The Research Of Digital Down Conversion Technology In Software Radio

Software radio is one of the hotspots in radio communication and military research. Due to the poor processing speed of A/D/A conversion and DSP processor, Software radio often adopts inter- specific schemes based on digital conversion technology. That is to say, by using specific DDC&DUC or running relevant algorithm , software radio transforms the sampling rate to enable DSP processors bring real-time signal processing to success. In this dissertation, signal processing of DDC is investigated, and the design of some key components in DDC is focused on.Because software radio is broad-band , open and easily-upgrated system, it requires NCO produce digital swatch signal with modulated-frequency and high resolution. Simultantiey, direct digital synthesizer (DDS) introduces the new idea of phasic progression and its output frequency can be controlled by programmable parameter , so it takes on many virtues such as high resolution and flexibility. Therefore, the DOS technology is adopted in NCO's design.DDS technology possess many virtues descripted above, but yamp , especially the vamp from phase truncation, is also very important. Therefore DDS's mechanism and phase truncation yamp are investigated in detail , then a random generator is cesigned and applicated in DDC, in order to choke back the periodic phase truncation yamp.In the first place, the dissertation presents the theory of signal processing and mechanism in DDC, then dissertates the design of numerically-controlled oscillator(NCO) and mixer. In the course of design, schematics, VHDL, LPM, MAX+plusII and FLEX10K are all applicated. Finally, on the basis of result of logic synthesis, the utilization rate of FLEXlOK's logic resource is analyzed.