Feasibility of current mediated amorphous silicon active pixel sensor readout circuits for large area diagnostic medical imaging

The most widely used architecture in large area amorphous silicon (a-Si) flat panel imagers is a passive pixel sensor (PPS), which consists of a detector and a readout switch. While the PPS has the advantage of being compact and amenable towards high-resolution imaging, reading small PPS output signals requires external circuitry such as column charge amplifiers that produce additional noise and reduce the minimum readable sensor input signal. This work presents a current mode amorphous silicon active pixel that performs on-pixel amplification of noise-vulnerable sensor input signals to minimize the effect of external readout noise sources associated with "off-chip" charge amplifiers. Preliminary results [1] indicate excellent small signal linearity along with a high, and programmable, charge gain, which is promising for diagnostic medical imaging. This work examines low frequency a-Si TFT thermal and flicker noise, which contribute to the overall noise performance of the APS.