Research On Sampling-zero Order Holding Spurious Model And Nonlinear Distortion Suppression Technology Of DDS

Compared with traditional frequency synthesis techniques,DDS provides fast switching speed,reasonably low phase noise and high frequency resolution simultaneously.However,as a digital synthesis method,DDS suffers from a relatively bad spurious performance.In recent years,scholars have conducted a lot of research on the spur theory and spur suppression technology of DDS.This greatly improve the spurious performance of DDS.In this dissertation,the sample-zero order hold model is introduced from the analysis of ideal DDS spectrum to the analysis of phase truncation spurs,which expands the application of it.Also,it helps to analyze the spurs of actual DDS simply and intuitively.Using the spur analysis method based on the sample-zero order hold model,all the intermodulation distortions with relatively large magnitude are found to gather close to the carrier or harmonics like combs when the carrier approaches the fractional division of the reference frequency.The spurious performance of DDS is poor under this condition.In this dissertation,frequency decomposition is performed on the DAC nonlinear error function.The intermodulation distortion close to the carrier is found to be caused by the intermediate frequency part of it.Therefore,amplitude dither can be used to suppress the intermodulation distortion close to the carrier.This technique has the following advantages:large amount of suppressed spurs,wide applicable frequency band and easy implementation.In this dissertation,a low-spurious DDS with the frequency range of 10?2200 MHz is implemented based on FPGA and DAC.The measurement results show that amplitude dither can effectively suppress the intermodulation distortion close to the carrier in a wide band.The SFDR is better than 90 d Bc,which is improved by 10?20 d B.