The Design And Implementation Of 2.45GHz Frequency Synthesizer Based On Phase-Locked Loops

The microwave oscillator is the source of LHCD system,and it is crucial device to whole system.The frequency synthesis technique based on phase-locked loop is applied for developing microwave source operating at 2.45GHz in this paper,according to the requirements of microwave source for the LHCD system,focus on the technique parameters such as frequency stability,output power,phase noise,spurs and so on.EAST device is used to do physics experiments and study nuclear fusion in this paper,to the requirement of microwave power source of LHCD system in our EAST device,it is urgent to update the old microwave power source.High stability temperature compensated crystal oscillator is used as the reference source of PLL frequency synthesizer in this paper,the frequency is up to ±1 ppm max./year.In order to test the performance of power amplifiers behind microwave source,micro-controller is used as the frequency controller.Because the technique parameters of phase noise and spurs are very important for microwave source,the source,influence,suppression measures of phase noise and spurs are discussed,the following methods are taken to improve phase noise and spurs:1,ADS and ADIsimPLL were taken to simulate the technique parameters of phase noise and spurs,and verify the feasibility of experimental methods,and also improve the design of loop filter;2,by post voltage regulator,series small resistance,parallel filter capacitors and isolate power,phase noise and spurs which come from power supply are reduced;3,four-layers PCB,reasonable wiring and drilling can reduce coupling interference and improve electromagnetic shielding;4,increasing the current of charge pump,setting the compensated current of charge pump,increasing phase comparison frequency and using single reference source can reduce phase noise and spurs;5,in order to improve RF output matching,the ? matching network was designed.In the paper,through the circuit analysis,test platform are built and the experiments are accomplished,two kinds of experimental methods are designed for comparsion.The test results show:The output of frequency synthesizer is 2.45GHz and its frequency stability is very high,where the power is adjustable.Both the technique parameters of phase noise and spurs meet the design requirements,so it can take the place of the old microwave power source of LHCD system.