Feedforward frequency control and precision phase detection eliminate rearrangement phase hits in telecom clocks

This paper describes a frequency control method as an alternative to the traditional phase lock loop (PLL). Precise digital phase-detection and deterministic feed-forward correction replace analog feedback iteration. It allows a free-running local oscillator (LO) to be simultaneously “locked” in steady-state to multiple references while the loop output tracks a selected reference. Seamless reference- and LO-switching, no precision analog circuitry, and synergistic use of instrument-grade phase data for tracking, characterizing LO and references, make this design attractive for a telecom clock