Reconfigurable Bandpass Sigma-Delta Modulator With Programmable NTF for Low-IF Multi-Mode Receivers

A new reconfigurable bandpass sigma–delta modulator (BPSDM) structure is proposed for low-IF multi-mode wireless systems. The proposed modulator can be reconfigured to operate in different signal bandwidths and at different signal-to-noise ratios by rearranging and optimizing the order of the noise transfer function of the loop while still maintaining stability. Compared with conventional multi-mode BPSDM, employing cascade structures and multi-bit sub-ADCs, the proposed modulator features many attractive advantages, such as (1) avoiding coefficient mismatch between analog and digital components in cascade structures, (2) avoiding DAC non-linearities that are otherwise introduced by commonly used dynamic element matching techniques, and (3) improving and varying the dynamic range performance while meeting the requirements of different wireless standards.