Current stimulator IC with adaptive supply regulator for visual prostheses

The current stimulation method is preferred over the voltage stimulation method in the visual prostheses based on functional electrical stimulation (FES) due to its accurate charge control property. Previous current stimulators are generally implemented using a static high supply voltage, because current stimulations require high output voltage compliance. This high static supply voltage, however, may harm the tissues or damage the electrodes. This paper proposes a novel integrated circuit (IC) current stimulator with adaptive supply regulator (ASR). In the proposed circuit, the internal power supply voltage is not static, but adaptively regulated to the minimum required voltage for stimulation. The current feedback loop in the ASR adaptively increases the internal supply voltage when the monitored current is smaller than the desired current, and reduces the internal supply voltage when the monitored current is higher than the desired current. With this method, the internal supply voltage of the stimulator is minimized, and potential damages of the tissues due to high voltage (HV) stimulation can be reduced. Also the current feedback loop in ASR enhances the accuracy of the output current and the robustness to the load impedance. The stimulator IC is fabricated using 0.35 micro m bipolar-CMOS-DMOS (BCDMOS) process, and the size of the chip is 2000 micro m by 1500 micro m.