Method and apparatus for quantization noise reduction in fractional-N PLLs

摘要

A first current source supplies a first charge amount responsive to a first pulse signal from the phase frequency detector and a second current source supplies a second charge amount according to a fixed value and a variable value. The variable value corresponds to a phase difference between a first feedback clock signal and a hypothesized feedback clock signal with reduced quantization noise. The first and second charge amounts are of opposite polarity. A single set of first and second current sources perform the functions of charge pump and noise reduction DAC.