An image sensor with pulse frequency modulation for a retinal prosthesis : Image acquisition and output frequency limitation

Abstract

For the application of a retinal prosthesis device, we formulate output pulse characteristic in a pixel circuit using pulse frequency modulation, and demonstrate that the pulse widening phenomena is caused by the competition between the photocurrent and the charge current. Based on the formulation, we fabricate a 128x128 pixel PFM array chip. We successfully demonstrate the image acquisition by using this chip. Finally, we demonstrate the pulse frequency limitation circuit by introducing a switched capacitor circuit and a leak transistor parallel inserted in the photodiode.