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 (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf>) 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 V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> 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 V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> shift of ±1 V.