The Design And Realization Of Digital Down Converter Based On Fpga

The foundamental idea of Software Defined Radio(SDR) is to establish an open,standard and modular universal hardware platform where the A/D converter is moved as close as possible to antenna and all of the communication function is realized by software.The aim is to research and develop a highly flexible and adaptable communication system. The coming of SDR innovates the way to implement the receivers.Recently,with the theory and application of SDR getting more matured,SDR technology has been widely used in cellular communication system as well as other civil and military wireless communication systems.Digital Down Converter(DDC) converts digitized IF data into baseband data and lowers the sampling rate of it which can be processed by a standard DSP microprocessor. It works after the A/D and is a core part of a SDR system.As a kind of special digital integrated chip configured by user,Field Programmable Gate Array(FPGA)has many advantages,such as miniaturization,low power dissipation,programmable logic, digitalization and velocity.FPGA has developed into important device for signal processing from a kind of flexible platform for logical design, since it's flexible and high-speed. FPGA has been applied extensively in many software radio productions.In this paper,a digital down converter(DDC) is designed and implemented by FPGA.The DDC can translate digital IF signal into baseband,and decimate The FPGA we choosed is the XC5VLX50T of Virtex-5 series produced by Xilinx Corparation..Using Top-Down design method,we first implement the design method of system DDC by referring the structure of GC4016.Then the whole design is divided into four basic units:the mixer unit,the CIC filter unit,the FIFO unit and the FIR filter unit.After that we design and realize these units and simulate and validate them.Finally,we design the whole system DDC and implement simulation and analysis of the results.In this paper,we first emphasize the basic theory of digital down convertinon, including bandpass signal sampling theory and the transition of sampling rate theory, which place foundation for the design of DDC.Then,we introduce the design principle of the basic units of DDC and inplement the design in ISE11.1.At the same time,we implement behavioral simulation and timing simulation using ModelSim and simulate and analyze the spectrum of the input and output signal using MATLAB.Finally,we design and realize system DDC and also implement behavioral simulation and timing simulation and simulate the spectrum of output data.Then we make a comparasion between the simulation results and academic results and give the analysis results and conclusion.