A CMOS Image Sensor With In-Pixel Two-Stage Charge Transfer for Fluorescence Lifetime Imaging

A CMOS image sensor for time-resolved fluorescence lifetime imaging with subnanosecond time resolution is presented. In order to analyze the fluorescence lifetime, the proposed CMOS image sensor has two charge transfer stages using a pinned photodiode structure in which the first charge transfer stage is for the time-resolved sifting of fluorescence in all the pixels simultaneously and the second charge transfer stage is for reading the signals in each pixel sequentially with correlated double sampling operation. A 0.18-mu m CMOS image sensor technology with a pinned photodiode process option is used for the implementation of a 256 x 256 CMOS image sensor. The decaying images and lifetimes of fura-2 solutions having different concentrations are successfully measured with a 250-ps time step using the CMOS image sensor and ultraviolet laser diode as a light source.