What are the major spectral impurity components of direct digital synthesizers?

Direct digital synthesizers (DDS) are excellent for fast frequency switching and fine tuning resolution, but their digital nature introduces specific types of spectral impurities. Because the waveform is constructed using discrete digital steps (quantization) and processed through a digital-to-analog converter (DAC), the mathematical rounding and DAC non-linearities generate spurious emissions, commonly called "spurs." These spurs appear as sharp, discrete frequencies in the output spectrum rather than as a general increase in broadband noise. Unlike traditional analog oscillators where harmonic distortion or broadband phase noise might be the primary concern, DDS impurities are mathematically tied to the clock frequency and the desired output frequency, showing up as distinct, unwanted peaks on a spectrum analyzer.