title: A Constant Energy-Per-Cycle Ring Oscillator Over a Wide Frequency Range for Wireless Sensor Nodes.
abstract: This paper presents an energy-efficient oscillator for wireless sensor nodes (WSNs). It avoids short-circuit current by minimizing the time spent in the input voltage range fromVthnto [Vdd- |Vthp|]. A current-feeding scheme with gate voltage control enables the oscillator to operate over a wide frequency range. A test chip is fabricated in a 0.18 μm CMOS process. The measurements show that the proposed oscillator achieves a constant energy-per-cycle (EpC) of 0.8 pJ/cycle over the 21-60 MHz frequency range and is more efficient than a conventional current-starved ring oscillator (CSRO) below 300 kHz at 1.8 V supply voltage. As an application example, the proposed oscillator is implemented in a switched-capacitor DC-DC converter. The converter is 11%-56% more efficient for load power values ranging from 583 pW to 2.9 nW than a converter using a conventional CSRO.
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109 USA.
authors.forename: Inhee
authors.initials: I
authors.lastname: Lee
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109 USA.
authors.forename: Dennis
authors.initials: D
authors.lastname: Sylvester
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109 USA.
authors.forename: David
authors.initials: D
authors.lastname: Blaauw
keywords: Current starved; converter; energy efficient; leakage based; low power; oscillator; switched-capacitor DC–DC; wide frequency range; wireless sensor node (WSN)