中文说明：
基于锁相环Top-down的建模方法在MATLAB环境下建立数字锁相环完整的仿真模型，并用SIMULINK对数字锁相环的仿真模型进行仿真。
English Description：
Based on the top-down modeling method of PLL, a complete simulation model of digital PLL is established in Matlab environment, and the simulation model of digital PLL is simulated with Simulink