12.5 A 25µW 100kS/s 12b ADC for Wireless Micro-Sensor Applications

Abstract

Micro-sensor nodes are highly energy-constrained and have timevarying performance demands. Accordingly, in this work an ultralow-power energy-scalable ADC is presented. The SAR architecture is well suited to environment monitoring. Recent micropower implementations have been limited to low resolutions (8 bits) [1]. The circuit and architecture enhancements presented in this paper efficiently increase precision to 12 bits. The ADC has two resolution modes: 12b and 8b. In 12b mode, its sampling rate is scalable, at a constant FOM, from 0 to 100kS/s, and, in 8b mode, from 0 to 200kS/s. At the highest performance point (i.e., 12b, 100kS/s) the entire ADC (including all digital, analog, and reference circuitry) consumes 25µW from a 1V supply. Several techniques have enabled this low-voltage low-power performance. Analog offset calibration in the latch improves the comparator power-delay product; weak-inversion operation