The Research And Design Of Frequency Synthesizer Based On Method Of Time-average-frequency

Frequency synthesizer,as the "heart" of many electronic systems,widely used in commercial,military and civil fields.Frequency synthesizer developes rapidly,there are a variety of ways to implement.However,most of them are hard to possess good frequency resolution,fast frequency switch ability,relatively wide frequency range,simple structure and the characteristic of low cost simultaneously.Therefore,the frequency synthesizer based on the method of Time-Average-Frequency comes into being.Under the condition of low cost,it provides chip designers with clock source of good frequency resolution and fast frequency switch ability.It has been a focus of research in recent years abroad and used successfully in many commercial products.Aiming at the frequency synthesizer based on the method of Time-Average-Frequency,which has not been widely involved in the domestic,this paper expects to achieve a kind of frequency synthesizer with fast frequency switch ability,arbitrary frequency set ability,good frequency resolution,relatively wide frequency range and more simple structure.Based on the analysis of several typical frequency synthesizers,this paper studies the two cornerstones of the existing frequency synthesizer based Time-Average-Frequency,the method of Time-Average-Frequency and Flying-Adder architecture.And then the frequency synthesizer based on Flying-Adder architecture is modeled and simulated in the Simulink.By the theoretical analysis,the relationship between middle signals and output signal is found.Then the time domain and frequency spectrum of the output signal are analyzed to find the relationship between the output signal and the frequency control word,as well as the range of frequency control word which should be avoided in the application.In addition,the analytic expression of the deterministic jitter existed in this kind of frequency synthesizer and its range are obtained.Then,this paper proposes a new architecture which improved in view of the quick stable part of the Flying-Adder.Compared with the frequency synthesizer based on Flying-Adder architecture,the structure is further simplified.And it makes the bits of frequency control word no longer limited by the circuit structure.Which to a certain extent,the range of output frequency is broadened.For the frequency switch speed,the speed is doubled,which decided by the circuit structure of both.When used in the complex system which multiple frequency sources are required,the degree of structure reuse of the design is higher.Finally,after analyzing the feasible scheme of each module,use the FPGA of Xilinx Virtex-5 series to complete the verification of the whole circuit.The function and timing simulation are carried out.Further,the board level test is carried out which result shows that the conditions of the circuit in the actual work are consistent with the simulation result,so the feasibility of the design is verified.The frequency resolution is 1~10ppm(parts per million),the minimum adjustable frequency step is about 96.60 Hz,the minimum output frequency is below 5MHz and maximum output frequency is 398.09 MHz when the frequency control word with 16 bits fractional part.The frequency switch time only takes one cycle duration of the previous clock pulse sequence.In addition,the spurious suppression circuit is designed.When using fewer memory cells,15,the intensity of the spur in the spectrum is generally reduced by 3-10 dB.