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。　-Top-down phase-locked loop based on the modeling method in MATLAB environment DPLL set up a complete simulation model, and use of digital phase-locked loop SIMULINK simulation mod