<title>Image sensor based on pulse frequency modulation for retinal prosthesis</title>

Abstract

We demonstrate an application of a CMOS image sensor using pulse frequency modulation for retinal prosthesis. To increase the sensitivity we use a pulse frequency modulation (PFM) instead of a conventional integration method. The fundamental device characteristics of PFM are described. Based on the results of the PFM pixel circuit, we have fabricated a 128 x 128 pixel array chip using O.35tm CMOS technology, and successfully demonstrated to capture images by using this chip. For the application of the PFM to retinal prosthesis, the output characteristics of PFM are modified in the frequency range, current stimulation, and biphasic output. Also future issues for implantation are discussed.