Optimum Operation Mode Of Electron Muliplying CCDs Based On The Noise Performance

From the low light level imaging system features we can see, low light level images are different from visible light images. They repeatedly experience photoelectric conversion and electron multiplying. Since the low illumination and poor background, the optical informantion obtained by the system is very weak. For this reason, the output image is accompanied by evident random flicker noise. The lower the illumination, the higher the noise. Besides, the contrast and brightness of low light level images decrease so that the signal to noise ratio and resolution of the output image are low. It is difficult to observe and recognize. Therefore, Noise is a key factor which constraints the limit performance of low light level imaging systems. In order to improve the image quality of the system and achieve the optimum condition, it is necessary to study the noise characteristics of the system. Then we can inprove the signal to noise ratio, enhance the visual effect, increase the range of visibility and optimize the system performance. The electron multiplying CCD is a new type of low light level imaging device. Due to its low noise, high sensitivity and high dynamic range, the electron multiplying CCD has great development potential and application prospects. Studying the noise characteristics of electron multiplying CCDs contributes to a profound understanding of the noise laws in the imaging process, thus lowering image noise, enhancing image quality, further improving the imaging performance of the electron multiplying CCD and making it work at the optimum mode.In this paper, we start with the working principle of the electron multiplying CCD. Various noise components of the electron multiplying CCD and their generating mechanism are discussed in detail, including photon shot noise, dark current noise, clock induced charge noise and readout noise. Noise factor of the electron multiplying CCD is discussed and its theoretical value is shown. The noise factor quantitatively describes input and output characteristics of the electron multiplying register and the additional noise introduced by signal multiplication process. A mathematical model of total noise of the electron multiplier CCD is established. This chapter lays a foundation for further study in the noise characteristics of electron multiplying CCD.All the imaging devices have their corresponding operating mode. According to the device design and manufacturing process, selecting an appropriate operation mode will make the device work at the best condition. Based on the noise characteristics of the electron multiplying CCD, the performance of dark current and clock induced charge at different operating modes are studied. The sum of dark current noise and clock induced charge noise is taken as a selection basis of the operation mode of the device. The noise performances of the electron multiplying CCD at different working modes are simulated through specific device parameters. The integration time is taken as the critical condition to determine the operation mode of the electron multiplying CCD. This method provides a practical and reliable theoretical basis for the operation mode selection of the electron multiplying CCD. It also contributes to a better understanding of the working condition and to design high performance devices.In the electron multiplying CCD, signal charge and dark current are amplified at the same time. Therefore, it is important to control the dark current level. Shockley-Read-Hal theory is applied to describe the generation progress of surface dark current. Recovery characteristic time of surface dark current is described through a quantitative analysis. Periodic inverted mode is proposed based on the timing character. The electron multiplying CCD periodically switches from inverted mode to non-inverted mode by clock modulation. Then the surface dark current of the electron multiplying CCD is suppressed dynamically. The detection sensitivity and signal to noise ratio of the electron multiplying CCD are further improved and the device operates at the optimum mode. This mode simplifies the manufacturing process of the electron multiplier CCD and reduces the processing difficulty. It is of important significance for improving the detection sensitivity and signal to noise ratio of the system.Signal to noise ratio is an important parameter for characterizing the limit detection characteristic of the electron multiplying CCD. Based on the signal to noise ratio theory of the linear system, the limit detection performance of the electron multiplying CCD is analyzed. Signal to noise ratio limit theoretical models of the electron multiplying CCD is established separately when the gain is zero or infinite. According to the length of integration time, signal to noise ratio models of the electron multiplying CCD are simplified and divided into different noise leading areas. The effects of pixel binning on the signal to noise ratio of the electron multiplying CCD are discussed. Signal to noise ratio performances of the ICCD and electron multiplying CCD are compared and the limit detection characteristics of two kinds of low light level imaging systems are evaluated. It is usefull for better guiding the practical applications of these two kinds of low light level imaging systems.Taking into account the need of scientific applications, the performance parameters test of the electron multiplying CCD imaging system is studied. Based on the photon transfer technique of the CCD, we make improvement and establish a new theoretical mode. A measurement method of specific performance parameters of the electron multiplying CCD is proposed. At the basis of theoretical research, an experimental platform is built to complete the parameters test of the electron multiplying CCD imaging system, including convert gain, full well, multiplication gain, resdout noise, dark current noise, clock induce charge noise, noise factor and so on. This method enables the measurement of various noise components of the electron multiplying CCD. The experimental results are really good and agree with the datasheet. It solves the problems which have troubled the scientists for many years.