Fully implantable, multi-channel microstimulator with tracking supply ribbon, multi-output charge pump and energy recovery

Abstract

A novel energy-efficient approach dedicated to high-density implantable stimulators such as visual prostheses is presented. Energy efficiency of the approach proposed in this work is achieved through two ideas: the 'tracking supply ribbon' technique and 'reverse charge pumping'. The proposed approach is implemented, in the multi-channel case, in such a way that power efficiency of each stimulation channel is enhanced according to its specific voltage/current condition and independently from other channels. For this purpose, a multi-channel power-efficient charge pump circuit with small integrated capacitors is proposed. Based on the proposed approach, a fully integrated 16-channel stimulation backend for a visual prosthesis was designed and simulated in the transistor level in a standard 0.18-mu m triple-well CMOS technology, occupying 1.41 mm(2) of silicon area. According to post-layout simulation results, power savings of up to 74% for a single channel and 81.5% for multiple channels are achieved compared to the conventional output stage with a constant supply voltage. Designed for the proposed stimulation backend, the charge pump generates output voltages of 3.48 V, -1.69 V, -3.38 V, and -5.05 V out of a 1.8 V input voltage and exhibits average power efficiency of 92.8% and 86.8% for one- and three-stage circuits, respectively, all in the case of a 100 mu A current load. All the aforementioned results are based on post-layout simulation. Moreover, a proof-of-concept prototype was developed using off-the-shelf components in order to demonstrate the operation of the proposed tracking supply ribbon idea.