Spur Reduction Techniques in Sine Output Direct Digital Synthesizer

Abstract

The drawback of the direct digital synthesizer (DDS) is the high level of spurious frequencies [Rei93]. In this chapter we only concentrate on the spurs that are caused by the finite word length representation of phase and amplitude samples. The number of words in the ROM (phase to amplitude converter) will determine the phase quantization error, while the number of bits in the digital-to-analog converter (D/A-converter) will affect amplitude quantization. Therefore, it is desirable to increase the resolution of the ROM and D/A-converter. Unfortunately, larger ROM and D/A-converter resolutions mean higher power consumption, lower speed, and greatly increased costs. Memory compression techniques could be used to alleviate the problem, but the cost of different techniques is an increase in circuit complexity and distortions (see Section 6.2).