A low-noise and fast-locking phase-locked loop

In this paper, a phase-locked loop (PLL) is introduced. The proposed PLL, denoted by NPLL, is similar to the standard PLL except that it incorporates a nonlinear element and a low-pass filter in its loop. It is shown that by appropriate choices of these two components, the NPLL outperforms the standard PLL in three respects: (1) it has a large acquisition range, i.e., it can achieve locking in situations where the standard PLL cannot; (2) it achieves locking fast; and (3) it has low noise in its output phase. The role of the nonlinear element in enhancing the locking capabilities and noise characteristics of the NPLL is carefully examined. Many tests, results of three of which are reported in this paper, show the superior performance of the NPLL.