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为精确计算直接数字式合成 (DDS)技术输出频谱中杂散谱线的幅度和位置 ,建立了 DDS的杂散产生模型 ,确定了杂散的 3个主要来源 :相位累加器的截断 ,正弦函数表的有限精度和数模转换器的非线性。由此产生的杂散谱可根据 DDS的频率控制字和 2 N 的最大公约数进行分类 ,N是DDS相位累加器的字长。归于同类的杂散谱相互间存在对应关系。这一结果可用于精确计算杂散谱线的幅度和位置。将应用此方法预测的杂散谱线与数值仿真的结果进行了对比 ,二者完全符合。此方法只要做 N组离散傅立叶变换(DFT)就可以得到全部的杂散谱 ,大大提高了运算效率
In order to accurately calculate the amplitude and position of stray spectral lines in the output spectrum of direct digital synthesis (DDS) technique, a spurious generation model of DDS is established and three main sources of spurs are determined: truncation of phase accumulator, sinusoidal function The finite precision of the table and the nonlinearity of the D / A converter. The resulting spurious spectrum can be classified according to the frequency control word of the DDS and the greatest common divisor of 2 N, where N is the word length of the DDS phase accumulator. Attributed to the same type of spurious spectrum there is a correspondence between each other. This result can be used to accurately calculate the magnitude and position of stray lines. The stray lines predicted by this method are compared with the numerical simulation results, and the two are in good agreement. This method can get all the spurious spectra as long as N sets of discrete Fourier transform (DFT), greatly improving the computational efficiency