An Ultra-Low-Voltage Single-Crystal Oscillator-Timer (XO-Timer) Delivering 16-MHz and 32.258-kHz Clocks for Sub-0.5-V Energy-Harvesting BLE Radios in 28-nm CMOS

• Published in: IEEE open journal of circuits and systems Vol. 4; pp. 126 - 138
• Main Authors: Lin, Liwen, Lei, Ka-Meng, Mak, Pui-In, Martins, Rui P.
• Format: Journal Article
• Language: English
• Published: New York IEEE 2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bluetooth low-energy (BLE); Budgets; clock; Clocks; CMOS; Costs; crystal oscillator-timer (XO-Timer); Crystal oscillators; Crystals; Electric potential; Energy harvesting; Generators; Internet-of-Things (IoT); micropower manager (μPM); Phase locked loops; Phase noise; Power efficiency; Single crystals; System-on-chip; ultra-low-power (ULP); ultra-lowvoltage (ULV); Voltage; Voltage control
• ISSN: 2644-1225; 2644-1225
• DOI: 10.1109/OJCAS.2023.3256368

This paper reports an ultra-low-voltage (ULV) single-crystal oscillator-timer (XO-Timer) for sub-0.5 V Bluetooth low-energy (BLE) radios that aims for self-powering by harvesting the ambient energies. Specifically, we tailor an on-chip micropower manager <inline-formula> <tex-math notation="LaTeX">(\mu </tex-math></inline-formula>PM) to customize the voltage and current budgets for each sub-function of the XO-Timer. Such <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula>PM shows a high power efficiency by introducing a 3-stage cascaded structure and a single voltage-regulation loop; they together uphold the performance of the XO-Timer amid supply-voltage and temperature variations. The core amplifier of the XO-Timer is ULV-enabled, and is reconfigurable (i.e., 1-stage and 3-stage gm) to balance between the power budget and performance under the high-performance mode (HPM) and low-power mode (LPM). Fabricated in 28-nm CMOS, the XO-Timer in HPM generates a 16-MHz clock with a power of <inline-formula> <tex-math notation="LaTeX">24.3 ~\mu \text{W} </tex-math></inline-formula>, and a phase noise of −133.8 dBc/Hz at 1-kHz offset, resulting in a Figure-of-Merit (FoM1) of −236 dBc/Hz. In the LPM, the XO-Timer delivers a 32.258-kHz clock while consuming <inline-formula> <tex-math notation="LaTeX">11.4 ~\mu \text{W} </tex-math></inline-formula>. The sleep-timer FoM2 is <inline-formula> <tex-math notation="LaTeX">14.8 ~\mu \text{W} </tex-math></inline-formula> and the Allan deviation is 35.1 ppb, achieving the lowest supply voltage (0.25 V) not only for a dual-mode XO-Timer but also for a MHz-range XO.