ANALYSIS OF TRANSIENT PROCESSES IN PLL FREQUENCY SYNTHESIZERS WITH VARIOUS CHARACTERISTICS OF NONLINEAR LINK

Abstract

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).