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.

Multi-channel stimulator IC using a channel sharing method for retinal prostheses.

A retinal stimulator is an implantable device restoring vision by supplying a controlled, stimulating electrical signal to people blinded by retinal diseases such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP). The resolution requirements of artificial retina systems become increasingly significant in their design as well as their usefulness. At least 32 x 32 pixels are required to provide a minimal visual function. However, a retinal stimulator with a high resolution imposes severe constraints on interface electronics. In this paper, a new stimulator IC (integrated chip) using a channel sharing technique is developed to minimize the circuit size, power consumption, as well as overheating of retina tissues. The proposed current-mode stimulator is fabricated by a 0.35 microm 2-poly/4-metal BCDMOS technology. Attention is given to minimizing the silicon area so that higher channel numbers can be implemented. The stimulator for each channel can provide output current in the range of 0-350 muA. The effective chip area excluding the pads is 1.2 mm x 1.2 mm.