Multipath adaptive cancellation of divider non-linearity in fractional-N PLLs

Abstract

The mismatch-induced fractional spurs have so far limited the adoption of phase-interpolation-based fractional-N PLLs. Only recently a background cancellation technique, embedded in a digital fractional-N PLL, has faced this issue. In this paper, we will show that this technique is equivalent to a multi-path adaptive circuit that cancels the effects of the phase interpolator non-linearity. This analysis allows highlighting the speed/accuracy trade-off inherent in these algorithms. Simulation results verify the validity of the proposed approach.