High frequency self-oscillating current switching for a fully integrated fail-safe stimulator output stage

Using blocking capacitors in biomedical stimulators is important to the safety of the developed systems. However, the capacitors should be large enough in order to minimize the required voltage headroom. On the other hand, integrating large capacitors of few micro-Farads alongside the stimulator is almost impossible in implantable systems. High frequency current switching is a method that enables reducing the size of blocking capacitors. However, this method needs high-frequency square pulses, which is power consuming for the stimulators. In addition, since the frequency of high-frequency pulses is fixed, the voltage headroom required to support the blocking capacitor is not bounded. The larger the amplitude of the stimulation current, the higher the voltage headroom becomes. In this paper, an improved high-frequency current-switching method is proposed to overcome the mentioned drawbacks of the original high-frequency current-switching method. The proposed method is designed, simulated and validated using a 0.18 mu m high-voltage SOI technology provided by XFAB.