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

2019; Institute of Electrical and Electronics Engineers; Volume: 54; Issue: 11 Linguagem: Inglês

10.1109/jssc.2019.2930360

1558-173X

Anand Savanth, Alex S. Weddell, James Myers, David Flynn, Bashir M. Al‐Hashimi,

Analytical Chemistry and Sensors

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.