Phase-locked loop with redundant reference input

Abstract

A phase-locked loop with redundant reference input signals compares each reference input signal to the loop feedback signal to generate corresponding phase correction signals. In response to a reference select signal, one of the phase correction signals is selected for supply as a loop correction signal. The loop correction signal is supplied through a filter as a control signal to a VCO. Phase and frequency detectors are included, each detector receiving a corresponding reference input signal and connected to receive the loop feedback signal for generating a phase correction signal indicating the phase and frequency difference between the corresponding reference input signals and the output signal. Also, a selector is provided in communication with each of the detectors that selects one of the phase correction signals in response to the reference select signal as the loop correction signal. Further a phase alignment circuit is used with phase and frequency detectors to assure tracking of the correct edge of the reference signal by each unselected phase and frequency detector.