High resolution and low distortion digital look-up-table sinusoidal oscillators

Abstract

We propose two new methods to reduce the spurious harmonic distortion of a digital sinusoidal signal generated using the look-up-table (LUT) method. Spurious harmonic distortion arises when we try to interpolate the value of a sample that is not present in the LUT. The first proposed method depends on a real time evaluation of the missing sample value without the need for any additional LUT length. The second proposed method requires an additional table and some real time processing to calculate the value of the interpolated sample. The two proposed methods are simulated and their performance is compared with that of the existing methods; namely direct LUT, linear interpolation and trigonometric interpolation. The simulation results show that our proposed methods are superior to both direct LUT and linear interpolation methods. Moreover, for practical table lengths, the performance of our proposed methods is of the same order as that of the trigonometric interpolation method.