Analysis of spur property of direct digital synthesis signal
Yue Xiang, Qin Shi · Journal of Tsinghua University(Science and Technology) · 2000
DDS (direct digital synthesizers) error model has been dcvcloped to calculate the amplitude and position of spurious noise lines in the output spectrum of DDS. The model shows that these spurious lines come from three sources: the truncation of the phase accumulator, the finite precision of the sine lookup table, and the nonlinearity of the digital to analog converter. The spurious lines caused by those sources can be classified into different sets according to the greatest common divisor of the DDS frequency control word (FCW) and 2 N, where N is the word length of the DDS phase accumulator. The spurious lines in each set of spectra are all related. A new method based on this relation is introduced to calculate the amplitude and position of these spurious lines. The spurious lines predicted by this method compare well with the results of number simulations. This efficient method can resolve all the spurious spectra after only N discrete Fourier transforms.