说明：  仿真了锁相环工作到一定时间后达到锁定状态的过程，程序采用的是一阶RC低通滤波器即二阶一型环
(Simulation of the PLL to work until after a certain period of time to achieve lock-state process, the procedure is used first-order RC low-pass filter that is second-order one-ring)