Apparatus for mitigating wandering spurs in a fractional-N frequency synthesizer

A fractional-N frequency synthesizer comprising a divider controller comprising a multistage noise Shaping (MASH) digital delta-sigma modulator comprising L Error Feedback Modulator (EFM) stages, wherein a jth EFM stage is configured to receive as an input a sum of an error of a preceding EFM stage and a high amplitude dither signal derived from an error of a kth EFM stage, where 1≤j≤k≤L, wherein the high amplitude dither signal comprises a dither signal which is obtained by passing the error of the kth EFM stage through a filter block with a dither transfer function DT(z).

A fractional-N frequency synthesizer comprising a divider controller comprising a multistage noise Shaping (MASH) digital delta-sigma modulator comprising a MASH 1-1-1 architecture with additive first-order dither comprising a first EFM stage, a second EFM stage and a third EFM stage, and

• wherein the third EFM stage of the MASH architecture is configured to receive as an input a sum of an error of the second EFM stage and a high amplitude dither signal derived from passing an error of the third EFM stage through a filter block.