Ultra-Low Power SAR ADC Using Statistical Characteristics of Low-Activity Signals

Abstract

Low-activity signals, such as voice, electrocardiogram (ECG), and ultrasonic signals, in the Internet-of-Things applications have both posed unique challenges and offered special opportunities for modern analog-to-digital conversion. This article presents a new successive approximation register (SAR) analog-to-digital converter (ADC) search methodology, which is aimed at low-activity signals for reducing comparator activity and switching energy of digital-to-analog converter (DAC). By using statistical histogram information of the low-activity signals, two search solutions are proposed. The first solution is designed for some part of signal that has small difference between two adjacent samples, while the second solution is designed for that with large difference. To engage one suitable solution, the digital interval between two adjacent samples needs to be detected. In addition, a new DAC tactic is proposed to reduce the activity of DAC switches. Our simulated 10-bit SAR ADC for voice signals shows that by using our proposed method, the comparator activity is reduced by 62.09%, and the DAC switching energy is decreased by 85.90% compared to the monotonic method. In addition, the activity of DAC switches is further trimmed by 39.66% compared to the monotonic method.