We present in this paper an integrating CMOS Active Pixel Sensor (APS) circ
uit coated with scintillator type sensors for intra-oral dental X-ray imagi
ng systems. The photosensing element in the pixel is formed by the p-diffus
ion on the n-well diode. The advantage of this photosensor is its very low
direct absorption of X-rays compared to the other available photosensing el
ements in the CMOS pixel. The pixel features an integrating capacitor in th
e feedback loop of a preamplifier of a finite gain in order to increase the
optical sensitivity. To verify the effectiveness of this in-pixel preampli
fication, a prototype 32 x 80 element CMOS active pixel array was implement
ed in a 0.8 mum CMOS double poly, n-well process with a pixel pitch of 50 m
um. Measured results confirmed the improved optical sensitivity performance
of the APS. Various measurements on device performance are presented. (C)
2001 Elsevier Science B.V. All rights reserved.