A fully-integrated charge pump for self-powered implantable retinal prostheses

This paper presents a compact fully-integrated charge pump based voltage doubler for self-powered implantable retinal prostheses. The target input voltage is 0.55 V to meet the output voltage of on-chip photovoltaic cells, and the target output is around 1 V to provide sufficient current for neuron stimulation. Several techniques are adopted in the proposed design, including gate-boosting circuits to enhance current driving capability, a time-interleaving technique to reduce the size of the output capacitor, and a non-overlapping clock generator to suppress the shoot-through current. The proposed charge pump was implemented in 0.18 μm CMOS process with core chip area of 700 μm × 280 μm. The measurement results demonstrate that the proposed charge pump is capable of providing around 1 V output from an input voltage of 0.55 V with 500 μA loading current. The peak power efficiency is 73.4 % and the total area is 700 μm × 280 μm.