All-Digital PLL for Bluetooth Low Energy Using 32.768-kHz Reference Clock and ≤0.45-V Supply

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 powerup and jointly performs an instantaneous channel hopping and Gaussian frequency shift keying (GFSK) modulation in a twopoint 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.