An Asynchronous Sampling-Based 128 \times 128 Direct Photon-Counting X-Ray Image Detector with Multi-Energy Discrimination and High Spatial Resolution

• Published in: IEEE journal of solid-state circuits 2013-02, Vol.48 (2), p.541-558
• Main Authors: Kim, Hyun-Sik, Han, Sang-Wook, Yang, Jun-Hyeok, Kim, Sunil, Kim, Young, Kim, Sangwook, Yoon, Dae-Kun, Lee, Jun-Su, Park, Jae-Chul, Sung, Younghun, Lee, Seong-Deok, Ryu, Seung-Tak, Cho, Gyu-Hyeong
• Format: Article
• Language: English
• Subjects: ADC; arrays; CMOS; Detectors; Energy states; image sensors; Noise; Photoconducting materials; photoconductor; photon counting; Photonics; preamplifiers; Resistors; sampling-based circuits; switches; X-ray imaging
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2012.2221196

This paper presents a direct photon-counting X-ray image detector with a HgI 2 photoconductor for high-quality medical imaging applications. The proposed sampling-based charge preamplifier with asynchronous self-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 architecture also reduces flicker noise and contributes to the achievement of high pixel-to-pixel uniformity. Discrimination of the energy level of the detected X-rays is performed by the proposed compact in-pixel ADC with low power consumption. Three 15-bit counters in each pixel count up energy-discriminated photons for the reconstruction of multispectral X-ray images. A 128 × 128 X-ray image detector with a pixel size of 60 × 60 μm 2 is implemented and measured using a 0.13-μm/0.35-μm standard CMOS process. It discriminates 3 energy levels of photon energy with a gain of 107 mV/ke - and a static power consumption of 4.6 μW/pixel. The measured equivalent noise charge (ENC) and minimum detectable energy level of the detector pixel are 68 e - rms and 290 e - , respectively. The measured maximum threshold dispersion in the pixel array is 164 e - rms without any calibration. The functionality of our chip is also successfully demonstrated using real X-ray images.