Abstract

In this paper a new stable high order Digital Phase Lock Loop (DPLL) design technique is proposed. This technique uses linear theory to design the DPLL. The stability of the DPLL is guaranteed by placing a restriction on the system gain. This stability boundary is found by transforming the system transfer function to the Z-domain and plotting the root locus of the LPLL for values of gain where all the system poles lie inside the unit circle. The max value of gain where all the poles lie inside the unit circle is the stability boundary. It is shown that the stability boundary of the LPLL is comparable to the stability boundary of the DPLL. Finally where the above Bessel filter system produces slow lock, gear shifting of the DPLL components is considered. This allows the DPLL to start off with a wide loop bandwidth and switch to the narrow bandwidth once the system has locked.