A Family of ΔΣ Modulators with High Spur Immunity and Low Folded Nonlinearity Noise When Used in Fractional-Frequency Synthesizers

Abstract

Phase locked loops for fractional frequency synthesis typically use Digital ΔΣ Modulators (DDSMs) as their divider controllers. Different types and configurations of DDSMs have been presented in the past which have distinctive characteristics in terms of spectral shaping of their quantization errors, spur immunity and implementation costs. This paper presents a family of DDSMs that have provably high spur immunity and low folded noise when used in fractional-N frequency synthesizers with polynomial nonlinearities.