An Asynchronous Sampling-Based 128 128 Direct Photon-Counting X-Ray Image Detector with Multi-Energy Discrimination and High Spatial Resolution Hyun-Sik Kim, Student Member , IEEE, Sang-Wook Han, Jun-Hyeok Y ang, Sunil Kim, Y oung Kim, Sangwook Kim, Dae-Kun Y oon, Jun-Su Lee, Jae -Chul Park, Y ounghun Sung, Seong-Deok Lee

Abstract

This paper presents a direct photo n-counting X-ray image detector with a photoconductor for high-quality medical imaging applications . The proposed sampling-based charge preampli fier with asynchronous sel f-reset enables a pixel to detect single X-ray photon energy with higher sensitivity and faster processing rate. The use of the correlated double sampling enabled by the sampling-based archi tecture also reduces flicker noise and contributes to the achievement of high pixel-to-pixel uniformity. Discrimination of t he energy level of the detected X-rays is performed by the propose d compact in-pixel ADC with low power consumption. Three 15-bit counters in each pixel count up energy-discriminated photons for the reconstruction of multi- spectral X-ray images. A 128 128 X-ray image detector with a pixel size of is implemented and measured using a 0.13- /0.35- standard CMOS process. It discriminates 3 energy levels of photon energy with a gain of 107 and a static power consumption of 4.6 .T h em e a s u r e d equivalent noise charge (ENC) and minimum detectable energy level of the detector pixel are 68 and 290 , respectively. The measured maximum threshold dispersion in the pixel array is 164 without any calibration. The functionality of our chip is also successfully demons trated using real X-ray images.