Study On High-Resolution Frequency Synthesizer At L-band

Frequency synthesizer is one of the most important parts of electronic system.In order to improve the whole system performance,higher requirements have been put to frequency synthesizer in the field of mobile communication,electronic measure instrument,radar and electronic warfare.High output frequency,high resolution,Low phase noise,pure output spectrum and fast frequency switching speed have been the main developing direction.In recent years,because of high resolution,fast frequency switching speed and being easy to realize various types of modulation of output frequency,Direct Digital Synthesizer(DDS)has been widely used.However,the maximum output frequency of DDS can only reach 400MHz for the reason of the limitation of Nyquist sampling frequency.There are two ways to improve the output frequency of DDS overseas.One is to improve internal DDS clock,the other is to use GaAs technique instead of CMOS technique.Both of the two ways can improve the output frequency of DDS a little,yet it can't reach the microwave frequency band.Therefore,conflict of high output frequency and high resolution is one of the main conflicts when a frequency synthesizer is designed. And this conflict can be more obvious and vital when the frequency synthesizer is used in frequency sweeping.The purpose of this thesis is to research the method to design the frequency synthesizer which has high output frequency and high frequency resolution.The high-resolution frequency synthesizer at L-Band designed in this thesis is used as a first local oscillator in a four-channel frequency conversion project.For the input RF frequency can be multi-spot frequency,the frequency synthesizer designed here can output different frequency with the change of input RF frequency.Compared with various frequency synthesis techniques,the technique of PLL driven by DDS unit is used in the thesis,which is one kind of hybrid frequency technique.Therefore,we obtain a high-frequency-resolution,low-phase-noise and high-frequency-stability frequency synthesizer with operation frequency between 1610MHz and 1710MHz.The main work of the thesis includes:1.According to the aim of the project,two modules have been designed in this thesis.One is a PLL frequency synthesizer with changeable frequency division ratio and outer reference in signal,the other is a DDS frequency synthesizer controlled by FPGA techniques. 2.DDS+PLL hybrid frequency techniques have been put forward to realize the frequency synthesizer with high output frequency and high frequency resolution.PLL driven by DDS method is used in this thesis,and feasibility analysis also has been taken.3.Two modules have been cascaded before debugging.MaxplusПhas been used to program the E~2PROM device to control the output frequency of frequency synthesizer.4.The method of PLL interpolated by DDS has been put forward to improve the frequency synthesizer according to the testing result.