Fpga-based Ddc In The Spectrum Analyzer Design

The coming of Software Defined Radio (SDR) redefines the way to implement receivers. With the theory getting more matured and completed, SDR technology has been widely used in wireless communication system as well as electronic measurement and test equipment. Digital-Down Convert (DDC), one of the core technologies used by SDR receivers, is getting more and more extensive application in spectrum analyzer.With the digital-IF realization approach, handheld spectrum analyzer can meet the requirement of facility, reconfiguration and low power consumption. The core component in digital-IF module in this project is Digital-Down Converter of ISL5216 made by Intersil Corporation. This DDC in conjunction with FPGA compose the digital front end of handheld spectrum analyzer. But there is some limitation about this design. Above all, signal processing bandwidth of 1 MHz per single channel as well as 3 MHz with 4 channels cascaded can not satisfy the customer incremental requirements on analysis speed and bandwidth. In addition, the density of system integration and cost of BOM and efficiency of power consumption can be improved, if the functionality of the DDC can be implemented and embedded in FPGA. Taking above concerns into consideration, and Relying on the project of handheld spectrum analyzer, DDC based on Xilinx Spartan3A-DSP FPGA with characteristic of high processing frequency and signal bandwidth has already put into design and evaluation.After introducing basic theory and architecture of DDC and summarizing various key theory and algorithms such as digital quadrature transformation, CORDIC, CIC, HB, polyphase Filtering etc, which are used by different function unit, this paper exhibits the digital signal processing trait and resource in current primary FPGA. And then descript not only the design and implementation of NCO, MIXER, CIC, HB, and 255 orders FIR in detail, but also compare the different realization method and analyze the module's performance based on test data. Finally, demonstrate chief application of DDC applied in handheld spectrum analyzer.