Fuzzy phase-locked loops

The problem of robust phase-locked loop (PLL) design has attracted attention for many years, particularly since the advent of the Global Positioning System. This paper proposes and demonstrates the use of a fuzzy PLL to estimate the time-varying phase of a sinusoidal signal. It is shown via simulation results that fuzzy PLLs offer performance comparable to analytically derived PLLs (e.g., Kalman filters and H_∞ estimators) when the phase exhibits high dynamics and high noise. The fuzzy PLL rules are optimized using a gradient descent method and a genetic algorithm