A high performance 19.2MHz digitally controlled crystal oscillator for NB-IoT

This design implements a 19.2MHz digitally controlled crystal oscillator (DCXO) for the narrow-band internet of things system (NB-IoTs). The paper uses positive feedback principle and phase analysis method to design the oscillator, and then the circuit is realized in a 55nm CMOS technology. The DCXO frequency is controlled by a capacitor matrix controlled by a 10bit digital signal. The results show that the crystal tunable range is more than 70ppm, with tuning step of 0.1∼0.2ppm. The phase noise in 1 KHz and 10 KHz offset were -137dBc/Hz and -159dBc/Hz, respectively. The maximum power consumption is 0.72mW at 1.2V power supply voltage, including an output buffer with 0.24mW power consumption. (paper)