This paper presents a direct photon-counting X-ray image detector with a 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.

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... iscrimination 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 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 . The measured 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 demonstrated using real X-ray images.