Increasing the stability of the synchronization mode of the PLL system

Abstract

Nowadays, the extremely rapid development of the global telecommunications network is accompanied by the search for new and the improvement of already existing radio- and other technologies, which are intended to further advance existing systems towards the construction of even more productive global transport networks, as well as networks of wireless broadband access, including 6G mobile communication networks and networks of subsequent generations. Among the important and widely used systems, it is worth highlighting the radio engineering system such as the Phase-Locked Loop (PLL) system, the capabilities for further improvement of which are far from exhausted. In particular, articles on various research issues and the use of the PLL systems for various applications are regularly published in world scientific and engineering publications. The use of PLL covers the issues of stabilizing the frequency of high-frequency generators, building high-precision frequency synthesizers and narrowband tracking filters, signal extraction against the background of noise in Doppler systems, demodulation of signals with frequency and phase modulation, the operation of magnetic recording playback devices, etc. This article analyzes the operating modes of the PLL system, in particular search, capture and hold, and it is found that when searching for the frequency of the reference generator, the system does not provide tuning of the frequency of the voltage-controlled generator as close as possible to this frequency. This, in turn, leads to the fact that after the frequency of the reference generator enters the capture range, the PLL system is instantly activated, which compensates for the current value of the frequency difference between the two generators, using part of the useful capability of the phase detector to process the frequency changes of both generators within the linear section of its discrimination characteristic. This situation is equivalent to not finding the frequencies of the reference and controlled generators, when their frequencies are equal, in the middle of the retention area, which negatively affects the stability of the PLL system as a whole. Based on the conducted analysis and the obtained conclusions, the paper proposes the principle of adjusting the PLL system as close as possible to the middle of the synchronization (holding) area, which ensures increased stability of the system against the influence of external factors, and also positively affects the reduction of the frequency noise level of this system. According to this principle of tuning, a corresponding block diagram of the PLL system was developed and an explanation of the operation of such a scheme was provided.