MODELING AND PARAMETERS OPTIMIZATION OF A PHASE-LOCKED LOOP SYSTEM WITH CONSIDERATION OF THE LOOP FILTER ORDER

Abstract

Frequency synthesizer models with a phase-locked loop (PLL) system have been obtained for the 4,4…4,99 GHz range, which is the most promising for the fifth generation (5G) communication systems in the Russian Federation. The 4,4...4,99 GHz operating band is intended to provide wireless communications of the 5G standard within the city and is not used by other wireless communications networks for civil or military purposes. The goal of this work is to determine the parameters of a PLL system to implement the frequency synthesizer that provides maximum attenuation of spurs with the minimum setting time of the specified frequency in the band allocated for 5G communication systems. In accordance with the present goal, the following problems are solved: description of frequency synthesizers models based on a PLL system with loop filters of various orders; analysis of the transfer characteristics of the PLL system in the frequency domain; determination of the dependences of the PLL system spurs attenuation and the operation speed upon the order and the parameters of loop filters; calculation of the optimal parameters of the loop filters to ensure maximum spurs attenuation and minimum setting time of the specified frequency. To solve the assigned problems, the dependences of the spurs attenuation upon the optimization parameters were calculated for the cases of using loop filters of the 2nd, 3rd and 4th orders. In addition, an analysis of the dependences of the setting time upon the optimized parameters was performed. It has been shown that the use of high-order loop filters with optimal parameters can significantly increase the level of attenuation of higher spurs and at the same time reduce the setting time of the specified frequency. In particular, the fourth-order loop filter makes it possible to provide 18 dB more attenuation of higher spurs and 12,5% less setting time of the specified frequency than the second-order loop filter. In addition, the use of higher-order filters makes it possible to increase the attenuation of the main spurs by 5 dB compared to the second- order loop filter.