Multiloop Hybrid Digital Phase-Locked Loop

Abstract

This paper presents a new technique to overcome the inherent restriction of locking band in a digital phase-locked loop(DPLL)by an additional arrangement for continuous control of the frequency of the local voltage control time generator (VCTG). The proposed loop, called a multiloop hybrid digital phase-locked loop (MHDPLL), incorporates afrequency comparator circuit and a direct synchronization path for controlling the instantaneous frequency of the VCTG in addition to an indirect path via sampler and digital filter. The analyses of phase and frequency step response of first and second order MHDPLLs clearly indicate the superior performance over a basic DPLL, particularly in achieving infinite locking band without disturbing its stability. This new loop finds useful applications, where quicker transient response is necessary i.e., for detection of FSK signal and as a carrier-tracking loop for a frequency ramp input.

Indexing Terms:

• Digital Phase-Locked Loop
• Locking Band