Hangup in Phase-Lock Loops

Abstruct-A phase-lock loop occasionally will take a long time to settle to equilibrium. Phase dwells at a large error for a prolonged in- terval. This phenomenon has been dubbed “hangup.” The periodic nature of phase detectors is responsible for hangup, which OCCUIS near the reverse-slope, unstable null. Restoring force is small in the vicinity of the reverse null, and noise causes the loop to equivocate about the null. Hanguivps e rtyr o ublesomwe hefn a sa tc quistioinns e eded withh i grh e liabilityO . nee x ample is synchronization of digital communications. Hangupsc anb ea voided if a larger estoringf orcei sa ppliedf or large phase errors and if equivocation is prevented. An implementation of an antihangup circuit is proposed.