一种基于FPGA的调制指数可调的数字化调频方案

A Method of Digitized FM with Controllable Modulation Index Based on FPGA

该方案实际上是一个输出频率受控的直接数字频率合成(DDS)系统。通过A/D转换器件将调制信号转换成数字信号,用该数字信号控制DDS的频率控制字,形成输出频率受模拟信号控制的正弦波,从而实现了调频。通过在A/D转换值后补零的方法,可控制调频波的调制指数。系统由FPGA实现。EDA软件Max+PlusⅡ的仿真和系统的实际输出波形都表明该数字化调频系统的调制指数可在很大范围内变化。

The digitized FM system is actually a Direct Digital Synthesis （DDS） system that the frequency of the output is controllable. The modulated signal which is converted into digital signal by A/D converter, and the frequency word of DDS is controlled by this digital signal, so the frequency of the output is determined by this modulated signal and realizes the FM. Also, we could change the FM index by adding zero behind the result of A/D converter. The system is realized by FPGA. The result of simulation is made by MAX-t-PLUS U and the actual wave form of system both show that FM index can be changed in large scale.