CCD成像系统中模拟前端噪声的研究

Research of Noise at Analog Front End in CCD Imaging System

为了提高CCD成像电子学系统的信噪比,设计了3种模拟前端电路,借助Orcad软件对它们的输出波形进行比较,分析电路结构与噪声产生机理的关系,从理论上比较3种电路结构的噪声水平。然后采用三线阵CCD探测器KLI8023和视频处理器TDA9965在硬件上实现3路模拟前端的电路设计,并通过X64-LVDS采集卡分别将3路图像信息显示在终端机上。每个像元成像50次,统计这50次的均方差(噪声)和信噪比,通过拟合曲线比较三路模拟前端的噪声水平和信噪比。在相同光照条件下,第1路的信噪比达到750dB,第3路只有600dB,验证了理论分析的结果,讨论不同像元频率、带宽与信噪比的关系,为今后的成像系统电路设计提供参考和实验依据。

In order to increase the signal noise ratio of the imaging system,three kinds of the analog front end design are proposed.By the electronic analysis software Orcad,the different output waveform of the three kinds of design are contrasted for analyzing the relationship between the circuit and the mechanism of noise generation.The noise level of the three circuits was compared theoretically.The PCB design of analog front end is finished with three-line array CCD KLI-8023 and 12 bit analog-to-digital interface TDA9965.The image information is displayed on the terminal computer through the frame grabber X64-LVDS.Every pixel images 50 times,and then the mean-square deviation（noise） of the 50 times is calculated.The noise level and SNR（signal noise ratio） at three-route front end are compared by the aid of fitting curves.Under the same condition of light signal,the SNR of the first route is 750 dB,and the SNR of the third route is only 600 dB.The result can testify pre-analysis in theory.The relationship among pixel frequency,bandwidth and SNR is discussed.The research can provide the experimental data as reference for the circuit design of imaging systems in future.