A 0.35 μm CMOS process has been used for on-chip integration of a sun sensor composed of a 2x2 photodiode array and a current-to-voltage amplifier. Unlike conventional sun sensors, a shade profile proportional to the angle of incidence of incoming light is projected onto the photodiodes. This concept enables an autonomous self-powered optical system with two the main functions (electrical power generation for the amplifier and the optical position measurement) implemented in the photodiodes by having these operated simultaneously in the photovoltaic and photocurrent mode respectively. The low-power current-to-voltage converter is used to readout the differential photocurrent, while powered from the photodiodes at minimum supply voltage level. Test structures have been designed, fabricated and used for validation of the concept. ©2009 IEEE.