Parallel Dds Frequency Source

Direct Digital frequency Synthesis, was advanced in early 1970s and has been developing owing to its entirely digital structure. However, it is for the structure ofthis type that the output frequency band of DOS is narrow and Spurious-Free Dynamic Range(SFDR) is bad. Especially, with the output band's expanding, the output SFDR is deteriorating. This is the key factor restricting DDS's applications. A frequency synthesizer is developed in the paper operating in linearity-step FM mode, and the single DDS technology can't meet the subject's requirements for the output frequency band and SFDR. Therefore, Coordinate DDSs technology, a novel method of frequency synthesis, is advanced in this paper.We choose AD9852, developed by ADI in US, whose RAMPED FSK mode of operation is applied in order to realize the function of linearity-step in the subject. In the Coordinate DDSs system the time-sharing output and the accurate synthesis of respective output frequency bands are the main problems, which are solved by Micro-processor PIC16F874 controlling the DATA FSK signal.In the paper, the principles of DDS are introduced firstly. Especially, the distribution and the restraint methods of the DDS spurs are discussed at length in this section. Secondly, the performance of AD9852 and PIC16F874 is introduced sketchily. Then, problems related to Coordinate DDSs system design with some author's special views are analyzed in the following section. At last, the arrangement, specifications, realizing and testing results of this subject are proposed in detail. The frequency source using the method of two DDSs' time-sharing output realized the operating mode the subject requiring. And the measured output frequency range is from 64MHz to 76MHz, and the output SFDR is -60dBc.It is proved that the Coordinate DDSs technology realizing the parameters requirements of the subject, and that the technology is feasible.