Research On Key Technologies Of Scientific CCD Imaging System

More than 400 years ago, the telescope was born. Under the impetus of the development of astrophysics and space science, astronomical telescope with large aperture and large field of view has been the goal which astronomer seeks constantly. Throughout the development process of the astronomical telescope, the astronomical telescope has extended from the optical band to all part of the electromagnetic spectrum, from the simple images of the observed objects to the spectrum of celestial observed bodies, from ground-based telescopes to space telescope, and even the moon-based telescope in the future. Astronomer can comprehend the chemical composition, physical state, and radial velocity of objects, thus reveals the image of the early universe by using these astronomical telescopes.With the rapid development of electronic technology, the scientific grade charge coupled devices (CCD) detector based on semiconductor materials has been widely used in astronomical imaging observation due to the high quantum efficiency, the ultra low readout noise and the wide dynamic range. However, the exposure time of the detector is usually very long, even up to a few hours of exposure time, especially observeing the faint object. In such a long time scale, the dark current noise can not be ignored. At the same time, the thermal noise caused by the electronic thermal motion of the imaging system can also drown out the original signal. Therefore, it is necessary to take appropriate cryogenic refrigeration measures to reduce the contribution of dark current noise and thermal noise. On the other hand, the dark current noise and the thermal noise of the system after cryogenic refrigerationcan be ignored when the observed objects are bright and the exposure time is very short. But the signals of celestial bodies target after detected by detectors cross the back-end electronics readout system output and imaging, the image contains various noise components. At this time, the readout noise occupies the leading position, so scientific grade CCD imaging system need to have ultra low readout noise.The scientific grade CCD imaging system’s key components which affect the imaging quality include detector subassemblies, optical subassemblies, imaging controller subassemblies and cryogenic refrigeration subassemblies. The ultra low noise readout technology, the low noise power supply output technology and the high-speed data transmission technology of imaging controller subassemblies and cryogenic refrigeration technology of refrigeration subassemblies for the scientific grade CCD imaging system have discussed. And the system architecture is studied for the requirements of strong commonality, good expansibility and high integration degree in this thesis.The scientific grade CCD imaging system which uses the cryogenic refrigeration technology need to solve the problem of low temperature refrigeration, low temperature maintenance, equipment maintenance and so on. At the same time, the cryogenic refrigeration system needs to meet the cryogenic refrigeration requirements of most scientific grade CCD detectors. So as a prototype design, the cryogenic refrigeration system based on the liquid nitrogen refrigeration’s cryogenic dewar technology is designed in this thesis, and the liquid nitrogen dewar equipment has fabricated. The target of controllable cooling temperature have achieved by using the PID algorithm and PWM drive mode.The ultra low readout noise is the key indicator for the scientific grade CCD imaging system. And the quality of power system determines whether the index is up to the requirements. In order to meet the detection needs of different detectors, the power supply system with low noise voltage output is designed based on an extended hierarchical architecture in this thesis. In addition, scientific grade CCD detectors detect and process the radiation signal by using a high speed and high precision digital correlated double sampling (DCDS) technology. The hardware circuites of DCDS readout which includes the analog low pass filter and high speed and high precision ADC data acquisition have designed, and the preliminary sampling of the image signal is completed. At the same time, the digital correlated double sampling logic based on FPGA is designed, and the digital correlation double sampling algorithm is implemented in FPGA. In addition, the other implementation forms of the digital correlation double sampling algorithm are also discussed. As a support technology for high speed and high precision digital correlated double sampling technology, and in order to meet the transmission needs of the large-sized scientific grade CCD and CCD mosaic with high bandwidth and large data volume, high-speed data transmission technology is the essential technology of imaging controller subassemblies of the scientific grade CCD imaging system, so the high bandwidth data transmission technology based on USB 3.0 is adopted in this thesis.Finally, based on the ultra low noise readout technology, the low noise power supply output technology, the high bandwidth data transmission technology, and the cryogenic refrigeration technology, the scientific grade CCD imaging prototype system has processed a series of tests in this thesis, and obtained the stage results of imaging.The innovation points of this thesis are presented below:1) Based on the research on system architecture with strong commonality, good expansibility and high integration, the scientific grade CCD imaging prototype system has completed which is compatible with most scientific grade CCD detector.2) Based on liquid nitrogen refrigeration’s cryogenic dewar technology research, the cryogenic dewar system is designed which is with strong versatility, long time for liquid nitrogen maintaining, high vacuum, low leakage rate, controllable refrigeration temperature, wide temperature control range, high precision of temperature control, adjustable temperature control speed.3) Based on the research on low noise technology, the low noise power supply and the high speed and high precision digital correlated double sampling technology readout scheme are completed. Moreover, the related hardware circuit and algorithm are completed. This scheme has low readout noise, high bandwidth, high integration degree, little affected by the environment and devices and low cost characteristics.