin distribution variations, over time and across different patients, ensuring effective and consistent stimulation across patients, enhancing both energy efficiency and visual perception quality. The 3 $\times$ 3 $mm^{2}$ IC, fabricated in 180nm CMOS, is coupled with a 100-channel custom optrode array fabricated using an InGaN process on a sapphire substrate. Experimental results demonstrate circuit-level performance, system-level efficacy, and in-vitro validation. Comparison tables highlight our work's advantages over state-of-the-art implantable spike detection systems and retinal prostheses.