Design And Implementation Of Low Phase Noise Frequency Synthesizer Based On Multi-Loop

With the rapid development of modern science and technology,the requirement which is widely applied to the electronic system of communication in economic society is higher and higher.Providing the signal source of stable and efficient vibration frequency of reference for electronic devices is also increasingly urgent.Therefore,to design a high resolution and low phase noise and stable and at the same time maintaining broadband and low spurious frequency source is now the focus and hotspot in the research of the frequency synthesizer.Multi-loop circuit output frequency spurious and phase noise are two aspects,which are designed and improved in this paper.It is found that the multi-loop circuit control parameters can be used to output the same frequency point and the corresponding parameters are sent after selecting the system design parameters through the analysis of the structure of the multi-loop circuit.Therefore,this design makes a detailed analysis of the fractional frequency ratio caused by spurious.Through the actual measurement and theoretical analysis,the correspondence between the fractional frequency ratio and the spurious occurrence position is obtained,which provides a strong basis and method for suppressing fractional spurs.By testing the multi-loop circuit,the multiloop circuit also has the disadvantage of the poor phase noise.Through the calculation and analysis,it is concluded that the phase noise of the original reference signal is poor.This dissertation mainly does some thorough research on the following aspects:1、Through the analysis of the location of decimal frequency division stray,the results show that the fractional frequency ratio corresponds to the corresponding sequence period is the main reason for producing the fractional spur.2、When the decimal frequency ratio is within a certain range of the corresponding period,the near end of the center frequency point will produce a more visible dispersion.When the corresponding period increases to a certain extent,the spurs signals are “submerged” in the entire spectrum,which is equivalent to white noise.When the corresponding cycle decreases to a certain range,spurs will appear in the remote area of the center frequency,and you can inhibit the remote spurs by setting reasonable loop filter bandwidth.3、So based on the above two kinds of ideas,this article can realize wide band,low phase noise,high resolution frequency synthesizer through the reasonable selection of parameters of polycyclic,“avoiding” spurs serious decimal frequency division ratio.4、Finally,in this paper,the frequency of the low phase noise is realized by the frequency doubling circuit,and is achieved the optimization of the phase spur of the multi-loop frequency synthesizer.Through the design,testing and commissioning of hardware circuit,the frequency source can achieve the signal output of 3 GHZ ~ 10 GHZ,with resolution ratio reaching 1 Hz,phase noise level reaching-110 dBc /Hz @ 10 kHZ,and spurs inhibition greater than 60 dBc.