The Research And Design Of Down Conversion Circuits In Software Radio

Software Defined Radio (Software Defined Radio), referred to as the software radio (Software Radio).Lots of communication functions can be realized by integrating function modules into wireless communication platform, it has broken the traditional communication systems that can only be realized by hardware. As an advanced method in system design, it is not only used in military communication equipment but also in the new generation of civil wireless communication system field because of its openness, flexibility and easy to upgrade extensions. Restricted to the level of digital signal processing devices, it is difficult to sampling the high-speed data stream directly in the front of RF, only through a digital frequency conversion to reduce signal sampling rate.Traditional digital down conversion is through a dedicated down conversion chip, but the function is relatively fixed, and the system compatibility is not good. In addition, it also increases the cost of updating the system. Based on the study of the frequency of digital basic theory and the current situation at domestic and abroad, a scheme of the IF signal down-sampling is presented, complete the conversion to a digital baseband signal by the digital IF signal spectrum moved, then process the baseband digital signal.Based on the analysis of DDC theory, realizing the conversion function by modular design. An NCO with high resolution is designed to mix intermediate frequency signal from ADC, spectrum is moved to baseband, with the CIC decimation filter and HB filter, then the signal down sampling, and finally the FIR filter, further optimization is taken to the former filters. With the IP core in FPGA, algorithm design of each module and the configuration of the FPGA, simulations are achieved in each module. Not only the bottleneck problem of digital signal processing in software radio is solved, but also meet the characteristics of flexibility and extension easily of the software radio. The simulation results of the main modules show that it solved the problem of signal frequency conversion and has a high application value.