高阶调制信号发生器可变参数基带模块设计

Design of Variable Parameter Baseband Module in High-order Modulation Signal Generator

基于FPGA可编程逻辑及NiosⅡ软核实现了高阶调制信号发生器设计,研究了奈奎斯特脉冲成型原理,分析了脉冲成型插值倍数、双边码元截断数、余弦滚降系数的选值,重点设计了基带处理模块部分的数字FIR脉冲成型滤波器,滤波器使用多相时变参数插值滤波结构,并针对AD9957串行IQ两路传输进一步优化了成型滤波FPGA逻辑结构,该方案大大节约了算法资源和逻辑单元.基带信号通过集成DDS+DAC的AD9957上变频模块实现载波调制,最后给出了Modelsim及Signal TapⅡ仿真图,并在示波器上显示了基带及调制信号的实验结果。

High-order modulation signal generator was implemented based on FPGA and NiosⅡ soft core. The Nyquist pulse forming principle was researched,and the interpolation multiple,truncation value of dual-edge code element,the coefficient of cosine roll-off were analyzed. The digital FIR pulse shaping filter of the baseband processing module was importantly designed. In order to save DSP resources and logic units, the multiphase time-varying coefficient interpolation filter structure was used and the FPGA logic structure of shaping filter was further optimized according to AD9957 IQ data path serial transmission. The carrier modulation of the baseband signals was implemented via using AD9957 upconverter with DDS ＋ DAC. Finally,the Modelsim ＆ Signal Tap Ⅱ simulation diagram was given and the baseband and modulation signals could be displayed on the oscilloscope.