An ambient light adaptive subretinal stimulator

This paper presents a subretinal stimulator which is able to automatically adapt to varying ambient light levels. Stimulation timing and intensity are controlled using an input amplifier with an offset current cancellation circuitry to eliminate offset current imposed on the pixel amplifier for accurate stimulation control and optimized power consumption. In order to enable the chip to operate over a wide range of luminance conditions without manual tuning, automatic ambient light adaptation is required. Comparing the local photosensor output with a global luminance reference signal forms the basis of the adaptation mechanism. Global brightness information is obtained by logarithmic conversion of the summed photocurrents to generate a global luminance reference voltage. The chip has been realized in Austria Micro Systems 0.35 mum CMOS Opto technology.