Title :
Numerical distortion in single-tone DDS
Author_Institution :
Dept. of Telecommun., Budapest Univ.
Abstract :
Spurious performance of direct digital synthesis (DDS) is partly caused by two quantization operations in its numerical (i.e. digital) part. These errors are deterministic and periodic in the time domain, therefore they appear as line spectra (undesired components: spurs) in the frequency domain. Hence it is quite natural to analyze the effects by DFT (discrete Fourier transform). The amplitude quantization (AQ), being present permanently, causes harmonically related spurs, while phase truncation (PT) produces spurs around the output frequency by phase modulation. However, as a consequence of DDS sampling process, spurs would be folding back into the DDS bandwidth (first Nyquist zone) and possibly overlapping. A simple procedure is presented for evaluating location and level of spurs, which are due to numerical distortion in a standard DDS system. Examples using an interactive math tool are available online
Keywords :
direct digital synthesis; discrete Fourier transforms; phase modulation; quantisation (signal); DFT; amplitude quantization; direct digital synthesis; discrete Fourier transform; first Nyquist zone; harmonically related spurs; line spectra; numerical distortion; overlapping; phase modulation; phase truncation; quantization operations; single-tone DDS; Application software; Clocks; Discrete Fourier transforms; Frequency synthesizers; Large scale integration; Oscillators; Phase modulation; Quantization; Table lookup; Tuning;
Conference_Titel :
Instrumentation and Measurement Technology Conference, 2001. IMTC 2001. Proceedings of the 18th IEEE
Conference_Location :
Budapest
Print_ISBN :
0-7803-6646-8
DOI :
10.1109/IMTC.2001.928173
