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 stages, wherein the jth stage is configured to receive as an input the sum of the error of the preceding stage and a high amplitude dither signal derived from the error of the kth 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 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 stage, a second stage and a third stage, and

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