说明：  AD9914是一款直接数字频率合成器(DDS)，内置一个12位数模转换器，目标工作速率最高达3.5 GSPS，产生单音信号，双音信号以及调幅调相信号
(AD9914 is a direct digital frequency synthesizer (DDS) with a 12 digit analog converter with a target operating rate of up to 3.5 GSPS, producing a single tone signal, a dual tone signal and a phase modulation signal.)