Low-frequency numerically controlled oscillator with decimal compensation and realization with FPGA

ZHU Feng1,2,3, LI Xiao-hui1,2, WANG Guo-yong1,2,3

(1. National Time Service Center, Chinese Academy of Sciences, Xi′an 710600, China;

2. Key Laboratory of Precision Navigation and Timing Technology, National Time Service Center,

Chinese Academy of Sciences, Xi′an 710600, China;

3. Graduate University of the Chinese Academy of Sciences, Beijing 100039, China)

Abstract: Bytaking low frequency signal as example, several factors of affecting the performance of the NCO (numerically controlled oscillator) are studied on the basis of analysing the principle of NCO. The influence of frequency control word error on the output frequency is discussed emphatically in the light of spurious characteristic, and it is presented to add the decimal compensation in the phase accumulator for reducing the threshold and improving the accuracy of the output signal. Finally an NCO with decimal compensation has been realized based on FPGA(field programmable gate array), which not only takes account of the hardware source, but also optimizes the system performance. The simulation has verified the feasibility of this method.

Key words: numerically controlled oscillator(NCO); look-up table; spurious characteristic; frequency control word; field programmable gate array(FPGA)