Analysis and design of ultra-low-voltage inductive ring oscillators for energy-harvesting applications

Abstract

This paper presents inductive ring oscillators that operate from supply voltages of around two times the thermal voltage (2kT/q), for energy-harvesting applications. Expressions for the oscillation frequency as well as the minimum transistor gain and supply voltage required for the start-up oscillations are derived. The ring oscillators were built with zero-VT transistors due to their high drive capability at low voltages. Measurement results obtained in a ring oscillator prototype integrated in a 130 nm technology confirmed operation of the oscillator with 53 mV of supply voltage.