This paper describes a 32.768kHz-to-1MHz RC-based oscillator (RCO) suitable for high- and low-duty-cycle sleep-mode timers in emerging sensor node applications. In contrast to crystal oscillators (XO) based frequency references which employ long and energy intensive restarts, the proposed RCO achieves a 1000X reduction in restarting time. Measurement shows that the implemented RCO achieves a temperature stability of 68.5ppm/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">○</sup> C @32.768kHz and 37.5ppm/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">○</sup> C @1MHz. A proposed autonomous digital scheme uses coarse and fine tuning to compensate for process and temperature variations. Measurements report an energy efficiency of 1.46nW/kHz@1MHz occupying an area of 0.055mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in a pure digital 180nm CMOS process node.
