US Patent 7679454 Hybrid phase-locked loop

A phase-locked loop (PLL) including a digital PFD, a digital loop filter, a decision circuit, a fractional-N PLL, and a frequency divider is provided. The digital PFD generates a first detection signal according to the phase error or frequency difference between an input signal and a feedback signal. The digital loop filter generates a first control signal according to the first detection signal. The decision circuit generates a divisor value according to the first control signal. The fractional-N PLL generates an oscillation signal according to the divisor value and a reference signal. The frequency divider divides the oscillation signal to produce the feedback signal. The fractional-N PLL includes a fractional-N frequency divider for generating a frequency-divided signal for use in tracking the reference signal according to the divisor value by employing phase swallow means.