Research And Implementation Of 10MHz～1GHz Frequency Synthesizer With Low Phase Noise

With the rapid development of modern industrial technology,various precise electronic systems has put forward higher requirements for the performance of frequency source.This thesis aims to design a frequency source with high resolution,low spurs and low phase noise.Combining with specific application requirements,various frequency synthesis methods are compared.Finally,a hybrid frequency synthesis scheme combining DDS and direct analog frequency synthesis technology is adopted.Aiming at the core requirement of low phase noise design,this thesis describes the effects of different types of noise on phase noise from the characterization of phase noise.On this basis,the synthesis principle and noise performance of direct analog frequency synthesis technology and direct digital frequency synthesis technology are introduced.The theoretical model of phase noise optimization by power synthesis is established,and the optimization effect of power synthesis on phase noise is verified by simulation and actual circuit respectively.Finally,the modularized frequency source uses multi-channel DDS for power synthesis and then outputs 10MHz～1GHz broadband signals with low phase noise,low spurs and high resolution by means of continuous frequency multiplication.The low phase noise frequency source designed in this thesis is mainly composed of1 GHz reference clock module,multi-channel DDS module,frequency expansion module and power control module.The reference clock module uses the nonlinear transmission line pulse compression technology to output the tenth harmonic of the 100 MHz thermostatic crystal oscillator.The phase noise of 1GHz reference clock can reach-147 d Bc/Hz@1k Hz.Each channel in the DDS module shares a 1GHz reference clock.The output signal of four-channel DDS is power synthesized,and the synthesized phase noise is optimized to nearly 6d B compared with that of single DDS.The frequency expansion module spreads the 10MHz～125MHz signal output of the DDS module to 1GHz,which is composed of three frequency doubling sub-modules.The passive diode bridge frequency doubling method is used to achieve low phase noise frequency doubling.The voltage tuning filter is designed based on the variation relationship between the equivalent capacitance of the varactor diode and the bias voltage to select the frequency of the frequency multiplier output.The power synthesis module consists of amplifiers,digital step attenuator and an ALC circuit.Through the coordination of roughly adjust by the digital step attenuator and precisely adjust by the ALC circuit,the power adjustment step of 0.1d B is achieved.The resulting frequency source has an output frequency resolution of up to 1m Hz and better spurious performance than-65 d Bc.The phase noise at 10 MHz,100MHz,500 MHz and 1GHz is-164 d Bc/Hz@20k Hz,-151 d Bc/Hz@20k Hz,-139 d Bc/Hz@20k Hz,and-133 d Bc/Hz@20k Hz,respectively.All the indicators meet the design requirements.