Study On Phase Spurious Reduction Techniques Of DDS

Frequency synthesis technique is a method by which we can obtain a large numberof frequency source with the same stability and precision, through the addition,subtraction, multiplication, and division arithmetic of one or more reference sourcewith high stability and high precision clock. The developments of frequency synthesistechnique have experienced three stages: direct analog frequency synthesis technique,indirect frequency synthesis technique based on Phase-Locked Loop (PLL).Direct digital frequency synthesis (DDS) is a new signal synthesis techniquedeveloped very fast in recent years, by which we can generate a output signal oftunable frequency and phase with the use of data signal processing modules. Thegenerated signals can be used as a precise clock source with fixed frequency. The DDStechnique has such advantages as high frequency resolution, fast frequency switchingspeed, low phase noise and high stability, flexible output signals and easy use, andpeople are paying much attention on it.CORDIC algorithm is Coordinate Rotation Digital Computer, and can find its wayin computing trigonometric, hyperbolic, exponential and logarithmic functions. Theprocessing of signals with CORDIC algorithm can use only shifts and adds to perform,which easies the hardware implementations.In this paper, we simply introduced the frequency synthesis theory, with theemphasis on Direct Digital Frequency Synthesis, and summarize the research results ofthe sources and analysis on spurious signals in DDS, especially, the spurious spectrumof the phase truncation errors. Finally, we used DSP Builder software to design a DDScircuit based on CORDIC algorithm with the restraint technique of spurious spectrumof the phase truncation errors. In the end of the paper, the spectrum analysis of outputsignals was undertaken using FFT.