Abstract
New techniques to efficiently increase the frequency resolution of digital sinusoidal oscillators based on look-up-table (LUT) methods are proposed. The increase in frequency resolution is achieved while maintaining very low level of spurious harmonic distortion. The proposed techniques increase the LUT length to a level at which the spurious harmonic distortion is negligible. The first proposed technique is based on partitioning the address register into three sets and dividing the available LUT length into three smaller tables addressed according to the content of the address register sets. The second proposed technique utilizes one LUT and interpolates the values of the samples that are not stored in the table. The third proposed technique is similar to the first technique with the advantage of simpler implementation and lower levels of spurious harmonic distortion. The proposed techniques are simulated and their performance is compared with that of the direct LUT and trigonometric interpolation methods. The simulation results show that the proposed techniques are superior to both direct LUT and trigonometric interpolation methods.
Highlights
Digital sinusoidal oscillators are essential elements in many applications
We propose three new techniques to increase the frequency resolution and at the same time reduce the spurious harmonic distortion associated with fractional addressing of the LUT
The proposed techniques have the advantage of increased frequency resolution and reduced spurious harmonic distortion over both the conventional LUT digital sinusoidal oscillator and that based on the trigonometric interpolation method
Summary
Digital sinusoidal oscillators are essential elements in many applications. They are used in communications, music synthesis, control, radar, and digital signal processing. The major disadvantage of a digital sinusoidal oscillator implemented using LUT method [1] is the spurious harmonic distortion due to fractional addressing of the memory [2, 3]. The fractional addressing is necessary to increase the effective LUT length and the frequency resolution of the digital sinusoidal oscillator. The spurious harmonic distortion can be reduced by the trigonometric interpolation method [4]. We propose three new techniques to increase the frequency resolution and at the same time reduce the spurious harmonic distortion associated with fractional addressing of the LUT. The proposed techniques have the advantage of increased frequency resolution and reduced spurious harmonic distortion over both the conventional LUT digital sinusoidal oscillator and that based on the trigonometric interpolation method.
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