The Digital Direct Frequency Synthesis Signal Generator Based On DSP

The Direct Digital Frequency Synthesis (DDS) is a kind of newfrequency synthesis method and also a revolution in the frequency synthesistechniques. With the development of digital integrated circuits andmicroelectronic techniques, DDS exhibits its advantages day by day.The direct digital frequency synthesizer is a kind of fully digitizedfrequency synthesizer, which consists of the phase accumulator, the sinelook-up table, the digital to analog convert: and the low pass filter. It is of highfrequency resolution, fast frequency switching speed, low phase noise, theability to switch frequencies while maintaining constant phase, and the agilityto producing arbitrary waveforms. Because of above features, DDS can beused in such fields as radar, communications, Electronic warfare andelectronic measurement instruments.The waveform generated by arbitrary waveform generators could bedivided into two kinds: sin-waveform and non-sine waveform. To thesin-waveform, data could be read out continuously or not, under this conditionthe distortion of waveform would become large which could be improved byfilter.To other non-sine waveform, the distortion of waveform could not bedecreased by simple filter because of harmonic. Data of the waveform shouldbe read out each by each when arbitrary waveform generated. To change theoutput frequency fo, it could be achieved by changing the reference clockfrequency fc or changing the number of waveform in the ROM. It is difficult togenerate arbitrary waveform by using commercial DDS chip because data inits ROM could not be changed.Based on the above analysis, considering the utility and performance, aDirect Digital Synthesis method was adopted to implement arbitrary waveformgenerator, in which data of the waveform was read out of waveform storageeach by each, and the desired waveform was outputted by D/A convert andlow-pass filter. The frequency of output waveform could be changed by alterthe frequency of reference clock or the step of counter.The full text is divided into six chapters altogether:Chapter one:After introduced the meaning of the subject research andsummarized the research current situations and development trends of thefrequency synthesis technology both at home and aboard, the basic structure,working principle,new structure and development trends of DDS wasdiscussed systemically.Chapter two: first synthesizes the direct digital frequency synthesizer inmathematics. Then in the case of no phase truncation error, no waveformROM finite word length effect ,and ideal D/A converter ,the spectrumcharacteristic of direct digital frequency synthesizer output is analyze.Chapter three:The key technology of the hardware design for DDS signalgenerator was introduced including control module,keyboard and displaymodule,memorizer module and PMU etc. During the realize processing,TMS320C5402 of TI company being chosen as processor, taking fulladvantage of its integration and fast speed, and provided the hardwarerealization combining with the FLASH memory and rounding analoguecircuit.Chapter four is software design part of system. Software developenvironment, code generator and test tools are introduced at the verybeginning. General flow and the flow of interrupt service routine and someparts of sub-modules are presented in the later part.Chapter five is result and error analysis part of system testing. Some outputwaveforms are given, and system error and man-made error which probablyexist are also indicated.Chapter six: The full text is summarized, summarized the research workand achievement of this text in an all-round way, analyzed the place to alsoneed to perfect further in the design, put forward the corresponding suggestionfor the work.