Digital sinusoidal oscillators with high frequency resolution and low harmonic distortion

In this paper, we propose two new techniques to significantly improve the frequency resolution of a digital look-up-table (LUT) tunable sinusoidal oscillator. The proposed techniques are based on storing and reading the sine and cosine components of two sinusoidal functions that are not harmonically related and then evaluating the sine or cosine of the phase difference. The proposed techniques are shown to be very efficient in increasing the effective table length and, hence, the frequency resolution of the oscillator. Further performance improvement can be achieved by using interpolation methods as demonstrated. Simulation results verify the analytical results and show that the total harmonic distortion of the generated sinusoid is of the same order as that of the conventional digital LUT tunable sinusoidal oscillator.