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

DDR SDRAM控制器的VHDL源代码，含详细设计文档。 The DDR, DCM, and SelectI/O™ features in the Virtex™ -II architecture make it the perfect choice for implementing a controller of a Double Data Rate (DDR) SDRAM. The Digital Clock Manager (DCM) provides t

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

Delay locked loop Exmples