Chaotic Oscillations in a Third Order PLL in the Face of Two Co - Channel Signals and Its Control

Abstract

A third order phase locked loop incorporating a resonant type second order filter is a conditionally stable system and shows complicated dynamics including chaotic oscillations for a range of loop parameters. In the face of two co-channel signals, an otherwise stable loop may be thrown into a chaotic state, depending on the relative strength and mutual frequency offset of the input signals. We have predicted the parameter zone for chaotic state of the loop through numerical studies and verified the prediction by hardware experiment. Then we modify the loop structure to incorporate an additional control signal which stabilizes the loop dynamics and removes the chaotic oscillations. The improved response of the loop is established numerically and experimentally.