The Design And Implementation Of S-band Frequency Synthesizer

The communication system,which works in RF range，is usually very easilydisturbed by the external environment so as to degrade its performance, especially as acore component of the system---frequency source. Thus, a high stability and be notdisturbed by the outside fequency source has a vital role in overall performance ofsystem. crystal oscillator, which has markedness in the industry, has the desired highfrequency stability, but the lower band limits its application in RF and microwavesegment. So, frequency source,worked in RF S-band, is usually designed by the way offrequency synthesis to output a high stability RF signal.This article is designed for a charge pump PLL frequency synthesizer,worked inS-band,output2.4-2.5GHz frequency. The paper is described by the traditionalway,theory-design–achieve, to narrate the work done by the author in the design. Thetheoretical part analysises the composition and theory of CPPLL, and establishs itsmathematical model to analyze the dynamic characteristics, phase noise and spurious ofthe PLL loop. The design part design the several major modules of the loop, includingthe loop filter, reference source, and VCO. The achieve part consists of drawing thePCB circuit, printing the required circuit board, and a reasonable electric assemble.The main body of the system uses the ADF4108integrated PLL chip, produced byAnalog Devices Inc, to build; VCO part uses MAXIM’s MAX2750chip to design; ituses MATLAB to calculate the parameters of loop filter; and the reference sourcedesigned is a overtone crystal oscillator with Pierce circuit. The design adopted theSTC12C4052AD microcontroller to control the latch of the phase-locked loop chip.Finally, through the integrated design of the system, this paper achieved a frequencysynthesizer which output the2.4-2.5GHz frequency range signal. The output power ofthe frequency synthesizer is more than-7dBm, the spurious suppression is more than50dBc and the step frequency is4MHz. These indicators are in line with the designrequirements.