Abstract: According to the output of DDS spectral characteristics and the Cordic algorithm，the stepped rotation angle and multi-regional phase mapping methods are taken to solve the uncertain iteration direction and non-integer period of DDS based on Cordic structure.The spectrum of the signal from the improved Cordic of DDS is pure and the spurious signal is suppressed.16-stage pipeline structure of DDS is designed with FPGA and VHDL.The study of Modelsim simulation and Quartus compilation shows effectiveness of these two improved methods with lower calculation errors of 10-5，less hardware consumption of 23％，and the band of SFDR is enlarged to 200 dB.

Key words: improved Cordic, Direct Digital Synthesizer（DDS）, spurious suppression, Field-Programmable Gate Array（FPGA）, iterate direction

摘要： 依据DDS（直接数字频率合成）输出频谱特性和Cordic（坐标旋转数字计算机）算法基本原理，针对基于Cordic结构的DDS设计中相位角迭代方向不确定性和旋转角度非整周期性的缺陷，采用了相位角分阶段旋转法和多区域相位映射法对Cordic结构的DDS进行改进。通过Matlab输出信号和频谱仿真验证了所用方法的正确性和可行性，使用VHDL语言设计出16级流水线结构的改进后Cordic型DDS。Quartus II综合编译和Modelsim仿真后得出改进后DDS计算误差为10-5、硬件消耗仅为23％、SFDR（无杂散动态范围）扩至200 dB。理论分析和实验结果证明了这两种方法改进综合后抑制杂散的有效性。

关键词: 改进型Cordic, 直接数字频率合成（DDS）, 杂散抑制, 现场可编程门阵列（FPGA）, 迭代方向