Frequency Synthesizer Transient Effects in FH-FSK

Abstract

Agile frequency synthesizers have been proposed for accomplishing the frequency-hopping and dehopping in FH-FSK communications. Since the design of such synthesizers generally involve divide-down phase-lock loops, transients exist that limit the ability of the loop to hop rapidly over the hopping band. These transients lead to effective energy loss that degrades the resulting decoding performance. In this paper, hopping transients are studied in terms of their dynamical equations, their relation to key loop parameters, and their effect on decoding operations. The importance of pre-tuning is shown. Suggested techniques to combat the transient loss, as delaying the decoder integration start-time, or ping-ponging two synthesizers, are evaluated.