LOOP STABILITY ANALYSIS IN FREQUENCY AND PHASE AUTOMATIC CONTROL SYSTEMS
Keywords:
frequency and phase automatic control, PLL (phase-locked loop), phase locking, regulation loop, stability, phase shift, low-pass filter, voltage-controlled oscillator (VCO), phase fluctuations.Abstract
This paper analyzes the stability characteristics of regulation loops in frequency and phase automatic control (FPAC/PLL) systems. The structures of first- and second-order PLL loops, along with their phase shifts and dynamic properties, are comparatively examined. It is shown that, due to the absence of a low-pass filter, first-order loops exhibit limited phase stability and increased sensitivity to noise. In contrast, the inclusion of a low-pass filter in the feedback path of second-order loops enables effective suppression of phase fluctuations, imparts inertial “flywheel” properties to the system, and ensures stable synchronization. In addition, the influence of the loop filter on the capture range and capture time is discussed. The obtained results are of practical importance for the selection and optimization of PLL loop configurations in the design of high-precision synchronization systems.
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