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

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