A matched biphasic microstimulator for an implant able retinal prosthetic device

This paper describes the design and implementation of an implantable microstimulator chip designed for stimulating electrodes in a retinal prosthetic device. The chip is capable of providing biphasic current pulses up to 600μA amplitude to a maximum load of 10kΩ with a anodic/cathodic matching of 1.3%. The current source operates at low voltage headroom of 0.5V by using an active feedback setup. The gain variations for output currents are less than 3%. A 1:8 demultiplexing is used for a stimulus frequency of 50-60Hz. A variable amplification scheme is implemented to maintain a high resolution throughout the entire stimulus range. The outputs are equipped with charge cancellation mechanism to ensure safety of the tissue. Measurement results of a prototype fabricated in AMI 1.6μm bulk CMOS technology are presented.