Research And Design Of A Low Phase Noise Frequency Source

With the continuous development of communication and electronic systems,the requirements on the performance of frequency sources are also increasing.Frequency sources occupy an important position in electronic communication systems.Frequency synthesis is a key technology for frequency source research.The development of frequency synthesis technology is an important means to achieve low phase noise and high spurious suppression of frequency sources.Therefore,the research of frequency synthesis technology is also imperative.The main research content of this paper is mainly based on a phase-locked frequency synthesis technology to achieve a low phase noise frequency source.The traditional phase-locked loop can achieve low phase noise,but the disadvantage is that the frequency conversion time is slow;direct frequency synthesis technology can achieve low phase noise and fast frequency hopping,but its narrow output frequency band is a problem.In order to satisfy the output broadband signal,fast frequency hopping is realized on the premise of ensuring low phase noise and low spur suppression.Finally,the "complex ring sampling and phase lock + DDS + frequency multiplication" scheme is determined and implemented.This topic is divided into the following three parts for research and implementation:1)Selection of the 3.5GHz point frequency source module device,cavity design and layout,and debugging of the post-circuit,mainly to achieve low-phase noise,high stability,and low spurious point-frequency signals with functional output.For low spurious requirements,double-loop phase locking is adopted.The first-stage phaselocking is used as the reference for the second-stage phase-locking.Microstrip coupling is used to suppress the spur in the ring.For low phase noise,low phase is used.Noise reference,and in-loop self-mixing structure,using analog phase detector to achieve analog phase lock;finally achieve output point frequency of 3.5GHz,phase noise-117dBc/Hz@1KHz,-126dBc/Hz@10KHz,spurious suppression >70dBc.2)DDS module layout design,testing and debugging,mainly to achieve the output DC-1.4GHz wideband signal;FM time up to 100 ns,frequency stepping 10 KHz,output power-5 ± 2dBm3)The layout design of the frequency multiplication filter module mainly realizes the spur suppression of the output frequency signal and the frequency selection.Subsection filtering can be used to achieve good suppression of spurs.Through the final test of the complete machine,an output frequency signal of 5.4 GHz-10.8 GHz is achieved,and the output power is 10±2 dBm.At 10.8 GHz,the phase noise is-110 dBc/Hz@1KHz,the harmonic suppression is >60 d Bc,and the spur suppression is with 60 dBc and frequency hopping time of 90 ns,the research and design of wideband,low phase noise,low-spurious agility frequency sources are realized.