A sub-0.5V Crystal Oscillator-Timer (XO-Timer) Combining 16MHz Reference and 32kHz Sleep Timer with a Single Crystal for Energy-Harvesting Radios in 28nm CMOS

For cost and size minimization of the IoT nodes, their implementation is towards self-powering by the ambient energy, and being less dependent on the bulky external units such as the kHz and MHz crystals (each $3.2 \times 2.5$ mm
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. Herein we report a sub-0.5V crystal oscillator-timer (XO-Timer) apt for the energy-harvesting Bluetooth Low Energy (BLE) radios, e.g. [3]. Sharing one crystal, our XO-Timer balances the performances of its 16MHz reference for the radio's phase-locked loop, and its 32kHz sleep timer that governs the radio wake-up accuracy.