A 16-channel 24-V 1.8-mA power efficiency enhanced neural/muscular stimulator with exponentially decaying stimulation current

This paper presents a current-mode neural/muscular stimulator with an exponentially decaying stimulation current. The use of exponentially decaying current makes the voltage on the stimulating electrode constant during the stimulation, which eliminates the headroom and increases the power efficiency. A simple exponentially decaying current generator is proposed based on Taylor series approximation and implemented in a 16-channel prototype stimulator IC. The prototype IC is fabricated in a 0.18-μm CMOS process with high-voltage LDMOS option, occupying a core area of 1.65 mm × 1.65 mm. The stimulator is tested with different loads, which mimics the electrode impedances, and the measured results show that maximum stimulation power efficiency of 95.9% can be achieved at the output stage of the stimulator. Depending on the electrode impedance and stimulation current, the power efficiency can be improved by nearly 10% at the output stage, compared to traditional constant-current stimulator.