TW236053B - Method and apparatus for clock recovery - Google Patents

Abstract

A method and apparatus for recovering the phase of a signal which may change at periodic intervals, such as a clocked data signal, is disclosed. The apparatus comprises gated voltage-controlled oscillators that are alternated or exchanged, to reduce phase deviations in the recovered signal induced by VCO frequency variation, and stabilized by respective phase-locked loops. Outputs of respective VCOs are selectively provided to a clock output in response to a positive-going transition in the input signal, to make the circuit more tolerant of waveform distortions. The circuit provides rapid bit-level sychronization of burst-mode and packed communications, reducing synchronization overhead and avoiding the over-sampling used for clock recovery in other circuits. In a particular version of the circuit uses a slot control signal to trigger a reset of the VCOs and PLLs, and the output of the NORed outputs of the VCOs is connected to clock output logic to provide phase realignment between VCO outputs. Another version changes off among more than two VCOs to provide improved drift resistance. This exchange continues in response to a reference periodic signal when positive-going transitions are absent for a given period, toprevent frequency drift in the recovered clock.