A 0.3 V, 49 fJ/conv.-step VCO-based delta sigma modulator with self-compensated current reference for variation tolerance

This work proposes an ultra-low voltage, VCO-based sigma delta modulator with self-compensated current reference against process and temperature variations. The proposed current reference generator sets the feedback current of the multi-bit Non-Return-to-Zero (NRZ) DAC and the VCO tuning coefficient (K_VCO) at ultra-low voltage. A test chip fabricated in 65nm CMOS technology demonstrated successful operation at 0.3 V. It consumes 510 nW and occupies 0.015mm². The proposed VCO-based delta sigma modulator achieves peak SNDR of 56.1dB at 0.3 V and 10 kHz input bandwidth, and FoM of 49fJ/conv.-step.