Switched-capacitor based implantable low-power wireless microstimulating systems

The main objective of this paper is to introduce a new category of implantable wireless microstimulators based on discharging a series of small capacitors to inject quantized lumps of electric charge into the excitable tissue, namely switched-capacitor based micro-stimulators (SCS). In this method, the total amount of charge per stimulation phase can be controlled by changing the initial and final capacitor voltages as well as the number of capacitors being discharged. The rate of discharge, which is the stimulus current, is also a controllable parameter that adds more flexibility to this stimulation approach, while improving the implant safety. The key reason for adopting SCS in implantable low-power devices was to combine the power efficiency of the voltage-controlled stimulators (VCS) with the safety and stimulation parameter controllability of the current-controlled stimulation (CCS) circuits. In addition, the SCS technique substantially simplifies the microstimulator architecture, and depending on the application, can potentially reduce the implant size and power requirements. It also provides an opportunity to apply different stimulus waveforms to the excitable tissue that can be more efficacious in activating the surrounding nerve or muscle fibers compared to the commonly used square-shaped pulses