基于AD9858的DDS＋PLL频率合成器

基于锁相频率合成技术（PLL）和直接数字频率合成技术（DDS）各有其优缺点,文章将两者结合,提出设计方案,并给出了主要的硬件电路设计,以产生符合预期要求的雷达信号。设计以AD9858为核心器件,输出DDS频率信号,为PLL提供参考输入信号。PLL中的鉴相器采用ADF4107,同时利用FPGA对两者进行方便的控制,可以获得较快的频率转换时间,相位噪声为-90dBc/Hz且杂散优于-70dBc的雷达信号。最终得到一个综合指标较高的系统。

DDS+PLL Frequency Synthesizer Based on AD9858

Phase locked loop and direct digital frequency synthesis technology have their merits and disadvantages respectively, so it is feasible to combine the 2 methods, perform their merits and to overcome their disadvantages, which can generate wideband and super wideband radar signal expected, and it puts up with design scheme and main hardware circuit design. In the design, with AD9858 as the core device, output of DDS is used to stimulate PLL, namely DDS provides the reference signal of PLL, with ADF4107 as the phase detector of PLL. Then FPGA controls conveniently DDS and PLL by procedures. As a result, the output signal has the fast conversion time, phase noise of which is -90 dBc/Hz, and the spur of which is better than -70 dBc. So this system has a high-performance aggregative indicator.