Frequency synthesis using low-pass single-bit multi-step look-ahead sigma-delta modulators in quadrature upconversion scheme

All-digital frequency synthesis using two low-pass single-bit Multi-Step Look-Ahead sigma-delta modultors (MSLA SDMs) is presented. MSLA SDMs provide better noise shaping characteristics, i.e. SNDR and bandwidth, than conventional SDMs at the cost of higher hardware complexity. The balance between complexity and performance is adjusted by the number of look-ahead steps, which is an additional design parameter. The frequency synthesizer system is comprised of two identical low-pass single-bit MSLA SDMs. Their inputs are orthogonal sinusoidals generated by a direct digital synthesizer (DDS). The frequency range of the synthesizer using a single clock signal is determined by the oversampling ratio (OSR) of the SDMs. A lower OSR results in a wider frequency range, but reduces the output SNDR. System-level simulation results of the frequency synthesizer are presented, showcasing the performance advantage of using MSLA SDMs instead of conventional ones.