Phase-locked loop (PLL) frequency synthesizers that use phase detectors (PD) with various nonlinear transfer characteristics have been considered. The goal of this work is comparative analysis of the frequency synthesizers operation speed depending on the type of the PD nonlinearity and mathematical description of the PD nonlinear characteristic which ensure the maximum operation speed of the frequency synthesizer. In accordance with the present goal, the following problems are solved in this work: the generalized model of the PLL frequency synthesizer is developed; mathematical models of static characteristics of the PLL system nonlinear link are described when using various types of known PDs and a modified PD with aperiodic characteristic; the analysis of the PLL system dynamics when changing the static characteristic of the nonlinear link is carried out. The modified PD provides relay control of transient processes when a large phase difference occurs. Numerical evaluation of the PLL synthesizers operation speed depending on the initial frequency deviation have been obtained when using known PDs and the modified PD. It is shown that the use of the modified PD allows to reduce frequency settling time about 1.5 times in comparison with the best in operation speed conventional PD. Optimal values of the control signal ensuring the maximum operation speed of the PLL synthesizer with the modified PD have been obtained for the specified frequency deviations in the large disturbance mode. The results of this work are valid for PLL frequency synthesizers of the UHF, L, S and C-bands (from 300 MHz to 8 GHz) which are used in wireless communication systems of the fourth generation (4G) and the fifth generation (5G).
