建立了一个基于新型光学/数字成像系统(三次位相板编码系统-CPP系统)的信噪比模型.该模型主要考虑了读出噪音及散粒噪音两种探测器噪音,同时加入光学系统调制传递函数(Modulation Transfer Function,MTF)的影响,考虑不同空间频率下噪音对信号的影响,推导出频率信噪比模型.利用该模型对一个光学/数字成像系统进行信噪比分析,结果表明,利用该模型进行分析后此光学系统可达到的理论焦深扩展范围为5个波长. A signal-to-noise ratio model based on the new optical / digital imaging system (CPP-CPP system) was established, which mainly considered the noise of both detector noise and shot noise, and added optical system modulation and transmission (Modulation Transfer Function, MTF), the signal-to-noise ratio (SNR) model is deduced considering the effects of noise on the signals at different spatial frequencies.The signal to noise ratio of an optical / digital imaging system is analyzed using this model. After the model is analyzed, the achievable theoretical depth of focus extended by this optical system is 5 wavelengths.