Design considerations of bandpass CT ΣΔ modulators for software-defined-radio receivers

This paper discusses design considerations of LC-based bandpass continuous-time ΣΔ modulators intended for the analog-to-digital conversion of radio-frequency signals in software-defined-radio receivers. A top-down high-level synthesis methodology - based on the combination of undersampling techniques, programmable notch frequency and adequate selection of loop-filter coefficients - is presented to design efficient modulator architectures, which can be adapted to fulfill the requirements of diverse wireless communication standards, while keeping stability and robustness to circuit errors. Main architectureand circuit-level design issues are analyzed, considering diverse case studies based on Gm-LC resonators and different kinds of digital-to-analog converters. Time-domain simulations validate the presented approach1.