In this paper, we introduce an all-digital phase-locked loop (ADPLL) for Bluetooth low energy (BLE) that eliminates the need for a crystal oscillator (XO) other than a 32.768-kHz real-time clock (RTC) already present in wireless systems. Specifically, we propose to replace the conventional channel settling with a band settling that would be carried out only once per global device power up. The ADPLL locks to the center of the Bluetooth band (2440 MHz) upon system power-up and jointly performs an instantaneous channel hopping and Gaussian frequency shift keying (GFSK) modulation in a two-point manner to overcome the narrow PLL bandwidth (BW) due to the 32.768-kHz reference. Extensive calibrations linearize the effective cubic digitally controlled oscillator (DCO) transfer function to achieve a precise frequency range of hopping and modulation. Realized in 16-nm FinFET, it consumes <1 mW at ≤0.45 V, while achieving best-in-class performance and <100-ns hopping time.

@en

Energy harvesting (EH) is a topic of intensive research promising battery-free operation of massive networks of wireless IoT devices. To simultaneously satisfy the EH and IoT, ultra-low-power (ULP) consumption with ultra-low-voltage (ULV) supply are required. Some, e.g., photovoltaic, EH output voltage (<0.3V) is below the threshold voltage (V_t) of even the most recent FinFET CMOS transistors, which makes it extremely challenging for circuit designers. Thus, new special circuit techniques are needed to make the IoT devices work properly with supplies below V_t.

@en

A tiny LC-tank-based ADPLL in 10nm FinFET CMOS achieves an area comparable to that of inverter-based ring-oscillator PLLs. A DCO occupying 0.016mm2 uses a controllable multi-turn magnetic coupling transformer to extend its tuning range to 10.8-19.3GHz (56.5%). A diversity of fine-tune capacitor banks limits the max/min step-size ratio to 2.3×. A new metastability-resolution scheme allows to use the frequency reference (FREF) clock directly instead of a retimed FREF (CKR) of conventional ADPLLs. A low-complexity estimator calculates inverse of the TDC. The fractional phase jitter (725fs) reaches sub-ps for the first time among PLLs of <;0.1mm2. Frequency pushing is 1.8%/V, which is at least 50× better than in traditional ring-type PLLs.@en