A 12b 22.5/45MS/s 3.0mW 0.059mm2 CMOS SAR ADC achieving over 90dB SFDR

Abstract

CMOS technology scaling has opened a pathway to high-performance analog-to-digital conversion in the nanometer regime, where switching is preferred over amplifying. Successive-approximation-register (SAR) is one of the conversion architectures that rely on the high switching speed of process technology, and is thus distinctively known for its superior energy efficiency, small chip area, and good digital compatibility. When properly implemented, a SAR ADC also benefits from a potential rail-to-rail input swing, 100% capacitance utilization during input sampling (thus low kT/C noise), and insensitivity to comparator offsets during the conversion process. The linearity-limiting factors for SAR ADC are capacitor mismatch, sampling switch non-idealities, as well as the reference voltage settling issue due to the high internal switching speed of the DAC. In this work, a sub-radix-2 SAR ADC is presented, which employs a perturbation-based digital background calibration scheme and a dynamic-threshold-comparison (DTC) technique to overcome some of these performance-limiting factors.