集成鎖相環提供更高的頻率性能，提高用戶的利益

　　鎖相環（PLL）是電子系統中最通用，靈活和有價值的電路配置之一，導致其在許多應用中的應用。它是用于時鐘同步和恢復，作為頻率合成器，并作為一個可調諧振蕩器，僅舉幾個例子。其結果是，PLL被發現在許多射頻設備項目，包括無線電接收機和測試設備。根據其具體實施，它可以從近DC到GHz和更高的頻率，實現了系統和電路中的許多關鍵角色。

　　PLL是一個閉環（負反饋）架構，基本鎖相環由這些塊組成（圖1）：

　　Figure 1： A basic PLL is a closed-loop， negative feedback system where the error between a reference signal and the VCO output is used to correct that output; the low-pass filter is a critical element in establishing the loop’s dynamics.

　　A phase/frequency detector （PFD） （often simply called a phase-detector PD） compares an input signal to a reference signal and produces an error signal which is proportional to their phase difference （keep in mind that phase and frequency are intimately related， as frequency is the time derivative of phase）; the phase-detector output usually goes to a charge pump which transforms the small current difference into a larger voltage

　　A low-pass filter （LPF）， which shapes the spectrum of the error signal; the design of this filter is often a combination of engineering science and intuitive art， and is a major factor in setting many of the dynamics of PLL operation

　　A voltage-controlled oscillator （VCO） with output phase/frequency controlled by the error signal

　　An optional frequency divider at the VCO output， which causes the PLL to generate frequencies at a multiple factor N of the reference frequency; N can be an integer， and many PLL designs support fractional-N non-integer division