An Adaptive-Resolution Quasi-Level-Crossing Delta Modulator With VCO-Based Residue Quantizer

This brief introduces an adaptive-resolution (AR) quasi-level-crossing delta modulator ADC with a voltage-controlled oscillator (VCO)-based residue quantizer for Internet-of-Things (IoT) wireless sensor nodes. The residue voltage signal is digitized by a VCO-based residue quantizer, thus leading to a straightforward implementation of level-crossing (LC) and AR algorithms in digital domain. The inherent and mismatch-induced dithering provided by the VCO-based residue quantizer increases the proposed modulator's dynamic range and average sampling rate for slowly-varying input signals, enabling accurate sampling and conversion. For fast-varying signals, the AR algorithm is adopted to reduce the average sampling rate by a factor of three compared to the straightforward LC algorithm at the edge of the modulator's signal bandwidth. Fabricated in 28-nm CMOS, the proposed modulator achieves a peak SNDR of 53dB over a signal bandwidth of 1.78MHz.