Array Of Dds Spurious Suppression Technique

Direct Digital Frequency Synthesis is a frequency synthesis method emerging in recent years,. DDS technology has a lot of advantages, such as high frequency resolution, high-frequency switching speed, phase-continuous frequency switching and easy for modulation, etc., so it has been widely used in communications, radar, navigation, remote telemetry, instrumentation and many other fields. DDS is made up mainly by the phase accumulator, sine lookup table ROM, DAC low-pass filter and so on. While DDS has so many advantages, because of the use of all-digital architecture different from the traditional frequency synthesis methods, as compared with the other frequency synthesizer, the output frequency bandwidth DDS is relatively narrow and the spurious is relatively much more, especially when increase the output frequency the spurious performance become worse. To some extent, these disadvantages limit the application of DDS.This paper describes the development of frequency synthesis technology, as well as several common frequency synthesis techniques, and lists several important technical parameters of one frequency synthesizer. After the introduction of DDS's basic structure and working principle, the output signal's spectrum characteristics of an ideal DDS is analyzed, then there is an analysis of the output spectrum of DDS with phase-truncation spurs, amplitude quantization spurs, as well as the error caused by the non-ideal properties of DAC. The phase-truncation spurs and amplitude quantization spurs have also been reflected in the simulation. What's more, there are many other spurious output found in the actual test of DDS chip, and these are related to the DDS's structure and manufacturing techniques.Further discussion on DDS spurious suppression methods are made on the basis of the study of DDS output spectrum characteristics, these methods include the ROM compression techniques, phase or amplitude jitter, parallel form of DDS and so on, which have played a significant effect on DDS spurious suppression. A cascade form of a non-truncated DDS program is analyzed specially, followed by a simulation on FPGA platform with a model of DDS built with VHDL, the hardware tests is carried out in succession.This paper focuses on the cascade DDS program, the array DDS is combined with parallel DDS and cascaded DDS,it ultimately achieves a low spurious, widely cover output, it also requires more further study in the future.