Amorphous Silicon Active Pixel Sensor Readout Circuit Architectures for Medical Imaging

Results from previous work indicate the feasibility of the amorphous silicon (a-Si) active pixel sensor (APS) readout circuit that performs on-pixel amplification for low-noise, real time imaging applications (e.g. fluoroscopy). In this paper, the noise contribution of the APS readout circuit is examined. In addition, due to the metastable nature of a-Si, the APS stability is discussed. Unlike conventional PPS systems with one thin film transistor (TFT) switch per pixel, the APS has three TFTs per pixel. The large number and sizes of a-Si TFTs can reduce the pixel fill factor if the TFTs are not embedded beneath the sensor as in continuous layer sensor architectures. In this paper, we present preliminary APS noise and stability measurements along with considerations of fully overlapped pixel architectures on APS performance.