环路滤波器是通信信号调制解调中最重要的一个部分，环路滤波器设计的好坏将直接影响到接收机的性能指标，二阶锁频辅助三阶锁相环路滤波器可以稳定跟踪具有加加速度的信号源，是现代通信中非常实用的技术，本文中详细编写了单载波信号产生模块、信道噪声模块、数字正交下变频模块、鉴频鉴相模块、环路滤波器模块，并包含了完整的testbench模块，对于初学者非常有用。(Loop filter is the most important part of communication signal modulation and demodulation. The design of loop filter will directly affect the performance index of receiver. The second-order frequency locking assisted third-order phase-locked loop filter can stably track the signal source with acceleration speed, which is a very practical technology in modern communication. In this paper, the single carrier signal generation module and channel noise are written in detail Sound module, digital orthogonal down conversion module, frequency and phase detection module, loop filter module, and contains a complete testbench module, which is very useful for beginners.)