A CMOS vision chip using modified Pulse-Frequency-Modulation (PFM) as an implanted retinal prosthesis device under the subretinal space

We propose a CMOS vision chip, an image sensor with pixel-level signal processing, to serve as a replacement for degenerated photoreceptor cells in the retina. In our approach, a vision chip is implanted underneath the retina (the subretinal space). For efficient electric stimulation, we utilize a pulse frequency modulation (PFM). Each pixel consists of a photosensor and a signal processor. Each pixel generates a PFM pulse, which frequency is proportionate to the intensity of incoming light. The control signal restricts the frequency within a certain range, which is suitable for the stimulation of the retinal neurons. We fabricate using 2P3M 0.6-μm CMOS technology and demonstrate to restrict pulse frequency range from 10Hz to 1kHz. Each pixel has the area of 83μm × 114μm and consists of 20 transistors.