In this work, design, implementation and test phases of a radiation sensor based on active pixel architectures are discussed. Fully standard CMOS technology has been exploited, allowing for easier integration of signal-processing circuitry. Alternative circuit schemes have been considered; a novel architecture, called WIPS, is introduced, aimed at a more efficient sparse-access mode of the sensor array. A first prototype of the chip has been fabricated, in a 0.18 μm CMOS technology. An automatic testing procedure has been devised, including design and fabrication of a suitable test board and of an optical bench. Preliminary results of the measurements are given, validating the overall approach and the operating principle of the WIPS architecture. © 2004 Elsevier B.V. All rights reserved.