Design of analog self-check figures for CCD imaging system

All of self-check figures are almost digital ones which can only test the FPGA component and image data transmitting component on the digital path and the video AD component is not tested because the complexity cannot satisfy the high reliability demands in space projects. A kind of circuit composed of the driving chip and the DAC chip was put forward. This circuit can generate analog signals which are similar to CCD video signals and make these signals directly couple with actual CCD signals into the input port of video AD. The key part was made up of a FPGA chip and a driver chip-EL7156. The FPGA chip generated the signals whose frequency was same as CCD video signals and then sends to the driver as logical input. The driver chip can switch low or high level according to the logical input. The low level was supplied by a DAC chip which is controlled by FPGA. When CCD circuit was working, FPGA can make the analog self-check circuit into three-state and have no effect to CCD work. Many experiments' results indicate that the analog self-check circuit and the CCD video circuit can work separately in different time with no interference.