Band-pass continuous-time ΣΔ modulators with widely tunable notch frequency for efficient RF-to-digital conversion

This paper presents a design methodology to synthesize band-pass continuous-time ΣΔ modulators with a widely programmable notch frequency for the efficient digitization of radio-frequency signals in the next generation of software-defined-radio mobile systems. The presented modulator architectures are based on a fourth-order loop filter-implemented with two LC-based resonators-and a finite-impulsive-response feedback loop to increase their flexibility and degrees of freedom, considering three different cases for the digital-to-analog converter waveform, namely: a return-to-zero, a non-return-to-zero and a raised-cosine waveform. In all cases, the notch frequency can be reconfigured from 0.1f_s to 0.4f_s, while keeping the noise shaping performance, stability and low sensitivity to circuit-element tolerances. This feature can be combined with undersampling techniques to achieve an efficient and robust digitization of 0.5-to-5GHz signals with scalable resolution and programmable signal bandwidth1.