This paper presents a frequency reference system that combines high frequency accuracy and low power consumption using a single-point temperature trim and batch calibration. The system is intended as a low-cost fully integrated crystal oscillator replacement. In this system, the oscillation frequency of a power-efficient, but Process, Voltage, Temperature (PVT) and Lifetime (L) sensitive current-controlled ring oscillator (CCO) is periodically (re)calibrated by the well-behaved frequency stability of an untuned LC-based Colpitts oscillator (LCO), which is optimized for stability over PVTL. During the single-point room temperature factory trim, the frequency of the LCO is determined and the result is digitally stored. An on-chip calibration engine tunes the ring oscillator to the target frequency based on the LCO frequency, temperature sensor information and digitally stored trimming information, thus effectively improving the frequency stability of the ring oscillator. The relatively high-power LCO is heavily duty-cycled to minimize the overall power consumption. A prototype fabricated in a 0.13 µm highvoltage (HV) CMOS SOI process and assembled in a plastic package demonstrates an inaccuracy lower than ±93 ppm over a temperature range from −63 to 165 °C across 18 samples. The presented frequency reference system, including on-chip voltage regulators and a temperature sensor, occupies a chip area of 0.69 mm 2 and consumes about 64 µA from a single 3.3 V supply. The frequency error due to supply variation is roughly 92 ppm/V. The mean frequency shift due to aging, measured before and after a six-day storage bake at 175 °C, is only 52 ppm.