A 7.1fJ/conv.-step 88dB-SFDR 12b SAR ADC with energy-efficient swap-to-reset

Abstract

In this work, a novel DAC reset scheme for SAR ADCs is proposed, which eliminates the reset energy consumption. This reset energy consumption can be significant and is seldom optimized in low power switching schemes. The scheme can be applied to all differentially reset and switched DACs. This `swap-to-reset' operation is applied to the 2 MSBs of a 12b SAR ADC fabricated in 65nm CMOS, resulting in an energy saving of 33% for the DAC or 18% for the whole ADC. Besides swapping, rotation is also applied to the 2 MSBs of the DAC to enhance the linearity to 88dB SFDR. The SAR ADC operates at 0.8V VDD and 40kS/s, achieving an SNDR of 64.2dB and a FoM of 7.1fJ/conversion-step.