Synchronous Synthesis of Microwave Modulated Signals: Transient Processes Control & Analysis

The issues of control and analysis of transient processes during synchronous synthesis directly on the carrier frequency of 3.2 GHz of a microwave signal modulated by the quadrature phase shift keying (QPSK) algorithm with an information rate of 200 Mbit/s are considered. A cascade circuit for constructing a synchronous microwave modulator using optimized synchronous structures related to phase-locked loop (PLL) devices is investigated: a frequency synthesizer of the indirect synthesis method and a synchronous QPSK signal modulator based on a globally linearized synchronization system (GLSS). The results of comparative analysis of transient processes in structures at different values of loop gain and damping factor are presented. The influence of these parameters on the shape and characteristics of the frequency response of the spectra of synchronous structures and the synchronization speed is analyzed. During the simulation, it was shown that the choice of the damping factor value affects the level of phase noise and the spectral envelope of the generated oscillation, while the dynamic parameters of the synthesizer frequency setting change. It was also shown that the duration of the transition to a new phase position of the voltage-controlled oscillator (VCO) signal and, accordingly, the quality of the generated QPSK signal depend on the choice of the ratio of the loop gain to the manipulation speed in the modulator.