Cyclone™ FPGA具有锁相环（PLL）和全局时钟网络，提供完整的时钟管理方案。Cyclone PLL具有时钟倍频和分频、相位偏移、可编程占空比和外部时钟输出，进行系统级的时钟管理和偏移控制。Altera® Quartus® II软件无需任何外部器件，就可以启用Cyclone PLL和相关功能。本文将介绍如何设计和使用Cyclone PLL功能。 PLL常用于同步内部器件时钟和外部时钟，使内部工作的时钟频率比外部时钟更高，时钟延迟和时钟偏移最小，减小或调整时钟

this describes the clock skew problems and how to resove it by using various techniques in digital design and implementation

FPGA设计中几个基本问题的分析及解决 多时钟系统，时钟设计，时钟歪斜，门控时钟，毛刺信号及其消除，FPGA中的延时设计，FPGA设计应注意的其它问题-FPGA design analysis of a few basic questions and solve multi-clock system, clock design, clock skew, clock gating, and the elimination of burr signal, FPGA design of the d

DCM includes a clock delay locked loop used to minimize clock skew for Spartan-3, Virtex-II, Virtex-II Pro, and Virtex-II Pro X devices. DCM synchronizes the clock signal at the feedback clock input (CLKFB) to the clock signal at the input clock