A resistor-based temperature sensor for a real time clock with ±2ppm frequency stability

A temperature sensor based on the temperature-dependence of integrated poly-silicon resistors is used to stabilize the quartz-crystal of a 131kHz real-time clock (RTC). After a 3-point calibration, the sensor achieves an inaccuracy of less than ±0.12°C (min-max) from -40°C to 85°C, which translates into a frequency stability of less than ±2ppm. The sensor also achieves 2.8mK (rms) resolution in a 32ms conversion time, which corresponds to a state-of-the-art resolution FOM of 8pJK².