The Study Of The Mixer In Hybrid Frequency Synthesizer

With the development of the technology,the requirement of frequency source is more and more highly in the field of electronics and communications.Synthesizers with high resolution,high pure spectrum and fast frequency jump speed have been dominating development directions of the frequency synthesis technology.Based on the goals of high resolution,fast frequency switching speed,and high pure spectrum,the frequency synthesizer is studied in this paper.After comparing kinds of the technique frequency synthesizers,the DDS+PLL hybrid frequency synthesizer with out of band mixing is researched.And the phase noise and spurious performance of the hybrid frequency synthesizer are especially analyzed.Firstly,the structure,principle of phase locked loop and direct digital frequency synthesizer are introduced in this paper.The output phase noise,loop stability and Loop tracking of PLL are especially analyzed.The DDS model is simulated in MATLAB,and the output spectrum and spurious of DDS are analyzed.There is a mathematical model to calculate the distribution of spurious introduced by phase truncation,amplitude quantization,and DAC conversion error.Secondly,the performance parameters of mixer are introduced in detail,and the output phase noise of mixer is theoretically deduced and verified by simulation.The mathematical relationship between the output phase noise and the input phase noise is obtained.Then,in this paper,I analyze the influence of mixer performance parameters on the phase noise and spurious,and summarize the simulation data.It can draw some conclusions as follow:The noise figure(NF)is the key parameter which effects on the mixer output phase noise;And the conversion gain and ports isolation are major parameters which effect on mixer output spurious.In a word,these rules provide some theories foundation for mixer design and offer some technical references to application and development of DDS+PLL hybrid frequency synthesis.