Highly Reliable Active Pixel Circuit Based on Dual-Gate TFTs for Dynamic X-Ray Medical Imaging

This paper demonstrates a highly reliable active pixel sensor (APS) based on dual-gate (DG) thin-film transistors (TFTs) for high-frame-rate dynamic X-ray medical imaging. By storing the threshold voltage (VT) in the auxiliary gate capacitor and amplifying the voltage signal through the primary gate electrode, the proposed APS circuit compensates for both positive and negative VT shifts of the amplifying TFT. Furthermore, using correlated double sampling by successively subsampling the same pixel without additional memory, the APS circuit eliminates low-frequency noise and DC offset, thereby effectively increasing the dynamic range and the signal-to-noise ratio. The charge-to-current gain of the proposed circuit is 4.50 μA/pC with a nonlinearity of 1.02%. Compared with the conventional 3-T pixel, the proposed APS features a decreased voltage error rate from 23.85% to 0.88% with a VT shift of ±1 V.