Breakthrough in Current Scientific Imaging with Active-Pixel Sensor Technology

A new class of pixel-based imaging devices being developed by a UK consortium is now being trialed in scientific imaging applications ranging from particle physics and space science to medicine and biology. Active-pixel sensor (APS) technology exploits mainstream CMOS technology to incorporate programmable transistors into each pixel of the image array.

This in-built programmability enables the pixels to perform signal-processing functions such as analogue-digital conversion and time-digital conversion. Other features include the ability to home in on specific regions of interest on the chip, and to enhance the sensitivity via back-thinning of the chip.

"With APS, we can put intelligent signal-processing on the chip and then we can do things like improve the sensitivity or quality of the images," said Nigel Allinson, professor of image engineering at the University of Sheffield and leader of the Multidimensional Integrated Intelligent Imaging (MI-3) project. This collaborative project, which was set up three years ago and involves 11 research centres, will receive funding totaling £4.4 million ($9 million) over its four-year lifetime.

According to Allinson, the extra features of APS sensors are needed to meet the demands of scientific applications. As well as low noise and high speed, such devices must offer a large dynamic range, high linearity and a large active area. Another must-have is a wide spectral range covering high-energy gamma rays and ionizing particles through to IR radiation.

APS-based detectors offer the potential to meet all these requirements. The first APS to come out of the MI-3 project is a 520¡Ñ520-pixel chip called Vanilla. The sensor contains 25 £gm pixels with a total active area of 13¡Ñ13 mm2, operates at 100 frames/s and is two-side buttable to provide a larger sensor area.

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