针对锁频锁相器( Phase and Frequency Detector, PFD) 应用于低信噪比、大频偏的条件, 通过理论分析和仿真验证阐述了窗口类型对系统频偏捕获速度、范围、噪声门限及相位噪声抖动的影响机理. 推导出等效相位噪声功率谱密度的表达式. 证明了大窗口具有更低的噪声门限和更小的稳态相位抖动, 但捕获速度较慢. 为了提高捕获速度, 对鉴相器输出值取极性运算得到改进的PFD 算法. 新算法不仅能增加鉴相增益提高捕获速度 还可以减少等效噪声功率谱密度降低相位抖动 同时新算法不需要乘法器便于硬件实现. 最后新算法的性能通过仿真得到了验证.-For frequency-locking phase-locked (Phase and the Frequency Detector PFD) conditions applied to the low signal to noise ratio, frequency offset, through theoretical analysis and simulation described the capture speed of the window type, the system frequency deviation, range, noise threshold and phase noise jitter mechanism. equivalent phase noise power spectral density expression is derived to prove the large windows with a lower noise threshold and the steady-state phase jitter, but to capture slow in order to improve the capture speed, The phase detector output value to take the polarity operator improved PFD algorithm. new algorithm not only can increase the phase gain to improve the capture speed　can also reduce the equivalent noise power spectral density to reduce the phase jitter　new algorithm does not require a multiplier to facilitate hardware implementation performance of the last new algorithm has been verified through simulation.