A charge accumulation-free voltage-controlled functional electrical stimulator with bi-phasic sinusoidal stimulation

Abstract

This paper presents a charge accumulation-free voltage-controlled (VC) bi-phasic sinusoidal functional electrical stimulator (FES) for bioelectronic application. Traditionally, constant current (CC) pulse-shaped FESs with active or passive charge balancers are used to compensate for accumulated charges arise from process, voltage and temperature (PVT) variation as a result of long-term stimulation. Unlike the CC pulse-shaped FES, the VC sinusoidal-shaped FES is adopted here to avoid charge accumulation over time. The charge balancer is not required, substantially reducing system complexity and the chip area of the FES. To demonstrate the feasibility of concept, in this paper, four channels of VC bi-phasic sinusoidal-shaped FESs are integrated with the bio-potential recording circuit to compare with four channels of CC bi-phasic pulse-shaped FESs that are integrated with the same neural recording system for comparison. Measurements indicate an absence of charge accumulation as a result of the VC FESs. In addition, here we adopt the sinusoidal stimulation to reduce transient effects on tissue in comparison to a pulse-shaped method. The bio-potential activities of a cockroach leg that is stimulated for 50 s by the proposed bi-phasic sinusoidal stimulation are recorded. The measured bio-potential activities of a cockroach leg show that no stimulation-evoked leg movement occurs under stimulation by the sinusoidal waveform.