Acquisition and tracking performance of a PLL using a class of nonlinear filters

Williamson (1979) has conducted a study, in which a nonlinear loop filter was used in the phase locked loop (PLL) instead of a conventional linear loop filter. It was found that the resulting PLL has wide 'effective' bandwidth for large initial tracking errors (and so reduced the time to synchronize) and yet has narrow 'effective' bandwidth once synchronism is attained. The present investigation is concerned with a modification to the loop filter considered by Williamson. An overall performance evaluation of a PLL incorporating a nonlinear filter (PLLN) is conducted, taking into account the acquisition and noise performance of the PLLN with frequency detuning. The advantage of the proposed modified structure is related to the reduction of the phase error variance in the pressure of frequency detuning from that obtained with the original structure.