Design Of Broadband Low Spur And Fast Hop Frequency Source

With the development of electronic equipments and communication systems,frequency source as the key component in the wireless device is playing a more and more significant role.As a result,the frequency synthesis technology has been paid more and more attention.Comparing different synthesis technologies,the phase-locked loop can easily synthesis a required frequency signal and restrain spur emission.With its relatively low harmonic components,it's not necessary to design complex filter banks to filter out unwanted ingredients,which is quite beneficial to modularization,integration and miniaturization of a device.Given to these benefits,this paper completed the frequency source design based on phase-locked loop system.The main work of the paper includes:(1)As for spur emission optimizing,double phase-locked loop structure is adopted,the first loop is used as a tunable reference for the second loop to avoid integer boundary spur.Besides,a metal cavity is also designed for the PLL to avoid EMI problems.(2)According to the optimization of phase noise,a low phase noise reference signal for PLLs and loop filter with appropriate bandwidth are designed,besides,parameters of PLLs such as charge pump current are carefully set.To avoid the power supply ripple deteriorating the phase noise of VCO,power supply for PLL is also well designed.(3)For the optimization of lock time,calibration of the VCO tuning voltage is taken by A/D converter to improve the accuracy of preset voltage.In addition,in order to realize the features of broadband,high harmonic suppression,high output power dynamic range,the double balanced mixer is used to extend the frequency range,filter banks are designed to suppress harmonics,amplifiers and digital step attenuators are taken to adjust output power.In circuit design,this paper discusses some details of the whole scheme,gives out the specifics which should be taken attention to in circuit realization.Besides,the key componentsof the circuits are assessed,the algorithm of dual loop setting and driven code for the hardware are completed-In this paper,a broadband frequency source is designed with low spur,low phase noise and fast-hop features.This frequency source can be used as signal source for college students or small companies.It can also be used as the local oscillator of receiver and transmitter.There is a wide application prospect of the broadband frequency source.