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本文提出了直接数字合成调频信号的一种新方法 ,它采用两级相位累加器对波形存储器寻址的结构。在第一级寻址结构中产生的调制信号幅度序列和载波频率值在加法器中相加 ,并将相加的结果作为第二级相位累加器的频率控制字 ;再将第二级寻址结构中产生的调频信号序列通过数字—模拟转换器和低通滤波器 ,就实现了调频信号的直接数字合成。仿真结果表明本文提出的直接数字合成调频信号的方法是可行的。采用该方法合成调频信号具有硬件电路简单 ,中心频率稳定度高 ,频率偏移大等优点。
This paper presents a new method of direct digital synthesis of the FM signal using a two-stage phase accumulator to address the structure of the waveform memory. The modulated signal amplitude sequence and the carrier frequency value generated in the first stage addressing structure are added in the adder and the result of the addition is used as the frequency control word of the second stage phase accumulator; The frequency modulated signal sequence generated in the structure realizes the direct digital synthesis of the frequency modulated signal through the digital-analog converter and the low-pass filter. Simulation results show that the proposed method of direct digital synthesis FM signal is feasible. The method of synthesizing the FM signal has the advantages of simple hardware circuit, high center frequency stability and large frequency offset.