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Design and evaluation of a CMOS-photosensor with in-pixel sigma-delta modulator for x-ray computed tomography

: Bäumer, C.; Eick, S.; Steadman, R.; Vogtmeier, G.; Gnade, M.; Kemna, A.; Weiler, D.


Enz, C.C. ; Ecole Polytechnique Federale de Lausanne -EPFL-; Institute of Electrical and Electronics Engineers -IEEE-:
ESSCIRC 2006, 32nd European Solid-State Circuits Conference. Proceedings : 18 - 22 September 2006, Montreux, Switzerland
Piscataway, NJ: IEEE, 2006
ISBN: 1-4244-0302-2
European Solid State Circuits Conference (ESSCIRC) <32, 2006, Montreux>
Fraunhofer IMS ()
computerised tomography; x-ray detection; sigma-delta modulator; CMOS imager; Röntgen-Detektion; CMOS Bildgeber; Sigma-Delta Modulation; Computer-Tomographie

A multi-channel sigma-delta-type analog-to-digital converter has been designed for data readout in CT scanners. A test-structure with a 4 x 4 photodetector array has been fabricated in a 0.8 µm CMOS process. Aiming at an integrated solution towards a "digital pixel", each sensor element is formed by a photodiode and a third-order sigma-delta-modulator. The switched-capacitor circuitry has been realized as a fully differential-path design. Test measurements have been carried out and analyzed in terms of dynamic range and noise. Simulations on layout level have been performed. A digital post-processing scheme has been devised for decimation and low-pass filtering of the modulator outputs.