An Energy-efficient Wirelessly Powered Millimeter-scale Neurostimulator with Optimized Inductive Loop Antenna and Custom Rectifier

This paper presents a wirelessly powered millimeter-scale neurostimulator based on an integrated circuit (IC) that is co-designed with an inductive loop antenna. The circuit uses a positive feedback to generate output stimuli eliminating the need for any control blocks. Low-voltage and high-voltage versions of the circuit are discussed, which can generate ~1 V and ~2 V stimulation intensities, respectively. The low-voltage design is implemented in a 180 nm CMOS process and occupies an area of 1 mm x 0.2 mm (including pads). A systematic co-design procedure is presented to optimize the rectifier and the inductive loop antenna, rendering the stimulator assembly to occupy an area of 5 mm x 7.5 mm. The stimulator was fully implanted on a rat sciatic nerve 2 cm under the skin and successfully excited the axons. A multi-receiver energy transfer system is further presented targeting future in-body sensor networks.