| Image acquisition in low light level (LLL) plays an important role in the military, astronomy, medicine and many other fields. The characteristics of LLL imaging vary in different experimental fields. Electron Multiplying CCD (EMCCD) has the capabilities of LLL image acquisition as well as inheriting the CCD in traditional characteristics, which can meet the requirement of LLL image acquisition in different fields. However, due to changes in its structure, EMCCD needs dedicated circuit to control it, and the design of the circuit directly affects the quality of the output image. Hence, it is a must to design a stable, low-noise EMCCD imaging system.To control EMCCD, two major problems involving the control of the EMCCD chip and the transmission of the image data should be solved. The CCD97 is chosen as the EMCCD chip in this paper. Based on the structural and working principle of CCD97, the characteristics of the control signal and the output signal are analyzed. The circuit of the system is built by discrete components and functional devices. To reduce the generated heat, sine wave signal is chosen as the multiply drive signal for EMCCD. A dual-channel 14-bit A/D converter chip is used to quantify the output signal. The Camera Link transfer protocol is applied to transfer the image data and the RS232 serial protocol is employed to receive control instruction during working or testing. Based on the principle of the basic noise in power supply, our research focuses on the design of the power supply unit with high efficiency and low noise level to provide power supply and adjust the multiplication gain for the system.The system test shows that the imaging system for EMCCD has the ability for rapidly imaging with a grayscale resolution of 14-bit and a transmission rate of 25 frames per second. In addition, the grayscale level of the image has a good linearity in long time integration. In a word, the EMCCD imaging control system can meet the needs of low light level imaging. |
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