Study on Active Pixel Circuit for Super-Fine-Pitch X-ray Image Sensor

• Main Authors: Yang, Cheng-Ta, 楊政達
• Other Authors: Tai, Ya-Hsiang
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/99701347711209471665

碩士 === 國立交通大學 === 光電工程學系 === 100 === With the rapid improvement of X-ray equipments, the next generation is a combination of the X-ray photography and the flat panel display technique, which is called digital flat panel detectors. For lower X-ray dosage and higher image quality, the pixel sensor circuit of the digital flat panel detector is evolving. Recently, a novel active pixel sensor (APS) circuit is proposed, which removes the drain bias bus and is equipped with one horizontal bus and one vertical bus per pixel only. The focus of this thesis is the feasibility of this new fine pitch APS circuit for application. To confirm its sensing function, the new APS circuit is directly compared with the previous one. We experimentally verify their sensing functions are the same, while the new APS eliminates the leakage error by eliminating the drain-source voltage. Moreover, we further analyze the new APS circuit by simulation. Considering the fixed pattern noise (FPN), it is verified that the threshold voltage (VTH) variation for APS is the most important factor. Another critical issue is IR drop, which is resulted from the unique way of providing output current horizontally. For image independent IR drop, we propose the dual-scanning APS circuit with storage capacitance (Cst) adjustment to solve this problem. For image dependent IR drop, the worst case is found. Finally, the noise of the circuit is analyzed and its operating condition is optimized accordingly.