Mostly Digital, Calibration-Free, Band-Pass Delta-Sigma Modulator Using Dual Time-Interleaved Noise-Shaping SAR ADCs

This work presents a highly digital, band-pass delta-sigma modulator (BPDSM) using dual, time-interleaved (TI) noise-shaping successive approximation register (NS-SAR) analog-to-digital converters (ADCs). Use of TI, low-pass DSM shifts digitization from intermediate frequency (IF) to baseband, and increases energy-efficiency as well as relaxes the realization of a sharp noise-transfer function (NTF). However, time-interleaving results in spurs that appear as images in the signal band and necessitates mismatch calibration. The proposed technique uses dual BPDSMs operating at different IFs to deterministically push all interleaving spurs out of the signal band without any calibration. Third-harmonic spurs fall out of band if the IF BW is less than Fs/10. A prototype test-chip fabricated in 65nm uses dual 4× TI BPDSMs and achieves 66.7dB SNDR in 2MHz bandwidth at 20MHz IF while consuming 1.36mW.