基于FPGA波形存储法合成大宽带DDS信号源设计与实现

Design of Wide-Band DDS Signal Generator by Using FPGA-based Direct Digital Waveform Storage Method

本文研究利用直接数字波形合成法(DDWS)进行直接数字合成(DDS)的设计原理,提出高速率、大带宽下用DDWS产生宽带雷达线性调频信号(LFM)的设计方法,给出系统硬件框图和软件设计模块.设计采用单片高速FPGA作为控制核心,双路单通道DAC芯片进行数模转换,利用ISE软件进行硬件程序设计.设计的信号源可产生时钟频率400 MHz、时宽16μs以内、带宽320 MHz以下的任意LFM.本文对基带信号的带内平坦度,脉冲压缩结果,调频斜率线性度,I/Q正交性等指标进行了分析.分析结果表明,杂散可以通过适当带宽的低通滤波器滤除,基带信号带内平坦度在0.452 dB之内,脉冲压缩最大旁瓣电平低于-12.8 dB.正交圆图、时频分析结果和理想情况相差不大.同时本设计在具体实践应用中获得良好的效果.

This article proposes a design method for high-speed wideband radar chirp signal generator based on the principle of using the direct digital waveform storage （DDWS） to perform the direct digital synthesis （DDS）, and gives out the system hardware and software design modules. The design employs a single-chip high-speed FPGA as the control core and double single-channel DAC for digital-to-analog conversion. It can generate any LFM signal that satisfies the conditions： clock frequency with 400 MHz, pulse width less than 16us, bandwidth within 320 MHz. Meanwhile, spurious frequencies, flatness in band, pulse compression re- sult, the linearity of the chirp rate and I/Q phase orthogonality are analyzed and compared. The results show that, the spurious frequencies can be filtered out through low-pass filter, the flatness in band is less than 0. 452 dB, the maximum side lobe level of the pulse compression results lower than - 12.8 dB, the orthogonal circle diagram and the time- frequency analysis agree with the ideal condition. This method is easy to be real- ized and suitable for engineering application.