Transient response of a 3-TFT hybrid active-passive pixel with correlated double sampling CMOS readout circuit for real-time medical X-ray imaging

This paper presents a new hybrid current-programmed, current-output active pixel sensor (APS) suitable for real time x-ray imaging (fluoroscopy) and an off-panel CMOS readout circuit. The pixel circuit is designed using hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) technology. Measurement based simulations show that the proposed pixel circuit can successfully compensate for characteristic variations (e.g. mobility and threshold voltage shift) in a-Si:H TFTs under prolonged gate voltage stress. Investigation of the APS transient response shows that the proposed circuit can fulfill the timing requirement of real time imaging. The readout circuit exploits correlated double sampling (CDS) technique to reduce the offset current, low frequency noise and fixed-pattern noise (FPN) on the array operation.