A High-Speed Wafer-Scale CMOS X-Ray Detector With Column-Parallel ADCs Using Oversampling Binning Method

Abstract

This paper presents a high-speed wafer-scale CMOS X-ray detector with an active area of 12 cm x 12 cm, which features 100 mu m-sized pixels. A horizontal row driver is adopted for implementing a three-side buttable detector with the tiling technique and thereby enabling the extension of the active area. The proposed detector employs 14-b column-parallel extended-counting analog-to-digital converters (EC ADCs) using digital correlated double sampling for high-speed operation and high-gray-scale resolution. The oversampling binning method using a Delta Sigma modulator in EC ADCs is proposed for high sensitivity and the pipelined timing method is adopted for a high frame rate, which results in reduction of the X-ray dose. An offset cancellation method for the input buffer is used to improve the uniformity between column ADCs. The proposed CMOS X-ray detector is fabricated using a 0.35-mu m CMOS process with the stitching technique. The measured differential column fixed pattern noise and random noise without X-ray exposure are 3.01 and 3.06 least significant bits, respectively, at a resolution of 14 b. In the full-resolution mode, the proposed detector operates up to a frame frequency of 108 frames/s with the pipelined timing and 60 frames/s without the pipelined timing.