Towards minimum achievable phase noise of relaxation oscillators

P.F.J. Geraedts, Adrianus Johannes Maria van Tuijl, Eric A.M. Klumperink, Gerhardus J.M. Wienk, Bram Nauta

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    8 Citations (Scopus)
    627 Downloads (Pure)


    A relaxation oscillator design is described, which has a phase noise rivaling ring oscillators, while also featuring linear frequency tuning. We show that the comparator in a relaxation-oscillator loop can be prevented from contributing to 1/f2 colored phase noise and degrading control linearity. The resulting oscillator is implemented in a power efficient way with a switched-capacitor circuit. The design results from a thorough analysis of the fundamental phase noise contributions. Simple expressions modeling the theoretical phase noise performance limit are presented, as well as a design strategy to approach this limit. To verify theoretical predictions, a relaxation oscillator is implemented in a baseline 65 nm CMOS process, occupying 200 µm × 150 µm. Its frequency tuning range is 1–12 MHz, and its phase noise is L(100kHz) = −109dBc/Hz at fosc = 12MHz, while consuming 90 μW. A figure of merit of −161dBc/Hz is achieved, which is only 4 dB from the theoretical limit.
    Original languageEnglish
    Pages (from-to)238-257
    Number of pages16
    JournalInternational journal of circuit theory and applications
    Issue number3
    Publication statusPublished - 1 Jan 2013


    • EWI-23022
    • IR-88767
    • METIS-302529
    • Oscillator
    • Low noise
    • Phase noise
    • Figure of merit
    • FoM
    • Jitter
    • Relaxation oscillator
    • Thermodynamics
    • Linear frequency tuning
    • Large frequency tunig range
    • Power efficiency

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