Integrated circuit interfaces for electrocortical stimulation

This chapter first reviews two conventional stimulation strategies, constant-voltage and constant-current stimulation methods, and adiabatic stimulation, which can achieve high stimulation energy efficiency at the cost of design complexity. Then, it presents a fully-integrated RF-powered neural stimulator that achieves adiabatic energy-replenishing operation without any bulky external components. Adiabatic supply voltages, which can reach a differential range of up to 7.2 V, are directly generated from an on-chip 190-MHz resonant LC tank via a self-cascading/folding rectifier network, bypassing the losses that would otherwise be introduced by the 0.8 V system supply-generating rectifier and regulator. Using a charge replenishing scheme, the stimulator redirects the charges accumulated across the electrodes to the system power supplies for 63.1% of stimulation energy recycling. To benchmark the efficiency of stimulation, a figure of merit termed the Stimulator Efficiency Factor (SEF) is introduced.