Analysis of Effect of Phase Dithering on SFDR of DDS

J.S. Mangat, Dr. Ravindra Kumar Sharma

DDS, Frequency Resolution, Frequency Synthesis, Phase dithering

Direct Digital Synthesizer (DDS) is a versatile programmable signal synthesis device. The important parameters of DDS are frequency resolution, number of frequency spots and frequency step size. These parameters are mainly dependant on the minimum phase increment of accumulator. Any improvement in these parameters requires width of the accumulator register to increase. As size of lookup memory grows exponentially with width of the accumulator output and hardware limitations restrict the size of memory which can be allocated for Lookup Table (LUT). To overcome this, accumulator output is truncated to match LUT size. Truncation, however results in generation of spurious signal which reduces Spurious Free Dynamic Range (SFDR). Phase dithering is employed to reduce truncation induced spurious. There are various phase dithering techniques available, some of the prominent ones are analyzed in this paper for their effect on SFDR.

https://dx.doi.org/10.31873/IJEAS.11.07.07