Adaptive Sensitivity TDI CCD sensor

Abstract

The pixel-level adaptive sensitivity technology enables image sensors to acquire wide dynamic range scenes without loss of detail, by adjusting the sensitivity of each individual pixel according to the intensity of light incident upon it. An adaptive sensitivity TDI (time delay and integrate) CCD sensor test circuit has been designed and fabricated. The sensor comprises 18 TDI integration stages, with a horizontal resolution of 32 pixels. The level of charge integrated in each pixel is monitored as the pixel charge packet progresses across the TDI array. If the charge accumulates to above a certain threshold level, the pixel is discharged. Such 'conditional reset' mechanisms are inserted after the thirteenth stage and again after the seventeenth stage. Thus, each individual pixel may be integrated over either 1, 5, or all 18 stages. Since in TDI scanning, as in all linear imaging situations, there is no concept of 'frames' and each pixel is imaged only once, the intensity sensing and the decision on how long to integrate must be performed 'on the fly.' But, while in regular linear sensors the perpendicular fill factor is unlimited and complex control circuits may be placed next to the detectors, the two dimensional nature of TDI sensors presents much more demanding architectural and circuit challenges.