We have developed an active microphotodiode array (MPDA) for retinal stimulation. The unique feature of the device is that each pixel acts as an independent oscillator, whose frequency is controlled by the incident light intensity. The design is based on a double inverter relaxation oscillator, and the photodiodes are of PIN-type. These oscillating pixels stimulate the nervous tissue with bipolar pulses. The prototype stimulator chips are realized in standard 0.35 mum CMOS technology. The reported preliminary data and performance demonstrate the potential of the new concept for future retinal prostheses. (C) 2003 Elsevier B.V. All rights reserved.