DDS技术在高频石英晶体测试系统中的应用

在此介绍了一种以DDS芯片AD9912作为信号源的高频石英晶体测试系统。AD9912是一款直接数字频率合成芯片。一方面，AD9912内部时钟速度可高达1GSPS，并集成了14位数／模转换器，可以直接输出400MHz信号；另一方面，AD9912的频率控制字为48位，可以小于4μHz的分辨率输出信号。由于采用了DDS芯片AD9912作为信号源，所设计的石英晶体测试系统能够在20kHz～400MHz范围内测试石英晶体的串联谐振频率。与国内目前普遍使用的基于振荡器和阻抗计测试方法的测试仪相比，该测试系统具有测试频率范围宽、重复精度高等优点。

Application of DDS technology in quartz crystal high-frequency testing system

A kind of quartz crystal high-frequency testing system taking a DDS chip AD9912 as the signal source is intro- duced in this paper. AD9912 is a direct digital synthesis chip. On One hand, its internal clock speed is up to 1 GSPS and it in- tegrates a 14-bit digit-to-analog converter, so it can directly output 400 MHz signal; on another hand, its frequency tuning word is 48-bit and it can synthesize frequencies in step sizes no larger than 4 μHz. Since it uses the DDS chip AD9912 as the signal source, the quartz crystal high-frequency testing system can test the resonant frequency of quartz crystal in the range of 20 kHz-400 MHz. Compared with the testing instruments widely used in China, which are based on oscillator and impedance testing method, this testing system features a wide frequency testing range and b.igh repeat accuracy.