Abstract:
Realizing the vision of a trillion IoT sensor nodes demands ultra low-power (ULP) compute, typically implemented using synchronous digital systems. These require low-powe...Show MoreMetadata
Abstract:
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.
Published in: IEEE Journal of Solid-State Circuits ( Volume: 54, Issue: 11, November 2019)