A Current-Mode Electrical Stimulator with Charge Balance for Neural Stimulation Applications

An eight-channel current-mode biphasic electrical stimulator with a charge compensation circuit is presented. This eight-channel current stimulator features a four-bit current-mode digital-to-analog converter (IDAC) that provides adjustable stimulation currents ranging from $0.5 \mu \mathrm{~A}$ to $60 \mu \mathrm{~A}$. This paper focuses on developing a biphasic current stimulator that receives digital signals indicating when to give stimulation and delivers the necessary stimulation current for neural cell stimulation. It generates a bidirectional symmetrical current stimulation waveform to perform electrical stimulation. In traditional constant voltage stimulation, the effect diminishes as the impedance of cellular tissue gradually increases. The designed electrical stimulator employs a constant current method to maintain a consistent level of electrical stimulation. However, due to the effects of the non-ideal process, the accumulated charge cannot be completely canceled by the biphasic current alone. Therefore, a class-AB amplifier-based charge compensator is employed. Utilizing the characteristics of a class-AB operational transconductance amplifier achieves low quiescent current and high compensation efficiency.