A phase-locked loop (PLL) has an oscillator, a counter and a register to sample the oscillator phase as an integer number. A phase predictor uses a fractional-N frequency control word (FCW) to calculate a predicted phase as an integer number. The integer difference between the sampled phase and the predicted phase is used as loop filter input, to generate an oscillator control signal that adjusts the oscillator frequency. The phase predictor may provide noise shaping, for example via a MASH modulator. A first sleep mode control signal blocks a reference clock and feedback of the oscillator clock to the counter. It may also freeze loop filter parameters and block the output clock. A second sleep mode control signal may stop the oscillator.