A MEMS Real-Time Clock with Single-Temperature Calibration and Deterministic Jitter Cancellation

This article presents a real-time clock (RTC) system based on a microelectromechanical system (MEMS) resonator coupled to an integrated circuit (IC) that implements a frequency-compensating machine. The MEMS resonator is built with a standard, industrial-grade polysilicon process characterized by a -30-ppm/K linear temperature coefficient of frequency ( $TCf$ ) and the frequency-drift compensation is entirely carried out within the IC using a fractional frequency division. The large, but deterministic, output jitter (≈1 $mu s_{rms}$ ) is then suppressed down to less than 40 $ns_{rms}$ with a low-power digital-to-time converter (DTC), whose usefulness in this kind of application is then analyzed. With a single-point temperature calibration, a ±8-ppm output frequency stability is demonstrated at ≈800-nA current consumption from a 1.2-V supply.