| From the early 70s, when direct digital frequency synthesizer (DDS) technologywas put forward, it became the focus. Its high frequency switching speed and theexcellent frequency resolving attract large number of scientists to do further research onDDS. As a result, DDS has gotten considerable progress.First of all, the basic theory of DDS and passive frequency multiplier as well astheir characteristics has been analyzed detailedly. By taking advantage of the low phasenoise properties, high frequency switching speed and the excellent frequency resolvingof DDS with the consideration of the target of the system, the frequency synthesizerbased on DDS and passive frequency multiplier has been devised. Then one×2, one×3 and one×5 frequency multipliers make the output frequency expand to X-band.Secondly the project has been reasoned roundly. Then the power performance hasbeen designed reasonably, and the feasibility about the phase noise, SFDR, hoppingtime, hopping step, bandwidth, has been analyzed. According to the request of thesystem, the DDS chip AD9858, the×2 frequency multiplier chip RK-2, the Schottkydiode multiplier HSMP3822 and HSMP8202, the amplifier and so on, have been chosento establish the system circuit. In this system, MCU PIC16F877A has been used for theinput of the DDS frequency control words under the software of MPLAB IDE. Forseveral filters of different bands which are key to the system, the simulation and designhave been done by combining the theoretical method with the software ADS, CST andFilter-Solution.Finally through the EMC design of the layout and grounding, the request has beenachieved by debugging all the whole circuits and programs time after time. Itsspecifications show as following: output frequency X-band, phase noise-105dBc/Hz@10kHz, SFDR-42dBc, harmonic restrain-40dBc, hopping time 240 ns. |
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