The Research Of The Phase-locked Loop Circuit In Microwave Communications

With the rapid development of the electronic communications industry, theperformance of the PLL (phase-locked loop) circuit which plays an important role onthe ODU(outdoor unit)system and the RF transceiver front-end, directly determines thekey technical indicators of the ODU system and transceiver. Although the performanceof the PLL circuit has been improved a lot, according to the current situation, with therapid development of the microwave communication, radar, navigation and electroniccountermeasure systems, higher requirements for the PLL circuit are desired, sostudying the PLL technology has a great significance.In order to meet the requirements of the ODU (outdoor unit) system, The mainwork of this paper is to do some research on the S-band phase-locked loop frequencysynthesizers and VCO (voltage-controlled oscillator).This paper systematicallyexpounds the composition of the PLL circuit, working principle and applications, andconducts an analysis in detail on its main performance indicators and further discussionson the external VCO. The performance of the VCO is very important to the entire PLLcircuit and ODU system, while the integrated VCO has some limitations, especially theperformance of its indicator (open-loop noise) and stability, which have a great effectsto the BER(bit error rate) of the ODU system. So the performance of the ODU systemcan be further improved by improving the performance of the VCO which can reducethe phase noise of the PLL circuit.The main content of this paper includes the following parts:1. A detailed overview of the PLL circuit in the second chapter, and an in-depthanalysis about the functions of its composition module is carried out. An S-band PLLfrequency synthesizer is designed using the ADI software in chapter IV, which showsspurious phase noise and suppression characteristics. The phase-locked loop frequencysynthesizer adopted an external VCO which consists of discrete components. Finally,the testing results which is obtained by debugging and testing the whole circuit, showthat the PLL frequency synthesizer achieved expected effects in the indicators of spurious suppression and phase noise.2. The VCO is designed using ADS software in Chapter three, and the PCB layoutof the VCO is designed using Cadence software. In order to improve the performanceof the PLL circuit, an external VCO is designed, which consists of discretecomponents. After debugging repeatedly, we found that although the circuit of theVCO which consists of discrete components is more complex, and has a relativelylarge size, and long design circles, compared to the integrated VCO, it has significantadvantages, such as excellent performance, better phase noise, convenient debuggingand improvement. Compared to integrated VCOs, this external VCO shows excellentperformance such as better phase noise and more convenient debugging, despite of thedisadvantages of complexity, long design circles and relatively lager size whichconflicts with the demand of miniaturization for portable wireless communicationdevices.3. The phase noise and spurious of the PLL are discussed in Chapter V. The designtechniques about low phase noise and low spurious are provided at the same time.