A matched biphasic microstimulator for an implantable 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 600 μA amplitude to a maximum load of 10 kΩ with anodic/cathodic matching of 1.3%. The current source operates at low voltage headroom of 0.5 V 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 50-60 Hz. 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 1.6 μm bulk CMOS technology are presented.