Master of Engineering Balram Sahu - Embedded Sensing ...

Chapter 1IntroductionA recent explosion in the applications that benefit from low energy operation has cravedout a significant niche for sub-threshold circuits. Digital circuits operating in subthresholduse a supply voltage that is less than the threshold voltages of transistors.In this region of operation, circuits consume less energy for active operation and dissipateless leakage power than higher voltage alternatives, but they operate more slowly.Until the emphasis on maximizing operational frequency in digital circuits dominated tothe point that sub-threshold operation received very little attention. But as the demandof energy constrained application is increasing, sub-threshold circuits as gaining moreattention.1.1 Energy Constrained ApplicationsEnergy Consumptions is a key metric for large number of emerging set of applications.These Energy constrained applications generally have low activity rates and low speedrequirements, but the system is required to have long battery lifetime, typically morethan 5 years. Ideally the power consumption of these systems will decrease to the pointthat they can harvest energy from their environments and have theoretically unlimitedlifetime.1