Single-bit-output all-digital frequency synthesis using multi-step look-ahead bandpass Σ-Δ modulator-like quantization processing

A configurable single-bit-output Σ-Δ modulator variant is presented, which improves upon stability and dynamic range. The derivation of the proposed modulation scheme from the Σ-Δ error-feedback structure and its mathematical description are analyzed, while its application in fractional-N frequency dividers and all-digital frequency synthesizers is investigated. It is shown that stable high-order noise shaping is possible even when using noise transfer functions that are unstable in a conventional Σ-Δ modulator loop. Furthermore, multipliers can be avoided if the noise transfer function coefficients are chosen appropriately, leading to a low complexity hardware implementation. In special cases the architecture is equivalent to another Σ-Δ modulator with a different, stable, NTF than the initial one. The effectiveness of the proposed modulation scheme is demonstrated by specific examples for each application.