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.