A Neural Stimulator Frontend With High-Voltage Compliance and Programmable Pulse Shape for Epiretinal Implants

This paper presents an integrated neural stimulator with highly efficient and flexible frontend which is intended for an epiretinal implant with 1024 electrodes. It features programmable stimulation pulse shapes, a high-voltage (HV) output driver with compliance monitor for supply voltage adaptation, active and passive charge balancers, and electrode impedance measurement. Area and power efficiency is achieved by global timing assignment and local amplitude control over a bus at the local stimulation units. Major power savings in the distributed digital control units are realized by implementing global and local clock gating. Two stimulator frontends have been fabricated in a 0.35 μm HVCMOS process. Each frontend features four demultiplexed outputs and consumes 0.2 mm² core area. A maximum voltage compliance of 20 V is achieved and up to 1 mA of output current can be adjusted with up to 50 dB dynamic range. In vitro experimental results performed on a platinum black electrode in 0.9% saline solution are given.