An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier

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.