Current mode active pixel sensor architectures for large area digital imaging

Abstract

The most widely used architecture in large area flat panel imagers is the amorphous silicon passive pixel sensor (PPS), which consists of a detector and a readout switch. While the PPS has the advantage of being compact, reading small PPS output signals requires external column charge amplifiers that produce additional noise and reduce the minimum readable sensor input signal. This work compares the SNR, metastability, area, and off-panel complexity of amorphous silicon active pixel sensor (APS) readout circuits based on three and two transistor current mode and current programmed designs that perform on- pixel amplification of noise-vulnerable sensor input signals to minimize the effect of external readout noise sources associated with "off-chip" charge amplifiers. The APS circuits presented are poised to replace PPS circuits for fast readout, noise- sensitive, large area, digital medical imaging applications such as dual mode radiography/fluoroscopy and mammography tomosynthesis. © 2008 IEEE.