High speed phase selector with a glitchless output used in phase locked loop applications

摘要

A digital phase selector circuit that switches an output clock between N input clock phases is described. The phase selector utilizes a special output mux and switches clock phases during a safe zone to avoid glitches. The phase selector is used in the feedback path of a PLL to implement functions such as spread spectrum or fractional reference clocks. An example with N=4 and an optimized latch mux is shown.