Fully-Integrated Timers for Ultra-Low-Power Internet-of-Things Nodes—Fundamentals and Design Techniques

Driven by the momentum toward compact and low-power Internet-of-Things (IoT) systems, the research on fully-integrated and energy-efficient kHz-to-MHz timers increased explosively. This article examines recent publications on timers and classifies them into two major categories: open-loop-based and close-loop-based timers. Upon introducing the basic parameters for characterizing a timer, we perform an extensive investigation to gain insights into recent state-of-the-art works. We also discuss in detail the comparison between the two classes of timers. With the aid of the state-of-the-art, we present a comprehensive review from multiple perspectives, such as
Energy Efficiency
,
Temperature Coefficient
,
Temperature Range, Figure-of-Merit
, etc.