Abstract: A phase-locked loop (PLL) has at least two parallel loops. The loops share an oscillator, a counter connected with the oscillator, a multiplexer, and a loop filter. Each loop has a register sampling the oscillator phase from the counter, and a phase predictor which uses a fractional-N frequency control word (FCW) to calculate a predicted phase as an integer number. The loop forwards the integer difference between the sampled phase and the predicted phase to the multiplexer, which selects one of the loops and provides the difference to the loop filter. Loops that are not selected use a monitor-and-adjust function to keep the difference in track with the difference of a selected loop. Loops may provide a loop sleep function and the PLL may also provide an oscillator sleep function.

Abstract: A phase-locked loop (PLL) has at least two parallel loops. The loops share an oscillator, a counter connected with the oscillator, a multiplexer, and a loop filter. Each loop has a register sampling the oscillator phase from the counter, and a phase predictor which uses a fractional-N frequency control word (FCW) to calculate a predicted phase as an integer number. The loop forwards the integer difference between the sampled phase and the predicted phase to the multiplexer, which selects one of the loops and provides the difference to the loop filter. Loops that are not selected use a monitor-and-adjust function to keep the difference in track with the difference of a selected loop. Loops may provide a loop sleep function and the PLL may also provide an oscillator sleep function.