Low noise CMOS active pixel sensor for digital radiography

Objective: CMOS based radiation detectors have significant cost, size, and power advantages over other systems, however, they traditionally suffer from noise artifacts when operated at ambient conditions. In this work we examined the properties of a low noise active pixel sensor (APS) for radiation detection. Methods: Two active-pixel sensors were evaluated as CMOS x-ray detectors. The response of a standard three transistor APS and a modified APS (with integrated feedback clamping the detector voltage) to exposure with 75 keV x-rays was simulated and experimentally verified. Results: Simulations and experimental measurements demonstrated ∼10X improvement in contrast-to-noise ratio (CNR) for the modified APS circuit over traditional APS systems. Conclusions: Contrast-to-noise ratio for solid-state radiation detectors can be improved through additional pixel-based feedback loops.