A 33-ppm/°C 240-nW 40-nm CMOS Wakeup Timer Based on a Bang-Bang Digital-Intensive Frequency-Locked-Loop for IoT Applications

Ming Ding*, Zhihao Zhou, Stefano Traferro, Yao Hong Liu, Christian Bachmann, Fabio Sebastiano

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    9 Citations (Scopus)
    120 Downloads (Pure)

    Abstract

    This paper presents a wakeup timer in 40-nm CMOS for Internet-of-Things (IoT) applications based on a bang-bang Digital-intensive Frequency-Locked Loop (DFLL). A self-biased Σ Δ Digitally Controlled Oscillator (DCO) is locked to an RC time constant via a feedback loop consisting of a single-bit chopped comparator and a digital loop filter, thus maximizing the use of digital circuits while keeping only the RC network and the comparator as the sole analog blocks. Analysis and behavior level simulations of the DFLL have been carried out to guide the optimization of the long-term stability and frequency accuracy of the timer. High frequency accuracy and a 10× enhancement of long-term stability is achieved by the adoption of chopping to reduce the effect of comparator offset and 1/f noise and by the use of Σ Δ modulation to improve the DCO resolution. Such highly digitized architecture fully exploits the advantages of advanced CMOS processes, thus enabling operation down to 0.7 V and a small area (0.07 mm2). The proposed timer achieves the excellent energy efficiency (0.57 pJ/cycle at 417 kHz at 0.8-V supply) over prior art while keeping excellent on-par long-term stability (Allan deviation floor < 20 ppm) and temperature stability (33 ppm°Cat 0.8-V supply).

    Original languageEnglish
    Article number9036068
    Pages (from-to)2263-2273
    Number of pages11
    JournalIEEE Transactions on Circuits and Systems I: Regular Papers
    Volume67
    Issue number7
    DOIs
    Publication statusPublished - 2020

    Bibliographical note

    Accepted Author Manuscript

    Keywords

    • Digital-intensive
    • Frequency locked-loop
    • internet of things
    • Low-power
    • Oscillator
    • Wakeup timer

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