By incorporating on-chip multiplication gain, the electron multiplying CCD achieves, in an all solid-state sensor, the single-photon detection sensitivity typical of intensified or electron-bombarded CCDs at much lower cost and without compromising the quantum efficiency and resolution characteristics of the conventional CCD structure.
Time Delay Integration (TDI) is an imaging process in which a frame transfer image sensor produces a continuous video image of a moving two-dimensional object. The translation of the specimen is exactly synchronized with the vertical charge transfer of each pixel on the CCD. This process offers on-the-fly integration of signal intensity of a moving object. By altering the speed of image motion and the related charge transfer, total integration time can be regulated. In addition, by providing more or less pixels in the vertical direction, total integration time can be adjusted at a fixed specimen speed.
This very flexible manner of image integration offers unique capabilities. Spatial resolution is limited only by the optical relationship of the optics and size of the pixels in the array. The image size in the horizontal direction is limited only by the number of horizontal pixels in the array and the image size in the vertical direction is limited only by the travel of the scanning device. A continuous image of any vertical size is possible and the speed of image acquisition at both high and low light levels is much faster than with raster scanning or step and repeat image stitching systems.