A Low-Power Relaxation Oscillator With Switched-Capacitor Frequency-Locked Loop for Wireless Sensor Node Applications

This letter presents a 600-kHz relaxation oscillator with 2.2-μW power consumption. A low-power frequency-locked loop (FLL) structure is proposed to increase the frequency immunity against process, voltage, and temperature variations. A front regulator is proposed to further enhance the voltage stability and widen the voltage range. A current-injection scheme is proposed to compensate the frequency shift due to the temperature shift of the on-chip resistor. Fabricated with 180-nm technology, this oscillator can operate at an unregulated supply from 1.1 to 3.3 V with 0.046%/V voltage stability. The measured temperature stability is 48.69 ppm/°C from -45 °C to 125 °C and the measured jitter_rms is 1.56 ns with 120-k bits.