Title: MODELING AND DESIGN OF ULTRA-LOW-VOLTAGE CIRCUITS FOR ENERGY HARVESTING APPLICATIONS
Carlos Galup Montoro and Márcio Cherem Schneider, Federal University of Santa Catarina, Brazil
Ultra-low-voltage (ULV) circuits have gained considerable attention in recent years because of the emergence of small batteries and self-powered applications.
Theoretically, the minimum supply voltage for the proper operation of a CMOS inverter is 2 (ln2) (kT/q) = 36 mV at room temperature, as shown by Swanson and Meindl in 1972. In this tutorial we analyze both the CMOS inverter and the Schmitt Trigger circuit in weak inversion operation, and discuss circuit techniques to approach the theoretical low voltage limit.
For analog circuits the minimum supply voltage has been usually considered higher than the minimum necessary for the operation of digital circuits. In this tutorial, we will present analog circuits such as rectifiers and oscillators that can operate from supply voltages below (kT/q).
Essential to the design of ULV circuits is an understanding of the transistor model and the meaning of its main parameters. We will review ultra-low-power circuits that allow the automatic extraction of the specific current IS and the threshold voltage VT of MOS transistors, which are fundamental parameters for circuit design and testing, as well as for technology characterization.
In the lecture we will discuss key issues for ULV circuits, such as MOS transistors with near zero threshold voltage, modeling features, ULV biasing and building blocks. A section on ULV circuits for energy harvesting is also included.