A 9-V-Tolerant Stacked-Switched-Capacitor Stimulation System With Level-Adaptive Switch Control and Rapid Stimulus-Synchronized Charge Balancing for Implantable Devices

This article proposes a stacked-switched-capacitor stimulation (SSCS) system that can provide up to 9-V stimulation without using an external high-voltage (HV) supply or HV conversion stages to supply the stimulator. With the level-adaptive switch control, SSCS can be HV tolerant using only low-voltage (LV) transistors. In addition, SSCS achieves high stimulation efficiency up to 71.4%, which includes charging and discharging efficiencies of 72.6% and 99.9%, respectively, to charge 1-<inline-formula> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula>F capacitor from 0 to 4 V by adopting the ac-to-capacitor charger and the stacked-capacitor stimulus discharger. Charge balancing (CB) can also be achieved in rapid time using the stimulus-synchronized CB (SS-CB) method which adaptively controls the pulsewidth of the recovery phase. The SSCS prototype verifies that the residual voltage up to 900 mV can be suppressed within four stimulation cycles and maintained within <inline-formula> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula>30 mV by utilizing SS-CB.