Time delay and integration

A Time Delay and Integration (TDI) clock is used to synchronize the movement of charged packets in a Charged Coupled Device (CCD) with that of another movement. For example, in some digital x-ray mammography systems, the x-ray tube and CCD detector move across the breast at a speed V+. At the same time, the CCD detector reads out the information in the opposite direction at speed V-. This compensatory motion essentially freezes the motion of the detected x-ray information. The TDI clock ensures that speed V+ equals V-.