A 2.2/2.7fJ/conversion-step 10/12b 40kS/s SAR ADC with Data-Driven Noise Reduction

Abstract

Low-power sensor applications e.g. for environmental monitoring, bio-potential recording, and wireless autonomous sensor networks require highly power-efficient ADCs, typically with resolutions of at least 10b. SAR ADCs are generally beneficial in terms of power efficiency. However, the most power-efficient designs currently lack the required accuracy for these applications [1, 2], as they are limited to 9b ENOB. Other designs that have sufficient accuracy (10b) are limited to power efficiencies above 10fJ/conv-step [3]. The aim of this work is to increase the accuracy of highly efficient SAR ADCs beyond 10b, while further improving the efficiency to 2.2fJ/conv-step. To do so, this work introduces a Data-Driven Noise-Reduction method to efficiently suppress comparator noise, applies a segmented capacitive DAC with 250aF unit elements for better efficiency and accuracy, and implements a self-oscillating comparator to locally generate the internally required oversampled clock.