Fast Locking Technologe In Wide-band Frequency Synthesizer Based On Fractional-N Phase-locked Loop

Frequency synthesis is a technology that uses several stable and accurate frequency sources to generate high-stability and high-accuracy reference frequencies through a series of processing technologies.Frequency synthesizer is a key component in wireless communication systems.It is widely used in transceivers,radars,communication equipment,testing instruments and other electronic equipment.Frequency hopping communication is a kind of communication method with strong anti-interference performance generated by frequency synthesis technology,which is put forward for the problems of eavesdropping and interference often encountered in traditional wireless communication.As a key indicator of frequency hopping communication closely related to its anti-interference performance,Frequency hopping speed has been a hot research topic in the field of electronic countermeasures at home and abroad in recent years.Because of its high frequency accuracy and strong anti-interference ability,phase-locked loop is popular in modern frequency synthesis technology.For frequency synthesizer based on phase-locked loop,the key to improve the frequency hopping speed is to increase the locking speed of the phase-locked loop.For the application background above,this paper first introduces the concept and development status of frequency synthesis technology.Then the phase-locked loop is put forward,As a key technology of coherent indirect frequency synthesis,phase-locked loop has the advantages of stable and accurate output signals compared with traditional frequency synthesis technology.Recently,A new type of phase-locked loop with Fractional divider has emerged.This kind of phase-locked loop can meet the requirements of small frequency stepping on the basis of ensuring a higher phase-detecting frequency,which further improves the noise performance of the loop.Secondly,the basic theory and basic analysis methods of phase-locked loop are elaborated,The definition and estimation methods of phase noise and spurs are given.Then The fast locking technology is analyzed by introduce several effective method at home and abroad improving fast lock performance,And the appropriate phase-locked chip is selected.when the high-integration phase-locked loop chip is applied to the fast lock frequency synthesizer,the fast lock function provided by the chip usually can not effectively improve the lock time.In response to this situation,the verification and analysis of fast-locking in the phase-locked loop based on the chip is proposed.Combine with the method of variable loop bandwidth,the specific design method of the fast lock frequency synthesizer is given.In the end,the design and workflow from the scheme design to the PCB layout to the system debugging are summarized in detail,and the highly integrated broadband frequency synthesizer based on phase-locked loop is completed.The practical application of the fast-locking function of the chip ADF4350 successfully solves the contradiction between lock time and low phase noise or low spur by changing the loop bandwidth when locking,finally,shorter lock time and better spur and phase noise indicators are achieved.In addition,for practical application considerations,on the base of the single-loop fast-locking frequency synthesizer,a fast-hopping frequency synthesize is designed by utilizing the "double-ring ping-pong" frequency hopping method,which can be a very proper example for the application of ADF4350 and other similar phase-locked loop chips.