Wide-band frequency synthesis using hardware-efficient band-pass single-bit multi-step look-ahead sigma-delta modulators

Abstract

Band-pass sigma-delta modulators (SDMs) can be used for all-digital frequency synthesis with low noise in the SDM passband. To avoid mixed-signal components such as DACs, a single-bit output is required. The noise shaping characteristics of single-bit sigma-delta modulators are limited by stability requirements. Look-ahead SDMs have been proposed to increase the bandwidth and signal-to-noise-and-distortion ratio (SNDR) of conventional single-bit ones. The cost is increased hardware complexity, but Multi-Step Look-Ahead sigma-delta modulators (MSLA SDMs) can significantly reduce the required hardware complexity, while retaining the advantages of look-ahead SDMs. This work demonstrates the hardware requirements of MSLA SDMs and proposes an all-digital frequency synthesizer architecture based on band-pass MSLA SDMs. The performance of the poposed synthesizer architecture is investigated for various configurations. Finally, the advantages of using MSLA SDMs instead of conventional single-bit ones in terms of bandwidth and SNDR are quantified.