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A Sub-nW/kHz Relaxation Oscillator with Ratioed Reference and Sub-Clock Power Gated Comparator

Research output: Contribution to journalArticle

A. Savanth, A.S. Weddell, James Myers, D. Flynn, Bashir M. Al-Hashimi

Original languageEnglish
Pages (from-to)3097-3106
JournalIEEE Journal of Solid-State Circuits
Issue number11
Early online date13 Aug 2019
E-pub ahead of print13 Aug 2019
PublishedNov 2019

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Realizing the vision of a trillion IoT sensor nodes demands ultra low-power (ULP) compute, typically implemented using synchronous digital systems. These require low-power clock sources which must be fully integrated to meet low system-cost requirements. Hence, relaxation oscillators (RxOs) are popular. Their need for precision references and high-speed comparators can challenge power budgets; hence, prior works have explored low-speed closed-loop control for RxOs to alleviate this issue. This paper adopts an alternative approach to minimize the RxO power: the use of a ratioed switched-capacitor reference and sub-clock power-gating of the high-power comparator. The stability of the proposed design is further enhanced through the integration of digital-assist. This mixed-signal approach allowed a 1.2-MHz RxO to be implemented in 0.005 mm2 in TSMC 65 nm, with silicon measurements showing 0.7%/V line and 100 ppm/°C temperature stability. The energy-per-cycle figure of merit is 0.68 nW/kHz-a 4× improvement over state-of-the-art for comparable stability.

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