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S.K. Kelly, J.L. Wyatt; Low-Power Techniques for a Retinal Prosthesis . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5064.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: During electrical stimulation of retinal tissue, significant energy is stored in the electrode capacitance. We have invented techniques for recovering some of that stored energy, and for reducing the dissipated power in the electrode driving circuitry during stimulation. Methods: Circuits and techniques to implement low-power stimulation and energy recovery were simulated in MATLAB and TSpice. A technique for delivering current in an energy efficient manner was tested by driving an iridium oxide electrode in physiologic saline with various voltage waveforms from a laboratory function generator, and measuring the resultant current waveforms. Using discrete components, we have built a prototype system to transmit power via magnetic fields and to receive and process that power. An elementary prototype stimulation system was also built from discrete components and tested. Portions of these systems have been implemented in 1.5 µm CMOS and fabricated through the MOSIS service. Results: Simulations have yielded voltage waveforms which deliver the required current pulses to iridium oxide electrodes with far less wasted power in the driver than is typical. Simulations and lab bench tests show that a single iridium oxide electrode may be driven in the typical biphasic current manner to a maximum charge of 1 µC (approximate human perception threshold), with less than 1 µJ of energy. This means the total driver and electrode power for stimulating 100 electrodes at 100 Hz is reduced from greater than 50 mW to less than 10 mW. We have also experimentally recovered energy from iridium oxide electrodes in saline. Conclusion: While this method of stimulation requires some level of circuit complexity, and therefore overhead circuit power, we have shown that the power savings outweigh the costs.
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