US Patent 10063246 Low-power fractional-N PLLs

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 code that adjusts the oscillator frequency. The phase predictor may provide noise shaping, for example via a MASH modulator. The PLL may be implemented with dedicated or off-the-shelf circuitry, in an FPGA, or with a programmable processor. A tangible non-transitory memory may hold an associated software instructions for fractional-N phase locking.