信噪比是微光像增强器的重要参数之一，其值的高低决定着微光成像系统在低照度条件下的探测距离和图像清晰度。根据线性系统信噪比链理论，借助系统噪声因子关系式，分析了微光像增强器的理论极限信噪比(S／N)_limit。在系统各级不附加任何噪声(即N_F=1)，或仅受输入光子及光电子数涨落噪声限制的理想条件下，给出像管不同量子效率(η)之最大信噪比(S／N)_limit的表达式；在η=1的极限情况下，求得该像管的理论极限信噪比(S／N)_limit≤64。

Signal-to-noise ratio (SNR) is an important parameter of image intensifiers,which determines the detection range and image quality of the photo-electronic imaging systems operating in low-light-level condition. On the basis of SNR chain theory of linear systems,the theoretical limiting SNR of the low-light-level image intensifier was analyzed by the noise factor expression of the system. The expression of maximum SNR for the photocathode quantum efficiency ηis given in the precondition of no additional noise in each part of the system,that is N_F=1,or in the ideal condition being restricted only by input photons and noise caused by the fluctuation of photoelectron quantity. The theoretical limiting SNR of the tube is ≤64,which is derived under the limiting condition of η=1.