A 80 nW, 32 kHz charge-pump based ultra low power oscillator with temperature compensation

This paper presents an area-efficient ultra-low-power 32 kHz clock source for low power wireless communication systems using a temperature-compensated charge-pump-based digitally controlled oscillator (DCO). A highly efficient digital calibration method is proposed to achieve frequency stability over process variation and temperature drifts. This calibration method locks the DCO's output frequency to the reference clock of the wireless communication system during its active state. The introduced calibration scheme offers high jitter immunity and short locking periods overcoming frequency calibration errors for typical ultra-low-power DCO's. The circuit area of the proposed ultra-low-power clock source is 100μm × 140μm in a 130nm RF CMOS technology. In measurements the proposed ultra-low-power clock source achieves a frequency stability of 10 ppm/°C from 10 °C to 100 °C for temperature drifts of less than 1 °C/s with 80nW power consumption.