基于DDS的RF频率合成器的应用考虑ADI

简介：

问：AD9852在工作时温度达到80度以上，设计PCB时，应注意哪些方面？
答： You have to calculate the power dissipation. And please select the right package. When do layout, try to use the PCB"s ground to distribute the heat. refer to the EVB of AD9852 is a good practice.

问：1、在使用DDS+PLL来产生RF信号时，怎样精确控制输出的相位，如果可以是否可以直接用这种方案来实现数字相位调制？那么调制带宽和环路带宽选择什么样的关系比较合适？如果用AD9854实现QPSK调制，调制速率能达到多少？
2、DDS输出信号和参考时钟在相噪问题上是否也有一个可以估算的公式？
答： 1. When using a PLL loop driven by a DDS, there is no way to precisely determine the phase - that is determined by the PLL loop. It will be a function of the phase at the phase detector, which will be kept constant by the loop.

Modulation bandwidt

问：我构想用AD9857，使用边带抑制的办法来实现SSB，不知道这样的方法，在实际实现中是否可行？
答： It is reasonable.

问：请问当利用PLL倍频后，GHZ的频率的精度依然有那么高吗？
答： Yes, of course.

问：使用DDS作频率合成时   选择的采样频率 一般是输出频率几倍时
效果最佳？  比如输入10MHz   合成30MHz  一般选择输入几倍频较合适？
答： Normally, the input clock or the system clock should be 2 times faster than the output. For 30MHz output, the system clock should be faster than 60MHz. Some parts may have multilier in the part. Ad9954 doe example.

问：数模转换模数转换在现在在电子行业已经是不可缺的东西，我想问模拟信号转换的时候现在大都是转成精确的数字信号，不知道能否用模糊逻辑，让模拟信号进行模糊存储，现在数字信号转换的最高的精度是多少。谢谢！
答： The highest ADc resolution is 24 bit. And ADC/DAC is necessary for almost all the system.

问：1，对基于dds的射频信号进行调幅有哪些方式？
2，如果用乘法器进行调幅，想输出15mhz的数字信号，一个周期内至少采样8点，又没有相应的乘法器完成调幅功能？
3，如果采用双d/a方式在模拟部分调幅，对幅度控制字数字化的dac的各种参数与哪些因素有关？

答： 1. I think you"re talking about QDUC series like AD9857 which has integrated Quadrature modulator. Then it can do 16QAM, 64QAM, 256QAM depending on your applications.
2. If you use multiplier for amplitude modulator, as multipier is analog devices

问：用DDS如何实现AM、FM、GFSK？
答： Please refer to the article from the link:
http://www.analog.com/UploadedFiles/Tutorials/54011189110016515183343533079104002517DDStutor.pdf

Or call 800 810 1742 for support

问：DDS如何与PLL结合用至更高频率？相噪如何测量？

答： Please refer to page 20-26 of the presentation. The phase noise is measured by the spectrum anlyser. Any technical support needed, feel free to contact 800 810 1742.

问：DDS输出信号频率的最大能支持到多少？DDS对后置ADC有什么特殊要求？
答： AD9858 can output up to 400MHz. But AD9858 is under the export control of American government.
DAC is integrated in DDS. The DAC in AD9858 is 10 bit.