Power efficient multiple voltage stimulation for implantable retinal prosthesis

Electrical stimulation of retinal neurons has been identified as a form of visual prosthesis to restore vision in blind patients affected by Retinitis Pigmentosa (RP) and Age-related Macular Degeneration (AMD). Experiments on a successful prosthetic device in a chronically implanted patient indicate that the threshold current varies depending on the retinal region. Power can be saved by reducing the stimulus current in these sites. Further power savings can be obtained by reducing the supply voltage for these sites. This paper proposes a multiple voltage scheme in a retinal stimulator for reducing the power dissipation. An analysis of power dissipation is performed that helps to identify the stimulus range where maximum power savings is possible. A prototype retinal microstimulator IC is fabricated in CMOS technology that is capable of delivering 600μA bi-phasic pulses. The performance of the chip is verified under multiple voltages and measurement results of the chip are presented.